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03-CTS-20CO.qxd 10/16/07 11:38 AM Page 1 (2,1)
Infrastructure Management
Condition Assessment Strategies and Protocols for
Water and Wastewater Utility Assets
Co-published by
03-CTS-20CO
CONDITION ASSESSMENT STRATEGIES
AND PROTOCOLS FOR WATER AND
WASTEWATER UTILITY ASSETS
by:
David Marlow, CSIRO
Simon Heart, MWH
Stewart Burn, CSIRO
Antony Urquhart, MWH
Scott Gould, CSIRO
Max Anderson, MWH
Steve Cook, CSIRO
Michael Ambrose, CSIRO
Belinda Madin, MWH
Andrew Fitzgerald, MWH
2007
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
ES-i
The Water Environment Research Foundation, a not-for-profit organization, funds and manages water quality
research for its subscribers through a diverse public-private partnership between municipal utilities, corporations,
academia, industry, and the federal government. WERF subscribers include municipal and regional water and
wastewater utilities, industrial corporations, environmental engineering firms, and others that share a commitment to
cost-effective water quality solutions. WERF is dedicated to advancing science and technology addressing water
quality issues as they impact water resources, the atmosphere, the lands, and quality of life.
For more information, contact:
Water Environment Research Foundation
635 Slaters Lane, Suite 300
Alexandria, VA 22314-1177
Tel: (703) 684-2470
Fax: (703) 299-0742
www.werf.org
[email protected]
This report was co-published by the following organizations. For non-subscriber sales information, contact:
IWA Publishing
Alliance House, 12 Caxton Street
London SW1H 0QS, United Kingdom
Tel: +44 (0) 20 7654 5500
Fax: +44 (0) 20 7654 5555
www.iwapublishing.com
[email protected]
© Copyright 2007 by the Water Environment Research Foundation. All rights reserved. Permission to copy must be
obtained from the Water Environment Research Foundation.
Library of Congress Catalog Card Number: 2006940526
Printed in the United States of America
IWAP ISBN: 1-84339-785-4
This report was prepared by the organization(s) named below as an account of work sponsored by the
Water Environment Research Foundation (WERF). Neither WERF, members of WERF, the
organization(s) named below, nor any person acting on their behalf: (a) makes any warranty, express or
implied, with respect to the use of any information, apparatus, method, or process disclosed in this
report or that such use may not infringe on privately owned rights; or (b) assumes any liabilities with
respect to the use of, or for damages resulting from the use of, any information, apparatus, method, or
process disclosed in this report.
CSIRO, MWH
The research on which this report is based was developed, in part, by the United States Environmental Protection
Agency (EPA) through Cooperative Agreement No. CP-83112101 with the Water Environment Research
Foundation (WERF). However, the views expressed in this document are solely those of CSIRO and MWH and
neither EPA, nor WERF, nor AWWA Research Foundation, endorses any products or commercial services
mentioned in this publication. This report is a publication of WERF, not EPA. Funds awarded under the Cooperative
Agreement cited above were not used for editorial services, reproduction, printing, or distribution.
This document was reviewed by a panel of independent experts selected by WERF. Mention of trade names or
commercial products does not constitute WERF, nor EPA, nor AWWA Research Foundation endorsement or
recommendations for use. Similarly, omission of products or trade names indicates nothing concerning WERF's or
EPA's positions regarding product effectiveness or applicability.
ii
ACKNOWLEDGMENTS
The researchers would like to acknowledge the kind assistance of all those who
contributed to this project. Special thanks are due to CSIRO for its role in the implementation of
this project and inkind contributions (staff days).
Report Preparation
Principal Investigators:
Antony Urquhart, Dip.Bus, CPEng., MWH
Stewart Burn, CSIRO
Project Team:
David Marlow, Ph.D., CSIRO
Simon Heart, M.S., PE, MWH
Scott Gould, BEng, BBus Admin., CSIRO
Max Anderson, CPEng., MWH
Steve Cook, M.S., CSIRO
Michael Ambrose, CSIRO
Belinda Madin, MWH
Andrew Fitzgerald, MWH
Project Subcommittee
Stephen Allbee, United States Environmental Protection Agency
Greg Cawston, Sydney Water
John Colbert, Massachusetts Water Resources Authority
Wayne Dillard, Burns & McDonnell
John W. Fortin, Asset Management Consultant, Cohasset, MA
Susan Karlins, City of Houston
Jon Schellpfeffer, Madison Metropolitan Sewerage Department
Jennifer Warner, AWWA Research Foundation
Water Environment Research Foundation Staff
Director of Research: Daniel M. Woltering, Ph.D.
Program Director: Roy Ramani, Ph.D.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
iii
ABSTRACT AND BENEFITS
Abstract
A Water Environmental Research Foundation (WERF) sponsored workshop held in
March 2002 identified that there were no standardized guidelines for conducting condition
assessments, and that there is a need for protocols to help utilities better understand asset
condition and performance. A research project jointly funded by WERF, the American Water
Works Association Research Foundation (AwwaRF) and the United States Environmental
Protection Agency (U.S. EPA) was developed to fill this gap. This report presents the findings of
this research, focusing on the following objectives: 1) documenting the broad range of available
asset assessment tools and techniques, and 2) providing guidance on how to incorporate
condition assessment strategies into a utility’s asset management philosophy.
The important links between accepted and emerging principles of asset management and
approaches to condition assessment are discussed. Generic approaches to assessment program
design and tool selection are offered for both strategic asset management and day-to-day
maintenance purposes, which can be applied across a range of asset types. The information
presented draws upon a range of case studies undertaken with utilities in the United States,
Australia, New Zealand, and the United Kingdom. A tool selection procedure is presented that
uses an exclusion process in which tools and techniques are excluded from further consideration
based on criteria relating to technical feasibility, technical suitability and utility technical
capacity. Remaining options must then be evaluated through economic or financial analysis so
that final selection is made with regard to available resources, the cost-benefits accrued and
utility affordability issues. The report outlines approaches that can be taken in this analysis.
The report also provides descriptions and reviews of 85 individual condition assessment
tools and techniques used in the water and wastewater industry, including a discussion of
principles, applications, practical considerations, advantages and limitations. A prototype expert
system was developed to investigate the use of this technology and also to facilitate the
production of tool selection tables for inclusion in the final report. While these tables are a
pragmatic paper-based solution, it is recommended that the prototype expert system be further
developed to provide the sector with 1) a more flexible selection tool, and 2) a framework for
future updating, maintaining and distributing refinements of the tool reviews and information.
Benefits
 Provides a step-wise approach for developing a cost-effective condition and performance
assessment program for water and wastewater utilities.
 Provides guidance for integrating condition and performance assessment programs into a
utility’s overall asset management framework.
 Recommends criteria for selecting assessment tools and techniques.
 Describes and reviews available condition assessment tools and techniques used in the
water and wastewater industry, including principles, applications, practical
considerations, advantages and limitations.
 Includes case study examples of applications of condition and performance assessment
techniques at leading water and wastewater utilities throughout the world.
iv
Keywords: Condition assessment, asset condition, asset performance, asset management, tool
selection, utility infrastructure, risk management, case studies, assessment tools
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
v
TABLE OF CONTENTS
Acknowledgments.......................................................................................................................... iii
Abstract and Benefits..................................................................................................................... iv
List of Tables .................................................................................................................................ix
List of Figures .................................................................................................................................x
List of Acronyms ………………………………………………………………………………………………....xi
Executive Summary .................................................................................................................. ES-1
53H
1.0
2.0
3.0
4.0
vi
Introduction.................................................................................................................... 1-1
54H
1.1
Introduction ............................................................................................................... 1-2
1.2
Project Delivery ........................................................................................................ 1-3
1.3
Linkage to Related Research .................................................................................... 1-3
1.4
Report Structure ........................................................................................................ 1-4
1.5
How to Use this Report............................................................................................. 1-5
1.6
Document Road Map................................................................................................ 1-6
5H
56H
57H
58H
59H
60H
Condition Assessment as a Strategic Asset Management Tool................................. 2-1
61H
2.1
Introduction ............................................................................................................... 2-2
2.2
Strategic Asset Management .................................................................................... 2-3
2.3
Condition Assessment as an Input to Strategic Asset Management ..................... 2-11
2.4
When to Undertake Condition Assessment ........................................................... 2-14
62H
63H
64H
65H
Developing an Assessment Program ............................................................................ 3-1
6H
3.1
Introduction ............................................................................................................... 3-2
3.2
The Role of Risk in the Design of an Assessment Program.................................... 3-2
3.3
Outputs from a Condition Assessment Program...................................................... 3-4
3.4
Designing a Condition Assessment Program......................................................... 3-15
3.5
Additional Implementation Issues.......................................................................... 3-24
3.6
Documentation and Reporting................................................................................ 3-27
67H
68H
69H
70H
71H
72H
Justifying a Condition and Performance Assessment Program ............................... 4-1
73H
4.1
Introduction ............................................................................................................... 4-2
4.2
Key Benefits of Condition and Performance Assessment Programs ...................... 4-2
4.3
Key Cost Elements for Effective Condition Assessment Programs........................ 4-4
4.4
Economic Justification.............................................................................................. 4-6
4.5
Other Approaches to Justification ............................................................................ 4-7
74H
75H
76H
7H
78H
4.6
5.0
6.0
7.0
8.0
Optimizing Cost and Benefits Associated with Assessment Programs .................. 4-8
79H
Condition Assessment as a Maintenance Management Tool.................................... 5-1
80H
5.1
Introduction ............................................................................................................... 5-2
5.2
Approaches to Maintenance ..................................................................................... 5-3
5.3
The Role of Condition Monitoring in Proactive Maintenance................................ 5-4
5.4
Risk-based Assessment Procedures.......................................................................... 5-6
5.5
A Generic Approach to Specifying Condition Monitoring Tasks......................... 5-13
5.1
Development of a Condition Monitoring Program................................................ 5-15
81H
82H
83H
84H
85H
86H
Selecting Tools and Techniques.................................................................................... 6-1
87H
6.1
Introduction ............................................................................................................... 6-2
6.2
A Protocol for Selecting Condition Assessment Tools ........................................... 6-2
6.3
Exclusion Criteria ..................................................................................................... 6-4
6.4
Application of Exclusion Protocol ........................................................................... 6-5
6.5
Development of a Prototype Expert System (ES).................................................... 6-8
6.6
The Impact of Risk and Cost on Tool Selection ...................................................... 6-8
6.7
An Iterative Approach to Asset Assessments ........................................................ 6-10
8H
89H
90H
91H
92H
93H
94H
Available Tools and Techniques .................................................................................... 7-1
95H
7.1
Introduction ............................................................................................................... 7-2
7.2
Representation of the Asset Stock............................................................................ 7-2
7.3
Mapping Tools onto the Asset Stock ....................................................................... 7-4
7.4
Tool Selection Process.............................................................................................. 7-7
96H
97H
98H
9H
Case Study Details.......................................................................................................... 8-1
10H
8.1
Introduction ............................................................................................................... 8-2
8.2
Purpose of the Case Studies...................................................................................... 8-2
8.3
Case Study 1: Scottish Water’s Program of Treatment Plant Assessments............ 8-3
8.4
Case Study 2: Scottish Water’s Approach to Grading of Water Mains .................. 8-7
8.5
Case Study 3: Water Corporation’s ACA Program ............................................... 8-10
8.6
Case Study 4: Water Corp’s Assessment Approach for Water Tanks ................. 8-13
8.7
Case Study 5: Water Corp’s Investigation of a Trunk Main Failure …. .............. 8-15
8.8
Case Study 6: Water Care Services Limited Assessments of Sewerage Assets ... 8-19
8.9
Case Study 7: Water Care’s Assessments of A Critical Sewer ............................. 8-21
8.10
Case Study 8: Melbourne Water’s Assessments of Steel Tanks ........................... 8-24
8.11
Case Study 9: Sydney Water’s Management of M&E Assets .............................. 8-28
10H
102H
103H
104H
105H
106H
107H
108H
109H
10H
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
1H
vii
8.12
Case Study 10: City of Bellevue’s Risk-Based Approaches ................................. 8-31
8.13
Case Study 11: Massachusetts Water Resources Authority RCM Program......... 8-33
8.14
Case Study 12: MWRA’s Strategies for Pipe Network Management .................. 8-35
8.15
Case Study 13: CSIRO’s Assessment of a Cast Iron Transmission Main ............ 8-37
8.16
Case Study 14: CSIRO’s Assessment of an Asbestos Cement Force Main ......... 8-40
12H
13H
14H
15H
16H
Appendix A: Utility Objectives and Related KPIs ................................................................... A-1
17H
Appendix B: Individual Drivers for Assessment ...................................................................... B-1
18H
Appendix C: Condition and Performance Assessment Criteria................................................. C-1
19H
Appendix D: A Generic Condition Assessment Form for Mechanical and Electrical
Equipment ............................................................................................................. D-1
120H
Appendix E: Development of a Prototype Expert System..........................................................E-1
Appendix F: Review of Condition Assessment Tools and Techniques.......................................F-1
Glossary of Terms....................................................................................................................... G-1
References................................................................................................................................... R-1
viii
LIST OF TABLES
2-1
Approaches to Asset Management Adopted.................................................................... 2-7
2-2
The Impact of Scale on Asset Management Resources (after Shaw 2001) ................... 2-11
2-3
Strategic Objectives, Related KPIs and Approach to Assessment ................................ 2-17
2-4
Drivers for Undertaking Condition and Performance Assessment................................ 2-20
3-1
Condition and Performance Assessment Criteria .......................................................... 3-11
3-2
Ofwat PR99 Information Sewer Grading System (Ofwat, 1998) .................................. 3-12
3-3
Approaches to Assessing Different Asset Types ............................................................3-.25
4-1
Benefits of Undertaking Condition/Performance Assessment ........................................ 4-3
4-2
Cost Elements .................................................................................................................. 4-4
5.1
Estimated Projection of the Vibration Monitoring Cost Avoidance Benefits ............... 5-19
5-2
Ten-Year Projected Condition Monitoring Costs .......................................................... 5-20
5-3
Estimated Projection of the Oil Analysis Cost Avoidance Benefits.............................. 5-21
6-1
Exclusion Criteria for Inspection and Survey Tools/Techniques .................................... 6-6
6-2
Exclusion Criteria for Asset Management and Assessment Tools/Techniques............... 6-7
6-3
Utility Criteria that Influence the Choice of Tools/Techniques....................................... 6-7
6-4
Sliding Scale of Assessment Standards ......................................................................... 6-11
7-1
Service Area: Water Supply............................................................................................ 7-3
7-2
Service Area: Wastewater Collection and Disposal ........................................................ 7-4
7-3
Hierarchical Representations for Complex Assets .......................................................... 7-5
7-4
Hierarchical Representations for Complex Assets .......................................................... 7-6
7-5
Hierarchical Representations for Complex Assets .......................................................... 7-6
7-6
Tool and Technique Selection Tables.............................................................................. 7-8
8-1
Guidance for the Grading of Condition. ........................................................................ 8-14
8-2
Weighted Scoring for Asset Components...................................................................... 8-27
8-3
Inspection Tools and Techniques Used by SWC........................................................... 8-30
0H
1H
2H
3H
4H
5H
6H
7H
8H
9H
10H
1H
12H
13H
14H
15H
16H
17H
18H
19H
20H
21H
2H
24H
23H
12H
123H
124H
125H
126H
127H
129H
130H
13H
132H
13H
134H
135H
136H
137H
138H
139H
140H
14H
142H
143H
14H
145H
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
146H
ix
LIST OF FIGURES
ES-1
A 10-Step Approach to Specifying a Condition Assessment Program..........................ES-3
ES-2
A Generic Approach to Specifying Condition Monitoring Techniques ........................ES-5
2-1
Business Drivers and Utility Capabilities ........................................................................ 2-2
2-2
The PAS 55 Physical Asset Management Framework .................................................... 2-5
2-3
Determining Data Requirements through Information Needs ......................................... 2-6
2-4
The Asset Management Cycle ......................................................................................... 2-8
2-5
The Relationship between Asset Condition, Age and Failure Probability .................... 2-12
2-6
The Process of Developing a Performance Management System ................................. 2-15
2-7
The Role of Condition Assessment in Utility Decision Making ................................... 2-18
2-8
Condition Assessment Undertaken in Response to Individual Drivers ......................... 2-19
3-1
Risk and Maintenance Strategies......................................................................................3-3
3-2
A 10-Step Approach to Specifying a Condition Assessment Program.......................... 3-18
5-1
Business Drivers and Utility Capabilities ........................................................................ 5-2
5-2
The Failure Process as Described by the P-F Curve........................................................ 5-5
5-3
A Generic Approach to Specifying Condition Monitoring Techniques ........................ 5-14
6-1
Process Flowchart for Developing Condition Monitoring Programs .............................. 6-3
6-2
Approach to Selecting Condition Assessment Tools....................................................... 6-4
6-3
Iterative use of Condition and Performance Assessments............................................. 6-12
8-1
Comparison of Assets in Condition Grade 4/5 by Asset Value....................................... 8-5
8-2
Schematic of Water Corporation’s ACA Process.......................................................... 8-11
8-3
Typical Failure Mode for Cast Iron Pipe ....................................................................... 8-37
8-4
Weibull Plot for Corrosion Data .................................................................................... 8-38
8-5
Expected Failure Rate per Year ..................................................................................... 8-39
8-6
Determining Residual Strength of the Cores ................................................................. 8-41
8-7
Weibull Plot for Deterioration Rates ............................................................................. 8-41
8-8
Distribution of Remaining Lives ................................................................................... 8-42
8-9
Life Time Distribution Along the Pipeline .................................................................... 8-42
25H
26H
27H
28H
29H
30H
31H
32H
3H
34H
35H
36H
37H
38H
39H
40H
41H
42H
43H
4H
45H
46H
47H
48H
49H
50H
x
147H
148H
149H
150H
15H
152H
153H
154H
15H
156H
157H
158H
159H
160H
16H
162H
163H
164H
165H
16H
167H
168H
169H
170H
17H
172H
LIST OF ACRONYMS & ABBREVIATIONS
3D
AC
ACA
AwwaRF
BBEM
C&B
CARD
CARE-S
CCTV
CG
CI
CMMS
CMOM
CSO
DCVG
DITP
DSS
DT
ECARD
ES
FMEA
FMECA
FTEs
GIS
GPR
GUI
ICA
ICGs
IE
I&I
INMS
Km
KPI
LPR
m
mm
M&E
mgd
MM
MO
MWRA
NASSCO
NRC
NDT
Three Dimensional
Asbestos Cement
Asset Condition Assessment
American Water Works Association Research Foundation
Broadband Electro Magnetic
Civil and Building
Condition Assessment and Risk Determination
Computer Aided Rehabilitation of Sewer And Storm Water Networks
Closed Circuit Television
Condition Grade
Cast Iron
Computerized Maintenance Management System
Capacity assurance, Management, Operation and Maintenance
Combined Sewer Overflow
Direct Current Voltage Gradient
Dear Island Treatment Plant
Decision Support System
Destructive Testing
Electrical Condition Assessment and Risk Determination
Expert System
Failure Modes and Effects Analysis
Failure Modes, Effect and Criticality Analysis
Full Time Equivalents
Geographic Information System
Ground Penetrating Radar
Graphical User Interface
Instrumentation, Control and Automation
Internal Condition Grades
Impact Echo
Infiltration and Inflow
Integrated Network Management System
Kilometers
Key Performance Indicator
Linear Polarization Resistance
Meters
Millimeter
Mechanical and Electrical
Million Gallons Per Day
Millimeter
Maintenance Optimization
Massachusetts Water Resources Authority
National Association of Sewer Service Companies
National Research Council of Canada
Non-Destructive Testing
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
xi
O&M
Ofgem
Ofwat
PARMS
PDF
PE
PG
PM
PMO
Q&S
QC
RBI
RCM
RPN
ROI
SAM
SASW
SCRAPS
SIMPLE
SRM
SSET
STPs
SPG
SWC
TEV
TFI
UID
U.S. EPA
Water Care
WERF
WIC
WRc
WQ
xii
Operations and Maintenance
Office of Gas and Electricity Markets
Office of Water Services
Pipeline Asset and Risk Management System
Probability Density Function
Polyethylene
Performance Grade
Preventive Maintenance
Preventative Maintenance Optimization
Quality and Standards
Quality Control
Risk-Based Inspection
Reliability Centered Maintenance
Risk Priority Number
Return on Investment
Strategic Asset Management
Spectral Analysis of Surface Wave
Sewer Cataloguing, Retrieval and Prioritization System
Sustainable Infrastructure Management Program Learning Environment
Sewer Rehabilitation Manual
Sewer Scanner and Evaluation Technology
Sewage Treatment Plants
Structural Performance Grade
Sydney Water Corporation
Transient Earth Voltage
Transverse Flux Inspection
Unacceptable Intermittent Discharge
United States Environmental Protection Agency
Water Care Services Limited
Water Environment Research Foundation
Water Industry Commissioner
Water Research Centre
Water Quality
EXECUTIVE SUMMARY
Water and wastewater utilities in developed countries are faced with the challenge of how
to most cost effectively manage a large investment in physical assets while providing safe and
reliable services to their customers. A strategic asset management (SAM) approach can help
utilities meet this challenge. A key element of SAM is the assessment of asset condition and
performance. The objective of this research was to provide water and wastewater utilities with
guidance and information on how to effectively use condition assessment tools and techniques to
improve both the long-term planning and day-to-day management of assets.
The research was undertaken in two phases. Phase 1 of the project involved a web-based
survey and a review of the literature and other information sources. Phase 2 was undertaken as a
refinement stage, where concepts developed in Phase 1 were developed further, drawing on the
knowledge from a range of case study partners and professionals working within the sector. To
this end, various case studies were undertaken during Phase 2 to gain input from a range of
utilities and industry practitioners across the globe.
This report is structured for two distinct audiences:
 Utility planning managers who are seeking to understand how to embark upon costeffective condition and performance assessment programs, in order to support long-term
planning decisions.
 Engineering or maintenance managers that are seeking to identify and understand the
advantages and disadvantages of various available tools and techniques for measuring the
condition and performance of utility assets, in order to support daily maintenance and
operation of assets.
The remainder of this Executive Summary, and the following report, is structured to
assist these two audiences.
Strategic Asset Management Focus for Utility Planning Managers
In the water and wastewater utility sectors, there has been an evolution of asset
management philosophies from a focus on managing assets to condition and performance targets,
to a focus on achieving service level and business risk targets. Because of this, more recent asset
management philosophies do not focus directly on managing asset condition as an output but
instead seek to deliver appropriate service levels to customers and minimize risk in the most
cost-effective manner.
However, there remains a very strong and direct relationship between the condition of
assets, their likelihood of failure, and subsequently, service reliability and risk. To provide a
sustainable service, utilities need to understand the way in which asset condition changes with
time, and how this relates to the provision of services to customers. Condition assessment is an
important element in enhancing this understanding at both asset-specific and system-wide levels.
Why Undertake Condition and Performance Assessments?
Condition and performance monitoring are typically undertaken for the management of
individual assets, but can also be undertaken in order to inform SAM decision making. In this
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
ES-1
latter case, the utility will ideally undertake high-level performance monitoring (through
appropriate key performance indicators) to drive SAM decision making, and only undertake
asset-level condition and performance assessments where there is a need to fill a specific gap in
the information arising from this performance monitoring. Asset-level condition and
performance assessment for SAM are also often undertaken because some form of internal or
external (e.g., regulatory) driver is imposed on the utility that necessitates these specific
assessments.
A key purpose of condition assessment is to establish the current condition of assets as a
means of prioritizing and forecasting maintenance and rehabilitation efforts. Some assets are,
however, more important than others and should receive proportionally more attention. A
standard way to characterize the importance of an asset is to evaluate the risk of it failing. Risk is
an important consideration in asset management and the design of cost-effective condition
assessment programs.
Condition assessment can be used to understand the level of asset deterioration and the
impact it has on the probability of asset failure, which is one component of risk; the other
component being the consequences of asset failure. The utility can then attempt to either reduce
the probability of failure through some operational or capital intervention, or accept the level of
risk associated with the asset’s condition.
When undertaking condition assessments, inspection data are collected using tools that
provide information on such things as the presence of defects and their severity. However, even
when a defect, such as a crack or corrosion is identified, the question still remains as to the
significance of the findings. Data collected during inspection of assets must be interpreted
through appropriate analysis to give an assessment of condition in terms of the operating
demands placed on the asset.
Assessment Program Design
A generic approach to designing a program of assessments has been developed that can
be applied within a range of asset management sophistications, using different approaches to
condition assessment across a range of asset types. Within this generic approach, the integration
of a condition and performance assessment program within asset management is achieved
through 10 steps, which are shown in Figure ES-1.
Assessment Program Cost and Benefit Considerations
Condition and performance assessment programs provide many benefits, but can also be
expensive and time-consuming activities. Ideally, the expenditure on assessment programs
should be balanced against the anticipated benefits. This requires that the cost and benefits
associated with the programs be identified and evaluated in some way.
 The costs associated with condition and performance programs can vary greatly
depending on a utility’s current state of program and tool development, and the current
training levels of its staff. Program-specific costs will also vary depending on the
frequency of asset inspection prescribed and the number of assets to be inspected.
 While benefits are typically more difficult to quantify than costs, several methods are
outlined, including: improved operations and maintenance efficiencies; catastrophic
failure avoidance; and improved service levels and program efficiencies.
ES-2
It was noted during the research that many of the utilities contacted did not carry out
explicit cost-benefit analyses to justify their assessment programs. Assessments were instead
commonly undertaken within the context of available budgets, and a justification process driven
more by affordability and cost-effectiveness issues than explicit consideration of cost-benefits.
Figure ES-1: A 10-Step Approach to Specifying a Condition Assessment Program.
Maintenance Management Focus for Engineering and Maintenance Managers
Effective maintenance practices help to preserve asset capabilities and in turn underpin
the delivery of service on a daily basis. In general, routine maintenance tasks should be carried
out in line with equipment manufacturer’s recommendations and/or industry standards, as
appropriate, since this prolongs the life of an asset. However, the level of maintenance applied
over and above these routine tasks should depend on the importance of an asset to the utility’s
business objectives and thus the role the asset plays in service delivery:
Protocols for Assessing Condition and Performance of Water and Wastewater Assets
ES-3
 For assets of low value and/or where the impact of failure is not significant, additional
maintenance is not cost-effective and utilities should adopt a reactive run-to-failure
strategy.
 At a certain level of asset importance, it becomes desirable to use proactive maintenance
strategies, including condition assessment or monitoring, to manage the probability of
failure.
Proactive Maintenance Strategies
A key requirement for the implementation of a proactive maintenance strategy is the
ability to anticipate when a failure will occur. Inspection of condition and monitoring of asset
performance, either by manual or automated means, plays a significant role in this. Development
of an effective inspection program is centered on knowing when, where and how to inspect. If a
utility finds evidence that an asset is in a state that will eventually lead to a functional failure, it
may be possible to take action to prevent it from failing completely and/or avoid/mitigate the
failure consequences. Many assets have failure modes that give some sort of warning that a
problem is about to occur. Inspection tasks designed to detect potential failure are often referred
to as condition-monitoring tasks.
Condition-monitoring task intervals must be determined based on the time between the
point at which the onset of the failure process becomes detectable, and the point at which a
functional failure occurs (referred to as the P-F interval). If a condition-monitoring task is
performed on intervals longer than the P-F interval, the potential failure may not be detected in
time to prevent failure. On the other hand, if the condition-monitoring task is performed too
frequently compared to the P-F interval, resources are wasted.
Specifying Appropriate Condition Monitoring Tasks
A number of approaches are available to help utilities develop an effective maintenance
strategy. These methods are based on the generation and comparison of relative risk for different
maintenance strategies, and include Reliability Centered Maintenance (RCM) and Risk Based
Inspection. A generic approach to specifying condition monitoring tasks is shown in Figure
ES-2.
ES-4
Figure ES-2: A Generic Approach to Specifying Condition Monitoring Techniques.
When considering a change to any maintenance activity, the key challenge faced by a
maintenance manager is to consider what level of activity is appropriate. In practice, this often
reduces to the need to determine what percentage of the maintenance budget and resources can
or should be dedicated to an activity such as condition monitoring. Various issues need to be
considered, including what condition monitoring technologies to use, the increase in
maintenance tasks anticipated (especially in the short term before the benefits of the improved
maintenance regime start to be observed), resources and equipment required and/or available,
and the anticipated cost and benefits of the program.
Selecting Condition Assessment Tools and Techniques
A key goal of this research was to provide a framework that would assist utilities in the
selection and use of condition assessment tools. Selection tables have been developed to
facilitate this and are based on summaries and detailed write-ups of the available inspection,
survey and condition assessment tools and techniques. The selection process is summarized as:
1. Determine technical feasibility - identify the types of tools that are appropriate to the
condition assessment application under consideration.
2. Review the tool summary information - identify applicable techniques.
3. Detailed review of potential tools – examine detailed tool descriptions to determine most
appropriate candidate tools.
Protocols for Assessing Condition and Performance of Water and Wastewater Assets
ES-5
4. For viable options, undertake cost-benefit analysis – give due consideration to the
accuracy of the tool, the level of asset risk, and the available budgets.
Selection criteria have been developed to guide the selection of tools and techniques.
Where relevant information could be found, the attributes relating to the exclusion criteria have
been evaluated for each of the tools and techniques identified and reviewed in this project. These
attributes therefore summarize the application and use of the tools, and provide the information
necessary to identify the range of tools and techniques that are applicable to the condition
assessment application under consideration. Initial work has also been undertaken to develop a
prototype expert system to facilitate this tool selection process, and it is recommended that this
work be completed as part of a follow-on project.
Cost Effective Condition Monitoring
Understanding the risk associated with an asset is critical to determining the appropriate
proactive level of attention to give that asset. A direct extension of risk-based arguments is that
the more important the asset is (the higher the consequences of failure), the more expense can be
justified in assessments undertaken to ensure the asset does not fail. However, to minimize costs,
inexpensive tools should still be used where possible. As such, the following can be stated:
 Inexpensive screening tools and approaches should be used routinely.
 The results of the screening approach may dictate that there is a need for additional
information and/or accuracy. This may require the use of more sophisticated/accurate
assessment or inspection tools.
 Additional expense should be considered only when justified in terms of risk costs
avoided or benefits accrued.
An iterative approach to the use of tools is therefore suggested, where increasing levels of
sophistication are used that build on the results of previous tools and assessments. In this
approach, tools are initially selected that perform a screening function; for example, to identify
the early signs of deterioration. More detailed inspection and analysis can then be used to
investigate the asset condition further, if and when justified.
ES-6
PROJECT RECOMMENDATIONS
A research project of this scope and depth inevitably leaves some issues unresolved and
identifies areas for future research. As such, the project team recommends the following actions
for future consideration by the project sponsors:
1. The prototype expert system for tool and technique selection be further developed into a
finished software tool, and that this tool be designed to allow the information contained
within it to be kept current through an effective update mechanism.
2. Work be undertaken to integrate effectively the outputs of this research and the expert system
into the Sustainable Infrastructure Management Program Learning Environment (SIMPLE)
web site. If possible, this should include a facility for utilities to provide representative costbenefit data for condition and performance assessment programs they undertake.
3. A drinking-water version of the SIMPLE web site be produced for the benefit of the drinking
water sector.
4. Further research is undertaken into the use of condition and performance assessment in the
estimation of asset remaining life across all key drinking and wastewater asset types.
5. Further research and development of non-destructive assessment techniques be considered,
especially research aimed at developing inspection techniques for buried pipe assets such that
appropriate condition information is gathered while the assets remain in service. (See also,
Section 5 of U.S. EPA, 2005, which calls for this type of research).
Protocols for Assessing Condition and Performance of Water and Wastewater Assets
ES-7
ES-8
CHAPTER 1.0
INTRODUCTION
Chapter Highlights
 This report represents the culmination of a two-year research project jointly sponsored by
the Water Environment Research Foundation (WERF), the American Water Works
Association Research Foundation (AwwaRF) and the United States Environmental
Protection Agency (U.S. EPA).
 Utilities throughout the world are faced with the challenge of how best to manage their
existing asset stock to provide satisfactory customer service with limited funds.
 A key element of effective asset management is a cost-effective program for assessing
the condition and performance of existing assets. However:
−
No standardized guidelines or protocols currently exist for utilities to understand
how to develop and implement condition assessment programs and to show how
these programs should fit into an overall asset management program.
−
No single resource currently exists for utilities to identify and understand the tools
and techniques that are available to assess the condition and performance of their
assets.
 This research has been undertaken as an initial effort to fill these two important voids. In
doing so, this report attempts to reach two audiences:
−
The utility planning managers who are seeking to understand how to embark
upon cost-effective condition and performance assessment programs and how
these efforts should fit within an overall asset management approach. This
audience will be most interested in Chapters 1.0-4.0 and the case studies
presented in Chapter 8.0.
−
The utility field engineering, operations and maintenance managers who are
seeking to identify and understand the advantages and disadvantages of various
available tools and techniques for measuring the condition and performance of
utility assets. This audience will be most interested in Chapters 5.0-7.0 and the
case studies presented in Chapter 8.0.
 To facilitate the use of the report further, an attempt has been made to anticipate
questions a user may wish to answer and to provide an indication of where in the
document related information can be found.
−
These questions are presented as a document road map within this chapter.
 While this report focuses on condition assessment tools and techniques more so than
performance assessment, the subject of performance assessment is recognized (and
covered to a lesser extent) as an important means of understanding asset condition.
Protocols for Assessing Condition and Performance of Water and Wastewater Assets
1-1
1.1
Introduction
Recent infrastructure studies undertaken in the United Kingdom, Australia and the United
States have shown a common cause for concern—there is widespread deterioration of critical
water and wastewater infrastructure assets, with significant shortfalls in the renewal/replacement
investment required to ensure that water and wastewater utilities can deliver sustainable services
to their communities. For example, in the United States, the American Society of Civil Engineers
(ASCE, 2005) released a report that assigned letter grades to 15 categories of public works. The
grades were allocated on the basis of condition and performance, capacity versus need, and
funding versus need. The rating given to water and wastewater infrastructure was D-, considered
to be a “poor” rating, and only one grade higher than “inadequate/failing.”
The long-term cost implications of continuing with a poorly structured replacement/
renewal regime could be dramatic. For example, the United States based Water Infrastructure
Network estimated that the gap between spending levels and the investment required to meet the
United States’ national environmental and public health priorities embodied in its Clean Water
Act and Safe Drinking Water Act will reach US$23 billion a year over the next 20 years (Water
Infrastructure Network, 2000). Similarly, the American Water Works Association estimated that
US$250 billion over 30 years might be required nationwide for the replacement of just water
distribution pipes and their associated valves and fittings (AWWA, 2001).
This situation is, to a greater or lesser extent, common to the water sectors of many
countries, and has largely come about through assets reaching the end of their life expectancy
without being replaced. This in turn can be related to the adoption of management practices with
a short-term focus, which has led to the deferral of investment required for asset renewals. For
example, in the United States, there has been a tendency to focus on 12-18 month funding cycles
and project deliverables due to the nature of annual government budgets. This funding trend,
combined with two to four year election cycles, has created an atmosphere that encourages shortterm decision making on infrastructure matters, rather than a long-term view (Rast, 2003).
The challenge for many water utilities today is to determine how best to manage their
asset stocks with limited replacement funds, while maintaining a satisfactory level of service in
the long term. Given this challenge, WERF held a workshop in March 2002, entitled “Research
Priorities for Successful Asset Management.” The workshop addressed asset management issues
across public water and wastewater utilities and recommended a research agenda to promote the
next generation of tools for reducing risk and improving competitiveness. Workshop participants
identified that there were no standardized guidelines for conducting condition assessments and
that there was a lack of protocols to help utilities better understand asset condition and
performance.
The workshop determined that undertaking condition assessment within an appropriate
asset management framework would be a significant step forward for the water utility sector of
the United States. For example, this step would enable a utility to better:
 Meet customer service expectations as well as legislative requirements.
 Determine the risk of failure (considering both failure probability and consequence)
associated with different assets, and therefore, prioritize spending within limited budgets.
 Understand asset condition and remaining life, allowing for proactive budgeting for
renewal/replacement of assets.
1-2
 Quantify the benefits of different management/operational strategies.
 Determine asset value and comply with accounting standards.
With these and other advantages in mind, a primary objective of this report is to
demonstrate the important link between accepted and emerging principles of asset management
and approaches to condition assessment. The report also provides information to facilitate the
selection and effective use of condition assessment tools and techniques when undertaking asset
inspection and condition monitoring within a framework of various levels of asset management
sophistication. A comprehensive scope of tools is considered, covering those applicable to above
and below ground assets (pipeline and non-pipeline assets) used in the delivery of potable and
wastewater services.
1.2
Project Delivery
This research project was undertaken in two overlapping phases. Phase 1 of the project
involved a review of literature and other information sources and led to the drafting of a
condition and performance assessment framework, along with an initial review of available tools
and techniques. Phase 2 was undertaken as a refinement stage, where concepts developed in
Phase 1 were developed further, drawing on the knowledge from a range of case study partners
and professionals working within the sector.
Phase 1 included a web-based industry survey undertaken as a means of obtaining
baseline information about the sector in the United States (some responses were also obtained
from utilities who accessed the survey in other countries). Phase 1 also included a review of the
literature relating to asset management and condition assessment tools and techniques. This
consisted of performing an initial electronic search of the literature using combinations of key
words, screening results and developing lists of articles pertaining to above and below ground
assets from journals, proceedings and conferences. This allowed a first pass assessment of the
tools and techniques used for condition and performance assessment in various sectors to be
made. These tools were researched further during Phase 2 of the project, drawing on information
sources available to the research team, the academic and commercial literature and the Internet.
Draft summaries of individual tools were then sent out to a range of industry
professionals, including venders, researchers and users for peer review. A data collection
spreadsheet that detailed all of the tools and techniques identified in the project was also sent to
each reviewer. The reviewers were asked to use the spreadsheet to confirm the applicability of
tools included on the list and to add any additional tools that were used by or known to them.
Conceptual design of a range of condition and performance related protocols were also
carried out in Phase 1, drawing on the available literature and the experience of the project team.
These protocols were developed further in light of industry interactions carried out as part of the
Phase 2 case studies.
1.3
Linkage to Related Research
In conjunction with other WERF and AwwaRF projects, the project outputs will help
utilities move towards better practice in both condition assessment and asset management. To
this end, the reader is referred to the Sustainable Infrastructure Management Program Learning
Environment (SIMPLE) tool accessible through the WERF web site (accessible to WERF
members only): http://simple.ghd.com.au/Default.aspx.
51H
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
1-3
SIMPLE is a web-based knowledge management tool that helps utilities in developing a
life-cycle asset management approach. The tool guides utilities on how to determine the most
cost-effective investments—acquisition, maintenance, renewal—in their asset portfolio,
including how to extend the life of existing assets by implementing optimal maintenance
practices and rehabilitation interventions.
1.4
Report Structure
The report is presented in eight chapters:
 Chapter 2.0 Provides background information on accepted and emerging principles of
asset management, why water and wastewater utilities (hereafter generally referred to as
‘utilities’) undertake condition and performance assessments and the role such
assessments should play in the overall strategic asset management process.
 Chapter 3.0 Discusses issues relating to the design of a condition assessment program
for strategic asset management and presents a generic 10-step approach to this design.
 Chapter 4.0 Considers how a condition assessment program can be justified.
 Chapter 5.0 Provides background information on why utilities undertake condition and
performance assessments and the role such assessments should play in day-to-day
maintenance; this chapter also includes a generic approach to selecting techniques for
condition monitoring.
 Chapter 6.0 Presents the approach developed in the project to aid the selection of
condition assessment tools/techniques.
 Chapter 7.0 Summarizes the tools and techniques available for use with different assets.
 Chapter 8.0 Presents details of the case studies.
Supporting appendices are presented at the end of the report:
 Appendix A: Utility Objectives and Related Key Performance Indicators
 Appendix B: Individual Drivers for Assessment
 Appendix C: Condition and Performance Assessment Criteria
 Appendix D: A Generic Condition Assessment Form
 Appendix E: Development of a Prototype Expert System
 Appendix F: Details of Available Tools and Techniques
1.4.1 Presentation of Detailed Information on Tools and Techniques
The detailed information on condition assessment tools and techniques has also been built
into a prototype electronic expert system to aid users in the tool/technique selection process
(described in Appendix E). It is a recommendation of this project that the prototype be developed
into a finished software tool and made available through the SIMPLE web site.
For the purposes of this report, however, the detail of the tools and techniques reviewed
in the project are incorporated into Appendix F, with selected summary information included in
Chapter 7.0 of the report to guide selection.
1-4
1.4.2 Note on Case Study Insets
Interactions with industry practitioners were undertaken throughout this research,
particularly during Phase 2 when a range of case studies were undertaken with a number of
utilities in the United States, Australia, New Zealand, and the United Kingdom. The case studies
are detailed in Chapter 8.0 of this report. Case Study Insets are also distributed throughout the
report to provide practical insight into the points under discussion. In general, these insets
provide summary information that has been drawn from one of the case studies detailed in
Chapter 8.0. Where this is the case, the linkage to the case study is explicitly stated so the reader
can refer to the relevant case study. In many cases, the full case study provides additional insight
into the issues under discussion.
1.5
How to Use this Report
The initial focus of this project was the consideration of condition assessment as a
strategic asset management tool. Direction from the Project Steering Committee after completion
of Phase 1, however, indicated that the focus of the project needed to be expanded to include the
use of condition monitoring techniques in maintenance. As a result of this guidance, this report
includes specific chapters relating to
1. Strategic Asset Management.
2. Maintenance Management.
Chapters with a Strategic Asset Management Focus
Readers interested in condition assessment from the perspective of strategic asset
management are directed to the following chapters:
 Chapter 2.0 Reviews a range of issues related to strategic asset management.
 Chapter 3.0 Considers the design of condition and performance assessment programs
from a strategic asset management perspective.
 Chapter 4.0 Outlines the approach to program justification using cost-benefit analysis.
 Chapter 6.0 Provides guidance on tool selection.
 Chapter 7.0 Considers the range of tools available for condition assessment.
 Chapter 8.0 Presents case studies.
Chapters with a Maintenance Management Focus
Readers interested in condition monitoring from the perspective of day-to-day
maintenance are directed to the following chapters:
 Chapter 5.0 Outlines maintenance practices and the role condition monitoring plays in
maintaining asset capabilities.
 Chapter 6.0 Provides guidance on tool selection.
 Chapter 7.0 Considers the range of tools available for condition assessment.
 Chapter 8.0 Presents case studies.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
1-5
1.6
Document Road Map
To further facilitate the use of the report, an attempt has been made to anticipate
questions a user may want to answer and to provide an indication of where in the document
related information can be found.
In line with the overall design of the document, questions are presented below and split
according to the two target audiences:
1. Questions relevant to strategic asset managers.
2. Questions relevant to maintenance professionals.
It is also anticipated that the user may want to access information relating to specific
asset types, so an indication is also given as to where this information can be found within the
report.
1.6.1 Road Map for Asset Managers
Gaining a General Understanding of Condition Assessment and SAM
 What are the key elements of SAM and how is this discipline developing?
−
See Section 2.2 and subsections.
 How is condition assessment used in SAM?
−
See Section 2.3 and subsections .
 When should I undertake condition assessment for SAM purposes?
−
See Section 2.4 and subsections and Appendix A and B.
 What is the link between condition assessment and a KPI management system?
−
See Section 2.4.1 and Appendix A.
Developing a Condition Assessment Program
 What role does asset risk play in the design of my program?
−
See Section 3.2.
 What outputs can I expect from a condition assessment program?
−
See Section 3.3.
 How do I design and use condition/performance grading system?
−
See Section 3.3.3 and subsections; Appendix C.
 How do I design a condition assessment program itself?
−
See Sections 3.4 to 3.5 and subsections.
 What factors do I consider in the design of an asset sample?
−
See Section 3.4.5.
 What data and information should I collect during an assessment program?
−
1-6
See Section 2.2.2, Section 3.6; Appendix D.
 How do I go about justifying my condition assessment program?
−
See Section 4.
Information on Tools and Techniques
 What factors should I consider when selecting tools and techniques?
−
See Chapters 6, specifically Table 6.1 and Table 6.2.
 How do I select which tools to use for a given asset type or situation?
−
See Chapters 6 and 7, specifically Figure 6.2 and Table 7.6.
 I need information on a specific tool, where can I find this?
−
See Appendix F.
1.6.2 Road Map for Maintenance Managers and Engineers
Gaining a General Understanding of Proactive Maintenance
 What are the key elements of proactive maintenance programs?
−
See Section 5.2 and subsections.
 How are asset inspections and performance monitoring used in such programs?
−
See Section 5.3 and subsections.
Developing Proactive Maintenance Programs
 What are risk-based assessment procedures in the context of maintenance?
−
See Section 5.4.
 What types of risk-based assessment techniques are available?
−
See Section 5.4.1 (for RCM) and Section 5.4.2 (for RBI).
 Is there a generic approach for specifying maintenance tasks on the basis of risk?
−
See Section 5.5 and subsections.
 How do I develop and justify my condition monitoring program?
−
See Section 5.6 and subsections.
Selecting Appropriate Tools and Techniques
 How do I select condition assessment tools?
−
See Chapter 6.0.
 What is the impact of asset risk on the tool selection process?
−
See Section 6.6 and subsections .
 Should I use the most accurate (and expensive) tool available?
−
See Section 6.7, specifically Figure 6.3 and Table 6.4.
 What factors should I consider when selecting tools and techniques?
−
See Chapters 6.0, specifically Table 6.1 and 6.2.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
1-7
 How do I select which tools to use for a given asset type or situation?
−
See Chapters 6.0 and 7.0, specifically Figure 6.2 and Table 7.6.
 I need information on a specific tool, where can I find this?
−
See Appendix F.
1.6.3 Asset Related Sections
Multiple Asset Types
 Where can I find general information relating to asset-specific assessments?
−
See Section 3.5.1 for summary approaches for a range of assets.
 Where can I find information relating to a generic (any asset) assessment program?
−
See case study 3.
 Where can I find information relating to asset-specific assessment criteria?
−
See Appendix C for condition and performance assessment criteria.
Pipe Assets
 Where can I find information relating to water distribution pipes?
−
See Sections 3.3.2 and 3.3.3; case studies 2, 10 and 12.
 Where can I find information relating to water transmission mains?
−
See Inset 6-2 (Section 6-7); case studies 5 and 13.
 Where can I find information relating to gravity sewers?
-
See Section 3.3.4; case studies 6, 7 and 10.
 Where can I find information relating to sewer force mains?
−
See case study 14.
Non-Pipe Assets
 Where can I find information relating to treatment work assessments?
−
See Inset 5-5 (Section 5.4.1); case study 1.
 Where can I find information relating to mechanical and electrical assets?
−
See Section 6.6, Inset 5.3 (Section 5.4.1); case studies 9, 11 and Appendix D.
 Where can I find information relating to water tank assessments?
−
1-8
See case studies 4 and 8.
CHAPTER 2.0
CONDITION ASSESSMENT AS A
STRATEGIC ASSET MANAGEMENT TOOL
Chapter Highlights
 Utilities share a common business driver: the need to provide sustained service delivery
at an acceptable cost and in accordance with regulatory requirements. They provide this
delivery of service through a combination of the utility’s business and asset capabilities.
 A key business capability of a utility is its ability to effectively manage and maintain its
asset stock.
 Strategic asset management philosophies have developed over time to facilitate this. The
more advanced approaches focus on risk and service, rather than condition and
performance. Condition assessment, however, remains a key component of risk-based
asset management.
 Various levels of asset management sophistication can be identified (informal, core and
advanced) and various drivers exist that create a tendency towards increasing levels of
sophistication.
 Utilities should manage asset condition and performance within the context of the
utility’s overall asset management strategy and service level goals.
 Condition and performance assessment activities should be designed to fill specific assetrelated information gaps in order to facilitate decision making.
 Since condition and performance data collection and management is costly, it is
important that a utility strive to collect only sufficient data to support the information
needs of the business.
 Ideally, various measures of performance (key performance indicators or KPIs) would be
used to drive asset management, with asset-level condition and performance assessments
only being undertaken when there is a need for additional information.
 In practice, however, utilities need to undertake asset-level condition and performance
assessments in response to a range of drivers unconnected with KPI management
systems, not least because of the need to satisfy the requirements of regulators.
Protocols for Assessing Condition and Performance of Water and Wastewater Assets
2-1
2.1
Introduction
Utilities are tasked with supplying critical water and wastewater services to communities
and the environment. From this perspective, a utility’s business drivers are to provide sustained
service delivery at an acceptable cost and in line with regulatory requirements such as the need to
maintain water and environmental quality and give due regard to public health and safety. The
capacity to deliver these services depends strongly on the business capabilities of the water
utility (e.g., the people, processes, data and technology used within the business) and asset
capabilities (e.g., the capacity, condition and performance of individual assets and systems).
The concept that service levels are dictated by the utility’s business drivers but
underpinned by business and asset capabilities is illustrated in Figure 2-1. For example, business
drivers such as customer expectations and requirements of regulators dictate the level of service
that must be delivered, whereas asset and business capabilities impose a limit on the level of
service that can be sustained over the long term. Where there is a disparity between the demand
for service and the capacity to deliver that service, investment is required in the utility’s asset
and/or business capabilities.
Figure 2-1. Business Drivers and Utility Capabilities.
In an asset-intensive sector, one of the key business capabilities a utility can develop to
facilitate service delivery is the effective management of its asset stock, which will in turn
underpin the construction and maintenance of an asset base that has the capability to sustain the
required service levels.
As discussed in Chapters 3.0 and 4.0, effective management of assets requires both
strategic management approaches and an effective approach to condition and performance
assessments undertaken in support of strategic asset management. In this context, condition and
performance assessments provide information on issues such as:
 The value of existing assets.
 Asset remaining life.
 The reasons for shortfalls in service provision.
 The potential for future problems; that is, the risk of failure (probability versus
consequence) associated with different assets.
2-2
The way in which condition and performance assessments are used, however, varies
significantly because of the range of asset management approaches adopted by different utilities.
This chapter explores the concepts that underlie the approaches to asset management
applied in the water sectors of countries such as the United States, Australia, New Zealand, and
the United Kingdom and illustrates the role condition and performance assessments plays within
various asset management philosophies. Since the meaning of asset management varies
significantly from practitioner to practitioner, the definition of asset management adopted within
this project is first presented, along with an outline of the overall asset management cycle. The
development of asset management and its underlying philosophies are then reviewed, including a
discussion of the emerging drivers for greater asset management sophistication.
A generic protocol for specifying when and where to undertake condition and
performance assessments is then presented. An ideal approach that uses performance
assessments based on KPIs to measure asset capabilities is outlined, along with a more pragmatic
approach where the need for assessments is dictated by discrete drivers. Examples of protocols
for undertaking condition assessment for the purposes of strategic management in other sectors
are also presented.
It should be noted that this chapter considers issues only from the perspective of strategic
asset management (defined below). Issues relating to day-to-day maintenance management are
discussed in Chapter 5.0.
2.2
Strategic Asset Management
Asset management remains an ill-defined term, and many definitions exist in the
literature. For example, Vanier & Rahman (2004) give the following definition:
Asset management is a business process and decision-support framework that: (1) covers the
extended service life of an asset, (2) draws from engineering as well as economics, and (3)
considers a diverse range of assets.
Similarly, the U.S. EPA (2002a) notes that:
Asset management is a continuous process that guides the acquisition, use, and disposal of
infrastructure assets to optimize service delivery and minimize costs over the asset’s entire
life.
Notwithstanding the value of these definitions, for the purposes of this project, the
following definition, modified from that given in the International Infrastructure Management
Manual (IPWEA, 2006), is considered by the authors to encapsulate the main features of this
emerging discipline as it is practiced today:
The combination of management, financial, economic, engineering and other practices
applied to physical assets with the objective of providing the required levels of service to
customers and the environment at acceptable levels of risk and in the most efficient manner.
While “asset management” is used as a general term throughout this report to indicate
issues relating to this definition, the expression “Strategic Asset Management” (SAM) is also
used to differentiate practices specifically with a medium to long term view, from those practices
specifically with a short to medium term view, which are considered to be part of maintenance
management discussed in Chapter 5.0.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
2-3
Many practitioners refer to asset management with a medium view as “Tactical Asset
Management,” however, this term is not used within this work.
2.2.1 Asset Management as a Framework
The adoption of formal asset management by utilities has generally lagged behind the
development of the asset stock. As such, asset management has commonly evolved and
developed around existing utility systems and in light of existing assets.
When starting to implement formal asset management approaches, utilities generally
begin from a position of poor knowledge regarding the asset stock. However, as discussed in
Section 2.2.2, a fundamental requirement of all asset management systems is information on the
assets. Utilities in this position must therefore address the six “whats” of asset management
(Vanier, 2000 & 2001):
1. What assets are owned?
2. What are they worth?
3. What is the deferred maintenance? (In this context, deferred maintenance is taken to be
an overview of the amount of expenditure required to bring the maintenance and repair
under control, rather than being a measure of renewal backlog).
4. What condition are the assets in?
5. What is the remaining service life of the assets?
6. What should be fixed first?
Various asset management tools and approaches are needed to help answer these
questions. In particular, condition and performance assessment are widely used, not least because
they provide the information required to answer the last three of the “whats” of asset
management listed above.
While these tools are important to the implementation of asset management, it should be
understood that they are not asset management per se. Instead, it is useful to consider asset
management as a framework within which various tools and approaches are applied. For
example, the “Publicly Available Standard” for asset management (PAS 55) in the United
Kingdom (BSI, 2004), provides a complex framework (scope) for asset management, which for
most practical purposes can be simplified to the process shown in Figure 2-2.
It is interesting to note that the later steps in Figure 2-2 (set condition and performance
targets, produce asset management plans, and implement and operate) indicate that the on-going
management of asset condition and performance is a key aspect of this framework. Management
of asset condition and performance can only be achieved if appropriate measures are available to
compare against the condition and performance targets, so the implementation of this particular
framework would, like the six “whats” of asset management given above, explicitly drive the
requirement for condition and performance assessments. However, as will be discussed later,
management of condition and performance is just one asset management philosophy adopted in
the water sector.
The reader is referred to national and international standards for more information on
asset management frameworks (for example, IPWEA, 2006; BSI, 2004).
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Figure 2-2. The PAS 55 Physical Asset Management Framework.
2.2.2 The Role of Asset Data and Data Systems
As noted in section 2.2.1, the first “what” of asset management requires a utility to
determine what assets are owned. An asset inventory (generally a formal list of assets, broken
down into an appropriate hierarchy and keyed with a unique tag number) is thus essential to asset
management. Furthermore, as illustrated in Figure 2-2, implementation of an asset management
framework is not a static process—monitoring, review and improvement of all stages are
essential. This requires a formalized feedback loop that leads to corrective actions, improvements
and evolution of the process in question. This feedback in turn relies upon having sufficient data
capture/collection and associated procedures. For these and other reasons, data is fundamental to
all asset management systems.
It is important to establish and maintain an up-to-date inventory of assets and to combine
this with a database of other asset-related data items (commonly implemented as a computerized
maintenance management system and/or a geographical information system). Creating such a
database is not a trivial task and may require several years and revisions (e.g. Zhao, 1998).
Data items incorporated into the database(s) will vary from asset type to asset type. For
example, Newton & Vanier (2006) state that the minimum sewer pipe physical data should be
the pipe location, length, material, diameter and year of construction. The next level of inventory
data includes invert depth, type of backfill, bedding material and ground water level, which are
important factors to consider when determining pipe condition. More generally, asset data is
required on:
 Asset physical aspects (asset type, material, rating, age, etc.)
 Asset location and/or geo-reference
 Design and construction information
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
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 Operational context
 Environmental conditions
 Information on reported defects and failures
 Maintenance and inspection records
Given the large number of assets involved in the provision of water and wastewater
services, there is potentially a great deal of data that could be included in a database. However,
since data collection and management is costly, it is important that a utility collect only sufficient
data to support the information needs of the business. This concept is illustrated in Figure 2-3,
which shows the relationship between data, business processes and information needs. To
optimize data collection, the utility should first consider the business information needs, which
will then dictate what input data are relevant, including the amount of asset condition and
performance data required. This mapping needs to be reviewed periodically as business
information and data needs change due to changes in emphasis given to different management
issues, changes in regulation, and so forth.
Figure 2-3. Determining Data Requirements through Information Needs.
2.2.3 Strategic Asset Management Philosophies
The flow chart presented in Figure 2-2 indicates a focus on the management of asset
condition and performance. However, other asset management approaches exist. In fact, the asset
management approaches applied in the water sectors of countries such as the United States,
Australia and the United Kingdom can be characterized in terms of a succession of dominant
philosophies. In reality, each successive approach has built on the previous one(s), so any
explicit division is somewhat artificial. Nevertheless, for the purposes of this discussion, it is
useful to consider the approaches as distinct. The following list indicates the staged development
of increasing asset management sophistication:
 Condition-based asset management
 Performance-based asset management
 Service-based (service level driven) asset management
 Risk-based asset management
In condition-based asset management, expenditure is focused on maintaining ‘what
assets are’ (the condition they are in). This is a natural approach for engineers to adopt; if the
condition is poor, the asset needs maintenance/investment to rectify defects.
In a similar vein, performance-based asset management focuses on ‘what assets do’ in a
local sense; that is, the question is posed, “is the asset doing the job that it was intended to?”
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(This question can often be related to the asset’s condition, but may not be.) If not, maintenance
and/or capital investment are required. Again, this is a natural way for engineers to consider
management of assets.
A more customer-focused approach is taken in service-based asset management.
Performance is not viewed in terms of local considerations (the design intent of individual
assets), but instead is considered in more inclusive terms and at a higher level. The question is
posed, “is the asset contributing appropriately to the delivery of service?” This consideration is
made independently of asset condition or its performance relative to design intent.
Service-based asset management thus seeks to maintain the service provided by the asset
stock at both the local and regional level. Due consideration is normally given to the need to
deliver at least minimum levels of service to all customers. This approach is less intuitive for
engineers, since it can mean that maintenance/investment is not always justified for poor
condition assets or even poor performing assets where the impact on service is acceptable.
Risk-based asset management seeks to achieve optimum life cycle management of assets
through consideration of risk to service provision, with risk generally being defined as the
product of ‘probability of failure’ and ‘consequence of failure’. The condition and performance
of an asset are simply factors in the assessment of risk. Other factors taken into account include
business risk factors such as those associated with safety and the environment, customer
expectations, reliability, efficiency and effectiveness, finance, reputation and regulatory
relationships.
In the web-based industry survey undertaken as part of this research, surveyed utilities
were asked to specify which of these categories best described their approach to asset
management. The results are shown in Table 2-1 for a sample of 30 respondents, 21 of which
were from the United States. The table shows that there is a wide range of philosophies still
being adopted within the sector, and that nearly one-third of the respondents indicated that there
was no defined strategy being used.
Table 2-1. Approaches to Asset Management Adopted.
Asset management approach adopted
Condition-based
Performance-based
Service-based
Risk-based
No defined strategy
Proportion
28%
19%
10%
14%
29%
2.2.4 The Building Blocks of Asset Management
Whatever philosophy is adopted, it can be generally stated that SAM seeks to optimize a
utility’s expenditure by determining the most appropriate time to intervene in the asset
deterioration process to maintain service delivery at an acceptable level of business risk and
within budget. Since assets deteriorate over different periods, asset management is thus
undertaken within the context of the life cycle of the asset stock and can be considered a cyclic
process of asset-related tasks, as shown in Figure 2-4.
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Figure 2-4. The Asset Management Cycle.
From the categorizations given in Table 2-1, it is clear that utilities address the asset
management cycle shown in Figure 2-4 in a variety of ways. Nevertheless, all utilities must, in
broad terms, deliver the same range of core services and manage an asset stock throughout its
life cycle. As such, all utilities must address various asset management building blocks in some
way, even when the overall asset management approach is not formalized. These include the
asset-related tasks shown in the asset management cycle (Figure 2-4), as well as other
fundamental building blocks such as:
 Asset information
 Condition and performance assessments
 Risk management
 Planning for maintenance and renewals
 Optimizing asset investment
 Monitoring service provision
 Setting appropriate pricing
The level of asset management adopted to co-ordinate and align these building blocks
depends in part on the utility’s business environment. For example, the more exacting the service
mandates are in relation to budgetary constraints, the more sophisticated the asset and business
capabilities need to be; these conditions then drive the need for adopting formalized asset
management approaches.
2.2.5 Three Levels of Strategic Asset Management
The International Infrastructure Management Manual (IPWEA, 2006) defines two levels
of formal asset management: core and advanced.
Core asset management relies primarily on the use of an asset register, maintenance
management systems, job/resource management, inventory control, condition assessment and
defined levels of service, in order to select appropriate interventions and make long-term
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cash flow predictions. Priorities are usually established based on financial return rather than
risk analysis and optimized decision making.
Advanced asset management employs predictive modeling, risk management and optimized
decision making techniques to establish asset lifecycle intervention options and related longterm cash flow predictions. Advanced asset management is heavily reliant on the use of
computerized systems and is possible only when detailed data on assets are available.
However, since data quality improves over time as it becomes embedded within a ‘business
as usual’ environment, early adoption of advanced asset management approaches can act as a
facilitator for improving the quality and accuracy of data.
Since the results given in Table 2-1 indicate that 29% of respondents have no defined
strategy for asset management, it can be inferred that a significant proportion of utilities in the
United States have not yet implemented core asset management, as defined in the International
Infrastructure Management Manual (IPWEA, 2006). As noted above, however, in an asset
intensive sector, all utilities must be undertaking management of assets in one form or another.
As such, for the purposes of this project, utilities undertaking management of assets without
adopting a formal approach to SAM, were deemed to be applying a third level, which can be
termed Informal Asset Management.
2.2.6 The Drive Toward Increasing Asset Management Sophistication
If there were no drive towards greater sophistication, it can be assumed that informal
asset management approaches would remain in place, since these are the least expensive
approaches to implement. In the United States, as with other countries, an informal approach has
been acceptable in the past; however, this trend appears to be shifting.
Some of the drivers behind this shift include decreased availability of federal grants for
capital projects, and more stringent service and cost drivers. Rast (2003) identified four key
drivers for the adoption of formal asset management approaches in the United States:
 Changes in demands placed on infrastructure and budgets.
 Changes in public perception relating to asset management.
 Changes in regulatory requirements.
 Availability of new technology.
The first of these drivers relates to the combination of increased demand on
infrastructure systems combined with a significant budget shortfall. The second driver relates to
public perception of the management of infrastructure assets and a growing awareness of the
impact of aging infrastructure and environmental factors on water quality and quantity. In a
similar vein, the U.S. Department of Transport (US DoT, 1999) noted that asset owners will be
facing increased system and budget needs with limited staff resources. At the same time,
individual states will be required to deal with increased system complexity and public demands
for accountability and expectations regarding levels of service. As noted in Chapter 1.0 of this
report, these demands are occurring at a time of deteriorating asset stocks.
The third driver noted by Rast (2003) is a change in regulations, which promote and/or
require the adoption of asset management principles. These regulations include the U.S.
Government Accounting Standards Board (GASB) issued Statement No. 34, and ‘Capacity
assurance, Management, Operation and Maintenance’ (CMOM), discussed further in Case Study
Insets 2-1 and 2-2. The final driver is the availability of new computer technology, which has
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
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prompted a significant increase in the availability of tools (e.g. GIS and hydraulic models) that
can assist in the complex analysis and decision making required for formal asset management.
Case Study Inset 2-1: GASB 34
In June 1999, the U.S. Government Accounting Standards Board (GASB) issued Statement
No. 34 (GASB 34), “Basic Financial Statements for State and Local Governments” (GASB,
1999). GASB 34 requires state and local agencies to produce financial reports in a manner
more consistent with that used by private sector companies. In particular, GASB 34 requires
infrastructure to be reported at its historical value and then depreciated. However, the
GASB 34 requirements also allow for a modified approach for infrastructure assets that are
part of a network or subsystem of a network.
With this modified approach, assets do not have to be depreciated if two criteria are met,
namely, 1) the public agency manages the asset using an asset management system and 2) the
agency demonstrates that the assets are being preserved at, or above, an established condition
level. The asset management system should:
 Have an up-to-date inventory of assets.
 Perform condition assessment of the infrastructure assets at least once every three
years.
 Estimate the annual investment required to maintain and preserve the infrastructure
assets at the condition level originally established for those assets.
GASB 34 therefore offers utilities the option of reporting the system at full historical cost,
rather than reporting depreciation, as long as asset management practices are adopted (U.S.
DoT, 1999). Under the modified approach, maintenance and preservation costs are expensed
and only additions and improvements to the system are capitalized (U.S. EPA, 2002a).
Case Study Inset 2-2: CMOM
Capacity assurance, Management, Operation and Maintenance (CMOM was developed by the
U.S. EPA in conjunction with municipal and other industry representatives. CMOM is an
information-based approach to setting priorities for activities and investments in sewer
collection systems.
CMOM embodies many asset management principles as they apply to collection systems.
These include defining goals, using an information-based approach to set priorities, evaluating
capacity and taking steps to ensure capacity is adequate, developing a dynamic, strategic
approach to preventive maintenance and conducting periodic program audits to identify
program deficiencies and ways to address those deficiencies (U.S. EPA, 2002a).
2.2.7 Economies of Scale in Asset Management
As a direct consequence of these drivers, United States’ utility managers are more
frequently being asked to adopt more sophisticated asset management practices. The dominant
belief is now that affordable technology is available to facilitate data and information
management, the adoption of a strategic asset management philosophy will focus capital,
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operational and maintenance strategies on the achievement of strategic business objectives and
deliver them in a cost effect manner and at an acceptable level of risk.
The added value (perceived or actual) realized by investing in asset management
approaches will, to a degree, depend on the size and complexity of the utility’s operations. The
issue of affordability and cost-benefits need to be considered in all cases, but economies of scale
favor the larger utility. For example, Shaw (2001) indicated that it is possible to increase the
assets under management without a proportional increase in asset management overheads. Table
2-2, gives an indication of how asset management labor input, in terms of full time equivalents;
(FTEs), might vary with the value of assets being managed.
Table 2-2. The Impact of Scale on Asset Management Resources (after Shaw, 2001).
Asset management FTEs
Asset base
Asset base x 2
114.8 FTEs
134.3 FTEs
(25% increase)
Asset base x 4
179.3 FTEs
(67% increase)
While such economies of scale may well exist, this does not preclude smaller utilities
from adopting sophisticated strategies for the management of specific asset types. For example,
small utilities may (and do) adopt sophisticated geographical information system (GIS) based
analytical approaches for the management of pipe networks.
2.3
Condition Assessment as an Input to Strategic Asset Management
As discussed in previous sections, there has been a succession of asset management
philosophies (from a focus on asset condition and performance, to a focus on service provision
and business risk) and an increase in asset management sophistication in the utility sectors of a
number of countries. Since the more developed asset management philosophies do not focus on
asset condition, it can be concluded that SAM does not seek to manage asset condition or
performance per se. For many types of assets, however, there is a general relationship between
age, condition and the asset’s propensity to fail, as illustrated schematically in Figure 2-5.
Such relationships occur when failure mechanisms such as fatigue, corrosion and wearout start to predominate as the asset reaches the end of its useful life. The rate of deterioration
(i.e., the worsening of condition and/or performance) is highly asset and context-specific, and
depends upon such factors as the type and design of the asset, the existence of deterioration
mechanisms such as corrosion and wear, any protection systems used, local environmental
conditions, its operating context and the maintenance strategy adopted. Relationships such as
those illustrated in Figure 2-5 are seldom straightforward. Nevertheless, the condition and
performance of many types of assets progressively deteriorate over a characteristic timescale,
eventually reaching the point where they need to be replaced or rehabilitated because they are
uneconomic to operate, provide unacceptable performance or are deemed to represent too high a
risk.
Given theses considerations, although it is true that SAM does not seek to manage asset
condition as such, measures of asset condition and performance are clearly an important input
into asset management decision making and other processes. In turn, the development of asset
management processes also facilitates the effective implementation of condition assessments, as
summarized in Case Study Inset 2-3.
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Figure 2-5. The Relationship between Asset Condition, Age and Failure Probability.
Case Study Inset 2-3: Increasing Condition Assessment Effectiveness through SAM
When it was corporatized in the early 1990’s, Melbourne Water inherited a fragmented
approach to the management of its water tanks. Basic information relating to the construction
of the tanks was available in the form of design drawings. However, on-going assessments
were undertaken separately by various departments focusing on individual issues, such as
corrosion, mechanical and electrical components, valves, etc. Information recorded during
these assessments was in a summary format (e.g., “asset satisfactory”) and not collated
together.
It was recognized that this assessment strategy did not provide the information required to
support effective stewardship of complex assets. As such, Melbourne Water started to develop
a structured approach to the management of these assets. Asset specific policies and
procedures were developed, in line with the development of corporate risk and asset
management policies, and with appropriate resourcing and lines of responsibility.
Subsequent experience within Melbourne Water has shown that detailed investigations can be
required when there is an unexpected failure or deterioration of any asset. The ability to
undertake these investigations and implement risk management strategies is greatly enhanced
by the development of asset management approaches.
See Case Study 8 in Chapter 8.0.
2.3.1 The Role of Condition Assessment
The challenge a utility faces is not managing the deterioration of one asset, or even one
asset type, but managing the on-going deterioration of numerous assets, of many types, with
different time scales of deterioration (months to many years), being affected by a vast array of
environmental and operational context and having differing impacts on the utility’s operations
and budgets.
To maintain service into the future in an affordable way, the utility must therefore
understand the change in structural condition of all its assets, both spatially and temporally.
Condition assessment can be used to develop or enhance this understanding in conjunction with
assessments of performance undertaken at both asset-specific and system levels. In fact, the U.S.
EPA (2002b) noted that 1) the best way to determine the remaining useful life of a system is to
conduct periodic condition assessments, and 2) that it is essential for utilities to complete
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periodic condition assessments in order to make the best life-cycle decisions regarding
maintenance and replacement.
In addition to playing a key role in the assessment and understanding of asset
deterioration, condition and performance assessments can also provide information to meet other
strategic asset management needs, for example:
 What assets are worth.
 How assets are performing in relation to requirements (in some cases, this involves
comparing asset performance to service measures).
 The impact of operation and maintenance practices on asset condition and performance.
Case Study Inset 2-4 illustrates the role condition and performance assessments can play
in regulatory reporting, which encapsulate these issues.
Case Study Inset 2-4: Use of Condition and Performance Assessment in Reporting
In Scotland, the assessment of asset condition and performance was required by the Economic
regulator for Scotland and included in the Asset Inventory and System Performance
Submission (Table H). Table H was part of the Scottish Water’s annual reporting
requirements and summarized the asset stock, its condition and performance and value
(modern equivalent). The guidance notes for the production of Table H indicated the
information in the table would form a record of the asset stock and provide a strategic
framework of investment levels for sustainable stewardship for coming years. The stated
objectives of Table H were to:
1. Enable Scottish Water to produce a strategic framework that provided asset stewardship
output measures, set against investment levels for each asset category.
2. Enable Scottish Water to demonstrate that asset information was adequate and that the
Authority had a comprehensive and systematic basis for the long-term stewardship of the
assets in regard to financial performance and customer service.
3. Enable Scottish Water to summarize the latest investigations and audits of their asset
stock. This included the level of risk, condition, age and performance of assets.
See Case Studies 1 and 2 in Chapter 8.0.
2.3.2 Data Requirements for Condition and Performance Assessments
The assessment of asset condition and performance involves the collection of data using
inspection tools/techniques. However, even at the asset level, this data is insufficient for decision
making because the condition of an asset does not in itself indicate whether an intervention is
required. Understanding condition requires other data from utility systems and/or surveys to
allow interpretation and contextualization of the results. In a wider context, understanding asset
condition is only part of the decision making process. As such, the utility will also need to
supplement condition and performance data with a range of other asset-related data, including:
 What the consequences of asset failure are (at a local and system level).
 What it will cost to replace/rehabilitate the assets.
 What alternatives exist, given the results of the condition and performance assessment
(partial replacement, non-structural repair, deferment, etc.).
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
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2.4
When to Undertake Condition Assessment
One challenge for this project was to consider the application of condition assessment for
the whole range of asset management approaches currently in use; from informal asset
management through to advanced asset management. To this end, the project team determined
what it considers to be the ideal practice for specifying the need for condition assessment, while
allowing for the fact that a significant proportion of utilities will not be in a position to adopt this
ideal. (It should be noted that the use of the term ‘ideal practice’ does not imply each utility
should aim to adopt this approach; what is practical and affordable also needs to be taken into
account – best practice for a given utility must be considered in terms of its business drivers,
existing systems and available budgets.)
The first step in developing an assessment program that will allow the utility to control
costs and sustain the desired level of service is the definition of required system-level
performance standards (ASCE, 2004). As such, and to aid discussion of the ideal route for
specifying condition assessment, it is worthwhile considering first the development of
appropriate performance standards, and then showing how the strategic measures of asset
management performance generated can be used to specify the need for asset-level condition and
performance assessments.
2.4.1 Strategic Goals and Performance Management
Each utility has a range of institutional aspirations (things the utility wants to do) and
imperatives (things the utility must do), commonly expressed in the form of business goals.
These business goals will in turn reflect the requirements of stakeholders and customers, and will
in part depend on the ownership model adopted (whether a public council/authority or private
business).
Ideally, the utility will establish strategic objectives that embody these goals and
imperatives, select appropriate KPIs and set corresponding targets that will allow the utility to
measure progress towards the strategic objectives, as well as measure operational/maintenance
performance. Case Study Insets 2-5 and 2-6 show a number of relevant KPIs and associated
targets for two of the case study partners in the United States.
The process of defining relevant KPIs is illustrated in Figure 2-6. The targets and
requirements box shows how the KPIs feed into the asset management cycle shown in Figure 2-4
(via the targets and requirements box in Figure 2-4).
Utilities need a set of KPIs that measure performance across a range of business
activities. Various types of KPIs can be specified, including: level of service KPIs; asset-related
KPIs; and derived KPIs. For the purposes of this work, these are defined as follows:
 Level of service KPIs (e.g., interruptions to service) give a measure of service as
perceived by the customer or environment and are an indirect measure of asset condition
and performance. These KPIs are often the driver behind asset management expenditure
and prioritization processes.
 Asset related KPIs (e.g., equipment or pipe failures) give a measure that can be related
directly to asset condition or performance. These KPIs are often used to target and
prioritize asset management expenditure effectively.
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 Derived KPIs (e.g., amount of rehabilitation and annual investment) are those that
measure asset management effort. These KPIs can reflect asset condition and
performance, but are strongly influenced by policy decisions and available budgets.
Figure 2-6. The Process of Developing a Performance Management System.
Case Study Inset 2-5: KPIs and Targets for a U.S. Utility
Massachusetts Water Resources Authority (MWRA) uses an extensive set of KPIs to measure
performance aspects of operations and maintenance programs; for example:
 Equipment availability (exceeds industry benchmark of 97%).
 Replacement asset value per maintenance technician (exceeds industry best in class
target range of $8M to $10M).
 Maintenance cost/replacement asset value (in range of industry benchmark of 1-2%).
 Preventive maintenance compliance > 95% per month completed.
 Predictive maintenance is increasing and currently accounts for 10% of all work
orders.
See Case Studies 11 and 12 in Chapter 8.0.
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Case Study Inset 2-6: KPIs and Targets for a U.S. Council
The City of Bellevue Council uses a suite of KPIs to drive asset management programs. KPIs
are organized according to effectiveness, efficiency and staff workload. Certain effectiveness
KPIs, such as water service interruptions, sewer system dry weather overflows and claims
relate to overall condition and performance of assets. KPIs and associated targets relevant to
this research include:
 Customer satisfaction rating (target > 85%).
 Claims per year (target <10 (wastewater) and <5 (water), with no single claim greater
than $20,000).
 Water service interruptions (target < 3 per 1,000 service connections).
 Wastewater pump station overflows (target<0.11 per 1,000 service connections).
 Sewer main line stoppages per year (target < 0.4 per 1,000 service connections).
 Percent completion of planned inspection programs (target 100%).
See Case Study 10 in Chapter 8.0.
Once an appropriate set of KPIs is selected and targets set, the data needed for KPI
measurement must be collected and/or collated as a routine activity and analyzed in an
appropriate manner. This includes analysis of supporting statistics required to help understand
variations and trends in KPIs.
Analysis of KPIs can be undertaken at a range of granularities (local to utility wide), as
an on-going management task and as a feed into periodic planning cycles for capital investment,
such as in Case Study Inset 2-7. Aitkin and Davis (2001) note that performance monitoring of
this type:
1. Provides a comprehensive picture of how the utility is progressing towards achieving its
strategic goals.
2. Provides early indications of emerging issues that may require remedial action.
3. Establishes a basis for service standard, resource and pricing negotiations between
stakeholders.
4. Provides a logical and defensible basis for changes in policy and/or practices and the
pursuit of negotiations with external stakeholders (e.g., customers and regulators).
The comparison of measured KPIs to the associated targets, in conjunction with trending
analysis, also informs and drives asset management effort; a shortfall in a KPI measured against
its target indicates that a strategic objective is not being met and that some action is required. For
example, Table 2-3 shows a number of strategic objectives and related KPIs applicable to the
management of water supply assets, along with an outline of the approaches used to assess why a
shortfall exists in the KPIs against targets. A more comprehensive list of strategic objectives and
related KPIs for both water and wastewater services is provided in Appendix A.
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Case Study Inset 2-7: Investment Planning through KPI Assessments
An approach akin to the high-level performance monitoring protocol was used by Scottish
Water in Quality and Standards (Q&S) II. Q&S II involved planned investment of £1.8 billion
between April 2002 and March 2006. Bursts and quality KPIs were used in a condition and
performance matrix to identify problem water supply zones. Once identified, more detailed
studies were undertaken.
A strategic gap analysis was also undertaken by Scottish Water as part of its third investment
planning cycle; referred to as Q&S III. Q&S III spans April 2006 to March 2014. This gap
analysis was essentially a systematic review of asset capabilities and service provision
compared to current and future targets, so as to identify where investment was needed. This
involved assessment of a range of KPIs and other data. As is the general practice in the United
Kingdom, the resulting investment program was driven by gaps in service levels and KPIs.
See Case Study 1 in Chapter 8.0.
Table 2-3. Strategic Objectives, Related KPIs and Approach to Assessment.
Strategic Objective
Improve water quality (WQ)
Invest in measures to reduce
discolored water complaints
Improve drinking taste and odor
Improve pressure of water supply to
customers ‘at risk’ of low pressure
Reduce interruptions to supply
KPI
WQ compliance at works
Turbidity at works
WQ compliance at tap
Coliform compliance (works,
service reservoirs)
Iron pick up in system
Number of complaints
Outline of Assessment Approach
Identify problem zones through analysis of
complaints and sample data. Undertake a
program of assessments to determine the root
cause (works capacity, pipe condition, etc.).
Preferably combine assessment with other service
problems so as to ensure an integrated approach
is taken and, eventually, interventions identified
that give the best value for money.
Unplanned interruptions
Interruption duration
Interruption frequency
Water pumping station failures
Bursts per unit length
Identify problem zones/cohorts through analysis of
failure event and sample data. Undertake a
program of assessments to determine the root
cause.
Again, preferable to combine analysis with other
service problems so as to ensure an integrated
approach is taken and, eventually, interventions
identified that give the best value for money.
2.4.2 Specifying Condition Assessment to Fill an Information Gap
While this high level monitoring of utility performance (in combination with on-going
monitoring of the condition/performance of individual assets, discussed more fully in Chapter
5.0) is a corner stone of asset management, routine activities do not generate all the data that is
needed to manage the asset stock and support decision making. This is especially true for below
ground assets that are hidden from view and can operate for many years before deterioration is
sufficient to cause operational issues. For example, a network of water transmission pipelines
may operate satisfactorily for many years with little or no operational failure data being
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
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generated. However, the assets are still deteriorating at an unknown rate and eventually will start
to fail, potentially with unacceptable consequences.
Even when strategic performance management is undertaken effectively, there is still a
gap in the information required to manage the assets, which can be filled by undertaking assetlevel condition and performance assessments. Figure 2-7 illustrates the process of using level of
service and asset related KPIs as a means of undertaking high-level performance assessment to
drive SAM decision making, only undertaking asset-level condition and performance
assessments specifically for the purposes of SAM where it is needed to fill a gap in the
information arising from this performance monitoring.
Figure 2-7. The Role of Condition Assessment in Utility Decision Making.
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It should be noted that the approach implicit in Figure 2-7 does not, in any way, imply
that condition assessment/monitoring should not be undertaken routinely by a utility for the
purposes of managing individual assets (see Chapter 5.0); it is only condition assessment
undertaken specifically for the purposes of informing SAM decision making that is being
considered here.
As in Figure 2-6, Figure 2-7 illustrates that a set of KPIs is used that embody the utility’s
strategic objectives. Data from routine operations and maintenance feed assessment of
performance through KPI measurement and thereby supports decision making. A gap in the
asset-related information from this KPI management system drives the need for undertaking
condition and performance assessment at the asset level.
2.4.3 Alternative Routes for Specifying Condition Assessment
This formalized approach to KPI management, which only uses asset-level condition and
performance assessment for the purposes of SAM to fill specific information gaps (as illustrated
in Figure 2-7), is considered ideal practice. However, asset-level condition and performance
assessment can also be undertaken without any formal asset management approach being in
place or because some form of internal or external driver is imposed on the utility that
necessitates the assessment. For example, there may be a requirement to report the overall
condition of the asset stock to a regulator, or to undertake condition assessment as part of
financial reporting procedures. Both of these drivers are independent of the ideal route for
specifying the need for asset-level condition and performance assessment.
This alternative route, which is (or can be) independent of KPI management systems, is
also depicted in Figure 2-7 as the steps below the horizontal dotted line and shown separately in
Figure 2-8 for clarity.
Figure 2-8. Condition Assessment Undertaken in Response to Individual Drivers.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
2-19
A range of individual drivers for specifying the need for asset-level condition and
performance assessments can be identified. For example, Table 2-4 lists a number of individual
drivers for undertaking condition and performance assessments. In essence, each driver still
relates to a gap in information that has to be filled, but the driver does not arise out of the
management of KPIs. A more comprehensive list of individual drivers for undertaking condition
and performance assessments is provided in Appendix B.
Table 2-4. Drivers for Undertaking Condition and Performance Assessment.
Focus
Assess renewal budgets and
timing of spend.
Driver
Condition and performance assessment to provide data for use
in budget setting and/or justification of capital deferment.
Asset type
Any asset type.
Prioritize capital programs.
Condition and performance assessment to target priorities for
renewal spend.
Any asset type.
Determine appropriate
intervention.
Condition assessment to determine the level of renovation
required and specify rehabilitation approach; selection of least
whole life costing approach (partial replacement, lining, etc.).
Any asset type, but more
likely to be pipes.
Financial reporting (GASB 34
modified approach).
Regulatory driver.
All assets.
Forensic investigations.
Condition assessment to understand failure and support
litigation.
Any asset type.
A clear case where the need for assessment and investigation is not driven by high level
performance measures is where there is an unexpected and serious failure of an asset, as
described in Case Study Inset 2-8. It should be emphasized that, except where the driver is
imposed by an external body (e.g., a regulator), this disjointed approach to specifying the need
for a condition and performance assessment program is not deemed ideal practice, although it
may be appropriate practice for a given utility taking into account its drivers and particular
circumstances.
Case Study Inset 2-8: A Forensic Investigation of a Trunk Main Failure
Water Corporation (West Australia) incurred a catastrophic failure of a trunk main, which
lead to severe traffic disruption as well as other impacts. Given the unusual circumstances of
the failure and failure mode, Water Corporation instigated a detailed condition assessment of
the trunk main, in conjunction with an assessment of risk, to determine if the particulars of the
failure represented an isolated case. The investigations were undertaken to:
 Identify any sections of pipe where a similar failure mode could occur (other locations
where drainage infrastructure intersected the trunk main).
 Investigate the condition of the asset in sections where similar levels of failure
consequence could be incurred.
The investigations were designed to improve knowledge of the likelihood of further failure so
that the risk of the main failing could be better managed.
See Case Study 5 in Chapter 8.0.
2-20
CHAPTER 3.0
DEVELOPING AN ASSESSMENT PROGRAM
Chapter Highlights
 The greatest value from condition assessment is gained when efforts focus on the more
critical (higher consequence of failure) assets.
 When undertaking condition assessments, inspection data is collected through a number
of tools and provides information on such things as the presence of defects and their
severity.
 Data collected during inspection of assets must also be contextualized through
appropriate analysis to give an assessment of condition in terms of the operating demands
placed on the asset.
 Outputs of the condition assessment process can be expressed in a variety of ways. For
example, probability of failure, remaining life estimations and condition and/or
performance grades are commonly used.
 Condition data collected over time can yield deterioration curves that can aid in the
estimation of asset remaining life; in addition to condition, performance standards and/or
risk factors should influence the age at which assets are considered for renewal.
 Condition and performance grading systems enable a useful categorization of assets and
summary of information collected to date on individual assets.
 A 10-step approach to specifying a condition assessment program is offered to align
information collection efforts with utility drivers and objectives as well as decision
support needs:
Step 1.
Document program drivers.
Step 2.
Specify program objectives.
Step 3.
Identify asset types to assess.
Step 4.
Collate and analyze available data.
Step 5.
Determine what assets to inspect, if any.
Step 6.
Select inspection/assessment technique.
Step 7.
Plan inspection program to minimize cost.
Step 8.
Undertake asset inspection and other data collection.
Step 9.
Analyze data and assess asset condition.
Step 10. Utilize condition assessment information for decision making.
 In addition to these 10 steps, documentation and reporting of the overall process, data and
information collected must be implemented as an ongoing process.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
3-1
 To this end, there is a need for effective data collection forms and information
management systems
3.1
Introduction
As discussed in Chapter 2.0, asset-level condition and performance assessments can be
undertaken in response to a number of strategic asset management drivers. These assessments
involve the collection of data using inspection tools/techniques, but other data are also required
to allow interpretation and contextualization of the results. When designing an assessment
program, it is thus necessary to have an understanding of what data are to be collected and how
the data are to be analyzed and used.
Assessing condition first requires an understanding of the assets and the business needs
that are driving the condition assessment. The process of condition and performance assessment
then involves a number of distinct steps, for example, determining what assets to inspect and
selecting tools for use.
This chapter describes the generic steps involved when designing an effective assessment
program. The role of risk in condition assessment is first discussed, followed by a consideration
of the outputs of the assessment process that may be sought. A number of protocols used in
developing condition assessment programs are then presented, including a detailed treatment of
the generic 10-step process adopted in this research.
3.2
The Role of Risk in the Design of an Assessment Program
As noted by Rahman & Vanier (2004), one of the functions of condition assessment is to
establish the current condition of assets as a means of prioritizing maintenance and rehabilitation
effort. Some assets are more important than others are, and asset condition is only one of the
metrics used when prioritizing interventions. Other measures are required that provide
information on the importance of the asset as well as the cost and benefits of available options.
A standard way to characterize the importance of an asset is to evaluate the risk of
failure. Risk is determined by taking into account both the probability and consequence of asset
failure. However, since consequences are related to the asset’s operational context and system
configuration, the potential consequences of asset failure generally remain relatively constant
over time. As such, consequence of failure is often used on its own to determine whether a
proactive or reactive maintenance strategy should be adopted, as shown in Figure 3-1.
In contrast, as discussed in Section 2.3, the probability of failure of many asset types does
not stay constant, but increases over the life of the asset as it deteriorates. Condition assessment
can therefore be used to understand the level of asset deterioration and the impact this has on the
probability of failure. The utility can then attempt to reduce that probability of failure through
some operational or capital intervention or accept the level of risk associated with the asset’s
condition.
When an intervention is carried out as a result of the assessment, the benefit derived is
proportional to both the reduction in probability of failure and the expected consequence of that
failure. This potential benefit (often difficult to quantify) must be balanced against the cost of
undertaking the assessment and subsequent interventions.
3-2
When undertaken as part of a risk management strategy, condition assessment is only
warranted when it has the potential for facilitating improved management of service delivery or
has for reducing risk sufficiently to justify the cost of the assessments. Where no action is taken
as a result of an assessment, the benefit is then implicit in the improved knowledge of the asset
and asset base.
From the perspective of risk and cost effectiveness, a utility will realize the greatest value
from condition assessments by targeting its resources on more critical (higher consequence of
failure) assets. This concept is embedded in the maintenance strategies shown in Figure 3-1,
which requires condition assessment to be undertaken for high consequence assets (this topic is
considered further in Chapter 5.0).
Figure 3-1. Risk and Maintenance Strategies.
While targeting important assets for condition assessment is standard practice, some
utilities perform condition assessment on each asset in their system to improve asset information.
Depending on the level of detail used, this approach could divert important resources away from
more urgent needs associated with the highest-risk assets. In some cases, this type of requirement
is imposed by a regulator, as in Case Study Inset 3-1.
Condition assessment is also undertaken within many utilities to understand the condition
and/or rate of deterioration of populations of assets that individually have a low failure
consequence, but together represent a significant investment. This is often done to justify a
replacement budget and involves the use of sampling programs, as described more fully in
Section 3.4.5 and Case Study 2 in Chapter 8.0.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
3-3
Case Study Inset 3-1: Regulatory Driver for Periodic Assessments
Sydney Water has an inspection program in which all assets are visually inspected and
appropriately tested every five years. The five-year interval is a statutory requirement and
was determined by the New South Wales Government (Australia).
See Case Study 9 in Chapter 8.0.
As well as being a useful metric with which to target condition assessment effort, the
management of utility risk itself is an important driver behind undertaking condition assessment.
In particular, third party risk associated with asset failure (such as property damage) may be
unconnected with the importance of the asset itself, as illustrated in Case Study Inset 3-2. It is
therefore important to characterize consequence in terms of business risk, considering issues
such as third party damage and environmental impacts.
Case Study 3-2: The use of Inspections to Manage Third Party Risk
The City of Bellevue Council is very interested in reducing claims from property damage or
business interruptions. This has increased focus on system performance and reliability.
A risk-based leak detection program has therefore been underway for several years. High-risk
pipes were identified by overlaying several property damage-related risk factors, including:
properties where home elevations were below adjacent street levels, areas where older (pre1986) ductile iron water mains were installed and areas of high percolation soils (likely to
transmit water rather than force it to the surface where it would be observed). Acoustic leak
detection efforts have targeted areas with these three risk factors to prevent minor leaks from
becoming major problems.
City staff have also performed hydraulic and surface water modeling to determine areas of the
system and hydraulic conditions that would cause the sewer hydraulic grade line to be above
basement floor levels and thus where the City may be susceptible to property damage claims.
Condition assessment and operations and maintenance activities are then prioritized
accordingly.
See Case Study 10 in Chapter 8.0.
3.3
Outputs from a Condition Assessment Program
Before addressing the design of a condition assessment program in more detail, it is
worthwhile to consider the outputs generally sought from condition assessment programs as
applied in the water utility sector.
When undertaking condition assessments, inspection data is collected through a number
of tools and provides information on such things as the presence of defects and their severity.
However, even when a defect such as a crack or corrosion is identified, the question still remains
as to the significance of the findings. Data collected during inspection of assets must therefore be
interpreted through appropriate analysis to give an assessment of condition in terms of the
operating demands placed on the asset. Outputs of this process can be expressed in a variety of
ways. For example, Engineering Calculations, Probability of Failure, Remaining Life
3-4
Estimations and Condition and/or Performance Grades (ratings) are commonly used. Each of
these approaches is discussed briefly below.
3.3.1 Engineering Calculations
Engineering calculations can be used to interpret inspection data deterministically. In this
approach, the results of a structural inspection (e.g., the presence of critical defects, remaining
wall thickness, etc.) are used to calculate whether the asset still provides sufficient safety
margins to comply with required standards and codes, considering both static and dynamic
operational loads (e.g., calculating the loads applied to the remaining cross-sectional area of a
corroded structural member). Case Study Inset 3-3 gives an example of the use of condition
assessment to determine the presence of critical defects, and the structural analysis subsequently
undertaken to assess the propensity for asset failures.
Case Study Inset 3-3: Remaining Life Calculations for a Sewer
Water Care operates an 18 km long reinforced concrete interceptor sewer, cast in situ in
sections of 30 feet (10 meters), and built between 1960 and 1965. Initial inspection of the
asset was carried out under a program to determine the overall condition of all sewerage
assets.
The initial condition assessment used visual inspection techniques that determined the
presence of defects. In some sections the concrete had corroded to the extent that the inner
reinforcement bar of the pipe wall was showing. Collapse of these sections would lead to
significant health, environmental and third party consequences.
The presence of the defect was, however, only a relative indicator of condition. Preliminary
structural analysis was undertaken to assess the risk of collapse in the sections subjected to
significant levels of acid attack. The implication of this preliminary analysis was that there
was a risk of collapse under certain conditions and on-going deterioration would increase the
likelihood of failure.
Early replacement of the asset was considered, but there was insufficient redundancy in the
network to allow the asset to be replaced. Further inspection of the asset was undertaken to
determine the rate of deterioration and the results of the inspections used in refined modeling
studies to put the asset deterioration into context.
The cost of the additional analysis was justified because of the high level of perceived risk
and the lack of available options to manage that risk. An iterative approach to assessment was
therefore justified on the basis of risk, in which more accurate (and expensive) techniques
were used to refine the knowledge of an asset and give better support to decision making.
See Case Studies 6 and 7 in Chapter 8.0.
3.3.2 Probability of Failure Estimations
Given the discussion on asset risk presented in the last section, an ideal output for many
purposes would be a direct measure of failure probability that accurately reflected the level of
asset deterioration. In combination with load/capacity information and failure consequence
assessments, condition assessment would then allow the utility to quantify risk. Given an
understanding of risk, utilities are able to determine appropriate operational, renewals and other
asset management strategies.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
3-5
The need to calculate probability of failure often arises because loading conditions are
inherently uncertain; understanding load-capacity relationships is of central importance to the
prediction of asset failure. From the perspective of condition assessment, however, the issue
often being considered (implicitly or explicitly) is how the probability of failure is changing over
time due to (say) reduction in structural capacity. In general, this information cannot be derived
from a single condition assessment. Repeated measurements over time are required to calculate
the rate at which conditions are reducing, and probability of failure increasing.
Condition data collected over time can be used to produce deterioration (or decay) curves
that allow the probability of asset failure to be modeled (see Case Study Inset 3-4 for an
overview of such an approach). Such deterioration (or decay) curves can also be used to give an
estimate of remaining life.
Case Study Inset 3-4: Estimating Probability of Failure for Water Pipes
There are principally two approaches used to determine the probability of failure of buried
water pipelines:
 Statistical approaches based on analysis of available failure records.
 Physical probabilistic approaches derived from physical principles of pipeline failure
combined with a stochastic representation of input variables. Physical probabilistic
approaches can also be compared to and calibrated against available failure records
data and can also use condition-monitoring data as input.
In both approaches, various asset parameters are considered in the analysis, such as pipeline
diameter, material type, installation year, etc., along with other risk factors such as operating
pressure, soil type and soil pH.
The outputs of failure probability predictions are of two main types:
 Failure rates for groups of pipes (i.e., statistical expectation of the number of failures
per length of pipe). This is typically given in predicted failures per unit length per
year.
 A probability density function for the time to first failure for a given pipe.
See Case Studies 13 and 14 in Chapter 8.0.
3.3.3 Remaining Life Estimations
In practice, it may be impractical or too costly to develop an assessment of failure
probability with any reasonable degree of certainty. It is, however, possible to estimate the
remaining service life with information on asset age, condition and knowledge of how the asset
deteriorates over time (Newton & Vanier, 2006). With this approach, the purpose of asset
condition assessment is to detect and quantify rates of degradation and to provide a measure of
the existing condition of the asset.
It is often more pragmatic to classify an asset in terms of condition and relate this to its
remaining life, as in the example given in Case Study Inset 3-5. In this context, remaining life
means the time left until the asset can no longer perform its primary function(s).
3-6
Case Study Inset 3-5: Remaining Life of Ferrous Pipes
In the approach used by Scottish Water, the structural condition of ferrous water mains is
determined via an estimation of remaining service life.
Remaining service life is assessed using excavated sections of water main, which are shotblasted to remove the graphitized corrosion products. Remaining life is predicted from the
derived corrosion rate (based on pit depths and age) in conjunction with the remaining pipe
wall thickness.
See Case Study 2 in Chapter 8.0.
Realistic remaining life estimations are required if this approach is to be used in asset
management. For mechanical and electrical assets, condition monitoring techniques (vibration
monitoring, oil testing, and thermography) can be used to track deterioration rates and therefore
estimate remaining life (condition monitoring in this context is discussed fully in Chapter 5.0).
For pipeline assets especially, a reasonable understanding of the degradation and failure
processes is required to define appropriate end of life criteria, as well as the expected life of
assets and/or the implications of critical defects to remaining life. For pipeline assets, the
identification of a defect does not in itself always given an indicator of asset remaining life. As
illustrated in Case Study Insets 3-6 and 3-7, significant amounts of analysis may be needed to
interpret the results of pipeline inspections.
To understand remaining life fully, utilities also need to consider other reasons why an
asset may need replacing, for example, when an asset is under-capacity, obsolete, under-utilized
or too expensive to maintain.
Performance standards and/or risk factors should also influence the age at which assets
are considered due for replacement. Performance is not always directly related to condition,
since assets can continue to perform their functions satisfactorily even when their condition has
significantly deteriorated. Hence, expenditure priorities are often more effectively determined by
assessing asset performance, rather than merely structural condition.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
3-7
Case Study Insets 3-6: Remaining Life Calculations for a Water Main
CSIRO undertook a condition assessment of a 250 millimeter (mm) diameter cast iron water
main on behalf of a client. The main was installed in the 1860’s and remained unlined until
1980 when it was cement lined in-situ.
Five sections of pipe, each approximately one meter long, were exhumed by the water
authority and assessed to determine the remaining wall thickness (in this case the defect under
consideration was loss of metal due to corrosion).
The raw data from residual wall thickness measurements was first used to derive a probability
density function (PDF) for the corrosion rate. This PDF was then used in conjunction with a
physical failure model to assess the propensity for asset failure. The failure model considered
both the resistance of the CI pipe as it corroded and the applied service loads (including
internal pressure, soil dead loads, and surface loads).
The outputs of the modeling study were summarized in terms of a plot that shows the
expected pipeline failure rate as the pipe ages. In combination with data on failure costs, this
type of plot can be used to analyze remaining economic life.
See Case Study 13 in Chapter 8.0.
Case Study Inset 3-7: Remaining Life Calculations for a Sewer Force Main
CSIRO undertook a condition assessment of a 300 mm AC pressure sewer pipe constructed in
1978 on behalf of a client.
Soil testing was carried out at seven locations along the route of the pipeline to determine the
soil aggressiveness (pH, soil characteristics). With this data, a preliminary analysis was
carried out to identify sections with high probability of failure (hot spots). Several of the
positions were recommended for core sampling of the AC pipe.
Cores were taken and the residual tensile strength of the pipe wall assessed (in this case the
defect under consideration was loss of wall strength due to material deterioration). The data
on residual strength was used to derive a PDF that quantified the variation in deterioration rate
for two distinct soil environments.
This PDF was then used in conjunction with a physical failure model to assess the propensity
for asset failure. The model considered both the resistance of an AC pipe as it ages and the
applied service loads (including internal pressure, soil dead loads and surface loads).
The outputs of the modeling study were summarized in terms of a plot that shows the
expected time to first failure for various loading conditions. In combination with data on
failure costs, this type of plot can be used to analyze remaining economic life.
See Case Study 14 in Chapter 8.0.
3.3.3.1 Techniques for Establishing Remaining Service Life
There are a number of techniques that can be used to establish the remaining service life
of infrastructure assets: including testing of materials or components, factor methods,
3-8
deterministic (decay) curves, analytical models or probabilistic models (see Vanier & Rahman,
2004 for more details):
 Testing of materials or components offer the possibility of obtaining data that can be
subsequently used in the development of models for service life prediction. The testing
may include the gathering of data either from the periodic inspection of components or
direct field measurements of performance indicators over months and years. Typically,
short-term tests are carried out in a laboratory. Long-term studies may be undertaken in
either laboratory or field conditions.
 The factor method is a weighted factor approach developed for use in management of
building assets. A number of independent factors affecting service life (e.g., design,
construction quality, load, maintenance level and material quality) are identified,
evaluated and rated. The estimated service life is calculated by multiplying a
predetermined reference service life by all of the weighted factors.
 Deterministic (decay) curves model the deterioration of assets. Curves can be developed
for asset types either based on the use of expert opinion or historical asset failure data.
 Analytical models calculate the remaining service life by modeling the deterioration
process itself.
 Probabilistic models attempt to account for the apparent randomness of the failure of
components and systems through appropriate means, including Markov chain and Monte
Carlo analysis.
Utilities can also develop in-house systems for estimating the remaining life of assets
based on operational experience. These can be combined with grading procedures, as illustrated
in Case Study Inset 3-8. Such approaches are pragmatic, especially when there is insufficient
data upon which to base quantitative assessments. However, the use of operational experience is
subjective, can be influenced by recent problems and is not generally auditable. As such, while
such approaches may be pragmatic in the short term, data collection systems would ideally be
put in place to provide the data required for more quantitative assessments in the future.
Case Study Inset 3-8: Estimating Remaining Life Using Operational Experience
Sydney Water has extended the use of grading procedures (see Section 3.3.4) to allow an
estimate of remaining life to be generated. Each asset is categorized into five grades by
analyzing information from the following sources:
1. Planned maintenance and overhaul.
2. Feedback from operators and maintenance staff.
Scores are given for a range of parameters, including consequence of failure and occurrence
of failure. Occurrence of failure is developed using an annual failure rate.
The scores for each of the grading systems are inputted into a formula that gives an estimate
of the remaining life of each asset. Depreciation is determined as well as required
maintenance and whether replacement or renewal of the asset is required.
See Case Study 9 in Chapter 8.0.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
3-9
3.3.4 Grading/Rating Systems
While desirable, assessing the probability of asset failure or specifying a meaningful
remaining life can be challenging and difficult to benchmark. It is often more feasible to simply
specify thresholds of condition and performance where interventions must occur, and identify if
a given asset has reached that threshold. This approach is implicitly incorporated into the design
of grading systems commonly used for strategic asset management purposes. Two types of grade
are commonly applied:
 Condition grades are allocated through visual inspection of an asset and with reference to
specified descriptions of each grade. Grading asset condition in this way gives a measure
of the level of physical deterioration with respect to the ‘as new’ condition. A condition
grade can be allocated reliably only after explicit visual examination of the asset.
‘Desktop’ assessments of an individual asset are less reliable. Various modelling
approaches can, however, be used to allocate grades that are valid in a statistical sense
(see for example Case Study 1 and 2 in Chapter 8.0).
 Performance grades give a broad categorization of an asset’s ability to function in
accordance with the utility’s requirements and are allocated using operational knowledge
of the asset, again with reference to specified descriptions of each grade. A performance
grade can only be allocated reliably with reference to detailed local operational
knowledge. Grading asset performance in this way gives a measure of asset performance
with respect to local (asset-level) requirements.
As noted in the International Infrastructure Management Manual (IPWEA, 2006),
grading systems can be developed that are simple (Grade 1 to 5), intermediate (Grade 1 to 5 with
subgrading for the worst three grades) and sophisticated (multi-faceted) ranking schemes,
although these multi-faceted schemes can be reduced to 1 to 5 when necessary.
The design of an effective grading system involves two stages:
 Asset observations that are deemed to be important to the condition or performance (as
appropriate) of the asset type in question are first identified (see examples in Table 3-1).
 These asset observations are then mapped to a given grading system.
With regards to the first point, it is possible to determine asset characteristics that reflect
good or bad condition/performance for any asset type. These characteristics then form the basis
of the grading system. For example, Table 3-1 presents asset observations that relate to the
condition and performance of various categories of assets.
Appendix C presents a more comprehensive list of asset characteristics used in grading
systems for a range of representative asset types.
3-10
Table 3-1. Condition and Performance Assessment Criteria.
Assessment type
Electrical Asset Condition
Mechanical Asset Condition
Assessment criteria
Electrically safe (O/M)
Level and urgency of maintenance required (O)
Visible wear and tear (V)
Condition of insulation (V/M)
Break downs and failure history (M)
Maintenance costs (M)
Health and safety issues (V/O)
Serviceability (V/O/M)
Soundness of unit; as new? (V)
Level and urgency of maintenance required (O)
Level of wear and tear (V)
Condition of protective coatings (V/M)
Corrosion (V/M)
Break down and failure history (M)
Maintenance costs (M)
Serviceability (V/O/M)
Health and safety issues (V/O)
KEY:
(V): Visual; an auditor would be able to evaluate the assessment criteria directly (visually).
(O): Opinion based; the auditor would be able to evaluate the assessment criteria indirectly (by interview).
(M): Measurable; the assessment criteria could be directly measured (inspected/monitored) or assessed through
analysis of available operations/maintenance data.
To illustrate the process of developing a grading system, it is informative to consider the
design of sewer grading systems commonly used in many countries, including the United States,
Australia and the United Kingdom. Structural condition of sewers is often assessed through
closed circuit television (CCTV) inspection. A range of defects are evaluated in these
inspections, including cracking, fractures, deformation, loss of fabric; including mortar loss,
brick displacement, etc., joint/connection defects and loss of level. A grading system must
incorporate consideration of these defects in a manner that reflects the various stages of asset
deterioration. The grading of individual assets then informs asset management by summarizing
asset condition and thus the requirement for some form of action.
Grading approaches for sewers often use a scoring procedure in which defects are given a
score corresponding to the severity of the defect and its potential impact on asset failure. Defects
observed during the CCTV inspection are noted in a standard report, which can then be run
through software to score the sewer lengths and provide an overall 1 to 5 grade. This grade
summarizes the condition of a sewer length, generally from manhole to manhole. The 1 to 5
grades can also be allocated directly by the inspector.
Table 3-2 shows a grading system that has been used by the Office of Water Services
(Ofwat) in the United Kingdom, and is consistent with the grading system presented in the Water
Research Centre (WRc) Sewer Rehabilitation Manual and other grade systems used in the United
States and Australia.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
3-11
Table 3-2. Ofwat PR99 Information Sewer Grading System (Ofwat, 1998).
Condition
grade
Description for brick sewers
For other sewers
1
No structural defects.
No structural defects.
2
Minor cracking or no deformation or loss of bricks
and mortar loss confined to surface and line and
level as built and connections satisfactory.
Circumferential cracking or moderate joint defects.
3
Deformation 0-5%, no fracture and only moderate
mortar loss or displaced bricks or total mortar
loss without other defects or occasional defective
connections.
Deformation 0-5% and cracked or fractured or
longitudinal/multiple cracking or occasional fractures
or severe joint defects or minor loss of level or badly
made connections.
4
Deformation 5-10% and fractured or total mortar
loss or small number of missing bricks or
displaced/hanging brickwork or moderate loss of
level or frequent badly made connections or
dropped invert.
Deformation 5-10% and cracked or fractured or
broken or serious loss of level.
5
Already collapsed or deformation >10% and
fractured or extensive area of missing bricks
and/or displaced/hanging brickwork or missing
invert.
Already collapsed or deformation >10% and cracked
or fractured or broken or extensive areas of missing
fabric.
The general interpretation of grades used in Ofwat’s regulatory reporting is consistent
with the interpretation placed on sewer grades used in the United States (e.g., National
Association of Sewer Service Companies or ‘NASSCO’ grades) and Australasia. This
interpretation is as follows:
 Grade 1: Asset as new.
 Grade 2: Asset showing initial signs of deterioration.
 Grade 3: Asset condition generally satisfactory (unless in an area of high risk, for
example, sewer prone to surcharging or in running sand).
 Grade 4: Asset in poor condition; action needed soon (especially in an area of high risk,
for example, sewer prone to surcharging or in running sand).
 Grade 5: Asset in need of urgent action.
These (or similar) interpretations can be placed on all grade systems, although as noted
previously there is no requirement for the grades to be based on a 1 to 5 system. For example,
some legacy grading systems used were based on a 3-grade system, as indicated in Case Study
Inset 3-9.
3-12
Case Study Inset 3-9: Legacy Grades used within MWRA
Massachusetts Water Resources Authority (MWRA) has performed closed-circuit television
(CCTV) inspection of its entire gravity sewer interceptor system, and used these data to assign
condition grades to each pipeline segment. MWRA recently shifted to the NASSCO standard
1-5 rating system, but much of their historical condition data are still in a legacy A, B, C
condition rating system.
See Case Study 12 in Chapter 8.
Condition and performance grades give a useful summary of structural condition and the
priority for action. However, the results of the grading procedures should be interpreted with
some care, as outlined in Case Study Inset 3-10.
Case Study Inset 3-10: Interpreting Condition and Performance Grades
With the 1 to 5 grade systems commonly used in the United Kingdom and other countries, it
is reasonable to conclude that capital investment is required for any asset in condition grade
(CG) 4/5 or performance grade (PG) 4/5.
Given knowledge of the replacement value of an asset in these grade bands, a first pass
assessment of the potential investment required can be made (however, this is likely to be a
worse case assessment, as it assumes the whole asset needs to be replaced). However, some
assets are in poor condition and perform badly (that is, are in both CG 4/5 and PG 4/5).
When considering investment needs, the intersect between assets with both condition and
performance grade 4/5 needs to be determined. For example, analysis undertaken by Scottish
Water at the time of the assessment program detailed in Case Study 1, indicated the percent
value of assets requiring investment was given by:
0.7 (% assets in PG 4/5 + % assets in CG 4/5)
In practice, the amount of investment needed must be calculated using more refined analysis
considering risk, service, alternative interventions and affordability issues. Nevertheless, the
value of assets in condition and/or performance grade 4/5 is a simple metric of the state of the
asset stock.
3.3.4.1 Granularity of Grading
Non-pipeline assets are often represented as a hierarchy in asset management systems,
from the facility level, through process stream, to individual units and their components (see
Section 7.3 for more details on asset hierarchies). Condition and performance grading can be
carried out at any level in this asset hierarchy, that is, grades can be allocated at the work,
process, unit or component level.
When determining at what granularity (level within the asset stock) to allocate grades, a
trade off is made between the level of detail, cost of assessment and quality of decision support:
 High level assessments provide a coarse level of detail, quicker and cheaper assessment
programs but poor discrimination (when assessing condition at a high level, the asset
must be allocated a “poor” grade if any part of it needs rehabilitation or replacement),
with relatively poor decision support.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
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 Lower level assessments provide a fine level of detail (grades are allocated at the unit or
lower level), require more time consuming and expensive assessment programs, but
provide better discrimination and decision support.
3.3.4.2 Recommended Approach to Grading
Although grade systems give a useful summary of data collected in the assessment of an
asset, the aggregation of asset observations into a single grade at the point of survey leads to a
loss of information. As such, all observations/defects observed during a condition or
performance assessment should ideally be recorded, with the combination of these observations
into a single grade being made subsequently and away from the point of survey.
When applied in practice, the accuracy and consistency of grading depends on the
inspector’s experience and the reliability of the grading system used. Auditing is therefore an
important aspect of grading programs, as discussed in Case Study Inset 3-11.
Case Study Inset 3-11: Auditing of Assessment Programs based on Grading
In a condition and performance-grading program undertaken by Scottish Water, on going
auditing and quality control (QC) checks were deemed essential for consistency purposes.
Repeat audited surveys were carried out as part of the QC checks; current condition and
performance grades had already been collected for units within selected works as part of the
assessment program. The teams were then required to re-survey the works in the presence of
an auditor. As such, two sets of separately collected current condition and performance grades
were available for those works; one set collected independently and one collected in the
presence of an auditor.
Having two such sets of condition and performance data allowed the consistency of allocated
grades to be assessed. Analysis of grades showed that the proportion of unacceptable grades
(assessment of the same asset resulted in an allocation of grades differing by more than one
grade) was about 1%. This definition of acceptability took into account the inherent
variability of the grading process; a grade difference of one can be attributed to different
interpretations of grade definitions and/or asset observations, and is considered acceptable.
See Case Study 1 in Chapter 8.0.
3.3.4.3 Limitations of Grading Systems
While useful, grading systems are often designed as screening tools, in which case
additional information is required to support decision making and prioritization, including the
analysis of risk and cost and the operational context of the asset. For example, in the case of
sewers, reliance on structural condition grades alone is not recommended, but this practice does
occur; utilities and their contractors often use internal condition grades (ICGs) in decision
support for management of critical sewers. However, in the original WRc process, from which
most if not all grade systems are derived, characterizing the ICG was just the first step in the
assessment. The priority for action was then determined through consideration of other factors;
the interpretation of a specific ICG would be modified by consideration of the type of soil and
the risk of surcharging. Hence, a sewer with ICG of three in running sand and subject to
surcharging, would be considered a higher risk and thus a higher priority than an ICG of four in
clay soil with no surcharging.
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The use of grade systems beyond their intended scope as initial screening tools may be
understandable given the effort in collecting them, but the impacts of this practice on the
effectiveness of decision support should be considered, since it may have implications on the
utility’s ability to optimize capital and operational expenditure. Limitations to the use of grading
schemes when used in regulatory reporting are highlighted in Case Study Inset 3-12.
Case Study Inset 3-12: Limitations of Grade Profiles as a Metric for Benchmarking
As part of the regulatory reporting and planning cycles, the regulators in the United Kingdom
required that companies summarize the state of the asset stock in terms of condition and
performance grade profiles.
Grade systems used by different utilities for above and below ground assets varied in the level
of detail and the specifics of grade definitions. Hence, while the overall interpretation of
grades 4 or 5 would be consistent (being indicative of assets requiring some investment),
differences in the level of detail of the grading procedures used, as well as differences in the
calculation of asset values meant that comparison with grade profiles produced was not a
rigorous benchmark.
Profiles of asset condition and performance grades do not therefore provide an appropriate
benchmark for inter-company comparisons due to uncertainties introduced by differences in,
for example:
 Grade definitions (including consideration of whether an asset’s design/capacity is
suitable in performance grades).
 Asset valuation techniques applied (assuming grade profiles are developed in terms of
the value of assets in a given grade band).
 Granularity of analysis (grading systems were developed by different companies in the
United Kingdom that were applied at the works level, process level and unit level).
Comparable results are only obtained with consistent grade definitions and grading
procedures, with grades allocated at the same level in the asset hierarchy. Calculation of asset
value must also be done in a consistent manner.
3.4
Designing a Condition Assessment Program
In reviewing current industry practices, a number of protocols for designing a condition
assessment program were identified. Two of these are included in Case Study Insets 3-13 and
3-14.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
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Case Study Inset 3-13 Infraguide’s Protocol for an Integrated Approach to Assessment
and Evaluation of Municipal Road Sewer and Water Networks
Given the social costs associated with infrastructure renewal and the need to deliver better
value, an integrated approach to the replacement of road, sewers and water systems is
desirable. As such, NGSMI (2003) proposed a five-stage approach for the assessment and
evaluation of these systems:
 Task 1: Compile a detailed asset inventory with physical attributes, and appropriate
cross- referencing and geo-referencing (preferably using GIS).
 Task 2: Undertake investigations of components at a frequency related to condition
and importance. Results of investigations should be documented to allow the rate of
deterioration to be understood.
 Task 3: Undertake condition assessment using condition-rating systems based on
performance indicators to identify and prioritize the renewal requirements. Some
consideration should be given to capacity issues within the rating system.
 Task 4: Evaluate performance over a specified planning horizon (e.g., 20 years),
projecting the investment required to maintain performance levels, considering both
proactive and reactive maintenance expenditure and availability of budgets.
 Task 5: Develop a renewal plan using appropriate economic tools to identify
appropriate interventions, taking into account socio-economic impacts, risk, capacity
issues, changes in regulations and policies, adjacent infrastructure condition and
emerging technologies.
It was noted that these tasks are not necessarily distinct, nor do they have to be conducted
sequentially.
Condition rating (grading) systems are used to identify and prioritize the renewal
requirements for roads, sewers and water mains. Several performance indicators (e.g.,
structural defects, capacity and asset importance) are used to assess asset structural condition
and functional adequacy. The number of indicators used in the condition rating system will
vary among municipalities, depending on the size of the municipality, the data available and
the specific conditions of the system.
The protocol indicates that all components of infrastructure should be assessed at a frequency
that is shorter than half its expected life.
The above protocol has also been applied specifically to the assessment and evaluation of
storm and wastewater collection systems (see NGSMI, 2004).
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Case Study Inset 3-14: Hydro One’s Asset Condition Assessment Protocol
This case study is drawn from Hydro One Networks' Applications to the Ontario Energy
Board. Hydro One’s asset condition assessment (ACA) protocol is as follows (after Hydro
One 2005).
Asset condition assessment information is routinely and consistently collected by Hydro One
and updated to support decision processes. Since gathering detailed condition information on
every individual asset is both practically and economically infeasible, Hydro One’s
distribution assets are grouped into 20 logical asset classes. These classes are prioritized into
three categories, Priority 1 (P1), Priority 2 (P2) and Priority 3 (P3), based on the value of the
asset class to the business. This in turn determines the importance of acquiring the condition
information. The ACA process is outlined below:
1. Identify asset classes and demographics, and prioritize the asset classes (P1, P2, P3).
2. Define the asset information needed to determine and evaluate asset condition for all P1
and P2 asset classes, including asset condition and asset end-of-life criteria.
3. For all P1 and P2 asset classes, determine the additional condition information required to
adequately assess asset condition.
4. Collect the necessary asset condition information from existing databases or through
regular testing, surveys or inspections. The objective is to collect statistically relevant
population samples of asset condition information, which will enable a condition
assessment of the asset population in question.
5. Analyze the asset condition and performance information to identify population condition,
performance trends and high risks and impacts of asset condition on meeting business
objectives, including service quality standards.
6. Verify and confirm that the asset condition assessment results reflect actual field condition
(spot audits).
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
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Notwithstanding the value of these and other approaches identified in the research, given
the range of asset management strategies currently being adopted within the water sector, a more
generic approach to designing a program of condition assessment was deemed necessary. A 10step approach was developed, drawing on the various protocols reviewed in the project (for
examples, see the case study insets above). This approach is in line with the best practice
concepts discussed in Chapter 2.0, and can be applied by utilities with a range of asset
management sophistications, using different approaches to condition assessment across a range
of asset types. The 10-steps are presented in Figure 3-2 and discussed in more detail below.
Figure 3-2. A 10-Step Approach to Specifying a Condition Assessment Program.
In addition to these 10 steps, documentation and reporting of the overall process, data and
information collected must be implemented as an ongoing process.
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3.4.1 Step 1: Document Drivers
Various general drivers can be identified for undertaking condition/performance
assessments and it is desirable that the utility explicitly states what these drivers are as part of the
program design. As detailed in Appendix B, these can include the need to:
 Understand/forecast budgetary requirements.
 Spend budgets effectively.
 Meet regulatory reporting requirements.
 Refine asset financial valuation.
 Undertake risk management.
 Improve asset management approaches.
 Improve operation and maintenance (O&M) strategies.
3.4.2 Step 2: Specify Explicitly the Objectives of the Assessment Program
It is important that the utility understands not only the drivers behind the assessments, but
the objectives of the assessment program itself. In particular, it is important to determine from
the outset how the results of the condition assessment (and/or data arising from the assessment)
will be used in decision making. Once the general drivers are understood, it is useful to
document what the objectives of the assessment program are, for example, see Case Study Inset
3-15.
Case Study Inset 3-15: Water Care’s Assessments of Sewerage Assets
In 1999, Water Care identified that the condition of Auckland’s trunk sewer assets were
unknown and that, in some cases, the consequences of failure would be significant. Project
condition assessment and risk determination (CARD) was implemented as a result. The stated
project goals of CARD included:
 Developing an asset condition monitoring and performance assessment strategy,
including data management, storage and analysis.
 Determining the condition of the identified high-risk pipelines and potential failure
modes.
 Identifying and quantify the risks of failure and economic life of the high-risk
pipelines.
 Identifying management and mitigation measures, including:
−
−
−
Maintenance and repair activities.
Rehabilitation needs.
Replacement needs.
 Developing programs for ongoing monitoring and assessment of the high-risk
pipelines.
See Case Study 6 in Chapter 8.0.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
3-19
Where KPIs are used to inform asset management, there may be a specific objective to
provide more information on a measured shortfall in a KPI. As noted previously, the relationship
between a range of asset management objectives, the associated KPIs and condition or
performance assessment is summarized in Appendix A.
In summary, the objectives in undertaking an assessment program are to:
 Understand the structural condition of individual assets or groups of assets where this
condition is not known (required for regulatory reporting, financial planning, asset
stewardship, due diligence and/or to identify deficiencies and areas of potential weakness
or concern).
 Understand the performance of individual assets or groups of assets where this is not
known and/or assess the reasons for poor performance.
 Detect the progression of deterioration and/or assess remaining lives including
collecting inspection data for use in deterioration models (for capital renewal planning
and risk management).
3.4.3 Step 3: Identify the Asset Type to Assess
Once the objectives of the program are clearly specified, the asset types that need to be
assessed may be obvious. Where this is not the case, or where multiple drivers exist, the
assessment program should be initially formulated in the context of all relevant asset types. For
example, given water quality incidents in a supply zone, it might be necessary to assess the
performance of treatment work assets, as well as assets involved in transmission and supply of
treated water.
At a later stage of the design process, it may be necessary to limit the asset types
considered and focus in on those where condition assessment will deliver most benefit (see
Chapter 4.0).
3.4.4 Step 4: Collate and Analyze Available Data
Data are routinely generated for many asset types and where there are records this may be
sufficient for the purposes of the condition and performance assessment; that is, the objective of
the assessment could be met by collating and analyzing available data. Since it is potentially low
cost relative to undertaking a program of asset inspection and environmental surveys, this
approach is recommended as a precursor to undertaking a detailed assessment program.
For assets that are managed proactively, condition and performance related data may
already be available from previous surveys, either on utility systems or in paper records. If this is
the case, the available data should be reviewed as a precursor to any inspection or survey work.
Failure event data are more generally produced for low consequence (reactive) assets, to
which a run-to-failure maintenance model is applied (see Chapter 5.0). The data may be
available on corporate systems (e.g., maintenance management systems), but not analyzed in the
manner required to understand asset condition or performance. Data of interest will vary
according to asset type, but will include such data items as:
 Asset-related data (material, wall thickness, configuration, vintage, etc.).
 Site/installation factors (surface and traffic, bedding, depth).
 Environmental data (e.g., for water mains, quality of conveyed water, soil category, soil
temp, soil pH, soil moisture content, soil resistivity).
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 Available asset condition and performance related data (from job management systems,
opportunistic condition assessments, local knowledge, etc.).
 Previous assessments of risk and consequence of asset failure.
 Service conditions (environmental attributes; operating context).
 Operational and maintenance data (from maintenance management system).
 Failure data (type of failure, probable cause of failure).
When assessing the data that could be used in this type of analysis, the utility must
consider both the quantity of data and the quality of data. The collated data should be assessed
according to specified confidence criteria, which can include some or all of the following aspects
of data quality:
 Accuracy – Are the available data reliable?
 Completeness – What is the data coverage; are there any gaps?
 Currency – Are the data sufficiently up to date?
 Consistency – Is there any contradictory data or information?
 Compatibility – Are the data produced on the same basis as other similar information?
 Credibility – Does the data align with local knowledge or typical ranges of values?
Analysis of suitable data should then be undertaken at an appropriate level of detail, as
dictated by the objectives of the assessment program. Through this analysis of data, an initial
assessment of system performance and asset condition can often be made. Gaps in data can also
be identified and/or clarified, which can be subsequently filled through environmental surveys
and asset inspections.
This initial data collation and review is an approach widely undertaken by (or on behalf
of) utilities that are in the process of developing formal asset management approaches, but that
have an immediate driver imposed on them to undertake some form of condition assessment.
Analysis of data can then be undertaken to provide summary statistics on the frequency, spatial
and temporal distribution of (say) failure events, costs, etc.
It should be emphasized that where corporate data systems do not exist, a significant
amount of information will still be available in the form of operator knowledge. This can be
collated through communication with operational and engineering staff, for example, in a
workshop setting. Capturing this information can be a critical step in design of an effective
assessment program.
3.4.5 Step 5: Determine What Assets to Inspect, if Any
After review and analysis of available data, it should be clear whether there remains a gap
in asset information, and thus whether or not assets will need to be inspected. If this is the case,
the specific assets to inspect are often dictated by the objectives of the assessment program. For
example, the objectives and/or outcomes of the initial data review (step four) may dictate those
assets to inspect, for example, problem assets or assets related to problems in service provision.
Where the assets to inspect are not obvious, some sort of sampling procedure is required.
As noted in the International Infrastructure Management Manual (IPWEA, 2006), statistical
samples can be designed with various approaches, including:
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
3-21
 Sampling all assets.
 Concentrating on high risk/high consequence or representative assets only.
 Actuarial sample (statistically valid) using appropriate means of stratification.
The type of asset being assessed has an influence on the sampling strategy adopted.
Above ground assets can be accessed and assessed more readily, so comprehensive programs
may be economic, though the benefits of the assessment must still be compared against the costs.
The assessment of below ground assets is more expensive and often focuses on important assets
that should not be allowed to fail. However, pipe sampling can also be driven by the need to
understand condition across a network, which requires the utility obtain a reasonable sample.
The number of samples taken is often based on affordability, rather than statistical,
considerations (see Case Study 2 in Chapter 8.0 for an example). Generally, it is easier to
undertake condition assessments of wastewater assets because of the open nature of the network;
access can be readily gained through the many access points.
If statistical samples are employed as part of the condition assessment program, the
rationale and sampling methods must be documented. Methods will ideally be applied
consistently over time, and any changes documented.
3.4.5.1 Stratified Sampling Schemes
When the assessment program is undertaken to comply with financial or regulatory
reporting requirements, statistical sampling can often be adopted because some of the
information relating to the asset stock can be obtained from data for a relatively small number of
assets (compared to the asset stock). In this approach, the asset stock is stratified according to
appropriate criteria, a sample of assets randomly selected and data collected for the samples
using a range of approaches according to the asset type. Case Study Inset 3-16 gives an example
of this approach.
Once collected, the data are analyzed and various techniques are used to determine the
statistics of the sample and to extrapolate this to the asset stock. For example, standard statistical
packages can be used to generate mathematical relationships that describe the probability that an
asset with a given set of characteristics will be within a certain condition grade. With appropriate
data for the rest of the asset stock, such relationships can then be used to give an assessment of
the condition profile for an asset type (that is, results of the analysis of the sample can be
extrapolated to the rest of the asset stock).
Greater precision is achieved by more intensive sampling. Intensity of sampling can be
considered to be the proportion of the assets sampled (by number or length) from a given
population of assets (individual pipelines, pipe cohorts, systems or utility-wide). The objectives
of the condition assessment program influence the precision required. For example, short-term
planning to maximize the benefit from available budgets can involve intense inspection of part of
the system, whereas long-term planning can be supported by less intensive inspection across the
whole asset stock.
Normally, the sample size is derived from two interrelated pieces of information: 1) the
degree of uncertainty that can be accepted in the estimates, and 2) the unexplained variability in
the statistical model. Higher levels of confidence require more data to be collected and analyzed.
If the sample is small, the estimates will tend to be more uncertain. Complete certainty requires
all the assets to be inspected.
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Case Study 3-16: Sampling to Understand the State of an Asset Stock
Profiles of condition and performance grade plotted against asset value (modern equivalent)
provide a useful insight into the state of an asset stock.
The overall (utility wide) condition and performance profile of the asset stock can be most
accurately defined when there are sufficiently valid (current) grades for all the assets. For
periodic reporting, this is likely to require reassessment of those assets where the grades are
too old to be considered valid.
Whilst having grades for all assets minimizes the uncertainty in the profiles generated, it
requires a costly rolling assessment program to be undertaken such that each asset is
periodically inspected to provide updated grades as the existing grades become invalid (the
existing grades become too old compared to the life category of the asset in question).
Conversely, a representative sample strategy allows the profiles to be produced at less cost,
but with defined levels of uncertainty in the profiles generated.
When Scottish Water used this approach, the asset stock (water and wastewater treatment
works) was stratified according to a range of criteria that biased the sample to larger, more
important works. Assets were then randomly selected. The overall sampling process can be
summarized as follows:
 Sites were categorized according to the categories already used in regulatory reporting
(categories based on service area – waste/clean –the treatment complexity used in the
works and works size band).
 Existing (legacy) condition data were used to classify the sites into three bands with
good, fair and poor overall condition. This allowed a bigger proportion of sites in poor
condition to be selected with the aim of gaining better confidence in the estimates of
asset value in condition grades four and five (since grades four and five imply
immediate investment is needed, these grade bands are of most interest).
 Within each condition band, sites were ordered by category (treatment type), then size
band and then geographical area.
 A systematic sample was chosen from each condition band; every nth site was
selected, with n chosen to give a reasonable sample number from each band.
An initial assessment of sample size was made by a statistical expert and, once the data was
collected, the confidence limits for the predicted grade profiles estimated to determine if
further data was required.
See Case Study 1 in Chapter 8.0.
The number of assets that must be assessed also depends on how prevalent a
characteristic of concern is within the asset stock; if the characteristic (for example, poor
condition) is common, then relatively fewer samples will be required than if the characteristic is
rare. Since the prevalence of a characteristic of interest will not be known in advance, the design
of a sampling program may need to be iterative. Expert judgment should be used to assess the
initial sample size deemed appropriate. The data should then be collected and analyzed and the
confidence (uncertainty) in the results assessed. If the results are considered too uncertain,
further data must be collected.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
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3.4.6 Step 6: Select Inspection Techniques
The selection of an inspection technique must be made in terms of technical suitability
given the asset type and objectives of the assessment program. For many strategic asset
management purposes, the grading approach discussed previously is likely to provide
satisfactory results.
Where such an approach is not deemed appropriate, the tool selection procedure
presented in Chapter 6.0 should be followed. Economic factors that influence affordability and
cost of the program must also be considered, these are discussed in Chapter 4.0.
3.4.7 Step 7: Plan Program of Inspection to Minimize Cost
A project plan should be drawn up that either:
 Minimizes the cost of undertaking the condition assessment program, or
 Maximizes the value derived from the assessments.
Costs can be reduced by clustering activities to minimize travel time and other costs.
Appropriate quality assurance procedures should be specified as part of the program plan,
including appropriate levels of third-party auditing.
3.4.8 Step 8: Undertake Inspection and Data Collection
The asset inspection may need to be augmented by additional data collection relating to
the operating context and or relevant environmental factors.
3.4.9 Step 9: Analyze Data and Assess Asset Condition
The raw data collected from individual inspections need to be analyzed to allow
assessment of asset condition/performance. As far as is practicable, data should be analyzed as it
becomes available as initial results can influence the way in which the rest of the program is
undertaken, preventing wasted effort.
As discussed in step five, data from a stratified sample may also need to be analyzed to
give a view on the overall asset stock, if this is required.
3.4.10 Step 10: Utilize Condition Assessment Information for Decision Making
The analysis undertaken in step nine is essentially the conversion of raw data into
information that can be either reported or used in decision making. When it is to be used in
decision making, the information is either implicitly or explicitly interpreted in risk management
terms; that is, the condition and performance data are used to give an assessment of risk, place
this assessment into context and determine interventions.
Condition assessment or inspection does not in itself affect the likelihood of failure.
Action must be taken in light of the assessed condition to repair or replace the assets (physical
intervention), modify operational, maintenance, failure response, or inspection procedures
(procedural changes), or address human factors (through increased supervision or training).
These mitigation activities reduce the failure frequency and hence the risk.
3.5
Additional Implementation Issues
As well as addressing the 10-step approach given above, a water utility embarking on a
condition assessment program should also consider the following implementation issues.
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3.5.1 Asset Specific Considerations
The type of asset has an important bearing on the overall approach to the design of the
assessment program. For example, Table 3-3 indicates approaches to assessment of condition
and performance for a range of asset classes.
Table 3-3. Approaches to Assessing Different Asset Types.
Asset class
Treatment works
Pumping stations
Sludge treatment
Raw water intakes
Sea outfalls
Suitable approach
Inspection of a representative sample (condition/performance grade
assessment and collection of other attributes) and estimation of the overall
grade profiles from that of the sample.
Water storage
Since service reservoirs have to be drained down for inspection and cleaning,
the sample inspected each year is influenced by operational considerations.
Dams/impounding reservoirs
Inspection frequency may be dictated by statutory requirements.
Potable mains, raw water aqueducts
Assess condition and performance using:
− Material, year laid, ground types and similar information.
− Quality problems.
− History of leaks or bursts, valve failures, etc., if any.
− Leakage monitoring.
− Potential consequences of failures through network modeling or other
risk assessment technique.
− Condition assessment/cut-out samples.
Mains (non-potable)
Generally as for raw water aqueducts but less detail is needed as consequence
of failure is lower.
Communication pipes
Assess problems by material, history of problems and possibly time period laid.
Water meters
Use metered customer data to assess potential problems; for example:
− Apparently stopped meters.
− Customers with anomalous low consumption.
− Meters that have passed unexpectedly high volumes of water.
Sewers
Assess condition and performance using:
− Material, year laid, ground types and similar information.
− CCTV inspection data.
− Potential consequences of failures (flow models, etc.).
− Drainage area studies .
− Statistical analysis of collapses or blockages.
Sewage and sludge pumping mains
Assess condition and performance using:
− Material, year laid, ground types and similar information.
− History of leaks or bursts, valve failures, etc., if any.
− Potential consequences of failures.
Combined sewer overflows (CSO)
and other sewer system structures
Inspect as part of drainage area (catchment) study program.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
3-25
As well as requiring different approaches to program design, the range of assets used in
the delivery of service means a utility will in general also need to use a variety of tools in its
condition assessment programs. For example, Case Study Inset 3-17 lists some of the condition
assessment tools used by Massachusetts Water Resources Authority (MWRA). The full range of
tools available for use by utilities is detailed in Chapter 7.0.
Case Study Inset 3-17: Condition Assessment Tools used by MWRA
MWRA use a range of condition assessment tools and techniques, including:
 Acoustic ultrasonic vibration tools.
 Ultrasonics for thickness determination.
 Thermography.
 Permanent condition monitoring (vibration and temperature monitoring for large
equipment).
 Oil sampling.
 CCTV sewer interceptor inspection (closed circuit television inspection system and
sonar scanner system).
 Portable acoustic pipeline leak detection equipment and continuous monitoring
acoustic equipment.
See Case Study 11 and 12 in Chapter 8.0 for details of how MWRA use these tools.
3.5.2 Consistency Requirements
The collection of consistent condition and performance data facilitates analysis and
interpretation and also allows preparation of deterioration curves that permit prediction of either
the probability of failure or the remaining life of assets. It is important to develop formal
assessment techniques that give repeatable and objective assessments and apply these
consistently over time. Individual asset groups may have their own specific grading or
assessment standards.
3.5.3 Frequency of Assessments
The 10-step procedure previously presented does not consider the frequency of inspection
over time. Assessment frequencies may be based on individual asset management drivers. For
example, GASB 34 requires that condition assessments be undertaken every three years.
For assets of high failure consequence, it may be necessary to provide continuous
monitoring or to undertake inspections at specified intervals. The concepts of risk-based
inspection can also be used to specify a variable interval; that is, the time to the next inspection
can be set given the results of a current assessment of condition, and with knowledge of
deterioration mechanisms, failure modes and asset risk. This approach is considered in more
detail in Chapter 5.0.
Condition monitoring can also be used in the context of asset systems. In this case,
condition monitoring is essentially periodic condition assessments undertaken to determine the
overall condition of the asset stock, usually for regulatory/financial reporting or to monitor asset
stewardship. Sampling can be used to determine what assets to inspect at any one time, or a
3-26
rolling program of inspection used to ensure that all assets are eventually assessed as part of the
condition monitoring program, as detailed in Case Study Inset 3-18.
Case Study Inset 3-18: A Rolling Program of Condition Assessments
Water Corporation has undertaken a rolling program of condition assessment of all
infrastructure assets, excluding water and wastewater collection system assets, under a
program termed Asset Condition Assessment (ACA).
There are 86,000 assessable elements in the program, covering most the asset types. These
include, water and sewer pipes, valves, pumps, motors, tanks and reservoirs, including the
roof, storage structure, appurtenances and buildings.
Once fully implemented it is anticipated that the program will require approximately 6,000
assessments to be undertaken each year.
See Case Study 3 in Chapter 8.0.
3.6
Documentation and Reporting
On-going documentation and reporting of condition assessments and inspection findings
is required if the information collected is to be utilized effectively, and to ensure traceability and
transparency of approach. Information must be documented at both the program level and for
individual assessments/inspections at the asset level.
At the asset level, it is useful to record information on a data collection form. The form
can be either paper-based or electronic (i.e., held on the inspector’s laptop, palm top or similar
computer device). Paper-based forms require little investment to implement, but the data must
eventually be transferred onto corporate systems if it is to be used for anything other than just a
record of the inspection. This inputting of data can be an expensive on-going task for large
inspection programs. Electronic forms are more expensive to implement, since they require
appropriate hardware and software, and need more investment in their design and development.
However, design features like pick lists and drop-down menus can be implemented to guide data
collection and help maintain data quality. The use of electronic forms also avoids errors
associated with the transfer of data from paper records into corporate systems. Whichever
approach is used in its design, the form should guide the inspection and facilitate the inspector to
collect relevant information, including:
 Asset information (name, type, location, asset-reference number, etc.).
 Inspection information (inspector, date, need for follow-up inspection etc.).
 Condition information (e.g., grade score and condition observations).
 Information on performance (e.g., grade score and performance observations).
 Any corrective action required and the priority for the action.
Appendix D gives an example of a paper-based form for condition assessment of
mechanical and electrical (M&E) assets. This form was designed for the Industrial Assets
Management Group within the Washington Suburban Sanitary Commission.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
3-27
Summary information is also required at the program level, so the specific information
required for decision making must also be extracted and presented in a manner useful to decision
makers. Decision makers are more often interested in the implications of the assessment, rather
than the details of the assessment process and inspection results. In this context, effective
reporting and communication requires that assessment results be contextualized and provided in
sufficient detail to support the recommended actions, and no more. Summary approaches such as
the use of traffic light systems (green for ‘asset in satisfactory condition’, amber for ‘asset
deteriorating, but OK’ and red for ‘asset requiring immediate attention’) can be useful in
management reports.
3-28
CHAPTER 4.0
JUSTIFYING A CONDITION AND
PERFORMANCE ASSESSMENT PROGRAM
Chapter Highlights
 There are numerous direct and indirect benefits to be weighed against program costs to
justify condition and performance programs.
 Key benefits relate to enhanced understanding of asset-related risks and improved
determination of the cost-effective time frame for asset renewal to avoid costly asset
failures.
 Direct benefits of undertaking condition and performance assessment can include: capital
deferment, budget justification, investment program prioritization, improved asset failure
forecasting and in some cases, facilitated regulatory reporting.
 Indirect benefits can include extension of asset life, reduction in risk management costs,
management of life cycle costs, improved productivity and efficiency, improved utility
image and staff morale, improved levels of service and improved financial valuation and
transparency.
 The costs associated with condition and performance programs can vary greatly depending
on a utility’s current state of program and tool development, and the current training levels
of its staff. Program-specific costs also vary depending on the frequency of asset inspection
prescribed and the number of assets to be inspected.
 While benefits are typically more difficult to quantify than costs associated with assessment
programs, several methods for quantifying benefits are outlined, including: improved
operations and maintenance efficiencies, catastrophic failure avoidance and improved
service levels and program efficiencies.
 The ideal balance of assessment program cost versus certainty of information for decision
making purposes are different for each utility, depending on the real or perceived asset risks,
preferences for performance and risk avoidance, customer and political demands and the
financial resources and liabilities of the utility.
 While it is acknowledged that an economic analysis is the ideal approach to justification,
many utilities do not carry out explicit cost-benefit analysis because many of the programs
undertaken are driven by a perceived need or are undertaken in response to explicit
regulatory requirements.
 The justification process is often driven more by affordability and cost-effectiveness issues
than explicit consideration of cost-benefits.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
4-1
4.1
Introduction
Condition and performance assessment programs provide many benefits, but can also be
expensive and time-consuming activities. Ideally, the expenditure on assessment programs should
be balanced against the anticipated benefits. This requires that the cost and benefits associated with
the programs be identified and evaluated in some way.
This chapter highlights the key cost and benefits of condition and performance assessment
programs and presents the steps that can be undertaken to justify these programs through economic
analysis, including potential methodologies for estimating program benefits.
Many of the benefits accrued are, however, indirect and/or intangible and thus difficult to
quantify. Furthermore, while the direct costs associated with the assessments are readily
determined, the indirect costs associated with setting up the necessary asset management systems
may not be. The economic value of undertaking condition assessment programs within the context
of asset management systems may therefore be difficult to estimate.
Perhaps for these reasons, it was noted during this research that many of the utilities
contacted did not claim to carry out explicit cost benefit analysis to justify their assessment
programs. Assessments were instead commonly undertaken within the context of available budgets
and the justification process driven more by due diligence, the need to understand performance
issues, and/or affordability and cost-effectiveness considerations, rather than explicit cost-benefit
analysis. These issues are considered in more detail in this chapter.
4.2
Key Benefits of Condition and Performance Assessment Programs
One of the key benefits of condition and performance assessment is that it allows utilities to
understand risk and determine when to intervene in the deterioration process to avoid failures that
impose unacceptable costs or consequences (social, environmental or economic). However, as noted
in Chapter 3.0, assessment of an asset in and of itself does not generate any of the benefits
associated with risk reduction. It is only when an intervention is undertaken that reduces the
probability of asset failure that a benefit is actually realized. The benefit is then proportional to both
the reduction in probability of failure and the expected consequence of that failure.
Where no action is taken, for example, where the asset is shown to be in reasonable
condition, it may be tempting to consider the assessment as wasted effort accruing no benefit.
However, in many cases the knowledge gained can be applied in a wider context (to other assets). In
such cases, the improved knowledge of the asset base can be considered an intangible benefit.
The magnitude of the benefits derived from any new assessment programs will depend on
the actual current physical state of the existing assets (probability of failure), the failure
consequences associated with assets and the value derived from the enhanced level of information
that is gathered beyond that already available. Since asset management is reliant on asset
information, the improved knowledge of assets also yields a range of asset management benefits.
Table 4-1 details many of the benefits associated with condition assessment programs. The
benefits are categorized as either direct or indirect. For the purposes of this discussion, direct
benefits are considered to arise directly from the condition assessment itself. As such, these benefits
would not be realized if the assessments were not undertaken. Indirect benefits are considered to be
those benefits that are facilitated by an effective assessment program, but rely heavily on other
business processes or are realized only after an intervention has occurred.
4-2
This categorization is used simply to highlight the fact that condition and performance
assessments are usually a feed into decision making and/or some other action, rather than being an
end in and of themselves.
Table 4-1. Benefits of Undertaking Condition/Performance Assessment.
Category of benefit
Direct
Benefit
Capital deferment.
Budget setting and/or justification.
Capital works prioritization.
Data that can be used in the production of deterioration curves (for some asset types).
Ability to predict probability of failures.
Demonstration of asset stewardship and the ability to adopt more favorable financial reporting
approaches (modified GASB 34).
Indirect
Extension of asset life (when subsequent work is undertaken following the assessment).
Reduced risk-cost associated with reduction in unanticipated asset failure (including avoidance of
social and environmental impacts).
Better management of life cycle costs and more effective capital planning and budgeting.
Improved productivity, efficiency and effectiveness.
Improved morale.
Improved availability of assets and levels of service.
Improved financial analysis.
4.2.1 Direct Benefits
As noted above, direct benefits are considered to be those benefits that are not realized if the
assessments are not undertaken. As shown in Table 4-1, these include:
 Capital deferment: undertaking condition and performance assessments can provide
information on an asset that allows renewal to be deferred. This provides additional financial
benefits, for example, increasing available budgets and thus potentially improving the
affordability of other projects.
 Prioritization of capital program investments: accurate asset condition and performance
data enables effective prioritization of capital investments and scheduling of projects
according to actual needs.
 Improved asset failure forecasting: with extensive data on asset condition and tracking of
asset failures, decay curves can be generated for certain asset types to better understand and
forecast the timing of asset failures.
 Regulatory reporting: condition assessments allow utilities to demonstrate effective
stewardship of their asset base. The use of condition assessments in this way forms the basis
of the GASB 34 modified approach, referred to in Chapter 3.0.
4.2.2 Indirect Benefits
Indirect benefits are those benefits that are facilitated by an effective assessment program,
but rely heavily on other business processes or are realized only after an intervention (maintenance,
replacement, change in operation, etc.) has occurred. As shown in Table 4-1, these include:
 Extension of asset life: asset life can be extended with appropriate monitoring and timely
proactive maintenance efforts.
 Reduction in risk costs: condition assessment and performance monitoring programs that
target the highest risk assets help to mitigate the occurrence of catastrophic asset failures. A
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
4-3
systematic, risk-based program for monitoring and proactive management will also reduce
overall utility risk, including liability for unforeseen damages.
 Management of life cycle costs: appropriate investments in understanding asset condition
and performance can reduce overall life cycle costs by, for example, avoiding costly failures
and reducing costly reactive maintenance requirements.
 Improved productivity and efficiency: in a similar vein, an effective assessment program
takes much of the guesswork out of asset repair efforts, leading to more efficient and
productive rehabilitation programs and improved overall economic efficiency of the utility.
 Improved utility image and staff morale: with improved asset condition and performance
understanding, staff members have a higher level of confidence in the cost-efficiencies and
service delivery of their programs.
 Improved levels of service: with better understanding of asset condition and performance,
appropriate measures can be taken to promote higher reliability of operation and improved
delivery of services to the customer.
 Improved financial valuation and transparency: more accurate and transparent asset
valuations are possible with improved data on asset condition and actual historical useful
lives of assets. The utility will also be able to present more transparent and defensible
justifications to its board members and customers.
4.3
Key Cost Elements for Effective Condition Assessment Programs
As with most activities undertaken by utilities, condition and performance assessment
programs have a range of fixed and variable costs associated with them. As shown in Table 4-2,
these include costs associated with both the collection and analysis of the data. There is also a
component related to the number of assets inspected and the frequency of that inspection over time.
These factors are a major consideration in the development of sampling programs.
Table 4-2. Cost Elements.
Category
Fixed costs
Time variable
Spatial variable
Other variable
Reliability variable costs
Cost element
Procedure development
IT system development
Tools costs (license and maintenance)
Cost of implementation
Frequency of asset inspection
Number of assets inspected
Access costs
Training
Analysis and interpretation
Reporting
Maintenance of tools, etc.
Cost of unnecessary intervention or incurred failures
With regard to the last category in Table 4-2, since many condition assessments and
inspections are undertaken to determine the need for action, the cost implications of assessment
reliability should also be considered in the justification process. In this context, ‘assessment
reliability’ is taken to be any unnecessary cost incurred as a result of imperfect information
4-4
generated by the assessment. As discussed further in U.S. EPA (2005), such reliability costs occur
when:
 A condition assessment indicated that an intervention was required, when in reality it was
not; or
 Asset failure costs are incurred because a condition assessment indicated an intervention
was not required, when in fact it was.
The first issue is particularly problematic when undertaking interventions for buried pipeline
assets based on the evidence provided by a limited sample; for example, when a pipe asset is
programmed for replacement because of poor condition, but only a small section of the asset was
inspected. The occurrence of such an error might only become apparent during the rehabilitation
process, which will incur some expense at least. Reliability costs are minimized by the use of either
inspecting more of the asset (or assets), more accurate tools or analytical approaches during the
inspection and assessment process. However, the result of this is higher condition assessment costs,
so these two conflicting cost drivers must be traded off against each other, depending on the
requirements of the assessment program.
In addition to the cost elements shown in Table 4-2, the costs of assessment programs
undertaken in the context of formal asset management also include a proportion of the costs
associated with the design and implementation of the asset management and other business systems
required to undertake strategic planning. Such costs include identification and collation of the
necessary data, data management systems, software tools and procedures. This up-front investment
is needed to maximize the impact of the condition assessment efforts and to utilize the information
within the utility’s strategic asset management systems.
To the knowledge of the researchers, however, there is little evidence that utilities formally
justify the investment in these and other improved asset management capabilities. Given the
increasingly wide acceptance of asset management as a business philosophy, it can be inferred that
there is an assumption that this investment will yield staff efficiencies, more consistent data, and
that the overall asset management effort will result in the desired utility benefits.
As such, the decision to go forward with the development of business systems is likely to be
undertaken as a strategic management decision, based on the assumption that there will be an
overall net benefit, rather than any detailed cost-benefit justification. There is, however, an
increasing body of evidence throughout the sector to show that the investment in asset management
sophistication and other business systems allows utilities to deliver improved levels of service to
customers and the environment with reduced operational and capital budgets. For example, the
privatized United Kingdom companies have delivered significant operational and capital efficiency
savings, while meeting increasingly stringent standards associated with European Union regulations
relating to the environment and water quality issues. Similarly, see Case Study Inset 4-1, which
relates to the efficiencies realized by Scottish Water since its formation in April 2002.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
4-5
Case Study Inset 4-1: Scottish Water’s Improvement in Efficiency
Scottish Water has reduced operational expenditure by £150million per year (from
£380million per year expenditure in 2002) and is delivering higher standards with around
£1billion removed from the capital program. Much of the saving is associated with the ability
to do more with less through better targeting of problem assets and/or necessary interventions.
This has been greatly facilitated through the improvements in data and a better understanding
of the condition and performance of the asset stock.
These improvements have come at a cost, however, with £100million being invested in IT
systems to provide a single asset management system across Scotland, and with an additional
£200million being invested in the transformation process required to integrate the three
former Authorities into Scottish Water. However, as noted above this has resulted in yearly
saving of £150million in Opex alone. (Figures quoted are approximate and as related in the
case study interviews; see Auditor General 2005 and references referred to therein for more
details).
See Case Studies 1 and 2 in Chapter 8.0.
4.4
Economic Justification
An economic justification of a condition and/or performance assessment program involves
three steps:
Step 1. Estimate (and quantify, to the extent practicable) the direct and indirect benefits of
several potential condition assessment program options (including the “no action”
option).
Step 2. Estimate the costs associated with each program option (including cost elements such
as equipment, training, inspections and management).
Step 3. Calculate the net benefits (in dollars) and benefit/cost ratio associated with each
option to help in ranking and potential program efforts.
4.4.1 Estimating Costs
For the most part, utility staff and managers are well versed in the methodologies for
estimating program costs, including labor, equipment, consumables, software, training and assorted
fees. As such, this issue will not be considered in detail herein.
4.4.2 Quantifying the Benefits of Condition Assessment Programs
In general, there are some direct and easily quantifiable benefits realized by an effective
condition assessment program. These often take the form of cost savings or deferred spend. For the
most part, however, this represents only a fraction of the overall benefits accrued by the utility. The
total expected benefits realized by condition assessment programs are more difficult to quantify,
since many are indirect or intangible in nature. Examples of methods to quantify different types of
program benefits in support of a business case to undertake a condition assessment program are
outlined below.
 Improved Operations and Maintenance Efficiencies. Benefits such as reduced energy costs
or avoided/deferred maintenance expenditures (e.g., capital renewal; oil changes on major
equipment) can be estimated directly, as can anticipated improvements in equipment
availability and reliability. For example, the cost differential between a proactive
4-6
maintenance effort (with all spare parts on hand and purchased without rush charges) and a
reactive, emergency repair (potentially with overtime labor costs) can be quantified as a
benefit.
 Catastrophic Failure Avoidance. These benefits can be quantified by calculating the
potential cost and probability of occurrence of a major asset failure. Costs incurred might
include emergency repair, permit violations and fees, liability and legal costs and reduced
public trust.
 The benefit can be quantified as the reduction in risk cost (due to reduced probability of
occurrence) with an effective risk-based condition assessment program in place. For
example, if the potential consequences of a catastrophic event (e.g., failure of large sewer
interceptor next to a sensitive water body) are estimated to be in excess of US$5 million, and
the probability of this occurring in a given year is reduced from a 2% chance to a 1% chance
due to proactive condition assessment efforts that trigger necessary maintenance activities or
other interventions, then the reduced risk cost (benefit) can be estimated at US$50,000
($5 million consequence) x (2% probability) – ($5 million x 1%) = $50,000 benefit.
 For many utility managers, the indirect consequences (such as job losses) associated with
this type of scenario helps justify the cost of condition assessment efforts. However, by their
very nature, it is difficult to assign a monetary value to such consequences.
 Improved Program Efficiencies. Another approach to quantifying benefits is presented in
the International Infrastructure Management Manual (IPWEA, 2006), where the program
budget (costs) multiplied by the anticipated improvement percentage is used to develop a
quantified benefit estimate. For example, if a utility has an annual sewer inspection and
maintenance budget of US$5 million, and risk-based screening efforts (i.e., better
determination of the critical assets to inspect) and targeted condition assessment efforts
(using the right tools to get data that will directly improve decision making) are anticipated
to improve the efficiency and effectiveness of this program by roughly five percent, then the
annual benefit could be quantified as:
US$5 million x 0.05 = US$250,000.
4.5
Other Approaches to Justification
While it is acknowledged that an economic analysis is the ideal approach to justification, as
noted earlier in this chapter, during the research it was determined that many utilities do not carry
out explicit cost-benefit analysis in justifying assessment programs. This is because many of the
programs undertaken are driven by some perceived need and/or due diligence requirements.
Similarly, other programs are undertaken in response to an explicit requirement, such as the need to
report condition to a regulator or other statutory body, or to provide evidence in support of a
proposed asset replacement program.
In these cases, justifications are often undertaken within the context of available budgets.
The justification process is driven more by affordability and cost-effectiveness issues than explicit
cost-benefit analysis. Nevertheless, it is still considered important for utilities to put together a
business case for the assessment program. In this approach, the perceived or actual need for
undertaking the condition assessment is outlined, along with any anticipated benefits (not
necessarily in monetary terms), along with an estimate of costs involved. This provides
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
4-7
management with the information necessary to determine whether or not the proposed assessment
program is necessary and viable.
4.6
Optimizing Cost and Benefits Associated with Assessment Programs
As noted in the previous sections, any expenditure on assessment programs should be
balanced against the benefits realized. Since these benefits are difficult to quantify, in practice, the
degree to which condition assessment is carried out is often a strategic management decision.
This has been demonstrated in a survey of asset management practices undertaken on behalf
of the Office of Gas and Electricity Markets (Ofgem), a utility regulator in the United Kingdom.
This survey found that there was a range of approaches to the definition, collection and recording of
asset condition information. Some utilities routinely collected and acted on condition information,
while other utilities considered that the effort involved in doing this produced insufficient benefits
for long-term stewardship and thus did not adopt this approach (see Ofgem, 2002).
There are, however, implications related to the amount of condition and performance data
collected. At one extreme, data collected is insufficient to support effective asset management. At
the opposite extreme, too much assessment effort is focused on assets where no significant risks are
present, thus leading to an inappropriate allocation of utility resources. A balance somewhere
between these two extremes is required, but the ideal balance is different for each utility depending
on the real or perceived asset risks, preferences for performance and risk avoidance, customer and
political demands and the financial resources and liabilities of the utility.
Given that there is no set practice for determining the extent of condition assessment, it is
important that the utility design assessment programs to obtain the outputs needed for its particular
asset management approach. In effect, this is the same argument presented in Figure 2-3, which
illustrates that a utility should consider its information needs before determining what asset-related
data it should collect.
It is also important to note that, in practice, a utility cannot explicitly determine whether or
not the ideal balance between assessment costs and other business metrics has been achieved.
However, by following the step-wise methodology outlined in Chapter 3.0, a utility can
continuously move towards the most appropriate investment level and maximize its potential for a
cost-effective program by:
 Understanding its drivers and objectives.
 Defining the critical information gaps that are affecting decision making.
 Limiting condition assessment efforts to those steps necessary to filling the critical
information gaps for enhanced decision making.
 Selecting appropriate tools and techniques that are fit for the purpose.
 Establishing the appropriate supporting people, processes and data management
infrastructure to effectively analyze and continuously benefit from the assessment data
captured.
4-8
CHAPTER 5.0
CONDITION ASSESSMENT AS A
MAINTENANCE MANAGEMENT TOOL
Chapter Highlights
 Effective maintenance practices help to minimize the whole life cost of asset ownership.
 The maintenance strategy (reactive or proactive) applied to an asset should depend on the
importance of that asset to the utility’s business objectives and the role the asset plays in
service delivery.
 Condition monitoring is applicable as a proactive maintenance task when the benefits of
undertaking the monitoring outweigh any avoided costs.
 Development of an effective condition monitoring program is centered on knowing when,
where and how to inspect different asset types. These programs should be geared towards
the stages of failure of individual asset types.
 Performance assessment also has a role as a condition monitoring technique. Observed
changes in operational variables such as pressure, temperature, power consumption and/or
asset capacity can indicate the on-set of failure.
 Several risk-based approaches, including reliability-centered maintenance (RCM) and riskbased inspection (RBI), are available to help utilities develop cost-effective maintenance
strategies and determine those assets that should be managed reactively and proactively.
 A generic approach to specifying condition monitoring tasks is offered, including the
following steps:
−
Characterize asset importance.
−
Assess failure modes and significance.
−
Identify potential performance monitoring approaches.
o Identify measurable parameters.
o Determine performance thresholds.
o Identify potential tests or monitoring approaches.
−
−
Identify potential condition inspection approaches.
o Identify degradation mechanisms.
o Determine critical defects.
o Identify potential inspection techniques.
Select appropriate condition and performance assessment approaches based on cost,
benefit and risk.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
5-1
 A case study is also presented to illustrate how a water utility went about changing its
condition monitoring practices in order to increase the amount of condition-based
maintenance being undertaken.
5.1
Introduction
Utilities are tasked with supplying critical water and wastewater services to communities
and the environment. From this perspective, a utility’s business drivers are to provide sustained
service delivery at an acceptable cost and in line with regulatory requirements, such as the need to
maintain water and environmental quality and give due regard to public health and safety. The
ability to deliver these services depends strongly on the business capabilities of the water utility
(i.e., the people, processes, data and technology used within the business) and asset capabilities (i.e.,
the capacity, condition and performance of individual assets and systems).
The concept that service levels are dictated by the utility’s business drivers but underpinned
by business and asset capabilities is illustrated in Figure 5-1 (this figure is also used in Chapter 2.0
and repeated here for the reader’s convenience given the difference in target audience of the
chapters). For example, business drivers such as customer expectations and requirements of
regulators dictate the level of service that must be delivered, whereas asset and business capabilities
impose a limit on the level of service that can be sustained over the long term. Where there is a
disparity between the demand for service and the capacity to deliver that service, investment is
required in the utility’s asset and/or business capabilities.
Figure 5-1. Business Drivers and Utility Capabilities.
In any asset-intensive sector, asset capabilities are a key component of service delivery.
Effective maintenance practices help to preserve asset capabilities and in turn underpin the delivery
of service over the short to medium term. However, as discussed in the Chapter 2.0, strategic asset
management approaches and other business capabilities are also required to sustain the service
provision over the medium to long term.
Vanier (2000) noted that asset maintenance generally consists of: 1) inspections that are
carried out periodically to monitor and record how systems are performing, 2) preventive
5-2
maintenance that ensures that systems or components will continue to perform their intended
functions throughout their service life, 3) repairs that are required when defects occur and
unplanned intervention is required, 4) rehabilitation that replaces one major component of a system
when it fails at the end of its service life and 5) capital renewal that replaces a system because of
economic, obsolescence, modernization or compatibility issues.
Approaches used in the specification of maintenance strategies are outlined in this chapter;
including the role that categorization of assets plays in determining whether a proactive
maintenance strategy should be adopted. The role that condition monitoring plays in proactive
management strategies is then discussed, including the concepts underlying P-F curves and the role
of asset inspection and performance monitoring. Risk-based assessment procedures are then
discussed, including reliability-centered maintenance (RCM) and risk-based inspection (RBI).
A generic approach to the specification of condition monitoring tasks is then presented,
which draws on the issues raised throughout the chapter.
5.2
Approaches to Maintenance
Effective maintenance practices help to minimize the whole life cost of asset ownership. De
Sitter’s “Law of Fives” (De Sitter, 1984, referred to in Vanier, 2000 & 2001) approximates this
effect: if maintenance is not performed, then repairs equaling five times the maintenance costs are
required. In turn, if the repairs are not carried out, then renewal expenses can reach five times the
repair costs. As will be discussed later in this chapter, the use of risk concepts in the development of
maintenance programs can also help to manage whole life costs by reducing the frequency of
significant failures and minimizing the impact of those asset failures that do occur.
The U.S. EPA (2002a) identifies two different approaches to maintenance: 1) the asset
management model and 2) the run-to-failure management model. In the asset management model,
components of assets are regularly maintained and finally replaced when deterioration outweighs
the benefit of further maintenance. Costs are well distributed over the life of the asset. In contrast, in
the run-to-failure management model, assets are not regularly maintained, and can deteriorate faster
than expected and led to higher replacement and emergency response costs.
While the treatment given in the U.S. EPA (2002a) applies explicitly to sewer network
management, this categorization is broadly applicable to maintenance for all buried assets. The
categorization can also be applied to above ground assets with the proviso that routine maintenance
tasks should in general be carried out in line with equipment manufacturer’s recommendations
and/or industry standards, as appropriate, to prolong the life of an asset and minimize the cost of
asset ownership.
The asset management model requires that planned maintenance tasks (i.e., maintenance
tasks that are scheduled in some way rather than being carried out in response to asset failures) be
carried out in an effective manner and in particular requires that proactive maintenance tasks be
undertaken when justified. Proactive maintenance tasks are, by definition, carried out to:
 Prevent failures before they occur; or
 Detect the onset of failures (or occurrence of hidden failures) before they have an impact on
the performance of the system.
In practice, utilities have far too many assets to carry out proactive maintenance on them all,
or at least any attempt to do so would be uneconomic. Even within the asset management model of
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
5-3
asset maintenance given above, a run-to-failure strategy should be applied to assets when
applicable. This approach will certainly apply to many pipeline assets of small diameter. However,
this strategy should not be the default maintenance philosophy. Instead, the level of maintenance
applied to an asset should depend on the importance of that asset to the utility’s business objectives
and, by inference, the role the asset plays in service delivery.
5.2.1 Proactive and Reactive Assets
While proactive maintenance might seem the most effective approach to the management of
assets, the cost of undertaking preventive maintenance is only justified where it helps to reduce the
whole life cost of asset ownership (e.g., by extending service life or avoiding failures) or avoids
unacceptable impacts. In light of this, an appropriate asset categorization scheme is one in which
assets are divided into proactive and reactive assets based on the different maintenance practices
applied.
As discussed in Buckland (2000), the term “reactive asset” refers to assets with a low
consequence of failure (see Figure 3-1 in Chapter 3.0). Since the impact of failure is low, with the
exception of any routine preventative maintenance tasks such as lubrication, etc., the assets can
generally be left to operate until failure. Once failed, a decision is made whether or not to replace
the asset. Such a decision would include consideration of the economics of continuing to operate the
existing asset (including the social impacts of ongoing failures), the levels of customer service
needed and operational strategies that could be economically implemented to reduce the impact of
retaining the failing asset. It is interesting to note that the condition of reactive assets can often be
predicted using statistical methods, because significant quantities of failure data are available.
As the consequence of failure increases, the assets may still be operated to failure, but many
utilities would prefer to take some failure prevention measures, providing they are economically
justifiable. At a certain level of consequence though, it becomes necessary to use proactive
maintenance strategies, including condition assessment or monitoring, to manage the probability of
failure. Active protection techniques such as cathodic protection may also be applied to mitigate
degradation for some asset types.
While proactive strategies tend to be more justifiable at the high consequence end of the
spectrum, they may also apply to lower consequence assets if the economics of this are favorable,
for example, if low-cost condition assessment is available. In theory at least, the converse is also
true for reactive strategies, whereby even though the consequence of failure of an asset may be
high, if the cost of failure prevention is prohibitive, that asset may be operated to failure. However,
in practice it is anticipated that utilities would use other strategies, such as redesign of assets or
reconfiguration of networks, to manage such risks.
5.3
The Role of Condition Monitoring in Proactive Maintenance
A key requirement for the implementation of proactive maintenance is the ability to
anticipate when a failure will occur. Inspection of condition and monitoring of asset performance
either by manual or automated means plays a significant role in proactive maintenance.
5.3.1
Asset Inspections
Inspection programs are established to detect and evaluate deterioration of assets due to inservice operation. The tools and techniques, frequency and acceptance criteria used in the
inspections can significantly influence the probability of component failure. Development of an
effective inspection program is thus centered on knowing when, where and how to inspect.
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If evidence can be found that an asset is in a state that will eventually lead to a functional
failure, it may be possible to take action to prevent it from failing completely and/or avoid/mitigate
the failure consequences. This approach presupposes that there is some kind of deterioration in
either asset condition or performance occurs and that this can be detected in some way. For asset
components whose failure modes are essentially random or cannot be detected, then other risk
management approaches must be used. Many failure modes will however give some sort of warning
that they are about to occur. Inspection tasks designed to detect potential failure are often referred
to as condition-monitoring tasks.
Figure 5-2 illustrates the stages of asset failure in a plot called a P-F curve. The conceptual
basis behind these curves is that asset condition of many assets deteriorates over time and the level
of deterioration eventually progress to the point where it is significant and can be detected (Point P).
At this point, it is possible to intervene in the deterioration process and correct the defects or replace
failing components (or at the very least, take action to minimize the consequences of failure). If the
deterioration is not detected and corrected, the asset continues to deteriorate until it reaches the
point of functional failure (Point F).
In practice, there are many ways of determining the onset of the failure process, for
example, hot spots showing deterioration of electrical insulation, vibrations indicating imminent
bearing failure or increasing level of contaminants in lubricating oil. The succession of techniques
that can be used is discussed in Chapter 6.0. Summaries of the available inspection tools and
techniques are detailed in Chapter 7.0.
Figure 5-2. The Failure Process as Described by the P-F Curve (adapted from ABS, 2004).
The time interval between point P and point F is called the P-F interval. This is the time
between the point at which the onset of the failure process becomes detectable and the point at
which a functional failure occurs. Condition-monitoring maintenance task intervals must be
determined based on the expected P-F interval. If a condition-monitoring task is performed on
intervals longer than the P-F interval, the potential failure may not be detected. On the other hand, if
the condition-monitoring task is performed too frequently compared to the P-F interval, resources
are wasted. The following sources may be referred to as an aid to determine the P-F interval (ABS,
2004):
 Manufacturer’s recommendations.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
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 Expert opinion and judgment.
 Published information about condition-monitoring tasks.
 Historical practices (e.g., current condition-monitoring task intervals).
The P-F interval can vary in practice and in some cases can be very inconsistent. For such
cases, a condition monitoring task interval should be selected that is substantially less than the
shortest of the likely P-F intervals.
5.3.2 The Role of Performance Assessment
The International Infrastructure Management Manual (IPWEA, 2006) notes that asset
condition and performance failure can be considered as a ‘cause’ and ‘effect’ respectively, in that
deterioration of condition is a cause of failure, and the effect of failure is poor asset performance.
In conjunction with an appropriate inspection regime, performance assessments therefore
represent another key component to management of asset capabilities. Performance assessments can
be undertaken at three levels of detail:
 Strategic assessments
 Tactical assessments
 Asset level
At a strategic level, a well-implemented performance management system provides
information that can be used for optimizing maintenance strategies and identifying issues related to
capacity. For example, through collection and analysis of asset-related KPIs, utilities can evaluate
the effectiveness of their maintenance programs and modify policies and procedures appropriately.
This type of strategic performance assessment is considered in more detail in Chapter 2.0.
At a tactical level, maintenance planning can be facilitated through prediction and trend
analysis based on reliable performance information, especially in the form of reactive maintenance
tasks (tasks undertaken in response to failure events). This functionality is often provided by a
computerized maintenance management system (CMMS). A CMMS facilitates utilities in creating
and tracking work orders and transferring data to and from other modules in corporate databases.
This allows the maintenance data within a CMMS to be mapped, analyzed and combined with other
condition assessment information to yield maintenance solutions (ASCE, 2004).
At the asset level, on-going assessment of asset performance against current and future
performance requirements helps to determine the assets current capability (considering issues such
as obsolescence and capacity requirements) and the need for preventive maintenance.
In this later context, monitoring asset performance is also a condition-monitoring technique.
As such, the process of identifying the onset of failure through monitoring of performance can also
be described using the P-F curve given in Figure 5-2. In condition monitoring of this type, however,
the approach is to anticipate the onset of a functional failure through the early identification of
changes in operational variables such as pressure, temperature, flow rate, electrical power
consumption and/or asset capacity.
5.4
Risk-based Assessment Procedures
As described previously, proactive maintenance can, in practice, only be applied to a limited
number of assets. As a sub-set of proactive maintenance tasks, condition monitoring is similarly
applicable only when the benefits of undertaking the monitoring outweigh the costs. A number of
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approaches are available to help utilities develop an effective maintenance strategy and to determine
the assets that should be reactively managed and the assets for which proactive maintenance is
required.
These methods are based on the generation and comparison of relative risk for different
maintenance strategies. Case Study Inset 5-1 encapsulates the key components of the analysis at the
asset level.
Case Study Inset 5-1: Classification of Asset Risk
A common practice for classifying asset risk is to allocate a grade according to the frequency
and severity of failure. This can be extended to consider the detectability of the failure. Such
an approach can be used in failure modes, effect and criticality analysis (FMECA) and is
applied by Sydney Water. Assets are allocated a risk category using the formula below.
Risk category = Occurrence X Severity X Detectability
Occurrence (or frequency) is an estimation of how frequently a specific failure may occur.
Rankings range from: 1 - unlikely, defined as ‘unreasonable to expect failure’ to a rank of 5 high, defined as ‘recurrent or certainty of failure.’
Severity (or consequence) is an assessment of the seriousness of the effect of the potential
failure mode with respect to equipment, process or consumer. Sydney Water uses the severity
rankings given in BS 5760-0:1986: Reliability of Systems, Equipment and Components.
Detectability gives an indication of how easy or difficult it is to detect the symptom of
failure, preferably before it occurs or before the process is adversely impacted. Sydney Water
uses predetermined rules to determine what detectability scores are assigned to an asset to
ensure consistency across similar assets. A rank of 1 corresponds to a ‘very high detection
probability; failure always preceded by a warning’ while a rank of 5 corresponds to a ‘remote
(detection) probability; failure always without a warning’.
The output of the analysis is a risk rating for each piece of equipment, known as the risk
priority number (RPN). The RPN represents the degree of risk associated with equipment or a
particular process. Through experience, Sydney Water has determined that a RPN equal to or
greater than 33 warrants an immediate detailed inspection of the asset. A decision is then
made as whether the asset should be repaired or renewed.
See Case Study 9 in Chapter 8.0.
When applied across a system of assets, the characterization of asset risk in conjunction with
assessments of cost allows the utility’s maintenance regime to be optimized in terms of the total
cost of proactive and reactive maintenance, including the impact of asset failures. Examples of riskbased assessment methods include risk based inspection (RBI) and reliability centered maintenance
(RCM).
RCM involves consideration of all proactive maintenance tasks and is applied across a range
of asset types, generally above ground assets, whereas RBI focuses more narrowly on the
optimization of inspection programs for static assets, especially pressure equipment and structures.
These techniques are considered in more detail below.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
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5.4.1 Reliability Centered Maintenance
Nowlan and Heap (1978) coined the term “reliability centered maintenance” as a process to
be used to draw up maintenance programs for aircraft before they entered service (Moubray, 1997).
In this original context, RCM was developed specifically for use in the design phase of an asset’s
life cycle. However, Moubray (1997) subsequently defined RCM as a process used to determine
maintenance requirements of any physical asset in a given operating context. As such, RCM is now
applied retrospectively to systems of assets well into their life cycle.
According to Moubray (1997) and SAE JA1011 (1999), the RCM process involves asking
seven questions about the assets/components within a system under review. The questions are asked
and answered in a structured manner by a facilitated RCM team. A process analogous to failure
modes and effects analysis (FMEA) is used to analyze the asset failures. Software tools can be used
to facilitate the process. It should be noted that RCM by design is intended to preserve system
function (Nowlan and Heap, 1978), rather than preserve the asset/equipment condition.
The seven RCM questions are shown in Case Study Inset 5-2 with additional comments
included in the discussion that follows.
Case Study Inset 5-2: The Seven RCM Questions
Q1.
Functions: what are the functions and associated desired standards of performance of
the asset in its present operating context?
Q2.
Functional failures: in what ways can the asset fail to fulfill its functions?
Q3.
Failure modes: what can cause each functional failure?
Q4.
Failure effects: what happens when each failure occurs?
Q5.
Failure consequences: in what way does each failure matter?
Q6.
Pro-active tasks: what can be done to predict or prevent each failure (proactive tasks
and task intervals)?
Q7.
Default actions: what should be done if a suitable proactive maintenance task cannot
be found?
The start of the RCM process requires that each asset function be determined and a
performance standard assigned (Q1). The functions of an asset must be specified in sufficient detail
to allow the analyst to define functional failures.
All failed states associated with each asset function must then be identified (Q2). If
functions are well defined, listing functional failures is a relatively straightforward task. For
example, if the defined function is “to keep system pressure between 4 and 7 bar,” then functional
failures will include – unable to raise pressure, unable to keep system pressure above 4 bar or
unable to keep system pressure below 7 bar.
All failure modes that are reasonably likely to cause each functional failure must be
identified (Q3). The list of failure modes should include 1) failure modes that have happened
before, 2) failure modes that are currently being prevented by existing maintenance programs and 3)
failure modes that have not yet happened but are thought to be reasonably likely given the operating
context.
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Failure modes are identified to allow the physical effects of a failure to be evaluated (Q4),
including what would happen if no action were taken to anticipate or prevent it. The consequences
of each failure mode must then be specified (Q5) as if nothing were being done to prevent it. RCM
assigns consequences to one of four categories: hidden, evident safety/environmental, evident
operational and evident non-operational.
The question is then asked, “what can be done to prevent the failure?” to determine what
maintenance tasks should be carried out to predict or prevent failures (Q6). As discussed previously,
only those tasks that are worth doing (to prevent consequences) should be undertaken. An important
corollary of this is that when considering existing maintenance schedules, tasks that have little
effect on failure rates or consequences should be eliminated. This elimination of redundant tasks is
an important part of the RCM optimization process.
The final task in the RCM analysis is to consider what should be done in the event that the
failure cannot be either predicted or prevented (Q7). Approaches that may be considered include
unscheduled failure management policies and changing the asset’s operating context (such as its
design or the way it is operated).
It can be seen that condition monitoring will form part of the actions undertaken to address
Q6, that is: “Pro-active tasks: what can be done to predict or prevent each failure (proactive tasks
and task intervals)?” The task interval would be set in proportion to the risk and the P-F interval
described earlier.
Case Study Inset 5-3 shows how one utility’s approach to RCM contributes to the
management of its pumping station assets. Case Study Inset 5-4 shows the scale of benefits that can
be accrued through the adoption of this approach.
Case Study Inset 5-3: Water Care’s Management of its Pumping Station
Water Care (New Zealand) has 51 pumping stations in its network (ranging from 10
liters/second to 4,000 liters/second). SCADA monitoring all stations includes alarms, hours
run and pump stop/start data.
The overall maintenance strategy is set using an RCM approach. Maintenance tasks and
frequency are set on the basis of past experience, review of manufacturer’s manuals and
feedback from maintenance teams. FMECA analysis is used to understand implications of
system, sub-system and component reliability.
Planned preventive maintenance program includes monthly inspections, scheduled wet well
cleaning, general civil and site maintenance and standard mechanical and electrical
maintenance tasks. Inspections include scheduled pump vibration analysis, thermography and
electrical mega testing.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
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Case Study Inset 5-4: Massachusetts Water Resources Authority (MWRA) RCM
Program
Implementation of a formal RCM program has been a very effective way for MWRA to
enhance asset reliability and performance and to reduce life cycle costs of its large facility
equipment. Benefits accrued have been primarily from the Deer Island Treatment Plant RCM
program and associated condition monitoring on major equipment. MWRA has recognized
the following benefits:
 Demonstrated reduction in over 20,000 maintenance work hours per year as a result of
all reliability programs including RCM, condition monitoring, preventive maintenance
optimization and productivity improvements, resulting in labor savings of over
US$700,000 annually.
 Proactive oil sampling program resulted in avoided (scheduled) oil changes valued at
roughly US$50,000 per year.
 Substantial (non-quantifiable) avoided and deferred costs due to enhanced equipment
reliability and performance, extended equipment life, avoided permit violations, etc.
 Qualitative staff improvements in terms of teamwork, communications and
commitment to success.
Investments in staff training, sophisticated mechanical alignment equipment and permanent
monitors on certain major equipment have also yielded savings in asset life cycle costs and
performance reliability.
See Case Study 11 in Chapter 8.0.
5.4.1.1. Reducing the Cost of RCM Analysis
By design, RCM is a comprehensive, detailed, and therefore time consuming and expensive
process to apply. As such, large companies require a screening approach to prioritize studies or
determine to which assets (treatment works, pumping stations, etc.) this (or a similar) procedure will
be applied.
Such an approach is summarized in Case Study Inset 5-5, though as noted, it is understood
that a formal RCM procedure was not adopted in the analysis. The process presented is, however,
equally applicable to RCM and other approaches to maintenance optimization.
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Case Study Inset 5-5: Scottish Water’s Screening of Treatment Works
When Scottish Water was designing the implementation of a risk based maintenance strategy,
it was determined that not every site (treatment works, pumping station, etc.) could be
analyzed in detail. As such, they ranked sites in terms of importance considering a range of
factors, including:
−
Size (population served)
−
Available standby capacity
−
Storage
−
Plant complexity (number of assets, SCADA, etc)
−
Stringency of consents (for wastewater)
From this ranking, the maintenance strategy to be adopted was specified such that: 1) the top
10% of assets were subject to full risk based maintenance planning procedure, 2) the next
20% were treated with a generic approach using task lists and 3) the final 70% were allocated
standard tasks and frequencies (e.g., an annual visit) associated with basic care.
For the full risk based maintenance planning procedure, a full failure mode analysis was
undertaken (using FMECA) at the unit level. The analysis was undertaken by a specialized
team in conjunction with operational and maintenance staff. Three fundamental questions
were asked of each asset to focus the analysis:
−
Is the asset operating?
−
Is the asset performing satisfactorily in terms of failures?
−
Is the asset ‘fit for purpose’?
As well as undertaking screening analysis to determine which assets the RCM process
should be applied to, the cost of undertaking RCM analysis can be reduced by adopting a
streamlined RCM approach. According to Moubray (2002), the different streamlined approaches are
characterized by a retroactive focus. The RCM starts not by defining the functions of the asset, but
with existing maintenance tasks. Furthermore, generic lists of failure modes are used and the
analysis performed on one system is applied to other similar systems (Backlund, 2003).
Proponents of streamlined RCM claim they achieve similar results to the full RCM process,
but with much less time and thus lower costs (Backland, 2003). In contrast, Moubray (2002)
considers that the use of such streamlined approaches do not achieve the same results as full RCM
studies. However, as noted by Turner (undated), few organizations have applied RCM to anything
other than their most critical assets, suggesting that there is a real need for an alternative. As such,
streamlined RCM approaches such as preventative maintenance optimization (PMO) offer a
pragmatic approach to the process of review for assets that have an established maintenance
program (formal or informal) but where that maintenance program was inefficient or misaligned
with business needs (Turner, undated).
5.4.2 Risk Based Inspection
In the past, inspection techniques and frequencies were typically based on manufacturer’s
recommendations, industry standards or regulatory requirements. Inspection frequencies were set in
terms of time-based or calendar-based intervals. Since knowledge of asset operation and
deterioration evolves over time through user experience, such practices do provide an adequate
level of maintenance and asset protection.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
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These traditional approaches do not, however, explicitly consider risk, the asset’s operating
context, or the impact of the assessed condition on the required inspection interval. As a result, the
inspection programs generated do not necessarily provide an optimal balance between cost of
inspection and asset-related risk throughout the asset lifecycle. In contrast, by considering current
condition, risk and operating context, an acceptable level of reliability and risk could be achieved at
lower cost.
Various sectors have recognized that significant benefits may be gained from adopting more
informed inspection scheduling techniques (ABS, 2003). Factors such as operating experience,
deterioration rates and consequences of failure are considered along with the asset condition to give
an inspection interval that seeks to achieve a balance between risk and the level of inspection effort.
A technique that applies this philosophy is RBI. RBI focuses on the optimization of
inspection programs for static assets; especially pressure equipment and structures. RBI begins with
the recognition that the essential goal of inspection is to prevent failures. By explicitly considering
risk, RBI assures inspection resources are focused on the areas of greater concern and provides a
methodology for determining the optimum combination of inspection methods and frequencies
(ABS, 2003). Case Study Inset 5-6 shows the basic elements of the RBI approach.
Case Study Inset 5-6: Risk Based Inspection
According to the American Bureau of Shipping (ABS, 2003), the basic elements in the
development of an RBI program are summarized in the following steps:
1. The determination of the risk introduced by the potential failures of each asset
component.
2. The identification of the degradation mechanisms that can lead to component failures.
3. The selection of effective inspection techniques that can detect the progression of
degradation mechanisms.
4. The development of an optimized inspection plan using the knowledge gained in the
three previous items.
5. The analysis of the data obtained from the inspections and any changes to the
installation in order to feed back into the RBI plan.
The setting of inspection frequency within RBI is not a rigid process with fixed,
predetermined inspection intervals. Inspection intervals may change throughout the life of the
asset as risk increases or decreases. There is, however, a general logic to the inspections and
frequency of the inspections, as highlighted in Case Study Inset 5-7, which can be summarized
thus:
 Higher risk systems/components generally have the shorter frequencies of inspection and
have potentially larger inspection population requirements.
 Lower risk systems/components often have extended inspection frequency (or even no
inspection) and have reduced inspection population requirements.
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Case Study Inset 5-7: Risk Based Inspection of Melbourne Water’s Tanks
In 2005, Melbourne Water operated thirty-eight steel service reservoirs (40 were being
operated at the time of writing), with an estimated replacement value of AU$190 million.
Due to a design issue inherited by Melbourne Water (see Case Study 8 for details), a number
of these tanks are prone to under floor corrosion. The failure mode associated with this under
floor corrosion is not catastrophic. However, significant leaks can occur. Given the high
visibility of water conservation issues in Australia, coupled with the proximity of the tanks to
residential areas, such leaks can result in significant adverse publicity as well as having the
potential for causing property damage and associated community distress.
Given the perceived level of risk, Melbourne Water’s steel service reservoirs are now
regularly inspected to ensure that the potential for asset failure is appropriately managed.
Inspection strategies have been developed in consultation with external consultants and are
considered by Melbourne Water to be industry best practice.
Comprehensive corrosion assessments are undertaken on a periodic basis ranging from one to
five years. Generally speaking, assets that are deemed to pose a significant risk are inspected
on a one to two year basis, whereas those that pose a smaller risk are inspected on a three to
five year basis. Outage strategies are implemented based on business risk and operational
needs with due consideration given to both water quality standards and structural integrity
requirements. The inspection can be timed in accordance with cleaning requirements; tanks
have to be cleaned every three to eight years, depending on the level of silt build up.
See Case Study 8 in Chapter 8.0.
5.5
A Generic Approach to Specifying Condition Monitoring Tasks
It is interesting to note that all risk-based assessment methods, including RCM, RBI and
FMECA, share a basic structure in that the methods all consists of an exploration of the system
under study to address issues that are, in essence, captured by the first five questions of the RCM
approach:
1. What are the functions and associated desired standards of performance of the asset in its
present operating context?
2. In what ways can the asset fail to fulfill its functions?
3. What causes each functional failure?
4. What happens when each failure occurs?
5. In what way does each failure matter?
The difference between the various approaches is the optimization process that is used,
whereby inputs (e.g., inspection/maintenance regimes) are compared against outputs (e.g., cost and
associated risk) to provide a desired outcome (e.g., an optimal inspection/maintenance regime).
Given the commonality between the approaches, it is a relatively straightforward task to
specify a generic approach to identification of condition monitoring tasks. This is illustrated in the
flow diagram shown in Figure 5-3. The selection process in the last box of Figure 5-3 is essentially
a cost benefit analysis taking into account the level of risk exposure.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
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It is again important to note that the selection process embedded in Figure 5-3 presupposes
that there is some kind of detectable deterioration in either asset condition or performance. For
assets or components whose failure modes are essentially random or cannot be detected, then
condition monitoring is not an appropriate strategy and other risk management approaches must be
used.
Figure 5-3. A Generic Approach to Specifying Condition Monitoring Techniques.
Optimization of condition monitoring should ideally be done across the asset stock, although
this optimization does not necessarily have to be undertaken formally; the process of analyzing risk
and assessing cost of condition monitoring relative to potential consequences will provide
optimization to a degree.
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5.5.1 Critical Defects and Performance Thresholds
The performance thresholds and critical defects indicated in Figure 5-3 should be taken as
being equivalent to point ‘P’ in the P-F curve shown in Figure 5-2, that is, they are thresholds that
indicate that the failure process has progressed to the point where action is required.
As noted previously, there is a tendency for engineers to manage the condition of assets, not
least because early intervention in the deterioration process can significantly prolong the life of an
asset. However, there are in general more tasks to do than there are resources with which to do
them. Therefore, it is important to prioritize activities in some way.
A key task in the development of any effective condition monitoring process is the need to
determine what critical defects and performance thresholds are, and what these mean in relation to
the asset’s remaining service life and need for action. For example, given that a defect is observed,
the interventions available range from doing nothing through repair or replace. In the later case, the
observed defect would indicate the asset was at the end of its useful life.
When determining what intervention to adopt for a particular asset, there is a great reliance
on expert opinion drawing on previous actions to address defects and taking into consideration a
range of data, including:
 The type and severity of the defect.
 The context of operation.
 Consequential impacts should the asset fail.
In essence, the engineer assessing the defect needs to decide if maintenance is needed, and if
so, what scale (repair, replacement) and if not, what action should be taken instead. This could
range from doing nothing through implementing condition monitoring or specify a re-inspection
within a time interval deemed appropriate to the risk.
In interpreting defects, there is a tendency for individuals to be risk averse in their
interpretations and recommendations. There is thus a need for standard guidance on what
constitutes a significant defect for a range of asset types in a range of operational contexts. Such
guidance is, however, beyond the scope of this report.
5.6
Development of a Condition Monitoring Program
When considering a change to any maintenance activity, the key challenge faced by a
maintenance manager is to consider what level of activity is appropriate. In practice, this often
reduces to the need to determine what percentage of the maintenance budget and resources can or
should be dedicated to a given activity. The remainder of this chapter considers this challenge from
the perspective of developing a condition monitoring program, including how such a program is
justified. For the purposes of this discussion, it is assumed that condition monitoring is already
undertaken in one form or another, so any program will involve a change to the current practices.
A case study is provided below to illustrate how a water utility went about changing its
condition monitoring practices to increase the amount of condition-based maintenance being
undertaken. While the case study shows some of the logic behind the development of a predictive
maintenance program, no attempt is made to give an exhaustive treatment of this subject; the
interested reader is referred to the literature on maintenance program development (e.g., the work of
R. Keith Mobley, The Plant Performance Group).
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
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The case study presented relates to a project undertaken in 2002/2003 by MWRA. The
project sought to determine how MWRA should build upon its existing condition monitoring
capacity at the Deer Island Treatment Plant (DITP). At the time the case study project was
conceived, various condition-monitoring technologies were already in use at the DITP; including
vibration monitoring, oil analysis, infrared thermography and ultrasonic detection. Data collection
and analysis had, however, not been fully implemented, and management of the technologies was
being undertaken by different groups, for example:
 The Electrical Engineering group managed the use of thermography.
 The Maintenance Work Coordination group managed the use of oil sampling.
Since a major strength of a predictive maintenance program is achieved when two or more
complimentary technologies are used together (an example of this would be when a gearbox
exhibits high levels of wear particles in an oil sample; vibration analysis could then be used to
determine how extensive the wear is), the MWRA management team at DITP recognized that this
separation of responsibilities and, more importantly, the inevitable separation of findings/data did
not allow the full benefit of the condition monitoring techniques to be realized.
The case study project was initiated to develop a program under which condition-monitoring
responsibilities could be brought together within a single group. In addition, a key objective was to
increase the predictive monitoring capacity at the DITP to create a more effective maintenance
regime and move away from interval based maintenance where possible.
5.6.1 Program Development
An important first step in any program development is to understand and document what is
to be achieved. In the case of a change to a condition-monitoring program, the main driver will
often be a reduction in overall cost through a combination of:
 Improvements to maintenance regimes, to increase asset reliability/availability and thereby
reduce the cost of asset failures and equipment downtime; and
 Justifiable reduction in overall maintenance effort; for example, converting a non-condition
based (interval based) preventive maintenance program to a condition based program, which
can realize significant savings in maintenance hours, parts, and so forth.
Once drivers are clarified, some technique must then be used to determine what condition
monitoring activities are required to achieve the program’s objectives. The necessary resources and
equipment must be identified.
When undertaking these tasks, two approaches can be adopted. The ideal approach is to
assess the maintenance tasks required through a systematic technique such as RCM, and then assess
the budgets and resources necessary to allow these tasks to be undertaken. The more pragmatic
approach is to assess what can be done given available resources and level of management
commitment, and tailor the plan to these constraints. Whichever approach is taken, the
implementation of a program to modify any maintenance practice requires a well-structured plan for
staffing and work management to be developed. In general, staff will be required to fulfill the
following functions:
 Management of the maintenance activities and team members.
 Collation and analysis of data.
 Undertake the condition monitoring tasks themselves.
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5.6.2 Planning for Program Success
Justification of a condition-monitoring program should ideally be based on economic
analysis in which the relative cost-benefits of the program are assessed. The data for costs can
generally be obtained from a utility’s records or by contacting practitioners who either offer the
required services or have experience using the condition monitoring techniques of interest. Accurate
information on benefits is, however, difficult to obtain because it requires that the benefits of
avoiding future failures are estimated in some way. Unfortunately, the variables that influence the
cost of failure are often unique (due to variations in conditions, events, equipment types, operational
situations, etc.), and various assumptions must be made when undertaking analysis of a proposed
program. The analysis can incorporate a high degree of subjectivity and associated uncertainty.
As well as issues relating to uncertainty of benefits, any change to a maintenance regime can
be expected to cause some disruption to the activities of maintenance staff. For example, converting
a non-condition based (interval based) preventive maintenance program to a condition based
program requires the reassigning of resources from the existing maintenance program to the new
program. However, there is often a lag between the introduction of the new maintenance regime and
the benefits of the program (e.g., reduction in failures). A period of disruption and additional
workload can be anticipated for the maintenance department until the results of the program start to
be seen. While additional resources and funding can be made available to help overcome this initial
period of net-disruption, it makes sense to start the predictive maintenance program with the least
amount of impact on the existing maintenance program, while supporting the effort well enough to
ensure a successful transition.
In recognition of these issues, a phased implementation plan can be developed in an attempt
to minimize the impact of uncertainties and any disruption. For example, in the case of the DITP
program, it was determined that the most logical approach for planning the implementation of a
predictive maintenance program was to:
•
Start out slowly, beginning with the implementation of the most versatile predictive
maintenance tools as they apply to a given facility.
•
Establish and ensure that the minimum amount of savings required to break even on the
investment of capital and resources was achievable.
•
Expand the program as “real” savings were realized and when the most beneficial
applications of the technology at the plant were identified.
In DITP’s case, significant capacity existed in vibration monitoring, oil analysis, and
thermography. Since all three of these technologies were being used, it was anticipated that each
would require little initial investment and minimal additional training to progress the programs.
Initial focus was given to the increased use of these technologies. It was also considered likely that
ultrasonic detection could be implemented due to the low cost of equipment and the simplicity of
the technology.
5.6.3 Resource Issues
Mobilizing sufficient resources to ensure a new program’s success can often be an issue,
given the demands of existing tasks. Again, a pragmatic approach may be needed in light of
resource constraints. For example, in the case study it was recognized that the most effective course
for guaranteeing the success of the overall program would be to devote selected maintenance
personnel to a new condition-monitoring group on a full time basis. The group consisted of a
condition-monitoring manager and two condition-monitoring engineers, with responsibilities for
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
5-17
analyzing all condition monitoring data, providing recommended corrective actions, and to organize
and implement condition-monitoring technologies. To supplement this group and to support the
condition-monitoring effort, technicians throughout the facility were trained on basic condition
monitoring techniques and to take all vibration readings and oil samples. These technicians work
part time each month on these activities. As the program evolved and demonstrated its cost
effectiveness, the commitment of technicians to supplement the group’s activities increased
significantly.
5.6.4 Cost Benefit Analysis
As noted above, justification of a condition-monitoring program is ideally based on
economic analysis in which the relative cost-benefits of the program are assessed. The development
of a cost-benefit analysis requires that the following tasks be undertaken:
 An evaluation of the condition monitoring tasks to be undertaken (in terms of the
technologies and approaches to be used, and frequency/asset coverage).
 An evaluation of equipment.
 An estimation of resources.
 An estimate of associated costs, including:
o
o
o
o
o
Training.
Software and equipment.
Labor.
Contracted support services (e.g., lab testing and specialized data).
Program management/administration.
 An estimate of benefits (in essence, an evaluation of failure avoidance and other benefits
such as improvements in asset reliability/availability and reduction in maintenance spend).
5.1.4.1 Case Study Example
In the case of the DITP, prior to providing a full commitment of resources to the program, a
cost benefit analysis was conducted for five condition-monitoring technologies: vibration
monitoring; oil analysis; thermography; ultrasonic detection, and motor current signature analysis.
However, rather than attempt to predict all potential savings that could be achieved at DITP, a cost
benefit analysis was undertaken to:
 Establish the costs associated with instituting a basic condition monitoring group, and then,
 Identify if there was the potential to recoup the investment based on the type of equipment,
the expected failures, and the estimated average savings that could safely be attributed to
predicting a percentage of those failures.
Resourcing of the Group
Given a pragmatic review of the available resources, and the level of condition monitoring
to meet the aims of the initial program, it was recommended the Condition Monitoring Group
structure as originally constructed included the following positions and associated labor dedication:
 Group Manager – 30% of full time for managing the group.
 Data Coordinator / Planner – 100% of full time.
 Vibration Technician – 20% of full time to begin evolving to a minimum of 50%.
5-18
 Oil Sampling Technician – 20% of full time to begin evolving to a minimum of 50%.
 Thermography Technician – 20% of full time to begin evolving to a minimum of 50%
 Ultrasonic Technician – 10% of full time to begin evolving to a minimum of 20%.
Specialized training in each of the specific technologies was recommended for each of the
positions, including training for the data coordinator and group manager in all of the technologies. It
was further recommended that the number of technicians to be trained should be based on the level
of back-up personnel required to cover for vacations, sickness and so forth. After further
development of the condition monitoring program additional resources were allocated, which
included a group manager and two data coordinators/planners. In addition, as noted above,
technician support throughout the facility is provided.
Program Costs
Based on the recommended group structure and estimated percentages of full time effort for
each position, MWRA was able to estimate the cost of operation for the Condition Monitoring
Group over a 10 year period, as summarized in Table 5-2. Much of the capital expenditure
(equipment costs) had already been made, so this cost element could be excluded from the analysis.
Vibration Monitoring Benefits
To quantify the benefits of the vibration-monitoring program over the course of 10 years it
was necessary to make the following assumptions:
 The program would be expanded from the initial population of 98 pieces of equipment to a
population of 318 pieces of equipment.
 The incidence of failure avoidance will increase at a rate of 3% per year as the plant
equipment began to experience more age related failures.
 The incidence of failure avoidance will increase at a rate of 2% per year as the vibration
monitoring personnel become more experienced.
The documented cost avoidance (the estimated cost of avoided damage directly attributable
to the condition monitoring) for the vibration-monitoring program over the previous two and a half
years was a total of US$57,700 for an average of US$23,080 per year.
Based on the above assumptions and documented cost avoidance, Table 5-1 shows the
estimated projection of the vibration monitoring cost avoidance benefits over a 10-year period.
Table 5.1. Estimated Projection of the Vibration Monitoring Cost Avoidance Benefits (US$).
Failure Cost
Avoidance
FY0 = 23k
FY1
FY2
FY3
FY4
FY5
FY6
FY7
FY8
FY9
FY10
10-Year Total
51.3k
82.4k
86.6k
91.0k
95.6k
100k
105k
110k
116k
122k
960k
A simple return on investment (ROI) calculation for the vibration-monitoring program over
a 10-year period was undertaken, as represented by the following:
ROI = [(US$960k (10 Yr Benefit) – US$483.1k (10 Yr Cost)) / US$483.1k (10 Yr Cost)] x
100
ROI = 98.7%
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
5-19
Table 5-2. Ten-Year Projected Condition Monitoring Costs (US$).
First Year Costs
Vibration monitoring
Oil sampling
Thermography
$16,000 (8 Persons)
$8,000 (4 persons)
$9,000 (4 persons)
Ultrasonic
detection
$4,800 (4 persons)
Included with equipment
Not required
Included with equipment
Not required
$40,000 (2 port. Units)
$1,000 (sample equip)
$40,000
$3,000
Manager labor
$4,600
$4,600
$4,600
$2,280
$6,920
Data coordinator labor
$16,800
$16,800
$10,080
$6,720
$16,800
Technician labor
$9,600
$9,600
$9,600
$4,800
$5,000 (analysis of data)
$9,000 (lab costs)
$0
$0
$52,000
$48,000
$33,280
$18,600
Initial training
Software purchase
Equipment purchase
Contracted support services
Total expenditure
Miscellaneous
group management
$23,720
Note: Total expenditure excluded Equipment Purchase as investment had already been made in the necessary equipment.
Subsequent Years Costs (average): all future costs are listed at present day values without consideration of discount rate (NOT net present value).
Training
$1,500
$1,500
$1,500
$500
Calibration and upgrades
$5,000
$0
$2,000
$0
Manager labor
$4,600
$4,600
$4,600
$2,280
$6,920
Data coordinator labor
$16,800
$16,800
$10,080
$6,720
$16,800
Technician labor
$24,000
$24,000
$24,000
$9,600
Contracted support services
$1,000
$18,000 (lab costs)
$0
$0
Annual costs
$47,900
$64,900
$42,180
$19,100
$23,720
Subsequent 9-year cost
$431,100
$584,100
$379,620
$171,900
$213,480
Estimated 10-year cost
$483,100
$632,100
$412,900
$190,500
$237,200
5-20
Oil Analysis Benefits
To quantify the benefits of the oil analysis program over the course of 10 years it was
necessary to make the following assumptions:
 The program would expand from the initial population of 106 pieces to approximately
300 pieces of equipment.
 The incidence of failure avoidance will increase at a rate of 3% per year as the plant
equipment begins to experience more age related failures.
 The incidence of failure avoidance will increase at a rate of 2% per year as the oil
analysis personnel become more experienced.
 The incidence of oil usage cost avoidance will increase at the rate of US$10,000/year as
equipment is added to the program over the next three years.
The documented failure avoidance cost (the estimated cost of avoided damage directly
attributable to the condition monitoring) for the oil analysis program over the previous eight
months was a total of US$56,970 for an average of US$85,455 per year. The documented annual
oil usage avoidance cost for the oil analysis program over the previous eight months was a total
of US$30,000.
Based on the above assumptions and documented cost avoidance, Table 5-3 shows the
estimated projection of the oil analysis cost avoidance benefits over a 10-year period.
Table 5-3. Estimated Projection of the Oil Analysis Cost Avoidance Benefits (US$).
Failure cost
avoidance
FY0 = 85k
Usage cost
avoidance
FY0 = 30k
FY1
FY2
FY3
FY4
FY5
FY6
FY7
FY8
FY9
FY10
10-year total
144k
208k
279k
293k
307k
323k
339k
356k
375k
394k
2.8M
40k
50k
60k
60k
60k
60k
60k
60k
60k
60k
570k
A simple ROI calculation for oil analysis program over a 10-year period was undertaken,
as represented by the following:
ROI = [(US$3.37M (10 Yr Benefit) – US$.632M (10 Yr Cost)) / US$.632M (10 Yr
Cost)] x 100
ROI = 433%
Thermography Benefits
Because DITP did not have documented data on cost avoidance for the thermography
program, a predictive maintenance consulting company was contacted for assistance in
developing cost benefit values. The consulting company provided figures that represented typical
costs and savings for a large facility; the annual gross benefits provided by the consulting
company were estimated at US$300k.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
5-21
A simple ROI calculation for the thermography program over a 10-year period was
undertaken using a more conservative annual gross benefits figure of $100k, as represented by
the following:
ROI = [($1.0M (10 Yr Benefit) – $.413M (10 Yr Cost)) / $.413M (10 Yr Cost)] x 100
ROI = 142%
Ultrasonic Detection Benefits
Because ultrasonic detection had not been used at DITP for any extended period of time
and data associated with failure avoidance was not available, anticipated benefits could not be
calculated.
The anticipated use of the ultrasonic unit was to include evaluation of rotating element
bearings on equipment where the criticality of the equipment did not warrant the time and effort
associated with vibration analysis. For the purposes of the analysis it was assumed that if it could
be determined that the program would detect a sufficient number of bearing problems to avoid
maintenance costs exceeding the cost of the program, the ultrasonic program would be
considered be viable. Actions that would avoid maintenance costs include alignment, lubrication
and bearing replacement prior to damaging pump/shaft. A value of US$1,000 per avoided cost of
bearing failure was used in the following calculation.
No. of Bearing Failures/yr = Avg. Annual Program Cost/Avoided Cost of Bearing Failure
No. of Bearing Failures/yr = US$19,050 / US$1,000
No. of Bearing Failures/yr = 19
Since the ultrasonic program would be surveying hundreds of bearings per year, it was
concluded that 19 bearing problems detected per year was almost certain.
Results of the Analysis
From the above analysis it was determined that continued implementation of vibration
monitoring, oil analysis, thermography and ultrasonic detection would produce a return on
investment.
Although justifiable from a cost benefit viewpoint, it was recommended that the
implementation of motor current signature analysis should be delayed in an effort to minimize
the commitment of labor resources and training for the condition-monitoring program.
5-22
CHAPTER 6.0
SELECTING TOOLS AND TECHNIQUES
Chapter Highlights
 A significant number of assessment techniques and inspection tools have been identified
in this project. Research has shown that the selection of an appropriate tool or technique
is highly context specific.
 A generic approach to tool selection is outlined, which uses an exclusion process to
identify options that can be considered. Tools are excluded on the basis of technical
feasibility, suitability and capacity. Useable options are then evaluated through economic
or financial analysis.
 A number of important selection criteria have been identified to guide the selection
process. Where possible, the attributes relating to the criteria have been evaluated for
each of the tools and techniques identified and reviewed in this research. These attributes
summarize the application and use of the tools and provide the information necessary to
undertake the selection process.
 A key goal of the research was to provide a framework that would assist organizations in
the selection of condition assessment tools. A paper-based solution is presented to
facilitate this process. Initial work has also been undertaken into the development of a
prototype expert system for this application.
 A direct extension of risk-based arguments used herein is that the more important the
asset is, the more expense can be justified in assessments undertaken to ensure the asset
does not fail. However, to minimize costs, inexpensive tools should still be used where
possible. As such:
−
Inexpensive screening tools and approaches should be used routinely.
−
The results of the screening approach may dictate that there is a need for
additional information and/or accuracy. This may require the use of more
sophisticated assessment or inspection tools.
−
Additional expense should be considered only when justified in terms of risk costs
avoided or benefits accrued.
 This logic is used to present an iterative approach to the use of tools, where more
sophistication and accuracy is used to fill information gaps left by screening tools.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
6-1
6.1
Introduction
A significant number of assessment techniques and inspection tools were identified in
this project. Furthermore, the research showed that the selection of an appropriate inspection tool
or condition assessment approach is highly dependent upon what outcomes are required from the
assessment, the capacity of the tool/technique to provide the necessary information, the
availability of appropriate data to interpret the results, the capacity of the utility to utilize the
selected tool/technique and economic factors. The issues involved in tool selection are thus
complex, and can be summarized by considering condition assessment from three overlapping
viewpoints, namely:
 Asset Focused View: how critical is the asset in question and what is justified to manage
the risk; this is the RCM type approach discussed in Chapter 5.0.
 Situation Focused View: what are the drivers and what is justified to address them; for
example, the need to understand risk and impact of capital deferral; need to address
litigation.
 Tool Focused View: when would a specific tool normally be used; for example,
opportunistically, as a screening tool, for the regular inspection of important assets,
monitoring of critical assets, etc.
This chapter presents an approach to aid utilities in selecting appropriate condition
assessment tools and techniques, which takes into account each of these views.
A generic approach to tool selection is first outlined, which uses an exclusion process to
identify options that can be considered. The role of risk and cost in determining what tool to use
for a particular set of circumstances is then considered, and a sliding scale of assessment
standards suggested.
6.2
A Protocol for Selecting Condition Assessment Tools
As noted above, a significant number of assessment techniques and inspection tools were
identified during this research. Listing all these tools and mapping them onto the asset stock is a
useful task, but it is more desirable to help utilities to undertake their own selection of suitable
tools and techniques given their unique knowledge of the assets that need assessing, the drivers
behind the assessment, and the likely end uses of the information.
The International Infrastructure Management Manual (IPWEA, 2006) presents an
approach to the selection of condition monitoring techniques that involves a process where the
utility 1) assesses the condition and performance assessment techniques being used already, and
2) develops an understanding of any shortfalls. This gap analysis then drives the selection of new
approaches and/or tools. This process is shown in Figure 6-1 (this is a simplified version of the
flow chart given in the International Infrastructure Management Manual (IPWEA, 2006). An
example of a utility using this type of approach is summarized in Case Study Inset 6-1.
While this approach is perfectly valid, it assumes that condition monitoring already plays
a central role in the utility’s asset management approach, and that the utility simply wants to
assess whether better approaches are available to those already in use. This logic is generally
applicable to the use of condition assessment/monitoring within day-to-day maintenance, as
discussed within Chapter 5.0.
6-2
Case Study Inset 6-1: Selection of a Tool at the Asset Level
When considering adopting a new condition assessment tool or technique, Sydney Water
compares the effectiveness of the new tool with the current tool, if a tool is currently used.
The comparison involves a cost-benefit evaluation per asset. Maintenance cost history for
each asset is used as the fundamental benchmark. If a new tool will cost more, it still may be
considered if it gives an earlier warning of failure.
See Case Study 9 in Chapter 8.0.
Figure 6-1. Process Flowchart for Developing Condition Monitoring Programs.
Within the context of SAM, as noted previously, some utilities adopt an informal
approach where condition and performance assessments are not yet undertaken or are undertaken
in a somewhat unstructured manner. At the other end of the spectrum, more sophisticated asset
management approaches do not focus on condition and performance, although condition
monitoring is undertaken for specific assets where it is shown to be a useful approach to risk
management (see Chapter 5.0) or where there is a regulatory driver to undertake the monitoring.
The protocol adopted for tool selection in this research has been designed with all these
potential end uses in mind, and is based on a process of exclusion according to a range of
criteria, followed by an economic assessment of the viable alternatives. An overview of the
approach is shown in Figure 6-2.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
6-3
Figure 6-2. Approach to Selecting Condition Assessment Tools.
As illustrated in Figure 6-2, the selection of a suitable tool (step six of the process
described in Chapter 3.0) requires consideration and evaluation of four factors:
 Technical feasibility: The utility identifies what inspection/assessment options are
feasible for the asset(s) in question.
 Technical suitability: The utility evaluates whether the potential options will meet its
specific needs, for example, by providing suitable data and/or level of decision support
required.
 Technical capacity: The utility then evaluates if it possesses the required technical
capacity to allow the potential options to be used and, if not, what the gaps in capacity
are, including an initial assessment of whether these gaps can be filled.
 Economic assessment: The utility evaluates whether the remaining options add value
based on the goals of the assessment, considering costs (including capacity building
and/or out-sourcing of work) and benefits, and whether one approach clearly gives the
best value compared to other available options. Final selection is made in terms of
available resources, the cost-benefits accrued and affordability issues.
6.3
Exclusion Criteria
According to the process described above, the selection of an appropriate inspection tool
or assessment technique involves a criteria-based technical exclusion process. Necessary and/or
desirable criteria are specified and tools approaches excluded based on their inability to satisfy
these criteria. For example, the assessment of technical feasibility is based on asset-related
criteria. Exclusion of tools on that basis provides a list of all feasible options for the asset type in
question. The subsequent assessment of technical suitability and technical capacity allow the list
6-4
of feasible options to be reduced to a list of options that could be used by the utility. An
economic appraisal allows this list to be ranked and the appropriate tool selected.
A number of important criteria related to the first three steps of the exclusion process
were identified to guide the selection of tools and techniques using the process illustrated in
Figure 6-2. Two separate sets of criteria are presented herein:
 Criteria relating to inspection tools: these criteria relate to specific inspection tools and
techniques, such as ultrasonic thickness gauges.
 Criteria relating to assessment tools: these criteria relate to asset management tools or
condition assessment tools that use inspection and other data to characterize asset or
system condition.
Table 6-1 details the criteria for inspection tool selection and Table 6-2 details the criteria
for selection of assessment tools.
Various characteristics of a utility also influence what approaches to condition and
performance assessment should be selected. Characteristics of significance are summarized in
Table 6-3.
6.4
Application of Exclusion Protocol
Where relevant information could be found, the attributes relating to the exclusion
criteria detailed in Tables 6-1 and 6-2 have been evaluated for each of the tools and techniques
identified and reviewed in this project. These attributes summarize the application and use of the
tools and provide the information necessary to identify the range of tools and techniques that
apply to the application under consideration.
It is assumed that once a list of useable options is identified, the utility will undertake a
cost-benefit analysis to select the appropriate tool. The factors shown in Table 6-3 influence this
analysis, along with economic factors such as:
 The capital and operational costs associated with the inspection.
 Costs associated with analysis and interpretation of the inspection data.
 The accuracy and precision of the results.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
6-5
Table 6-1. Exclusion Criteria for Inspection and Survey Tools/Techniques.
Category
Technical
selection
Technical
suitability
Utility technical
capacity
6-6
Selection criteria
Notes
Assets covered
What type of asset is covered by the tool?
Material type
What material is covered by the tool?
Service area
Potable or wastewater?
Access requirements
Are there any specific access requirements (launch
assemblies, power, etc.)?
Limitations relating to asset condition
Is there a restriction if the asset is in bad condition (this
includes presence or absence of lining/coating)?
Limitations relating to asset size/geometry
Is there a size/diameter restriction and is there a restriction
in asset geometry?
Continuous/discrete
Does the technique give continuous/discrete readings (in
time and space)?
Destructive/non destructive
Is the asset (or part thereof) destroyed or is it a nondestructive test?
Interruption to supply/function
Can the inspection be undertaken on-line or must the asset
be taken off line?
Assessment parameters
What is measured (defects, blockage, integrity, wall section,
etc.)?
Integration with software tools
Is the tool/approach stand-alone or can the output be
integrated into utility systems easily (e.g., telemetered, up
loading via mobile phones)?
Commercialization of tool
Is the approach/tool fully developed? Can it be used off-theshelf?
Previous/existing use of the tool in sector
History of use in terms of uptake in the water and other
sectors and acceptability to stakeholders?
Accuracy/reliability
Any measure of accuracy (qualitative and/or quantitative)?
Ease of validation of results
Can the results be easily validated or are they indicative at
best?
Asset management sophistication required
Is the approach associated with high levels of asset
management sophistication or can any utility use it?
Skills required (level of tool sophistication),
usability
What level of operator skill is needed?
Technology required (level of tool
sophistication)
What level of technological sophistication is needed (high
power computers, sophisticated assets)?
Documentation
Is the tool documented? Are standards available?
Availability of technical support
Is the tool supported (helpline or other point of contact)?
Table 6-2. Exclusion Criteria for Asset Management and Assessment Tools/Techniques.
Category
Technical
selection
Technical
suitability
Utility technical
capacity
Selection criteria
Notes
Assets covered
What type of asset is covered by the tool?
Granularity
What level of detail is covered (asset level, area/zone,
utility)?
Service area
Potable or wastewater?
Focus of analysis
What is assessed (remaining life, probability of failure, level
of service, risk, etc.)?
Scalability of tool/approach
Is the tool/approach only suitable for small/large utilities?
Commercialization
Is the approach/tool fully developed? Can it be used off the
shelf?
Previous/existing use of the tool
History of use in terms of uptake in the water and other
sectors and acceptability to stakeholders?
Ease of validation
Can the results be validated?
Flexibility with respect to analysis (asset
types) and granularity (system, asset level)
Is the tool flexible in terms of service or asset focus?
Integration with other tools/GIS
Can the tool be integrated with existing system?
Asset management sophistication
Is the approach associated with high levels of asset
management sophistication or can any utility use it?
In-house skills required
What level of skill is needed (technician, engineer, etc.)?
Technology required
What level of technological sophistication is needed (high
power computers, sophisticated networks)?
Documentation
Is the tool documented? Are standards available?
Data Requirements
What data are required by the tool?
Linking to asset data
Does the tool provide facility to use ‘TAG’ numbers or other
asset identifications?
Availability of software and technical
support
Is the tool supported (helpline or other point of contact)?
Usability
Is the approach considered useable?
Table 6-3. Utility Criteria that Influence the Choice of Tools/Techniques.
Attribute
Characteristics
Size
Location
Service areas
Large/medium/small (population served)
Urban/rural/mixed
Drinking/waste water, pipeline assets/non-pipeline assets
Data quality/quantity
Good/average/poor
Technical development of asset stock
High (state-of-art)/average (mix)/low (obsolete)
Degree of asset management process development
Well developed/developing/not developed
Available budgets
Cash rich/cash poor
Managerial commitment
Board-level commitment/engineers/etc.
Network state
Good/mixed/near collapse
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
6-7
6.5
Development of a Prototype Expert System (ES)
A key goal of this research was to provide a framework to assist a utility in the selection
and use of condition assessment tools. A paper-based solution has been developed to facilitate
this process (see Chapter 7.0). However, the complexity of tool selection, in combination with
the number of tools and techniques used within the water sector, make such an approach
unwieldy.
The research team considers that a better approach is to incorporate the information and
selection procedure within a software tool. After review of a number of options, an ES was
identified as an appropriate vehicle for delivering the research outputs for the following reasons:
 Importantly from the perspective of the research, the development of the ES provided a
focus for the development of the tool selection logic and criteria and guided the tool
reviews and design of the paper-based selection process.
 Within the context of the research deliverables, an ES provides a user-friendly tool that
helps a utility to identify tools and techniques appropriate to its needs.
 The ES also provides a means of organizing information in a way as to allow easy access.
 Unlike a purely paper based approach, an ES can be expanded and refined as new
information becomes available and made available via the world wide web.
With these issues in mind, initial development was undertaken of a prototype ES for this
application, as described in Appendix E.
6.6
The Impact of Risk and Cost on Tool Selection
The role of risk in determining the level of attention given to an asset has been discussed
in various sections throughout this report. A direct extension of these risk-based arguments is
that the more important the asset is (the higher the consequences of failure are), the more
expense can be justified in assessments to ensure the asset does not fail. However, to minimize
costs, inexpensive tools should still be used where possible. As such, the following can be stated:
 Inexpensive screening tools and approaches should be used routinely.
 The results of the screening approach may dictate that there is a need for additional
information and/or accuracy. This may require the use of more sophisticated/accurate
assessment or inspection tools.
 Additional expense should be considered only when justified in terms of risk costs
avoided or benefits accrued.
These basic guidelines led to the conclusion that, while there may be a range of tools and
techniques available to inspect/assess a given asset, the utility should select the cheapest of any
suitable options available that meets its immediate needs. Take, for example, the case of a large
(>300 horsepower) centrifugal pump, for which the following condition monitoring techniques
are feasible:
 Visual observation
 Performance monitoring (pump performance trending)
 Oil Analysis
6-8
 Vibration analysis
 Bearing temperature trending
 Acoustic monitoring techniques
 Ultrasonic thickness measurement
 Infrared thermography
 Motor circuit analysis
While it is useful to identify the tools that are feasible, the question still remains, “which
of the techniques should be applied?”
To help manage costs, the most inexpensive screening tools should be applied first.
Therefore, since they are the cheapest monitoring techniques available, as a minimum,
maintenance and operators should perform a routine monitoring role (e.g., listening for
unexpected noise, making visual assessments of deterioration and providing feedback on
performance issues to maintenance planners). When appropriate data capture systems have been
set up (e.g., telemetry), trending of operational parameters should also be carried out routinely as
part of condition monitoring and for energy efficiency purposes.
Depending on the importance of the asset, and its operating context (e.g., whether there is
any redundancy or significant levels of storage available), other condition monitoring tasks
might be deemed necessary. Risk-based approaches like RCM provide a means of determining if
a maintenance task is worth doing and at what interval inspections should be undertaken. In this
example, it is likely that a utility would find it cost-effective to undertake periodic oil testing,
vibration analysis of the pump and motor and trending of bearing temperatures.
Once a trigger threshold has been detected by one of the routine monitoring approaches,
some action needs to be taken. This action could be:
 A repair/replacement of a failing component.
 A change to the monitoring regime (to monitor the asset more closely to determine when
a critical condition is reached or to provide information on the rate of deterioration).
 Additional inspections using other feasible, but more costly, techniques than those used
for screening.
The cost of any additional investigation should be in proportion to the cost of subsequent
maintenance tasks. For example, if the inspection cost is a significant proportion of the
maintenance task, then further investigation is only warranted under specific circumstances (such
as the lead time for spare parts and the operational context means is desirable to continue to run
the asset, but the level of risk associated with this decision needs to be understood). For other
cases, it can be assumed that when averaged across a number of assets, carrying out the
maintenance immediately, rather than undertaking additional investigation, would realize cost
savings.
In such circumstances, the utility may develop a policy for determining when to
undertake additional investigations, in light of overall maintenance costs and operational
experience.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
6-9
6.7
An Iterative Approach to Asset Assessments
The example of the centrifugal pump given above can be generalized to give an iterative
approach to the use of tools where increasing levels of sophistication are used that build upon the
results of previous tools and assessments.
In this approach, tools are initially selected that perform a screening function, for
example, to identify the early signs of deterioration. More detailed inspection and analysis can
then be performed to investigate the asset condition further, if and when justified. If an
appropriate screening tool cannot be identified, it may be necessary to use a more sophisticated
approach in the first instance.
A similar approach to this was adopted by a company in the United Kingdom in the
analysis of water transmission pipe failures, as summarized in Case Study Inset 6-2. The concept
of a sliding scale of assessment standards presented in the case study is considered useful,
especially when generalized to consider assessments undertaken for reasons other than failure
investigation. Such an approach is outlined in Table 6-4.
As shown in Table 6-4, the assessment standard applied is dictated by the type of asset
(reactive or proactive), access considerations and the driver behind the assessment (condition
monitoring, failure investigation, etc.).
Case Study Inset 6-2: A Sliding Scale of Failure Investigations
A water company in the United Kingdom is reported to have around 150 trunk main failures
per year (Ham, 2006; personal communication). The failures vary in severity from near
inconsequential to catastrophic involving millions of dollars of claims and litigation.
To standardize its approach to failure investigations, the utility determined the level of
investigation to be undertaken for a range of failure circumstances and mapped out criteria to
allow operational staff to determine what level of assessment was to be undertaken given the
particular circumstances of a failure. These ranged from opportunistic investigations
undertaken at the time of the failure through to the use of expert test house and expert
witnesses to investigate a failure and to contribute to legal proceedings. In essence, the
approaches represent a sliding scale:
Bronze: opportunistic investigations only.
Silver: bronze level tasks plus additional investigations.
Gold: silver level tasks plus additional investigations.
Platinum: gold level tasks plus additional investigations.
There is an increasing level of sophistication with increasing importance of the asset failure.
At the highest level (platinum), cost is not considered an issue. As such, a range of techniques
will be used, from opportunistic investigations through to expensive destructive tests
undertaken and reported by experts.
In general, it can be concluded that the more there is at stake, the greater the level of
assessment that is justified. As in the example in Case Study Inset 6-2, the application of lower
assessment standards should always precede higher assessment levels where possible. In
6-10
particular, opportunistic and routine assessments should be carried out as a precursor to more
detailed assessments when practicable (see Case Study Inset 6-3).
Table 6-4. Sliding Scale of Assessment Standards.
Standard
Opportunistic
Typical
asset
Reactive
Focus
Sample
Frequency
Data collection
Representative
Opportunistic
Typical
tools
Visual
Accuracy
Expertise
Qualitative
Operations
Routine
Proactive
asset with
access
Regular
inspection and/or
routine
monitoring
undertaken to
anticipate
impending faults
Asset specific
Regular to
continuous
Visual, low
cost
screening
Qualitative,
low accuracy
quantitative
Maintenance
specialist
Bronze
Proactive
asset with
some access
restriction or
deemed to be
of concern
due to age or
condition
Regular
inspection and/or
routine
monitoring
undertaken to
anticipate
impending faults,
individual
assessment for
renewal planning
Representative
or asset
specific
Regular to
continuous
Higher end
NDT
Qualitative,
low to
moderate
accuracy
quantitative
Engineer
Silver
Proactive
assets with
difficult
access
Individual
assessment for
renewal planning
Representative
or asset
specific
Infrequent
Higher end
NDT or DT
High
accuracy
quantitative
Consultant
Gold
Known
problem
asset with
poor
performance
Individual
assessment for
renewal planning
Asset specific
Individual
assessment
Higher end
NDT or DT
High
accuracy
quantitative
Specialist
consultant
Platinum
Failed asset
with potential
or actual
litigation
associated
with failure
event
Forensic
investigation
Asset specific
Individual
assessment
High end
NDT and
DT, with
lab tests as
required
Highest
achievable
accuracy
Expert in
field
This concept is shown in Figure 6-3, which indicates that once initial condition and
performance assessments have been undertaken, there is an explicit requirement to consider if
the information gap has been filled, or if the decision being considered necessitates an increase in
data quality or quantity. In the later case, additional assessments are undertaken, using more
sophisticated tools and techniques, until the information gap is filled.
In the case of large important assets where risk analysis (e.g., RCM or FMECA) shows
that on-going condition monitoring tasks using sophisticated tools and techniques is justified,
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
6-11
opportunistic and routine assessments should still be carried out in conjunction with the more
sophisticated techniques to improve the reliability of the overall asset monitoring.
Case Study Inset 6-3: Water Corp’s Approach to Assessment of Water Tanks
Inspection of tanks by Water Corp is undertaken periodically under its asset condition
assessment (ACA) program. Often, this is aligned with maintenance activities. Similarly,
when emptied for cleaning, operators will undertake visual inspection.
The tank site is divided into assessable elements for the purposes of condition assessment.
Inspection templates are used to guide the inspector to assess the components of the tank that
should be examined, for example, walls and floor, stand and roof to facilitate the capture of
information about the appearance of the asset.
More detailed or technical assessments are normally undertaken on the basis of some
perceived need: 1) visual inspections reveal some issues (defects) that warrant further
investigation, 2) issues with assets of a similar type have been identified or 3) it is known that
visual inspection will be insufficient to identify defects for example, under floor corrosion. A
range of non-destructive techniques can be used in these assessments, including:
 Magnetic flux leakage floor scanners to scan floor plates.
 Ultrasonic sensors (to evaluate floor scanner results, and to test walls and areas of
floor not accessible to the floor scanner).
 Concrete cover meter.
See Case Study 4 in Chapter 8.0.
Figure 6-3. Iterative use of Condition and Performance Assessments.
6-12
The cost of inspection should be considered in light of the cost of subsequent tasks, such
as repair or replacement. For example, if the cost of inspection is likely to be a significant
proportion of the cost of replacement, it could be more cost effective to just to replace the asset.
In this context, Elliot et al (AwwaRF, 2001) noted that prior to initiating test procedures on
electric motors, it is necessary to compare the cost of replacing the motor to the cost of the
testing. For some small commodity size (less than 25Hp) motors, it is cheaper to replace them
than to completely evaluate and repair them. Motors that are 25 Hp and larger may or may not be
cheaper to replace outright instead of evaluating and repairing. Even for high consequence
assets, the cost of the condition assessment should be considered in light of the cost of
subsequent maintenance tasks.
Given the impact on risk and operational budgets, it is up to individual utilities to
determine what they consider to be an appropriate balance between the cost of further
investigation and the cost of subsequent maintenance tasks.
In some cases, an asset type known to be performing poorly can be replaced
opportunistically, without any further consideration of the asset condition, because over a
number of assets this approach will accrue benefits for the utility. For example, see Case Study
Inset 6-4.
Case Study Inset 6-4: Bellevue’s Asbestos Cement Pipe Replacement Program
Bellevue council determined that its asbestos cement (AC) pipes were in poor condition
through on-going review of failure data; over the last nine years, roughly 69% of the main
breaks occurred in AC pipes.
Due to this high failure rate, an AC pipe replacement program is underway; pipes are replaced
when breaks occur and/or when the roadways are resurfaced.
This replacement was undertaken without any additional condition assessment of the pipe.
See Case Study 10 in Chapter 8.0.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
6-13
6-14
CHAPTER 7.0
AVAILABLE TOOLS AND TECHNIQUES
Chapter Highlights
 The categorization of assets used in this project to allow tools and techniques to be
mapped on to the asset stock is:
−
Service Area: clean, waste; then
−
Pipeline assets: valves, meters, fittings and pipes, or
−
Non-pipeline assets: mechanical, electrical, ICA, civil and building.
 A summary table is provided showing the applicability of various tools and techniques in
terms of these asset categories and other selection criteria.
 The selection process is summarized as follows:
1. Determine technical feasibility; determine the part of the selection table that is
appropriate to the application under consideration.
2. Review summary information; to identify techniques that could be used.
3. Review each of the potential tools; refer to the detailed write up in Appendix F and
consider the information presented.
4. For viable options undertake cost-benefit analysis; with due consideration given to
the accuracy of the tool, the level of asset risk and the available budgets.
Protocols for Assessing Condition and Performance of Water and Wastewater Assets
7-1
7.1
Introduction
A large range of condition assessment tools and techniques can be applied to different
water and wastewater service areas and to different parts of the asset stock. These include
inspection tools, environmental surveys and condition monitoring techniques. In presenting the
available tools and techniques, it is necessary to first consider how to categorize the asset stock
and then to map the available tools and techniques onto this representation.
This chapter describes the categorization of the asset stock adopted in this project. The
various condition and performance assessment techniques identified are then mapped onto this
representation.
This mapping is then developed to provide a tabular approach to initial selection of
tools/techniques by asset type, in line with the selection protocol detailed in Chapter 6.0.
7.2
Representation of the Asset Stock
Various approaches are used to categorize asset stocks in different sectors. For example,
the categorization of assets used in the International Infrastructure Management Manual
(IPWEA, 2006) is given in terms of static and dynamic assets. The Manual applies to a range of
sectors, including roads, electricity, water supply, property, wastewater and gas. Given the range
of sectors (and thus asset types) considered in the Manual, categorizing the asset stock as
dynamic and passive is an effective way of dealing with the range of asset types covered.
However, given that the current project is focused on one sector, it is more logical to consider the
asset stock in terms of the two main service areas - water and wastewater.
It is also natural to consider discrete non-pipeline assets and distributed pipeline assets
separately. Discrete assets are generally above ground, contained within a given site, more
accessible and easier to assess than pipeline assets. In contrast, pipeline assets are spatially
distributed, generally below ground and more difficult to access and assess. Various other
descriptors can be used to help describe the asset under consideration.
The representation of the asset stock used in this project is presented in
Tables 7-1 and 7-2. As indicated in the tables, assets are categorized according to unit type; a
unit being defined as a sub-system of a larger asset or a section of pipeline considered separately
for asset management purposes. For above ground (non-pipeline assets), units are categorized as:
 Mechanical and electrical (M&E) assets.
 Civil and building (C&B) assets.
 Instrumentation, control and automation (ICA) assets.
7-2
Table 7-1. Service Area: Water Supply.
Asset category
Pipeline
(below ground)
Non-pipeline
(above ground)
Asset
Abstraction meters
Raw water (non potable) conduits
Bulk water meters
Transmission pipes
District meters
Distribution pipes
Commercial meters
Service pipes
Domestic meters
Valves (block/stop, pressure
reducing, etc.)
Air valves
Hydrants
Dams and impounding reservoirs
Source pumping stations (including
bore holes)
Raw water intakes
Raw water storage
Intake (works) pumping stations
Treatment works
Booster pumping station
Service reservoirs
Water towers
Other civil structures (roads, walls,
etc)
Buildings
Unit* definition by
Pipe lengths, fitting
Pipe lengths, fitting
Pipe lengths, fitting
Connection
-
Other descriptors
Size, type
Material, diameter, pumped
Size, type
Material, diameter, pumped
Size, type
Material, diameter
Size, type
Material, diameter
Size, type
M&E, C&B, ICA
Size, type, open/closed
Size, type
Size, type
Size, type
M&E, C&B, ICA
M&E, C&B, ICA
M&E, C&B, ICA
M&E, C&B, ICA
M&E, C&B, ICA
M&E, C&B, ICA
M&E, C&B, ICA
M&E, C&B, ICA
Capacity, type
Size, type
Size, type
Capacity
Size, source-type,
process/complexity
Capacity
Size, configuration
Size, configuration
-
Use
Use
*A unit is considered to be a sub-system of a larger asset or a section of pipeline considered separately for asset management
purposes. Note: M&E: Mechanical and Electrical; C&B: Civil and Building; ICA: Instrumentation Control and Automation
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
7-3
Table 7-2. Service Area: Wastewater Collection and Disposal.
Asset category
Pipeline
(below ground)
Non-pipeline
(above ground)
Asset
Laterals (service connections)
Non-critical sewers
Critical sewers
Man holes
Valves (block/stop, etc.)
In-line (underground) storage
Force mains
Air valves
Surface water outfalls
CSOs
Marine outfall
Pumping stations
Detention tanks
Treatment works
Storm water storage
Sludge treatment works
Other civil structures (roads, walls, etc)
Buildings
Unit* definition By
Connection
Pipe lengths, fitting
Pipe lengths, fitting
Pipe lengths, fitting
M&E, C&B, ICA
M&E, C&B, ICA
M&E, C&B, ICA
M&E, C&B, ICA
M&E, C&B, ICA
-
Other descriptors
Material, diameter
Material, diameter, depth
Material, diameter, depth
Material, diameter, depth
Size, type, open/closed
size, type
Material, diameter, pumped
Size, type
Material, diameter
Design, size
Material, diameter, length
Capacity
Size
Size, process/complexity
Size
Size, disposal route
Use
Use
*A unit is considered to be a sub-system of a larger asset or a section of pipeline considered separately for asset management
purposes. Note: M&E: Mechanical and Electrical; C&B: Civil and Building; ICA: Instrumentation Control and Automation.
7.3
Mapping Tools Onto the Asset Stock
As noted in previous chapters, when designing an assessment program, one of the key
steps is to identify tools and approaches that can be used for the asset types under consideration.
A key selection criterion is thus the type of asset that can be assessed by a tool/technique. Tool
selection can be facilitated by mapping the tools onto a categorization of the asset stock.
In line with Tables 7-1 and 7-2, a logical approach is to map available tools onto the asset
stock categorized in terms of the main divisions of assets, namely, pipeline/non-pipeline assets.
7.3.1 Mapping for Pipeline Assets
For pipeline assets, the mapping of tools is relatively straightforward, because various
characteristics of the assets given in Tables 7-1 and 7-2 constrain tool selection; for example, the
number of tools under consideration can be reduced according to:
 Service area (potable or wastewater).
 Hierarchical considerations (whether pipe or networks are being considered).
 Asset type (whether pipe, fitting, valve, or meter).
 Asset size (many approaches used for larger mains are not suitable for smaller pipes).
 In the case of pipes and fittings, material type (for example, some approaches used for
cementituous pipes are not suitable for plastic or ferrous pipes).
The approach to mapping tools onto assets adopted herein is simply to define the
relationship between the tools and assets categorized in these ways.
7-4
7.3.2 Mapping for Non-Pipeline Assets
Mapping of tools onto non-pipeline assets is not so straightforward because of the range
and type of assets used within the sector.
Complex assets, such as wastewater and water treatment facilities, are however often
categorized in terms of an asset hierarchy. The hierarchies used by utilities differ in detail, but
follow the same overall logic, namely, dividing a discrete facility into distinct parts according to
the needs of the management system. For example, Table 7-3 shows a range of hierarchies used
in the sector.
Table 7-3. Hierarchical Representations for Complex Assets.
Level 1
Site
Facility
Facility
Notes:
Level 2
Stage
System
-
Level 3
Sub-stage
Subsystem
Sub-facility
Level 4
Unit
Unit
Unit
Level 5
Component
Component
-
Level 6
Assembly
-
1)
Component in this context means the mechanical, electrical and civil component of the unit.
2)
Unit is often considered to be an asset that does a defined job and is large enough to be included as a
separate item in a renewal program.
The use of hierarchies is an important feature of asset management information systems.
While the asset hierarchy has an important bearing on the design of an assessment program,
especially when designing grading systems (see Chapter 3.0), this hierarchical representation of
the asset stock has no direct bearing on the mapping of inspection tools and techniques, because
most tools are used at the lower end of the hierarchy (at the unit level, component level or
lower).
One potential approach to mapping tools and techniques onto the asset stock would be to
expand the hierarchy to identify all the assessable assets within a utility’s operations and to
subsequently map the tools and techniques onto these assets. Table 7-4 shows how the asset
hierarchy for a clarifier is expanded. When expanded in this way, the number and variety of
components becomes clear; there are a significant number of assessable components within just
this one asset type. As such, mapping inspection devices onto all the asset types involved in
delivery of water and wastewater services was not considered practicable.
One alternative considered was to select just a few key assets and determine the tools
applicable to them. However, given the fact that the specific assets of interest will vary over time
and between different utilities and sector professionals, this approach was considered too
limiting. An alternative simplified approach to categorization of the asset stock was therefore
sought.
During the initial phase of the research, it became clear that exact type of asset does not
have a great bearing on the selection of condition and performance assessment tools, techniques
or approaches. Of more use is the categorization of assets lower in the asset hierarchy. A useful
categorization that is already applied within the water sector is:
 Civil and building (C&B) assets.
 Instrumentation, control and automation (ICA) assets.
 Mechanical and electrical (M&E) assets.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
7-5
Using this approach, the hierarchical representation given in Table 7-4 reduces to that given in
Table 7-5.
Table 7-4. Hierarchical Representations for Complex Assets.
Facility
Water treatment plant
System
Water treatment
Subsystem
Clarifier
Units
Basin
Gates/actuators
Clarifier Mechanism
Components
Access hatches, ladders, rungs, stairs
Coating system
Drain
Floor
Foundation
Gratings
Handrail
Launder supports
Launders
Tray
Walls; baffle
Walls; structural
Weirs
Actuator
Body
Frame
Seals/seats
Stem/operator (manual)
Trim
High torque cutouts/controls
Associated electrical support system
Baffles
Corner sweeps
Drive
Gear box
Motor
Rake arm
Table 7-5. Hierarchical Representations for Complex Assets.
Facility
Water treatment
plant
System
Water treatment
system
Subsystem
Clarifier
Units
Components
Basin
Gates/actuators
Clarifier mechanism
Civil
Mechanical
Mechanical, electrical
This simplified asset categorization of asset components was used to allow the tools and
techniques available to be mapped onto the asset stock. The selection of tools and techniques
therefore depends on:
 The type of component in question (whether mechanical, electrical, etc.).
 A range of selection criteria (used to refine the potential list of techniques).
 The relative cost of the condition assessment, relative to the benefits accrued.
7-6
7.4
Tool Selection Process
As noted in Chapter 6.0, the selection of tools and techniques is a complex issue,
involving review of a significant amount of information and consideration of a range of factors.
A prototype expert system developed in this project (see Appendix E) was intended to facilitate
this selection process, but there is still a need to represent the information within this report.
A manual selection process has therefore been developed, which is based on a tabular
summary of the tools reviewed and includes a few of the key selection criteria, as presented in
Table 7-6. The selection process using Table 7-6 is summarized as follows:
Step 1. Determine technical feasibility: identify the part of Table 7-6 that is appropriate
to the application under consideration.
Step 2. Review summary information: identify techniques that could be used.
Step 3. Review each of the potential tools: refer to the detailed write up in Appendix F
and consider the information presented.
Step 4. Undertake cost-benefit analysis for viable options: with due consideration given
to the accuracy of the tool, the level of asset risk and the available budgets.
For example, consider a user that is interested in the inspection of a wastewater pump,
which is both a mechanical and electric asset. For simplicity, consider the mechanical aspect
only. The user would turn to the part of Table 7-6 relating to Non-Pipeline Assets; Mechanical
assets. The service area of interest is wastewater, which in this case does not exclude any of the
inspection techniques. The remainder of the selection criteria includes:
 Assets covered
 Assessment (what is measured)
 Access requirements
 Service interruption
 Accuracy
 Commercialized
 Skills required
From a brief review of the remainder of the attributes, it is clear that the techniques under
consideration are: 1) oil testing, 2) performance testing and 3) vibration analysis.
A review of the descriptions of these techniques (given in Appendix F), indicates that
each of these techniques is still feasible. Cost-benefit analysis would therefore be required,
which necessitates obtaining information from venders. However, it is again stressed, that this
analysis should be undertaken within a risk-informed framework, such as those described in
Chapters 5.0 and 6.0, which balances cost of inspection/monitoring against the risks of failure.
This approach is focused on the selection of a tool to undertake the condition assessment.
The use of grading schemes and performance monitoring could also be selected, depending on the
requirements of the assessment program. The reader is referred to the sections on these approaches
(for condition grading, see Chapter 3.0; for performance monitoring, see Chapter 5.0).
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
7-7
7-8
Pipe sample tests - Destructive
Physical property testing
Pipeline assets
Non-destructive
Table 7-6. Tool and Technique Selection Tables.
Tool or
technique
Barcol hardness
Service
type
Waste and
potable
Assets
covered
NA
Material
Assessment
Plastics and
cementituous
Material
hardness
Carbonation
testing and
petrographic
examination
Corrosion burial
test
Schmidt hammer
Waste and
potable
NA
Cementituous
Depth of
carbonation
in mm
Waste and
potable
Waste and
potable
NA
Ferrous
NA
Concrete and
brick
Condition
assessment of
plastic pipes
Core/coupon
sampling
Waste and
potable
Pipes
Waste and
potable
Cut-out sampling
Service
interruption
NA
Accuracy
Commercialized
Skills required
Semiquantitative
Yes – widely
available
Basic
NA
Quantitative
Yes – widely
available
Basic
Soil
corrosivity
Compressive
strength
NA
Relative
-
Basic
NA
Quantitative
Yes – widely
available
Basic
Plastics
Material
properties
Off line on
sample
Quantitative
Through Testing
Labs
Specialized skills
Pipes
Any
-
NA – dependent
on test
Pipes
Any
-
NA –
dependent on
test
NA
NA – dependent
on test
Fracture
toughness C-ring
Indirect tensile
strength test
Methylene
chloride gelation
Pit depth
measurement
Waste and
potable
Waste and
potable
Waste and
potable
Waste and
potable
Waste and
potable
Cores can be
taken under
pressure
Off-line
Pipes
PVC
Quantitative
Pipes
AC and
Conc.
PVC
Pipes
Ferrous
Off line on
sample
Off line on
sample
Off line on
sample
Off line on
sample
NA – dependent
on test
Specialized skills
Pipes
Fracture
toughness
Tensile
strength
Level of
gelation
Pit depth to
infer rate of
corrosion
NA – dependent
on test
Through Testing
Labs
Through Testing
Labs
Through Testing
Labs
Yes – widely
available
Phenolphthalein
Indicator
Waste and
potable
Any
cementituous
Cementituous
Carbonation
depth
Off line on
sample
Qualitative
Yes – widely
available
Basic
Slow crack
growth
resistance
Waste and
potable
Pipes
PE
Resistance
to slow crack
growth
Off line on
sample
Quantitative
Mostly applied
as research tool
Specialized skills
Quantitative
Qualitative
Quantitative
Specialized skills
Specialized skills
Basic
In-pipe (man entry)
Inspection technique
Pipeline assets
Tool or
technique
Active acoustic
inspection
Service
type
Waste and
potable
Assets
covered
Pipes
Material
Assessment
Cementituous
Presence of
defects
Barcol hardness
Waste and
potable
Waste and
potable
Pipes
Plastics and
Cementituous
Cementituous
Waste and
potable
Concrete
assets
Electrical
potential (half
cell)
Man entry
inspection
Waste and
potable
Pull-off adhesion
testing
Schmidt hammer
Carbonation
testing and
petrographic
examination
Cover meter
Service
interruption
Man entry
Access
Commercialized
Skills required
Man entry
Yes – widely
available
Material
hardness
Depth of
carbonation
in mm
Man entry
Man entry
Man entry
Man entry
Yes – widely
available
Yes – widely
available
Tool training
required, with
confined space
Basic with
confined space
Basic with
confined space
Reinforced
concrete
assets
Cover depth
to
reinforcement
Man entry
Man entry
Yes – widely
available
Basic with
confined space
All
reinforced
concrete
Pipes
Reinforced
concrete
Detection of
corrosion
Man entry
Man entry
Yes – widely
available
Basic with
confined space
Any
Man entry
Man entry
Yes – widely
available
Basic with
confined space
Waste and
potable
Coated
assets
Any coated
assets
Man entry
Man entry
Yes – widely
available
Basic with
confined space
Waste and
potable
Pipes
Concrete and
brick
Qualitative
assessment
of condition
Adhesive
strength of
applied
coatings
Compressive
strength
Man entry
Man entry
Yes – widely
available
Basic with
confined space
Waste and
potable
Pipes
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
7-9
In-pipe (non-man entry)
Inspection technique
Pipeline assets
7-10
Tool or
technique
Broad band
electro magnetic
Service
type
Potable
Assets
covered
Pipes
Material
Assessment
Steel, cast
iron and
ductile iron
Remaining
wall
thickness
CCTV
Mostly waste
Pipes
Any (less
useful for
plastics)
Waste and
potable
Pipes
Any
In-pipe acoustic
inspection tools
(sonar)
In-pipes
hydrophones
Intelligent pigs
Waste and
potable
Pipes
Any
Potable
Pipes
Any
Potable
Pipes
More suited
to steel
Structural
condition –
qualitative
assessment
Qualitative
assessment
of condition
Pipe defects
and
geometry
Leak
detection
Geometry or
corrosion
Fiberscope
inspection
Magnetic flux
leakage
Waste and
potable
Pipes
Iron and
steel
Metal loss
Service
interruption
Off line as
pipe needs to
be
depressurized
Low flow or
offline for
pressurized
pipes
Online or off
line
On line
On line
May cause
water quality
issues
Off line
Access
Commercialized
Skills required
Full bore
access
Yes
Specialist
service
Internal use;
mostly limited
to assets
≥90mm
Entry point
(e.g., tapping)
Yes – widely
available
Interpretation
requires
specialist skills
Yes – widely
available
Limited use in
water sector
Interpretation
requires
advanced skills
Interpretation
requires
specialist skills
Specialist
service
Specialist
service
Yes - specialist
consultants
Specialist
service
Access to pipe
interior is
required
Large diameter
mains
Mostly large
diameter mains
specialized
insertion point
Available for
external and
internal use
direct access
to pipe wall
required
Yes – widely
available
Yes
In-pipe (non-man entry)
Inspection technique
Pipeline assets
Tool or
technique
Multi-sensor pipe
inspection robots
Passive acoustic
inspection
Service
type
Mainly waste
Assets
covered
Pipes
Material
Assessment
Any
Waste and
potable
Pipes
Prestressed
concrete
(PCCP)
Remote field
eddy current
Waste and
potable
Pipes
Smart Digital
Sewer Pipe
Diagnostic
System (VTT)
Smoke testing
Waste
Pipes
Iron, steel
and
prestressed
concrete
(PCCP)
Any
Depends on
sensors used
Detect
failures of
prestressed
wires
Internal or
external
defects
Waste
Gravity
sewer
Any
Service
interruption
Depends on
sensors used
On line
Off line
Automated
analysis of
defects
On line
Indicates
illegal
connections
On line
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
Access
Commercialized
Skills required
Access to pipe
interior
Access
required for
hydrophone
entry
Cut-ins
required; pipes
>150mm
diameter
No – under
development
Yes – tool
available from
commercial
supplier
Yes - specialist
consultants
Advanced
Scanner
inserted – not
suited to small
diameter pipes
Manhole
access to
sewer
No – under
development
Advanced
Yes – equipment
available
Basic
Training required
for tool use
result analysis
requires expert
Advanced skills
for interpretation
tool applied by
specialist
7-11
On-pipe
Inspection technique
Pipeline assets
7-12
Tool or
technique
Acoustic
emission
Service
type
Waste and
potable
Assets
covered
Pipes
Material
Assessment
Any
Active acoustic
inspection
Barcol hardness
Waste and
potable
Waste and
potable
Pipes
Cementituous
Pipes
Plastics and
cementituous
Detection
and location
of material
defects
Presence of
defects
Material
hardness
Broad band
electro magnetic
Potable
Pipes
Steel, cast
iron and
ductile iron
Carbonation
testing and
petrographic
examination
Cover meter
Waste and
potable
Pipes
Waste and
potable
Concrete
assets
Drop test
Waste and
potable
Pipes
Electrical
potential (half
cell)
Waste and
potable
Holiday detector
Waste and
potable
Service
interruption
On line
Access
Commercialized
Skills required
NA
Yes –
commercially
available from
selected vendors
Yes – widely
available
Yes – widely
available
Operator training
is required
Off line and
dewatered
On line
Access to
asset surface
Direct access
to pipe surface
Tool training
required
Basic
Remaining
wall
thickness
Off line as
pipe needs to
be
depressurized
Exposure of
pipe surface
Yes
Specialist
service
Cementituous
Depth of
carbonation
in mm
On line
Direct contact
with concrete
surface
Yes – widely
available
Basic
Reinforced
concrete
assets
Any
Cover depth
to
reinforcement
Water loss
from pipe
On line
Direct access
to pipe surface
Yes – widely
available
Basic
Off line
General
approach
Basic
All
reinforced
concrete
Reinforced
concrete
Detection of
corrosion
On line
Access to
monitoring
points
Direct access
to pipe surface
Yes – widely
available
Basic
Coated
assets
Ferrous and
concrete
assets with
coating for
corrosion
protection
Location of
defects in
asset
coatings
Off line if
internal
coating is to
be tested
Direct contact
with coating
Yes – widely
available
Basic technical
skills
On-pipe
Inspection technique
Pipeline assets
Tool or
technique
Leak detection –
Including
acoustic, tracer
gas and infrared
photography
Linear
polarization
resistance
Service
type
Potable
Assets
covered
Pipes
Material
Assessment
Any –
effectiveness
depends on
technique
Leak
detection
Waste and
potable
Buried
ferrous
assets
Results relate
to ferrous
assets
Waste and
potable
Pipes
Iron and steel
Soil linear
polarization
resistance
(LPR)
Metal loss
Magnetic flux
leakage
Measurement of
strain
Waste and
potable
Any
component
made of
homogenous
material
NA
On-line leak
detection
systems
Potable
Pipes
Any
Passive acoustic
inspection
Waste and
potable
Pipes
Prestressed
concrete
(PCCP)
Pit depth
measurement
Waste and
potable
Pipes
Ferrous
Access
Commercialized
Skills required
Most tests
require access
to pipe
Yes – tools
widely available
and applied
Dependent on
technique used
On line
Access to soil
at point of
interest
Equipment is
widely available
Operator training
required
Off line
Direct access
to pipe wall
required
Yes - specialist
consultants
Specialist
service
Stress and
strain
analysis
On line
Access to
surface
Yes –
commercially
available
Engineer trained
in operation of
tool
Change in
flow
parameters
that indicates
leak
Detect
failures of
prestressed
wires
Pit depth to
infer rate of
corrosion
On line
NA
Automated
monitoring
(sophisticated
tool)
On line
Exposed
surface for
accelerometer
Can be on
line when
done in-situ
Quantitative
Developed for oil
and gas sector,
not yet widely
applied in water
sector
Yes – tool
available from
commercial
supplier
Yes – widely
available
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
Service
interruption
On line
Training required
for tool use
result analysis
requires expert
Basic
7-13
On-pipe
Inspection technique
Pipeline assets
7-14
Tool or
technique
Pipe potential
survey
Service
type
Waste and
potable
Assets
covered
Pipes
Material
Assessment
Ferrous
Radiographic
testing
Potable
Pipes
Ferrous,
cementituous
and plastics
(not GRP)
Schmidt hammer
Waste and
potable
Pipes
Concrete and
brick
Measures
electrical
potential
between pipe
and soil to
infer
corrosion
potential
Changes in
material
structure
(inclusions,
voids and
corrosion)
Compressive
strength
Ultrasonic
measurement –
continuous
(guided wave)
Waste and
potable
Pipes
Iron and steel
Ultrasonic
measurements discrete
Waste and
potable
Pipes
Visual inspection
Waste and
potable
All
Service
interruption
On line
Access
Commercialized
Skills required
Electrical
contact with
asset is
required
Yes- available
from commercial
suppliers
Specialist
training required
Off line – as
water absorbs
radiation
Access
required to
both sides of
pipe
Yes – tool and
service
commercially
available
Advanced –
requires
specialized
contractor
On line
Direct access
to pipe surface
Yes – widely
available
Basic
Level of wall
thickness
and corrosion
pit depth
On line
Direct contact
required with
pipe wall
Yes
Basic – tool
operation
Advanced –
analysis of
results
Iron and steel
Level of wall
thickness
and corrosion
pit depth
On line
Yes – widely
available
Trained
technician
Any
Qualitative
visual
assessment
On line
Direct contact
with asset surface must
be smooth and
clean
Physical
access
required
NA
Interpretation
requires training
Meter
Valve
Inspection technique
Pipeline assets
Tool or
technique
Visual inspection
(see notes on
water meters in
Table 3-3)
Volumetric X-ray
or radiographic
testing
Service
type
Waste and
potable
Assets
covered
Meter
Material
Assessment
NA
Qualitative
visual
assessment
Waste and
potable
Welded
joints,
castings,
electronic
assets, etc.
Metal
Integrity of
assets
CCTV
Mostly
waste
Valves
Any
Fibrescope
inspection
Waste and
potable
Valves
Any
Radiographic
testing
Potable
Valves
Valve exercising
Potable
Valves
Ferrous,
cementituous
and plastics
(not GRP)
NA
Structural
condition –
qualitative
assessment
Qualitative
assessment
of condition
Integrity of
assets
Visual inspection
Waste and
potable
Valves
NA
Valve
condition and
operability
Qualitative
visual
assessment
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
Service
interruption
On line
Access
Commercialized
Skills required
Physical
access
required
NA
Interpretation
requires operator
training
Off line for
laboratory
testing or
when meter
interior is
assessed
Low flow or
off line for
pressurized
pipes
On line or off
line
Direct access
required to
asset
Yes –
commercially
available from
selected vendors
Advanced –
requires
specialized
contractor
Internal use;
mostly limited
to assets
≥90mm
Entry point
(e.g., tapping)
Yes – widely
available
Interpretation
requires training
Yes – widely
available
Interpretation
requires training
Off line – as
water
absorbs
radiation
On line
Direct access
required to
asset
Yes – tool and
service
commercially
available
Equipment
required widely
available
NA
Advanced –
requires
specialized
contractor
Basic – operator
needs training
On line
Physical
access
required
Physical
access
required
Interpretation
requires operator
training
7-15
Strategic planning
Pipeline assets
7-16
Tool or
technique
Service
type
Assessment focus
Data needs
Commercialized
Integration
Skills required
AQUA-Selekt
Waste
Sewer condition
CCTV
inspection data
Yes – has had
limited
application in
Europe
No –
standalone
tool
Professional
engineering
skills
AQUA-WertMin
Waste
Requires CCTV
data
Professional
engineering
skills
Basic to
advanced
Waste
Yes – available
from Germany;
limited
application
No – research
applications only
No –
standalone
tool
CARE-S
No –
standalone
tool
Professional
engineering
skills
Basic to
advanced
CARE-W
Potable
Planning of CCTV
inspection, rehabilitation
and construction for
sewer networks
Service levels, budget
setting, life cycle cost
and rehabilitation
planning
Service levels, budget
setting, life cycle cost
and rehabilitation
planning
Dependent on
models applied
No – some
application in
European cities
No –
standalone
tool
Professional
engineering
skills
Basic to
advanced
FailNet – Stat
Potable
Failure forecasting
model for water
pipelines
Good asset
and failure data
needed
No –
standalone
tool
Professional
engineering
skills
Basic to
advanced
KANEW
Potable
Good asset
and failure data
desirable
No –
standalone
tool
Professional
engineering
skills
Basic to
advanced
KureCAD
Waste
Good GIS data
required
Yes
Links to GIS
Potable
Good asset
and failure data
needed
Yes – used by a
number of
Australian
utilities
No –
standalone
tool
Professional
engineering
skills
Professional
engineering
skills
Basic to
advanced
PARMS
Planning
Strategic tool that
estimates length of
water mains to replace
or repair each year
Applies GIS analysis for
prioritization of sewer
rehabilitation
Long term asset
management planning
using asset failure
curves developed from
utility data
No – only
research
application in
Europe
Yes – basic
version available
through AwwaRF
Dependent on
models applied
Asset
management
sophistication
Basic to
advanced
Basic to
advanced
Strategic planning
Hydraulic Assessment
Network assessment
Pipeline assets
Tool or
technique
Service
type
Assessment focus
Data needs
Commercialized
Integration
Skills required
PARMS Priority
Potable
Decision support
system to assist in
asset renewal decisions
Good asset
and failure data
needed
Yes – used by a
number of
Australian
utilities
No –
standalone
tool
Professional
engineering
skills
PiReP/PiReM
Potable
Good asset
and failure data
needed
Professional
engineering
skills
Basic to
advanced
Waste
No – under
development
with commercial
release planned
Yes – available
from WERF
No –
standalone
tool
SCRAPS
Potable
Good asset
and failure data
needed
No – currently at
prototype stage
No –
standalone
tool
No –
standalone
tool
Professional
engineering
skills
Professional
engineering
skills
Basic to
advanced
UtilNets
Decision support
system for rehabilitation
planning of water
networks
Expert systems that
prioritizes sewer
inspections
Reliability based
decision support system
for managing pipeline
maintenance
WARP
Potable
Good asset
and failure data
needed
Yes – planned
release in 2006
No –
standalone
tool
Professional
engineering
skills
Basic to
advanced
FailNet-Reliab
Potable
Long term asset
management planning
using asset failure
curves
Hydraulic reliability
Potable
and waste
Relationships between
flow, pressure,
roughness, capacity
and service
No –
standalone
tool
Can link to
GIS
Professional
engineering
skills
Professional
engineering
skills
Inflow and
infiltration –
sewer flow
survey
Leak detection
Waste
Inflow and infiltration to
sewers
High
No – only limited
research
application
Yes – many
commercial and
public domain
software
available
NA – framework
approach
Basic to
advanced
Hydraulic
modeling
Good asset
and failure data
needed
High – good
quality asset
data needed
Professional
engineering
skills
Basic – generic
approach
Potable
Detection of leaks
NA
Potential to
link with GIS
and hydraulic
models
NA
Operator
training
required
Basic – generic
approach
Information on
critical assets
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
Tools widely
available
Asset
management
sophistication
Basic to
advanced
Basic to
advanced
Basic – generic
approach
7-17
Network Condition
Environmental Survey
Network assessment
Pipeline assets
7-18
Tool or
technique
Service
type
Assessment focus
Data needs
Commercialized
Integration
Skills required
Leak detection
Potable
Detection of leaks
NA
NA
WRc sewer
rehabilitation
man
Waste
High – but
can be
customized to
be affordable
Operator
training required
High –
professional
engineering
skills
WRc trunk main
structural
condition
assessment
Ground
penetrating
radar
Linear
polarization
resistance
Potable
Cost effective
management of assets;
identify service
problems in drainage
areas
Current structural
condition and remaining
service life of water
transmission pipes
Location of buried
assets
Tools widely
available
Framework
available as
manual
Moderate
Framework
available as
manual
NA
Minimal data
requirements
NA
Waste and
potable
LPR gives indication of
soil corrosion rate for
buried ferrous assets
NA
Pipe potential
survey
Waste and
potable
NA
Soil
characterization
Waste and
potable
Measures electrical
potential between
ferrous pipe and soil to
infer corrosion potential
Soil parameters relevant
to deterioration of buried
assets
Yes- available
from commercial
suppliers
Yes- equipment
available from
commercial
suppliers
Yes- available
from commercial
suppliers
NA
Soil corrosivity
Waste and
potable
Soil resistivity
survey
Waste and
potable
Predicts corrosion rate
for ferrous assets from
soil characteristics
Indication of soil
corrosion potential for
buried ferrous pipeline
assets
Waste and
potable
NA
Asset
management
sophistication
Moderate
Basic – generic
approach
High –
professional
engineering
skills
Requires
trained operator
Basic – generic
approach
Results can
be input to
GIS
Requires
trained operator
Basic – generic
approach
Results can
be input to
GIS
Specialist
training required
Basic – generic
approach
Equipment and
testing services
widely available
Results can
be input to
GIS
Basic – generic
approach
Pipe
characteristics
Testing services
widely available
NA
Equipment and
testing services
widely available
Results can
be input to
GIS
Results can
be input to
GIS
Operator
training;
interpretation
requires expert
Requires
trained operator
Requires
trained operator
Basic – generic
approach
Basic – generic
approach
Basic – generic
approach
Electrical assets
Non-pipeline assets
Tool or
technique
AwwaRF’s
Manager
Software
Service
type
Potable
Assets
covered
Water
treatment
works
Assessment
Access
requirements
NA
Service
interruption
NA
Current
monitoring
Waste and
potable
Electric motors
Measurement of
current in a circuit
and comparison
with design loads
No
On-line with
safety
precautions
in place
Ductor testing
Waste and
potable
Electrical
connections,
busbars and
contacts
Determines the
contact resistance
in draw–out
contacts such as
circuit breakers
Electrical
insulation
performance
Access to
normally live
parts
Off-line
Insulation test
Waste and
potable
Motor winding,
cables,
switchboards
and motor
control centers
Access to
conductor and
insulation
Off-line –
Equipment
needs to be
isolated
Load rejection
test
Waste and
potable
Power
generation
systems
Performance of
power generation
systems under
these sudden load
changes
Detection and
monitoring of
electrical motors
and circuits
Site specific
Motor circuit
analysis
Waste and
potable
Electric motors
Oil testing
Waste and
potable
Mechanical
assets with oil
as lubricant or
coolant
Impurities and
dielectric strength
of oil, which may
indicate asset
condition
Treatment work
condition and
value
Accuracy
Commercialized
Skills required
NA
Available from
AwwaRF
Professional
asset manager/
engineer
Good –
comparison with
historical
recordings can be
used to identify
onset of faults
Good
Yes
Electrician
required
Yes – widely
available
Trained
electrical
technicians or
engineers
Good accuracy
Yes – widely
available
Trained
electrical
technicians or
engineers
On-line
Dependent on
approach
Widely available
in other sectors
High – team of
engineers
No – portable
hand-held
equipment
Off-line
Good accuracy
Yes – widely
available
Trained
electrical
technicians or
engineers
Sample of oil
required
Dependent
on equipment
Oil analysis is
accurate, but only
indicative of asset
condition
Yes –
commercially
available
Laboratory
analysis
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
7-19
Electrical assets
Non-pipeline assets
7-20
Tool or
technique
Process control
system
(integrated)
Service
type
Waste and
potable
Assets
covered
Networked
instrumentation
or electrical
equipment
Thermographic
testing
Waste and
potable
All electrical
assets
Transformer
circuit
protection
coordination
Transient earth
voltage
Waste and
potable
High value
electrical
assets
Waste and
potable
Ultrasonic
emission
inspection
Visual
Inspection
Assessment
Access
requirements
Assets
connected to
field bus
network
Service
interruption
On line
Accuracy
Commercialized
Skills required
Dependent on
measured variable
Yes – widely
available
Trained
operator can
assess
condition data
Infrared imagery to
locate defects and
potential failures
by scanning for
thermal
abnormalities
Testing of
electrical
protective systems
Direct access
to live assets
On line
Qualitative
Yes
Field service
engineer
Access to high
voltage areas
Off line –
power supply
disruptions
Indicative tool
Yes
Field service
engineer
All electrical
assets
Detects
discharges to
earth through
voids or insulation
breakdown
No
requirement
for direct
contact
On line
Qualitative
inspection tool
Yes
Field service
engineer
Waste and
potable
Electrical
assets such as
switchboards
Identify ultrasound
waves that can
indicate defects or
failures
Qualitative visual
assessment; can
include grading
system (see
section 3.3)
Physical
contact
required to
outer casing
Physical
access
required
On line
Qualitative
inspection tool
Yes
Field service
engineer
Waste and
potable
Electrical
assets
On line
Qualitative
NA
Operator
training
required
Monitors assets
and provides
preventive
maintenance data
Mechanical assets
Non-pipeline assets
Tool or
technique
AwwaRF’s
Manager
Software
Service
type
Potable
Assets covered
Assessment
Access
requirements
NA
Service
interruption
NA
Accuracy
Commercialized
Skills required
Water treatment works
Treatment work
condition and
value
NA
Available from
AwwaRF
Professional
asset manager/
engineer
Measurement
of strain
Waste
and
potable
Any component made
of homogenous
material – e.g., motor
shaft
Measurement of
strain
No specific
requirements
On line
Accurate
Yes –
commercially
available
Engineer trained
in operation of
tool
Oil testing
Waste
and
potable
Mechanical assets
with oil as lubricant or
coolant
Impurities and
dielectric strength
of oil, which may
indicate asset
condition
Sample of oil
required
Dependent on
equipment
Yes –
commercially
available
Laboratory
analysis
Waste
and
potable
Pumps, fans, motors,
air blowers, mixers,
etc.
No specific
requirements
On line
Yes
Operator
requires training
for interpretation
of results
Process
control system
(integrated)
Waste
and
potable
Networked
instrumentation or
electrical equipment
Assets
connected to
field bus network
On line
Yes – widely
available
Trained operator
can assess
condition data
Thermographic
testing
Waste
and
potable
All electrical assets
Direct access to
live assets
On line
Qualitative
Yes
Field service
engineer
Ultrasonic
emission
inspection
Waste
and
potable
Electrical assets such
as switchboards
Performance of
rotating
machinery, such
as head, pressure,
noise and vibration
Monitors assets
and provides
preventive
maintenance data
Infrared imagery to
locate defects and
potential failures
by scanning for
thermal
abnormalities
Identify ultrasound
waves that can
indicate defects or
failures
Oil analysis is
accurate, but
only
indicative of
asset
condition
Dependant
on the
accuracy of
measuring
device
Dependent
on measured
variable
Performance
testing of
rotating
machinery
Physical contact
required to outer
casing
On line
Qualitative
inspection
tool
Yes
Field service
engineer
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
7-21
Mechanical assets
Non-pipeline assets
7-22
Tool or
technique
Vibration
analysis
Service
type
Waste
and
potable
Assets covered
Assessment
Rotating machinery,
such as pumps,
electric motors and
fans
Condition fault
diagnosis by
measurement and
analysis of
vibration
Visual
Inspection
Waste
and
potable
Electrical assets
Waste
and
potable
Welded joints,
castings, electronic
assets etc.
Qualitative visual
assessment; can
include grading
system (see
section 3.3)
Non-destructive
method used for
checking the
integrity of metal
assets
Volumetric Xray or
radiographic
testing
Access
requirements
Fixed point
testing to ensure
consistent
measuring point
Service
interruption
On line
Physical access
required
On line
Unobstructed
view of area of
interest
Off-line for
laboratory
testing
Accuracy
Commercialized
Skills required
Qualitative –
assessment
based on
comparison
with previous
tests
Qualitative
Yes – fully
developed and
commercially
available
Field service
engineer
NA
Operator training
required
Accuracy
dependent on
operator
expertise
Yes –
commercially
available from
selected vendors
Operator
requires training
for image
interpretation
Civil and Building Assets
Non-pipeline assets
Tool or
technique
Acoustic
emission
Service
type
Waste
and
potable
Assets covered
Assessment
Material
Storage tanks,
pressure vessels,
aerial lift devices,
welded joints
Detection and
location of material
defects
Any
Service
interruption
On-line
Air
permeability
Accuracy
Commercialized
Skills required
Qualitative
estimates of
material
damage
Yes –
commercially
available from
selected vendors
Operator training
is required
Waste
and
potable
Concrete elements
with flat surfaces
(slabs, walls,
pavements, etc.)
Permeability,
quality class and
capillary suction of
concrete
Concrete
On line
Excellent
measure of
resistance of
concrete
against
aggressive
media
NA
Yes – limited use
in water sector
Basic technical
skills
AwwaRF’s
Manager
Software
Potable
Water treatment works
NA
NA
Barcol
hardness
Waste
and
potable
Pipes
Representing
asset and
condition data
within a consistent
framework
Material hardness
Available from
AwwaRF
Professional
asset manager/
Engineer
Plastics and
cementituous
On line
Semiquantitative
Yes – widely
available
Basic
Carbonation
testing and
petrographic
examination
Waste
and
potable
Tanks, walls, dams,
buildings, etc.
Reinforced
concrete assets
Concrete
electrical
resistance
Waste
and
potable
Tanks, walls, dams,
buildings, etc.
Presence of
carbonation to
determine
concrete quality
and protection of
steel
reinforcements
Corrosion rate of
reinforcement bars
in concrete
On line
Qualitative
Yes
Basic
Reinforced
concrete assets
On line
Indicative of
asset
condition
Basic technical
skills
Reinforced
concrete assets
NA
NA –
dependent on
test
Yes –
commercially
available from
selected vendors
NA – dependent
on test
Core sampling
Waste
and
potable
Civil assets
Sample core taken
for analysis and
testing
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
NA – dependent
on test
7-23
Civil and Building Assets
Non-pipeline assets
7-24
Tool or
technique
Cover meter
Service
type
Waste
and
potable
Assets covered
Assessment
Material
Concrete assets slabs, beams, walls,
tunnels and dams, etc.
Cover depth to
reinforcement
Reinforced
concrete assets
Crack
measurement
Waste
and
potable
Concrete assets slabs, beams, walls,
tunnels and dams, etc.
Reinforced
concrete assets
Electrical
potential (half
cell)
Waste
and
potable
All reinforced concrete
assets
Measuring linear
deformations,
cracks,
settlements and
shrinkage
coefficients
Detection of
corrosion
Holiday
detector
Waste
and
potable
Coated assets
Location of defects
in asset coatings
Impact echo
method
Waste
and
potable
Concrete assets slabs, beams, walls,
tunnels, dams, etc.
Determine
concrete thickness
or location of
internal defects
LPR for
corrosion
monitoring
Waste
and
potable
Concrete assets slabs, beams, walls,
tunnels, dams, etc.
Magnetic flux
leakage
Waste
and
potable
Metal assets – tanks,
etc.
Concrete
temperature that
allows structure’s
long-term
performance to be
determined
Metal loss
Service
interruption
On line
Accuracy
Commercialized
Skills required
Accurate
survey of
reinforcements
in concrete
assets
Yes – widely
available
Basic
On line
Quantitative
Yes – widely
available
Basic
Reinforced
concrete
On line
Up to 95%
Yes – widely
available
Basic
Ferrous and
concrete assets
with coating for
corrosion
protection
Concrete
Off line if
internal
coating is to
be tested
Qualitative
Yes – widely
available
Basic technical
skills
On line
Good
accuracy for
thickness
measurements
Yes- available
from commercial
suppliers
Reinforced
concrete
On line
Results are
indicative only
Yes –
commercially
available from
selected vendors
Basic skills for
operation;
categorization of
defects requires
expertise
Basic
Iron and steel
Off line
Quantitative
assessment
Yes - specialist
consultants
Specialist skills
Tool or
technique
Measurement
of strain
Civil and Building Assets
Non-pipeline assets
Phenolphthalein
indicator
(carbonation
testing)
Service
type
Waste
and
potable
Waste
and
potable
Assets covered
Assessment
Material
Service
interruption
On line
Accuracy
Commercialized
Skills required
Any component made
of homogenous
material, dams
Any cementituous civil
assets
Measurement of
strain
No specific
requirements
Accurate
Cementituous
On line
Qualitative
Yes –
commercially
available
Yes – widely
available
Engineer trained
in operation of
tool
Basic
Carbonation depth
Pull-off
adhesion
testing
Waste
and
potable
Coated tanks, etc.
Adhesive strength
of applied coatings
Any coated
assets
On line
Quantitative
Yes – widely
available
Basic
Schmidt
hammer
Waste
and
potable
Any cementituous civil
assets
Compressive
strength
Concrete and
brick
On line
Quantitative
Yes – widely
available
Basic
Ultrasonic
measurements
- discrete
Waste
and
potable
Steel civil assets
Level of wall
thickness and
corrosion pit depth
Steel
On line
Quantitative
Yes – widely
available
Trained
technician
Visual
Inspection
Waste
and
potable
Civil assets
Any
On line
Qualitative
NA
Operator
training required
Volumetric Xray or
radiographic
testing
Waste
and
potable
Welded joints,
castings, electronic
assets, etc.
Qualitative visual
assessment; can
include grading
system (see
section 3.3)
Non-destructive
method used for
checking the
integrity of metal
assets
Metal
Off line for
laboratory
testing
Accuracy
dependent on
operator
expertise
Yes –
commercially
available from
selected vendors
Operator
requires training
for image
interpretation
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
7-25
7-26
CHAPTER 8.0
CASE STUDY DETAILS
Chapter Highlights
 During the case studies the research team sought input from a range of utilities and
industry practitioners across the globe in an effort to:
−
Sense-check the protocols being proposed by the research team.
−
Ground the report in practicalities and provide industry insights.
−
Identify good practice in condition and performance assessments.
−
Provide examples of implementation in different utilities.
 The following case studies are detailed in this chapter:
−
Case Study 1: Scottish Water’s Program of Treatment Plant Assessments
−
Case Study 2: Scottish Water’s Approach to Grading of Water Mains
−
Case Study 3: Water Corp’s Asset Condition Assessment (ACA) Program
−
Case Study 4: Water Corp’s Assessment Approach for Water Tanks
−
Case Study 5: Water Corp’s Investigation of a Trunk Main Failure
−
Case Study 6: Water Care’s Assessments of Sewerage Assets
−
Case Study 7: Water Care’s Assessments of a Critical Sewer
−
Case Study 8: Melbourne Water’s Assessments of Steel Tanks
−
Case Study 9: Sydney Water’s Management of M&E Assets
−
Case Study 10: City of Bellevue’s Risk-Based Approaches
−
Case Study 11: Massachusetts Water Resources Authority RCM Program
−
Case Study 12: MWRA’s Strategies for Pipe Network Management
−
Case Study 13: CSIRO’s Assessment of a Cast Iron Transmission Main
−
Case Study 14: CSIRO’s Assessment of an AC Force Main
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-1
8.1
Introduction
An important objective of this research was to draw upon the experience of a wide range
of water industry professionals and utilities, and thereby reflect the current state of the art in
condition assessment practices across the sector. Various aspects of the research program were
designed to facilitate this. For example, a web-based survey was used to gain baseline
information on the U.S. sector. The list of tools identified as having relevance to the water sector
was also distributed to industry practitioners, along with the reviews of individual tools.
Comments received were subsequently integrated into the research outputs.
A major portion of the industry interaction was carried out in Phase 2 of the project.
During this phase, various utilities were approached and asked to provide information on case
studies for inclusion in this report. Case studies were subsequently undertaken with a sample of
utilities across Australia, New Zealand, the United States and the United Kingdom. Information
on each case study was collated using a questionnaire and interview based approach, written up
in a standard format, and sent to each case study partner for review.
This chapter briefly outlines the purpose of the case studies and the utilities that
contributed information. The full texts of the case studies are then presented. Insets relating to
the case studies are distributed throughout the report in appropriate sections and referenced to the
case studies below.
8.2
Purpose of the Case Studies
During the case studies, the research team sought input from a range of utilities and
industry practitioners across the globe in an effort to:
 Review and comment on the protocols being proposed by the research team.
 Provide industry insights and practical experience.
 Identify good practice in condition and performance assessments.
 Provide examples of implementation in different utilities.
Case study partners providing a significant contribution to the project were:
 Scottish Water, Scotland, United Kingdom
 Water Corporation, Perth, Australia
 Water Care, Auckland, New Zealand
 Melbourne Water, Melbourne, Australia
 Sydney Water, Sydney, Australia
 City of Bellevue, Washington, United States
 Water Resources Authority, Massachusetts, United States
Two asset-specific case studies have also been included that draw upon the research
team’s previous research and consultancy experience. These case studies illustrate the
complexity of analysis that can be required to interpret the results of inspection data.
8-2
8.3
Case Study 1: Scottish Water’s Program of Treatment Plant Assessments
Case Study Summary
Key issues covered in this case study include:
 The response of a water utility to the consolidation of three utilities into one large
service provider.
 The role of condition assessment in regulatory reporting.
 The use of condition and performance grading to categorize the state of assets within
treatment works.
 The use of representative sampling and modeling to give a strategic assessment of the
overall asset stock.
See case study insets 2-4, 2-7, 3-11, 3-16 and 4-1.
8.3.1 Utility Details
Scottish Water was established in April 2002 from a merger of the three previous water
authorities (West of Scotland Water, East of Scotland Water and North of Scotland Water). Its
main functions are to provide clean water to 2.2 million households and 133,000 non-domestic,
mainly business, properties in Scotland and to treat their wastewater. It is funded largely from
charges to customers and from borrowing approved by the Scottish ministers.
Scottish Water is the fourth-largest water services provider in the United Kingdom and
one of the 20 largest businesses in Scotland. It has an annual turnover approaching £1 billion,
and it is estimated that its capital assets are worth £28.2 billion at full replacement cost (Auditor
General, 2005).
8.3.2 Case Study Focus
In 2004, Scottish Water undertook a systematic condition assessment of assets within
critical water and wastewater treatment works. This effort was combined with an overall data
improvement program undertaken in parallel to the development of corporate data systems,
which was necessitated by the merger of three authorities into one service provider for the whole
of Scotland - Scottish Water.
At the same time, Scottish Water assessed the condition of a representative sample of
water and wastewater treatment works (randomly sampled), to provide a profile of asset value
against condition and performance grade, which was used as an input to the regulatory reporting
process.
8.3.3 Assets Considered in the Program
For this case study, the assessment program of interest focused on treatment works.
8.3.4 Key Drivers
The assessment program was driven by the regulatory reporting and the capital
investment planning cycle.
Given the consolidation of the three legacy systems into one corporate system, an
additional driver for undertaking the assessments was to supplement legacy data of varied and
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-3
uncertain quality with new consistent data of known quality, so that strategic assessments could
be made with more confidence. The program in question was therefore undertaken to provide
assessments of asset condition and performance grade profiles across Scotland based on newly
collected (rather than legacy) data.
Scottish Water is/was required to report on the condition and performance of its asset
stock each year. In contrast, England and Wales were required to report similar information
every five years. The program of condition assessment was thus partly driven by the desire of
Scottish Water to understand better the use of condition and performance data in regulatory
reporting in England and Wales.
8.3.5 Key Program Features
Since the program was driven by regulatory reporting needs and was strongly influenced
by the (one-off) circumstance of bringing together three legacy systems into one, the assessment
program had to be undertaken. As such, it was designed more on the basis of affordability and
cost minimization, rather than justified through an explicit cost-benefit analysis.
8.3.5.1 Grading and Assessment of Assets
A system of condition and performance grading was used in the program similar to those
described in Section 3.3.4; the reader is referred to this section for detailed information on this
approach to condition and performance assessment. As noted in Section 3.3.4, with this
approach, condition and performance grades are allocated to assets through visual assessment,
performance review, and with reference to standard grade definitions. The grade definitions used
by Scottish Water arose from a system stipulated by U.K. industry regulators (Ofwat in England
and Wales and the Water Industry Commissioner (WIC) in Scotland). Grading systems are/were
used to give an assessment of asset condition/performance and thus the grade profile across the
asset stock (the proportion of asset value in each grade band).
There was also a fully developed set of guidelines on how to subdivide complex assets
into a consistent asset hierarchy. The grading systems allocated a condition and performance
grade to units (assets) within treatment works. A unit was defined as the smallest type of asset
recorded separately on the asset inventory; a unit was considerably larger than items commonly
found in maintenance management systems. For example, a complete pump set was recorded as
one unit rather than being broken down into its components - the pumps, motors, control gear,
delivery pipework and valves, and so forth.
An assessment of ‘fitness for purpose’ (asset capability) was also made (this allowed the
impact of upstream assets to be considered; a unit may be ‘fit for purpose’ but still be graded as
‘performing badly’ because of an upstream asset). The operational status of units was also
collected along with other asset-related data.
8.3.5.2 Stratified Sampling of Assets
In guidance for regulatory reporting, WIC stated that there was no formal requirement for
Scottish Water to survey its entire asset stock. Instead, the authority could survey sufficient
assets to give a representative view. A representative sampling strategy and statistical modeling
of data was identified as an appropriate means of meeting the objectives of the study; this meant
a sample of treatment works could be surveyed and used to estimate the state of the whole asset
stock.
The approach involved the design of a stratified sampling scheme that focused on
important assets, but also sampled the rest of the asset stock. Data was collected for the sample
8-4
during site surveys. Visual assessment was used to grade assets using data collection protocols
developed by external consultants drawing on grading systems previously used within the legacy
authorities.
8.3.5.3 Analysis of Sample Data
The sample of grades and associated data were analyzed in a statistical package.
Generalized linear modeling was used to produce models that described the probability of an
asset being within a given condition/performance grade. The factors considered in the modeling
exercise were:
 Works type (water treatment or wastewater treatment)
 Treatment type
 Geographical area (former East, North or West of Scotland)
 Unit class
 Asset life category
 A risk grade (good, fair or poor)
As noted, the resulting models expressed the probability that an asset would be in one of
the condition grades, and were of the form:
Probability (Grade) = aX +bY + cZ…
where: a, b and c are coefficients derived from the analysis and X, Y and Z were the
covariates used (works type, treatment type, etc.).
8.3.5.4 Extrapolation across the Asset Stock
In combination with data on the overall asset stock and the value of different assets (in
modern equivalent terms), these models allowed the grade profile for the asset stock to be
calculated; the expected value of assets in each grade band was estimated for all of Scottish
Water’s treatment works. As shown in Figure 8-1, this profile was then used to compare the state
of Scottish Water’s asset stock to that of companies in England and Wales. However, the project
also concluded that interpretability of such plots is limited due to significant differences in the
underlying data and grading procedures.
Figure 8-1. Comparison of Assets in Condition Grade 4/5 by Asset Value.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-5
8.3.6 Key Lessons and Tips for Success
8.3.6.1 Commitment to Data Improvement
Given the starting position of disparate data sources spread across three legacy data
systems, a key strength was the commitment by Scottish Water to improve data on assets and
asset condition/performance to allow analysis to be undertaken for strategic planning and other
purposes.
8.3.6.2 Cost Saving
While a representative sampling approach was used in the assessment program, an
attempt was also made to substitute works that were being assessed as part of the capital
investment planning process when this had no effect on the representative nature or the sample
(the impact of substitution was determined by an expert in statistics). Cost saving was realized
because some works were assessed to meet two drivers: 1) to provide information on capital
investment requirements and 2) to provide the profiles of asset condition and performance to be
used in regulatory reporting.
Cost savings were also realized by clustering assessment tasks to minimize travel time
and to increase the efficiency of the assessment program. Substitutions were again used in this
process, for example, where randomly selected sites were very remote, substitution for similar
but more accessible works was allowed.
8.3.6.3 Consistency of Grading
Grading is a subjective process and effort needs to be expended to ensure consistency. To
facilitate this, Scottish Water therefore provided leveling training to all assessors and also
audited the grading process across a number of teams. In general, consistency of application was
good, although some issues were noted with respect to the consistency of subdivision of assets
into a consistent hierarchy (e.g., what was considered a unit differed between assessors).
8.3.6.4 Focus on Grades of Concern
Generalized linear modeling of allocated condition and performance grades was used to
extrapolate the survey results across the asset stock. However, after undertaking initial analysis,
it was noted that there was an issue with the confidence limits of the statistical modeling of the
grade profiles. This meant that while a 1 to 5 grade system was used in the assessment of assets,
there were insufficient assets of grade 4 and 5 to model in a statistically significant sense. As
such, these grades were combined. Furthermore, it was noted that there was no interest in the
distinction between whether or not an asset was in condition grade 1 or 2, so these grades were
also combined. The final models thus gave the probability that assets would fall into grade bands
1 and 2, 3, and 4 and 5.
8.3.6.5 Confidence Grades
It is desirable to allocate a confidence grade against the condition and performance grade
to indicate the information upon which the grade was allocated (for example, full visual
inspection, opinion of operator, inferred, etc.), and thus the relative confidence in the grading.
8-6
8.4
Case Study 2: Scottish Water’s Approach to Grading of Water Mains
Case Study Summary
Key issues covered in this case study include:
 The development and use of sophisticated decision support IT systems for
management of water infrastructure assets.
 The use of opportunistic and planned sampling in development of models.
 Stepwise justification and development of decision support systems.
 Extrapolation of condition/performance across the asset stock and the use of surrogate
data to fill gaps in necessary data sets.
See case study insets 2-4, 3-5 and 4-1.
8.4.1 Utility Details
See Case Study 1 for details.
8.4.2 Case Study Focus
Within Scottish Water, condition and performance assessments for water mains are
undertaken using a combination of 1) failure data and 2) predictive models generated from pipe
samples. These are incorporated into a GIS-based system that facilitates the prediction of the
condition and performance of the entire water distribution network through extrapolation of data
and predictive models.
8.4.3 Assets Considered in the Program
For this case study, the assessment program of interest focused on water mains. The
approach discussed is broadly equivalent to Scottish Water’s treatment of sewers, although the
assessment procedure for individual assets is based on CCTV inspection, rather than cutout
sampling.
8.4.4 Key Drivers
In Scotland, grades need to be allocated to water mains to provide information for
regulatory reporting, expressed in terms of the percentage of asset value in different condition
and performance grades.
In previous planning cycles, grades were also used to give an indication of investment
needs; condition and performance grades were used in a matrix to identify areas for further
investigation. More sophisticated approaches are now being developed and applied that are in
line with service-driven, risk-based asset management approaches.
8.4.5 Key Program Features
8.4.5.1 Development of INMS
Scottish Water has implemented a system called Integrated Network Management
System (INMS), which was initially developed in-house by the former Authority, East of
Scotland Water. INMS is a comprehensive GIS-based tool used for understanding the
performance of water distribution systems. INMS provides an assessment of the condition and
performance of distribution mains, the level of risk associated with each pipe and the predicted
degree of tuberculation.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-7
8.4.5.2 Use of Pipe Sampling
INMS uses a range of information collected through the operation of the network and via
pipe sampling. As discussed further below, both planned and opportunistic sampling has been
used to provide the data from which the models of pipe condition and performance were
developed. All samples were physically cut out and analyzed; none were assessed using nondestructive testing (NDT).
The INMS models were developed in a stepwise manner. Initial sources of data were
available in the form of previously collected and stored pipe samples and photographs. These
data were re-inspected and the resulting data analyzed to allow relationships between the pipe
characteristics and pipe condition to be generated. For example, corrosion rates of the buried
ferrous mains were calculated using information on pit depth and age. Tuberculation growth
rates for different materials were calculated using tuberculation height measurements, pipe
diameter and material.
The initial pipe samples had, however, been taken in known problem areas and/or taken
opportunistically from exposed sections of burst or leaking water main at the time of excavation
for repair. Opportunistic samples were also taken during other maintenance work, such as the
installation of valves and meters or as part of a rehabilitation program. Opportunistic sampling is,
by definition, unplanned, though selective use of samples may be undertaken to reduce bias (for
example, exclusion of samples from any analysis that would obviously skew the data set). When
compared to random samples taken in structured programs, the use of opportunistic data can
skew the predictive capacity (leading to pessimistic predictions).
To aid the development of INMS, and to improve the models, pipe samples were also
taken in structured programs (essentially a gap filling exercise to supplement the opportunistic
sampling). Random samples were taken in a representative manner; samples being identified
according to combinations of pipe characteristics (material, diameter, age, etc) and factors
relating to the pipe environment (soil type, conveyed water type, etc.). Three pipe samples were
taken from each combination.
Overall, the models have been built up from 7,000 pipe samples, with the sampling being
focused on problem pipe materials (less sampling of plastics pipe). In an average year, a further
200 samples are now taken and used to refine deterioration curves. These samples are taken as
part of rehabilitation schemes and also to investigate areas adjacent to known problem areas (to
determine if the problems are likely to propagate). The samples taken are also used to improve
the model of condition grade. This approach provides data that is not entirely representative, but
is less skewed than opportunistic sampling during failure events (burst repairs) or in the problem
areas themselves.
8.4.5.3 Grading Procedures within INMS
The condition grading procedures used in INMS assign a condition grade of 1 to 5. Two
distinct approaches are used to grade the condition of pipes 1) burst history and 2) a predictive
condition grade model.
The performance grading procedure used in INMS uses a rules-based approach to band
assets. The base data (pipeline attributes) on water mains, held on the GIS, are analyzed to assign
performance grades. Performance grades can be allocated according to three separate
approaches:
8-8
 A pipe-sample based predictive model (grades relate to predicted deposits and degree of
tuberculation).
 Corporate data (grading based on historical complaints and water quality failures).
 Cost grading (grading based on operational costs).
The data sources used within the condition and performance grading procedures are thus
related to structural condition information, characteristics of the pipeline, internal and external
environment and the performance of the system. Similarly, the models relate explanatory
variables to the observed condition/performance grade. For pipe condition, explanatory variables
include pipe characteristics (diameter, material, lining, wall thickness), age, soil type, material
and corrosion rate.
8.4.5.4 Extrapolation across the Asset Stock
To apply the models of condition and performance grades across the asset stock, the
attributes (variables) used in the models must be available for all assets.
Where there are data gaps, various surrogate data are used to allow these gaps to be filled.
For example, the use of material installation dates and housing age to estimate unknown pipe
ages. If no surrogate data exists, such that there is still a data gap, default data (assumed values)
are used. However, the use of default data can have a significant impact on the degree of
certainty associated with the predictions.
8.4.6 Key Lessons and Tips for Success
8.4.6.1 Managing Costs
Costs were minimized by the use of data collected from opportunistic samples. A
stepwise development of models was also adopted that involved collection of data, analysis,
integration into predictive models, review and subsequent improvements.
8.4.6.2 Number of Samples
The spatial extent of the sampling was dictated by affordability issues; predictive
capacity of models would improve with more samples, but the number of samples used in the
production of the models was in line with statistical requirements.
The frequency of sampling in time is not meaningful in this application; the models
describe mathematically the way a pipe deteriorates from new to very poor condition based on
the observed relationship between model determinants and condition.
8.4.6.3 Stepwise Development
Development of INMS was undertaken as discrete projects subject to a formal approval
process in which the additional expenditure had to be justified to management. This approach
made the development costs affordable and ensured that a business case was made for each
stage.
8.4.6.4 Corrosion Rates
Corrosion rates for ferrous pipes were calculated from the recorded internal pit depths
measured on the samples. Linear corrosion rates were initially assumed (known to be simplistic);
non-linear corrosion rates are now assumed.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-9
8.5
Case Study 3: Water Corporation’s ACA Program
Case Study Summary
Key issues covered in this case study include:
 The implementation of a comprehensive condition assessment program using
corporate systems as a repository of information collected and collated.
 A systematic process for the condition assessment of assets undertaken for multiple
purposes.
 The use of a common assessment framework across the majority of asset types.
See case study inset 3-18.
8.5.1 Utility Details
Water Corporation provides water and wastewater services to thousands of households,
businesses and farms in towns and communities spread over 2.5 million square kilometers.
Water Corporation also maintains drainage and irrigation services for both residential and
commercial properties.
8.5.2 Case Study Focus
Water Corporation has undertaken a rolling program of condition assessment of all
infrastructure assets, excluding water distribution and sewer network assets, under a program
termed ACA.
ACA involves a fit for purpose assessment, which takes into account condition,
performance, the availability of spares, etc.
8.5.3 Assets Considered in the Program
There are 86,000 assessable elements covering most the asset types. These include water
and sewer pipes (larger transmission pipes only), valves, pumps, motors, tanks and reservoirs,
including the roof, storage structure, appurtenances and buildings.
Once fully implemented, it is anticipated that the program will require approximately
6,000 assessments to be undertaken each year.
8.5.4 Key Drivers
The key driver for implementing ACA was to achieve a better understanding of asset
condition and to provide a sound basis for good asset management. This included the need to
develop a better understanding of remaining asset life and the potential asset renewal costs in the
medium to long term.
ACA also provides a structured process for the routine inspection of assets that would not
otherwise have been undertaken.
8.5.5 Key Program Features
8.5.5.1 Overview of ACA
ACA had the over-riding objective to develop a corporate register of asset condition to be
used for various purposes, including maintenance planning, renewals planning, management
reporting and financial reporting (end of asset life). As such, the ACA program provides:
8-10
 A register of asset condition.
 Information for replacement and refurbishment programs.
 Information for maintenance planning.
 Information for asset depreciation.
 Corporate reporting of condition.
8.5.5.2 The ACA Process
The ACA process provides a consistent assessment of asset condition across a range of
asset types. Information collected and collated during assessments is stored on a custom-built
add on to an existing corporate management system. The ACA database provides a common
framework for the storage of condition-related data, including the interventions (maintenance
tasks, refurbishment, etc.) deemed necessary to address asset deterioration. The ACA database
can be interrogated in various ways, for example, to allow management reports to be generated
and programs of assessments to be compiled for a given period. The ACA process is shown in
Figure 8-2.
Figure 8-2. Schematic of Water Corporation’s ACA Process.
Figure 8-2 shows that there are two routes through the assessment process. The first is the
formal ACA process, where condition assessments are made routinely at a time informed by
findings of any previous assessment. The second is an asset deficiency process that runs in
parallel to ACA. Through this second process, assessments and/or interventions can be
undertaken in response to any deficiencies in assets reported by routine operation/maintenance.
The main ACA process involves collecting information on the asset to determine if it is
fit for purpose. Any required interventions are identified and programmed in for action.
Assessment records are updated and the date and requirements of the next assessment specified.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-11
8.5.5.3 Grading of Assets
In the ACA process, information about the asset, which may include data collected
during an inspection, performance history, compliance with regulations, availability of spares
and criticality is used to generate two ratings for the asset. These are on a scale 1 to 5 (1 being
excellent and 5 being very poor condition).
The first rating is current condition, which takes into account inspection results and other
relevant information about the asset performance. The second rating is required condition. This
is dependent on the importance of the asset, but can never be 1 or 5 (an asset can not be required
to be in either new or in derelict condition). The difference between the current and required
condition grades is the gap rating, for example, if the required rating is 3 and the assessed
condition is 5 then the gap rating will be -2.
Where a negative gap rating is generated, it is a requirement that an intervention is
proposed to bring the asset up to the required condition. This may be a capital solution such as
replacement or an operational intervention such as an overhaul or minor refurbishment. There is
also the option to recommend increased monitoring or undertake a more extensive inspection.
The financial year that the intervention needs to be implemented and the estimated cost are also
required.
An assessment of remaining asset life is also made (in three bands: life remaining less
than five years, five to 10 years and more than 10 years). Where the asset is assessed to have less
than 10 years of remaining life, the assessor must assign an intervention if one has not already
been assigned as a response to a negative rating.
8.5.5.4 Data Sources and Inspection Techniques
Since the ACA program covers a wide range of assets, various techniques are used to
provide data on asset condition. Depending on the asset in question, these may include visual and
camera inspection and occasionally inspection techniques such as pressure testing, direct current
voltage gradient (DCVG), incotest (eddy current), phenol, ultrasonics, and magnetic flux leakage
monitoring.
For mechanical and electrical assets, the assessment is usually based on the availability of
spares, support, performance and obsolescence. Pump efficiency and condition monitoring are
carried out, but this is often to optimize maintenance timing and efficiency rather than as part of
the ACA process.
For important (critical) and/or high-risk assets, in depth techniques can be required. In
such cases, the assessment techniques are selected and assets inspected by a specialized team of
personal. Water Corporation has a centre of expertise (the Mechanical and Electrical Services
Branch) that provides technical support to the rest of the organization, including determining the
most appropriate inspection technique (see Case Study 4).
8.5.6 Key Lessons and Tips for Success
8.5.6.1 Size of the Assessment Program
The size of the assessment program has resulted in a significant workload for staff
members and resources have been stretched, especially in clearing the initial backlog. The
development of future assessment programs will have an increased focus on asset criticality to
ensure the prioritization of assessments is effective. However, the commitment to assess all
assets has driven data improvement across the asset stock.
8-12
8.5.6.2 Need for Auditing and Quality Control
Ensuring consistency of assessments is difficult as the utility’s activities are spread across
a large area. Effort needs to be expended in the form of quality control, training and auditing to
ensure this consistency is achieved.
8.5.6.3 Use of Confidence Grades
The ACA system requires confidence grades to be allocated that characterize the data
source upon which the assessment has been made. This is considered good practice.
8.6
Case Study 4: Water Corporation’s Assessment Approach for Water Tanks
Case Study Summary
Key issues covered in this case study include:
 An iterative approach to the inspection and assessment of complex assets like tanks,
based on the ACA process given in the previous case study.
 The use of a range of tools and techniques to support condition assessment undertaken
for asset-specific and general asset management purposes.
See case study inset 6-3.
8.6.1 Utility Details
See Case Study 3 for details.
8.6.2 Case Study Focus
This case study focuses on the approaches used by Water Corporation to assess the
condition of water tanks as part of the ACA program (see Case Study 3).
8.6.3 Assets Considered in the Program
Water Corporation manages water tanks of various design including ground level and
elevated steel plate and steel panel tanks and concrete structures with steel reinforcement.
8.6.4 Key Drivers
Assessments of water tanks are undertaken within Water Corporation primarily to
determine whether the tank is, and will remain for the foreseeable future, safe and functional and
to identify maintenance or renewal requirements.
A specific issue of corrosion control has also been identified on some tanks, for example,
tanks with steel floors have a known failure mode in that the steel floor can corrode from below.
8.6.5 Key Assessment Features
8.6.5.1 The Standard ACA Inspection Procedure
Inspection of tanks by Water Corporation is undertaken periodically under its ACA
program (see Case Study 3). Often this is aligned with maintenance activities and the internal
inspection is sometimes carried out by divers who also clean the tank; the divers give the asset
manager a report of the internal condition and defects, which can be accompanied by video
footage. Inspection of the other elements of the tank, such as roof and external condition, are
reported by Water Corporation personnel. Similarly, when emptied for cleaning, operators
undertake visual inspection.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-13
The tank site is broken down into assessable elements for the purposes of condition
assessment. These assessable elements usually comprise the water retaining structure, the roof,
the pipes/valves, the ladders/landing and where applicable, the tank stand and the membrane
liner. Each of these elements has their own condition assessment.
Inspection templates are used to guide the inspector to all the components of the tank that
should be examined, for example, walls and floor, stand, roof, and to facilitate the capture of
information about the appearance of the asset. An example of the guidance provided for the walls
and floor is shown in Table 8-1.
Table 8-1. Guidance for the Grading of Condition.
Walls and floor – reinforced concrete/steel plate/panel
A New or near new walls/floor with few minor defects and meeting all functional requirements.
B
Walls/floor remain in excellent condition requiring little attention; all functional requirements are met.
C
Steel: some external coating defects with surface corrosion to exposed areas – some internal coating defects but
steel is cathodically protected.
Reinforced concrete: some cracking but sealed/calcified and no evidence of active rebar corrosion.
Remains functional; optimal life is not threatened; little remedial action is required at this time.
D
Steel: external coating breaking down, significant pitting corrosion to exposed areas – some internal coating defects
with some corrosion of exposed areas (steel not cathodically protected).
Reinforced concrete: cracks/joints weeping but no rebar corrosion; some minor spalling but little metal loss to rebar.
Remains safe/functional but optimal life at risk; increased monitoring or remedial action required.
E
Steel: general breakdown of coating; areas of severe pitting corrosion.
Reinforced concrete: cracks/joints leaking (water running); severe spalling of concrete; severe rebar metal loss.
Safety/functionality of tank at risk; optimal life being severely impacted; early remedial action.
When an asset falls into category D or E, it is required that the inspector provide adequate
comments to support the observations. For category E assets, photographs and/or a report is
required.
8.6.5.2 More Detailed Assessments
More detailed or technical assessments are normally undertaken based on some perceived
need: 1) visual inspections reveal some issues (defects) that warrant further investigation, 2)
issues with assets of a similar type have been identified, or 3) it is known that visual inspection
will be insufficient to identify defects, for example, under floor corrosion.
The asset manager and specialist engineers within Water Corporation’s Mechanical and
Electrical Services Branch discuss the context of the asset and determine the scope of the
assessment. A range of non-destructive techniques can be used in these assessments, including:
 Magnetic flux leakage floor scanners to scan floor plates.
 Ultrasonic sensors (to evaluate floor scanner results and to test walls and areas of floor
not accessible to the floor scanner).
 Concrete cover meter.
8-14
8.6.6 Key Lessons and Tips for Success
8.6.6.1 Support Material for Condition Assessments
Checklists are a useful aid to the assessment of complex assets. Taking a photographic
record of defects or issues of note provides valuable information.
8.7
Case Study 5: Water Corporation’s Investigation of a Trunk Main Failure
Case Study Summary
Key issues covered in this case study include:
 An investigation into a trunk main’s (large diameter water transmission pipe)
condition driven by a significant failure event with an unusual failure cause and failure
mode.
 The impact of other infrastructure assets on asset risk.
 The use of screening tools and analysis to understand areas of potential risk and to
target more detailed investigations.
 The use of indirect inspection techniques (DCVG survey) and other data to identify
sites for pipe excavation and detailed on-pipe inspection.
 The use of condition assessment to inform risk management strategies.
 The application of experience gained through a specific study to other assets to
leverage value from inspection data.
See case study inset 2-8.
8.7.1 Utility Details
See Case Study 3 for details.
8.7.2 Case Study Focus
The investigations considered were driven by a catastrophic failure of a trunk main (large
diameter water transmission pipe) in a metropolitan area. This resulted in extensive flooding,
damage to property and severe disruption to traffic on a freeway. The case study focuses on the
subsequent assessments of condition and risk undertaken in response to this failure.
8.7.3 Assets Considered in the Program
The failed asset was a 1065 mm diameter steel transmission pipe constructed in 1959;
nominally 9.5 mm thick with a 19mm cement mortar lining. Its operating pressure was
approximately 16 bar.
8.7.4 Key Drivers
The key driver for the program was the catastrophic failure of a transmission pipe
through an unexpected failure mode leading to severe traffic disruption and other impacts.
Given that catastrophic failure of steel is unusual, Water Corporation needed to determine
if the circumstances associated with the failure were an isolated case or if there were similar risks
along the pipe (and other similar assets) that needed to be managed.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-15
8.7.5 Key Program Features
8.7.5.1 Condition Assessment Approach
Water Corporation’s trunk mains are mostly wrapped steel pipes with cement mortar
lining. The trunk main network has a significant level of flexibility, such that a significant
number of trunk mains can be taken off-line without affecting service provision. As such, Water
Corporation has implemented a routine CCTV inspection program whereby trunk mains are
inspected when the pipes are taken out of service for maintenance purposes. This allows
inspection of the integrity of the lining (e.g., the presence of any significant cracking or
delamination can be determined). In addition, the cement mortar may become stained where
there is corrosion of the steel. This can also be identified during the CCTV inspection, which
allows additional investigations to be undertaken if necessary.
The inspections are undertaken using a proprietary system called Challenger. In addition
to CCTV functionality, Challenger has recently been developed to include the ability to conduct
metal thickness testing at selected locations.
8.7.5.2 Details of the Asset Failure
While significant effort is expended to understand the condition of the trunk mains using
these inspection techniques, a trunk main failure still occurred that led to severe disruption. The
failure mode was due to external scouring of the trunk main by water flowing in two drainage
assets that intersected the trunk main in a drainage pit. Scouring by the drainage water led to
external erosion and corrosion of the trunk main over a significant area.
The CCTV inspection program did not pick up the deterioration of the asset since there
was little internal corrosion to stain the lining. Furthermore, and common for steel mains, the
failure mode was catastrophic. The more usual failure mode for steel pipes is pinhole corrosion,
which leads only to small leaks. Catastrophic failure is related to general loss of metal due to
corrosion/erosion over large areas and is a rare occurrence when normal levels of asset protection
and maintenance are applied.
8.7.5.3 Forensic Investigations
Given the unusual circumstances of the failure and failure mode, Water Corporation
instigated a detailed condition assessment of the trunk main in conjunction with an assessment of
risk to determine if the particulars of the failure represented an isolated case. The investigation
was undertaken to:
 Identify any sections of pipe where a similar failure mode could occur (other locations
where drainage infrastructure intersected the trunk main).
 To investigate the condition of the asset in sections where similar levels of failure
consequence could be incurred.
The investigations were designed to improve knowledge of the likelihood of further
failure so that the risk of the main failing could be better managed. An extensive study including
coating integrity (DCVG) investigations, metal thickness testing (ultrasonic), internal camera
inspections and visual inspection of the main at selected locations was carried out over a period
of several months. The timeline of the program is summarized as follows:
May
June
July
8-16
Burst occurred.
Direct Current Voltage Gradient survey.
Critical infrastructure audit.
July
July/Aug
Sept – Dec
Oct
Oct
Nov
Dec
Dec
Internal CCTV inspection.
Inspection of drainage infrastructure.
Excavations and metal thickness testing at defect locations.
Final report on cause of failure event in May.
Contingency plan for future burst event.
Arborist report on trees located near main.
Design report for installation of cathodic protection.
Findings and recommendations reported.
8.7.5.4 Identification of At-Risk Sites
Eight sections along the main were identified where there could be similar damage
associated with drainage assets. The trunk main and surrounding infrastructure was excavated at
these points and the condition of the main and coating assessed.
 At all locations, full assessment of damage was difficult due to the close proximity of
third party infrastructure.
 At three locations, there was no obvious indication of damage having occurred.
 At three locations, corrosion of the trunk main was evident and detailed investigations
were carried out; coating damage, corrosion, gouging of the main and buried
infrastructure in direct contact with the trunk main were noted.
 Two further locations were also investigated but no drainage was found and the main was
in good condition.
8.7.5.5 Survey and Inspections
As indicated, a DCVG survey was also undertaken along the trunk main. The survey
identified a total of 183 coating defects, considered a very high number, particularly with regard
to the relatively short (2800 meters) length of pipe inspected. Of these 183 defects, 40 were
deemed to be medium or significant in terms of the soil voltage gradient present.
To gain a better understanding of the severity of defects located by DCVG, it was
decided to excavate a number of the identified coating defect sites. These sites were chosen to
reflect locations with an increased likelihood of significant corrosion. The main survey
parameters indicating increased probability of significant corrosion were considered to be:
 Low soil resistivity (<5000 ohm-cm).
 Pipe – soil potentials more positive than -500mV.
 Large (significant) soil voltage gradient indications at coating defect sites.
 Crossings or proximity to buried third party structures.
 Presence of groundwater.
 Likelihood of sulfate reducing bacteria and related corrosion inducing bacterial activity.
The secondary survey parameters indicating increased probability of significant corrosion
were considered to be:
 Specific grouping or spacing of coating defects sites at pipe field joints or third party
damage.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-17
 Trees and associated regrowth along the pipe route.
 Evidence of marine sediment in pipe right of way.
Representative sites were selected for excavation that had a minimum of two of the main
and one of the secondary indicators given above. As a result, the pipe was exposed and coating
defect investigations carried out at 24 sites.
At each site, the condition of the coating and pipe was investigated and any remedial
work necessary carried out before reinstatement. The characteristics of the defects were also
related to the findings of the DCVG survey. The information gained from the investigation can
be applied in the management of other trunk mains. The observed defects were used to calibrate
the results from the DCVG to improve the interpretability of subsequent surveys on other trunk
mains.
It was concluded that while the internal condition of the main was good, there were a
large number of external defects present. Most external damage existed where third party
infrastructure (especially drainage) impinged on the main and included damage to the coating,
gouge marks, chain marks and pitting. Wall thickness was reduced to around 6 mm over a few
small areas and 3 mm in localized areas of pitting (c.f. original wall thickness of 9.5 mm).
Structural analysis indicated that the trunk main would fail at 287 meters(m) head, which was
still significantly above the operating pressure of 160m head and design pressure of 210m head
(based on design pressure of fittings).
8.7.5.6 Outcomes of the Investigation
As a result of this inspection and survey work, a number of recommendations were made.
These included options for the long and medium term management of the trunk main, as well as
for management of large diameter mains.
Risk reduction strategies for the section of main that failed ranged from the relocation of
the entire length to the replacement of fittings. These options were assessed using a corporate
risk matrix and risk assessment process. The preferred option included the installation of
cathodic protection, remediation of any interference from or to adjacent infrastructure,
replacement of fittings and the monitoring of leakage.
8.7.6 Key Lessons and Tips for Success
8.7.6.1 Use of Risk Analysis to Focus Investigations
Risk along a trunk main should be characterized and used to focus investigations,
preferably before a failure occurs where this is deemed justified. The risk analysis should
consider all risk factors in a systematic way as well as unusual failure modes.
8.7.6.2 Leveraging Value from Investigations
Value was derived from the extensive program of investigations presented in this case
study because it:
 Provided insight into the residual risk associated with the asset.
 Ensured that replacement of the asset could be deferred with no increase in risk exposure.
 Allowed results to be applied in the management of other assets.
8-18
8.7.6.3 Third Party Interference
Third party interference is a significant source of risk for pipeline assets. In particular,
where other infrastructure have been buried in close proximity to a trunk main, it is very likely
that damage to the coating and/or pipe has occurred.
8.7.6.4 Use of a Common Datum
When using in-pipe techniques in conjunction with on-pipe techniques, it is important to
have a common datum (the point measurements are taken from and referenced to) to allow
matching of internal and external observations.
8.8
Case Study 6: Water Care Services Limited Assessments of Sewerage Assets
Case Study Summary
Key issues covered in this case study include:
 Condition assessment of a trunk sewer network using various inspection techniques.
 The use of existing operational knowledge to prioritize assessments.
 The use of a risk-based approach to contextualize the results of inspection.
 The use of the results of a condition assessment program to specify on-going
inspection and monitoring activities.
See case study insets 3-3 and 3-15.
8.8.1 Utility Details
Water Care Services Limited (Water Care) is New Zealand’s largest company within the
water and wastewater industry. The company supplies bulk water to Auckland through a regional
water network. An average of 347,000 M3 of water is supplied daily. The water is drawn from 12
sources comprising of 10 dams, the Waikato River and an aquifer at Onehunga. The company
also operates a regional wastewater network and treats 288,000 M3 of wastewater a day at the
Mangere Wastewater Treatment Plant.
8.8.2 Case Study Focus
In 1999, Water Care identified that the condition of Auckland’s trunk sewer assets were
unknown and that, in some cases, the consequences of failure would be significant. Project
Condition Assessment and Risk Determination (CARD) was implemented as a result; CARD for
wastewater mains (2000 to 2003) was complimented by ECARD – an assessment of wastewater
pump stations electrical systems, undertaken in 2001-2003.
8.8.3 Assets Considered in the Program
The condition assessment of large diameter sewerage assets; Water Care operates
approximately 300km of trunk sewers (>300DN) of various materials.
8.8.4 Key Drivers
The main drivers for project CARD were to understand condition, risk and economic life
of assets in more detail and to provide a feed into the asset management strategies for wastewater
assets.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-19
8.8.5 Key Program Features
8.8.5.1 Project Goals
Through various risk assessment processes and workshops with staff, Water Care
identified that the condition of the sewer mains was unknown and that in some cases the
consequences of failure would be significant. Project CARD was implemented as a result of this
work. The stated project goals of CARD included:
 Develop an asset condition monitoring and performance assessment strategy, including
data management, storage and analysis.
 Determine the condition of the identified high-risk pipelines and potential failure modes.
 Identify and quantify the risks of failure and economic life of the high-risk pipelines.
 Identify management and mitigation measures, including:
−
−
−
•
Maintenance and repair activities.
Rehabilitation needs.
Replacement needs.
Develop programs for ongoing monitoring and assessment of the high-risk pipelines.
8.8.5.2 Identification of Inspection Technologies
The inspection technologies used in the program were researched through the World
Wide web, discussions with other utilities, reference to technologies available locally (in New
Zealand) and research trips to the United Kingdom and Canada (mainly to establish the
capabilities of sonar survey equipment and the management of overflows). The techniques
eventually selected for use in the program included:
 CCTV of wastewater mains.
 Sonar for siphons.
 Walk through for larger diameter mains and larger duplicate siphon pipes. Visual
assessment of defects was augmented through video, still photos and cover meter
measurements. Concrete cores were also taken for laboratory testing. Some sections of
sewers had dimensions checked using laser technology.
 Manholes were inspected during CCTV sewer inspections or on an ad-hoc basis if
opened for other purposes.
8.8.5.3 Program Implementation and Outcomes
Risk analysis was undertaken at the beginning of the CARD project to identify priorities
for inspection using available operational knowledge.
The project was managed as a normal engineering project; both CCTV and sonar surveys
were undertaken by external contractors. Sonar contracts were awarded by competitive
quotations, CCTV by identifying best level of service (i.e., contractor equipment/capability)
available. It was initially thought that the budget would not allow all pipes to be inspected, but
by 2005, nearly all pipes had been surveyed. Over the period 2000-2005 Water Care undertook a
complete inspection of the entire 300km trunk network, mainly using CCTV and visual
inspection (approximate cost AU$1.5 million).
The condition data, together with previous history and criticality assessment, was
analyzed using Weibull analysis to look for correlations between age, criticality, observed
8-20
condition and fault history. Correlation was poor, and a more detailed analysis using factors such
as pipe material, soil condition, pipe bedding, construction standard and so forth is thus being
developed.
The assessments provided a ranking of critical mains for further monitoring,
rehabilitation or renewal. As well as undertaking necessary maintenance and replacement work,
Water Care’s on-going strategy is to monitor sewers with the poorest internal condition rating
(condition rating grade 5), representing approx 5% of the total network, which includes
monitoring of key brick and concrete sewers. Monitoring is undertaken using CCTV or, in some
limited cases, visual inspection. Where condition dictates, patch lining is undertaken. If the
structural condition of the sewer is compromised, full structural lining is installed. Where
structural lining is not practical, the sewer is either renewed or is relayed on a new alignment
(often using directional drilling).
8.8.6 Key Lessons and Tips for Success:
8.8.6.1 Use of Local Knowledge
An assumption at the start of project CARD was that Water Care and local consultants
did not have the requisite knowledge to put together the program. Water Care professionals now
consider that it is important not to underestimate the value of in-house and local knowledge, nor
overestimate the state of the art in other countries.
8.8.6.2 Capturing Available Operational Knowledge
Capturing available operational knowledge was a key aspect of the prioritization of the
assessment program. While no formal assessments had been undertaken, operational staff had a
reasonable feel for those assets that were in poor condition.
8.8.6.3 Leveling Assessments
Problems can occur in a large program of condition assessment because some
assessments can be more conservative than other assessments, depending upon who performs the
assessment. Water Care now attempts to overcome this by having the same team do the analysis
and reporting.
8.9
Case Study 7: Water Care’s Assessments of a Critical Sewer
Case Study Summary
Key issues covered in this case study include:
 A detailed investigation of a critical concrete sewer in poor condition and subject to
significant H2S related corrosion.
 The limitation of using defects alone as a means of characterizing condition and risk
of failure.
 The iterative use of more detailed studies to understand asset risk, support decision
making and defer capital programs.
 The use of structural analysis to understand the probability of asset failure under a
range of loading scenarios.
 The collection of auxiliary data to refine the analysis.
See Case Study inset 3-3.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-21
8.9.1 Utility Details
See Case Study 6 for details.
8.9.2 Case Study Focus
A detailed investigation into the risk and condition of an interceptor sewer crossing an
environmentally sensitive area with potential for significant aesthetic and environmental impacts
should the asset fail catastrophically.
8.9.3 Assets Considered in the Program
An 18 kilometers (km) long reinforced concrete interceptor sewer, cast in situ in sections
of 30 feet (10m), and built between 1960 and 1965. The shape and size of the pipeline varies
along its length, as does the earth fill above the pipe. The sections of the pipeline of specific
interest to the case study are 85 inches semi-elliptical.
8.9.4 Key Drivers
Initial inspection of the asset was undertaken under a program to determine the overall
condition of all sewerage assets (see Case Study 6). Preliminary structural analysis was then
required to assess the risk of collapse in sections subjected to significant levels of acid attack.
Collapse of these sections would lead to significant health, environmental and third party
consequences. The implication of this analysis was that there was a risk of collapse under certain
conditions and on-going deterioration would increase the likelihood of failure.
Additional analysis was undertaken to understand better the rate of deterioration and the
risk. In part, the additional analysis was driven by the fact that there was insufficient redundancy
in the network to allow the asset to be replaced.
8.9.5 Key Program Features
8.9.5.1 Results of Initial Condition Assessments
The condition assessment of the sewer was initially undertaken using walk through
inspection techniques. Data was collected in terms of observed defects, supplemented through
photographs and notes. The distance along the asset was measured by wheeling above the
waterline.
The assessment indicated that the interceptor sewer was in poor condition; about 5.5 km
having been subject to significant acid attack, penetrating more than 30mm. A relatively short
section of the sewer (171m) was found to be in very poor condition; 80mm (+/-10mm) having
being lost from the original (as-built) wall thickness of 180mm.
This section was between two siphons (thus having limited air exchange) with a large
connection discharging into it, these factors providing conditions for the generation and release
of H2S. The concrete in the section had corroded to the extent that the inner of two sets of
reinforcement bars (cast within the pipe wall) were exposed in places. In addition, there was
relatively little earth cover above the section, a situation that can lead to a higher live load being
imposed on the sewer.
8.9.5.2 Implications of Structural Analysis
Initial structural analysis was undertaken to consider the impact of existing soil and
groundwater loads as well as traffic on the deteriorated asset. The sewer structure was analyzed
as a two-dimensional plane frame with the sewer modeled as a series of beam elements with
nodes at 150 to 300mm centers and support from the soil being considered as elastic springs at
8-22
the node points. The top one-third of the pipeline was modeled with reduced wall thickness to
represent the impact of acid attack.
Various loading scenarios were analyzed and the calculated safety factors compared to
the requirements of applicable codes. The results of these assessments implied that there was a
risk of structural failure under certain conditions, but that more information was required to
refine the analysis.
Subsequent investigations into the amount of earth cover, water table depth, concrete
thickness, concrete strength and soil parameters were undertaken to refine the assumptions made
in the analysis. The conclusions from the refined analysis were that the sewer could safely
sustain existing soil, ground water and expected traffic loads. However, the remaining wall
thickness was still uncertain and results indicated that the sewer would be over stressed under
certain traffic loading conditions. Significant on-going deterioration of the asset was expected to
occur and increase the probability of failure over time.
8.9.5.3 Risk Mitigation and Additional Investigations
As a result of the assessment, it was determined that immediate remedial action was
required using a sulfate-resistant spray-on lining system. Furthermore, the asset was deemed at
risk and early replacement was considered. Such replacement was not practicable given there
was insufficient capacity in the network to allow the replacement to be readily undertaken. An
expansion of the network was, however, already planned that would provide the spare capacity
required to undertake the capital works.
Additional investigations were undertaken to understand the risk associated with the asset
and to determine if the capital renewal could be deferred until after the additional network
capacity was constructed.
Mapping of the corrosion was undertaken along the section of asset in poor condition. A
cover meter, which induces a magnetic field in the reinforcement bars, was used to measure the
depth of cover to the reinforcement bars along the asset. The results of this inspection were used
in combination with laser profiling to determine the amount of material lost from the wall and
the rate of asset deterioration and thereby predict the change in asset condition over time (in
terms of wall thickness).
More refined structural analysis was then undertaken using three dimensional (3D) finite
element modeling. The modeling showed that the loss of material down to the first reinforcement
bar was not as significant as first thought; the pipe would lose structural integrity when there was
corrosion down to the outer of the two reinforcement bars, rather than the inner. It was concluded
that the level of risk associated with the asset was acceptable and that its renewal could be
deferred until after the network capacity was expanded through other capital projects.
In summary, the initial condition assessment was undertaken using a screening approach
that determined the presence of a significant defect; concrete had corroded to the extent that the
inner reinforcement bar of the pipe wall was showing. The presence of the defect was, however,
only a relative indicator of condition. Structural analysis was required to determine what the
defect meant in terms of asset risk.
Inspection of the asset was then undertaken to determine the rate of deterioration and the
results of the inspections used in refined modeling studies to put the asset deterioration into
context. The cost of the detailed analysis was justified by the need to understand the risk in more
detail and by the lack of affordable risk management options.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-23
8.9.6 Key Lessons and Tips for Success
8.9.6.1 Limitations of Defects as a Metric of Condition
While condition assessment undertaken through visual assessment is a pragmatic
technique in many instances, the presence of structural defects needs to be contextualized to
understand risk fully. In this case, an exposed reinforcement bar was interpreted as being
indicative of a high risk of failure. Additional detailed analysis indicated the probability (and
thus risk) of failure was lower than anticipated. This allowed deferral of a capital project to a
time when the network could support the rehabilitation of the interceptor sewer.
8.9.6.2 Justifying Additional Analysis through Better Knowledge
The cost of the additional analysis was justified because of the high level of perceived
risk and the lack of available options to manage that risk. An iterative approach to assessment
can therefore be justified based on risk, in which more accurate (and expensive) techniques are
used to refine the knowledge of an asset and give better support to decision making.
8.10
Case Study 8: Melbourne Water’s Assessments of Steel Tanks
Case Study Summary
Key issues covered in this case study include:
 A comprehensive and planned approach to the inspection and assessment of steel
water storage tanks.
 The historical development of condition assessment and other maintenance practices,
from ad hoc approaches used in the early 1990s to the systematic investigations
carried out today in line with strategic asset management needs.
 The identification of an unexpected source of asset deterioration associated with
construction of water storage tanks on limestone foundations contaminated with
chlorides and the development of an assessment program to manage the associated
risk.
 The use of scoring procedures to facilitate condition grading of complex assets.
See Case Study insets 2-3 and 5-7.
8.10.1 Utility Details
Melbourne Water is a supplier of bulk water services in Melbourne, Australia and the
surrounding region. Owned by the Victorian Government, Australia, Melbourne Water is
responsible for managing water supply, sewerage and drainage assets valued at AU$8.4 billion.
Services provided to the community include management of Melbourne's water supply
catchments, removal and treatment of most of Melbourne's sewage and management of rivers,
creeks and major drainage systems throughout the region.
8.10.2 Case Study Focus
The case study considers investigations into the deterioration of steel water storage tanks.
The discussion is contextualized in terms of the historical development of assessment practices
for steel water storage tanks, from ad hoc assessments undertaken up until the time when
Melbourne Water was incorporated in 1994 to the systematic strategies for inspection and
8-24
corrosion management that are now undertaken, which fully align with corporate asset
management policies.
8.10.3 Assets Considered in the Program
Fully enclosed steel water storage tanks constructed on a limestone foundation according
to designs based on standards from the American Petroleum Industry Standard (API 651).
8.10.4 Key Drivers
The need to manage assets of significant value in an effective manner and to address risks
associated with asset deterioration and corresponding water loss.
8.10.5 Key Program Features
Steel water storage tanks started to be constructed in and around Melbourne in the 1960s.
During the 1970s and 1980s a relatively large number of steel tanks were constructed to meet
increased demand or to replace open basins where water quality standards needed to be
improved. In 2005, Melbourne Water operated 38 steel service reservoirs (40 were being
operated at the time of writing), with an estimated replacement value of AU$190 million.
8.10.5.1 Development of Approaches to Management of Water Tanks
When it was incorporated in the early 1990s, Melbourne Water inherited a fragmented
approach to the management of its water tanks. Basic information relating to the construction of
the tanks was available in the form of design drawings. However, on-going assessments were
undertaken separately by various departments focusing on individual issues such as corrosion,
mechanical and electrical components, valves, and so forth. Information recorded during these
assessments was in a summary format (for example, “asset satisfactory”) and was not collated.
As in other water companies, water storage reservoirs represented a significant capital
investment and the assets provided played a critical role in the provision of water services and
management of risk. Furthermore, there was a developing understanding that ad hoc approaches
to management and maintenance were not providing the information necessary for long-term
asset stewardship. Melbourne Water started to develop a structured approach to the management
of these assets drawing on the knowledge of management practices being applied to large
diameter steel pipes. At the time these asset management procedures were being developed, a
particular and unexpected failure mode started to become evident - the corrosion of the tank’s
steel plate floor.
8.10.5.2 A Legacy Design Issue
Melbourne Water’s steel water storage tanks are constructed from steel plates that are
welded in situ. Tank floors are specified as uncoated steel plates, lapped at joints and laid over a
base course of 100mm nominal thickness of crushed limestone; the limestone overlays a subbase of crushed basalt rock. The choice of limestone as a base material was primarily for the
purpose of providing a protective alkaline barrier to the uncoated floor plate underside. However,
limestone also has natural propensity to contain large volumes of chlorides (as salts). This issue
was not considered in the original specifications.
During the early 1990s a steel service reservoir floor-plate was found to have perforated.
During October 1994, substantial water leakage was observed coming from the reservoir, which
had to be immediately taken out of service to allow emergency repairs. While the perforation
failure was confirmed as being due to corrosion, the mechanism of deterioration was not
immediately obvious. At the time of the incident, another service reservoir began to show similar
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-25
signs of corrosion and steps were taken to reduce the corrosion rate by implementing cathodic
protection.
Subsequent investigations into the asset deterioration confirmed that the limestone was
heavily contaminated with calcium chlorides. The impact of this salt on the floor plate underside
is typically characterized as pitting corrosion. As a result of these investigations, Melbourne
Water began a program of assessment. Twenty-two tanks were confirmed as having high levels
of chloride contamination within the limestone base-course material with associated high levels
of corrosion. Specifications for new service reservoir construction were revised during the 1990s,
to ensure that this problem did not occur in the future. Nevertheless, Melbourne Water still has to
monitor for, and treat, corrosion in reservoirs that were built prior to this period.
The failure mode associated with this under floor corrosion is not catastrophic, however,
significant (order ML/day) leaks can occur. Given the high visibility of water conservation issues
in Australia coupled with the proximity of the tanks to residential areas, such leaks can result in
significant adverse publicity as well as having the potential for causing property damage and
associated community distress.
8.10.5.3 Current Inspection and Management Strategy
Given the perceived level of risk, Melbourne Water’s steel service reservoirs are now
regularly inspected to ensure that the potential for asset failure is appropriately managed.
Inspection strategies have been developed in consultation with external consultants and are
considered by Melbourne Water to be industry best practice.
Comprehensive corrosion assessments are undertaken on a periodic basis ranging from
one to five years. Generally speaking, assets that are deemed to pose a significant risk are
inspected on a one to two year basis, whereas those that pose a smaller risk are inspected on a
three to five year basis. Outage strategies are implemented based on business risk and
operational needs with due consideration given to both water quality standards and structural
integrity requirements. The inspection can be timed in accordance with cleaning requirements;
tanks have to be cleaned every three to eight years, depending on the level of silt build up.
Melbourne Water tends to avoid the use of divers to undertake structural assessments.
Nevertheless, divers may be used on an ad hoc basis where circumstances limit outage
opportunities. When dewatered, the tanks are inspected using a range of techniques. In particular,
magnetic flux leakage floor scanners are used to map corrosion of steel floor plates. Other
components of the asset are also assessed, typically through visual inspection. Observations are
recorded and reported in a standard format that details the observed feature (asset component)
and any salient remarks. The conditions of functional components of the asset are also assessed
against a standard scoring scheme developed by Melbourne Water. This results in weighted
scoring for various asset components, as illustrated in Table 8-2.
8-26
Table 8-2. Weighted Scoring for Asset Components.
Category
Structural stability
Light gauge roof adequacy
Road and storm water drainage
Extraneous fittings
Protective coatings adequacy
Reservoir security
Weighting
6(0-30)
1(0-2)
1(0-3)
1(0-5)
1(0-2)
1(0-2)
Score
3
1
0
0
1
1
Total
18
1
0
0
1
1
Cathodic protection systems
1(0-3)
2
2
TOTAL
23
The scores are interpreted using the following grading procedure:
 If the total is 31 or more then the condition is 5.
 If the total is between 24 and 30 then the condition is 4.
 If the total is between 14 and 23 then the condition is 3.
 If the total is between 8 and 13 then the condition is 2.
 If the total is between 0 and 7 then the condition is 1.
 In the example given above, the tank was awarded an overall condition grade of 3.
Results of assessments are compiled into asset-specific reports that include remarks
relating to specific issues identified for action along with recommendations and priorities. The
condition of all Melbourne Water’s steel tanks are also periodically summarized in a
management report, which uses a traffic light system to highlight problem areas (for example,
assets with a condition grades 4 and 5 are flagged by red cells).
8.10.6 Key Lessons and Tips for Success
8.10.6.1 Alignment of Condition Assessment and Asset Management
Ad hoc assessment strategies spread across a number of departments do not provide the
information required to support effective stewardship of complex assets. Instead, asset specific
policies and procedures must be developed with appropriate resourcing and lines of
responsibility. These asset-specific approaches should be developed in line with the development
of corporate risk and asset management policies.
Detailed investigations can be required when there is an unexpected failure or
deterioration of any asset. The ability to undertake these investigations and implement risk
management strategies has been greatly enhanced by the development of asset management
approaches.
If justification for management strategies is presented in both engineering and
financial/economic terms, the process of obtaining the necessary buy-in from senior management
is greatly facilitated.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-27
8.11
Case Study 9: Sydney Water’s Management of M&E Assets
Case Study Summary
Key issues covered in this case study include:
 The use of qualitative and quantitative techniques to assess and monitor the condition
of important electrical and mechanical assets.
 The use of a CMMS in condition and maintenance management.
 The range of inspection tools used in asset inspection and condition monitoring of
important mechanical and electrical assets.
See case study insets 3-1, 3-8, 5-1 and 6-1.
8.11.1 Utility Details
Sydney Water Corporation (SWC) supplies clean water to more than 1.6 million homes
and businesses in the greater Sydney region, New South Wales, Australia. Raw water is treated
at nine water filtration plants; the largest plant at Prospect treats more than 80% of the area’s
water. The water is distributed to customers via a network of 259 service reservoirs, 151
pumping stations and nearly 21,000 km of water mains.
SWC also collects and treats more than 1.2 billion liters of wastewater each day. The
sewerage network consists of about 23,500 km of sewer pipes in 25 separate sewerage systems
with 30 sewage treatment plants (STP). Around 75 per cent of the wastewater is processed at the
three largest plants at Malabar, North Head and Bondi.
8.11.2 Case Study Focus
The management of important electrical and mechanical assets through the use of a
combination of qualitative and quantitative techniques that integrate traditional practical
engineering level practices with a more strategic level approach to maintenance management.
8.11.3 Assets Considered in the Program
Important above ground electrical and mechanical assets.
8.11.4 Key Drivers
SWC developed its condition assessment programs with the prime objective of ensuring
that critical assets do not fail. The perspective taken is to focus on assets that are required to run
the business; various business risk factors are evaluated to promote the effective management of
these important assets (including cost, risk of failure and environmental risk).
8.11.5 Key Program Features
SWC has developed an approach to condition assessment and management that
incorporates a suite of quantitative and qualitative tools. Quantitative methods include obtaining
numerical results from inspection and performance monitoring and use of software and
mathematical algorithms to analyze this and other data. Qualitative methods include
incorporating experienced staff members’ intuitive reasoning into the analysis of an asset’s
condition as well as non-quantitative condition assessment techniques such as visual inspection.
8-28
Prior to adopting this approach (termed “Quali-Quanta” by SWC), SWC applied high
standards and regular planned maintenance with little analysis or optimization. The analysis of
asset management information now occurs simultaneously on two levels:
 Level 1: Higher level analysis based on qualitative and quantitative analysis. Important
aspects of this level include planning, analysis of long term behavior of assets and
application of experienced staff members’ intuitive reasoning. An asset’s condition is
analyzed in terms of a wide range of detailed parameters including, number and nature of
past failures, meantime between failures, experienced operators’ and managers’ intuition
and cross-checks between the failure and running history of related/linked assets.
 Level 2: A more practical level and is based on engineering analysis. Each asset’s
condition is categorized by assigning it a grade after site inspection and condition
assessment.
8.11.5.1 Sources and Use of Data and Information
To facilitate the management of assets, information from a range of sources is collated
and analyzed. Much of the data is held on a CMMS. The CMMS documents asset history,
scheduling, preventive maintenance, work orders, labor and expense tracking, procurement and
reporting associated with assets. Data from the CMMS is supplemented with condition
assessment information such as that from maintenance staff. Desktop information is also added
to this, including the opinions of a wide range of personnel, such as maintenance supervisors.
The collated data is statistically analyzed for each individual asset. Statistical analysis
commonly consists of a Bayesian approach and Weibull correlation analysis. SWC has found
that Weibull analysis is useful when there is limited failure data available, such as a small sample
size.
8.11.5.2 Inspection Tools Used
Table 8-3 outlines the main inspection and condition monitoring tools used by SWC for
electrical and mechanical assets. Condition monitoring is conducted on selective assets
depending on their importance. For example, if a failure would result in significant downtime or
a major replacement cost, the asset is regularly condition monitored or inspected.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-29
Table 8-3. Inspection Tools and Techniques Used by SWC.
Tool
Oil testing and
analysis
Applicable assets
Large motors, transformers,
diesel engine generators, gas
engines at Malabar STP.
Purpose and details
Used on all critical and large assets using oil.
Used where lubrication of engines is critical.
Determines how long oil will last.
Frequency of use
Monthly, done through a
service provider.
Infrared
thermography
Switchboards and motor circuit
motor control centers.
To take snapshots of hot panels and cables in
order to allow hot spots to be pin-pointed.
A program that covers all
plants ensures testing every
six months to a year.
On-line
condition
vibration
monitoring
Machines with bearings or
couplings.
Determines whether bearings, footings or
couplings have adequate integrity and have not
gone ‘soft’.
Includes a data logger.
Once a month or three times
monthly, depending on the
criticality.
Vibration
analysis
1000kW raw sewage pumps
and centrifuges.
Collects data on machines running uninterrupted.
For instance, analysis of friction losses on
bearings. SWC has in-house vibration analysis.
specialists who analyze testing data output such
as spectra. Data is extracted into software and a
reactive work order is created in the CMMS. This
allows SWC to do more of its reactive
maintenance in a planned manner.
On-line data collected every
half an hour.
Motor circuit
analysis
Motors.
Used to assess a range of items, including the
integrity of the motor circuit operating the motor,
the condition of insulation between the winding
and the frame of the motor, integrity of the motor
starter and to determine if the winding is shortcircuiting. Offline testing, very reliable.
Every six months.
‘Level 1’ plant
condition
assessment
All critical plant assets.
All assets within a facility are visually inspected.
Regularly scheduled as part
of ongoing preventive
maintenance program.
x-ray testing
Pressure vessels, welded pipe
joints, castings.
Weld testing.
Ultrasound
Mostly used on concrete
structures such as digester
walls and pipelines.
Usually only carried out on a one-off basis on
assets requiring assessment of structural integrity.
Usually only carried out on a
one-off basis rather than
regularly.
Not commonly used.
Testing is periodically conducted as part of SWC’s regular planned maintenance
program. In addition to regular in-house testing, specialist contractors conduct testing of specific
assets, such as pressure vessels. Contractors receive certification for a specific interval.
When considering adopting a new condition assessment tool or technique, SWC
compares the effectiveness of the new tool with the current tool, if being used. The comparison
involves a cost-benefit evaluation per asset. Maintenance cost history for each asset is used as the
fundamental benchmark. If a new tool costs more, it still may be considered if it gives an earlier
warning of failure.
8-30
8.11.6 Key Lessons and Tips for Success
8.11.6.1 Use of Desktop Studies
SWC has demonstrated over a number of years that there is a strong correlation between
results from site condition assessment and desktop analysis. This has enabled SWC to justify
condition assessment programs that have a smaller number of site inspections than previously.
Approximately 10% of site inspections are routinely conducted on an ongoing basis to prove that
the correlation between the desktop and on-site condition grading is being maintained.
8.12
Case Study 10: City of Bellevue’s Risk-Based Approaches
Case Study Summary
Key issues covered in this case study include:
 The range of condition assessment programs instigated by a provider of infrastructure
management services to manage risk and reduce costs.
 Coordinating with the transportation department to target inspections and minimize
pipe replacement sewer and water main replacement costs.
 A focus on system performance and reliability of water and wastewater pipes to
reduce claims from property damage or business interruptions.
 The use of risk-based approaches to target inspection effort, including the targeting of
water and sewer pipes that could lead to flooding of basements and property damage.
See Case Study insets 2-6, 3-2 and 6-4.
8.12.1 Utility Details
The City of Bellevue provides infrastructure management services, including wastewater
collection, water distribution and stormwater collection for approximately 130,000 customers.
Other utility companies provide water and wastewater treatment services.
The water and wastewater systems are each comprised of roughly 500 miles of pipelines.
The oldest pipelines in the water and wastewater systems date back to 1948; a large portion of
the system (nearly 50%) was installed in the 1960s.
8.12.2 Case Study Focus
A range of condition related programs undertaken by an infrastructure management
service provider to improve management of the asset stock.
8.12.3 Assets Considered in the Programs
Bellevue has undertaken a range of condition related programs to improve the
management of the asset stock and to reduce costs. These include a review of asbestos cement
(AC) pipe break data and subsequent replacement strategy, CCTV inspection of sewers and a
leakage reduction program for water mains.
8.12.4 Key Drivers
Bellevue is interested in reducing claims from property damage and business
interruptions. This has increased focus on system performance and reliability.
There is also a need to justify the reserves set aside for renewal and replacement of assets
and to determine the most appropriate means for targeting asset renewal expenditures.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-31
8.12.5 Key Program Features
Bellevue has undertaken a range of condition assessment programs to improve the management
of the asset stock, as summarized below.
8.12.5.1 AC Pipe Replacement Program
A review of historical water main break data in the 1970s and 1980s determined that 80% of
main breaks occurred in AC pipes between four to six inches in diameter. This led to a program
of replacing all asbestos cement water pipe in the system. This program is still underway; pipes
are replaced when breaks occur and/or when the roadways are resurfaced.
8.12.5.2 Sewer Pipe CCTV Program
A comprehensive CCTV program is underway, in which it is planned to CCTV all sewer
pipelines over a 10 year period. Given this strategy of inspecting all sewers, initial city efforts
focused on the most critical pipelines (with regard to economic, public health or environmental
impact). The program started with critical pipelines (20% of the system), then moved through the
system with newer pipes getting lowest priority.
Pipelines are scored according to the NASSCO system, and those receiving poor condition
scores (4 or 5) are evaluated by senior staff to determine need for renewal.
Any pipe under a roadway scheduled for resurfacing is scheduled for CCTV as a high priority,
this allows pipe replacement to be undertaken in conjunction with the road resurfacing.
City staff members have also performed hydraulic and surface water modeling to determine
areas of the system and hydraulic conditions that would cause the sewer hydraulic gradeline to
be above basement floor levels, and thus where the city may be susceptible to property damage
claims. Condition assessment and operations and maintenance activities are then prioritized
accordingly.
8.12.5.3 Leakage Reduction Program
A risk-based leak detection program has been underway for several years. This initially focused
on reducing system water loss, but subsequently focused on avoiding property damage and the
associated claims.
High-risk pipes were identified by overlaying several property damage-related risk factors,
including properties where home elevations are below adjacent street levels, areas where older
(pre-1986) ductile iron water mains are installed and areas of high percolation soils (likely to
transmit water rather than force it to the surface where the water would be observed).
Acoustic leak detection efforts have targeted areas with these three risk factors to prevent minor
leaks from becoming major problems.
8.12.6 Key Lessons and Tips for Success
8.12.6.1 Coordination with Transportation Department
A critical driver for the pipeline assessment efforts is the schedule for resurfacing of the
roadways in the service area.
Due to considerable savings for the utility if pipeline replacement projects do not incur
repaving costs, much of the sewer CCTV efforts and AC pipe replacement efforts are targeted as
a result of the roadway resurfacing schedule.
8-32
8.13
Case Study 11: Massachusetts Water Resources Authority RCM Program
Case Study Summary
Key issues covered in this case study include:
 The use of RCM to optimize maintenance practices at a treatment work facility.
 The range of condition monitoring techniques used in condition monitoring of the
assets.
 The coordination of various initiatives to increase the effectiveness of maintenance
practices.
See Case Study insets 2-5, 3-17 and 5-4.
8.13.1 Utility Details
The Massachusetts Water Resources Authority (MWRA) provides wholesale drinking
water supply, treatment, and distribution and wastewater collection, treatment and disposal
services for 61 member communities serving a population of roughly 2.5 million customers in
the greater Boston area. The water distribution and wastewater interceptor systems are comprised
of roughly 300 and 257 miles of pipeline, respectively. Typical daily water delivery is
approximately 225 million gallons per day (mgd). The regional wastewater treatment plant at
Deer Island is among the largest in the country with an average daily flow of 350 mgd and a wet
weather treatment capacity of 1.2 billion gallons per day.
8.13.2 Case Study Focus
A reliability centered maintenance program undertaken at the Deer Island Treatment
Plant.
8.13.3 Assets Considered in the Program
Wastewater treatment work assets.
8.13.4 Key Drivers
MWRA has a general focus on cost-effectiveness and reliability, which served as primary
drivers for efforts to minimize asset lifecycle costs and for development of an extensive
reliability centered maintenance program at the Deer Island Treatment Plant.
8.13.5 Key Program Features
8.13.5.1 MWRA’s RCM Program
MWRA has implemented RCM and condition monitoring programs, primarily focused
on the Deer Island Treatment Plant (wastewater) facilities. At an early stage in the development
of these approaches, MWRA assigned dedicated staff members to lead the development of asset
management efforts for the utility. Early efforts included benchmarking other RCM programs
inside the water/wastewater industry (Broward County) and outside the industry (Coors Brewing,
Dofasco Steel).
Nearly 200 plant systems were identified and prioritized based on criticality for formal
RCM program development. At the time of writing, RCM programs had been implemented for
55 of these systems. This involved extensive workshop efforts to determine optimum
operational, maintenance and condition monitoring strategies. As noted in earlier chapters, RCM
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-33
workshops determine frequency and type of maintenance for individual equipment, often
recommending condition-monitoring tasks.
MWRA considers that the implementation of a formal RCM program has been very
effective in enhancing the reliability and performance and reducing life cycle costs of its large
facility equipment.
8.13.5.2 Other Related Initiatives
Over US$140 million in equipment is currently monitored via a proactive condition
monitoring program. Condition monitoring programs for the major equipment use a range of
techniques, including oil analysis, temperature analysis, acoustic ultrasonic and vibration
analysis. For larger equipment (value of roughly US$400,000 or greater), permanent vibration
and temperature monitoring equipment has been installed for enhanced trend analysis.
Staff members are also trained in specialized maintenance (e.g., laser alignment)
techniques for equipment rebuilds to improve equipment reliability.
8.13.5.3 Benefits Associated with Initiatives
Specific benefits of these initiatives include:
 Demonstrated reduction in over 20,000 maintenance work hours per year as a result of all
reliability programs including RCM, condition monitoring, preventive maintenance
optimization and productivity improvements, resulting in labor savings of over
US$700,000 annually.
 Proactive oil sampling program resulted in avoided (scheduled) oil changes valued at
roughly US$50,000 per year.
 Substantial (non-quantifiable) avoided and deferred costs due to enhanced equipment
reliability and performance, extended equipment life, avoided permit violations, etc.
 Qualitative staff improvements in terms of teamwork, communications and commitment
to success.
8.13.6 Key Lessons and Tips for Success
 A program champion is key, whether for the overall asset management and condition
assessment effort, or for the individual condition assessment programs.
 Implementation of the formal RCM program has been a very effective way for MWRA to
enhance the reliability and performance, and reduce life cycle costs of their large facility
equipment;
 Proactive maintenance programs for critical equipment have focused on oil, temperature,
acoustic ultrasonic, and vibration analysis.
 Investments in staff training, sophisticated mechanical alignment equipment, and
permanent monitors on certain major equipment have yielded savings in asset life cycle
costs and performance reliability.
8-34
8.14
Case Study 12: MWRA’s Strategies for Pipe Network Management
Case Study Summary
Key issues covered in this case study include:
 The use of different condition-based approaches used for management of pipeline
assets.
 The use of condition-related data to drive operational and capital interventions.
See Case Study insets 2-5, 3-9 and 3-17.
8.14.1 Utility Details
See Case Study 11 for details.
8.14.2 Case Study Focus
MWRA use a range of condition-based approaches to facilitate the management of their
network assets. In particular, water and wastewater strategic planning is undertaken using a riskbased approach that utilizes both asset condition and consequence of failure to prioritize future
asset renewal needs. Water system condition assessment is based primarily on analysis of leak
data, while wastewater system condition data is based on comprehensive CCTV data.
8.14.3 Assets Considered in the Program
Water and wastewater pipeline assets.
8.14.4 Key Drivers
MWRA has a general focus on cost-effectiveness and reliability, which serve as primary
drivers for efforts to minimize asset lifecycle costs in the management of pipeline assets. Water
loss and safe yield issues are primary drivers for an extensive leak detection program.
8.14.5 Key Program Features
For the pipeline assets, CCTV inspection (wastewater) and leak detection and valve
exercising (water) programs have been the basis for condition assessment and renewal planning
programs. Highlights of these programs are described below:
8.14.5.1 Water Main Leak Detection Program
Three work crews (8 people) are assigned full time to water system leak detection, using
a combination of hand-held portable equipment (leak correlators), and continuous monitoring
acoustic equipment. The equipment is used on all MWRA water mains, which are constructed of
various materials including steel, cast iron, ductile iron, prestressed concrete cylinder pipe, and
reinforced concrete (MWRA has no plastic pipe installed).
The work crews have the goal to survey the entire system (300 miles) each year, and
survey each of the steel mains twice a year. One crew works only at night to minimize
interferences of traffic and other city noise. Magnetic ‘permaloggers’ are attached to pipes
overnight, allowing data to be uploaded remotely. The equipment can then be rotated to a
different location the next day or week, as appropriate.
8.14.5.2 Water Main Renewal Forecasting
MWRA staff have attempted to use historical leak and failure data to forecast water
system renewal needs. Statistical analyses has been performed based on correlating failures to
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-35
several factors including age, material, size, c-value, literature-based expected life, and local
factors such as known material defects, salt storage and saltmarsh locations.
Once condition scores were established, pipe redundancy (e.g. loop systems to serve
customers) was considered in renewal prioritization scoring. Since MWRA are a wholesale
provider, all retail systems (customers) were considered equally critical, and no consequence of
failure analysis was used. Results of statistical analyses were used in water system master plan
forecast of renewal needs and costs.
8.14.5.3 Wastewater Interceptor Inspection and Renewal Planning Program
MWRA has performed closed-circuit television (CCTV) inspection of its entire gravity
sewer interceptor system, and used these data to assign condition scores to each pipeline
segment. MWRA recently shifted to the NASSCO standard 1-5 rating (grading) system, but
much of their historical condition data are still in a legacy A, B, C condition rating system.
As part of master planning efforts, the pipe sections were prioritized using a scoring
approach to analyze the probability and consequence of failure. The probability-side
prioritization considered physical pipe characteristics such as age material, pipe condition rating,
etc. The consequence of failure analysis utilized GIS to determine what land area would be
negatively impacted in the event of a failure. This analysis also considered the hydraulic
vulnerability of a pipeline (based on capability to divert/bypass flow if failure occurs).
8.14.5.4 Benefits Associated with Initiatives
Specific benefits of these initiatives include:
 Experience has shown that equipment works well to identify and pinpoint location of
leaks, triggering staff to prepare a repair work order. MWRA have quantified substantial
reductions in system leaks in recent years; reported system leaks were reduced from 92
per year to 10 per year over an 8-year period.
 Systematic programs of condition assessment both improved asset/network performance
and provided the data required for undertaking strategic planning.
8.14.6 Key Lessons and Tips for Success
 As with MWRA’s RCM program, it is considered that a “program champion” is key,
whether for the overall asset management and condition assessment effort, or for the
individual condition assessment programs;
 MWRA maintains a suite of Key Performance Indicators (KPIs) that drive program
efforts; performance against the KPIs is published quarterly to the Board of Directors.
8-36
8.15
Case Study 13: CSIRO’s Assessment of a Cast Iron Transmission Main
Case Study Summary
Key issues covered in this case study include:
 The standard approach to inspection of a large diameter main using grit blasting
(removal of corrosion products using a high-pressure stream of grit and water) and
measurement of residual wall thickness.
 The use of physical failure models to assess the remaining life of the asset.
See Case Study insets 3-4 and 3-6.
8.15.1 Case Study Focus
The condition assessment of a 250 mm diameter cast iron water main. The main was
installed in the 1860s and remained unlined until 1980 when it was cement lined in-situ.
8.15.2 Assets Considered in the Program
Large diameter transmission mains constructed from cast iron.
8.15.3 Key Drivers
Five pipe failures had occurred along the main, with two failures also reported in tapping
bands.
8.15.4 Key Program Features
8.15.4.1 Asset Details
Figure 8-3 shows a typical failure for the main. The photograph shows a section of the
pipe wall was removed with two longitudinal splits. This indicates combined corrosion and
fracture failure, a failure mode that was also observed in other failed sections exhumed from the
main.
Figure 8-3. Typical Failure Mode for Cast Iron Pipe.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-37
8.15.4.2 Sampling and Inspection of Pipe
Five sections of pipe, each approximately one meter long, were exhumed by the water
utility and assessed. Each section was grit blasted to remove graphitized corrosion product and
expose the remaining metallic material. A grid pattern of 150 mm x 150 mm was then scribed on
the outer surface of each exhumed section. Exhumed sections were then cut to allow access with
calipers and the minimum remaining wall thickness in each 150 mm x 150 mm grid square
measured.
Values ranged from a maximum remaining wall thickness of 13.9 mm to minimum
values of 0 mm (indicating through wall corrosion). The scatter in residual wall thickness data
illustrates that corrosion damage is inherently uncertain and varies not only between samples, but
also across the surface of each sample.
8.15.4.3 Assessment of Condition
As outlined in the literature (Davis et al. 2004), raw data from residual wall thickness
measurement can be used to forecast failure rates in buried cast iron mains following four steps:
1)
Converting measured residual wall thickness data to corrosion rate.
2)
Quantifying variations in corrosion rate as a probability density function (PDF).
3)
Defining a physical failure model for buried cast iron pipe.
4)
Combining the corrosion rate PDF with the physical failure model for buried
pipes in a Monte Carlo Simulation of long pipelines.
3
2
1
ln (max. corr rate)
-7
-6
-5
0
-4
-3
-2
-1
-1 0
-2
-3
y = 1.6396x + 5.5431
R2 = 0.9831
Figure 8-4. Weibull Plot for Corrosion Data.
8-38
-4
-5
-6
ln(-ln(S(max. corr rate))
In this example, a survivor function (S(x)) for the measured corrosion data was calculated
and used in a Weibull plot, as shown in Figure 8-4 (a survivor function is the probability that a
variable ‘x’, in this case the maximum corrosion rate ‘max corr rate’, is greater to or equal to a
given value; see Davis et al. 2004 for more details). Since the plot was linear, it indicated that a
Weibull PDF could be used to quantify the variation in corrosion rate. This PDF was then used in
conjunction with a physical failure model to assess the propensity for asset failure. The failure
model considered both the resistance of a CI pipe as it corrodes and the applied service loads
(including internal pressure, soil dead loads and surface loads).
Expected failure rate (per km/per
year)
The outputs of the modeling study were summarized in terms of a plot that shows the
expected pipeline failure rate as the pipe ages, as illustrated in Figure 8-5.
5
4.5
4
3.5
3
2.5
2
1.5
1
Calculated failure rate
(eqs. 10) and 11))
0.5
0
0
10
20 30 40
50 60 70
80 90 100 110 120 130 140 150
Pipe age (years)
Figure 8-5. Expected Failure Rate per Year.
8.15.5 Key Lessons and Tips for Success
8.15.5.1 Technical Issues of Note
Corrosion rates vary both between pipe samples and across the surface of individual
samples.
Measurement of residual wall thickness does not in itself provide a useable metric of
asset deterioration; the results must be contextualized in terms of the asset age and the original
dimensions.
8.15.5.2Use of Economic Factors to Determine Remaining Life
The use of pipeline failure models allows the probability of failure to be constrained. In
conjunction with an evaluation of consequential impacts along the pipeline, the model can be
extended to give a quantified assessment of risk and thereby allow an investigation of economic
life to be undertaken.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-39
8.16
Case Study 14: CSIRO’s Assessment of an Asbestos Cement Force Main
Case Study Summary
Key issues covered in this case study include:
 A novel approach to assessment of an AC main using coring techniques and tensile
strength testing to assess asset deterioration.
 The use of physical failure models to assess the remaining life of the asset.
See Case Study insets 3-4 and 3-7.
8.16.1 Case Study Focus
The assessment of a 300 mm AC pressure sewer pipe, constructed in 1978.
8.16.2 Assets Considered
Large diameter pressure sewer mains constructed from AC.
8.16.3 Key Drivers
Five failures had occurred in the AC section, the first in 1986 and the last in 2004. Due to
the critical performance requirement of the pipeline in an environmentally sensitive area, there
was a need to assess the condition of the AC pipeline and assess the risk of failure.
8.16.4 Key Program Features
8.16.4.1 Soil and Asset Sampling
Soil testing was carried out at seven locations along the route of the pipeline to determine
the soil aggressiveness (pH, soil characteristics). With this data, a preliminary analysis was
carried out to identify sections with high probability of failure (hot spots). Several of those
positions were recommended for core sampling of the AC pipe.
Following the sampling, data was available in terms of soil type boundaries, soil loads,
soil sampling positions, core-sampling positions and the internal pressure extrapolated from
hydraulic analysis of the pumping main information.
8.16.4.2 Determining the Level of Deterioration
To assess the residual tensile strength of the pipe wall, each core sample was tested
according to AS 1012 (1972, Part 10, Method for Determination of Indirect Tensile Strength of
Concrete Cylinders). As shown in Figure 8-6, core samples were compressed (crosshead
movement of 50 mm per minute) by a uniformly distributed load applied along their length while
constrained at their ends. In combination with data on the age of the asset and original tensile
strength of the AC pipe, these measurements were used to give an assessment of asset
deterioration.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-40
y
x
Uniformly distributed load F/L
z
σyy
σzz
Cylinder diameter D
(constrained in axial z direction
σxx
Cylinder length L
Figure 8-6. Determining Residual Strength of the Cores.
8.16.4.3 Condition Assessment
As with the previous case study, the raw data from measurement of asset deterioration
can be used to forecast failure rates following four steps:
1)
Converting measured tensile strengths to deterioration rates.
2)
Quantifying variations in deterioration as a PDF.
3)
Defining a physical failure model for buried AC pipe.
4)
Combining the deterioration rate PDF with the physical failure model for buried
pipes in a Monte Carlo Simulation of long pipelines.
ln(-ln S(d))
In this case, a Weibull probability density derived from the Weibull plot shown in Figure
8-7 was used to quantify the variation in deterioration rate for two distinct soil environments.
This PDF was then used in conjunction with a physical failure model to assess the propensity for
asset failure. The model considered both the resistance of an AC pipe as it ages and the applied
service loads (including internal pressure, soil dead loads, and surface loads).
2
1
ln (degradation rate, d)
0
-1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
52.010-01
y = 5.7317x + 3.5472
52.010-02
R2 = 0.9709
Linear (52.010-01)
-1
0
-2
-3
Linear (52.010-02)
y = 7.6153x + 4.9025
-4
2
R = 0.9576
Figure 8-7. Weibull Plot for Deterioration Rates.
The outputs of the modeling study were summarized in terms of a plot that shows the
expected time to first failure for various loading conditions, as illustrated in Figure 8-8.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-41
prob. density f(t)
0.09
Pressure = 0.45 MPa, Cover depth = 1.23 metres, Live load = Rail Crossing
0.08
Pressure = 0.45 MPa, Cover depth = 1.18 m, Zero Live Load
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
0
10
20
30
40
50
Time to first failure t (years)
Figure 8-8. Distribution of Remaining Lives.
The results of the investigation were also summarized for the entire pipeline, as
illustrated in Figure 8-9.
Soil environment
Expected failure time (years) 52.010-01
Degradation rate
unknown
Soil environment
52.010-02
40
+ 1 std dev
35
30
25
- 1 std dev
20
15
0
500
1000
1500
Chainage (meters)
Figure 8-9. Life Time Distribution Along the Pipeline.
8.16.5 Key Lessons and Tips for Success
8.16.5.1 Technical Issues of Note
Degradation in cement-based pipelines is strongly influenced by the surrounding soil
environment and variations in relevant soil properties cause variation in pipe degradation. For
example, variations in soil pH and sulfate content can influence the degree of cement leaching
and consequent reduction in pipe wall strength (Dorn et al., 1996)
Measurement of residual tensile strength does not in itself provide a useable metric of
asset deterioration; the results must be contextualized in terms of the asset age and the original
tensile strength. Where the original tensile strength is not known, it is reasonable to adopt a
measure based on the original pipe specification given in national standards.
8-42
8.16.5.2 Use of Economic Factors to Determine Remaining Life
The use of pipeline failure models allow the probability of failure to be constrained. In
conjunction with an evaluation of consequential impacts along the pipeline, the model can be
extended to give a quantified assessment of risk and thereby allow an investigation of economic
life to be undertaken.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
8-43
8-44
APPENDIX A
UTILITY OBJECTIVES AND RELATED KPIS
The following tables show a range of utility objectives that are linked in some way to the
condition and performance of various asset types. KPIs that are used to measure performance
against utility requirements are also listed. Where there is a shortfall in a measured KPI, some
form of assessment will be required. A brief description of the assessment procedure is also
presented.
Table A-1. Objectives Related to Wastewater Assets.
Strategic objective
Invest in alleviation of flooding from sewers
KPIs
Flooding events (freq./vol)
Flooding due to
asset/equipment failures
Surcharging in sewers
Improve sewerage infrastructure to prevent
collapses
Reduce infiltration and inflow
Number of collapses
Improve sewerage infrastructure to reduce
break/choke risk
Reduce/remove unacceptable intermittent
discharges (UID)
Improve performance of sewage treatment works
Improve performance of sludge disposal assets
Address community expectations regarding odor
complaints
Measures of infiltration
Measures of inflow
Number of chokes, bursts,
leaks
UIDs at CSOs
UIDs at pumping stations
Pumping station blockages
UIDs from sanitary sewers
UIDs from combined sewers
Consent failures
Pollution incidents
Equipment failures
Biochemical oxygen demand in
relation to requirements
Suspended solids in relation to
requirements
Nutrient removal
Odor complaints
Consent failures
Measures of sludge
consistency
biosolids reuse
Number of complaints
Outline of assessment approach
Use KPIs to identify problem zones,
ideally considering all other service
drivers to ensure an integrated approach
and eventual identification of solutions
that give best value for money.
Focus in on those assets where there is
a regulatory driver or the biggest scope
for adding-value.
Select additional information required,
including CCTV etc. and undertake
analysis within each hot spot area. In
general involves a complex assessment
of hydraulic, environmental and
structural condition
assessments/modeling.
Review the works level performance of
sewage treatment works; identify
shortfalls in relation to consents,
standards and customer
complaints/expectations.
Prioritize surveys in terms of importance.
Review the works level performance and
of sludge quality/quantity, identify
problem areas and cause.
In order of serious (number of
complaints), review assets in area,
identify problem and cause.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
A-1
Table A-2. Objectives Related to Drinking Water Assets.
Strategic objective
Improve water quality
Invest in measures to reduce discolored water
complaints
Improve drinking taste and odor
Improve drinking hardness
Improve pressure of water supply to customers at
risk of low pressure
Reduce bursts
Reduce interruptions to supply
Reduce leakage; achieve and maintain a
sustainable economic level of leakage
KPI
Water quality compliance at
works
Turbidity at treatment plants
Water quality compliance at tap
Coliform compliance (works,
service reservoirs)
Iron pick up in system
Number of complaints
Outline of assessment approach
Identify problem zones through analysis
of complaints and sample data.
Undertake a program of assessments to
determine the root cause (works
capacity, pipe condition, etc.).
Preferable to combine with other service
problems to ensure an integrated
approach is taken and eventually,
interventions identified that give the best
value for money.
Bursts per unit length
Unplanned interruptions
Interruption duration
Interruption frequency
Water pumping station
performance (Mean Time
Between Failure)
Bursts per unit length
Identify problem zones/cohorts through
analysis of event and sample data.
Undertake a program of assessments to
determine the root cause
Again, preferable to combine analysis
with other service problems so as to
ensure an integrated approach is taken
and, eventually, interventions identified
that give the biggest bang for the buck.
Identify problem zones through district
meter area analysis or similar. Analyze
pipe populations to make an assessment
of the problem and undertake
assessments, active leakage control or
pressure management as appropriate.
Infrastructure Leakage Index
Leakage
Table A-3. Objectives Related to Asset Stock.
Strategic objective
Maintain asset stock at a given level of condition
and performance (maintain backlog)
KPI
Condition and performance
grade profiles
Improve asset stock condition and performance
(reduce backlog)
Condition and performance
grade profiles
A-2
Outline of assessment approach
Determine sample scheme based on
risk, capacity, environmental, financial
and other factors. Determine
condition/performance profile through
sampling.
Assess expected life within asset
cohorts; this allows a measure of the
replacement required to maintain or
improve the asset stock condition profile
to be made.
APPENDIX B
INDIVIDUAL DRIVERS FOR ASSESSMENT
The following tables list a range of individual drivers that can necessitate a utility to
undertake a program of condition and performance assessment, independently of any KPI
management approach.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
B-1
Table B-1. Drivers in Which Condition and Performance Assessment Play a Major Role.
Category
Focus
Assess/determin
e remaining asset
lives
Asset type
Any asset type.
Assess renewals
budgets and
timing of spend
Driver
Condition assessment to provide data for analysis of
asset lives and thus timing of required spend, could be
done spatially or temporally. Remaining life estimates
can also be undertaken as a risk-screening approach;
with refined assessments being specified for assets with
a 'moderate' remaining life (assets with little life
remaining will need replacing in any case, assets with
significant remaining lives can be removed from further
consideration).
Condition and performance assessment to provide data
for use in budget setting and/or justification of capital
deferment.
Any asset type.
Assessment of budget
requirements in relation
to asset lives and/or
deterioration.
Smooth renewals
spend and/or
reduce spend
Condition and performance assessment to provide data
for use in refining budgets; identifying optimal
interventions based on affordability.
Any asset type.
Optimization of
budgets in terms of
affordability.
Prioritize capital
programs
Condition and performance assessment to target
priorities for renewal spend.
Any asset type.
Assessment of budget
requirements in relation
to asset lives and/or
deterioration.
Determine
appropriate
intervention
Condition assessment to determine the level of
renovation required and specify rehabilitation approach;
selection of least whole lifecycle cost approach (partial
replacement, lining, etc.).
Any asset type,
but more likely
to be pipes.
Determine structural
condition in relation to
the needs of available
interventions.
Improve service
delivery
Assessment of condition to understand level of service
issues (including firefighting capacity), could involve
sampling in areas where service problems occur.
Any asset type.
Hot spots and causes
of service failures.
Improve system
reliability
Assessment of condition/performance to understand
non-service related shortfalls; e.g., high cost of
maintenance to prevent outages.
Any asset type.
Hot spots and causes
of asset failures.
Determine asset
stock
condition/perform
ance
Collection of condition and performance data for asset
management.
Any asset type.
Condition and
performance grades.
Prevent the
collapse of asset
stock
Demonstrating
asset
stewardship
Assessment to determine the condition of key assets.
Any asset type.
Assets in derelict state.
Condition and performance assessment to demonstrate
the overall condition and/or value of the asset stock
(condition/performance profiles by asset value).
All assets.
Determine profile of
asset condition and
performance grades.
Sewerage only.
Determine profile of
asset condition and
performance grades.
Regulatory/Financia
l Reporting
Asset Management
Develop
deterioration
curves
Comply with
CMOM
regulations
B-2
Any asset type,
but more likely
to be pipes.
Assessment
Determine level of
deterioration in relation
to expected asset life
(defined in terms of
risk).
Characterize level of
deterioration.
Focus
Financial
reporting (GASB
34 modified
approach)
Due diligence
Driver
Asset type
All assets.
Assessment
Determine profile of
asset condition and
performance grades.
Assessment of condition to understand the value of the
asset stock and financial risk exposure.
Any asset type.
Overall assessment of
asset condition and
performance.
Identify high risk
assets
Condition assessment to understand risk, given
knowledge of failure consequences.
Any asset type.
Determine condition as
a proxy for probability
of failure.
Identify/prioritize
risk management
interventions
Estimate
probability of
failure/ predicting
failure
Condition assessment to identify priorities for risk
mitigation.
Any asset type.
Condition assessment to quantify/constrain risk.
Any asset type.
Assessment of budget
requirements in relation
to asset lives and/or
deterioration.
Forensic
investigations
Condition assessment to understand failure and support
litigation.
Any asset type.
Understand causative
factors.
Understand
causes of failures
(similar to
forensic)
Risk-informed
inspection
programs
Targeted condition assessment in an attempt to
understand asset failures. Could involve sampling of
assets in similar environmental and/or operating context
to determine if at risk.
Determine current condition and consider interval for
next inspection based on assessment of risk and current
condition.
Any asset type.
Understand causative
factors relating to asset
failures.
Above ground
assets, could
be used for
some important
pipes.
Condition as an
indicator of risk and
thus time until next
inspection.
Increase
reliability
Again, similar in focus to the RCM/MO driver, but no
need for formalized approach. Attempting to find poor
condition/performing assets or components and replace
them to improve reliability and reduce direct/indirect
costs.
Above ground
assets.
Reasons for failure, hot
spots, remaining life
assessments.
Table B-2. Drivers in which Condition and Performance Assessment Play a Minor Role.
Category
Operations
Operations
Risk Management
Category
Focus
Refine RCM/MO
Driver
Assess condition/performance of components with
preventive maintenance and determine if there is scope
to modify the maintenance regime; additional preventive
maintenance could result in better
condition/performance; less maintenance could result in
cost savings, if condition/performance where not to
deteriorate.
Asset type
Above
ground
assets.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
Assessment
Level of
proactive
maintenance
given reliabilitytype issues.
B-3
Asset Management
B-4
Reduce O&M
costs
Essentially the same as RCM/MO refinement, but does
not necessarily rely on these formalized approaches
being in place. Focus in on reducing direct cost of O&M
activities, including identification of problem assets to
reduce call outs, pumping costs, etc.
Above
ground
assets.
Comprehensive
data
collection/capture
program
Asset capability
assessments
Collect data for asset management purposes, including
an assessment of condition/performance -- likely to be in
terms of grades.
Any asset
type.
Collect data and opinion on whether or not assets are
currently fit for purpose; ideally this would be a
performance assessment carried out independently of
condition, but could involve assessing if condition was
affecting ‘fitness for purpose’ (capability).
Assessment of condition and performance to
understand the impact of maintenance strategies on
asset life.
Above
ground
assets.
Improve the
management of
asset life cycle
Any asset
type.
Ideally
identification of
problem assets,
but could be a
general
assessment of
maintenance
and operational
practices in light
of costs.
Condition and
performance
grades.
Performance
grade and or
simple flag of
whether fit for
purpose.
Asset condition
in relation to
asset
management
practices.
APPENDIX C
CONDITION AND PERFORMANCE
ASSESSMENT CRITERIA
Table C-1 provides some asset observations that relate to the condition of various
categories of asset.
Note:
 (V): visual; an auditor would be able to evaluate the assessment criteria directly
(visually),
 (O): opinion based; the auditor would be able to evaluate the assessment criteria
indirectly (by interview),
 (M): measurable; the assessment criteria could be directly measured
(inspected/monitored) or assessed through analysis of available operations/maintenance
data.
Table C-1. Condition Assessment Criteria.
Asset Type
Buildings
Assessment criteria
Security (V/O)
Weatherproof/leaks (V/O)
Damp/rising damp (V/O)
Level and urgency of maintenance required (O)
Rust staining (V)
Cracking of brick work or masonry (V)
Pointing condition (V)
Broken slipped roof tiles (V)
State of woodwork; sound to rotten (V)
Structural integrity (V/M)
Serviceability; useable or not? (V/O/M)
Safety of building; considered unsafe? (V/O)
Civil assets
Soundness of structure (V/O)
Level of wear and tear (V)
Corrosion (V/M)
Level and urgency of maintenance required (O)
Presence of cracking/spalling (V)
Presence of staining (V)
Leakage (V/O)
Deformation of structure (V/M)
Safety of structure; considered unsafe? (V/O)
Contamination of potable water (O/M)
Electrical assets
Electrically safe (O/M)
Level and urgency of maintenance required (O)
Visible wear and tear (V)
Condition of insulation (V/M)
Break downs and failure history (M)
Maintenance costs (M)
Health and safety issues (V/O)
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
C-1
Asset Type
Assessment criteria
Serviceability (V/O/M)
Mechanical assets
Soundness of unit; as new? (V)
Level and urgency of maintenance required (O)
Level of wear and tear (V)
Condition of protective coatings (V/M)
Corrosion (V/M)
Break down and failure history (M)
Maintenance costs (M)
Serviceability (V/O/M)
Health and safety issues (V/O)
Sewers
Cracking (V)
Fractures (V)
Deformation (V/M)
Loss of fabric; including mortar loss, brick displacement, etc. (V)
Joint/connection defects (V)
Loss of level (V/M)
Water mains
Smoothness of bore/tuberculation (V)
Level of corrosion (V/M)
Soundness of lining (V/M)
Operational history; bursts, etc. (M)
Levels of service (V/O/M)
Operating costs (M)
Presence of deposits (M)
Design regarding current standards (O)
C-2
Table C-2 provides some asset observations that relate to the performance of various
categories of asset.
Note:
 (V): visual; an auditor would be able to evaluate the assessment criteria directly
(visually).
 (O): opinion based; the auditor would be able to evaluate the assessment criteria
indirectly (by interview).
 (M): measurable; the assessment criteria could be directly measured
(inspected/monitored) or assessed through analysis of available operations/maintenance
data.
Table C-2. Performance Assessment Criteria.
Asset Type
Buildings
Assessment criteria
Adequacy for current and foreseeable use; size, location, facilities;
current/anticipated shortcomings (O)
Operational security
On-site standby capacity (V/O)
Mobile standby capacity and availability (V/O)
Number of grid supplies (V/O)
Level of manning (V/O)
Level of monitoring and control (V/O)
Level of telemetry (V/O)
Fail-safe systems (V/O)
Operational response capacity (V/O)
Risk (or history) of consent/quality failure (M)
Risk (or history) of service failure (M)
Control and monitoring equipment
Capacity to meet current and future requirements; current/anticipated
shortcomings; needs to consider hardware and software (O)
General performance grades
Hydraulic adequacy at all flows (O/M)
Process capacity at all flows (O/M)
Process stability; ability to control (O)
Headroom with respect to inefficiencies in upstream/downstream
processes (O/M)
Distribution between and within assets (V/O)
Level of mixing (V/O)
Process retention times (O/M)
Adequacy for current and foreseeable use (O)
Sewers
Service measures (M)
Water mains
Service measures (M)
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
C-3
Asset Type
Raw water storage
Assessment criteria
Flexibility of draw-off arrangements (O)
Susceptibility to eutrophication (O/M)
Effectiveness of circulation/de-stratification (O)
Effectiveness of scour valves (O)
Control of compensation volumes? (O)
Raw water intakes
Hydraulic adequacy at all flows (O/M)
Pump capacity (V/O)
Pump standby capacity (V/O)
Siltation (O/M)
Exclusion of surface films/slicks (O)
Gross solid/screenings removal (O)
Ease of well isolation and impact on capacity (O)
Ground water source
Hydraulic adequacy at all flows (O/M)
Draw down at maximum pumping capacity (O/M)
Pump capacity with respect to license (O)
Turbidity issues (O/M)
Cavitation issues (O)
Air entrainment issues (O)
Protection from surface contamination (O/M)
Ease of well isolation and impact on capacity/quality (O/M)
Pre-treatment
Hydraulic adequacy at all flows (O/M)
Capacity of process with respect to loads and required standards (O/M)
Distribution of flows over weirs (V/O)
Chemical dosing plant
Ability to dose at all flow rates (O/M)
Quality of control; automatic/manual (V/O)
Level of storage (O)
Frequency of blockages of dosing lines (O/M)
Effectiveness of delivery area drainage (O)
Ability to handle changes in raw water quality (O/M)
Hydraulic adequacy at all flows (O/M)
Capacity of process with respect to loads and required standards (O/M)
Efficiency and distribution of air saturated water (V/O)
Effectiveness of surface skimmer (O)
Degree of solids depositions (O)
Dissolved air flotation
Sludge blanket clarifiers
Hydraulic adequacy at all flows (O/M)
Capacity of process with respect to loads and required standards (O/M)
Degree of mixing and flocculation retention prior to tank (O/M)
Ability to maintain a stable sludge blanket (O)
Efficiency of sludge remove facilities (O)
Degree of turbidity and Ph measurement (V/O)
Solids carry over (O)
Water filtration
Ability to ‘buffer’ poor clarification (O)
Capacity of process with respect to loads and required standards, including
with units off-line (O/M)
Ability to achieve filter run-times (O/M)
Presence/absence of turbidimeter (V/O)
Quality of control (O)
Quality of backwash (O)
Signs of media growth (O/M)
C-4
Asset Type
Assessment criteria
Chlorination/dechlorination
Specification of installation; telemetry, triple validation chlorine residual
monitors, chlornine-time values and mixers, etc. (O)
Control of residuals at all flow rates (M)
Wash Water and Sludge Disposal
Effectiveness of wash water settlement facilities (O)
Quality of supernatant water produced with respect to consent standards
(M)
Effectiveness of sludge withdrawal and consolidation facilities (O)
Facility to divert returned supernatant (O)
Effectiveness of sludge dewatering (M)
Degree of automation (V/O)
Distribution pumping/boosting
Hydraulic output capacity (M)
History or risk of service impacts; pressure or interruptions (M)
Secondary disinfection
Specification of installation; telemetry, triple validation chlorine residual
monitors, chlorine-time values and mixers, etc. (O)
Control of residuals at all flow rates (M)
Sewage force mains
Hydraulic adequacy at all flows, including storm (O/M)
Appropriate velocity maintained (O/M)
Ease of access for maintenance (O)
Septicity problems (O)
Sewage Pump Stations (including in let works
pumping station)
Hydraulic adequacy at all flows (O/M)
Capacity of pumps with respect to loads (O/M)
Standby capacity (V/O)
Capacity of sump and storm tanks (O/M)
Ease of access for maintenance and emergency tinkering (O)
Capacity to handle solids/rags (O)
Blockage history (M)
Service history with respect to upstream flooding or premature overflow
(M)
Overflow history with respect to events, loads, consent, and environmental
impact (M)
Service history with respect to odor and noise (M)
Telemetry/alarms
Inlet works
Hydraulic adequacy at all flows (O/M)
Overtopping of screens and grit channel (O)
Efficiency of screenings washing, dewatering, handling equipment (O)
Return of organics to flow; from grit removal (O)
Efficiency of grit removal (O/M)
History of blockages (M)
Suitability of screen size (O)
Spillage inside and outside of structure (O/M)
Storm tanks
History of discharge to overflow with respect to events, loads, consents
and environmental impact (M)
History of complaints (M)
Return arrangements (automatic?) and impact on downstream processes
(O/M)
Requirement for tank cleaning after use (O)
Overtopping of structure (O)
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
C-5
Asset Type
Primary settlement
Assessment criteria
Hydraulic adequacy at all flows (O/M)
Carry over of solids (O)
Efficiency of scum trapping and removal (O)
Efficiency of sludge removal (O)
Adequacy of sludge thickness (M)
Presence of rising sludge, septicity or rising gases (O)
Impact on inlet or outlet channels (O)
Flow distribution over weirs and between units (V/O)
Biological filters
Condition of media; blockages, etc. (O/M)
Distribution and ventilation (O)
Occurrence of ponding (O)
Ability to ‘buffer’ inefficient primary settlement stage (O)
Condition of film (/M)
Impact on downstream processes (O/M)
Odor problems (O/M)
Humus tanks
Carry over of solids at all flows (O)
Efficiency of scum trapping and removal at all flows (O)
Efficiency of sludge production (required thickness) and removal (O/M)
Presence of rising sludge, septicity or rising gases at all flows (O)
Clarity of effluent (O/M)
Backing up of inlet and outlet channels (O)
Flow distribution between weirs and units (V/O)
Impact on downstream processes (O/M)
Activated sludge plant
Hydraulic adequacy at all flows (O/M)
Efficiency of mixing of settled sewage and returned activated sludge (RAS)
(O)
Distribution of air/oxygen (O/M)
Efficiency of aeration control (O/M)
Ability to ‘buffer’ inefficient or over-loaded primary settlement stage (O/M)
Ease of maintenance of mixed liquor suspended solids (O/M)
Impact on works performance and downstream processes (O/M)
Final tanks and RAS pumps
Hydraulic adequacy at all flows (O/M)
Carry over of solids (O)
Ability to ‘buffer’ inefficient or over-loaded upstream processes (O)
Efficiency of scum trapping and removal (O)
Presence of rising sludges, gases or septicity (O)
Control of RAS and surplus sludges (O)
Backing up of inlet/outlet channels (O)
Flow distribution over weirs V/O)
Clarity of effluent (O/M)
Tertiary treatment
Ability to buffer inefficient or over-loaded upstream processes (O)
Clarity/quality of effluent (O/M)
Adequacy of run times for solids filters (O/M)
Efficiency of backwash/solids removal (O)
Signs of media growth (O/M)
Effectiveness (channeling of flow) and condition of grass plots and reed
beds (V/O)
Sludge reception and screening
Sufficiency of reception capacity with respect to economic tankering,
considering normal demands and breakdowns/operational problems (O)
Efficiency of sludge screens and handling equipment (O)
C-6
Asset Type
Assessment criteria
Occurrence of downstream problems or blockages from screenings (O/M)
Ease of control/operation (O)
Sludge holding and consolidation tanks
Sufficiency of buffer holding capacity regarding economic tank sizing,
considering normal demands and breakdowns/operational problems (O)
Consolidation regarding percent dry solids target (M)
Ease of control/operation (O)
Occurrence of blockages (M)
Environmental impacts (M)
Complaints (M)
Sludge presses and mechanical thickening
Consolidation regarding percent dry solids target (M)
Effectiveness of sludge feed and output equipment (O)
Consistency of sludge production (O/M)
Ease of control/operation (O)
Occurrence of blockages (O/M)
Sludge digestion
Consistency of sludge production (O)
Stability of sludge (O/M)
Adequacy of retention times (O)
Efficiency of circulation, mixing, gas collection and holding, heating and
heat exchange (O)
Ease of control/operation (O)
Occurrence of blockages (O/M)
Environmental impacts (M)
Complaints (M)
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
C-7
C-8
APPENDIX D
A GENERIC CONDITION ASSESSMENT FORM
FOR MECHANICAL AND ELECTRICAL EQUIPMENT
ASSET DETAILS
Asset Name:
Asset Type: (Pump, Blower, MC
Location:
Asset Age:
COMPASS No.:
Asset No.:
Date of Inspection:
Inspector:
Output Requirements: (flow, temperature,etc)
Reference W ork Orders: (as a result of a PM, CM)
C, Motor)
CONDITION CODE (check one which best describes the assets current condition)
___ Excellent
(no noticeable defects, no reason to expect failure, PMs being done, new asset)
___ Satisfactory
(minor defects/wear, low possibility of failure, Some PMs being skipped, )
___ Poor
(significant defects/wear, high probability of failure, heath/safety issue, Not being PM'd)
___ Failed
(excessive defects/wear, unit is in a failed state/inoperable)
FAILURE MODES (check all that apply)
___ Coating Failure/Rust/Corrosion
___ Vibration/Excessive Noise
___ Excessive Heat/Hot to Touch
___ Fluid Leaks/Drips
___ Unit Failed
___ Reduced Output/Capacity
___ Lack of Lubricant/Zirk Fittings Dirty
___ Design Issue
CORRECTIVE ACTION (Check one)
___ Corrective Maintenance Work Order (Minor Repairs)
___ By Elect. ___ By Mech. ___ By Instr
___ Engineering/Construction Project
___ Candidate for PdM Program (oil analysis, vibration, IR)
___ Instrument/Control Failure
___ Other: ________________
Comments: ___________________________________
_____________________________________________
_____________________________________________
_____________________________________________
CORRECTIVE ACTION PRIORITY (Check one)
___ Low (PM program adequately covers asset, high level of redundancy, consequence/cost of failure is low)
___ Med (Can be covered in upcoming upgrade/project, minimal level of redundancy, consequence/cost of failure > $10k)
___ High (Health/Safety issue, failure < 1 year, secondary damage possible, immediate CM needed, beyond useful life)
CORRECTIVE ACTION BENEFITS (Check all that apply)
___ Continue to maintain output/service levels
___ O&M Cost Savings due to energy savings
___ Other: ____________________________________
___ Process/operational improvements
___ Extend Asset Life
MAINTENANCE RECORDS (Check all that apply)
___ PM History Available
___ PM Being Done
___ PMs Being Skipped
___ CM Count High
___ List PM Job Plans (this might be something we'd like to review on the first Condition Assessment as part of a PM
Optimization process. Print the Job Plans from COMPASS out with the CA Inspection Form. Some
automation would be required.
PM Job Plans (Tasks and Frequency here)
CONDITION ASSESSMENT WORK ORDER DETAILS (Complete ALL Prior to Closing IPM - Required Fields)
Time to complete inspection - _____ minutes/hours
Name of Inspector: ______________
Date: _____________
Re-inspection required ( Y / N ) (CA Priority 1 only) within _____ days / months
Inspection PM data entered into COMPASS system on ____________________(date) by __________________________
Comments: __________________________________________________________________________________________
____________________________________________________________________________________________________
____________________________________________________________________________________________________
Form prepared for the Washington Suburban Sanitation Commission’s ‘Industrial Assets Management Group’
by John W. Fortin; PSC member and Asset Management Consultant.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
D-1
D-2
APPENDIX E
DEVELOPMENT OF A PROTOTYPE EXPERT SYSTEM
Overview of Expert Systems
An expert system (ES) is a software tool that attempts to simulate the reasoning applied
by a human expert. The ES contains a knowledge base, a set of questions and a logical rule set,
which are used to guide a non-expert through the diagnosis of a problem. ES have been widely
applied in a number of areas, including assisting in medical diagnosis, computer troubleshooting
and product selection.
A well-designed ES provides the non-expert with an intuitive process for assessing a
problem. However, the usefulness of an ES is limited by the difficulty of representing the
knowledge, experience and logic of a human expert with a computer program. This inherent
limitation means an ES is often used as a first cut approach, which focuses attention on the range
of likely options. For example, in the context of this research, the output from an ES could be
used prior to more detailed analysis, which would include an economic analysis of useable
options and consideration of specific operational requirements.
Design of the Expert System
As noted above, a prototype ES was designed with the objective of enabling the selection
of technically viable condition or performance assessment tools that are appropriate to the
operational context. To achieve this, the ES designed for this project implemented the selection
logic detailed in Chapter 6.0, Sections 6.2 and 6.3. However, the process was modified to reflect
the way in which an expert would ask questions relating to the tool selection, based on its
intended use and utility preferences.
In line with the exclusion procedure detailed earlier, there are three distinct stages to the
selection process, which for the purposes of the ES implementation are summarized as follows:
 Technical selection: Questions that narrow the selection of possible tools and techniques
to those tools and techniques that are technically feasible.
 Operational selection: Questions that focus on the context of the assessment, which
includes data availability, asset accessibility and importance to the network.
 Utility preferences: Questions that identify the preferences and the characteristics of the
utility to undertake the assessment, which includes availability of technical skills,
commercial status and level of technical support for the tool or technique.
Figure D-1 provides a conceptual overview of the pathways that can be taken through the
ES. The pathway the user follows is dependent on the purpose and focus of the assessment. As
Figure D-1 shows, there are a number of key divergent points that separate pathways through the
ES on the basis of factors such as service type, assessment, asset type, assessment focus, utility
characteristics and operational context.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
E-1
Expert System Implementation
A prototype ES was developed within the commercial package Expert System Builder
(http://www.esbuilder.com/). This software package was selected because it is shareware and
thus low cost. However, while suitable for a prototype version, the package has a number of
limitations. The most significant limitation is the inability to exclude options on the basis of
user’s response to specific questions. For example, if the user indicates that only tools relevant to
inspection of wastewater assets are of interest, then tools specific to drinking water assets are
assigned a negative score, but are not removed from further consideration. However, the
software package still provided an efficient way to rapidly develop a prototype ES that
demonstrates the functionality and usefulness of the approach.
52H
An ES contains a knowledge base, a set of questions and a logical rule set. Expert System
Builder has three modules that help to capture these components of the ES:
 Question editor: This module develops the structure of the questions to be used in
distinguishing between feasible and unfeasible options. A key feature is the ability to
create reliance so that the asking of a particular question is reliant on a response from a
previous question. This ensures that only appropriate questions are asked. For example, if
a user indicates focus on non-pipeline assets, all other questions related to pipelines are
not asked.
 Knowledge acquisition: This module builds a database of knowledge that is used within
the ES. The knowledge acquisition process involves answering each of the questions for
each potential option. This process involves assigning a score for every possible question
response. For example, if the option was Barcol Hardness test and the question related to
granularity of assessment (the level within the asset stock the assessment is undertaken),
then a response indicating the user was focused on network-wide assessment would be
scored -10, while a response indicating the focus was asset specific would be scored +10.
A “don’t know” response has a neutral impact with a score of 0 assigned.
 User interface: The final module brings together the question file and the knowledge
database within a user interface. The interface enables the user to navigate through the ES
and input responses to each question. As the user moves through the ES, the scores for
each question are aggregated. This combined score is then used to rank all options and
identify the most appropriate tool or technique. The output result for the user is a list of
all options ranked by confidence interval, with the most suitable options at the top of the
list.
E-2
Figure D-1. Conceptual Overview of Pathways in the Tool Selection Expert System.
The following principles were applied in developing the ES prototype questions:
 Keep questions to a minimum and focus only on critical factors. Redundant questions
were avoided; if the question did not narrow down the selection it was removed.
 Allow questions to be by-passed. If the user in unsure or does not have sufficient
knowledge then they can move to the next question.
 Weighting of questions. Weighting was applied to ensure that critical questions had the
greatest influence on the outcome.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
E-3
E-4
APPENDIX F
REVIEW OF CONDITION ASSESSMENT
TOOLS AND TECHNIQUES
Introduction
This Appendix presents summary reviews of 85 condition assessment tools and
techniques identified during the research.
As noted in Chapter 1 - Introduction of the report, a first pass assessment of the tools
and techniques used for condition and performance assessment in various sectors was made in
Phase 1 of the project. This was achieved through a review of literature and other information
sources relating to asset management and condition assessment tools and techniques. Draft
summaries of relevant tools were written and incorporated into the preliminary report.
The summaries were then sent out to a range of industry professionals for peer review
during Phase 2 of the project. A data collection spreadsheet that detailed all of the tools and
techniques identified in the project was also sent to each reviewer. The reviewers were asked to
use the spreadsheet to confirm the applicability of tools included on the list and to add any
additional tools that were used by or known to them.
The scope of this peer review exercise was entirely dependent on the goodwill of the
reviewers. Given this fact, the response was considerable, and the project team would like to
acknowledge the kind assistance of the following individuals:
Aidan O'Donoghue
Alan Watts
Alan Whittle
Ashok Sharma
Axel Konig
Balvantrai Rajani
Barry Allred
Bill Nadeau
Brian Mergelas
Dan Skorcz
David Alleyne
David Ellis
Doug Crice
Duncan Massie
Farshad Ibrahimi
Gerald Gangl
Gordon Burr
Greg Johnston
Greg Moore
Jayantha Kodikara
Jim Cull
John De Grazia
Kevin Laven
Leif Wolf
Marcus Hitzel
Mark Heathcote
-
Pipeline Research Limited
South East Water Limited
Iplex Pipelines
CSIRO
SINTEF
National Research Council Canada
Ohio State University
Corvib
the Pressure Pipe Inspection Company
Pacific Tek Inc.
Guided Ultrasonics Ltd
South Australian Water Corporation
Wireless Seismic Inc.
Monash University
City West Water
Graz University of Technology
South East Water limited
Sensors & Software Inc.
South Australian Water Corporation
Monash University
Monash University
Melbourne Water
the Pressure Pipe Inspection Company
Universität Karlsruhe
Inspector Systems
PIPA
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-1
Matthew Poulton
Mike Lowe
Nicola Telcik
Philip Ferguson
Raimund Herz
Richard Bonds
Sveinung Sagrov
Tristan Day
Wayne Ganther
Yves Legat
F-2
-
Cemagref
Imperial College London
YVW
Earth Tec
Technische Dresden Universität
Ductile Iron Pipe Research Association
SINTEF
Austeck Pty Ltd
CSIRO
Cemagref
Table of Contents
Introduction.................................................................................................................................. 1
F1.0
Acoustic Emission ....................................................................................................... 5
F2.0
Active Acoustic Inspection .......................................................................................... 9
F3.0
Air Permeability......................................................................................................... 11
F4.0
AQUA-Selekt............................................................................................................. 15
F5.0
AQUA-WertMin ........................................................................................................ 17
F6.0
AwwaRF’s Manager Software................................................................................... 20
F7.0
Barcol Hardness Test ................................................................................................. 22
F8.0
Broadband Electromagnetic....................................................................................... 25
F9.0
Carbonation Testing and Petrographic Examination ................................................. 28
F10.0
CARE-S ..................................................................................................................... 31
F11.0
CARE-W.................................................................................................................... 34
F12.0
CCTV Inspection ....................................................................................................... 37
F13.0
Concrete Electrical Resistance (Resistivity).............................................................. 41
F14.0
Condition Assessment of Plastic Pipes ...................................................................... 44
F15.0
Core/Coupon Sampling.............................................................................................. 47
F16.0
Corrosion Burial Testing............................................................................................ 49
F17.0
Cover Meter - Reinforcement Location & Measurement .......................................... 51
F18.0
Crack Measurement Tools ......................................................................................... 53
F19.0
Current Monitoring .................................................................................................... 55
F20.0
Cut-out Sampling ....................................................................................................... 57
F21.0
Drop Test ................................................................................................................... 59
F22.0
Ductor (Micro Ohm Resistance) Testing................................................................... 61
F23.0
Electrical Potential (Half Cell) Measurement of Concrete Reinforcement ............... 63
F24.0
FailNet-Reliab............................................................................................................ 67
F25.0
FailNet-Stat ................................................................................................................ 69
F26.0
Fiberscope Inspection ................................................................................................ 71
F27.0
Fracture Toughness (C-Ring) Testing ....................................................................... 74
F28.0
Ground Penetrating Radar (GPR) .............................................................................. 77
F29.0
Holiday Detector........................................................................................................ 81
F30.0
Hydraulic Modeling ................................................................................................... 85
F31.0
Impact Echo Testing .................................................................................................. 88
F32.0
Indirect Tensile Strength Testing............................................................................... 92
F33.0
Infiltration and Inflow – Sewer Flow Survey ............................................................ 94
F34.0
In-Pipe Acoustic Inspection Tools (Sonar)................................................................ 97
F35.0
In-Pipe Hydrophones ............................................................................................... 101
F36.0
Insulation Test.......................................................................................................... 103
F37.0
Intelligent Pigs ......................................................................................................... 105
F38.0
KANEW................................................................................................................... 109
F39.0
KureCAD ................................................................................................................. 112
F40.0
Leak Detection ......................................................................................................... 114
F41.0
Linear Polarization Resistance of Soil (Soil LPR) .................................................. 117
F42.0
Load Rejection Tests................................................................................................ 119
F43.0
LPR for Corrosion Monitoring ................................................................................ 121
F44.0
Magnetic Flux Leakage............................................................................................ 124
F45.0
Man Entry Inspection............................................................................................... 128
F46.0
Measurement of Strain............................................................................................. 131
F47.0
Methylene Chloride Gelation Assessment............................................................... 136
F48.0
Motor Circuit Analysis ............................................................................................ 139
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-3
F49.0
F50.0
F51.0
F52.0
F53.0
F54.0
F55.0
F56.0
F57.0
F58.0
F59.0
F60.0
F61.0
F62.0
F63.0
F64.0
F65.0
F66.0
F67.0
F68.0
F69.0
F70.0
F71.0
F72.0
F73.0
F74.0
F75.0
F76.0
F77.0
F78.0
F79.0
F80.0
F81.0
F82.0
F83.0
F84.0
F85.0
F-4
Multi-sensor Pipe Inspection Robots ....................................................................... 141
Oil Testing ............................................................................................................... 145
On-Line Leak Detection Systems ............................................................................ 149
PARMS-Planning .................................................................................................... 151
PARMS-Priority ...................................................................................................... 154
Passive Acoustic Inspection of Pipes (Acoustic Emission)..................................... 157
Performance Testing of Rotating Machinery........................................................... 160
Phenolphthalein Indicator (Carbonation Testing).................................................... 163
Pipe Potential Surveys ............................................................................................. 166
PiReP/PiReM ........................................................................................................... 169
Pit Depth Measurement............................................................................................ 171
Process Control Systems (Integrated)...................................................................... 174
Pull-off Adhesion Testing........................................................................................ 176
Radiographic Testing ............................................................................................... 180
Remote Field Eddy Current (RFEC and RFEC/TC Tools) ..................................... 183
Schmidt Hammer ..................................................................................................... 187
SCRAPS (Sewer Cataloging, Retrieval and Prioritization System) ........................ 190
Slow Crack Growth Resistance of PE Pipes............................................................ 193
Smart Digital Sewer Pipe Diagnostic System (VTT) .............................................. 196
Smoke Testing ......................................................................................................... 198
Soil Characterization................................................................................................ 200
Soil Corrosivity........................................................................................................ 204
Soil (Electrical) Resistivity ...................................................................................... 207
Thermographic Testing............................................................................................ 210
Transformer Circuit Protection Coordination and Protection Relays...................... 212
Transient Earth Voltage (TEV)................................................................................ 215
Ultrasonic Emission Inspection ............................................................................... 217
Ultrasonic Measurements; Continuous (Guided Wave) .......................................... 220
Ultrasonic Measurements; Discrete ......................................................................... 223
UtilNets .................................................................................................................... 228
Valve Exercising...................................................................................................... 231
Vibration Analysis ................................................................................................... 234
Visual Inspection (Pipes) ......................................................................................... 237
WARP ...................................................................................................................... 239
WRc Sewer Rehabilitation Manual ......................................................................... 242
WRc Trunk Main Structural Condition Assessment Approach............................... 246
Volumetric X-Ray or Radiographic Testing............................................................ 249
F1.0 Acoustic Emission
F1.1 Overview
Acoustic emissions are transient elastic waves that are generated by the rapid release of
strain energy from within a material. A common source of acoustic emission is the sudden
appearance or propagation of a microscopic crack within a material under load.
Material defects such as cracks, pits and gas bubbles act as local stress concentrators
that promote crack propagation. Acoustic emissions indicate the presence of these material
defects. Frequent acoustic emissions are an indication that there are numerous points of high
stress concentration, and that the material is approaching failure. Other sources of acoustic
emission that do not involve material failure include active corrosion, cavitation of pumps, delamination of a composite material, turbulent flow through a leak in a pressure vessel and
phase transformation of a monolithic material.
Acoustic emissions can be detected by a sensor and recorded. In this way, acoustic
emission monitoring can be used as a non-destructive method of condition monitoring. The
frequency of acoustic emissions can be increased by placing a structure under a higher than
normal stress (load). Acoustic emission testing can thus be used to gather additional
information where a structure is tested under high loads for another reason, for example,
factory acceptance testing of pressure vessels.
F1.2 Main Principles
Acoustic emission testing is different to ultrasound testing (see reviews of ultrasonic
techniques for more information), which involves sending an ultrasound signal into a material
and measuring any echoes produced. In contrast, acoustic emission testing involves measuring
the signals that are generated from within the material itself. Each acoustic emission is a unique
real-time event, for example, caused by a crack expanding and cannot be exactly repeated.
Acoustic emission instrumentation typically includes the following items:
♦ A sensor.
♦ A preamplifier and/or a postamplifier.
♦ Signal processing electronics for feature extraction and waveform capture.
♦ A microprocessor and a digital signal processor.
♦ Acoustic emission analysis software.
An acoustic emission sensor is a transducer, typically constructed of a piezoelectric
material. Most sensors measure in the ultrasonic frequency range between 20 kHz and
1 MHz. However, sensors outside this range are commercially available. Strongly attenuating
materials, such as concrete and masonry, are monitored at lower frequencies while metals,
polymers and composite structures are monitored at higher frequencies. Acoustic emission
sensors typically have a diameter and depth of approximately one inch. The sensors can be
attached to the material or structure under analysis using either magnetic hold-downs, a
couplant layer or thick glue.
Since the output voltage of an acoustic emission sensor is very small, a preamplifier or
a postamplifier should be connected to the sensor output. The amplifier output should be
connected to signal processing equipment, typically a computer with the relevant software or a
purpose-built hand held instrument for acoustic emission testing.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-5
The intensity of an acoustic emission event will decrease as the distance from the
source increases. By setting up several sensors on the structure and by knowing the attenuation
properties of the material, the location of the acoustic emission source can be determined.
F1.3 Application
Acoustic emission testing is most commonly used for detecting and locating material
defects in pressure vessels, storage tanks, pipes, heat exchanges, aerial lift devices and welded
joints.
Many other applications for acoustic emission testing are currently being researched
and developed. One example is the local, long-term monitoring of civil engineering structures
such as bridges and pipelines. Acoustic emission testing of glass-fiber reinforced parts, such as
fan blades, is also becoming more common.
A number of standards reference this technique for a variety of products ranging from
small parts to pressure vessels.
♦ ASTM-E1067-96, ASTM-E1106-86(1992)e1, ASTM-E1118-95, ASTM-E1139-97,
ASTM-E1211-97, ASTM-E1419-96, ASTM-E1781-98, ASTM-E1888-97, ASTME1930-97, ASTM-E1932-97, ASTM-E569-97, ASTM-E650-97, ASTM-E749-96,
ASTM-E750-98, ASTM-E751-96, ASTM-E976-98, ASTM-F1430-98, ASTM-F179798, ASTM-F914-98.
♦ AAR Procedure for AE Evaluation of Tank Cars and IM101 Tanks.
♦ ASME V, Article 12, Acoustic Emission Examination of Metallic Vessels During
Pressure Testing.
♦ SPI Recommended Practice for Acoustic Emission Testing of Fiberglass Reinforced
Plastic Resin (RP) Tanks/Vessels.
F1.4 Practical Considerations
♦ A trained operator is required to carry out acoustic emission inspections.
♦ The equipment is commercially available.
♦ In many applications, acoustic emission testing requires that a load be put on the asset.
For piping and tanks this is normally achieved by over pressurization by 10%.
F1.5 Advantages
♦ The ability to observe the creation and growth of material defects within a material over
the entire load history of the structure (with permanently placed sensors).
♦ Testing does not need to disturb the structure/specimen.
F1.6 Limitations
♦ Only qualitative estimates of material damage and failure predictions are possible.
♦ Environments are often noisy and the acoustic emission signals are weak so
distinguishing noise from the measurements can be difficult.
F-6
Table F-1. Summary Acoustic Emission.
Technical
selection
Criteria
Assets covered
Material
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Utility technical
capacity
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Economic
factors
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Pipes, aerial lift devices, pressure vessels,
storage tanks.
Concrete, masonry, metals, polymers,
composites.
Potable and wastewater.
None.
None.
None.
Continuous in time and space.
Non-destructive.
Tests can be undertaken while the asset is online.
Material defects.
Acoustic emission remote monitoring equipment
is commercially available.
Commercially available acoustic emission
equipment is readily available from a limited
number of suppliers.
Widely used in other sectors.
Qualitative estimates.
Only through further inspection of components.
Generic approach.
A trained operator is required. Training and
certification courses are commercially available.
A straightforward acoustic emission instrument
hardware design includes a transducer,
preamplifier, bandpass filter, amplifier and
several digital signal processors.
Refer to the Standards listed.
Commercially available.
Depends on application.
Depends on application.
F1.7 Bibliography
1. AAR Procedure for AE Evaluation of Tank Cars and IM101 Tanks.
2. ASME V, Article 12, Acoustic Emission Examination of Metallic Vessels During Pressure
Testing.
3. ASTM-E1067-96 Standard Practice for Acoustic Emission Examination of Fiberglass
Reinforced Plastic Resin (FRP) Tanks/Vessels.
4. ASTM-E1106-86(1992)e1 Standard Method for Primary Calibration of Acoustic Emission
Sensors.
5. ASTM-E1118-95 Standard Practice for Acoustic Emission Examination of Reinforced
Thermosetting Resin Pipe (RTRP).
6. ASTM-E1139-97 Standard Practice for Continuous Monitoring of Acoustic Emission from
Metal Pressure Boundaries.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-7
7. ASTM-E1211-97 Standard Practice for Leak Detection and Location Using SurfaceMounted Acoustic Emission Sensors.
8. ASTM-E1419-96 Standard Test Method (STM) for Examination of Seamless, Gas- Filled,
Pressure Vessels Using Acoustic Emission.
9. ASTM-E1781-98 Standard Practice for Secondary Calibration of Acoustic Emission
Sensors.
10. ASTM-E1888-97 STM for Acoustic Emission Testing of Pressurized Containers Made of
Fiberglass Reinforced Plastic with Balsa Wood Cores.
11. ASTM-E1930-97 STM for Examination of Liquid Filled Atmospheric and Low Pressure
Metal Storage Tanks Using Acoustic Emission.
12. ASTM-E1932-97 Standard Guide for Acoustic Emission Examination of Small Parts.
13. ASTM-E569-97 Standard Practice for Acoustic Emission Monitoring of Structures During
Controlled Stimulation.
14. ASTM-E650-97 Standard Guide for Mounting Piezoelectric Acoustic Emission Sensors.
15. ASTM-E749-96 Standard Practice for Acoustic Emission Monitoring During Continuous
Welding.
16. ASTM-E750-98 Standard Practice for Characterizing Acoustic Emission Instrumentation.
17. ASTM-E751-96 Standard Practice for Acoustic Emission Monitoring During Resistance
Spot-Welding.
18. ASTM-E976-98 Standard Guide for Determining the Reproducibility of Acoustic Emission
Sensor Response.
19. ASTM-F1430-98 STM for Acoustic Emission Testing of Insulated Aerial Personnel
Devices with Supplemental Load Handling Attachments.
20. ASTM-F1797-98 STM for Acoustic Emission Testing of Insulated Digger Derricks.
21. ASTM-F914-98 STM for Acoustic Emission for Insulated Aerial Personnel Devices.
22. SPI Recommended Practice for Acoustic Emission Testing of Fiberglass Reinforced Plastic
Resin (RP) Tanks/Vessels.
F-8
F2.0 Active Acoustic Inspection
F2.1 Overview
This non-destructive technique uses the transmission of sound to assess defects in the
structure of pipes; generally of cementituous materials. A known force is imparted to the asset
and sensors measure the response. Cracks, delamination and other discontinuities affect the
transmission of sound. Generally damaged pipes will display lower wave speeds and propagate
less energy to the sensors. Depending on the response, the assessor can thus identify if the asset
has cracks and other defects.
F2.2 Main Principles
The active acoustic inspection tool consists of a means of imparting sound energy and
sensors to detect that energy.
An impact, generally from a steel ball, is used to impart sound energy which propagates
along the asset’s length. Sensors are placed to detect the sound propagated. Assets with defects
such as crack or voids will experience some reflection of the sound reducing the energy that
reaches the sensors.
F2.3 Application
Active acoustic inspection is applied to cementituous pipes to identify cracks,
delamination, or other defects. It can be used to assess wire breaks, delamination and cracks in
pre-stressed cylinder concrete pipe (PCCPs).
♦ No ASTM or ISO standards were identified for this application.
F2.4 Practical Considerations
♦ The technique is also known as seismic pulse echo.
♦ Active acoustic inspection is widely used in many industries for inspecting concrete
assets. As such it is fully commercialized. This method relies heavily on operator skill,
but is probably the most commonly used NDE inspection technique used for
cementituous pipes.
♦ The tools are portable and the approach relatively easy to use. The output is a
qualitative assessment indicating the presence of pipe defects.
♦ Manual inspection is most sensitive to defects near the inside diameter, and prone to
missing defects near the outside diameter of the pipe. This is a problem for inspecting
PCCPs, but is especially problematic when inspecting pre-cast, post-tensioned pipe, as
a common failure mechanism in this pipe type is failure of the tensioning metal by
outside diameter corrosion, and this damage is difficult to detect manually.
♦ Both inside diameter and outside diameter defects can be more readily detected using
instrumented testing.
♦ The asset must be exposed prior to inspection to allow access to points on the pipe
surface. Pipe assets can be inspected internally using man entry techniques.
♦ The pipe should also be dewatered prior to inspection as the water will alter the sound
propagation properties.
F2.5 Advantages
♦ This technique can be conducted quickly with results immediately available.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-9
♦ The results of this technique give information about the overall condition of the pipe.
F2.6 Limitations
♦ Pipe assets must be dewatered before inspection.
♦ Asset must be exposed prior to inspection. However, full exposure of the asset is not
required; exposure only need allow access to points on pipe surface.
♦ This technique may not locate specific small defects).
Table F-2. Summary Active Acoustic Inspection.
Technical
selection
Technical
suitability
Utility technical
capacity
Economic factors
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Pipe assets.
Cementituous, PCCPs
Potable and wastewater.
Access to asset surface is required.
None.
None (man entry for pipes).
Discrete.
Non-destructive test.
Inspection conducted while pipe is off-line and
dewatered.
Presence of defects.
None.
Approach is widely used and available from
numerous suppliers.
Widely used in civil industries.
Qualitative measure.
Results validated by exhumation of pipe.
Generic approach.
Training in tool use required.
Can be instrumented or manual.
Supplied with tool, no standards identified.
From suppliers.
Relatively low.
Man power sufficient to expose asset and for
confined spaces when applicable.
F2.7 Bibliography
1. Dingus, M., Haven, J. and Austin, R. Nondestructive None Invasive Assessment of
Underground Pipes, AwwaRF, USA, 2002.
2. Makar, J. M. ; Chagnon, N. Inspecting systems for leaks, pits, and corrosion, National
Research Council of Canada, Institute for Research in Construction, NRCC-42802, 1999
(downloaded from www.nrc.ca/irc/ircpubs).
3. Lillie, K., Reed, C. and Rodgers, M. A. R., 2004, Workshop on Condition Assessment
Inspection Devices for Water Transmission Mains, AwwaRF, USA, 2004.
F-10
F3.0 Air Permeability
F3.1 Overview
Air permeability is a non-destructive test that can be used to determine the permeability
and quality class of concrete. Concrete permeability is an excellent measure of the resistance of
concrete against aggressive media. The ingress of water and air into the concrete can cause
corrosion of steel reinforcement, which leads to a deterioration in the durability of the concrete.
Air permeability testing is also referred to as ‘gas’ permeability testing.
There are two main methods for testing air permeability: the Torrent method, which
measures the reduction of an applied vacuum over time, and the Cembureau method for
oxygen permeability. The Torrent method is described here due to its more extensive use as a
concrete durability assessment tool, and its widespread use on road, bridge and tunnel assets.
F3.2 Main Principles
The Torrent method involves creating a vacuum at the surface of the concrete and
monitoring the rate at which the pressure in the test chamber increases after the vacuum pump
has been disconnected. The distinctive features of the method are a double chamber cell and a
pressure regulator that balances the pressure in both chambers during the test. A
microprocessor processes and stores test results.
The vacuum cell (Figure F-1) is held against the concrete surface by a vacuum. It has
an inner circular chamber surrounded by an outer annular chamber. The outer chamber forces
the air inflow to the inner chamber to be virtually uniaxial. A membrane pressure regulator
brings the inner cell to a standard vacuum and is then turned off. The reduction in vacuum is
measured over a time period. The permeability coefficient kT and the depth of penetration of
the vacuum are calculated on the basis of a simple theoretical model and the permeability of
the concrete is determined.
In the case of dry concrete, the quality class of the concrete cover can be read from a
table using the kT value. In the case of moist concrete, kT is combined with the electrical
concrete resistance p (rho) and the quality class is determined from a numerical relationship.
Figure F-1. Torrent Permeability Tester (Mastrad, 2006).
F3.3 Application
Air permeability testing can be conducted on any concrete structure, including but not
limited to; buildings, tanks, slabs and other such structures.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-11
Standards which reference this test method are:
♦ DIN 28400 ‘Vacuum Technique’ Deutsches Institut fur Normung (DIN)
♦ C497-05 Standard Test Methods for Concrete Pipe, Manhole Sections, or Tile
♦ ASTM C204-05 Standard Test Method for Fineness of Hydraulic Cement by Air
Permeability Apparatus
F3.4 Practical Considerations
♦ Instrumentation for carrying out air permeability testing is widely available from a
number of commercial providers.
♦ The instrumentation is portable and does not require specialist skills to use. Individual
tests can be completed in less than five minutes and the results are reproducible.
♦ Air permeability testing has been widely applied throughout both the water and other
industry sectors for evaluating the durability of concrete.
♦ When testing is conducted on moist concrete, it should be complemented with the nondestructive determination of the electrical resistivity.
F3.5 Advantages
♦ The testing method is suitable for both laboratory and onsite application. Testing is
non-destructive and allows a rapid and reliable comparison between laboratory samples
and site concrete.
♦ Measurements taken in the field are usually in good agreement with laboratory methods
such as oxygen permeability, capillary suction, chloride penetration.
♦ Capillary suction can also be estimated from permeability results obtained from testing.
Capillary suction is known to be related to permeability if the surface tension effects are
not disturbed by water repellents.
F3.6 Limitations
♦ The concrete needs to be dry for accurate testing, as permeability times are influenced
by the moisture content of the concrete.
♦ When concrete is moist, air permeability values are significantly lower than when it is
dry. This can result in a distortion in the evaluation of the quality of the concrete,
particularly when it is performed in-situ.
F-12
Table F-3. Summary Air Permeability.
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Economic
factors
Asset management sophistication required
Skills required (level of tool sophistication);
usability
Technology required (level of tool
sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Concrete elements with a flat surface such as slabs,
beams, columns, walls and pavements
Coated and uncoated concrete.
Potable and wastewater.
Direct contact with surface of asset. If asset is buried
then it must be exposed. Surface coatings need to be
removed in order to test permeability of concrete.
Sufficient room is required for an operator where an
asset has been exposed for testing.
Concrete surface must be level and not be too porous
or rough as the chambers of the vacuum cell need to
seal effectively against the surface.
No limitations relating to size of concrete element.
Surface must be flat.
Discrete reading.
Non-destructive.
The asset can remain in use and does not need to be
taken off-line.
Permeability, quality class and capillary suction of
concrete.
Compatible with a RS 232 data interface gives a
printout of measured objects and can be transferred
to PC with MS Hyperterminal.
Equipment is fully developed, available from selected
commercial vendors.
Widespread use internationally on bridges, road, and
tunnel infrastructure. Limited application in the water
industry.
Accuracy better than 3% variation from reading.
Results are easily validated by conducting other
standard tests for permeability such as ASTM C
1202.
Generic approach.
Easy to use by following simple procedure.
Unqualified staff can take measurements.
Apparatus comes in a digital version, which calculates
and displays permeability. Quality class of concrete,
capillary suction and carbonation depth of concrete
can be estimated using supporting software by
exporting data. The data from up to 200 tests can be
stored and downloaded.
DIN 28400 Vacuum Technology.
Technical support available from distributors.
Low cost per inspection.
Resources required depend on asset being
inspected. Buried assets need to be exposed and
surface cleaned and made smooth to ensure a seal
with vacuum cell.
F3.7 Bibliography
1. Torrent, R. The gas permeability of high-performance concretes: site and laboratory tests.
ACI Special Publication 186. pp1-4, 1999.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-13
2. Papworths, Corrosion Monitoring Equipment, ‘TORRENT Water Permeability’ ‘Defelsko
Positest CarbonationTester for Concrete and Metal. Papworths Pty Ltd Concrete
Consultancy Service and NDT Equipment. 2005.
3. DIN 28400 Vacuum Technology.
4. C497-05 Standard Test Methods for Concrete Pipe, Manhole Sections, or Tile.
5. ASTM C204-05 Standard Test Method for Fineness of Hydraulic Cement by Air
Permeability Apparatus.
6. Mastrad, http://www.mastrad.com/torrent.htm, accessed 2006.
F-14
F4.0 AQUA-Selekt
F4.1 Overview
AQUA-Selekt is a software package developed in Germany, designed to assist
infrastructure managers forecast sewer condition using representative CCTV inspection data
(see CCTV Visual Inspection review). A qualitative condition inspection of a representative
sample is first assessed. This data is then used to forecast the condition of sewers that are not
inspected.
F4.2 Main Principles
AQUA-Selekt is a PC based software tool that is used to determine the condition of
assets within a sewerage network. The approach used is to infer the condition of the asset stock
from the known condition of a representative sample of assets.
The CCTV inspection strategy used is dependent on the size of the network, requiring
10-20% of the network to be inspected. As the size of the network increases, the percentage
inspection required decreases.
The condition of the inspected sample is used to extrapolate the condition trend of the
sewers that have not been inspected by means of statistical evaluation.
F4.3 Application
AQUA-Selekt is designed to assist with the forecasting of sewer condition using
representative CCTV-inspection data.
♦ The selection strategy used by AQUA-Selekt is in accordance with DIN EN 752-5.
F4.4 Practical Considerations
♦ The software is readily available, commercialized, and used by several European
authorities with a handful of users in other areas. It uses a Windows Explorer-style
navigation structure.
♦ The method has been successfully tested in Germany on the sewer systems at
Volkswagen plants in Wolfsburg, Emden and Brunswick, and is currently being
developed further within the scope of a research project supported by the Ministry of
Education and Research for various cities.
F4.5 Advantages
♦ AQUA-Selekt allows the forecasting of sewer condition of an entire network based on
the CCTV data from a representative sample. This helps in the overall planning and
evaluation of sewer rehabilitation and maintenance and helps to target problem areas.
♦ This method used is claimed to be efficient with clear cost benefits, particularly for
large sewer systems of 1000 km and over.
♦ System sections that are in particular need of rehabilitation can be detected early and
given priority for complete inspection and rehabilitation.
♦ PC based software that requires MS-Windows 95/98 and MS Access 2000 to be
installed as minimum requirements (software cannot be used on other operating
systems).
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-15
F4.6 Limitations
♦ AQUA-Selekt was developed for the European context. Vendors only available in
Germany. Requires CCTV data of selected sewer sections in order for the forecasting
model to be effective.
Table F-4. Summary AQUA-Selekt.
Technical
selection
Technical
suitability
Criteria
Assets covered
Granularity
Service area
Focus of analysis
Scalability of tool/approach
Commercialization
Previous/existing use of the tool
Utility technical
capacity
Ease of validation
Flexibility with regard to analysis (asset types) and
granularity (system, asset level)
Integration with other tools/GIS
Asset management sophistication
In-house skills required
Technology required
Documentation
Data Requirements
Linking to asset data
Availability of software and technical support
Usability
Assessment
Sewer pipes.
System and asset level.
Wastewater.
Forecasting of sewer condition using
representative CCTV-inspection data.
Better suited to medium to large authorities
where CCTV data is available.
Commercial software available from Germany.
Used by several European authorities and has a
handful of users in other areas.
Validation is possible only through site surveys.
Wastewater only; system level only.
None.
Aimed at level of asset management where
CCTV data is available.
Professional asset manager/engineer
PC based tool. Windows based operating
system. Requires Microsoft Access 2000
On-line help and detailed documentation
provided.
CCTV data required and MS Access data files
used.
Exports and imports to/from Microsoft Access
database.
Technical support available. On-line forum.
Simple operation of the Windows 32-Bit
program using Explorer-style navigation
structure.
F4.7 Bibliography
1. Eisenbeis, P., P. Le Gauffre, and S. Saegrov, Water Infrastructure Management: An
Overview of European Models and Databases, AwwaRF Infrastructure Conference,
Baltimore MD, 2000.
2. Herz, Raimund K., Aging Processes And Rehabilitation Needs Of Drinking Water
Distribution Networks, Journal of Water, SRT-Aqua Volume 45, pp 221-231, 1996.
3. AQUA-Selekt homepage, http://www.sewer-rehabilitation.com/, accessed 2006
3
4. DIN EN 752-5: 1997 Drain and sewer systems outside buildings - Part 5: Rehabilitation.
F-16
F5.0 AQUA-WertMin
F5.1 Overview
AQUA-WertMin is a software package developed in Germany to assist infrastructure
managers with the planning of CCTV-inspection, rehabilitation and new construction strategies
for sewers networks.
AQUA-WertMin calculates the current market value of assets, forecasts the
deterioration of pipe condition and assesses future rehabilitation needs using inbuilt models
and CCTV inspection data. It enables users to compare the costs of different rehabilitation
strategies based on an economic analysis of costs and time of repair.
F5.2 Main Principles
AQUA-WertMin is a PC based software tool. The user enters pipe and manhole (assets)
condition scores derived from CCTV inspections into the application. The software then
assigns one of the following six classifications to each asset in the network, as described in the
Table F-5.
Table F-5. Asset Condition Classification System.
Classification
Class 6
Description
Excellent condition – no observed defects.
Class 5
Good condition – few defects observed, repair as needed.
Class 4
Fair condition – minor defects observed that will require repairs in long-term plan.
Class 3
Poor condition – defects observed that will require major repairs, but no rehabilitation in the mid-term plan.
Class 2
Very poor condition – defects observed that require major rehabilitation, but not replacement in the nearterm plan.
Class 1
Pipe failed – needs immediate replacement.
The software calculates the probability of an asset (or group of like assets) transitioning
from one condition class to the next lower (worse) class. To determine the transitional
function, the software applies a survival model for groups of similar sewer sections. The
survival functions are calibrated using data collected from the network inspection records
including year of pipe installation, year of inspection, pipe diameter, and pipe condition.
Modules are also provided for the calculation of asset values, and
replacement/rehabilitation costs, which enables the user to compare the costs of different
rehabilitation strategies based on an economic analysis.
F5.3 Application
AQUA-WertMin is designed to assist with the planning of CCTV-inspection,
rehabilitation and new construction strategies for sewer network assets. The program follows
the guidelines for cost-minimizing maintenance of sewers by the Ministry of Environment and
Transport of the German federal state Baden-Württemberg of December 2000.
F5.4 Practical Considerations
♦ The software is readily available, commercialized, and used by several European
authorities with a handful of users in other areas.
♦ The software uses a simple Windows Explorer-style navigation structure.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-17
♦ All data can be selected using specific fields and exported to Microsoft Access 2000 or
97 databases.
F5.5 Advantages
♦ Program installation is simple with step-by-step instructions.
♦ AQUA-WertMin has a consistent and easy-to-use user interface with Explorer-style
navigation structure. On-line help is also available
♦ Freely-configurable import function for Access databases from version 2.0 and
databases linked using ODBC.
♦ All data can be selected using specific fields and exported to Microsoft Access 2000 or
97 databases.
F5.6 Limitations
♦ AQUA-WertMin was developed for the European context.
♦ Vendors are only available in Germany.
Table F-6. Summary AQUA WertMin.
Technical
selection
Technical
suitability
Criteria
Assets covered
Granularity
Assessment
Sewer pipes.
System and asset level.
Focus of analysis
Planning of CCTV-inspection, renovation and new
construction strategies for wastewater networks.
Better suited to medium to large authorities where
CCTV data is available.
Commercial software available from Germany.
Used by several European authorities and has a
handful of users in other areas.
Validation is possible only through site surveys.
Wastewater only; asset to system level.
Scalability of tool/approach
Commercialization
Previous/existing use of the tool
Utility technical
capacity
Ease of validation
Flexibility with regard to analysis (asset types)
and granularity (system, asset level)
Integration with other tools/GIS
Asset management sophistication
In-house skills required
Technology required
Documentation
Data Requirements
Linking to asset data
Availability of software and technical support
Usability
None.
Aimed at higher level of asset management where
CCTV data is available.
Professional asset manager/engineer.
PC based tool. Windows based operating system.
Requires Microsoft Access 2000.
On-line help and detailed documentation provided.
CCTV data required and Microsoft Access data
files used.
Exports and imports to/from Microsoft Access
database.
Technical support available. On-line forum.
Simple operation of the Windows 32-Bit program
using Explorer-style navigation structure.
F5.7 Bibliography
1. Herz, Raimund K., Aging Processes And Rehabilitation Needs Of Drinking Water
Distribution Networks, Journal of Water, SRT-Aqua Volume 45, pp 221-231, 1996.
F-18
2. Eisenbeis, P., P. Le Gauffre, and S. Saegrov, Water Infrastructure Management: An
Overview of European Models and Databases, AwwaRF Infrastructure Conference,
Baltimore MD, 2000.
3. AQUA-WertMin homepage, http://www.sewer-rehabilitation.com/, accessed 2006.
4H
4. Stone, S., Dzuray, E. J., Meisegeier, D., Dahlborg, A-S., and Erickson, M. DecisionSupport Tools for Predicting the Performance of Water Distribution and Wastewater
Collection Systems, EPA, EPA/600/R-02/029, 2002.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-19
F6.0 AwwaRF’s Manager Software
F6.1 Overview
AwwaRF’s Water Treatment Plant Infrastructure Assessment Manager (Manager
Software) is a software based tool that allows the user to manage information relating to
treatment plant assets. The software provides procedures and instructions to gather information
on the condition and criticality of water treatment facilities and their components, and includes
financial accounting capabilities from the unit level through the facility level.
F6.2 Main Principles
There are three parts to the Manager Software: the toolbar, tree and data viewer. The
tree allows the structure of the treatment plant facility to be input according to a consistent
asset hierarchy. For example, from the facility level, the plant is conceptually broken down in
terms of systems (e.g., raw water systems) and subsystems (e.g., raw water intake), units (such
as screening), and finally individual components such as bar screens and control panels. The
user can represent the treatment plant hierarchy using the options in the tree.
Once the tree has been set up, the user navigates throughout Manager Software by
clicking on different systems, subsystems, and units, and can then record information against
the assets detailed at that level in the hierarchy. The user can input the following data:
♦ Criticality (to show relative importance of the plant item).
♦ Condition assessment, a unit can have a condition grading/rating 0 (inoperable) through
to 4 (excellent), with a capacity to record ‘unknown’.
♦ Safety impact to human health if it should fail.
♦ Weighting and criticality; to give relative importance to an asset within the hierarchy.
Other information can be input such as, photos, assessment considerations, acquisition
cost, replacement cost, and so forth.
A condition scoring system is used to summarize condition. This incorporates both a
condition rating at the unit level and a weighting of the unit's importance to the plant's overall
ability to produce water. The Manager Software tabulates the scoring at the subsystem, system,
and facility levels and generates various reports.
F6.3 Application
AwwaRF’s Manager Software is designed to facilitate the management of condition
and asset data for water treatment works.
F6.4 Practical Considerations
♦ The product is an output of a research project and is freely available through AwwaRF.
F6.5 Advantages
♦ The Manager Software provides procedures and instructions to gather information on
the condition and criticality of water treatment facilities and their components.
♦ Through the tree structure, the software organizes the assessment process around the
evaluation of systems rather than engineering/maintenance disciplines. A review of
non-destructive assessment methods is also included within the Manager Software.
F-20
♦ The Manager Software allows for wide variations in the type and size of facilities and
in the experience of the staff who will perform the assessment.
♦ It includes financial accounting capabilities from the unit level through the facility
level.
F6.6 Limitations
♦ Functionality would ideally be integrated into corporate systems, rather than a standalone tool.
Table F-7. Summary AwwaRF’s Manager.
Technical
selection
Technical
suitability
Criteria
Assets covered
Granularity
Service area
Focus of analysis
Scalability of tool/approach
Utility technical
capacity
Commercialization
Previous/existing use of the tool
Ease of validation
Flexibility with regard to analysis (asset types)
and granularity (system, asset level)
Integration with other tools/GIS
Asset management sophistication
In-house skills required
Technology required
Documentation
Data Requirements
Linking to asset data
Availability of software and technical support
Usability
Assessment
Water treatment works.
System down to unit and component level.
Potable.
Representing asset and condition data within a
consistent framework.
Useable by any utility, but better suited to
utilities without equivalent functionality in
corporate systems.
Software available from AwwaRF.
Practical use is unknown.
N/A
System level, water treatment plants only.
None.
Aimed at level of asset management where
corporate systems have not been developed.
Professional asset manager/engineer.
PC based tool. Windows based operating
system.
Documented through AwwaRF report.
Asset hierarchy, cost and condition data.
Asset hierarchy embedded in software.
Supported in help files and through AwwaRF
report.
Simple operation of the Windows 32-Bit
program using Explorer-style navigation
structure.
F6.7 Bibliography
1. AwwaRF. Water Treatment Plant Infrastructure Asset Management: Users Manual,
prepared by L. Elliot et al, AWWA Research Foundation and American Water Works
Association, USA, 2001.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-21
F7.0 Barcol Hardness Test
F7.1 Overview
The Barcol hardness test is a quick and simple non-destructive test using a Barcol
Impressor, which gives a relative measure of the hardness of rigid materials. It is can be used,
for example, on plastic and cementitious pipes.
Barcol hardness can be converted to other hardness measures such as Vickers hardness
but does not relate to any other physical quantity (Dorn et al., 1996).
F7.2 Main Principles
The Barcol Impressor is either manually operated by pressing the device into the
sample a set distance and reading hardness off a graduated dial between 0 and 100, or is
electronically controlled. Electronically controlled devices can be hand held or mounted
depending on the samples to be tested. Harder materials give a higher reading, with materials
that are either too hard or too soft not registering.
The Barcol hardness test provides a relative measure of material hardness. Barcol
hardness is most useful for cementitious pipes, as changes in hardness can indicate areas of
deterioration, but the technique can also be used on materials such as plastic, aluminum and
brass.
F7.3 Application
The Barcol hardness test can be used to measure the surface hardness of any asset
dependant on material. Asset that can be inspected include pipes and coatings, testing can be
conducted in the lab or in the field.
♦ The Barcol Impressor is referred to in a number of standards ASTM D2583-95, ASTM
B 648-78, ASTM E140-97.
F7.4 Practical Considerations
♦ The Barcol Impressor is widely available from numerous commercial suppliers. The
Barcol Impressor is simple to use, hand held and readily portable, weighing less than 1
kg.
♦ Manual testers require no power and the reading is taken from dial on tester. Hand held
digital versions are also available.
♦ Variance in the results depends on the material being tested; homogenous materials
have a lower variance than heterogeneous materials. A large number of tests should be
undertaken to provide statistically meaningful averages, especially for heterogeneous
materials.
♦ The tester should be used on flat surfaces; the legs of the tester do not have to be on the
sample but should be supported so that the indenter is perpendicular to the surface
being tested. Multiple tests should be conducted on all materials, with heterogeneous
materials needing significantly more readings than homogenous materials. Different
models of the Barcol Impressor are available that give higher accuracy depending on
the hardness of the material being tested (ASTM D2583).
♦ Resources required depend on the assets being inspected. Buried assets need to be
exposed and have any coatings removed, man entry such as into manholes may require
multiple personnel, dependant on safety requirements.
F-22
♦ The Barcol hardness test has been used to assess deterioration of AC and cementitious
pipes.
F7.5 Advantages
♦ The Barcol Impressor is quick and easy to use and has repeatable measurements on
homogeneous materials. The test can be used on both cementituous and polymeric
materials (Dorn et al., 1996).
F7.6 Limitations
♦ Due to the small area tested each time, the Barcol Impressor is used the results can
show a high degree of scatter in heterogeneous materials, requiring large numbers of
measurements to be taken.
♦ Hardness measurement is an arbitrary scale and does not relate to any other physical
property such as strength (Dorn et al., 1996)
Table F-8. Summary Barcol Hardness.
Technical
selection
Criteria
Assets covered
Material type
Service Area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Utility technical
capacity
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Assessment
Tester can be used on assets made from the
materials listed below.
Rigid Plastics, uPVC, ABS, mPVC, oPVC and
GRP and cementituous materials.
Potable and wastewater.
Portable hand held device, but requires access
to the asset surface.
Any coating applied to the surface of the asset
should be removed prior to testing.
Test should be preformed on a flat surface,
excessive curvature is an issue.
Discrete.
Non-destructive.
For man entry standard safety procedures
should be followed, otherwise the asset can
remain on-line.
This technique measures the Barcol hardness,
Barcol hardness can be converted to other
measurements of hardness such as Vickers
Hardness.
Stand alone; no integration with computerize
tools/equipment.
Barcol Hardness testers are available off the
shelf.
Some use in assessing deterioration of
cementitious materials.
Semi quantitative (relative) measure. Good
repeatability for homogeneous materials. High
variance for heterogeneous materials.
Indicative results only.
Generic approach.
Easy to use by following simple procedure.
Stand alone tool.
ASTM D2583-95, ASTM B 648-78, ASTM E14097.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-23
Criteria
Availability of technical support
Economic factors
Cost per inspection
Resource requirements
Assessment
Technical support available from retailers and
from Internet.
Low cost per inspection.
Resources required depend on assets being
inspected. Buried assets need to be exposed
and have any coatings removed, man entry
such as into manholes may require multiple
personnel dependant on safety requirements.
F7.7 Bibliography
1. ASTM D2583 95, Standard test method for indentation hardness of rigid plastics by means
of a Barcol Impressor.
2. ASTM E140-97 Standard Hardness Conversion Tables for Metals E1842-96 Standard Test
Method for Macro-Rockwell Hardness Testing of Metallic Materials.
3. ASTM B648-78 Standard Hardness Conversion Tables for Metals E1842-96 Standard Test
Method for Macro-Rockwell Hardness Testing of Metallic Materials.
4. Dorn, R., Howsam, P., Hyde, R.A. and Jarvis, M.A. Water mains: Guidance on assessment
and inspection techniques, CIRIA Report 162, Construction Industry Research and
Information Association, London, England, 1996.
5. Randall-Smith, M., Russell, A. and Oliphant, R., Guidance manual for the structural
condition assessment of trunk mains, WRc, UK, 1992.
F-24
F8.0 Broadband Electromagnetic
F8.1 Overview
The broadband electro magnetic (BBEM) technique is an eddy current method. In eddy
current methods, the thickness of a pipe wall is measured by inducing magnetic fields in the
material. While conventional eddy current inspection techniques use a single frequency (or a
narrow frequency bandwidth), BBEM induction techniques record data over a broad range of
frequencies. Since the depth of penetration is dependent on the frequency of excitation, this
allows information from a range of depths to be obtained.
The BBEM technique works by passing an alternating current through a transmitter coil
at the surface of the pipe, which generates an alternating magnetic field. Flux lines from this
magnetic field pass through the metallic pipe wall, generating a voltage across it. This voltage
produces eddy currents in the pipe wall that produce their own, secondary magnetic field. By
measuring the strength of this magnetic field or the eddy current that produces it, the remaining
metallic wall thickness can be detected.
The technique is non-destructive and commercial suppliers of BBEM state that signal
can be received through all forms of external coating, and in all ferrous materials.
F8.2 Main Principles
Eddy current methods measure the wall thickness of a pipe by sensing the attenuation
and phase delay of an electromagnetic signal that has passed through the pipe wall. Defects on
the pipe are detected because they change the distribution of the eddy currents in the objects
being examined. For example, if the pipe wall is cracked, the currents are forced to go round or
under the crack, causing the magnetic field produced by the eddy currents and the voltage in
the pick-up coil to change. Eddy current inspection techniques are most sensitive to cracks and
other abrupt changes in the metal, and are least sensitive to gradual changes to wall thickness
on the far side of the pipe wall from the coils. For these reasons, and the low frequencies
necessary to overcome the 'skin effect', the classical eddy current technique is not applied to
water pipelines.
While conventional eddy current inspection techniques use a single frequency (or a
narrow frequency bandwidth), BBEM induction techniques record data over a broad range of
frequencies and consequently have advantages over conventional techniques. The principle of
BBEM is to transmit a signal that covers a broad frequency spectrum (i.e., perhaps three
decades). The received signal resulting from a broadband transmission contains more
information, and allows detection and quantification of various wall thicknesses, as well as the
effective conductivity of the complex through-wall components of the pipe.
Tools based on BBEM techniques measure the full-wave secondary magnetic field
resulting from a transient input signal. By recording the full waveform response, it is possible
to obtain information on both the magnetic and the electrical properties of ferrous pipes. The
transient input signal generates multiple frequencies, typically 50 Hz to 50kHz. The wide
acquisition bandwidth negates the requirement for tuning or setting fixed frequencies
depending upon pipe wall thickness and composition.
Instruments for acquiring BBEM data are based on the time-domain electromagnetic
technique (TDEM), where the transient decay of the magnetic field is measured following the
interruption of current flow in the transmitter coil. The BBEM variant has been specifically
designed for the study and assessment of water supply systems.
The technique can be used either internally or externally. Internal inspection requires
full-bore access. When used externally, the pipe is exposed at the site of investigation and the
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-25
BBEM tool scans the pipe outer surface. Results are reported graphically or as color contour
plots, as in shown Figure F-2.
Figure F-2. Color Contour Plot Representing Variations in Pipe Wall Thicknesses.
F8.3 Application
♦ Broadband electromagnetic techniques can be used to assess ferrous pipe wall condition
and locate illegal tap-ins.
♦ Tools are available for both external and internal use.
F8.4 Practical Considerations
♦ BBEM inspection tools and services are commercially available.
♦ Practical use of this technique is reported in the literature and trade journals.
♦ The tool gives quantifiable results in the form of contour plots.
♦ The condition assessment (internal) probe can be winched or rodded through depressurized pipes.
F8.5 Advantages
♦ Non-destructive condition monitoring techniques based on electromagnetic induction
principles can provide useful information to assist with pipeline replacement and
rehabilitation decisions for critical mains.
♦ Pipe wall condition assessment is by means of an internal condition assessment probe;
this allows continuous data to be recorded along extensive lengths of pipeline.
♦ The technique is able to survey through external coating and internal linings.
♦ There is no upper limit on pipe diameter.
F8.6 Limitations
♦ Use of the tool requires pipe to be depressurized during the assessment and full bore
access for internal inspections.
Internal inspection rate is reportedly only a few feet per day in large diameters.
F-26
Table F-9. Summary Broadband Electromagnetic.
Technical
selection
Criteria
Assets covered
Material type
Service Area
Access requirements
Limitations relating to asset condition
Technical
suitability
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Economic factors
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Water pipes.
Steel, cast iron, ductile iron.
Potable.
Internal: full bore access required;
external: exposure of pipe surface.
No limitations relating to asset condition
provided direct contact with the pipe wall is
available.
Minimum 3”.
Continuous.
Nondestructive.
Pipe must be depressurized.
Remaining wall thickness.
Fully integrated software for analysis of data.
Commercially available.
Commercial use of the tools reported in
literature and trade journals.
Quantitative assessment; but varied sensitivity
to defects.
Validation by other measurement is required,
though data collected can be recalibrated at any
time after the inspection.
Associated with high levels of asset
management sophistication.
Tool operation typically by a third party.
Specialized equipment and dedicated computer
software.
Use and development documented in the
literature.
Tool operation typically by a third party.
High cost associated with access and tool use.
Sufficient manpower to undertake enabling work
and inspection.
F8.7 Bibliography
1. Burn, L.S., Eiswirth, M., DeSilva D. and Davis P., Condition Monitoring and its Role in
Asset Planning, Pipes Wagga Wagga 2001, Charles Sturt University, Wagga Wagga,
N.S.W., 2001.
2. Lillie, K., Reed, C. and Rodgers, M. A. R., 2004, Workshop on Condition Assessment
Inspection Devices for Water Transmission Mains, AwwaRF, USA, 2004.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-27
F9.0 Carbonation Testing and Petrographic Examination
F9.1 Overview
In normal high quality reinforced concrete, the steel reinforcement is chemically
protected from corrosion by the alkaline nature of the concrete. This alkalinity causes the
formation of a passive oxide layer around the steel reinforcement. However, over time the
concrete reacts with atmospheric carbon dioxide and sulfur dioxide to cause gradual
neutralization of the alkalinity from the outside surface inwards. This process is known as
carbonation and over time the concrete around the steel reinforcement is neutralized allowing it
to corrode, leading to the deterioration of the concrete through cracking and spalling.
Carbonation testing measures the depth of carbonation and can be determined using onsite or
laboratory based assessment techniques. Core samples are taken, but the technique is in
essence non-destructive.
F9.2 Main Principles
The depth of carbonation can be measured on a freshly exposed core section of concrete
by spraying with a phenolphthalein indicator spray solution. The indicator spray will turn pink
in color when the concrete is alkaline (pH ≥ 9.2). If the indicator spray remains colorless then
the concrete is found to be carbonated. The depth of carbonation exists in a more or less even
zone extending to a critical depth from the surface.
The rate at which carbonation occurs is a function of concrete quality, in particular the
water/cement ratio and compaction achieved during construction. It is generally accepted that
the rate in which carbonation occurs is inversely proportional to the square root of the age of
the structure. However, recent research suggests that the square root relationship is only
applicable for concretes which have been exposed to nominal humidity’s of 50%. As humidity
increases, the power function is found to decrease. As a result of this relationship, the
carbonation depth is found to be lower for concretes that have been continuously exposed to
higher humidity.
Assessments conducted in the laboratory such as petrographic examination, allow a
much more detailed assessment to be conducted on the concrete quality than can be undertaken
by other methods. Petrographic examination typically involves cutting a 20 mm thick slice
(plate) from a concrete core with the plate then polished to give a high quality surface that can
be examined with a microscope. The following characteristic properties of the sample are then
determined:
♦ The size, shape and distribution of coarse and fine aggregate.
♦ The coherence, color, and porosity of the cement paste.
♦ The distribution, size, shape, and content of voids.
♦ The composition of the concrete in terms of the volume proportions of coarse
aggregate, fine aggregate, paste and void.
♦ The distribution of fine cracks and micro-cracks. Often the surface is stained with a
penetrative dye, so that these cracks can be seen. Micro-crack frequency is measured
along lines of traverse across the surface.
F-28
F9.3 Application
Carbonation testing is commonly undertaken on structures constructed from concrete
materials, to determine the existence and level of carbonation.
♦ BS 8110 Structural use of concrete. Code of practice for design and construction
F9.4 Practical Considerations
♦ Onsite analysis using phenolphthalein is a quick and simple method to obtain an
indication of carbonation without the need to obtain core samples.
♦ More complex assessment techniques conducted in the laboratory require skilled
laboratory staff to prepare samples from cores for analysis and interpretation of
experimental results.
♦ While the phenolphthalein test is a good indication the presence of free lime, it only
indicates a pH above 9, and passivation requires a pH ≥ 11.
F9.5 Advantages
•
Analysis techniques conducted onsite using phenolphthalein can, in some applications,
be undertaken without the need to take core samples.
F9.6 Limitations
♦ A phenolphthalein test may return a positive result even if alkalinity has reduced to a
pH < 11, where passivation has been lost.
♦ Materials that contain carbonation along micro-cracks and diffusion paths in poorly
compacted concrete may not be readily revealed by the phenolphthalein analysis
methods.
♦ Laboratory based assessment techniques require skilled technical staff who have been
trained and have relevant experience in the preparation, analysis and interpretation of
experimental results.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-29
Table F-10. Summary Carbonation Testing.
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Economic
factors
Cost per inspection
Resource requirements
Assessment
Concrete assets in contact with air or soil. Can also
be used on dispersive soils and crushed stone
base materials.
Cementituous.
Potable and wastewater.
Direct contact with concrete surface. Surface
coatings should be removed.
No restriction.
No limitations relating to size.
Discrete readings.
A core is required to be removed.
The asset can remain in use and does not need to
be taken off-line.
Depth of carbonation in mm.
Stand alone tool.
Test methods are fully developed and are available
from a wide range of commercial vendors.
Widespread use throughout many sectors.
Qualitative or quantitative measurement of depth of
carbonation can be obtained.
Direct measurement.
Generic approach.
Easy to use by following simple procedure. Basic
training is recommended.
Low level of technological sophistication is needed
for hand held, manual tools.
AASHTO T-259 and AASHTO T-260.
BS 8110.
Technical support widely available from
distributors.
Low cost per inspection.
One operator required.
F9.7 Bibliography
1. BS 8110 Structural use of concrete. Code of practice for design and construction.
2. Chemical Analysis’ article on MG Associates Construction Consultancy Ltd website.
http://www.mg-assoc.co.uk/serv04.htm Accessed 2006.
5H
F-30
F10.0 CARE-S
F10.1 Overview
CARE-S (Computer Aided Rehabilitation of Sewer and Storm Water Networks) is a
computer-based system for sewer and stormwater network management developed under a
collaborative research project supported by the European Commission under the 5th
Framework program, intended to contribute to the implementation of the key action
“sustainable management and quality of water.”
CARE-S aims to allow cost-efficient programs of maintenance, repair and rehabilitation
of sewer networks to be developed. In structure, CARE-S is a suite of PC based software tools
developed separately, and linked within a common framework by a decision support system
(DSS).
The overall rehabilitation planning process is derived from the European Standard; BS
EN 752-5:1998 “Drain and sewer systems outside buildings. Rehabilitation.” This planning
process is done within the context of an integrated catchment management approach.
F10.2 Main Principles
A CARE-S project is used as the basis of the analysis. A project is a collection of data
items, analyzes and results pertaining to an area or areas of interest, which may be geographic
(e.g., a city network) or thematic (flooding or environmental issues).
CARE-S has a central rehabilitation manager module and variations in data holdings
are handled by import/export protocols. Specific CARE-S tools are included that provide the
following functions:
1. Performance indicator management.
2. Structural condition (CCTV data classification models, sewer assessment models,
deterioration process models).
3. Hydraulic performance.
4. Rehabilitation technology information system (operational and structural
rehabilitation options).
5. Socio-economic consequences (impact of rehabilitation on socio-economic costs,
rehab impact on social life quality, public acceptance).
6. Multi-criteria decision support (choice of rehabilitation technology, selection of
priority projects, exploration of rehab programs and technologies).
The CARE-S approach can be used at a range of granularities. CARE-S is not intended
to bind together the external tools in a fixed and constraining way, but rather to allow the user
to use them individually or in a sequence appropriate to the data available for the analysis.
F10.3 Application
CARE-S is a flexible computer-based system for improving sewer and stormwater
network management. The overall rehabilitation planning process is derived
♦ BS EN 752-5:1998 “Drain and sewer systems outside buildings. Rehabilitation”
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-31
F10.4 Practical Considerations
♦ The tools are PC based and run under the Windows operating system. While not
commercialized as yet, the CARE-S exists in prototype form. The use by third parties
should therefore be supported by some of the developers for the time being.
♦ Several projects based on the CARE-S methodology are emerging in Europe and
Australia. These projects will serve to verify the suitability of CARE-S modules to
support management of wastewater networks, and are expected to show the pathway
towards full commercialization.
♦ For full details on the CARE-S project and prototype tool see, http://care-s.unife.it/
and/or Saegrov (2006) (see Bibliography).
6H
F10.5 Advantages
♦ CARE-S has allowed the integration of tools for managing sewerage and stormwater
networks. The results can be presented by reports, in tables and graphically (GIS).
♦ A significant effort has been made to allow companies to maintain their own data
formats, yet import them into CARE-S in the standard form required by the suit of
tools.
F10.6 Limitations
♦ The software is still a prototype and thus in need of further development.
♦ The adoption by water authorities is in an early stage and the practical results from
using CARE-S have not yet obtained.
♦ Although the methodologies of CARE-S are generic and independent of worldwide
practice, there are some designs that are made in light of European practices (e.g.,
classification of CCTV inspection).
♦ Approaches in the United States may differ from those adopted by the European
partners, which could affect relevance to the United States market.
F-32
Table F-11. Summary CARE-S.
Technical
Selection
Technical
suitability
Criteria
Assets covered
Granularity
Service area
Focus of analysis
Scalability of tool/approach
Commercialization
Previous/existing use of the tool
Ease of validation
Flexibility with respect to analysis (asset types) and
granularity (system, asset level)
Integration with other tools/GIS
Utility technical
capacity
Asset management sophistication
In-house skills required
Technology required
Documentation
Data Requirements
Linking to asset data
Availability of software and technical support
Usability
Assessment
Wastewater networks.
Spatially drainage area and below; thematic
analysis is also supported.
Wastewater.
Service levels, budget setting, environmental
impact, life cycle cost, rehabilitation planning.
Procedure and individual tools can be used by
any size company. However it should be noted
that the complete integrated package is dataintensive and has the associated cost issues.
Not commercialized.
Used during case studies for development of
tool and for succeeding projects.
Validity depends on models and data;
independent validation difficult.
Wastewater only; asset to system level.
Not integrated; but data interface (import/export)
provided.
Generic approach; intended to map onto
company specific systems. CARE-S provides a
suite of tools that compliment existing asset
management approaches.
Professional engineering skills required.
PC based.
A range of papers written on approach; help
files included in package.
Flexible, some tools can be used with limited
data, while other tools are data hungry.
Data import facilities are provided.
Software is not in a fully commercial format;
technical support is available from an
international networks of developers on a
consultancy basis.
Installation and help tools provided Support
from developers required.
F10.7 Bibliography
1. De Silva, D., Burn, S., Davis, P. and Moglia, M. Development of a Decision Support
System for Sewer Rehabilitation, Pipes Wagga Wagga 2003, Wagga Wagga, NSW,
Australia, 21–23 October 2003.
2. BS EN 752-5:1998 “Drain and sewer systems outside buildings. Rehabilitation”.
3. CARE-S homepage, http://care-s.unife.it/, accessed 2006.
7H
4. Saegrov, S. CARE-S – Computer Aided Rehabilitation of Sewer and Storm Water
Networks, IWA Publishing, London. 2006.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-33
F11.0 CARE-W
F11.1 Overview
CARE-W is a computer-based system for water network rehabilitation planning
developed under a collaborative research project supported by the European Commission under
the 5th Framework program. CARE-W is a suite of PC-based software tools operated via a
decision support system (DSS).
F11.2 Main Principles
CARE-W is intended to enable a utility manager to manage water distribution assets in
a cost-effective manner and help to rehabilitate the right pipe at the right time, to avoid
premature rehabilitation (i.e. rehabilitation of the wrong pipe), minimize interruption of water
supply (i.e. due to unexpected pipe break), and resolve issues of poor water quality. Specific
CARE-W tools include:
1. A scenario writer for developing consistent scenarios.
2. A performance indicator tool to measure the performance of the network with a range
of key indicators.
3. A set of statistical tools to obtain probabilistic forecasts of pipe failures (bursts and
leaks).
4. An annual rehabilitation planning system that uses a multi-criterion selection and
ranking system that combines results from other CARE-W tools with additional
information supplied by the user. It provides recommendations for pipes or groups of
pipes that should be considered for rehabilitation in the short term.
5. A combined hydraulic/reliability model to analyze the loss of water supply due to
bursts and leaks.
6. A long-term planning module, which analyzes the necessary investment level in the
coming decades and how this is influenced by different rehabilitation strategies.
The CARE-W suite of tools is designed to be used together, though individual tools can
be used in isolation.
F11.3 Application
CARE-W is a PC based suite of tools to enable the effective use of water pipes,
including when to rehabilitate a pipe.
F11.4 Practical Considerations
♦ The tools are PC based and run under the Windows operating system. By the end of the
research project the tools were provided in a prototype form.
♦ The use by third party should, until commercialization, be supported by at least one of
the developers.
♦ Several projects based on the CARE-W methodology are emerging in Europe. These
projects also serve to verify of the suitability of CARE-W modules to support
management of drinking water networks, and are expected to show the pathway
towards full commercialization.
F-34
F11.5 Advantages
♦ An attempt has been made to provide an integrated tool for managing water supply
networks. The results are presented by reports, in tables and in graphical/GIS format.
♦ The methodologies of CARE-W are generic and not limited to European practices
worldwide, allowing implementation independent of location.
F11.6 Limitations
♦ As noted above, the software is still in development and is not fully commercialized.
Adoption by water authorities is in an early stage.
Table F-12. Summary CARE-W.
Technical
selection
Technical
suitability
Criteria
Assets covered
Granularity
Service area
Focus of analysis
Scalability of tool/approach
Commercialization
Previous/existing use of the tool
Ease of validation
Flexibility with respect to analysis (asset
types) and granularity (system, asset level)
Integration with other tools/GIS
Utility technical
capacity
Asset management sophistication
In-house skills required
Technology required
Documentation
Data Requirements
Linking to asset data
Availability of software and technical support
Usability
Assessment
Water networks.
Networks, pipe cohorts and pipe level.
Potable.
Service levels, budget setting, environmental
impact, life cycle cost, rehabilitation planning.
Scaleable; procedure and individual tools can be
used for any size company. The integrated
package is data-intensive and the cost of its use is
likely to be justified only by companies representing
more than 50.000 customers.
Not commercialized.
Used during case studies for development of tool.
Some European cities have started using the tools
for their water network management, in the first
stage to define management information needed.
Validity depends on models and data; independent
validation difficult.
Potable only; asset to system level.
Not integrated; though data interface
(import/export) provided.
Generic approach; intended to map onto company
specific systems. CARE-W provides a suite of tools
that compliment existing asset management
approaches.
Professional engineering skills required.
PC based.
A range of papers written on approach; help files
included in package.
Flexible, some tools can be used with small
amounts of data while others are data demanding.
Data import facilities are provided.
Software is not in a fully commercial format;
technical support is available from an international
network of developers on a consultancy basis.
Installation and help tools provided. Support from
developers required.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-35
F11.7 Bibliography
CARE-W Homepage, http://care-w.unife.it/intro.html, accessed 2006.
8H
Undated papers from the CARE-W project CD reviewed include:
♦ S Sægrov, What is CARE-W?.
♦ Algaard, E. and P. Campbell, Critical Needs for Rehabilitation Planning.
♦ P Conroy, P. Using CARE-W to manage water distribution pipes.
♦ H. Alegre; L. Tuhovcak & P. Vrbkova, Performance Management and Historical
Analysis: The Use of the CARE-W PI Tool by the Brno Waterworks Municipality.
♦ P. Eisenbeis; M. Poulton; K. Laffréchine,Technical Indicators for Rehabilitation: failure
forecast and hydraulic reliability tools.
♦ Le Gauffre, P & Laffréchine, K; Schiatti, M; Baur, R., Identifying priority projects for
annual rehabilitation planning.
♦ Hulance, J., The CARE-W Rehabilitation Scheme Developer.
F-36
F12.0 CCTV Inspection
F12.1 Overview
CCTV inspection is the standard technology for the non-destructive assessment of the
internal condition of sewers and stormwater pipes and has been employed for over 20 years.
CCTV inspection is conducted by introducing a CCTV module into the pipe being inspected.
As the pipe is inspected, the operator records features of interest, which are used for condition
assessment of the pipe. This enables maintenance budgets to be allocated and provides value
by identifying problems before they become engineering and financial issues.
CCTV inspection can also be conducted on water pipes, but this use is less common.
However, CCTV is commonly used as part of water main rehabilitation processes such as in
situ lining.
F12.2 Main Principles
A typical CCTV module comprises of a color CCTV camera and lighting system
mounted on a wheeled carriage. Small modules are moved through the sewer by a winch and
pulley system. Larger pipes allow self propelled modules to be used, some with on-board
power. The larger modules all use an umbilical cord system. The umbilical cord systems
supply power, allows for communication to the control center and acts as a retrieval device
should the module become wedged in the pipe or lose power. The images captured by the
CCTV camera are sent to the control center to allow remote control of the module and for
image storage. Images are sent along coaxial or twisted pair cable in most units, with more
advanced units using optical fiber.
In most modules the CCTV camera can be panned and tilted for close up observation of
defects. The image captured from the CCTV camera is stored straight to hard drive (some
systems use DVD, or VHS tape in older systems). More advanced units such as the
PanaramoTM and Sewer Scanner and Evaluation Technology (SSET) systems have fish-eye
optics for 360° view of the pipe, coupled with digital image manipulation for an unfolded view
of the whole pipe circumference. The fish-eye lens allows a view of the whole pipe
circumference without needing to pan or tilt the camera. Condition assessment of connections
can also be made using axial/lateral inspection cameras which deploy from specially designed
modules.
Condition assessment is made by professionals, either during inspection or at a later
time using the recording. For wastewater pipelines, standards are available for qualitative and
quantitative grading of defects and a system for ‘condition grading’ commonly used on which
rehabilitation decisions can be based. A condition grade is allocated that represent the range of
conditions from “like new” to “collapsed” or “collapse imminent.” The accuracy of a condition
grading depends on an inspector’s experience.
CCTV inspection provides only an assessment of the internal surface, based on which
further inspection utilizing tools that provide specific information on the pipe wall could be
initiated.
Advances in digital imaging and computer software mean that progress is being made
in the development of automated defect recognition and defect size quantification systems. In
the future, when coupled with laser projection systems that provide quantitative data about the
pipe ovality and cross sectional area, this technology may eliminate the need for human
intervention in visual interpretation of the CCTV images.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-37
F12.3 Application
CCTV inspection is used to view and record visual images of the internal pipe surface.
Generally CCTV inspection is used in gravity flow wastewater and stormwater pipes to
establish the condition of the asset.
CCTV is also used in water pipes to assess the condition of internal cement mortar
linings, evidence of internal corrosion in these lined pipes (corrosion shows up as staining on
the cement mortar), build up of corrosion products and other obstructions.
F12.4 Practical Considerations
♦ CCTV inspection is widely used by water authorities to inspect wastewater and
stormwater pipelines on a regular basis, for trouble shooting as well as for prioritizing
renewal and rehabilitation expenditure. CCTV services are provided by numerous
specialist contractors.
♦ Tool access in gravity flow wastewater and stormwater systems is through maintenance
structures. Tool access in pressure pipelines requires cut-ins at regular intervals (100 m
to 500 m, depending on cable length and pipe alignment).
♦ In some pipes, flow can potentially submerge the camera, for this reason inspection
should be performed during low flow times between midnight and 5 AM. Alternately,
sewers can be temporarily plugged to reduce the flow.
♦ For optimum results, pipes should be flushed and cleaned prior to inspection to remove
surface encrustations and bio film layers, and expose the structure of the inner surface.
♦ The visual image needs to be analyzed manually by an experienced operator, although
defect recognition software is being developed. The operators should be trained in order
to ensure consistency and uniformity of the inspection results. Accurate data on pipe
ovality is required.
F12.5 Advantages
♦ Defects present above the flow surface can be located, identified and ranked by a
trained operator.
♦ Technology is proven and widely available. Long lengths of mains can be inspected
relatively quickly (greater than 1 km/day, depending on site conditions, state of pipe
and flow conditions).
♦ Greater coverage per day is possible with large diameter pipes when remotely operated
vehicles are used.
♦ Systems which incorporate fish-eye technology record a full view of a pipe during a
single pass and allow full inspection to be done off-line using the recording. This
reduces the time spent in each pipe system.
F12.6 Limitations
♦ CCTV inspection provides only an assessment of the internal surface. The results are
qualitative and require manual interpretation for analysis. The accuracy of a condition
grading depends on an inspector’s experience.
♦ Storage of records on VHS tape is cumbersome (this is overcome by digital recording
and storage on hard drive or DVD).
F-38
Table F-13. Summary CCTV Visual Inspection.
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Economic factors
Cost per inspection
Resource requirements
Assessment
Pipes; stormwater and wastewater pipeline
infrastructure, water mains, although less so.
Any pipe material.
Predominantly wastewater, but also potable.
Tool available for internal use only. Defects visually
observable. Access to tool and umbilical cord has
to be provided through manholes (wastewater) or
through cut-ins at regular intervals depending on
cord feed length and bends and obstructions on
pipeline.
No limitations relating to asset condition provided
obstructions do not impede forward movement of
camera.
Generally limited to pipes 90 mm and greater.
However axial cameras can traverse pipes down to
25mm.
Continuous recording of CCTV image on VHS tape
(analogue) or computer memory (digital).
Non-destructive.
Low flow conditions are required for gravity pipes.
Pressure pipes need to be off-line.
Visual image of pipe internal surface analyzed
manually. This can be used to allocate a condition
state for the pipe.
Software available for converting defect codes into
grades.
Commercialized, widely available.
CCTV inspection routinely used by water
authorities.
Qualitative.
Validation possible only by comparison with other
inspection techniques.
Generic approach.
Interpretation of results for consistent data requires
training. Professional skills required to utilize the
information provided.
CCTV camera and related accessories, together
with recording equipment.
Technique widely documented – generally only for
waste and stormwater though sewer inspection
codes.
Tech support for tool is widely available. Support
on analysis of results can be obtained from
specialized consulting organizations.
Varies depending on pipe size, accessibility and
purpose of survey. Can be priced on an hourly rate,
a meter rate, or a per observation rate.
Requires team to operate camera and provide
entry into pipeline. Extent of manpower required
depends on pipe type and flow levels.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-39
F12.7 Bibliography
Dorn, R., Howsam, P., Hyde, R.A. and Jarvis, M.A. Water mains: Guidance on assessment
and inspection techniques, CIRIA Report 162, Construction Industry Research and
Information Association, London, England, 1996.
Randall-Smith, M., Russell, A. and Oliphant, R, Guidance manual for the structural condition
assessment of trunk mains, WRc, UK, 1992.
Ratliff, A., An overview of current and developing technologies for pipe condition assessment,
Pipelines 2003, Pipelines 2003, ASCE 2004.
F-40
F13.0 Concrete Electrical Resistance (Resistivity)
F13.1 Overview of Tool
Resistivity meters are used for measuring the electrical potential fields to evaluate the
corrosion rate of the reinforcing bars in the concrete. The influence of various concrete
components on the electrical resistance can be investigated.
The electrical resistance of the concrete is measured according to the Wenner four-point
method. Resistivity measurements can be performed for measuring the permeability of seal
coats on concrete.
F13.2 Main Principals
The corrosion of steel in concrete is an electrochemical process which generates a flow
of current and can dissolve metals. The lower the electrical resistance, the more readily the
corrosion current flows through the concrete and the greater is the probability of corrosion.
Measurements of resistivity of concrete can provide an indication of the presence, and possible
amount, of moisture in a concrete structure and therefore evaluate the extent and rate of
corrosion of reinforcement indirectly.
Equipment consists of a resistivity probe with integrated electronics for resistivity
measurement by the four-point method, a control plate for resistance probe and a display unit.
F13.3 Applications
Resistivity meters can be used to investigate the influence of various concrete
components on the electrical resistance of reinforcement. Resistivity meters are used in
conjunction with corrosion analyzing instrument to evaluate the corrosion rate of the
reinforcing bars in the concrete.
•
There are no specific standards for concrete electrical resistance; however ASTM D257, ANSI/ESD STM11.11, and ANSI/ESD STM11.2 cover resistivity meters which
are specifically suited to the manufacturing industry and are used for making surface
and volume resistivity measurements.
F13.4 Practical Considerations
♦ Before taking resistivity measurements the reinforcement grid is marked out and
electrical resistance measurements are taken between the bars to minimize the effect of
the reinforcement.
♦ The results should be taken in the concrete’s natural state i.e. natural moisture content.
This value can be used to adjust the permeability measurements made using
permeability testing techniques. After completing permeability testing an additional
resistivity test can give the saturated (worst case) resistivity of the concrete.
F13.5 Advantages
•
Resistivity meters provide immediate on-site measurement of concrete resistivity.
F13.6 Limitations
♦ Resistivity measurements are sensitive to the type of reinforcement, so assessment of
the condition of a structure and the likelihood of corrosion needs to be made with
careful reference to its construction.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-41
♦ Testing often requires that at least two holes in the order of 6.5mm to a depth of
approximately 10mm are drilled in order to insert probes.
Table F-14. Summary Concrete Electrical Resistance (Resistivity).
Technical Selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Asset management sophistication required
Skills required (level of tool sophistication);
usability
Technology required (level of tool sophistication)
Documentation
Economic factors
F-42
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Reinforced concrete structures such as tanks,
pipes, walls, dams, buildings, channels, weirs.
Reinforced concrete.
Potable and wastewater.
Direct contact with surface of asset. If asset is
buried, it must be exposed.
Concrete surface must be fairly level.
No limitations relating to size of concrete
element. Surface must be flat.
Continuous reading.
Almost entirely non destructive, small drill holes
may be required for certain tests.
The asset can remain in use and does not need
to be taken off-line unless internal (water side)
surfaces need to be assessed.
Corrosion rate of reinforcement bars in
concrete.
Stand alone.
Equipment is fully developed, available from
selected commercial vendors.
Widespread use internationally on bridges and
road infrastructure. Limited application in the
water industry.
Quantitative measurement.
Results are indicative and can be validated by
using two other testing techniques: rebar linear
polarization resistance and rebar electrical
potential.
Generic approach.
Relatively easy to use by following simple
procedure. Trained staff can take
measurements.
Low level of sophistication.
No specific standards, although tool is well
documented by distributors. ASTM D-257,
ANSI/ESD STM11.11, and ANSI/ESD STM11.2
cover resistivity meters which are specifically
suited to the manufacturing industry and are
used for making surface and volume resistivity
measurements.
Technical support available from distributors.
Low cost per inspection.
One operator required. Battery powered. Probe
array, low frequency constant magnitude
alternating current drive to probes and LCD
display. The probes come in many types for
embedding in new infrastructure, retrofitting to
existing infrastructure, and a surface probe for
more impromptu inspection.
F13.7 Bibliography
ASTM D-257 Standard Test Methods for DC Resistance or Conductance of Insulating
Materials.
ANSI/ESD STM11.11:2001—Surface resistance measurement of static dissipative planar
materials.
ANSI/ESD STM11.2:2000—Volume resistance measurement of static dissipative planar
materials.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-43
F14.0 Condition Assessment of Plastic Pipes
F14.1 Overview
Assessing the condition of plastics pipelines requires different approaches to those used
for cementituous and ferrous pipelines. This is because the degradation of plastics pipes with
time is completely different from that of these other materials. The difficulty in assessing the
condition of plastics pipes arises because they do not lose material from the pipe wall. Instead,
fracture in plastic pipes occurs by crack initiation from defects either inherent in the pipe wall
or damage sites at the pipe outer surface.
Non-destructive condition assessment for plastic pipes requires that sub-critical crack
growth through the pipe wall be detected before ultimate fracture failure occurs. Currently no
non-destructive techniques are available to locate cracks in plastic pipes before failure occurs.
However, destructive condition assessment techniques can be used to assess the level of
resistance to this kind of failure.
F14.2 Main Principles
Failure of plastic pipes occurs by crack growth through the pipe wall. Depending on
conditions and material, this can result in failure by short cracks that grow slowly through the
pipe wall (the ‘leak before break’ scenario) or by brittle failure, where a whole pipe length can
be completely fractured.
Currently, no non-destructive techniques are available to detect this type of sub-critical
damage. However, several condition assessment techniques are available that use samples
extracted from the pipe to measure important fracture properties. Although such tests are
destructive and do not indicate the extent of sub-critical crack growth in the pipe wall, they do
indicate how well the pipe material would resist such damage should it be initiated. Condition
assessment techniques that can be used in this context are fracture toughness testing, gelation
testing and slow crack growth resistance testing; see reviews of these techniques for more
information.
The remaining service life of a specific asset can only be estimated based on the
expected size of inherent defects in the pipe wall and damage at the pipe outer surface. Such
estimates of inherent defects and damage size can be made from microscopic examination of
similar pipes that have previously failed by fracture in service. Extensive experimental fracture
property data has been published in the literature, which indicates the expected material
properties (strength etc) for well-manufactured and poorly manufactured plastic pipes.
Comparing measured values from pipe samples with this published data may indicate an
inferior section of pipe.
Material quality data can be used in conjunction with known service conditions to
predict the likely remaining life of pipes in a population of assets. Stochastic models can be
utilized in this analysis.
F14.3 Application
The current techniques used to assess plastic pipes are only able to assess the quality of
plastic pipes. The lifetime of a plastic pipe is dependant on a number of factors, such as
pressure and external loads, which can be measured, and on defect size, which cannot. As
defect size can only be measured after failure the remaining life predictions can only be applied
to a batch of assets using stochastic allocation of defect size and not to a specific asset.
F-44
F14.4 Practical Considerations
♦ The material properties of a plastic pipe sample will give a quantitative assessment of
physical parameters, but can only be used to give a qualitative indication of its
likelihood of failure. An assessment of failed plastic pipes can be conducted to assess
the quality of pipes that have already been exhumed.
♦ For reactive assets (such as distribution mains), statistical analysis of failure data
provides a more practical approach to the identification of problem assets.
F14.5 Advantages
•
Condition assessment of samples from important assets could provide information that
would prevent an expensive and unforeseen failure.
F14.6 Limitations
♦ Condition assessment of plastic pipes is currently very difficult, as no techniques are
available to give the remaining service life of an individual pipe.
♦ Approaches available are destructive and can only give a relative measure of pipe
quality; for example, material properties of the sample in comparison to industry
benchmarks.
♦ Gathering field samples for testing will cause a disruption to service while taking such
samples.
Table F-15. Summary Condition Assessment of Plastic Pipes.
Technical
selection
Technical
suitability
Utility technical
capacity
Economic factors
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Pipes.
Plastic.
Potable and wastewater.
Pipe samples must be exhumed for testing.
None.
None.
Discrete.
Currently all plastic assessment tests are
destructive.
Pipes must be exhumed for testing.
Material properties of pipe sample.
N/A
Tests are conducted to Standards; see specific
test review for details.
see specific test review for details.
Relative measure of pipe ‘quality’.
Direct measurements.
Could be used by any utility.
Specialized test house.
Specialized test house.
See specific test review for details.
See specific test review for details.
See specific test review for details.
See specific test review for details.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-45
F14.7 Bibliography
References for the tools used for the condition plastic pipe can be found in their reviews:
♦ Fracture Toughness C-Ring Testing (F27.0).
♦ Methylene Chloride Gelation Assessment (F47.0).
♦ Slow Crack Growth Resistance (F66.0).
F-46
F15.0 Core/Coupon Sampling
F15.1 Overview of Inspection Tool
Core/coupon sampling is a method for obtaining small samples on which to conduct
testing. The samples obtained by this method are small enough so that pipes can be repaired
using repair clamps. As such, while it is not destructive to the pipe, it does require repair work
to be conducted.
F15.2 Main Principles
Core/coupon sampling is conducted when a test is to be carried out that requires only a
small piece of the asset or asset material. Sampling can be conducted on any pipe type and
material with the exception of vitrified clay pipes due to its brittle nature.
If the required sample size is such that its removal can be repaired by normal repair
techniques, such as clamping, the pipe is exposed, the sample cut from the pipe wall, and the
pipe then repaired. If the sample size required is too large to allow clamping type repairs, cutout sampling may be required (see Cut-out Sampling review).
Core and coupon sampling are similar with the exception that core samples are
generally removed using a drill (cylindrical through wall sample), while coupons are cut from
the wall and can be any size without being fully circumferential. These samples can be used for
phenolphthalein testing, carbonation testing, pit depth measurement and other tests depending
on the pipe material.
F15.3 Application
Core/coupon sampling is used to obtain a sample from the wall of any pipe type. The
core/coupon removed can then be tested using techniques appropriate to the material. Core
sampling can also be undertaken on civil assets.
♦ No standards are available to which reference this technique.
F15.4 Practical Considerations
♦ Core/coupon sampling is widely used and simple to conduct.
♦ Often core/coupon samples can be obtained during normal work practice, such as when
a new connection is made to a water pipe; the section removed can be used as a core
sample.
F15.5 Advantages
♦ Samples can be obtained without removing a section of pipe and so does not require
extensive repair work.
♦ Core/coupon samples can be obtained during normal work practice.
♦ In the case of core samples, samples can be obtained from water pressure pipes without
interrupting service using under pressure tapping techniques.
F15.6 Limitations
♦ Samples taken can only be used for a limited range of tests.
♦ Due to small sample size, samples may not be representative of the entire pipe
circumference nor the condition along the pipeline.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-47
Table F-16. Summary Core/Coupon Sampling.
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Utility technical
capacity
Economic factors
F-48
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Pipes and civil assets.
All except VC.
Potable and wastewater.
Access to pipe surface is required and access
for tapping machine.
If pipe in poor condition, may not be suitable to
take coupon, this could induce a stress
concentrator.
None.
Discrete.
Sampling technique, not destructive to pipe but
does require repair work to be conducted.
Pressure pipes must be taken off-line before
sampling, unless sample (tapping) can be made
under-pressure.
N/A
None.
Contractor services could be used.
Industry collects coupons but these are
underutilized for analysis.
N/A
Direct measurements.
Generic approach.
Sample as required for installing pipe
connections and basic repairs.
Low.
WSAA under pressure tapping code.
N/A
Varies with the size of coupon and pipe.
Crew as required for installing pipe connections
and basic repairs.
F16.0 Corrosion Burial Testing
F16.1 Overview
Corrosion of metals in disturbed soils, such as occurs when pipes are laid in trenches, is
complex and not fully understood. Burial testing is used to give an indication of soil corrosivity
assessed over time, rather than as a snap shot as is obtained from most test methods.
This type of testing is conducted by burying multiple samples near a pipeline, which are
then exhumed incrementally over several years to give an indication of soil corrosivity that
takes into account the seasonal and other variations that the pipe is subject to. This method
allows corrosion measurements to be undertaken without destructive sampling from the
pipeline of interest.
F16.2 Main Principles
While tests such as soil resistivity (see Soil (electrical) Resistivity review) and pH are
useful for indicating the corrosivity of a soil, they do not capture the variation in corrosivity to
which a pipeline is exposed over time. In order to determine the corrosivity of a soil taking into
account these variations, burial testing can be used in which multiple samples are exposed to
the same corrosive environment as the pipe over extended time periods.
Burial testing is conducted for metallic pipes, generally ferrous materials, by burying
several samples of the same material as the pipeline. The samples are then exhumed over time
and examined to assess the level of corrosion.
By comparing samples exhumed over multiple years, an indication of corrosion and
pitting rates can be obtained. It should be noted that due to differences in geometry these
samples only indicate corrosion rate and do no give the actual corrosion the pipe is subject to at
its outer surface.
F16.3 Application
Burial testing is conducted to obtain an understanding of soil corrosivity over time,
rather than a ‘snapshot’ measurement technique. This testing can be conducted for any asset
type, however is generally limited to ferrous assets without protective coatings.
F16.4 Practical Considerations
♦ The samples should be buried near to and at a similar depth as the pipeline in an effort
to ensure that environmental conditions of the samples are as similar as possible to
those of the pipeline.
♦ If the pipeline of interest includes welds, then the test samples should also include
welds so that the samples are representative of the pipeline.
♦ When multiple samples are to be exhumed at the same time, they should be connected
with a polymeric rope to aid location.
F16.5 Advantages
♦ As testing takes place in real time under real conditions, the results represent corrosion
conditions more accurately than tests which only provide a ‘snapshot’ of soil
conditions.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-49
F16.6 Limitations
♦ In the vast majority of pipelines where corrosion is causing problems, the nature of the
corrosion damage is not uniform along the pipeline. Often this is also true along a
single pipe length, limiting the value of results obtained from burial samples.
♦ Corrosion burial testing needs to be planned prior to installation of the pipe for optimal
results.
♦ As there are geometrical, time and location variations between the burial sample and
the actual pipe, results from the sample may not represent the actual corrosion rate at
the pipe outer surface.
♦ Burial testing is a long term test method where results are obtained over many years;
samples need to be buried for extended periods before useable results can be obtained.
Table F-17. Summary Corrosion Burial Testing.
Technical
selection
Technical
suitability
Utility technical
capacity
Economic factors
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Pipe.
Generally ferrous.
Potable and wastewater.
None.
None.
Generally applicable to large diameter mains,
but no inherent restrictions.
Discrete.
Non-destructive.
Asset on-line.
Corrosivity of the soil environment.
None.
N/A
Not a common practice in the water sector.
Relative assessment.
Validation through assessment of pipe.
Generic approach.
Skills associated with evaluation of test piece;
depends on technique used.
Low.
N/A
N/A
Depends on technique used.
Samples must be exhumed.
F16.7 Bibliography
1. Korb, L., Olsom, D., Davis, J., Destefani, J., Frissell, H., Crankovic, G., Jenkins, D.,
Stedfeld, R., Mills, K., Johnson, J., Kiepura, R. and Humphries, D. Metals Handbook, 9th
edition Volume 13 – Corrosion, ASM International, United States of America, 1987.
F-50
F17.0 Cover Meter - Reinforcement Location and Measurement
F17.1 Overview of Tool
Cover meters are a non-destructive means for determining the depth to concrete
reinforcement, the location of reinforcement at different depths up to 360mm, bar spacing and
anchor setting points in concrete assets. Cover meters use the eddy current testing method.
F17.2 Main Principles
Along with concrete quality, cover thickness is the single most important durability
parameter for concrete structures.
In the pulse current method, a pulse of current transmits a magnetic field through the
reinforcement. Following the pulse, an eddy current induced in the reinforcement bar produces
a second magnetic field that creates a decay time signal in the coils proportional to the bar size
and cover. Coils housed in the cover meter tool’s measuring head can be tuned for sensitivity
to bar spacing or cover depth. The pulse current method can be combined with a scan car that
measures the position of the measuring head relative to the concrete surface.
Some cover meters have a built-in facility to measure half-cell potential measurements
as well as the Eddy current method. The combination of both methods results in accurate
surveys of reinforcement in concrete structures. BS1881:242 stipulates accuracy requirements
for cover meters when measuring in different ranges. Advanced cover meters have an accuracy
within ±1 mm.
F17.3 Application
Cover meters can be used on concrete slabs, walls, columns, pipes and spiral mesh.
♦ British Standard BS1881:242
F17.4 Practical Considerations
♦ Cover meters are sophisticated tools that come in digital versions, and calculate and
display the location of reinforcement instantaneously. Their operation is menu driven
with on-screen guidance. Generally logged data is date and time stamped. Results are
downloadable to PC or printer.
♦ Some tools are designed for large scale and detailed investigations, and have a range of
cover functions incorporated in their program. These allow a comprehensive range of
characteristics and logging of up to 30,000 measurements.
♦ Many cover meters display the location of reinforcement in large black characters on a
LCD that can be backlit in poor light conditions.
F17.5 Advantages
♦ Non-destructive methods for checking cover have become faster and more accurate in
recent years.
♦ Cover meters are more accurate for determining the penetration depth of the
carbonation front than the traditional method of dye penetration where a freshly
fractured surface is sprayed with a pH indicator, such as phenolphthalein or
thymolphtalein.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-51
F17.6 Limitations
♦ Cover meters lose accuracy at greater depths. Even ‘long range’ cover meters can only
be relied upon to detect rather than measure bars at depths between 250 and 300mm;
and this is subject to bar size.
Table F-18. Summary Cover Meter – Reinforcement Location and Measurement.
Technical
selection
Criteria
Assets covered
Material
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Asset management sophistication required
Skills required (level of tool sophistication);
usability
Technology required (level of tool
sophistication)
Documentation
Economic
factors
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Concrete elements such as slabs, beams, columns,
walls, pavements, tunnels, pipes and dams.
Reinforced concrete.
Potable or wastewater.
Direct contact with asset.
No limitations relating to asset condition.
No limitations relating to size/geometry: the maximum
thickness of concrete which can be tested is 300mm.
Cover meters measures to over 250mm depth and
detect to over 300mm, subject to bar size.
Continuous readings in time and space.
Non-destructive.
The asset can remain in use; needs to be taken off-line
only if an internal surface is required to be accessed.
Cover depth to reinforcement, location of reinforcement
at different depths up to 360mm, bar spacing and
anchor setting points.
Can be integrated with software tools.
Equipment is widely available from selected commercial
vendors.
Widespread use in the water and other sectors, and
acceptable to stakeholders.
Advanced cover meters have an accuracy within ±1mm.
Results can be validated. Some cover meters have a
built-in facility to measure half-cell potential
measurements as well as the Eddy current method. The
combination of using both methods results in accurate
surveys of reinforcement in concrete structures.
Generic approach.
Easy to use by following simple procedure.
Measurements can be taken by unqualified staff.
Cover meters are sophisticated tools which come in
digital versions which calculate and display the location
of reinforcement instantaneously.
Cover meters are thoroughly documented British
Standard BS1881:242.
Technical support widely available.
Low cost per inspection.
One operator required. Battery powered. Resources
required can also depend on asset being inspected.
Buried assets need to be exposed.
F17.7 Bibliography
1. BS 1881 Part 204:1988: Recommendations on the Use of Electromagnetic Covermeters.
2. BS1881:242 British Standard 1881.
F-52
F18.0 Crack Measurement Tools
F18.1 Overview of Tools
Cracks in concrete structures can be measured with a range of tools. Crack
measurement tools and their corresponding measuring ranges and accuracies are listed below.
F18.2 Main Principals
Deformation Meters: Deformation Meters are used for measuring linear deformations,
cracks, settlements and shrinkage coefficients. Two base plates are attached to the concrete to
give fixed reference points approximately 300 mm apart. The gauge is then used to accurately
measure the change in length as the structure ages. Deformation meters can have a measuring
length of 300 mm. They are two versions of dial gauges: analog 5 mm x 0.001 mm and digital
25 mm x 0.001 mm. The meters include a setting and calibration bar, base plates and adhesive.
Measuring Magnifier: The measuring magnifier typically has a magnification of 8×.
Crack widths are normally limited to 0.2mm or 0.3mm in concrete structures. This crack width
measuring device enables accurate determination of whether cracks exceed this limit.
Crack Width Meter: The crack width meter is used as a comparator to give an
approximate crack size during visual surveys. Combined with 10 reduction scale rules.
Crack Monitor: The crack monitor is used on structures where the rotation at cracks is
also significant. The crack monitor gauge is specifically designed to measure rotation,
transverse and longitudinal movement. Special fittings are available to measure external and
internal corners.
F18.3 Application
Crack measurement tools can be applied to a wide range of substrates including steel.
They are most commonly used on concrete structures.
♦ ASTM E1457-00 Standard Test Method for Measurement of Creep Crack Growth
Rates in Metals
F18.4 Practical Considerations
♦ Crack measurement tools are widely used for the condition assessment of concrete
structures and can be purchased for a number of commercial suppliers. The tools are
easy to use and often handheld.
♦ When measuring crack widths with deformation meters, it is important to measure
across the crack and across adjacent intact concrete so that adjustment to the crack
width movement can be made.
♦ Table F-19 gives a summary of the tools.
Table 19. Summary of Tools.
CRACK MEASUREMENT TOOL
Deformation meter
Measuring magnifier
Crack width meter
Crack monitor
ACCURACY/ MEASURING RANGE
Accuracy ± 0.001mm.
Magnification 8x Measuring range 15 mm x 0.05 mm. Accuracy ± 0.05mm.
Graduations from 0.05 – 5 mm.
Measuring scale for horizontal and vertical measurements: horizontal ± 25
mm and vertical ±10 mm.
Reading accuracy of ±1mm on grid and ± 0.1 mm with a caliper.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-53
F18.5 Advantages
♦ Crack measurement tools are accurate, reliable, non-destructive, easy to use, relatively
inexpensive and very portable.
F18.6 Limitations
♦ Results are likely to vary according to changes in parameters such as the water level in
concrete tanks and temperature of concrete due to exposure to sunlight and seasonal
variation.
Table F-20. Summary Crack Measurement Tools.
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Utility
technical
capacity
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication);
usability
Economic
factors
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Reinforced concrete structures such as dams, walls tanks,
large pipes, buildings, etc.
Most commonly used on reinforced concrete.
Potable or wastewater.
Direct contact with surface of asset. If asset is buried then
it must be exposed.
Generally no restriction. However surface may need
cleaning in order to accurately locate edges of cracks.
No limitations relating to size of concrete element.
Discreet readings.
Non-destructive.
The asset can remain in use and does not need to be
taken off-line.
Crack width. Rotational, transverse and longitudinal
movements at any point on a structure where there is
crack movement can also be measured.
The majority of tools are stand alone.
Equipment is fully developed, available from a wide range
of commercial vendors and can be used off the shelf.
Widespread use internationally in the water industry.
Quantitative.
Direct measurement easily validated.
Generic approach.
Relatively easy to use by following simple procedure.
Crack measurement tools do not require specialist
knowledge or training.
Range from low to moderate level of sophistication.
ASTM E1457-00.
Technical support widely available from distributors.
Low cost per inspection.
One operator required.
F18.7 Bibliography
1. ASTM E1457-00 Standard Test Method for Measurement of Creep Crack Growth Rates in
Metals.
F-54
F19.0 Current Monitoring
F19.1 Overview
Current monitoring is a non-destructive on-line condition assessment method that can
be used on assets that contain electric motors. By monitoring variations in current flow the
onset of electrical faults can be identified before equipment breakdown occurs. Current
monitoring analysis can be used to detect electric motor problems such as broken rotor bars,
broken/cracked end rings, flow or machine restriction and machinery misalignment.
F19.2 Main Principles
This technique involves monitoring the current flowing through one of the power leads
located at the motor control center or starter, typically by using a clamp-on ammeter. By
measuring the electrical current variations and trending the recorded data over time, changes in
the equipment operating conditions and performance can be monitored and compared to the
design loads recorded during commissioning. The data can then be used for determining the
onset of electrical faults or equipment breakdown.
The clamp-on ammeter (also known as Tong Tester) measures current by the strength
of the magnetic field around it rather than by becoming part of the circuit. One modern method
uses a small magnetic field detector device called a Hall-effect sensor. Hall-effect devices
produce a very low signal level and thus require amplification.
The clamp on ammeter makes for quick and safe current measurements, because there
is no conductive contact between the meter and the circuit.
F19.3 Application
The technique of current monitoring can be used on electrical induction motors,
synchronous motors, compressors, pumps and motor operated valves, to determine changes in
the level of performance that occur over time and enable repair or replacement prior to
electrical faults or equipment breakdowns occurring.
♦ There is no specific standard for test method.
F19.4 Practical Considerations
♦ Current monitoring is a technique widely used for condition monitoring and can be
easily undertaken on all electrical motors by a trained electrical technician or engineer
using a hand held testing apparatus.
♦ Clamp-on ammeters are widely available from numerous suppliers; older units can only
be used on AC equipment while newer equipment can measure both AC and DC. The
older probe consists of a core of ferromagnetic material, which when closed forms the
core of a transformer of which the wiring passing through the clamp is the primary
winding.
♦ The least expensive clamp on ammeters use an average-detecting rectifier circuit that is
then calibrated to read in RMS units; it is assumed in their design that the current is a
sine wave of the local mains frequency, that is, either 50 or 60 Hz. When such meters
are used with non-sinusoidal loads such as electronic equipment, the readings produced
can be quite inaccurate. Meters that use true-RMS converters give accurate readings in
almost any situation.
♦ Hall-effect sensor gives accurate readings over a wider frequency range from DC to
thousands of hertz.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-55
♦ The sensitivity of portable clamp-on ammeters is often dependant on cost, however
most units can measure current flow with high accuracy.
F19.5 Advantages
♦ Monitoring can be undertaken with the equipment on-line with minimal disruption.
♦ Routine current monitoring enables determination of equipment electrical faults prior to
failure.
F19.6 Limitations
♦ Trained electrical technicians are required to undertake assessment, as equipment must
be under load to enable for reliable results.
♦ While the results obtained typically indicate that a possible problem is present, further
analysis required to identify the exact equipment or component fault.
Table F-21. Summary Current Monitoring.
Technical
selection
Technical
suitability
Utility technical
capacity
Economic factors
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Any electrical load.
N/A
Potable or wastewater.
None.
None.
None.
Continuous in time.
Non-destructive.
Must be on-line with suitable precautions taken
against operator direct contact with live parts.
Current.
Stand alone.
Fully developed and off the shelf.
Standard industry practice.
Quantitative.
Direct measurement.
Generic approach.
Electrician will already be trained to use.
N/A
Well documented.
N/A
Low cost per inspection.
Low; one person no more than a few minutes
per load.
F19.7 Bibliography
1. Weschler instruments, http://www.weschler.com, accessed 2006.
9H
F-56
F20.0 Cut-out Sampling
F20.1 Overview
Cut-out sampling is a method for obtaining a short pipe ring sample on which a range
of tests can be undertaken. It is a destructive technique that can be applied to pipes of any
material, but is more generally used on smaller diameters.
F20.2 Main Principles
Cut-out sampling is conducted when a pipe asset is to be assessed with a test that
requires only a small section of the asset. The length of pipe removed is dependant on the test
to be conducted. Sampling can be conducted on any pipe type and material; however it is
unlikely to be conducted on vitrified clay pipes due to its brittle nature.
If the sample required is not a ring sample and is small enough so that the area could be
repaired using a clamp type repair, then core/coupon sample may be a better option (see
Core/Coupon Sampling review).
Samples obtained can be used in compressive strength testing, pit depth measurement,
fracture toughness testing and other tests depending on the pipe material.
F20.3 Application
Cut-out sampling is used to obtain a short pipe length for testing from the wall of any
pipe type. The cut-out removed can then be tested to assess the pipe it was removed from. It is
more generally used for assessment of water distribution pipes, but could be applied to
wastewater pipes. No Standards are available to which reference this technique.
F20.4 Practical Considerations
♦ Cut-out sampling is widely used and simple to conduct.
♦ When obtaining samples from wastewater pipes the emptying of the pipelines and
storage of sewage during sampling are important considerations.
F20.5 Advantages
♦ Samples can be obtained without removing a full pipe length section of pipe, thereby
minimizing repair work.
♦ Most condition assessment tests can be conducted on cut-out samples.
F20.6 Limitations
♦ The sample obtained may not be representative of the condition along the pipeline
entire pipe.
♦ Pipes must be taken out of service and pressure pipes emptied to allow sampling.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-57
Table F-22. Summary Cut-out Sampling.
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Technical
suitability
Utility technical
capacity
Economic factors
F-58
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication);
usability
Technology required (level of tool
sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Pipes.
All.
Generally potable.
Access to pipe surface is required. Pipeline to
be depressurized.
None.
None.
Discrete.
Sampling technique, which requires repair work
to be conducted. Destructive.
Pipes must be taken off-line.
N/A
None.
N/A
Technique has been widely used in industry.
Direct measurement.
N/A
Generic approach.
Sample as required for conducting pipe repairs.
Low.
N/A
N/A
Varies dependant on location, size, type, etc.
Crew as required for conducting pipe repairs.
F21.0 Drop Test
F21.1 Overview
Water loss control programs are widely used throughout the water industry (see Leak
Detection review). Drop tests are a simple non-destructive method for identifying areas of a
network containing significant leakage.
A drop test can be undertaken for individual pipelines both new (at the time of
installation) and old, small pipe network areas and larger areas. Drop tests work by isolating
the area of interest and observing either the level of water in a reservoir or water pressure. Loss
of water head/height (beyond normal use if all connections cannot be closed) indicates that
either the pipe(s) or valve(s) are leaking. Similar testing has also been used to measure
exfiltration in sewers.
Leak detection gives both an indication of condition and performance of the asset,
depending upon the amount of leakage on a section of pipe. However, it does not give detail
regarding the overall condition of the pipe.
F21.2 Main Principles
The drop test involves isolating a section of pipe or pipe network and observing
whether water is lost during the test. If the upper end of the pipeline is fed by a reservoir, as in
a gravity-fed system, the level in the reservoir can be monitored. If this level drops during the
test, the level of leakage can be determined by calculating the volume lost from the reservoir.
If the pipeline is not fed by a reservoir, leakage can be identified by monitoring the
pressure associated with the falling water level in the pipeline. When the section has been
isolated, a pressure monitor fitted below the uppermost water level will enable any drop in the
level of the water to be detected.
F21.3 Application
Drop tests are generally applied to detect leakage in large diameter transmission mains,
or area of a network. They can also be applied to sewerage assets to assess exfiltration.
♦ There are no known Standards which reference drop testing.
♦ Practical considerations
♦ As a general approach to assessing water tightness, drop testing can be undertaken by
any utility. The simple nature of the test has let it to be widely used in the water and
other industry sectors. It has been used in the U.K. water sector as a low technology
approach to assessing leaks in transmission mains. It has also been used in research to
assess the level of exfiltration from sewers.
♦ The accuracy of drop testing is limited by the type of method used to assess leakage
(level or pressure drop) and the size of the area being tested.
♦ Advantages
♦ Low tech approach for assessing leakage within pipelines. This technique can also be
applied to pipe sections.
♦ The drop test can be used to gain a quantitative measure of leakage for a pipe or area of
the network.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-59
F21.4 Limitations
♦ The time involved in isolating pipe sections and monitoring the reservoir makes this
method impractical except on an annual basis.
♦ Only the presence of leaks is indicated, no indication is given of location. Leaks can be
associated with the down stream valve.
♦ The drop test requires assets to be taken off-line.
♦ The test does not give detail regarding the overall condition of the pipe.
Table F-23. Summary Drop Test.
Technical
selection
Technical
suitability
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Utility technical
capacity
Economic factors
F-60
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication);
usability
Technology required (level of tool
sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Pipelines.
Any.
Potable or wastewater.
Requires ability to isolate pipeline and access to
monitoring points and/or service reservoirs.
None.
Large diameter pipelines.
Discrete measurement in time.
Non-destructive.
Asset be taken off-line.
Water loss from pipe either due to exfiltration
(gravity sewers) or leakage (pressurized pipes).
Stand alone.
General approach.
Used in the UK for leak assessment on
transmission mains, used in Australia for
assessment of exfiltration.
Quantitative.
Direct measurement.
Generic approach.
Technical skills associated with pipeline
management .
Low tech.
No.
No.
Depends on test.
Depends on test.
F22.0 Ductor (Micro Ohm Resistance) Testing
F22.1 Overview
The Ductor (proprietary name) test is a non-destructive assessment to determine the
contact resistance in draw–out contacts such as circuit breakers on high current devices and bus
bar interconnections located in electrical power distribution boards and switchboards. The test
is normally carried out by applying a high current across the device which is being assessed,
allowing the detection and isolation of a poor connection so that corrective action can be
undertaken.
F22.2 Main Principles
Typically the four-wire Kelvin Bridge method is used consisting of two current and two
voltage wires. The two current leads are connected across the joint to be tested. A high current
(typically 0-600A) is passed through the joint or contact under assessment at a low voltage (04V DC). The two sensing leads measure the voltage across the joint. The resistance is
calculated from the test current and sense voltage, with the resistance measured in micro Ohms
(µΩ).
The voltage sensor leads are in parallel to the joint and only carry a miniscule current.
As such, the test lead resistance can be ignored.
The test can determine the condition of switch gear and circuit breakers, which can
deteriorate over time as a result of heat build up and the formation of carbon deposits during
operation. Surface contamination, overloading with resultant heat build up or incorrect torque
settings can also result in poor quality joints.
F22.3 Application
The Ductor assessment method is commonly undertaken to determine the condition of
electrical circuit breakers contacts, switchgear contacts, cable joints and bus bars joints where
high currents are encountered. It is commonly used on new installations for initial verification
and benchmarking, followed by periodic tests.
♦ There is no specific standard for test method.
F22.4 Practical Considerations
♦ Ductor test assessments should be conducted by trained electrical technicians or
engineers with experience in undertaking diagnostic analysis of electrical equipment
and components.
♦ Auxiliary supply voltage to the test unit is typically 100 – 250V AC. The duration of
output current is limited (dependant upon manufacturer) but need only be long enough
to get a steady reading. For repetitive tests, cool off intervals may be required. Test
equipment with download facilities are available.
♦ When assessing new equipment/joints, knowledge of the materials electrical properties
is required. This may be the manufacturer’s stated contact resistance or the conductivity
of the bus bar material.
♦ For periodic testing, previous assessment results, typically those obtained during
commissioning, are required for comparison in order to determine the current condition
and likelihood of future equipment breakdown.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-61
♦ Access to epoxy resin filled cable joints is not possible. The equipment to be tested
must be electrically isolated and accessible.
♦ A higher test voltage than that specified above is not required nor is it desired. Higher
voltages can break down the joint resistance.
F22.5 Advantages
♦ Ductor test assessments are sensitive and provide measurements of micro Ohms (µΩ).
F22.6 Limitations
♦ Prior to undertaking Ductor testing, the equipment being assessed must be isolated.
♦ Previous test results are required to assess the current condition of the asset.
Table F-24. Summary Ductor (Micro Ohm Resistance) Testing.
Technical
selection
Technical
suitability
Utility technical
capacity
Economic
factors
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Electrical connections, busbars and contacts.
The conductor.
Potable and wastewater.
Access to normally livened parts which must be
made dead. Portable hand held equipment.
None.
None.
Discrete reading.
Non-destructive.
Off-line.
Resistance.
Stand alone.
Off the shelf.
Widely used.
Quantitative.
Direct measurement.
Generic approach.
Qualified electrician.
Test instrument only. Data requires no further
manipulation.
Well documented.
Commercially available.
Labor costs only.
One person, typically two hour
period/switchboard.
F22.7 Bibliography
1. T&R test equipment, http://www.trtest.com, accessed 2006.
10H
2. Transpower homepage, http://www.gridupgrade.co.nz, accessed 2006.
1H
F-62
F23.0 Electrical Potential (Half Cell) Measurement of Concrete Reinforcement
F23.1 Overview of Tool
Electrical potential measurement is a non-destructive technique that can be used to
identify areas of reinforced concrete in need of repair or protective treatment before corrosion
causes cracking and spalling. It does this by measuring the electrical potential between the
reinforcing and a reference electrode at the surface. By taking regular measurements, the
behavior of new and relatively new structures can be monitored and maintenance costs
minimized.
F23.2 Main Principals
Steel corrosion is an electrochemical process involving anodic (corroding) and cathodic
(passive) areas of the metal. To measure the electrical potential, an electrical connection is
made to the steel reinforcement of the asset to be assessed. This is connected to a high
impedance digital millivoltmeter, often backed up with a data logging device. A standard
reference electrode, either copper/copper sulfate or silver/silver chloride half cell, is also
connected to the millivoltmeter. The electrode used has a porous connection at one end that can
be touched to the concrete surface, see Figure F-3. The millivoltmeter will then register the
corrosion potential of the steel reinforcement nearest to the electrode’s point of contact. By
measuring results on a regular grid and plotting results as an equipotential contour map, areas
of corroding steel may readily be seen. Using 3D mapping techniques, a more graphical
representation of the corrosion can be shown.
Figure F-3. Electrical Potential Measurement Technique.
(Reprinted with permission from: Gu, P. and Beaudoin, J, 1998).
F23.3 Application
Electrical potential measurement is used to assess the corrosion potential of steel
reinforcement in civil concrete assets.
♦ ASTM Standard C876 provides general guidelines for evaluating corrosion in concrete
structures. Electrical potential measurement is also referenced in BS 1881: Part 201.
F23.4 Practical Considerations
♦ Equipment typically has a large digit display which is backlit for ease of reading in
poorly lit environments.
♦ Extensible probe holders are available for remote surveying.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-63
♦ Many different electrode configurations have been tried in practice and several of these
have been found to have advantages over standard arrangements.
♦ Surfaces in excess of 4000m2 can be measured.
♦ The reinforcement at the point of measurement has to be electrically connected to the
millivoltmeter for reliable results to be obtained. If multiple sheets of reinforcement
were used and not electrically connected a point of contact must be made to each sheet.
♦ Electrical potential measurement equipment typically readily portable and consists of
electrode rods or wheel, connecting cables and display unit.
F23.5 Advantages
♦ Electrical potential measurement is a safe, rapid, cost-effective and non-destructive
method of condition assessment, which offers key information on the evaluation of
corrosion.
♦ It is the simplest way to assess the severity of steel corrosion, as it measures corrosion
potential, which is qualitatively associated with steel corrosion rate.
♦ Confidence in electrical potential measurement as an indication of corrosion potential
has developed greatly as a result of bridge deck corrosion surveys. An indication of the
relative probability of corrosion activity was empirically obtained through
measurements during the 1970s.
♦ According to the ASTM C876 method, corrosion can only be identified with 95%
certainty at potentials more negative than -350 mV. However experience has shown
that passive structures tend to show values more positive than -200 mV and often
positive potentials. Potentials more negative than -200 mV may be an indicator of the
onset of corrosion. The patterns formed by contours on graphical representations of
corrosion can often be a better guide than single potential readings in these cases.
F23.6 Limitations
♦ Electrical potential measurement does not directly indicate the rate of corrosion. There
are difficulties associated with making reliable quantitative measurements. The factors
influencing the electrical potential measurements are affected by the resistivity of the
concrete and the pH of the pore solution (carbonation). It could be necessary to use a
statistical analysis of measurements on individual structures to establish areas where
corrosion of reinforcement occurs.
♦ Several factors can alter the precision of potentials measured:
−
−
−
−
−
−
−
−
−
−
−
F-64
Concrete cover depth
Concrete resistivity
High resistive surface layers
Polarization effects
Organic coatings and sealers
Concrete patch repair
Epoxy coated and galvanized reinforcement
Use of corrosion inhibitors
Chloride ion concentration
Carbonation
Oxygen concentration
♦ These factors influence electrical potential readings because when surface potentials are
taken they are measured remotely from the reinforcement due to the concrete cover.
The potentials measured are therefore affected by the potential drop over the distance
between the reinforcement and the electrode.
♦ Electrical potential measurement cannot be used on structures with active cathodic
protection systems. An energized cathodic protection system and stray current will
make electrical potential measurements meaningless.
♦ Electrical potential measurement should never be used in isolation. It should be
combined with the measurement of the chloride content of the concrete and its variation
with depth and also the cover to the steel and the depth of carbonation.
Table F-25. Summary Electrical Potential (Half Cell) Measurement of Concrete Reinforcement.
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Assessment
All reinforced concrete assets.
Reinforced concrete.
Potable and wastewater.
Direct contact with asset. If asset is buried then it
must be exposed, surface coatings do not need
to be removed.
No limitations relating to asset condition.
No limitations relating directly to geometry.
There are limitations relating thickness of
concrete. With increasing concrete cover, the
potential values at the concrete surface over
actively corroding and passive steel become
similar. Thus the location of small corroding
areas becomes increasingly difficult.
Continuous readings in time and space.
Non-destructive.
The asset can remain in use and does not need
to be taken off-line unless an internal surface is
required to be accessed.
Detection of corrosion.
Can be integrated with software tools to produce
potential mapping: equipotential lines that allow
the location of the most corroding zones at the
most negative values.
Equipment is widely available from selected
commercial vendors.
Widespread use on bridge deck corrosion
surveys. Use increasing in the water sector,
gradually becoming acceptable to stakeholders.
Corrosion can be identified with 95% certainty at
potentials more negative than -350 mV.
For validation purposes, electrical potential
measurement can be combined with the
measurement of the chloride content of the
concrete and its variation with depth and also the
cover to the steel and the depth of carbonation.
Generic approach.
Easy to use by following simple procedure.
Measurements can be taken by unqualified staff.
Sophisticated digital tools. For many tools,
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-65
Criteria
Documentation
Availability of technical support
Economic
factors
Cost per inspection
Resource requirements
Assessment
measurements are automatically converted and
displayed as equipotential lines that allow the
location of the most corroding zones at the most
negative values potentials.
ASTM C876 and BS 1881:Part 201.
Technical support widely available from
distributors.
Low cost per inspection.
One operator required. Battery powered.
Resources required can also depend on asset
being inspected. Buried assets need to be
exposed.
F23.7 Bibliography
1. Gu, P. and Beaudoin, J., Obtaining Effective Half-Cell Potential Measurements in
Reinforced Concrete Structures, Construction Technology Update No. 18, pp1-3, July
1998.
12H
2. Naumann, J. and Haardt, P. NDT Methods for the inspection of highway structures’.
International Symposium (NDT-CE 2003). Non-Destructive Testing in Civil Engineering,
pp2-5, 2003.
3. Torrent, R. and Frenzer, G. A method for the rapid determination of the coefficient of
permeability of the “Covercrete”. International Symposium Non-Destructive Testing in
Civil Engineering (NDT-CE). pp985-992, 26-28.09.1995.
4. ASTM Standard C876 provides general guidelines for evaluating corrosion in concrete
structures.
5. BS1881-201:1986 Testing concrete. Guide to the use of non-destructive methods of test for
hardened concrete.
6. Technical brochures produced by MG Associates Construction Consultancy Ltd, 2006.
F-66
F24.0 FailNet-Reliab
F24.1 Overview
FailNet-Reliab is a hydraulic reliability model for water pipelines developed by the
French research organization Cemagref. The approach is based on a hydraulic model (see
Hydraulic Modeling review) of the network coupled with reliability analysis. The output is an
assessment of the networks hydraulic performance expressed in terms of the ability to meet
demand.
F24.2 Main Principles
FailNet-Reliab is a computer modeling tool that can be used to assess the reliability of
water distribution networks. Reliability is considered in the context of water demand
satisfaction; essentially it is the quotient between the available consumption and the water
demanded.
After a specific hydraulic modeling study, where available consumption is computed
according to the pressure head at each node, several reliability indices are assessed and can be
used as performance indicators. Different scales of assessment are undertaken:
♦ Pipes – the impact of a pipe break on all the nodes of the network.
♦ Nodes – the reliability of supply at the node in relation with all the links.
♦ Global network – the overall reliability of the network.
♦ The model is implemented in two steps:
♦ Firstly, a hydraulic model is constructed. This differs from a classical hydraulic model
because water consumptions are not fixed and depend on computed pressure heads and
water demands. The Newton-Raphson method is used to solve the hydraulic equations
and compute the outputs.
♦ Secondly, reliability indices are assessed. The reliability indices depend on the results
of the hydraulic models (with or without pipe breaks), on the weight of each nodes
(quantity, vulnerability) and on pipe failure probabilities (which can be assessed with
probability models, such as Failnet-Stat). The indices represent the volume of nonsupplied water in the year because of failure risk.
F24.3 Application
FailNet-Reliab is used to assess the reliability for water supply networks utilizing
hydraulic models and failure probability estimates. This allows the reliability of a network to
be improved by modeling to compare different asset management strategies.
F24.4 Practical Considerations
♦ The tool is not fully commercialized and the approach has only had limited use in
France and with research groups.
♦ Data requirements are similar to that of classical hydraulic data. For nodes, altitude,
water demand and type of water use are required. For pipes, the roughness, length and
diameter are required. The volume and altitude are required for tanks.
♦ Failure probability, as calculated by FailNet-Stat (see FailNet-Stat review) can also be
incorporated into the model, but is not mandatory.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-67
♦ The software was to be reprogrammed in 2006/2007 to support all hydraulic features
and to improve functionality.
F24.5 Advantages
♦ Provides engineers with a different view of the networks hydraulic performance by
factoring in reliability indices into the modeling process.
F24.6 Limitations
♦ Has only had limited use in France and with research groups.
♦ FailNet-Reliab requires additional information such as failure probability and mean
repair time to gain the full benefit from the package, and these have to be
developed/determined separately.
♦ Some hydraulic features are not supported and may need to be replaced by equivalent
sources/demands.
Table F-26. Summary FailNet-Reliab.
Technical
selection
Technical
suitability
Criteria
Assets covered
Granularity
Service areas
Focus of analysis
Scalability of tool/approach
Commercialization
Previous/existing use of the tool
Ease of validation
Utility technical
capacity
Flexibility with regard to analysis (asset types) and
granularity (system, asset level)
Integration with other tools/GIS
Asset management sophistication
In-house skills required
Technology required
Documentation
Data Requirements
Linking to asset data
Availability of software and technical support
Usability
Assessment
Water pipes.
System and sub system level.
Potable
Hydraulic reliability for water pipelines.
Better suited to medium to large authorities
where good data is available.
Software available from Cemagref, France. Is
not full commercial version.
Only limited use in France and with research
groups.
As for hydraulic modeling and reliability tools;
independent validation is through field work.
Potable only; system or sub system level.
CARE-W manager.
Aimed at higher level of asset management.
Asset manager/engineer.
PC based tool.
Only limited documentation available.
Typical hydraulic modeling data is required.
Pipe IDs.
Software available from Cemagref, France
Not fully commercialized.
F24.7 Bibliography
1. Stone, S., Dzuray, E. J., Meisegeier, D., Dahlborg, A-S., and Erickson, M. DecisionSupport Tools for Predicting the Performance of Water Distribution and Wastewater
Collection Systems, EPA, EPA/600/R-02/029, 2002.
F-68
F25.0 FailNet-Stat
F25.1 Overview
FailNet-Stat is a failure forecasting model for water pipelines developed by the French
research organization Cemagref. The approach uses historical data to define survival functions
that are then used in Monte-Carlo analysis to forecast the number of failures within pipe
cohorts.
F25.2 Main Principles
FailNet-Stat is a computer modeling approach that is applied in three steps:
1. Analysis of historical failure records using a proportional hazard model. The system
analyzes historical data, evaluates factors that influence failures, and identifies
factors that maximize the likelihood of failures.
2. By incorporating the information above, the system uses a Weibull distribution to
determine the time between successive failures. Separate models may be used for
pipes grouped according to their material and number of previous failures.
3. Forecasting the number of failures for a defined period using a Monte-Carlo
method. The system then forecasts the number of failures from the survival
functions for each group of pipes (materials and current condition). This forecast
can be used in combination with a hydraulic reliability model, in an economic
model, or alone as one of the rehabilitation criteria.
F25.3 Application
FailNet-Stat is designed to allow water authorities to establish failure probabilities for
the various pipe materials in their water distribution system.
F25.4 Practical Considerations
♦ The tool is not fully commercialized and the approach has only had limited use in
Europe and with research groups. It requires good quality asset data and failure history
data. Furthermore, optimum usage of the tool requires experience, particularly with
regards to the statistical significance of the results.
♦ An alternative model is being developed which is capable of producing better
estimations of failure risk for individual pipes. This will form the basis of new software
in 2007. The software will also facilitate result interpretation by incorporating a benefit
index.
F25.5 Advantages
♦ FailNet-Stat enables reliable failure probabilities to be established for a utility’s water
network (at individual pipe level), which can then be used to more effectively manage
the network and undertake additional analysis functions such as reliability analysis, etc.
F25.6 Limitations
♦ FailNet-Stat has only had limited use in Europe and with research groups. It requires
good asset and failure data. Over-estimation of failure rates for individual pipes is
common if the failure observation period is short. However, the relative failure risk is
considered to be more accurate.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-69
Table F-27. Summary FailNet-Stat.
Technical
selection
Technical
suitability
Criteria
Assets covered
Granularity
Service areas
Focus of analysis
Scalability of tool/approach
Commercialization
Previous/existing use of the tool
Utility technical
capacity
Ease of validation
Flexibility with regard to analysis (asset types) and
granularity (system, asset level)
Integration with other tools/GIS
Asset management sophistication
In-house skills required
Technology required
Documentation
Data Requirements
Linking to asset data
Availability of software and technical support
Usability
Assessment
Water pipes.
System and sub system level.
Potable
Failure forecasting model for water pipelines.
Better suited to medium to large authorities
where good data is available.
Software available from Cemagref, France. Is
not full commercial version.
Only limited use in Europe and with research
groups.
Statistical validation.
Potable only; system or sub system level.
Through CARE-W Manager.
Aimed at higher level of asset management.
Asset manager/engineer.
PC based tool.
Only limited documentation available.
Good asset and failure data is required.
Pipe ID.
Software available from Cemagref, France.
Not fully commercialized
F25.7 Bibliography
1. Stone, S., Dzuray, E. J., Meisegeier, D., Dahlborg, A-S., and Erickson, M. DecisionSupport Tools for Predicting the Performance of Water Distribution and Wastewater
Collection Systems, EPA, EPA/600/R-02/029, 2002.
F-70
F26.0 Fiberscope Inspection
F26.1 Overview
Fiberscope inspection works similar to CCTV inspection (see CCTC Visual Inspection
review) but relies on optical fibers to gather images, which can be observed using an eyepiece.
This technique can be used to inspect small diameter pipes and valves. One important feature is
that fiberscope allows internal inspection of charged water mains. Fiberscopes are generally
used to visually inspect a main for corrosion or sediment build-up. A camera can be attached to
the eye piece of the fiberscope to record the inspection.
F26.2 Main Principles
A fiberscope consists of three parts: 1) a steerable end for capturing imaging; 2) a
viewing and control end; and 3) a flexible tube body.
The steerable end of the tool is manipulated by control wires that allow up to 120° of
movement (depending on the specific tool used) and contains optical fibers for both lighting
and image capture. The viewing and control end of the tool consists of an eye piece, which can
also be attached to a CCTV or similar device to record the images, and controls that allow the
tip to be manipulated and focusing.
Generally a 10 foot flexible tube will allow a pipe to be inspected for five feet on either
side of the inspection point for corrosion, sediment build-up or other features of interest.
The tool can be inserted into empty or charged water mains via fire hydrants, air valves,
tapping points and other similar access points.
The minimum size main that can be inspected is approximately 2½ inches. There is no
specific maximum size, however flow through the main can affect positional control of the
tool, and in larger diameter mains lighting may be insufficient for viewing the pipe internal
surface.
F26.3 Application
Fiberscope inspection is suitable for capturing visual images of the internal surface of
water mains, primarily small diameter mains, and can be used to assess the condition of
internal linings, the build up of corrosion products, and other features of interest. This
technique can also be used for in-service inspection of valves.
F26.4 Practical Considerations
♦ Fiberscope inspection technology is widely available, easy to use and readily portable.
♦ It is used often in the aviation, power generation and other industries for inspection;
however it is not widely used by water authorities who generally favor other techniques
for obtaining data on the internal surface of pipes, such as physical inspection after
exhumation.
♦ When conducting inspections in charged mains the flow through the main can affect
controllability of the tool.
♦ The visual image needs to be analyzed manually, and so is dependant on image quality.
The presence of particulate matter or bubbles will reduce image quality, potentially to a
level that no useful information can be obtained.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-71
F26.5 Advantages
♦ Internal condition of water main assets can be inspected without exhumation.
♦ Tool allows for in service inspection of valves.
♦ Inspection can be conducted in charged mains; however the actual pressure allowable is
dependant on the pressure rating of the product.
F26.6 Limitations
♦ Particulate matter in mains reduces visibility, potentially to a level that no useful
information can be obtained.
♦ The limited observations achievable may not be representative of the rest of the pipe.
♦ Maximum size of main that can be inspected is limited by the intensity of the available
light source.
♦ Flow in charged mains can affect the controllability of the tool.
Table F-28. Summary Fiberscope Inspection.
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Technical
suitability
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Asset management sophistication required
Skills required (level of tool sophistication);
usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Economic factors
F-72
Cost per inspection
Resource requirements
Assessment
Water pipes and valves.
Any.
Potable.
An entry point into the asset is required such as a
fire hydrant or a tapping.
No restrictions based on asset condition.
The minimum size main that can be inspected is
approximately 2½ inches. Upper size limited by
light source.
Discrete.
Non-destructive.
Inspection can be undertaken on line or off line.
Visual image of pipe internal surface analyzed
manually for features such as sediment build up,
corrosion products, etc.
None.
Fiberscopes are widely available.
Tool not widely used.
Qualitative/visual assessment of pipe surface or
internal condition of valves.
Validation possible only by comparison with
manual /direct observation.
Generic approach.
Interpretation of results for consistent data requires
training. Utility should have the competence to
utilize the information provided by the tool operator.
Fiberscope and related accessories.
No Standards found or other.
Technical support should be available from
manufacturer.
Relatively low cost per inspection.
Requires team to operate camera and provide
entry into pipeline.
F26.7 Bibliography
1. Dorn, R., Howsam, P., Hyde, R.A. and Jarvis, M.A., Water mains: Guidance on
assessment and inspection techniques, CIRIA Report 162, Construction Industry Research
and Information Association, London, England, 1996.
2. Randall-Smith, M., Russell, A. and Oliphant, R., Guidance manual for the structural
condition assessment of trunk mains, WRc, UK, 1992.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-73
F27.0 Fracture Toughness (C-Ring) Testing
F27.1 Overview
Fracture toughness testing gives an indication of the materials resistance to fracture
failure. Many standards require PVC pipes to achieve a minimum “short term” fracture
toughness value.
Fracture toughness testing is a destructive test where a specimen is statically loaded and
the time to failure measured. It is generally used for quality control testing, but it could be
applied to the testing of samples taken from in service PVC pipes. Fracture toughness can be
measured on many materials, including steel. However, this review focuses on the fracture
toughness testing of PVC used for pressure pipe.
F27.2 Main Principles
C-ring fracture toughness testing allows the susceptibility of a PVC pipe to fracture
failure to be determined. A section of (exhumed or new) pipe is marked with a line along the
pipe axis. Several rings approximately 13/16 inches (30mm) in width are then cut from one end
of the section.
The remaining length is subjected to the methylene chloride test (see Methylene
Chloride Gelation Assessment review). If the results from this test are either type 1 or 2 then
the ring is notched at the inside surface of the pipe parallel to the line drawn earlier. If however
the test result is type 3, then the location of greatest attack is marked on all of the rings. The
ring is then notched at the inside surface at this location.
A section is removed from the ring opposite to the notch to create a “C-ring”. A static
force is then applied, as shown in Figure F-4. The mass applied depends on the requirements of
either a standard or the utility.
Figure F-4. Schematic of C-Ring Fracture Toughness Testing.
Testing can be conducted to either establish if the PVC pipe material meets a minimum
15 minute standard for which a single test is needed (although multiple tests are
recommended), or multiple tests using a range of applied masses to establish fracture
toughness behavior over time; including instantaneous fracture toughness via extrapolation. A
typical requirement for PVC 15 minute fracture toughness is 4.5 MPa/m2.
F-74
F27.3 Application
C-ring fracture toughness testing is used to determine if a section of PVC pressure pipe
exceeds a minimum fracture toughness set by the relevant standard or water utility (user).
♦ Standards which describe this test are as follows: ISO 11673, AS/NZS 1462.19:2006.
F27.4 Practical Considerations
♦ This test is widely used in the plastic pipe industry by both manufacturers and users. It
should only be conducted in a laboratory by qualified personnel.
♦ If the notch is not located at the point of lowest gelation (point of greatest attack during
methylene chloride testing), the test results cannot be considered reliable.
F27.5 Advantages
♦ This test gives an indication of the pipe susceptibility to fracture failure.
♦ The test can be extended to obtain information about the probable lifetime of a pipe
section.
F27.6 Limitations
♦ The test is destructive and requires exhumation of pipe samples.
♦ The test is subject to variation, so a number of tests may need to be performed.
♦ The test must be conducted at the location of lowest gelation.
♦ The test only relates to the toughness properties of the material and not its susceptibility
to failure due to point loading.
Table F-29. Summary Fracture Toughness (C-Ring) Testing.
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Utility technical
capacity
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Assessment
Pipes.
uPVC or unplasticised poly(vinyl chloride).
Potable and wastewater.
Pipe sample test.
None.
None on commonly used pipe sizes, specialized
equipment may be required for testing of larger
diameter pipes.
Discrete results.
Destructive test.
If pipe to be tested is in service it must be
exhumed; supply will therefore be interrupted.
Fracture toughness.
Stand alone.
Test houses can supply testing capacity.
Tool is widely used by plastic pipe industry.
Quantitative. Multiple measurements may need
to be taken to ensure a reliable result.
Results can be validated by repeated testing.
Generic testing procedure.
Operator should be suitably trained in the
procedure.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-75
Criteria
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Economic factors
Cost per inspection
Resource requirements
F-76
Assessment
Test requires specialized notching tool.
ISO 11673, AS/NZS 1462.19:2006.
Test can be conducted by test houses if
required.
Low cost. Cost will vary depending on the time
taken to complete testing.
Test requires a stable temperature environment
and equipment to measure time to failure.
F28.0 Ground Penetrating Radar (GPR)
F28.1 Overview
Ground Penetrating Radar (GPR) is a technique for acquiring subsurface information.
GPR works by emitting short bursts of electromagnetic radiation into the ground and recording
the radiation reflected to locate buried assets of any material.
The amplitude of each emitted pulse received by the GPR unit is recorded on a time
scale (distance if wave velocity is known) giving a vertical plot for each pulse (called a trace).
As the unit is moved along the ground, a series of traces are taken and colors or grey scale
allocated to the amplitudes of each. The ‘colored’ traces are then placed along a distance scale
and the 2D profile created (Ground Penetrating Radar, 2005).
The depth to which assets can be located is dependant on soil type and the size of the
asset. The location of assets is achieved quickly in the field, though accurate interpretation of
the results requires a skilled operator.
F28.2 Main Principles
The GPR unit is moved across the ground surface to create a 2D profile of the area
directly beneath its path. The profile can then be interpreted by the operator to identify features
of importance. In order to locate buried assets, a series of profiles are taken, which can be used
to find the boundaries of assets such as tanks, or their direction in the case of pipes. A series of
profiles can also be used to create a 3D representation of an area.
GPR uses short bursts of VHF-UHF electromagnetic radiation, between 100 MHz and
1000 MHz, directed into the ground to acquire subsurface information. The actual frequency
used varies but is a compromise between the depth of penetration and the accuracy required.
By using longer wavelengths, increased penetration into soil can be achieved but there is a
corresponding loss of resolution.
The depth of penetration is also dependant on soil type. Soils with low electrical
conductivity provide the deepest penetration. In soils with high electrical conductivity,
penetration is limited by the attenuation of the wave pulse by its conversion into thermal
energy. Also, soils with large numbers of discontinuities will cause signal scattering, reducing
the penetration of the pulse deeper into the subsurface.
The wave pulse emitted by the GPR is reflected from areas where there is an interface
between two materials with different electrical properties, including objects, soil type
interfaces and ground water (Ground Penetrating Radar, 2005). The depth at which these
interfaces are located is calculated using the time it takes for the emitted pulse to travel into the
ground, reflect and travel back to the receiver and the wave velocity. The velocity of the wave
is dependant on the electrical permittivity or dielectric constant of the host material and a range
of standard values is generally supplied with the GPR unit.
F28.3 Application
GPR can be used to locate buried assets of any material type, but because of its cost,
complexity, and limitations, GPR is usually the method of choice only for targets not locatable
by other means, such as plastic or clay pipe.
♦ ASTM D6432-99 Standard Guide for Using the Surface Ground Penetrating Radar
Method for Subsurface Investigation
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-77
F28.4 Practical Considerations
♦ GPR units are available from a number of suppliers world wide. A trained operator is
required to use the device effectively.
♦ The depth accuracy of GPR assessments is influenced by the knowledge of wave pulse
velocity in the soil; where this is known, accuracy is quite high (usually within 10% of
total depth). Where wave pulse velocity is unknown or estimated the accuracy can vary
by a significant percentage of total depth. The horizontal accuracy is not affected by the
wave pulse velocity, thus the surface location of the asset can be found within inches
even though the depth may not be known with great accuracy.
♦ The repeatability of measurements is very high when there has been no change in soil
conditions; variations in soil conditions will affect the results due to the change in the
soil’s wave pulse velocity and signal attenuation. Exact depth calculation is dependant
on the quality of wave velocity information.
♦ The best results are achieved when the GPR unit is as close to the ground as possible,
as any air gap will reduce the penetration and can induce interference at ground level.
F28.5 Advantages
♦ GPR is quick and gives immediate results. Skilled operators can interpret data in the
field or can it can be post processed.
♦ Unlike other location techniques GPR is able to locate polymer and clay assets.
F28.6 Limitations
♦ Penetration into soils with high electrical conductivity, like mineralogical clays, can be
limited to less than one meter (Ground Penetrating Radar, 2005).
♦ The ability to detect an asset below the water table is reduced by signal loss due to
scattering at water table boundary and signal attenuation due to the high electrical
conductivity below the water table.
♦ Uneven ground may require the unit to be raised off the ground, reducing the
penetration depth and accuracy of the results.
♦ The equipment can be difficult to move on steep slopes.
♦ Skilled operators required for interpretation of data in the field.
F-78
Table F-30. Summary Ground Penetrating Radar (GPR).
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Technical
suitability
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility
technical
capacity
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Economic
factors
Cost per inspection
Resource requirements
Assessment
Environmental survey (buried assets).
All materials.
Potable and wastewater.
GPR needs clear space at ground level, obstacles
and very uneven ground can prevent use.
No restrictions.
Assets of any size can be located. However small
assets may be difficult to locate depending on their
depth and the wavelength used. Rule of thumb is
objects with a depth to size ratio of 12:1 to 24:1 are
usually detectable with GPR, providing the signal
can penetrate down to them before being
attenuated.
Discrete. GPR uses sets of readings over a short
distance gathered at a number of locations to locate
assets. More advanced systems can use sets of
images to create a 3D map of the subsurface.
Non-destructive.
Inspection does not cause an interruption to supply.
Location of buried assets.
Depending on the model used, GPR equipment can
be fed into computer programs to extract more data
from the results obtained.
Equipment is available from a number commercial
vendors.
GPR has been available for over 20 years, but has
begun to be adopted by the utility locating industry
only in the last 10 as more convenient, user friendly,
and economical units have become available.
Quantitative, though the accuracy of depth
measurements is dependant on frequency and
knowledge of soil properties and so can vary by
several percent of depth. Claims on horizontal
readings accuracy vary from inches to a foot. Ability
to detect assets varies with material.
Results can be validated only through exposure of
the asset.
Generic.
Use of GPR requires a skilled operator to gather
useful information.
Depending on the amount of data processing
desired, computing can be done onsite by the unit
or post processing can be done on to obtain more
information including 3D plots.
ASTM D6432-99.
Training courses are offered by the equipment
manufacturers.
US$1,000 – $2,000 per day with a skilled operator.
GPR can be undertaken by a single person.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-79
F28.7 Bibliography
1. Burn, L.S., Eiswirth, M., DeSilva D. and Davis P., Condition Monitoring and its Role in
Asset Planning, Pipes Wagga Wagga 2001, Charles Sturt University, Wagga Wagga,
N.S.W., 2001.
2. Dingus, M., Haven, J. and Austin, R. Nondestructive None Invasive Assessment of
Underground Pipes, AwwaRF, USA, 2002.
3. Dolphin, L., A brief background on ground penetrating radars,
http://www.ldolphin.org/GPRbkgnd.html , accessed 2005.
13H
4. Eiswirth, M., Burn, L.S. New Methods for Defect Diagnosis of Water Pipelines, 4th
International Conference on Water Pipeline Systems, 28-30, York, UK, March 2001.
5. Ground Penetrating Radar, http://fate.clu-in.org/gpr_main.asp , accessed 2005.
14H
6. Trenchless technology Network Underground Mapping, Pipeline Location Technology and
Condition Assessment, (downloaded from
http://www.ttn.bham.ac.uk/Final%20Reports/Pipe%20Location%20and%20Assessment.pd
f accessed 2006), 2002.
15H
7. ASTM D6432-99 Standard Guide for Using the Surface Ground Penetrating Radar Method
for Subsurface Investigation.
F-80
F29.0 Holiday Detector
F29.1 Overview of Tool
This is a non-destructive method used to detect flaws such as pin holes, air bubbles,
thin points and porosity in non-conductive (insulation type) coatings on conductive substrates
and on concrete (for some detectors).
The substrate of the asset being inspected is connected to a current and a conductive
brush is passed over the coating surface. Flaws are located when the brush moves over a flaw,
which completes the electrical circuit.
Holiday detectors are also commonly known as porosity detectors, spark testers or
jeepers.
F29.2 Main Principles
Holiday detectors can be used on any asset which has a conductive substrate and nonconducting (insulating) coating, from DI pipes to tanks. Holiday detectors work by applying a
constant current source to the coating substrate, which results in an applied test voltage. There
are two main types of holiday detectors: 1) high voltage DC and 2) electric pulse units.
A typical DC detector delivers a stabilized DC output of up to 30kV with a resolution
of 10V. Flaws are located by moving the detector over the coated surface; when the detector
moves over a flaw, the applied potential ‘jumps’ from the substrate to the detector. A visual
and/or audible alarm indicates when a fault is found. A range of accessories are available to be
used with holiday detectors including:
♦ Internal pipeline disc and spiral wound brushes up to two meters diameter.
♦ External pipeline coil electrodes up to 1420 mm diameter.
♦ Flat brass wire brushes up to 600 mm long, fan brushes.
Pulse models can be used for determining porosity and location of pinholes in carbon
impregnated coatings such as carbonated rubber, thick coatings such as rubber linings and on
‘plastic’/fiberglass type coatings likely to become electrostatically charged. Models with 20kV
and 40kV are designed for use in moist conditions and on wet or contaminated coating
surfaces.
Some holiday detectors use the wet sponge method to detect pinholes in coatings. This
method is recommended for thin film porosity testing (coatings under 150 µm), or in favor of
high voltage testing, particularly when working with coatings in corrosive environments.
F29.3 Application
Holiday detectors are useful for detection of flaws in coatings and wrappings on both
flat and curved surfaces, such as pipes, tanks, valves and steel structures.
♦ Holiday detectors are required to comply with the requirements of AS3894.1-2002.
They are also addressed in the National Association of Corrosion Engineers (NACE)
Standards: TM0186-94; TM0384-94; RP0490-2001; RP0274-98 & RP0188-99
F29.4 Practical Considerations
♦ Holiday detectors are handheld and come in a variety of types for the inspection of a
wide range of asset types and can be obtained from a number of suppliers. They are
used widely in industries where the integrity of coating is important and can detect
cracks, blow holes, burrs, air bubbles and inclusions (Figure F-5).
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-81
Figure F-5. Defect Types Detectable by Holiday Testing
(Reprinted with permission from: Buckleys, 2006).
♦ A holiday detector should be used as soon as time and conditions permit after the
coating has been applied and properly cured and, if possible, again prior to final project
completion. When electrical inspection is conducted at the time of coating application,
voids in the coating can be readily located and repaired, plus, it allows the applicator
the opportunity to develop better coating application techniques.
♦ Electrical inspection prior to project completion is recommended as the protective
coating may have been damaged during construction.
♦ Proper grounding of the holiday detector to the coated concrete substrate is essential in
order to complete the electrical circuit of the holiday detector.
♦ Test voltage adjusted at the job site takes into consideration every aspect of the output
circuit in relation to; ground resistance, structure resistance, coating thickness,
capacitance losses, barometric pressure and electrode configuration.
♦ An alternative to setting test voltages in the field is to use the formula developed by the
NACE and incorporated into several standards. The formula for the voltage to be
applied to thin film coatings applied up to 30 mils (0.76 mm) thickness is V = 525 T ,
where T is the coating thickness in mils.
♦ Example: A coating 25 mils (0.64 mm) thick would work out to an inspection voltage
of 2600V. For thicker applied coating the constant changes to 1250. Example: a coating
125 mils (3.175 mm) thick would work out to an inspection voltage of 14,000V.
♦ Care needs to be taken to not exceed the coating manufacturer’s recommendations of
test voltages. Manufacturers of the protective coating should always be consulted by the
consumer with regards to dielectric strength of properly cured coatings and
recommendations of maximum test voltages to be used on every formulated coating.
♦ It is not recommended that electric pulse (low voltage) detectors be used for the
electrical testing of protective coating having a dry film thickness in excess of 0.51
mm.
♦ DC Pinhole/Holiday Detectors are far more efficient and accurate at finding pinholes,
in coatings than AC spark testers.
F29.5 Advantages
♦ Holiday detectors can be used to rapidly test the quality of a coating, including defects
that cannot be detected by visual inspection.
F29.6 Limitations
♦ Holiday detectors can only be used to find flaws in coatings whose substrate is made
from a conductive material such as metal and concrete.
F-82
♦ Pulse type detectors are completely ineffective for inspection of prefabricated films
such as PVC or polyethylene (PE) protective linings.
Table F-31. Summary Holiday Detector.
Technical
selection
Criteria
Assessment
Assets covered
Material type
Coated assets.
Corrosion protection coatings on concrete and
steel substrates.
Potable and wastewater.
Direct contact with coating. If external coating is
buried then it must be exposed. Tool comprises
of several components and is hand held.
Sufficient room is required for an operator and
electrical isolation area where an asset has
been exposed for testing.
No specific restriction related to asset condition.
Testing cannot be conducted during rainfall.
No limitations relating to size of concrete
element.
Continuous readings.
Non-destructive.
The asset must be taken off-line if an internal
coating is to be tested.
Location of pin holes, air bubbles, thin points
and porosity on non-conductive (insulation type)
coatings.
Compatible with an RS 232 data interface gives
a printout of measured objects and can be
transferred to PC with MS Hyperterminal.
Equipment is fully developed, readily available
from commercial vendors and can be used off
the shelf.
Widespread use internationally on bridges, road
infrastructure in the petrochemical in the water
industries.
Accuracy is typically 2% at high resolution when
calibrated on a known thickness location.
Certified high voltage DC and pulse crest
meters can be used to verify the output voltage
and the calibration of DC and crest holiday
detectors respectively.
Generic approach.
The technique does not require specialist
knowledge. Requires minimal training. Operator
will need to know be aware of safety procedures
associated with the use of holiday detectors.
Apparatus digitally displays applied voltage,
constant test current, and fully adjustable
voltage and sensitivity controls.
AS3894.1-2002 and NACE Standards: TM018694; TM0384-94; RP0490-2001; RP0274-98 and
RP0188-99.
Technical support available from distributors.
Low cost per inspection.
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Economic
Availability of technical support
Cost per inspection
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-83
factors
Criteria
Assessment
Resource requirements
One operator required. Battery powered.
F29.7 Bibliography
1. Buckleys, A Guide to Using DC Holiday Detectors at
http://www.buckleys.co.uk/holidayguide.htm, accessed 2006.
16H
2. Byerley, D. D. Electrical Inspection of Protective Coatings Applied to Concrete Surfaces,
at http://www.tinker-rasor.com/tech/concrete.html.
17H
3. AS3894.1-2002 Site testing of protective coatings - Non-conductive coatings - Continuity
testing - High voltage ('brush') method.
4. NACE Standard Test Method TM0186-94. Holiday Detection of Internal Tubular Coatings
of 250 to 760 µm (10 to 30 mils) Dry Film Thickness.
5. NACE Standard Test Method TMO384-94. Holiday Detection of Internal Tubular Coatings
of Less Than 250 µm (10 mils) Dry Film Thickness.
6. NACE Standard Recommended Practice RP0490-2001 - Holiday Detection of FusionBonded Epoxy External Pipeline Coatings of 250 to 760 um (10 to 30 mils.
7. NACE Standard Recommended Practice RPO274-93. High Voltage Electrical Inspection
of Pipeline Coatings Prior to Installation.
8. NACE Standard Recommended Practice RP0188-99 Discontinuity (Holiday) Testing of
New Protective Coatings on Conductive Substrates.
F-84
F30.0 Hydraulic Modeling
F30.1 Overview
Many commercially available software packages are available that model the hydraulic
behavior of pressure and gravity pipelines or networks. Hydraulic models are calibrated against
measured values of pressure and/or flow. Calibration is further fine tuned by adjusting
parameters like friction factors until the model reproduces the measured system response under
a range of conditions.
Once calibrated, the hydraulic model can be used to identify hydraulic issues within the
pipeline or network. When identified, asset inspection and other survey techniques can be used
to investigate further.
F30.2 Main Principles
Hydraulic models represent mathematically the relationships between flow parameters
such as pressure, diameter, roughness and slope, and service demand. Hydraulic models are
used at different stages of a pipe networks life which can include the following stages:
♦ Master planning – hydraulic models are used to predict the improvements and additions
to the system which may necessary to accommodate future customers. In this situation
models focus at a macro level with emphasis placed on larger transmission mains,
pump stations and storage tanks.
♦ Preliminary design – hydraulic models are used to identify the facilities required to
serve a particular area. In this situation modeling is usually focused to a limited portion
of the network.
♦ Subdivision layout – hydraulic models determine the capacity requirements for the
subdivision.
♦ Rehabilitation – hydraulic models are used to ensure that adequate capacity is
maintained after rehabilitation of a pipeline. This is a very important consideration.
For stormwater and combined sewers, a verified model can be used to simulate network
performance with respect to various performance indicators such as surcharge/flooding
conditions. To do this, a verified model is run for storms of a range of intensities and durations
to establish that each pipeline and overflow achieved the appropriate performance criteria (e.g.,
onset of surcharge).
F30.3 Application
Hydraulic modeling is used for the analysis and design of pressure and gravity pipelines
and networks.
♦ There are no Standards which require the use of hydraulic models.
F30.4 Practical Considerations
♦ Hydraulic models are widely used in the water industry so there are a large number of
hydraulic modeling packages available, from both private vendors and public domains.
Some are designed to undertake a specific hydraulic modeling task, while others are
capable of a range of modeling processes.
♦ Most of the packages available enable network design, simulation and optimization. In
addition many packages also incorporate water quality analysis and link to GIS.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-85
♦ Costs of models vary dramatically, models such as EPANET (analysis only) and Netis
are free, while other commercial packages are costly. However, the commercial
packages come with more advanced features and better user interfaces than those freely
available.
♦ Models require good data to be effective and collecting and assembling the data can be
time consuming. In order to preserve their usefulness, the underlying input data must be
maintained.
♦ Model calibration through adjustment of friction factors gives some indication of the
pipe’s internal condition. Where issues relating to service are predicted, asset inspection
and other survey techniques can be used to investigate further.
F30.5 Advantages
♦ Hydraulic models relieve engineers from tedious, iterative calculations and are able to
take account of much more of the complexity of real world systems.
♦ Optimization tools/modules attached with the analysis module help in obtaining least
cost solutions.
♦ They enable alternatives to be explored under a wide range of conditions resulting in
more cost effective and robust interventions.
F30.6 Limitations
♦ Hydraulic modeling software can be expensive to purchase for small companies and
requires the training of staff to use the models.
♦ The majority of costs are mainly related to model development and the benefits are not
realized until later in the form of quicker calculations and better decisions.
♦ Some packages have limitations on the number of network nodes they are able to
handle, while others have limitations on their ability to link to a GIS system.
Table F-32. Summary Hydraulic Modeling.
Technical
selection
Technical
suitability
Criteria
Assets covered
Granularity
Service area
Focus of analysis
Scalability of tool/approach
Commercialization
Previous/existing use of the tool
Ease of validation
Flexibility wrt analysis (asset types) and granularity
(system, asset level)
Integration with other tools/GIS
F-86
Assessment
Water and wastewater networks.
System and sub-system level.
Potable and wastewater.
The relationships between flow, pressure,
roughness, capacity and service.
Better suited to medium to large authorities
where good asset data is available, but simple
models available for small authorities.
Many commercial and public domain software
models are available.
Widely used worldwide. Majority of large
authorities would have some form of modeling
software.
Validation through data collection and
comparison to network response.
Designed for both network level modeling and
sub network level modeling. Models are
generally specific to water or wastewater service
area (pressurized v open channel).
Can link directly to GIS.
Criteria
Asset management sophistication
In-house skills required
Technology required
Utility technical
capacity
Documentation
Data Requirements
Linking to asset data
Availability of software and technical support
Usability
Other
IT integration
Tools costs (license and maintenance)
Assessment
Generic approach.
Asset manager/hydraulic engineer.
Computer based tool. Many systems link to GIS
data.
Depends on software being used. Most come
with detailed documentation.
Good quality asset data required, calibration
data is necessary.
Through asset IDs.
Widely available through many vendors. Some
models can be freely downloaded from the
Internet.
Depends on software. Most systems have an
graphical user interface (GUI) that greatly
improves the usability of the model.
PC based software.
Varies depending on package. Some models
are free, while some commercial packages are
thousands of dollars. Many also have an annual
license fee.
F30.7 Bibliography
1. Dorn, R., Howsam, P., Hyde, R.A. and Jarvis, M.A. Water mains: Guidance on assessment
and inspection techniques, CIRIA Report 162, Construction Industry Research and
Information Association, London, England, 1996.
2. EPANET, http://www.epa.gov/ORD/NRMRL/wswrd/epanet.html, accessed 2005.
18H
3. SWMM, http://www.epa.gov/ednnrmrl/models/swmm/index.htm, accessed 2005.
19H
4. Stone, S., Dzuray, E. J., Meisegeier, D., Dahlborg, A-S., and Erickson, M. DecisionSupport Tools for Predicting the Performance of Water Distribution and Wastewater
Collection Systems, EPA, EPA/600/R-02/029, 2002.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-87
F31.0 Impact Echo Testing
F31.1 Overview
The impact echo testing method is a non-destructive method primarily used for
assessment of concrete assets. However, impact echo testing can also be performed on stone,
plastic, masonry materials, wood and some ceramics. Application suitability depends on the
properties and internal structure of the material being tested. Testing is conducted by impacting
the asset surface, recording the signal reflected back to a transducer and analyzing that signal.
Impact echo tests are most often used to find the thickness of plate-like concrete
elements from one side. Another major use is for locating and diagnosing internal flaws such
as voids, honeycombing, delaminating, depth of surface opening cracks, and other damage in
concrete.
If the member thickness is known, impact echo testing can also be performed to predict
the strength of early age concrete. Impact echo testing can also be used to determine relative
concrete quality for test cylinders and other samples with known thickness. This is achieved by
measuring the concrete compression wave velocity.
F31.2 Main Principles
Impact echo testing detects flaws in concrete based on reflection of compression waves
from the bottom of the structural member or from any hidden discontinuity within the member.
Concrete element thickness is determined by measuring waves that reflect off the backside of
the concrete.
The waveform resulting from an impact to the asset is measured. The resulting time
versus amplitude data includes energy from the initial impact as well as energy from echoes
that have traveled through the concrete and echoed off of the back side or any discontinuity
parallel to the test surface.
Impact echo testing apparatus consists of three main components:
♦ Impact source, often referred to as an impactor.
♦ Receiving transducer, often referred to as a displacement transducer.
♦ Waveform analyzer.
The selection of the impact source is important for successful impact echo testing. The
size of the impactor is selected based on the depth and size of flaw that is to be detected. Steel
spheres on spring rods are commonly used as the impact source.
The receiving transducer needs to be capable of accurately measuring surface
displacement. A conically tipped transducer is often used in impact echo testing. Receiving
transducers are secured in a special housing so that they can be used on vertical surfaces. A
thin lead strip is used to provide acoustic coupling between the transducer and the test surface.
A waveform analyzer, or computer with high-speed digital data acquisition hardware, is
used to capture the transient output of the displacement transducer, store the digitized
waveforms, and perform signal analysis. The waveform analyzer needs to have a minimum
high sampling frequency of 500 kHz. The receiving transducer should preferably be a
broadband displacement transducer. Accelerometers have been used but they must not have
resonant frequencies in the range of those measured during impact echo testing and additional
signal processing is required.
F-88
Specialist software allows the data acquisition parameters to be set up and performs the
data analysis.
F31.3 Applications
The impact echo technique is most extensively used on flat areas but can also be used
for tests on other geometries. Impact echo testing can be used, but is not limited to, the
following asset types:
♦ Concrete slabs, pavements
♦ Concrete slabs consisting of two layers, including slabs with asphalt overlays
♦ Bond quality at internal interfaces
♦ Circular columns
♦ Square and rectangular beams and columns
♦ Walls
♦ Dams
♦ Hollow cylinders such as pipes and tunnels
♦ Post-tensioned structures for instance locating voids in grouted tendon ducts
♦ Depth of surface-opening cracks
In 1998, ASTM adopted a standard test method on using the Impact echo testing
method to measure the thickness of concrete members:
♦ ASTM C 1383 ‘Standard Test Method for Measuring the P-wave Speed and Thickness
of Concrete Plates Using the Impact echo testing Method’.
The standard test method involves two procedures. The first procedure determines the
P-wave speed in the concrete by measuring the travel time between two surface receivers
separated by a known distance. The second procedure measures the thickness using impact
echo testing. The method is applicable to plate-like structures in which the smallest lateral
dimension is at least six times the thickness of the member.
F31.4 Practical Considerations
♦ The impact echo technique does not require specialist knowledge or training. Thickness
measurements can be taken by unqualified staff. However experienced persons are
required to check for flaws such as delamination.
♦ A telescoping pole can be used on flatwork or overhead.
♦ Generally impact echo testing instruments have built-in default concrete parameters.
However for greater accuracy some instruments can be calibrated by testing at a point
of known concrete thickness as a calibration reference.
♦ Impact echo testing equipment typically has a thickness range of 66mm up to 1.8m.
The technology has the capability to be able to measure a minimum thickness of 38mm
and a maximum thickness of 3.0m. However the ratio of width to thickness must be at
least three. Accuracy is typically 2% at high resolution when calibrated on a known
thickness location.
♦ If the thickness of the concrete being tested is not known, and two sides of the concrete
element cannot be accessed, a second receiving transducer will need to be added in
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-89
order to enable Spectral Analysis of Surface Wave (SASW) testing. This second
receiving transducer is often mounted on a detachable arm. In combination with the
impact echo technique, SASW can be used for correlating strength vs. velocity in the
field to laboratory tests of concrete specimens (cubes, beams or cylinders). SASW can
also be combined with ultrasonic pulse velocity measurements for this purpose. The
combination of impact echo thickness and internal flaw detection with SASW velocity
measurement results in the most powerful and accurate way of determining the location
and nature of defects.
♦ An underwater impact echo testing apparatus for point by point testing is also available.
F31.5 Advantages
♦ Impact echo testing measures the thickness of concrete slabs and walls without the need
for drilling, coring, or other destructive means.
♦ Only one side of the structure needs to be accessible for testing.
♦ The impact echo testing method can be used on existing coated structures. It works
through paints, coatings and tiles.
♦ Additional analysis of the echo data allows multiple cracks and other complex internal
flaws to be detected.
F31.6 Limitations
♦ Impact echo testing is restricted in terms of the thickness and geometry of elements to
be measured. The minimum thickness of concrete which can be tested is 38mm.
♦ Naumann and Haardt (2003) argue that there is a need for improved quantification of
capabilities for measuring thickness, mapping or sizing layers of reinforcement,
detecting and mapping of delaminations and cracks parallel to the surface for the
impact echo method. This is especially the case where there is reinforcement
congestion.
Table F-33. Summary Impact Echo Testing.
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
F-90
Assessment
Concrete slabs, beams, columns, walls,
pavements, tunnels, pipes, dams and other
plate-like structures.
Concrete, stone, plastic, masonry materials,
wood and some ceramics.
Potable and wastewater.
Direct contact with asset. If asset is buried then
it must be exposed, surface coatings do not
need to be removed.
No limitations relating to asset condition.
Some limitations relating to size/geometry: the
minimum thickness of concrete which can be
tested is 38mm and a maximum thickness of
3.0m. However the ratio of width to thickness
must be at least three.
Discrete reading.
Non-destructive.
The asset can remain in use and does not need
to be taken off-line.
Technical
suitability
Criteria
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Economic
factors
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Thickness of concrete element, location and
diagnosis of internal flaws, strength of early age
concrete, and relative concrete quality.
Can be integrated with software tools.
Equipment is available from selected
commercial vendors.
Widespread use.
Accuracy is typically + 2% at high resolution
when calibrated on a known thickness location.
Results can be easily validated. For instance
Spectral Analysis of Surface Wave testing
(where a second receiving transducer is added
when conducting echo impact testing) can be
combined with ultrasonic pulse velocity
measurements for determining concrete
strength.
Generic approach.
Easy to use by following simple procedure.
Thickness measurements can be taken by
unqualified staff. However experienced persons
are required to check for flaws such as
delaminations.
Apparatus comes in digital versions which
calculate and display a graph concrete
thickness along the member length. Thickness
data table importable into popular spreadsheet
programs. The data from up to 300 tests can be
stored and downloaded. Some tools have a
super thin concrete and surface wave analysis
options built in. Velocity calibration at known
thickness locations.
ASTM C 1383.
Technical support available from distributors.
Low cost per inspection.
One operator required. Battery powered.
Resources required can also depend on asset
being inspected. Buried assets need to be
exposed.
F31.7 Bibliography
1. Naumann, J. and Haardt, P. NDT Methods for the inspection of highway structures.
International Symposium (NDT-CE 2003). Non-Destructive Testing in Civil Engineering,
pp2-5, 2003.
2. ASTM C 1383 ‘Standard Test Method for Measuring the P-wave Speed and Thickness of
Concrete Plates Using the Impact echo testing Method’.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-91
F32.0 Indirect Tensile Strength Testing
F32.1 Overview
The tensile strength of cylindrical cores (see Core/Coupon Sampling review) taken
from concrete or asbestos cement pipes is used as a measure of the residual tensile strength of
the pipe. Once extracted, the cores are compressed to failure. The compressive stress at failure
can be used to indirectly obtain the residual tensile strength of the pipe from which the core
was taken.
The testing of the cores is itself destructive. Since only cores are taken, the pipe itself
must be repaired. If only one core is extracted, the pipe can be clamped. However, a common
practice is to remove a section of pipe from which multiple cores are then taken. In this case,
the pipe section must be replaced.
F32.2 Main Principles
The tensile strength of a concrete or asbestos cement pipe reduces over time due to
leaching of free lime; in a pipe where all the free lime has been leached, the residual tensile
strength of the pipe will have been significantly reduced.
The tensile strength of the core can be used to determine the residual tensile strength of
the pipe. A solid cylindrical core is cut from either a concrete or asbestos cement pipe section.
The core is then subjected to a compressive load along its axis while the ends are constrained.
By constraining the ends, the stress state in the core can be resolved in 2D allowing the
residual tensile strength of the core to be calculated. The core is tested to failure.
By measuring the current tensile strength of the core and comparing that to values for
virgin pipe, the rate of deterioration of the cement matrix can be estimated and applied to
predict the time to failure of the pipe under known operating and installation conditions.
The phenolphthalein and carbonation tests can be used prior to this test to give an
indication of the depth of free lime depletion through the pipe wall (see Phenolphthalein
Indicator review).
F32.3 Application
Indirect tensile strength testing is a method for obtaining the residual tensile strength of
cementituous pipes in water and wastewater networks. The test procedure for this tool is based
on the following standard;
♦ AS 1012.10 – 2000 “Determination of indirect tensile strength of concrete cylinders
(‘Brazil’ or split test) and ASTM C-496-96 “Standard Test Method for Splitting Tensile
Strength of Cylindrical Concrete Specimens”
F32.4 Practical Considerations
♦ This is a new test method and had yet to be adopted widely by industry.
F32.5 Advantages
•
Tool can be used to predict the remaining life of a cementituous pipe asset.
F32.6 Limitations
♦ This is a new test that is not widely used. The pipe must be exhumed for removal of test
sample, and the pipe repaired or pipe section replaced.
♦ Testing of asbestos cement pipe samples is subject to health and safety considerations.
F-92
Table F-34. Summary Indirect Tensile Strength Testing.
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Utility technical
capacity
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Economic factors
Cost per inspection
Resource requirements
Assessment
Pipe.
Asbestos cement, concrete.
Potable and wastewater.
Need access to pipe surface to remove core
sample.
No restrictions due to asset condition, pipe
lining /coatings need to be removed prior to
testing.
No restriction.
Discrete.
Destructive.
Pipe must be taken off-line to extract core
sample.
Tensile strength.
None.
Technique is new and only provided by
specialized consulting groups.
Limited; utilized in condition assessment of
several AC wastewater pressure mains.
Quantitative.
Direct measurement.
Generic approach.
Service is provided by specialized consulting
groups.
Low tech.
AS 1012.10 – 2000 and ASTM C-496-96.
Service is provided by specialized consulting
groups.
Depends on level of analysis required.
Personnel and equipment required to remove
cores. Test and lab equipment.
F32.7 Bibliography
1. Davis, P., De Silva, D., Gould, S. & Burn, L.S. Condition assessment and failure
prediction for asbestos cement sewer mains, presented to Pipes Wagga Wagga 2005 Conf.,
Charles Sturt University, Wagga Wagga, NSW, Australia, 17–20 October, 2005.
2. AS 1012.10 – 2000 “Determination of indirect tensile strength of concrete cylinders
(‘Brazil’ or split test).
3. ASTM C-496-96 “Standard Test Method for Splitting Tensile Strength of Cylindrical
Concrete Specimens”.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-93
F33.0 Infiltration and Inflow – Sewer Flow Survey
F33.1 Overview
Sewers flow surveys are often used to calibrate hydraulic models (see Hydraulic
Modeling review), but they can also be used to determine where infiltration of groundwater or
inflow of water (other than infiltrated groundwater such as rain water) into the system is a
problem. Specialized flow surveys can be used to locate the areas of the system where the
flows originate and estimate their magnitude.
The aim of a flow survey is to obtain actual flows in the sewer system during both dry
and wet weather conditions. A calibrated hydraulic model can also be used to analyze scenarios
for reducing infiltration through various interventions.
F33.2 Main Principles
Infiltration and inflow (I&I) are important because water from these extraneous sources
reduces the available capacity of sewer systems and capability of treatment facilities to treat
waste waters. Infiltration occurs when existing sewer lines are poorly designed and
constructed, or undergoes material and joint deterioration allowing groundwater to enter.
Inflow may occur when rainfall enters the sewer system through direct connections such as
drains, sump pumps, manhole covers and indirect connections with storm sewers.
Flow surveys can be used to identify parts of the system where I&I flows originate and
estimate their magnitude. To do this, the utility must first identify if the sewerage system has
problems through review and analysis of existing flow records such as treatment plant influent
data, pump run time data, overflow locations and estimated amounts, customer complaints, etc.
The system is then divided into subsystems and the key manholes located at the outlet
of each subsystem. Flows to these key manholes are monitored and compared to the expected
sewer flows from the subsystems.
Once the problem subsystems are identified, physical inspection, rainfall data, and
rainfall simulation are used to further define the I&I problem. Smoke testing, visual and CCTV
inspections (see Smoke Testing, Visual Inspection and CCTV Visual Inspection reviews
respectively) can then be undertaken to provide to identify and prioritize the repair and/or
rehabilitation if an intervention is deemed appropriate.
F33.3 Application
I&I sewer flow surveys are used to obtain a better understanding of I&I issues in
wastewater networks. There are no Standards which require the use of I&I flow surveys
F33.4 Practical Considerations
♦ Flow surveys have a wide application in the water sector and can be undertaken either
in-house or through specialist contractors/consultants.
♦ Groundwater maps can be constructed for high, medium and low water levels and
overlaid with asset depth data to help isolate areas of interest.
♦ Flow meters should be selected that record both the depth and velocity of flow. Once
data is collected it should be analyzed to give several flow parameters including
average dry-day flow, maximum and minimum diurnal flow, inflow, rainfall-induced
infiltration, seasonal infiltration, etc.
♦ A calibrated hydraulic model can also be used to analyze scenarios for reducing I&I
through various interventions strategies.
F-94
F33.5 Advantages
♦ I&I flow surveys allow the detection of excessive flows and the targeting of capital
investment to solve operational issues in sewer networks and treatment plants.
♦ Identification of I&I problems can allow for rehabilitation and/or replacement to reduce
the stress of pipe systems and treatment plants.
F33.6 Limitations
♦ Identification of the problem through flow surveys and analysis does not necessarily
lead to solutions.
♦ Reduction in I&I though capital investment in sewerage infrastructure has a variable
impact.
♦ Other interventions and drivers need to be considered in conjunction with the results of
I&I studies.
Table F-35. Summary Infiltration and Inflow – Sewer Flow Survey.
Technical
selection
Technical
suitability
Criteria
Assets covered
Granularity
Service area
Focus of analysis
Scalability of tool/approach
Commercialization
Previous/existing use of the tool
Ease of validation
Flexibility with respect to analysis (asset types) and
granularity (system, asset level)
Integration with other tools/GIS
Utility technical
capacity
Asset management sophistication
In-house skills required
Technology required
Documentation
Data Requirements
Linking to asset data
Availability of software and technical support
Usability
Assessment
Wastewater networks.
Spatially drainage area and below.
Wastewater
I&I.
Scaleable; survey approach can be used for any
size company.
Framework approach; commercial survey
services could be contracted.
Wide application.
Validity depends on the quality of hydraulic
models and, in turn, the quality of flow and other
data; independent validation difficult.
Wastewater; asset to sub-system level.
Flow data could be analyzed in GIS framework
as well as hydraulic models.
Generic approach.
Professional engineering skills required.
PC based analysis; modern flowmeters.
A range of papers written on approach.
High; data is needed to identify areas.
N/A
N/A
N/A
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-95
F33.7 Bibliography
1. Vass, R. Pugh, A, Inflow and Infiltration Study, Ozwater 2003, Proceedings AWA 20th
Convention, Perth, April 2003.
2. Ellis, J. B Sewer inflitration/exfiltration and interactions with sewer flows and groundwater
quality. 2nd International Conference Interactions between sewers, treatment plants and
receiving waters in urban areas – Interurba II 19-22 Feb. 2001, Lisbon, Portugal, 311-319,
2001.
3. Joannis, C., Commaille, J-F and Dupasquier, B. Assessing infiltration flow-rates into
sewers, Proceedings 9th ICUD, Global Solutions for Urban Drainage, Portland, USA, 2003.
4. Berthier, E., Andrieu, H, Fasquel, M and Creutin, J-D. Generation of flows in urban
stormwater drainage systems: The role of soil, 2001
http://www.lcpc.fr/en/sources/blpc/pdf/bl231-079-en.pdf.
20H
F-96
F34.0 In-Pipe Acoustic Inspection Tools (Sonar)
F34.1 Overview
CCTV inspection is the industry standard technology for measuring the internal
condition of sewers and stormwater pipes. However, this technique is limited in that it only
allows inspection above the flow line – interpretable CCTV images can not be obtained below
the flow line due to the turbidity of sewage (see CCTV Visual Inspection review).
An alternative technique, sonar, also provides pictorial evidence of sewer condition.
Unlike CCTV, sonar can be used in full sewers, or to inspect the sewer beneath the flow line.
Sonar can also be used to give an image of the sewer above the flow line. However, different
transducers and electronics are required for operation in air and water. As such, sonar suitable
for below the flow line can not give an image of the sewer above the flow and vice versa.
During the survey, a sonar head is introduced into the sewer on a suitable module (a
tractor, crawler, float, etc.). The head transmits ultrasonic signals that are reflected from the
surface of the sewer; the reflected signals are detected by the head. The time delay associated
with the reflected signal is used to generate a profile of the pipe surface.
Sonar can generate a real time 360-degree outline of the interior of a full pipe, or the
outline of the wetted area in a partially full pipe (or the non-wetted area for air sonar).
In the case of a partially full pipe, sonar can be used in conjunction with CCTV to
allow inspection of the entire sewer, with sonar being used to provide information about the
sewer condition below the flow line.
Sonar inspection has been utilized mainly in sewer pipelines. In water mains, the
resolution of the inspection technique is not sufficient to detect small defects that are
significant in pressure applications. Furthermore, other competing inspection technologies
(including leakage detection) can provide the required information. Nevertheless, the principle
of sonar inspection can still be used to measure the distance to the pipe wall.
Acoustic systems for flaw detection are also available that are based on detecting
vibrations and other phenomena caused by the spreading of mechanical sound waves, and are
suitable for detecting cracks and for determining the state of connections and pipe bedding.
F34.2 Main Principles
Sonar technology involves the emission of an acoustic pulse from a transducer and the
subsequent detection of the pulse echo reflected from a surface. The time between the
transmission and reception of the acoustic signal can be used to determine the distance from
the transducer to the surface that reflected the pulse.
Sonic pulses are reflected from any acoustic impedance boundary. The greater the
difference in the impedance of two materials, the more sonic energy is reflected. The
impedance mismatch between water and the wall of a pipe, between air and the pipe wall, or
the interface between air and water are all excellent sonic reflectors.
In the case of sewer inspection, the sonar transducer is mounted in an appropriate
housing and towed (or propelled) through the sewer. An acoustic signal is transmitted radially
toward the sewer wall using a rotating transducer. By analyzing the received echo, the distance
from the transducer to the wall can be calculated.
As the inspection progresses, the signal is analyzed to generate images of the sewer’s
interior perimeter in real time. The profile is displayed on a monitor and allows features such
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-97
as the pipe wall, displaced bricks and silt/growths to be identified. Results can be recorded on
video or digitally.
When used in conjunction with CCTV equipment, the sonar tool is suspended in the
sewage below the rig. CCTV images are taken of the sewer above the flow line, and sonar
allows inspection below the flow line.
In some applications (for example, inspection of furnace tubes), this technology is used
to give a measure of both the internal pipe geometry and the thickness of the wall. Thickness
measurement is achieved because, on arrival at the tubing wall a portion of the sound pulse
energy reflects back towards the transducer, while a fraction of the energy propagates into the
steel tube wall. At the outer tube surface a similar reflection occurs, sending energy back in the
direction of the inner wall and transducer.
On-board digital signal processing of the returned echoes determines the ‘time of flight’
in the tubing wall. The time between the transmission and reception of the acoustic signals are
then used to compute the tubing wall thickness and radial measurement based on the known
acoustic propagation properties of the tubing material.
F34.3 Application
The primary use for sonar equipment is to inspect and assess the structural condition of
otherwise inaccessible or flooded sections of large diameter sewers. The technology is applied
to inspection of pipes in the process industry and could be adopted for inspection of water
mains, though competing technologies are available for this application.
Acoustic systems based on detecting vibrations and other phenomena caused by
mechanical sound waves, are suitable for detecting cracks as well as for determining the state
of connections and pipe bedding.
F34.4 Practical Considerations
♦ Sonar inspection is a commercially developed technology, which provides a practical
alternative to CCTV in large diameter or surcharged mains.
♦ The precision of sonar inspection is a function of several factors including the speed of
movement through the sewer, the quantity of suspended solids in the sewage, and the
degree of turbulence:
−
Under ideal operating conditions using slow forward advancement, sonar could
indicate small openings or cracks, around 5 mm wide. Under normal operating
conditions, however, very small defects may not be seen. The sonar image will,
however, identify those defects clearly requiring action.
−
Heavy suspended solids and debris in the sewage can block the sonar signal.
−
Incoming flow from connections causes air entrainment in the main sewer
downstream of the connection. The entrained air bubbles tend to block the sonar
signal, and as a result interference may be seen in the image.
♦ When combined with CCTV, sonar allows an inspection of the entire sewer, with sonar
providing the images below the flow line. A large number of combined sonar and
CCTV surveys have been undertaken in North America.
♦ The ultrasonic calliper and the rotating sonic calliper (RPC) are examples of
commercially available tools. The RPC has been used to inspect plastic, concrete, brick
and clay pipes. It can be operated in pipes as small as 0.5 m or as large as 4 m. The
RPC cannot operate in both air and water simultaneously, because different electronics
F-98
and transducers are needed. It records only the part of the pipe that is above water, or
the part that is below water level.
♦ Studies in the United States showed that air sonar used for measurement above the flow
line was not sufficiently accurate over the larger distances involved in 3.6 m diameter
pipes to allow valid condition assessment.
F34.5 Advantages
♦ Sonar provides a convenient way to measure the cross-sectional area of a sewer.
♦ Sonar can be used to inspect and assess the structural condition of otherwise
inaccessible or flooded sections of large diameter sewers.
♦ Sonar allows inspection of the portion of the sewer below the flow line. When
combined with CCTV, sonar allows an inspection of the entire sewer, with sonar
providing images below the flow line.
F34.6 Limitations
♦ The technique requires specially trained personal to undertake the inspection and
interpret the results.
♦ Sonar can not be operated in air and water simultaneously, as different transducers and
electronics are required.
♦ Sonar is a more specialized service than CCTV, with less service providers.
Table 3-36. Summary In-Pipe Acoustic Inspection Tools (Sonar).
Technical
selection
Technical
suitability
Utility technical
capacity
Economic
factors
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Assessment
Pipes.
Any.
Potable and wastewater.
Access to sewer interior is required.
Sewer must be passable.
Limited to large diameter pipes.
Continuous.
Non-destructive.
Inspection can be undertaken on-line.
Sewer defects and geometry.
Software used to process signals.
Fully commercialized.
Wide use, especially in conjunction with CCTV.
Semi-quantitative indication of defects.
Validation through direct observation required.
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Cost per inspection
Generic approach.
Highly skilled.
Highly technical.
Service likely to be provided by third party.
Service likely to be provided by third party.
Varies depending on pipe size, accessibility and
purpose of survey.
Requires team to operate equipment and provide
entry into pipeline.
Resource requirements
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-99
F34.7 Bibliography
1. ASCE, Sanitary Sewer Overflow Solutions, American Society of Civil Engineers, EPA
Cooperative Agreement CP-828955-01-0, April 2004.
2. McDonald, S.E.; Zhao, J.Q. Condition assessment and rehabilitation of large sewers,
National Research Council of Canada, Institute for Research in Construction, NRCC44696, 2001 (downloaded from www.nrc.ca/irc/ircpubs).
21H
3. Ratliff, A., An overview of current and developing technologies for pipe condition
assessment, ASCE 2004.
4. Zhao, J. Q. Trunk Sewers in Canada, APWA International Public Works Congress
NRCC/CPWA Seminar Series “Innovations in Urban Infrastructure,” 1998.
F-100
F35.0 In-Pipe Hydrophones
F35.1 Overview
Water loss control programs are widely used throughout the water industry and a major
phase of these programs is leak detection. Leak detection is used to determine the exact
location of a leak. Repair of the leak saves revenue and conserves water and energy.
To locate a leak precisely, a hydrophone can be inserted directly into a pipe. Leaks are
identified by the noise they create. Once a leak is identified, it can be located by moving the
hydrophone to the position where the noise is clearest, then determining the location of the
hydrophone at this point.
F35.2 Main Principles
Hydrophones are used to detect leaks due to the noise created as the water is forced out
under pressure through the pipe wall. Leaks generally make three sounds, a medium frequency
sound, 500-800 Hz, associated with the water passing through the orifice/leak, and two low
frequency noises, 20-300 Hz, associated with the water stream impacting the soil and
circulating outside of the pipe (Burn et al, 1999). The sound of the leak is also able to give an
indication of leak magnitude.
Hydrophones are generally tethered systems, although some free swimming
technologies are also available. In either case, an underwater microphone is inserted into a pipe
and moves along the pipe with the flow. The hydrophone is introduced to the pipe via a valve
and tapping made for the purpose of the inspection. There is also potential to utilize existing
access points provided by hydrants or fittings.
F35.3 Application
Hydrophones are used for the detection of leaks in water distribution and transmission
pipelines. Research has also been undertaken into the use of the technology for pressurized
sewers (force mains).
♦ There are no a standards for In-Pipe Hydrophone use.
F35.4 Practical Considerations
♦ A tethered system offers the least risk of inspection systems getting stuck, zero or
minimal supply disruption, and requires a single access point for entry and recovery of
the hydrophone.
♦ A new system is also available where the hydrophone and recording equipment is
encapsulated into a single unit that is inserted into the main without a tether and
collected down stream. The recorded data can then be downloaded and analyzed.
♦ Non-tethered or free-flying systems have the potential to cover much greater range of
the pipe network during each use; however there is a risk of losing the tool. Tethered
hydrophones can become fouled in valves and have limited range, and require a
minimum flow rate to pull them along the main.
♦ For tethered systems, when a leak is detected the hydrophone can be moved back along
the pipeline in order to pinpoint the leak.
♦ Currently, the most widely used commercial system is SaharaTM. This tool has been in
operation within North America since 2004. It was developed by the Water Research
Centre (WRc) in the United Kingdom.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-101
F35.5 Advantages
♦ As an in-pipe technique, factors like pipe material and diameter do not influence the
detection of leaks, as they do in on-pipe techniques (see Leakage Detection).
♦ Tethered hydrophone technology can be used to accurately pinpoint leaks.
♦ Non-tethered systems can survey a large length of pipe than tethered systems in each
use.
F35.6 Limitations
♦ The Sahara technology is relatively expensive, so other techniques and equipment
should be used to target and prioritize area to identify where it would be most useful.
♦ Tethered hydrophones can become fouled in valves and have limited range, and require
a minimum flow rate to pull them along the main.
♦ There is a risk of losing free swimming hydrophones.
Table F-37. Summary In-Pipe Hydrophones.
Technical
selection
Technical
suitability
Utility technical
capacity
Economic factors
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Pipelines.
Any.
Potable.
Hydrophones need special assemblies to allow
entrance into main.
None.
Restricted to large diameter mains.
Continuous.
Non-destructive.
Inspection be undertaken on-line.
Presence and location of leaks.
Software used to analyze data.
Fully commercialized service.
Used in the United States since 2004.
Quantitative assessment of location, semiquantitative assessment of leak size.
Only through excavation at leak site.
Generic approach.
Specialist service.
Sophisticated tool.
Use reported in the technical and trade literature.
Via specialist service providers.
Relatively expensive.
Team to undertake survey and patented
equipment.
F35.7 Bibliography
1. Burn, L.S., DeSilva, D., Eiswirth, M., Hunaidi, O., Speers, A. and Thornton, J. Pipe
Leakage – Future Challenges & Solutions, Pipes Wagga Wagga, 1999.
2. Chastain-Howley, A Transmission Main Leakage: How to reduce the risk of a catastrophic
failure, Leakage 2005 - Conference Proceedings, 2005.
F-102
3. Sahara homepage, http://www.wrcplc.co.uk/sahara/, accessed 2006.
2H
F36.0 Insulation Test
F36.1 Overview
Overtime the performance of the insulation in an electrical circuit may deteriorate with
exposure to heat, moisture, vibration or corrosive materials. Deteriorated insulation allows a
steady flow of electricity to escape from the electrical circuit during operation. This can lead to
equipment failure. Potentially dangerous voltages can become present if protective measures
are inadequate.
The procedure for determining equipment insulation resistance is widely used and readily
understood by trained electrical technicians, can be easily undertaken by using a hand held
testing device and is a non-destructive assessment technique.
F36.2 Main Principles
As part of an electrical and conditioning monitoring program, electrical insulation
testing is commonly undertaken to determine the insulation resistance of electrical circuits,
since the efficiency and running costs of equipment are increased when electrical circuits
exhibit poor insulation properties.
In order to assess an electrical circuit for its electrical insulation performance, a hand
held megaohmmeter is used to test the insulation resistance by applying a known voltage
(500V or 1000V DC for low voltage systems) to the circuit being assessed and measuring the
current flow to ground. From this measurement the resistance of the equipment insulation can
be determined, with a result exhibiting a low resistance between phases or phase to earth
indicating that insulation breakdown may be occurring, or moisture ingress and/or partial short
circuits may be present. The DC test voltage is applicable to both AC and DC circuits.
F36.3 Application
Electrical insulation testing is a commonly used and recognized technique for assessing
electrical circuits and equipment insulation performance in motor windings, cables,
switchboards and motor control centers.
♦ Insulation testing is referred to in AS/NZS 3000-2000.
F36.4 Practical Considerations
♦ Insulation testing to determine the condition of electrical equipment and circuits should
be undertaken by trained electrical technicians and engineers, since knowledge and
experience of electrical circuits and interpretation of the readings obtained from the
analysis is required.
F36.5 Advantages
♦ Insulation testing is common practice, inexpensive and easy to use.
F36.6 Limitations
♦ When determining the insulation resistance, the piece of equipment or circuit is
required to be isolated prior to assessment and as a result can not be undertaken as an
on-line assessment technique.
♦ When assessing electrical motors, minor faults may not be identified and sensitive
equipment must be disconnected to avoid possible damage.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-103
Table F-38. Summary Insulation Test.
Technical
Selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Technical
suitability
Utility technical
capacity
Economic factors
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Motor winding, cables, switchboards, motor
control centers.
Electrical insulation.
Potable and wastewater.
Access to conductor and insulation.
None.
None.
Discreet readings.
Non-destructive (providing electronic
components isolated).
None.
Insulation strength.
Stand alone.
Fully developed and off the shelf.
Standard sector practice.
Good accuracy.
Direct measurement.
Generic approach.
Electrician will already be trained to use.
None.
Well documented. Electric motor.
N/A
Low cost per inspection
One man no more than half an hour per motor
(allows for disconnection/reconnection).
F36.7 Bibliography
1. AS NZS 3000-2000 Electrical Installations (known as wiring rules).
F-104
F37.0 Intelligent Pigs
F37.1 Overview
Intelligent pigs use different technologies to locate defects or gather other information
about large diameter pipelines. Several non-destructive inspection technologies can be
integrated into these tools:
♦ The Magnetic Flux Leakage technique, used to detect corrosion or thin walls.
♦ Ultrasonic sensors, used to detect coating delamination, cracks, dents and gouges.
♦ Global Positioning System (GPS) technology is being adapted to obtain the exact
location of any problem in the pipe or to map the pipe itself.
♦ Geometry tools, which use mechanical arms or electro-mechanical means to measure
the bore of pipe. In doing so, the tool identifies dents, deformations, and ovality. It can
also sense changes in girth welds and wall thickness. In some cases, these tools can also
detect bends in pipelines.
F37.2 Main Principles
A pig is a device inserted into a pipeline that travels freely driven by the flowing media
to do a specific task within the pipe, such as cleaning. An intelligent pig carries complex
monitoring technologies that provide information on the condition of the pipe and/or its
contents. With a few exceptions, intelligent pigs simply gather data, which is then analyzed by
engineers to determine and report on the condition of the pipe.
Intelligent pigs are inserted into the pipeline at a location that has a special
configuration of pipes and valves where the tool can be loaded into a receiver. The receiver can
then be closed, sealed, and the flow of the pipeline product directed to launch the tool into the
main line of the pipeline.
A similar setup is located downstream, where the tool is directed out of the main line
into a receiver. The tool is then removed and the recorded data retrieved for analysis and
reporting.
The two most common requirements are for tools that can undertake geometry/diameter
measurement and detect metal-loss/corrosion. However, the information that can be provided
by these tools covers a much wider range of inspection and troubleshooting needs, including:
♦ Diameter/geometry measurements
♦ Curvature monitoring
♦ Pipeline profile
♦ Temperature/pressure recording
♦ Bend measurement
♦ Metal-loss/corrosion detection
♦ Photographic inspection
♦ Crack detection
♦ Wax deposition measurement
♦ Leak detection
♦ Product sampling
♦ Mapping
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-105
Three common technologies incorporated into smart pigs are described further below.
Geometry Tools: Geometry tools use mechanical arms or electro-mechanical means to
measure the bore of pipe. In doing so, the tool identifies dents, deformations, and other
variation is cross-section. It can also sense changes in girth welds and wall thickness. In some
cases, these tools can also detect bends in pipelines.
Ultrasonic Tools: There are two types of tools commonly used for inspections of
hazardous liquid pipelines based on ultrasonic measurements.
♦ Compression Wave Ultrasonic Testing (UT) tools measure pipe wall thickness and
metal loss. The first commercial application of UT technology used compression
waves. These tools are equipped with transducers that emit ultrasonic signals
perpendicular to the surface of the pipe. An echo is received from both the internal and
external surfaces of the pipe and, by timing these return signals and comparing them to
the speed of ultrasound in pipe steel, the wall thickness can be determined.
♦ Shear Wave Ultrasonic Testing (also known as Circumferential Ultrasonic Testing, or
C-UT) is the non-destructive examination technique that most reliably detects
longitudinal cracks, longitudinal weld defects, and crack-like defects (such as stress
corrosion cracking). Because most crack-like defects are perpendicular to the main
stress component (i.e., the hoop stress), UT pulses are injected in a circumferential
direction to obtain maximum acoustic response.
Magnetic Flux Tools: There are two types of tools commonly used for inspections of
pipelines based on magnetic flux measurements (for more information see Magnetic Flux
Leakage review).
♦ Magnetic Flux Leakage (MFL) tool: an electronic tool that identifies and measures
metal loss (corrosion, gouges, etc.) through the use of a temporarily applied magnetic
field. As it passes through the pipe, this tool induces a magnetic flux into the pipe wall
between the north and south magnetic poles of onboard magnets. A homogeneous steel
wall – one without defects – creates a homogeneous distribution of magnetic flux.
Anomalies (i.e. metal loss (or gain) associated with the steel wall) result in a change in
distribution of the magnetic flux, which, in a magnetically saturated pipe wall, leaks out
of the pipe wall. Sensors onboard the tool detect and measure the amount and
distribution of the flux leakage. The flux leakage signals are processed, and resulting
data is stored onboard the MFL tool for later analysis and reporting.
♦ A Transverse MFL/Transverse Flux Inspection tool (TFI) identifies and measures metal
loss through the use of a temporarily-applied magnetic field that is oriented
circumferentially, wrapping completely around the circumference of the pipe. It uses
the same principal as other MFL tools except that the orientation of the magnetic field
is different (rotated 90°). The TFI tool is used to determine the location and extent of
longitudinally-oriented corrosion. This makes TFI useful for detecting seam-related
corrosion. Cracks and other defects can be detected also, though not with the same level
of reliability. A TFI tool may be able to detect axial pipe wall defects – such as cracks,
lack of fusion in the longitudinal weld seam, and stress corrosion cracking – that are not
detectable with conventional MFL and ultrasonic tools.
F37.3 Application
Intelligent pig technology is generally used for inspection of large diameter steel
pipeline assets in the oil and gas sector.
F-106
These tools only have limited applicability to the water/wastewater industry, although
some critical steel mains may be candidates for intelligent pig technology.
F37.4 Practical Considerations
♦ In selecting the tools most suitable for in-line inspections, pipeline operators must know
the type, thickness and material of the pipe being measured; the types of defects that the
pipe might be subject to (e.g. internal corrosion, external corrosion, weld cracks, stress
corrosion cracks); and the risk presented by the pipe section being measured.
♦ Intelligent pigs are expensive devices that require specialized insertion and retrieval
arrangements. These are commonly designed into oil and gas pipelines, but are not
incorporated into the design of water transmission mains.
♦ Intelligent pigs are commercialized and widely used in the oil and gas sector. It is
unlikely that there will be widespread use of pigging in the water sector because of the
high capital cost of pig launch/recovery equipment, discoloration problems caused by
abrasion as the pig passes along the line, and the obstructions in many transmission
pipes due to corrosion, valve construction, and changes in size.
♦ Pigging would also require the main to be taken out of service for some hours.
♦ Some of the new pigs are able to alter size to allow them to be used for multi-diameter
pipes (Willke, 1998).
F37.5 Advantages
♦ High resolution intelligent pigs can accurately detect, size, and locate corrosion or any
other anomalies in pipelines. Once the problem is detected the information can be used
to develop a pipeline de-rating schedule, implement a repair or replacement program,
determine if re-inspection is necessary, and evaluate effectiveness of a corrosion
inhibitor program (Jones et al, 1995).
F37.6 Limitations
♦ Intelligent pigs are expensive devices that need specialized insertion and retrieval
structures. Traditionally they have been used in the gas and oil industry and will only
have only limited applicability to the water/wastewater industry.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-107
Table F-39. Summary Intelligent PIGS.
Technical
Selection
Criteria
Assets covered
Material type
Service Area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Economic factors
Asset management sophistication required
Skills required (level of tool sophistication);
usability
Technology required (level of tool
sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Pipelines.
Large diameter pipes of rigid material; more suited to
welded steel.
Potable.
Require specialized insertion point (pig traps) to avoid
interruption to flow.
Asset needs to be in relatively good condition to avoid
the pig getting stuck.
Pigs are generally designed for large diameter pipes.
Changes in diameters, including those associated
with valves and other fittings, can be an issue
Smart/intelligent pigs provide continuous readings for
a variety of factors.
Non-destructive technique.
Pigs are propelled by the product flow, so no
interruption is required. However, likely to cause
quality issues in water mains. Also, there must be
appropriate launch facilities for uninterrupted function.
Most common requirements are for
geometry/diameter measurement and for metalloss/corrosion.
Specialized software tools used to interpret data.
Large number of commercial providers.
Originally developed to remove deposits in pipes.
Now used for a wide variety of purposes. Limited use
in water sector.
Quantitative assessment.
Only through visual assessment; though calibration of
tools is done.
Associated with high levels of sophistication
Smart pigs require trained specialists.
Highly sophisticated tool that requires specialized
technology.
Large range of product information available.
Large number of providers all offering support.
Relative high cost.
More advanced pigs require specialists to deploy.
F37.7 Bibliography
1. http://www.ppsa-online.com/about-pigs.php, accessed 2005.
23H
2. Willke, T. Five technologies expected to change pipe line industry, Pipe line & gas
industry, vol. 81, No 1, pp. 36-37, 1998.
3. Jones, D.G., Dawson, S.J., and Brown, M. Smart Pigs Assess Reliability of Corroded
Pipelines, Internal Pipeline Corrosion Assessment, Pipeline & Gas Journal, March 1995.
F-108
F38.0 KANEW
F38.1 Overview
KANEW is a software tool used in strategic asset management that estimates lengths of
water distribution mains to be rehabilitated or replaced each year.
KANEW contains a network inventory module, a failure and break forecasting module,
an economic data module and a strategy comparison module. Through these modules,
KANEW predicts when select pipe sections will reach the end of their service lives,
differentiated by date of installation and by type of pipe sections with distinctive life-spans.
F38.2 Main Principles
KANEW is a cohort survival model for infrastructure developed at Karlsruhe
University, used to predict future rehabilitation needs for water infrastructure. Based on this
approach, Dresden University of Technology developed a Windows based software application
called KANEW, which was tested in an AwwaRF Research Project "Quantifying Future
Rehabilitation and Replacement Needs of Water Mains" (Arun et al, 1998). Essentially,
KANEW evaluates groups of pipes of the same material and diameter (i.e., cohort groups) and
estimates the percentage of pipes in each group requiring replacement or rehabilitation each
year.
The general framework of the KANEW approach is shown in Figure F-6.
Failure statistics
Network
Inventory
Pipe types
Pipe lifetimes
Ageing functions
Cohort survival model
Options of rehabilitation
Decision criteria
for rehab strategies
Economic
input data
Choice of best rehabilitation strategy
Figure F-6. Framework for Exploring Network Rehabilitation Strategies
(Adapted with permission from Stone, S., Dzuray, E. J., Meisegeier, D., Dahlborg, A-S., and Erickson, M., 2002).
The tool assumes service-life to be a random variable, starting after some time of
resistance and being characterized by a median age and a standard deviation, or age that would
be reached by a certain percentage of the most durable pipe section.
KANEW allows the user to calculate residual service lives and annual rehabilitation
needs of water pipes on the basis of their specific service life distributions. Specific
rehabilitation programs, defined for the medium term, can be analyzed with respect to their
economic and other long-range effects. An acceptable strategy is found through an
iterative/heuristic process.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-109
F38.3 Application
KANEW is a Windows based software package, used to predict the future rehabilitation
needs for water pipeline networks.
F38.4 Practical Considerations
♦ KANEW has been used by water authorities in Germany and the United States to assess
and develop water main replacement and rehabilitation programs.
♦ Data availability is a problem in some water utilities. The biggest issue is when there is
a data gap in historical water main rehabilitation and replacement. This data is required
for estimation of survival functions. As a result, a lack of data would introduce
considerable uncertainty into the survival functions for each category of water main.
♦ Due to this and other sources of uncertainty, the software uses optimistic and
pessimistic assumptions to predict an upper and lower range of miles to be rehabilitated
or replaced for each category of water mains.
♦ Version 1.0 is available with user manual for AwwaRF subscribers free of charge and
requires Microsoft Access 97 to run. It allows calculation of residual service lives and
annual rehabilitation needs of types of water main on the basis of their specific service
life distributions.
♦ The current commercial version is an extended version allowing specific rehabilitation
programs to be defined for the medium range and to forecast their economic and other
effects on the long range.
F38.5 Advantages
♦ KANEW can be used for planning water main rehabilitation and replacement strategies.
♦ The model can be used both for pipeline renewal planning and for budgeting for future
renewals.
♦ Windows based system that will run on a standard PC
F38.6 Limitations
♦ KANEW is a macro model that estimates a broad range of lengths of water mains to be
rehabilitated or replaced each year. The model does not predict specific water mains
that should be rehabilitated or replaced each year.
♦ The methodology adopted means that factors such as soil and pressure are not taken
into account.
F-110
Table F-40. Summary KANEW.
Technical
selection
Technical
suitability
Criteria
Assets covered
Granularity
Service areas
Focus of analysis
Scalability of tool/approach
Commercialization
Previous/existing use of the tool
Utility technical
capacity
Ease of validation
Flexibility with regard to analysis (asset types)
and granularity (system, asset level)
Integration with other tools/GIS
Asset management sophistication
In-house skills required
Technology required
Documentation
Data Requirements
Linking to asset data
Availability of software and technical support
Usability
Assessment
Water pipes.
System and sub-system level only.
Potable
KANEW is a cohort survival model for infrastructure
to predict future rehabilitation needs for water
infrastructure.
KANEW can be used for planning water main
rehabilitation and replacement strategies. The
model is useful both for older utilities having an
urgent need for renewal plans, and younger utilities
budgeting for future renewal plans.
Commercial software available through AwwaRF.
Used by authorities in the United States and in
Germany.
Difficult to validate except by statistical means.
Potable only; cohort to system level.
None.
Since good data is required, more associated with
higher levels of asset management sophistication.
Professional engineer.
PC based, version 1.0 requires MS Access 97.
Tool fully documented.
Comprehensive data on pipe assets.
Linkage through database.
Available through AwwaRF and commercially.
KANEW has GUIs and is capable of providing 13
different sets of graphical and tabular outputs.
F38.7 Bibliography
1. Baur, R. and R. Herz Proceedings of the 13th European Junior Scientist Workshop held at
Dresden University of Technology on “Service life management of water mains and
sewers”. ISBN 3-86005-238-1, 1999.
2. Deb, A.K., Hasit, Y.J., Grablutz, F.M. and Herz., RK. Quantifying future rehabilitation and
replacement needs of water mains. AwwaRF Research Report, 1998.
3. Stone, S., Dzuray, E. J., Meisegeier, D., Dahlborg, A-S., and Erickson, M. DecisionSupport Tools for Predicting the Performance of Water Distribution and Wastewater
Collection Systems, EPA, EPA/600/R-02/029, 2002.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-111
F39.0 KureCAD
F39.1 Overview
KureCAD was developed by the Viatek Group in Finland and uses a GIS to assist in the
management of sewer pipe network rehabilitation. The system can store information on all
infrastructure assets, prioritize the rehabilitation of pipes, and provide the necessary documents
to implement rehabilitation.
F39.2 Main Principles
Once the KureCAD system contains all the necessary data, it enables managers to
assess system conditions and prioritize work. For each pipe section, the system enables users to
record three basic types of data:
♦ Structural condition (strength and shape).
♦ Functional condition (its ability to transport water).
♦ Leakage rates (estimated leakage from the pipe).
Users can employ data from internal inspections or maintenance records to summarize
the pipe’s condition by assigning a score from 1 (good, no repairs required) to 4 (very bad,
needs to be repaired immediately). Users can also rate each pipe using other factors.
The system records whether the entered data is based on estimates or actual inspections.
The KureCAD system then combines all of the condition scores into one condition index
which is displayed via the GIS.
F39.3 Application
KureCAD is used to assist asset managers in identifying and prioritizing the
repair/rehabilitation of sewer pipes.
F39.4 Practical Considerations
♦ KureCAD is still under development but has been trialed in Europe. As the user
interface is based on GIS, a digital map of the network is required.
♦ The KureCAD system provides instruction to ensure consistency for data collection
during field inspections and maintenance.
F39.5 Advantages
♦ GIS approach to managing data and providing decision support.
♦ The KureCAD software is able to generate the paperwork necessary to initiate
repair/rehabilitation work, including detailed maps specifications.
F39.6 Limitations
♦ The tool is still in its development stages and at this point in time has only been trialed
in Europe.
♦ If GIS data is not available then maps have to be manually digitized.
F-112
Table F-41. Summary KureCAD.
Technical
Selection
Suitability
Criteria
Assets covered
Granularity
Service area
Focus of analysis
Scalability of tool/approach
Commercialization
Utility technical
capacity
Previous/existing use of the tool
Ease of validation
Flexibility with respect to analysis (asset types) and
granularity (system, asset level)
Integration with other tools/GIS
Asset management sophistication
In-house skills required
Technology required
Documentation
Data Requirements
Linking to asset data
Availability of software and technical support
Usability
Assessment
Sewer pipes.
System and asset level.
Wastewater
Uses GIS to manage sewer pipe rehabilitation.
Prioritizes the rehabilitation of pipes and
provides the necessary documents to
implement the rehabilitation.
Better suited to medium to large authorities
where good GIS data is available.
Commercial software available from Viatek
Finland.
Used by several Scandinavian authorities.
Difficult to validate except by statistical means.
Wastewater; asset to system level.
Integrates with GIS system.
Aimed at higher level of asset management
where GIS data is available.
Professional asset manager/engineer.
PC based tool. Windows based operating
system.
Product in development.
GIS data required.
Through pipe IDs.
Unknown.
Still under development.
F39.7 Bibliography
1. Stone, S., Dzuray, E. J., Meisegeier, D., Dahlborg, A-S., and Erickson, M. DecisionSupport Tools for Predicting the Performance of Water Distribution and Wastewater
Collection Systems, EPA, EPA/600/R-02/029, 2002.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-113
F40.0 Leak Detection
F40.1 Overview
Water loss control programs are widely used throughout the water industry and a major
phase of these programs is leak detection. Leak detection is used to determine the exact
location of a leak in a pipeline. The repair of leaks saves revenue and conserves water and
energy.
Leak detection is currently undertaken using a number of techniques, including acoustic
techniques, tracer gas and infrared photography. Drop tests and in-pipe hydrophones are also
used and are discussed in separate reviews (see Drop Test and In-Pipe Hydrophones reviews).
Leak detection gives an indication of condition and performance of a network or asset,
depending upon the amount of leaks found.
District metered areas (DMA) are used to aid with leak detection of the distribution
system. Also, because DMAs can encompass portions of the transmission system, this
approach is also used as an aid to locating transmission system leaks.
F40.2 Main Principles
Leak detection is generally conducted after primary and secondary surveys that assess
areas of a network to determine their level of leakage, which is used to identify specific areas
in need of further investigation. Once small areas of the network have been identified as
containing significant leaks (through the use of various techniques, including data logging,
district meter area data audits, and monitoring of night flows), these are surveyed in more
detail to determine the exact location of the leaks.
A common technique to determine the location of leaks uses acoustic sensors to detect
the noise/vibration made by water escaping the pipe under pressure. Leaks generally make
three sounds, a medium frequency sound, 500-800 Hz, associated with the water passing
through the orifice/leak and two low frequency noises, 20-300 Hz, associated with the water
stream impacting the soil and circulating outside of the pipe (Burn et al, 1999). Acoustic
techniques can not detect very small leaks such as weeping and seepage from cracks and joints,
commonly referred to as background leaks.
There are two principal methods of detecting sounds from leaks; noise correlators and
data loggers:
♦ Noise correlators are computer controlled systems that measure noise at either side of
the suspected leak location and locate the leak automatically.
♦ Data loggers consist of units containing audible leak detection hardware coupled with a
data logger, radio transmitter and extended life battery (10+ years). These units are
installed at multiple locations around a pipe network for extended periods (from
overnight to indefinitely) and the data collected by the inspection team at regular
intervals.
While leak detection by this method can be conducted regardless of the pipe material,
plastic pipe materials tend to be “quieter” than metallic or cementituous materials and so make
it harder to detect leaks using acoustic methods.
Techniques such as the tracer gas are not yet widely used in the water industry. The
tracer gas technique involves the introduction of a non-toxic water-insoluble lighter-than-air
gas such as hydrogen or helium into the pipe system. These tracer gases escape at leaks and
F-114
permeate through the cover soil and pavement to be located by specialized gas detectors above
the leak.
The infrared photography technique or thermography is more commonly used and is
based on water having different thermal characteristics to the surrounding soil and in turn act
like a heat sink relative to the soil. Infrared scanners are the used to detect thermal anomalies
outside of the pipes. Devices used for this can be either hand held or vehicle mounted (Burn et
al 1999).
The use of thermography from fixed or rotary wing aircraft can identify potential areas
of leakage from water mains. The technique detects ground water anomalies (water escaping
from the main creates ‘wet’ patches on the ground) through infrared thermography. Arial
thermography can potentially cover large areas relatively quickly. The technique is limited by
ground conditions (it is not recommended in urban areas), the line of the main, the local ground
temperatures (compared to the water temperature), and local drainage.
Arial thermography can potentially cover large areas relatively quickly. In practice, the
aircraft has to fly a straight line along the main. At every change in course of the pipeline, a
fixed wing aircraft has to circle in order to obtain a level approach to the new line. Helicopters
are not limited as much because they can fly at lower levels and execute level turns, but unit
cost for helicopters are higher.
F40.3 Application
Large leaks in water distribution networks can be identified quickly as the amount of
water flowing from the pipe has noticeable affects at ground level. However, pipe assets which
contain small leaks do not release enough water for surface affects to be seen at ground level.
Leak detection techniques are used to locate these leaks.
♦ There are no a standards for Leak Detection.
F40.4 Practical Considerations
♦ Leakage testing is widely used, both in the water and many other industries, although
techniques used vary.
♦ Generally all techniques require some level of operator skill to obtain reliable results.
F40.5 Advantages
♦ Active leak detection allows leaks that would otherwise have gone unnoticed to be
found.
♦ Data logging techniques can be used to focus the search for leaks.
♦ Arial thermography can potentially cover large areas relatively quickly.
F40.6 Limitations
♦ Noise correlators and data loggers are less suited for use on non-metallic pipe materials
due to the pipe’s low sound propagation properties.
♦ Detection success is sensitive to background noise levels.
♦ Acoustic detectors do not detect weeping type small leaks.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-115
Table F-42. Summary Leak Detection.
Technical
selection
Technical
suitability
Utility technical
capacity
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Economic factors
Cost per inspection
Resource requirements
Assessment
Pipes.
All, effectiveness depends on technique used.
Potable.
Noise correlators require access to the pipe; fire
hydrants are sufficient. Data loggers may need
to be located ‘on’ pipes, requiring excavation.
None.
None.
Continuous readings can be achieved.
Non-destructive.
Assessment should be conducted on-line.
Locates leaks.
Software packages used to interpret data
Tools are widely available in industry.
Techniques and tools are widely used.
Quantitative or semi-quantitative; accuracy is
dependant on the technique used.
Validated by exhuming the asset.
Higher levels of asset management
sophistication will generally result in more
efficient inspections but it is not required.
Operator needs to trained.
The level of technology required depends on the
technique to be used.
Techniques widely documented
Tools are supported by suppliers and by
consultants.
Depends on technique.
Requires teams to conduct surveys, actual
manpower depends on technique to be used.
F40.7 Bibliography
1. Burn. L. S., DeSilva. D., Eiswirth. M., Hunaidi. O., Speers. A. and Thornton. J. Pipe
Leakage – Future Challenges & Solutions, Pipes Wagga Wagga, 1999.
2. Chastain-Howley, A (2005) Transmission Main Leakage: How to reduce the risk of a
catastrophic failure, Leakage 2005 - Conference Proceedings.
3. Dingus, M., Haven, J. and Austin, R. (2002) Nondestructive None Invasive Assessment of
Underground Pipes, AwwaRF, USA.
4. Eiswirth, M., Burn, L.S. (2001) New Methods for Defect Diagnosis of Water Pipelines, 4th
International Conference on Water Pipeline Systems, 28-30 March, York, UK, 2001.
5. http://www.owue.water.ca.gov/leak/leaktech/leaktech.cfm, accessed 2005..
24H
6. Makar, J. M. ; Chagnon, N. Inspecting systems for leaks, pits, and corrosion, National
Research Council of Canada, Institute for Research in Construction, NRCC-42802, 1999
(downloaded from www.nrc.ca/irc/ircpubs).
F-116
F41.0 Linear Polarization Resistance of Soil (Soil LPR)
F41.1 Overview
Linear Polarization Resistance of soil (LPR) is a characteristic used to predict the
corrosion rate of buried ferrous assets. LPR has a negative correlation with corrosion rate in
ferrous assets, meaning that soils with high LPR values will exhibit low corrosion rates.
The empirical relationship between LPR and corrosion rate was initially investigated
for cast iron, establishing a base relationship between corrosion rate and LPR. In a subsequent
study for wrought iron, a much weaker relationship was established, and there was too much
variation in measurements to fully establish a correlation. Consequently there is some debate
over the usefulness of LPR for materials other than cast iron.
F41.2 Main Principles
LPR is measured for soil samples obtained from near the location of interest, usually a
buried asset or its future location. Several methods are available for measurement of LPR, the
simplest of which will be described here. The soil samples are brought to their wilting point
before testing (the wilting point is defined as the soil moisture content at which plants are
unable to extract water and varies with soil type). A small potential is applied across two
‘identical’ electrodes in a cell containing the prepared soil sample. The current at each
electrode is measured. This measurement is repeated over a range of potentials.
The resulting relationship between current and applied potential is called the
polarization curve. The reciprocal of this curve at the corrosion potential is called the
polarization resistance, where the corrosion potential is the potential that exists between a
metal and its environment (see Soil (electrical) Resistivity review). Different metals can have
different polarization resistance values in the same soil type. The linear polarization resistance
is taken from the region where the polarization resistance curve is considered to be linear and
can be applied to numerous metals without specific knowledge of their corrosion potential in
the soil being tested.
F41.3 Application
LPR is used to indirectly determine the corrosion rate of buried ferrous assets using an
empirical relationship.
♦ No standards are known to directly reference this technique; however AS/NZS
2280:2004 does mention its use.
F41.4 Practical Considerations
♦ Equipment that can be used for determining LPR (probes) is widely available and come
with two or more probes. Additional probes are intended to reduce error in readings.
The accuracy of readings is dependant on equipment used and sample preparation.
♦ The sample preparation requirements generally require testing be conducted in a
laboratory.
F41.5 Advantages
♦ Low cost technique.
♦ LPR is a simple method which can be used to give an indication of corrosion rate.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-117
F41.6 Limitations
♦ There is disagreement as to the reliability of the method and the relationship with
corrosion rate is empirical only.
♦ The assumption of linearity is not always representative of real conditions and so
reduces the accuracy of the technique.
Table F-43. Summary Linear Polarization Resistance of Soil (Soil LPR).
Technical
selection
Technical
suitability
Criteria
Assets covered
Material type
Service Area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Utility technical
capacity
Economic factors
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Environmental survey (pipeline assets).
Results relate to ferrous assets.
Potable and wastewater.
Access to soil at point of interest.
None.
None.
Results are discreet.
Non-destructive.
Test does not affect assets.
Soil linear polarization resistance (LPR).
None.
Equipment is widely available.
Currently being used in Australia as a screening
approach to corrosion.
Information on accuracy of the technique is
varied and can depend on measurement
method.
Validation by assessment of the asset.
Generic approach.
Operator training is required.
Specialized equipment required.
Technique described well in literature.
Information available in literature.
Low cost.
Measurements undertaken by a single person.
F41.7 Bibliography
1. Burn, L.S., Eiswirth, M., DeSilva D. and Davis P., Condition Monitoring and its Role in
Asset Planning, Pipes Wagga Wagga 2001, Charles Stuart University, Wagga Wagga,
N.S.W., 2001.
2. Heathcote, M. and Nicholas, D., Life Assessment of Large Cast Iron Watermains, Urban
Water Research Association of Australia, Research Report No 146, 1998.
3. Moglia M., Davis P., Farlie M. and Burn S. Indirect Measurements of Corrosion rates in
buried Wrought Iron pipelines: an application of Linear Polarization Resistance, 6th
National Conference of the Australasian Society for Trenchless Technology, Melbourne
Exhibition and Convention Centre. 27-29 September 2004.
4. AS/NZS 2280:2004, Ductile iron pipes and fittings.
F-118
F42.0 Load Rejection Tests
F42.1 Overview
Power generation systems can experience sudden changes in load as a result of an
emergency shutdown, failure of equipment or changes in consumer power demand. Load
rejection tests or models are intended to analyze and predict the performance of power
generation systems under these sudden load changes.
Either full load rejection tests or partial load rejection tests can be conducted. However,
many tests attempt to examine full load rejection since this is the worst case scenario.
F42.2 Main Principles
Load rejection tests are most commonly applied to power generation systems such as
hydro-power plants, wind turbines and steam turbine power plants. When undertaking load
rejection assessment, analysis may either be carried out on the actual plant or modeled using
commonly available computer software programs developed for undertaking load rejection
analysis. In order to create a computer model, an adequate amount of information and data on
the operating characteristics of the plant needs to be collected, such as turbine characteristic
curves, penstock construction details and any available hydraulic transient test data.
An example of a load rejection event would be if the load on a hydro-powered
generator is suddenly removed, as a result the turbine will rapidly accelerate the generator
before the turbine governor has time to correct the turbine speed. The occurrence of such an
event could have a catastrophic impact, if sufficient controls are not in place to deal with this
type of load rejection. Within a hydro-power station, a relief penstock is usually available to
divert water away from the turbine in the case of load rejection event.
F42.3 Application
Load rejection assessments are often conducted or simulated using computer programs,
to gain an understanding of the effects of power station performance when sudden load
changes are found to occur.
♦ Load rejection tests are covered in the National Grid Code, United Kingdom and the
Transmission Code 2003, Germany.
F42.4 Practical Considerations
♦ Technical staff that are trained and have experience in undertaking, assessing and
simulating load rejection events are required.
F42.5 Advantages
♦ By undertaking load rejection tests, the risks and consequences associated with the
event of sudden load rejections of power generation systems can be determined.
F42.6 Limitations
♦ When modeling load rejection events using computer simulation programs, the time in
setting up a computer model is often time consuming.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-119
Table F-44. Summary Load Rejection Tests.
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Technical
suitability
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Economic
factors
Cost per inspection
Resource requirements
Assessment
Generators.
N/A
Potable and wastewater.
Access requirements will be site specific.
Before a load rejection test is performed on an
actual plant, a hazard identification and risk
assessment is carried out. This will be site
specific and should take into consideration the
condition of the plant.
No restrictions.
Continuous.
Non-destructive.
On-line.
Turbine overspeed, penstock pressures,
structural adequacy of surge tanks, pipelines,
penstocks, etc.
Load rejection tests would usually be carried out
as stand alone tests.
Tests need to be developed so that they are site
specific.
Commonly used in the power generation
industry; limited use in water sector.
Dependent on the instruments used to record
data.
Computer models can be calibrated using
hydraulic transient test data.
High level of AM sophistication.
Usually a team of engineers would be required
to design and carry out the tests.
Reasonably high powered computers are
required to run the computer software models.
No current ASTM standards.
There are suitable software packages available
with customer support.
Expensive.
Usually a team of engineers would be required
to design and carry out the tests.
F42.7 Bibliography
1. Rebizant, W. & Terzija, V. Asynchronous Generator Behavior after a Sudden Load
Rejection, http://zas.ie.pwr.wroc.pl/wr_bpt03-2.pdf, accessed 2006.
25H
2. Tzuu Bin Ng, Walker, G.J. and Sargison, J.E. Modeling of Transient Behavior in a Francis
Turbine Power Plant, The University of Tasmania, Hobart,
www.aeromech.usyd.edu.au/15afmc/proceedings/papers/AFMC00084.pdf.
26H
F-120
F43.0 LPR for Corrosion Monitoring
F43.1 Overview of Tool
Linear polarization resistance (LPR) corrosion monitoring equipment measures
corrosion rate directly. The probes come in many types for embedding in new infrastructure,
retrofitting to existing infrastructure and a surface probe for more impromptu inspection.
F43.2 Main Principles
Linear polarization resistance is measured by passing a small current from the auxiliary
electrode to shift the potential of the steel by a fixed amount. The polarization resistance is the
potential shift divided by the current applied. It is inversely proportional to the corrosion rate.
Faraday's Law can be used to convert the corrosion rate current in μA/cm2 to steel section loss
in microns per year. A section loss rate of approximately100 microns will cause cracking and
spalling of concrete.
Probes measure the polarization resistance, which approximately relates to actual
corrosion rate of steel reinforcement in existing concrete structures.
F43.3 Application
Linear polarization resistance has been used in tunnels, bridges and road decks in the
United Kingdom, Singapore and India since 1998. Often linear polarization resistance
measurements are obtained in conjunction with electrical potential and/or concrete resistivity.
♦ The LPR technique is described in ASTM G59.
F43.4 Practical Considerations
♦ A range of corrosion monitoring probes are available. Probes can be located in core
holes that are retrofitted into existing structures. Probes use silver/silver chloride
reference half cells with mixed metal oxide coated titanium auxiliary electrodes. The
probe is fitted into a core hole and a connection is made to the reinforcement using the
probe flying lead. An electronic identification chip within the probe identifies the probe
and its physical location to the corrosion rate meter or to an automated data logging
system.
♦ Other corrosion monitoring probes include: a rack of probes that can be embedded
during the construction of new concrete structures; hand held probes that allow surfaces
to be monitored manually.
♦ An embedded rack of probes can measure the corrosion rate and corrosion potential for
a single element probe and the reinforcement, as well as the concrete resistivity and
concrete temperature. It is designed to monitor new structures where deterioration of
the structure or initiation of corrosion is of interest.
♦ Multi condition rack probes have been designed to provide information over a varying
depth profile. Four independent linear polarization resistance electrodes at varying
levels of concrete cover allow the determination of corrosion rate and half potential for
the element probes and the reinforcement. Concrete resistivity at three points,
temperature, and the derivable rate of ingress of corrosive substances can also be
determined.
♦ Working similar to a potentials survey, a connection to the reinforcement is made and
then measurements can be taken up to 25m from the connection. The mobile probe uses
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-121
conductive foam to control the spread of current. Probes come in a range of sizes. Small
probes are useful for tight fitting areas; however large probes give greater accuracy.
♦ It is useful to measure the temperature in different areas of a concrete structure in order
to determine differential temperature gradients and their affect on a concrete structure’s
long-term performance.
F43.5 Advantages
♦ Hand held mobile probes allow linear polarization resistance measurement to be carried
out at any position on the structure chosen by the user.
♦ Surveys of structures can readily be made in dry and wet situations to model best and
worst-case scenarios.
♦ LPR data loggers can be integrated with corrosion data management software. By
inputting rebar alloy density, dimensions and exposure data, the software can calculate
metal loss and corrosion rate.
F43.6 Limitations
♦ Testing often requires that at least two holes in the order of 6.5mm to variable depths
drilled in order to insert probes.
♦ It is important that sufficient time is allowed for a current value to stabilize at a certain
potential (or vice versa). For example, in certain LPR techniques such as potentiostatic,
it will typically take several minutes for the current to reach a stable level after the
polarizing voltage is applied. Shorter times could lead to significant measurement
errors.
♦ Some LPR testing technologies such as testing apparatus with a guard ring do not allow
quick assessing of large concrete surface areas. To reduce evaluation times to
acceptable, practical levels, the corrosion potential values can be mapped, followed by
a selective application of such testing apparatus to critical areas.
Table F-45. Summary LPR for Corrosion Monitoring.
Technical
Selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Integration with software tools
F-122
Assessment
Reinforced concrete structures such as tanks, pipes,
walls, dams, buildings, channels, weirs.
Reinforced concrete.
Potable and wastewater.
Direct contact with surface of asset. If asset is buried
then it must be exposed.
No restriction.
No limitations relating to size of concrete element.
Continuous reading.
Almost entirely non destructive, small drill holes
required.
The asset can remain in use and does not need to be
taken off-line unless internal (water side) surfaces
need to be assessed.
Concrete temperature that in turn allows differential
temperature gradients and their affect on a concrete
structure’s long-term performance to be determined.
The data can be transmitted to a central location
using telemetry.
Criteria
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Asset management sophistication required
Skills required (level of tool sophistication);
usability
Technology required (level of tool sophistication)
Documentation
Economic
factors
F43.7
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Equipment is fully developed, available from selected
commercial vendors and can be used off the shelf.
Widespread use internationally on bridges and road
infrastructure. Growing application in the water
industry.
Quantitative.
Results are indicative and can be validated by using
two other testing techniques: concrete electrical
resistance and rebar electrical potential.
Generic approach.
Relatively easy to use by following simple procedure.
Trained staff can take measurements. Linear
polarization resistance meters do not require
specialist knowledge or training.
Range from moderate to high level of sophistication.
Many automatic corrosion transmitters are capable of
measuring and transmitting data from all types of
corrosion probes. Optional technology includes
programmable alarm circuits.
ASTM G59. Further guidelines specifically for on-line
in-plant corrosion monitoring are given in ASTM G96.
Technical support available from distributors.
Low cost per inspection.
One operator required. LPR uses a series of
electrodes, a voltmeter, an ammeter and a current
source.
Bibliography
1. ASTM G59-97(2003) Standard Test Method for Conducting Potentiodynamic Polarization
Resistance Measurements.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-123
F44.0 Magnetic Flux Leakage
F44.1 Overview
A magnetic flux leakage (MFL) tool is an electromagnetic tool that identifies and
measures metal loss due to corrosion, physical damage, and so forth through the detection of a
temporarily applied magnetic field. The tool provides a non-destructive means of assessing
ferrous pipes. Tools using the same principle are available for inspecting tank floors.
As illustrated in Figure F-7, as the tool moves along the pipe, it induces a magnetic flux
in the pipe wall. A homogeneous steel wall – one without defects – creates a homogeneous
distribution of magnetic flux. Anomalies such as metal loss associated with corrosion of the
pipe wall result in a change in distribution of the magnetic flux, which, in a magnetically
saturated pipe wall, leaks out. Sensors onboard the tool detect and measure the amount and
distribution of the flux leakage. The flux leakage signals are processed, and resulting data is
stored onboard the MFL tool for later analysis and reporting.
PERMANENT
MAGNET
BLACK IRON (TO
COMPLETE MAG.
CIRCUIT)
PIPE
WALL
STEEL
BRUSHES
MAGNETIC
FLUX LINES
CORROSION
MAGNETIC PIT
SHIELD
LEAKAGE
FIELD
MAGENTIC
SENSOR
Figure F-7. Schematic Representation of MFL Internal Detection Device.
A transverse MFL/transverse flux inspection (TFI) tool uses the same principal as other
MFL tools with the exception that the magnetic field is oriented perpendicular to that used in
the other techniques.
F44.2 Main Principles
Typically, an MFL tool consists of two or more bodies. One body is the magnetizer
with the magnets and sensors and the other bodies contain the electronics and batteries. On the
very rear of the tool are wheels that travel along the inside of the pipeline to measure the
distance and speed of the tool.
A strong magnetic field is established in the pipe wall; brushes typically act as a
transmitter of magnetic flux from the tool into the pipe. High field MFL tools saturate the pipe
wall with magnetic flux until the pipe wall can no longer hold any more flux. The remaining
flux leaks out of the pipe wall and strategically placed sensor heads measure the leakage field.
Damaged areas of the pipe can not support as much magnetic flux as undamaged areas,
resulting in an increase in the flux field at the damaged areas. An array of sensor around the
circumference of the tool detects the magnetic flux leakage and notes the area of damage.
Magnetic flux leakage is a vector quantity and the sensors can only measure in one
direction. As such, three sensors must be oriented within a sensor head to accurately measure
the axial, radial and circumferential components of an MFL signal (earlier MFL tools recorded
only the axial component).
F-124
With large diameter pipes, space is available for multiple magnet arrays that can
saturate the entire pipe circumference. However, since the mass of the magnets and backing
steel need to be greater than the pipe wall, it has not been possible to develop internal tools to
suit small diameter distribution pipes.
Direct contact with the pipe wall is required. As such, the pipe surface must be clean.
The tool is mounted on a wheeled carriage and connected to an umbilical cord. Larger units
have onboard computers and power; an umbilical cord is not required.
Access has to be provided by cut-ins at regular intervals depending on the umbilical
length, as well as bends and obstructions in the pipeline.
The TFI tool is used to determine the location and extent of longitudinally-oriented
corrosion. This makes TFI useful for detecting seam-related corrosion. Cracks and other
defects can be detected also, though not with the same level of reliability. A TFI tool may be
able to detect axial pipe wall defects – such as cracks, lack of fusion in the longitudinal weld
seam, and stress corrosion cracking – that are not detectable with conventional MFL and
ultrasonic tools. External units are available for small diameter pipes.
F44.3 Application
MFL tools detect corrosion in ferrous pipelines. MFL detectors are generally used in the oil
and gas industry, incorporated into intelligent pigs for metal loss detection in steel pipelines
(see intelligent pigs review). The MFL probes are bulky and heavy and not suitable for internal
use in small diameter pipes.
Although commonly used in internal inspection, they have been adapted for external inspection
of pipes including water pipes. The external units are available for small diameter pipes.
Tools using the same principle are available for inspecting tank floors.
F44.4 Practical Considerations
♦ This technique is used in the oil and gas industry for large diameter pipelines.
Sophisticated electronics on board allow this tool to accurately detect features as small
as 1 cm by 1 cm.
♦ To more accurately predict the dimensions (length, width and depth) of a corrosion
feature, extensive testing is performed before the tool enters the pipeline. Using a
known collection of measured defects, tools can be trained and tested to accurately
interpret MFL signals.
♦ There is limited data available from the water industry as the degree of detail and
accuracy achievable with these tools is not generally warranted for water pipelines.
F44.5 Advantages
♦ When used in the oil sector, accurate assessment of pipeline defects improves decision
making within an Integrity Management Program. Excavation programs can then focus
on required repairs instead of calibration or exploratory digs.
♦ Units used on the pipe external surface can be used without supply interruption.
♦ Wall thickness reductions detected with a high degree of accuracy.
F44.6 Limitations
♦ The magnetic flux leakage techniques used in oil and gas pipe inspection have proven
ineffective for water pipes.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-125
♦ Internal inspection requires pipe cleaning prior to inspection. Pipe has to be off-line and
dry.
♦ Cost is significantly high corresponding to the accuracy, which is not generally
warranted in the water sector.
♦ As MFL techniques require good magnetic contact with the pipe wall internal
inspection is not possible for cement lined pipelines unless the lining is removed.
Table F-46. Summary Magnetic Flux Leakage.
Technical
selection
Feature
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Technical
suitability
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization
Previous/existing use of the tool
Accuracy/reliability
Ease of validation
Utility technical
capacity
Asset management sophistication
Skills required (level of tool sophistication);
usability
Technology required
Documentation
Economic factors
F-126
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Pipes and tank floors.
Iron and steel.
Potable and wastewater.
Tool available for internal and external use.
Direct contact with pipe wall required. Access to
tool has to be provided by cut-ins at regular
intervals depending on umbilical cord feed length
and bends and obstructions on pipeline.
Regularly spaced cut-ins not required for larger
units with on-board computers and power.
No limitations relating to asset condition provided
direct contact with the pipe wall is available;
when used internally, pipes can not be lined.
Pipe surface must be clean.
Internal tools: generally limited to pipes 250 mm
and greater. External tools: 150 mm and larger.
Continuous readings.
Non-destructive, though tool access requires cutins at regular intervals (100 m to 500 m,
depending on cable length, pipe alignment).
Internal requires pipe to be off-line.
Metal loss due to corrosion or physical damage.
Computerized software is used for data
interpretation.
Commercialized, but availability through
specialized companies engaged in this work.
Commercial use of the MFL probes reported in
literature and trade journals.
Accurate quantitative assessments possible.
Validation possible only by comparison with
manual /direct measurements.
More suited to sophisticated utilities.
Utility should have skills to interpret output data.
Tool operation typically by a third party.
Specialized equipment and dedicated computer
software.
Tool principles and description of reports
generated by tool will be available.
Service provided by special operator.
Greater than US$10,000 per site, plus civil costs.
Typically three person crew.
F44.7 Bibliography
1. Burn, L.S., Eiswirth, M., DeSilva D. and Davis P., Condition Monitoring and its Role in
Asset Planning, Pipes Wagga Wagga 2001, Charles Sturt University, Wagga Wagga,
N.S.W., 2001.
2. Eiswirth, M., Burn, L.S. New Methods for Defect Diagnosis of Water Pipelines, 4th
International Conference on Water Pipeline Systems, 28-30 March 2001, York, UK, 2001
3. Makar, J. M. ; Chagnon, N. Inspecting systems for leaks, pits, and corrosion, National
Research Council of Canada, Institute for Research in Construction, NRCC-42802
(downloaded from www.nrc.ca/irc/ircpubs), 1999.
27H
4. Trenchless Technology Network Underground Mapping, Pipeline Location Technology
and Condition Assessment, (downloaded from
http://www.ttn.bham.ac.uk/Final%20Reports/Pipe%20Location%20and%20Assessment.pd
f accessed 2006), 2002.
28H
5. Makar, J. M. ; Chagnon, N. Inspecting systems for leaks, pits, and corrosion, National
Research Council of Canada, Institute for Research in Construction, NRCC-42802
(www.nrc.ca/irc/ircpubs, 1999.
29H
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-127
F45.0 Man Entry Inspection
F45.1 Overview
While CCTV is now the industry standard approach for inspecting the internal
condition of sewers, in larger diameter sewers it becomes economical to carry out man entry
inspections. In this approach, the internal condition of the asset is assessed using a walkthrough inspection technique. This requires a team of operatives to enter the pipeline, and
assess the condition of the manhole and the sewer walls above the flow line.
Defects are assessed visually and recorded along with distance using a standard coding
system. Photographs of features of interest can also be taken. When this is done, the picture
reference should ideally be cross-referenced with the survey distance. Hand held videos can
also be used to provide a permanent record of the inspection.
The safety implications of man-entry inspections should be given appropriate
consideration. In particular, when entering a manhole sewer line, it is very important to observe
the appropriate confined space regulations.
F45.2 Main Principles
A man entry condition assessment is conducted as a walk through inspection. Since
sewers are hazardous confined spaces, manholes are first vented and tested for gases such as
hydrogen sulfide. When conditions are confirmed as being safe, a team of operatives carries
out the survey using appropriate safety equipment (e.g., gas detectors, breathing apparatus,
harnesses, winches, protective clothing, and communication systems).
During the inspection, the crew assesses the appearance of the sewer, the presence of
flow disturbances, the extent of corrosion, and the structural condition of the sewer.
Photographs should be taken of any observed defects, and a hand-held video camera can also
be used to videotape the internal surface of the sewer.
Acoustic tests may also be performed by striking the crown, sidewalls, and invert of the
sewer with a hammer and noting whether the generated sound is dull or solid. This provides
qualitative information regarding the sewer structure and, depending on construction, can
indicate the presence of voids in the sewer wall.
Other inspection techniques can be applied depending on material; for example, the use
of cover meters in reinforced concrete sewers. To assess the extent of corrosion activity, field
measurements of pH, dissolved oxygen, ambient hydrogen sulfide, and dissolved hydrogen
sulfide may also be taken.
F45.3 Application
Man-entry inspections are performed on large-diameter sewer pipelines and tunnels.
This kind of inspection can also be undertaken on large diameter water pipelines.
♦ A number of systems are used for sewer condition grading, a Standard version of which
is EN 13508-2:2001 (CEN 2001).
F45.4 Practical Considerations
•
F-128
Man entry inspections are a commonly applied technique in the water sector, and
inspection services are supplied by specialist contractors. However, due to the
hazardous conditions in the sewer and confined space requirements, safety precautions
are paramount, in particular:
−
If the flow of wastewater cannot be diverted, inspections should be performed at
night and during dry weather conditions so that the flow is minimal.
−
Ventilation fans should be used to ensure good ventilation.
−
During the survey, the atmosphere should be constantly monitored and emergency
evacuation procedures strictly adhered to.
−
The inspection should be performed by at least two persons and they should have
constant communication with the personnel outside the sewer line.
♦ The crew who carry out the inspection should be trained in order to ensure consistency
and uniformity of the inspection results.
♦ For wastewater pipelines, standards are available for qualitative and quantitative
grading of defects and a system for condition grading commonly used. Condition
assessment is performed by allocating a grade to the sewer that represents the range of
conditions from “like new” to “collapsed” or “collapse imminent.” The accuracy of a
condition grading depends on the inspector’s experience.
F45.5 Advantages
•
Man entry inspection is cost-effective for the inspection of large diameter pipelines.
F45.6 Limitations
♦ There are significant health and safety issues associated with the inspection; all
operatives must be fully trained in safety requirements.
♦ The results are qualitative and require manual interpretation for analysis.
♦ The accuracy of a condition grading depends on an inspector’s experience.
Table F-47. Summary Man Entry Inspection.
Technical
selection
Technical
suitability
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Assessment
Pipelines.
Any.
Potable and wastewater.
Man entry access required.
Must be safe to access.
Man entry access required.
Continuous.
Non-destructive.
Flow must be minimized, but inspection can be
undertaken on-line.
Pipeline defects.
None.
Service is provided by specialized contractors.
Common approach.
Qualitative assessment of condition.
Direct observations.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-129
Utility technical
capacity
Criteria
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Economic factors
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Generic approach.
Inspectors must be trained in confined spaces
and condition assessment.
Low tech inspection, but high tech safety
equipment.
No.
No.
High personnel and mobilization costs.
Team size in line with confined spaces
regulations.
F45.7 Bibliography
1. ASCE, Sanitary Sewer Overflow Solutions, American Society of Civil Engineers, EPA
Cooperative Agreement CP-828955-01-0, April 2004.
2. European Committee for Standardization EN 13508-2:2001 Condition of Drain and Sewer
Systems Outside Building – Part 2: Visual Inspection Coding System, CEN Brussels, 2001.
F-130
F46.0 Measurement of Strain
F46.1 Overview
Several techniques are used to measure strain of assets; electrical resistance strain
gauges and photoelastic techniques are discussed herein.
F46.2 Principles
Electrical Resistance Strain Gauge
The electrical resistance strain gauge is the most common type of strain gauge used
today. This simple strain gauge consists of a very fine wire filament (a resistor) arranged in a
long zig-zag pattern, with the long lengths parallel to the measured strain. The fine wire is
bonded to the strained surface by a thin layer of epoxy resin. As the surface and hence the wire
filament is strained, the wire will become elongated and the diameter will reduce. The
reduction in diameter will cause the resistivity of the wire to increase. An electrical signal
passed through the filament will vary depending on the strain.
‘Gauge Factor’ is a parameter equal to the fractional change in electrical resistance
divided by the actual strain. Since the magnitude of strain rarely exceeds the order of 10-3 and
the Gauge Factor is often about 2, the fractional change in electrical resistance can be
extremely small. This means that the measurements need to be extremely accurate to avoid
errors. To improve the accuracy of the measurements, the strain gauge is inserted into an
electric circuit such as the Wheatstone bridge.
Photoelastic Strain Gauge
A birefringent material is a transparent material such as calcite crystal that exhibits two
different refractive indices. The polarization of the light traveling through the material
determines the extent each refractive index plays.
A photoelastic material is a material that only exhibits the property of birefringence
when the material is under stress. A polarized light beam traveling through a stressed
photoelastic material will be resolved into two components such that the electric field vector in
each component is aligned with one of the two principal stress axes in the material. Each
component of the light beam will experience a different refractive index, causing the two
components to travel at different speeds and thus be out of phase with each other when they
exit the photoelastic material. Photoelastic strain analysis equipment generally consists of the
following:
♦ A polarized source of light.
♦ A model made of a photoelastic material or the actual body covered in a photoelastic
coating.
♦ A polariscope to detect the refracted or reflected light.
The projector emits polarized light onto either the actual body (Figure F-8) or a model
of the actual body (Figure F-9). Models are made of a photoelastic material so the polarized
light travels through the model and the refracted light travels to the analyzer. Coatings applied
to the actual body consist of a layer of photoelastic material (paint or adhesive sheets) with a
reflective layer underneath. The incident light is diffracted through the photoelastic layer and
then reflected back through the photoelastic layer by the reflective layer.
The light traveling through the model or coating will only experience birefringence at
locations of stress. The greater the stress concentration, the more the two component waves
will be phase shifted.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-131
The two diffracted components of light emerging from either the model or the coating
are then bought together in a polariscope, which determines the relative phase shifts by
analyzing the interference “fringe” patterns created. An example of a fringe pattern is shown in
Figure F-10. Areas of high stress concentration are identified by thinner fringes, as stress
concentration decreases the fringes become wider.
Figure F-8. Use of a Photoelastic Coating on the Actual Body.
(Reprinted with permission from: Brad Boyce, VP, Stress Photonics, Inc., Madison, WI)
Figure F-9. Use of a Photoelastic Model.
(Reprinted with permission from: D. Roylance, 2001)
Figure F-10. Fringe Pattern on a Centrally Loaded Arch.
(Reprinted with permission from: Doyle, J.F. and Phillips, J.W. , 1989)
F46.3 Application
Electrical resistance strain gauges are used for:
F-132
♦ Crack width measurement/monitoring in concrete structures.
♦ Small deflections in machines or structures.
Photoelastic strain gauges can be used in any components made of a homogeneous material,
such as a motor shaft.
Standards which reference electrical resistance strain gauges;
♦ ISO 4965:1979 Axial load fatigue testing machines - Dynamic force calibration - Strain
gauge technique.
♦ BS 6888:1988 Methods for calibration of bonded electrical resistance strain gauges.
Standards which reference photoelastic strain gauges;
♦ ASTM D4093-95(2005)e1 Standard Test Method for Photoelastic Measurements of
Birefringence and Residual Strains in Transparent or Translucent Plastic Materials.
♦ ASTM C978-04 Standard Test Method for Photoelastic Determination of Residual
Stress in a Transparent Glass Matrix Using a Polarizing Microscope and Optical
Retardation Compensation Procedures.
♦ ASTM C1279-05 Standard Test Method for Non-Destructive Photoelastic
Measurement of Edge and Surface Stresses in Annealed, Heat-Strengthened, and Fully
Tempered Flat Glass.
F46.4 Practical Considerations
♦ Variations in temperature can affect the accuracy of measurements with electrical
resistance strain gauges. For instance, errors may arise due to thermal expansion of the
object under analysis and also from the change in resistance of the electrical strain
gauge. Errors due to temperature fluctuations can be minimized but not completely
eliminated.
♦ A practical consideration of the photoelastic strain gauge is that either a model of the
object needs to be made using a birefringent material, or the actual object needs to be
coated in a photoelastic layer. This may not be feasible in many situations.
F46.5 Advantages
•
Electrical resistance strain gauge:
−
Relatively inexpensive.
−
Overall fractional errors can be less than ± 10%.
−
Possible to measure different types of strain, for example, shearing strain, poisson
strain and torsional strain.
♦ Photoelastic strain gauge:
−
−
−
−
−
−
Can provide full-field displays of the strain distribution.
Can be applied to parts with complicated geometry and/or complicated loading
conditions.
Sensitive and accurate.
Can measure residual stresses in materials.
Can be used to determine areas of critical stress and stress concentration factors.
Can measure dynamic strains.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-133
F46.6 Limitations
♦ Electrical resistance strain gauge
−
−
Errors due to temperature fluctuations.
A strain gauge only measures strain at one point. Multiple gauge arrangements are
required to analyze strain along different axes and to determine bending and
torsional strains.
♦ Photoelastic strain gauge
−
Operate best under laboratory conditions.
Table F-48. Summary Measurement of Strain.
Technical
selection
Technical
suitability
Utility technical
capacity
Economic factors
Technical
selection
Electrical resistance gauge
Criteria
Assets covered
Material
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/ geometry
Continuous/ discrete
Destructive/ non-destructive
Interruption to supply/ function
Assessment parameters
Integration with software tools
Commercialization
Previous/ existing use of the tool
Ease of validation
Accuracy/reliability
Asset management sophistication required
Skills required (level of tool sophistication)
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Photoelastic strain gauge
Criteria
Assets covered
Material
Service area
Access requirements
F-134
Assessment
Crack growth monitoring of dams; civil structures
e.g. concrete
Potable.
No specific requirements.
No specific limitations.
No specific limitations.
Continuous.
Non-destructive.
None.
Strain analysis.
None
Widely available.
Extensive use in the manufacturing industry. Limited
use in the water industry.
Direct measurement.
Quantitative
Generic approach.
Informed engineer.
Strain gauges.
N/A
N/A
N/A
One or two people.
Assessment
Any components made of a homogeneous material,
such as a motor shaft.
Potable or wastewater.
Objects made of photoelastic materials can be
analyzed directly. Other objects need to have a
photoelastic coating applied.
Objects are usually analyzed in a laboratory
environment.
Photoelastic strain gauge
Criteria
Limitations relating to asset condition
Limitations relating to asset size/ geometry
Continuous/ discrete
Destructive/ non-destructive
Interruption to supply/ function
Technical
suitability
Assessment parameters
Integration with software tools
Commercialization
Previous/ existing use of the tool
Utility technical
capacity
Ease of validation
Accuracy/reliability
Asset management sophistication required
Skills required (level of tool sophistication)
Technology required (level of tool sophistication)
Economic factors
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
If necessary, a model made of a photoelastic material
or a model with a photoelastic coating can be used to
analyze strain under different loading conditions
without loading the real object.
No apparent limitations in principle but objects are
usually analyzed in a lab.
Continuous real time recording of fringe patterns is
possible.
Non-destructive.
Objects are usually analyzed in a laboratory
environment.
Stress and strain analysis.
None
Commercially available equipment, e.g., GFP 1200
Grey-Field Polariscope.
Extensive in the manufacturing industry.
Used as a quality monitoring tool in the glass industry.
Limited use in the water industry.
Direct measurement.
Quantitative
Generic approach.
An informed engineer is required to perform the tests
and analyze the results.
A polariscope and preferably the relevant software to
eliminate the need for manual fringe counting.
N/A
N/A
Inexpensive.
One or two people.
F46.7 Bibliography
1. ISO 4965:1979 Axial load fatigue testing machines - Dynamic force calibration - Strain
gauge technique
2. BS 6888:1988 Methods for calibration of bonded electrical resistance strain gauges
3. ASTM D4093-95(2005)e1 Standard Test Method for Photoelastic Measurements of
Birefringence and Residual Strains in Transparent or Translucent Plastic Materials
4. ASTM C978-04 Standard Test Method for Photoelastic Determination of Residual Stress in
a Transparent Glass Matrix Using a Polarizing Microscope and Optical Retardation
Compensation Procedures
5. ASTM C1279-05 Standard Test Method for Non-Destructive Photoelastic Measurement of
Edge and Surface Stresses in Annealed, Heat-Strengthened, and Fully Tempered Flat Glass
6. Roylance, D. Experimental Strain Analysis, (accessed from
http://web.mit.edu/course/3/3.11/www/modules/expt.pdf), 2001
30H
7. Doyle, J.F. and Phillips, J.W. Manual on Experimental Stress Analysis, 5th Edition, Society
of Experimental Mechanics, Inc., 1989
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-135
F47.0 Methylene Chloride Gelation Assessment
F47.1 Overview
The methylene chloride (dichloromethane or methylene dichloride) test is a destructive
test used to give an indication of the degree of gelation in a PVC pipe.
A short section of chamfered pipe is immersed in a bath of methylene chloride for at
least 15 minutes and the chamfered surface then inspected for attack. The degree and location
of attack gives an indication of the degree of gelation around the pipe circumference.
F47.2 Main Principles
The methylene chloride test is a qualitative method used to give an indication of the
level of gelation in a PVC sample. The degree of gelation is directly related to the conditions
experienced by the pipe during manufacturing and so can also be used as a measure of quality
assurance.
Gelation is the process by which particulate PVC is formed into a homogenous
material. The degree of gelation achieved during the extrusion of a PVC pipe is related to the
toughness of the material produced. A low level of gelation results in a material with reduced
toughness. As such, pressure pipes made from a low level of gelation material will fail before a
pipe with a high level of gelation under the same operating conditions.
Methylene chloride testing is conducted on a short length of pipe, approximately 8
inches in length. One end of this length is chamfered and that end immersed in methylene
chloride for at least 15 minutes at 68°F. After this time, the length is removed and allowed to
dry. After drying the chamfered end is inspected for signs of attack.
Areas of the pipe which have been attacked will become whitened or bleached. The
chamfered surface will also become rough where attack has occurred. Generally there are three
results from the methylene chloride test:
Type 1 – where the surface exhibits no apparent attack.
Type 2 – where the surface exhibits uniform attack.
Type 3 – where the surface exhibits non-uniform attack.
F47.3 Application
Methylene chloride assessment is a qualitative method used to determine the gelation
level of PVC pipes. The test is used to identify areas in a pipe sample with the least gelation as
part of the fracture toughness testing.
♦ Standards which include this test are: BS 3505:1986, AS/NZS 1462.19:2006.
F47.4 Practical considerations
♦ This test is widely used in industry where fracture toughness testing is conducted.
♦ Methylene chloride is toxic and so should be handled and stored in an appropriate
fashion.
♦ Where quantitative measurement of gelation is required other methods are available
(see DSC Gelation Assessment review).
F47.5 Advantages
♦ Test gives an indication of the quality of the manufactured pipe.
F-136
F47.6 Limitations
♦ When used for condition assessment, requires a pipe section to be removed for testing.
♦ Test solution (methylene chloride) is toxic and should be handled by trained personnel
only.
♦ Test is broadly qualitative only.
Table F-49. Summary Methylene Chloride Gelation Assessment.
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Economic factors
Cost per inspection
Resource requirements
Assessment
Pipe assets.
PVC.
Potable and wastewater.
Lab based test; requires samples to be taken.
No limits due to asset condition.
No limitations due to sample size.
Discrete.
Destructive test.
Asset must be exhumed from pipeline before
testing.
The level of gelation in a PVC sample.
No integration with software tools.
Tool is a procedure
Test is widely used in industry.
Test is broadly qualitative.
Results are indicative.
Generic approach.
Operator should be trained in use of methylene
chloride.
Test requires methylene chloride and timing
device.
BS 3505:1986, AS/NZS 1462.19:2006.
Test can be conducted by consultants if
required.
Low cost per test.
Test requires a fume hood.
F47.7 Bibliography
1. Dorn, R., Howsam, P., Hyde, R.A. and Jarvis, M.A. Water mains: Guidance on assessment
and inspection techniques, CIRIA Report 162, Construction Industry Research and
Information Association, London, England, 1996.
2. Randall-Smith, M., Russell, A. and Oliphant, R. Guidance manual for the structural
condition assessment of trunk mains, WRc, UK, 1992.
3. BS 3505:1986 Specification for unplasticized polyvinyl chloride (PVC-U) pressure pipes
for cold potable water.
4. AS/NZS 1462.19:2006 Methods of test for plastics pipes and fittings - C-ring test for
fracture toughness of PVC pipes.
5. ISO 9852 : 1995 Unplasticized Polyvinyl Chloride (PVCU) pipes – Dichloromethane
resistance at specified temperature (DCMT) – Test method.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-137
6. Fillot, L.A Hajji, P. UPVC Gelation level assessment Part 1: Comparison of different
techniques, Journal of Vinyl and Additive Technology, 2006.
F-138
F48.0 Motor Circuit Analysis
F48.1 Overview
Motor circuit analysis is a non-destructive low voltage method for testing electric motor
cables, connections, windings and rotors for developing faults, to reduce the likelihood of
electrical failure occurring during operation. The results are not a definite indication of
impending failure but need to be compared with previous tests to identify trends. The test can
also indicate motor efficiency losses over time. The additional running costs could be a factor
in any decision for remedial works or replacement.
F48.2 Main Principles
When undertaking motor circuit analysis, a low voltage is applied to enable the testing
of electric motor cables, connections, rotor and windings for the onset of equipment breakdown
or faults. An insulation resistance test to earth is performed at either 500V or 1000V DC. The
measurements which are typically undertaken when conducting motor circuit analysis include:
DC resistance (R), impedance (Z), inductance (L), phase angle (Fi), multiple current/frequency
response (I/F) and insulation to ground. Based on the readings obtained, the physical and
electrical properties of a particular electrical component can be determined in accordance with
the following guidelines.
♦ Resistance (R) is used for determining the continuity of electrical cables and
connections.
♦ Impedance (Z) and Inductance (L) are compared to evaluate the insulation condition
of winding contamination.
♦ Phase angle (Fi) and Current/Frequency (I/F) are used to detect winding shorts.
The above three measurements will be balanced in a fully serviceable motor. Imbalance
in itself is not a definite indication of impending failure. Routine testing is required to enable
trends to be generated on which failure predictions can be based. The level of imbalance before
action should be fairly tolerant for non-critical motors and have a low tolerance for critical
equipment.
Impedance imbalance will cause the operating temperature of the electric motor to
increase placing further electro-mechanical stresses on the motor winding and rotor.
Imbalances also affect efficiency as well as reliability. As the balance between phases varies, it
becomes harder for the magnetic fields to turn the rotor, reducing efficiency of the motor.
F48.3 Application
Motor circuit analysis is applicable to all types of plant that contain electrical motors
and circuits.
F48.4 Practical Considerations
♦ Analysis of electrical motors and circuits using motor circuit analysis is widely used
throughout the manufacturing industry.
F48.5 Advantages
♦ Motor circuit analysis allows for changes in electric motors and associated circuits to be
trended. Action can then be taken prior to reliability being affected. Identification of
efficiency loss can form part of the financial case for repair/ replacement.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-139
♦ All tests are conducted using portable hand held non-specialized equipment, which
enables assessment to be conducted by non electrical trained personnel. Motor circuit
analysis can be conducted without the need to disassemble the motor prior to analysis.
F48.6 Limitations
♦ During the assessment, the electrical motor must be electrically isolated.
Table F-50. Summary Motor Circuit Analysis.
Technical
selection
Technical
suitability
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Economic factors
Cost per inspection
Resource requirements
Assessment
Electric motors.
Windings.
Potable and wastewater.
Portable hand held equipment.
None.
None.
Discrete readings.
Non-destructive.
Off-line.
Electrical properties of winding.
Standalone.
Fully developed and off the shelf.
Standard industry practice.
High accuracy.
Can be validated by measuring separately
winding resistance insulation and comparing to
as installed information.
Generic approach.
Electrician.
Standard computer.
Documented but no formal standard as yet.
Suppliers offer service to undertake
assessments.
Relatively low cost per inspection.
One person no more than half hour per motor.
F48.7 Bibliography
1. American Bureau of Shipping, Guidance Notes on Reliability Centred Maintenance, 16855
Northchase Drive, Houston, TX 77060 USA, July 2004,
http://www.aptgroup.com.au/elec_moto.htm.
31H
F-140
F49.0 Multi-sensor Pipe Inspection Robots
F49.1 Overview
Pipeline inspection is undertaken in a number of sectors using “intelligent pigs” (see
Intelligent Pig review) that travel with the product in the pipeline. These devices incorporate a
range of inspection technologies and are effective tools for inspections undertaken over long
distances, but are expensive and so their cost cannot be justified over short distances.
As an alternative, automated inspection of the inner surface of a pipe can be achieved
by a mobile robot. In this approach, a robot with multiple sensors is introduced into the pipe to
undertake a condition assessment using various non-destructive techniques.
The technology for these tools is still under development, but a number of systems have
been produced, though not fully commercialized. The robots being developed all incorporate
an array of non-destructive techniques that simultaneously assess pipeline condition. Research
has also focused on the automatic interpretation of the collected data.
To date, the development of these tools has generally concentrated on assessment
systems for sewers, but conceptually there is no reason why the approach could not be adopted
for water mains. Nevertheless, the information provided below pertains to the inspection of
sewers.
F49.2 Main Principles
Multi-sensor robotic systems have been developed by a number of international bodies
that incorporate several sensor technologies, including:
♦ Visual images: CCTV images can be used in conjunction with other sensors such as
laser profiling. Lateral connection cameras are capable of traveling up small diameter
service connections (see CCTV Visual Inspection review).
♦ Acoustic monitoring techniques: acoustic techniques can be used to assess pipe wall
thickness and locate flaws in the pipe wall. Sonar uses sound to produce an image of
the pipeline, which can be used to identify the pipe surface and other softer materials
such as plant matter and silt (see In Pipe Acoustic Monitoring Techniques (Sonar)
review).
♦ Electromagnetic: electromagnetic techniques such as remote field eddy current,
magnetic flux leakage and broad band electromagnetics can be used to assess wall
thickness of metallic assets (see Remote Field Eddy Current, Broadband
Electromagnetics and Magnetic Flux Leakage reviews).
♦ Ground Penetrating Radar: ground penetrating radar can be used in-pipe to find
cavities in the soil surrounding the pipe (see Ground Penetrating Radar review).
♦ Microwave sensors: microwave backscattering sensors can be used similar to ground
penetrating radar to explore anomalies in a medium range behind the pipe outer surface.
♦ Hydrochemical sensors: hydrochemical sensors can be used to assess water quality,
and for sewer pipelines can be used to indicate the presence of infiltrated groundwater.
♦ Laser profiling: measurement of pipe diameter and deviations including ovality can be
important, particularly in plastic pipes in which such deflection indicates stresses that
can cause premature failure of the pipe. Laser profiling systems are available to
measure pipe diameter during normal CCTV inspection.
Examples of robot platforms include:
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-141
♦ The KARO and PIRAT multi-sensor robotic development projects were aimed at
producing ‘smart’ sewer inspection vehicles equipped with several different sensor
devices. The robots were connected to a mobile control and surveillance unit by a cable.
One research focus of both projects was to develop methods for the automatic
interpretation of sensor data to identify and characterize pipe damage. KARO, an
inspection platform with exchangeable sensor modules, employed fuzzy logic to fuse
and interpret data from different types of sensors. In the PIRAT project, an expert
system analyzed laser images and ultrasonic data allowing classification of pipe
damage.
♦ The Sewer Scanner and Evaluation Technology (SSET) is a flexible non-destructive
evaluation data acquisition tool. At present, the prototype has a diameter of 130 mm
and a length of 850 mm and weighs 25 kg. In the prototype, higher quality information
on sewer condition is obtained through optical scanner and gyroscope technology.
SSET records a 360° image as it travels through the pipe. This allows the pipe
condition to be assessed after the inspection. This reduces the in-pipe time because the
operator is not required to locate and analyze defects during the inspection itself. The
interpretation system SSET implements fuzzy set theory and fuzzy logic techniques to
automatically identify, classify and rate pipe defects.
♦ SAM an interdisciplinary German research and development project on “Sewer Defect
Characterization by Multisensor Systems” involves the development and linkage of
different sensor systems. SAM includes a commercial CCTV system as well as a
number of sensors, including, microwave backscattering, hydro chemical, acoustic
impact, optical triangulation, geophysical and radioactive probes. The interpretation
system of SAM also implements fuzzy set theory and fuzzy logic techniques to
automatically identify, classify and rate pipe defects.
♦ The MAKRO robot is an autonomous sewer robot and its frame is flexible both
horizontally and vertically. The robot is equipped with a set of internal sensors, which
serve mainly to determine the robot's relative and absolute position within the pipe. The
robot's external sensors enable analysis of its environment and include obstacle
detection, collision avoidance, motion control, and landmark detection - a subtask of
self-localization.
♦ Pipe Rover is currently being developed in Hong Kong for assessment of pipes over
one meter in diameter. It is an underwater robot for inspection of water ducts, pipes and
foul water drains. It is especially suitable for offshore sewer outlets or power station
outfalls, where the pipes may terminate kilometres offshore and run deep in water. Pipe
Rover has two propulsion mechanisms. For flat-bottomed ducts with few obstructions;
tracks propel the robot, while for pipes, legs are used. The sensors include a color video
inspection camera with pan, tilt and lights, ultrasonic obstacle detection and
distance/depth/temperature/heading/pitch and roll information.
F49.3 Application
Intelligent inspection of sewer pipelines using multiple sensor robots to simultaneously
obtain a wide range of condition data.
F49.4 Practical Considerations
♦ Multi sensor systems are generally still in the development stage, and as such these
systems are not widely used. Nevertheless, various platforms have been subject to field
tests:
F-142
−
SSET was introduced to North American market in 1997; field trials covered 38.5
kms (126,612 ft) of sewer inspection in 13 participant cities. More recently, a 5.7km
(19,000 ft) sewer evaluation project for City of Atlanta and a project for Eastman
Chemical Company, Tennessee, have been completed.
−
PIRAT has been tested in 5 km of sewers in Melbourne.
−
SAM is currently being field-tested in several German cities.
♦ The evaluation of SSET is on-going. Work on KARO has stopped, though parts of it
are integrated into a new project SAM. PIRAT is unlikely to be commercialized.
♦ The external sensors available on MAKRO at the moment are very limited and
considerable development is still needed in this area before it would be usable for
automated pipeline inspection.
F49.5 Advantages
♦ Robots can be used to simultaneously gather large amounts of useful information about
a pipeline.
♦ Tools can be customized to gather data of specific interest for each asset type.
F49.6 Limitations
♦ The capital cost of inspections systems can be high due to the sensors incorporated in
them.
♦ Robots are not yet commercially available.
Table F-51. Summary Multi-sensor Pipe Inspection Robots.
Technical
Selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Technical
suitability
Utility technical
capacity
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Assessment
Pipe assets.
Any.
Mainly wastewater.
Access to interior of pipe for inspection probe
(robot).
Blocked and clogged assets cannot be
inspected past blockages.
Depends on equipment but minimum diameter
of around 150mm.
Continuous.
Non-destructive test.
Depends on sensors being used.
Depends on sensors being used.
Fully integrated software for analysis of data.
Systems are either still in development or have
been abandoned.
Limited testing for development purposes.
Quantitative.
Depends on sensors being used.
Associated with high levels of asset
management sophistication.
Training in use of specific device and
associated sensors is required.
Highly sophisticated.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-143
Criteria
Documentation
Economic factors
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Use and development documented in the
literature.
Limited.
High at present.
Robot and team to operate device.
F49.7 Bibliography
1. Burn, L.S., Eiswirth, M., DeSilva D. and Davis P., Condition Monitoring and its Role in
Asset Planning, Pipes Wagga Wagga 2001, Charles Sturt University, Wagga Wagga,
N.S.W, 2001.
2. Ratliff, A. An overview of current and developing technologies for pipe condition
assessment, Pipelines 2003, ASCE 2004.
F-144
F50.0 Oil Testing
F50.1 Overview
In many different types of equipment, oil is either used as a lubricant to reduce the rate
of wear and deterioration of internal moving components (e.g., in an air compressor, gearbox,
diesel/petrol engines), or used as a cooling medium to transfer heat (e.g., from the core and
coils contained in an electrical transformer).
Routine assessment of a sample of oil is a non-destructive method that can be used to
give an indication of the current condition of the plant. A number of tests are conducted on the
oil sample that can identify component wear, fatigue and corrosion. The analysis can also give
an indication of oil contamination and deterioration, which can indicate when oil should be
changed.
F50.2 Main Principles
F50.2.1 Oil as a Lubricant
In many different types of equipment (petrol/diesel motors, gearboxes, compressors and
hydraulic systems), analysis of the lubricating oil for the presence of sediment particles,
corrosion, fatigue and changes in the properties of the oil (such as density and viscosity) can
often provide an indication of the equipment’s current state of operation and internal condition.
Over time the level of oil and the changes in the oil properties have an influence on the
rate of wear and deterioration of moving internal components, with the formation of ferrous
particles in the lubricating oil providing an indication of the rate of wear of internal plant
components.
The following laboratory-based assessments are typically undertaken on a routine basis
to gain an indication of the condition of equipment through analysis of its lubricating oil.
♦ Ferrographic analysis is a technique that can be used to determine the density and size
of particles that have formed in the lubricating oil as a direct result of wear, fatigue
and/or corrosion. A sample taken from the equipment is analyzed by diluting the
sample in a fixer solvent that is then passed over a glass slide subjected to a magnetic
field. The applied magnetic field results in the separation of the ferrous particles from
the non-ferrous particles. The density of the particles and the ratio of the large to small
particles indicate the type and the extent of the wear that is occurring to internal
components.
♦ Particle counter analysis is a method undertaken to monitor particles in lubricating
and hydraulic oils caused by corrosion, wear and contamination. The two most
common methods used for particle counting are light extinction and light scattering. In
the light extinction method, an incandescent light is used to shine on a cell that the oil
sample moves through under controlled flow and volume conditions. A particle counter
measures the light that passes through the sample to determine the number of particles
in a predetermined size range. In the light scattering assessment technique, a laser is
used to shine light through an object cell that the oil sample fluid moves through under
controlled flow and volume. As opaque particles pass through the laser, the scattered
light created is measured and translated into a particle count.
♦ Atomic emissions spectroscopy can be used to determine the presence of corrosion
and wear products, contaminants and additives in hydraulic and lubricating oils. The
characteristic radiation emitted when samples are subjected to high energy and
temperature are measured to determine the presence of elements such as iron,
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-145
aluminum, chromium, copper, lead, tin, nickel and also components of oil additives
such as boron, zinc, phosphorus and calcium.
♦ Kinematic viscosity assessment provides an indication of the deterioration of oil over
time as well as an indication of the contamination of the oil by fuel and other oils.
During the assessment, the oil’s resistance to flow under controlled pressure and
temperature is measured by forcing a sample to flow through a capillary viscometer.
The viscosity of the oil can be determined from the results obtained.
F50.2.2 Oil as a Heat Transfer/Insulating Medium
In transformers, oil is used primarily as a cooling medium to transfer heat from the core
and coils to the external radiator banks, while also forming part of the insulation system. Oil
filled transformers have the core and coil assembly placed in a tank filled with dielectric
cooling oil. The primary insulation system used in an oil-filled transformer is Kraft paper,
wood, porcelain and oil. In more modern transformers, paper that is chemically treated to
improve its tensile strength properties and resistance to decay caused by immersion in oil are
commonly used.
Over time, the insulating properties of the oil may deteriorate as a result of
contamination and the formation of moisture leading to transformer break down. In order to
determine the condition of the oil and the electrical insulating properties to reduce the likely
hood of transformer break down, the following laboratory based oil tests are commonly
undertaken.
♦ Sediment tests (ASTM D – 1698), to determine the properties of sediment that has
formed in the oil due to contamination and or deterioration over time. The analysis
involves taking a sample of the oil and using a centrifuge to separate the sediment from
the oil to enable assessment of the sediment properties.
♦ Karl Fisher titration test (ASTM D – 1744), can be used to determine the amount of
moisture in an oil sample by measuring the electrical current flow between two
electrodes immersed in the sample solution with the result reported as the amount of
water in parts per million.
♦ Dielectric strength tests are used to measure the insulating properties of electrical
insulating oils. The electrical insulating properties of oil can change due to the
deterioration as a result of contamination or oil breakdown. The test is conducted by
subjecting the sample to an electrical stress at a given temperature by passing a voltage
through the sample.
In addition to the laboratory assessments outlined above, a visual inspection conducted
at six monthly intervals of the transformer dehydrating breather silica gel crystals can also be
undertaken, to ensure the color of the crystals has not changed. If on inspection more than 50%
of the crystals have changed color, replacement is recommended due to the possibility of
moisture entering the unit during warming up/cooling down cycles and resulting in premature
insulation failure of the oil. Insulating oil decay is found to be the single greatest cause of
power transformer failure.
F50.3 Application
Oil testing methods are used to assess the properties of oil and can be used to determine
the condition of internal moving components in petrol/diesel engines, gearboxes and
transmissions, and also those types of plant that use oil as a heat transfer medium, such as
electrical transformers, to provide a effective method of determining the current condition and
rate of deterioration of plant equipment.
F-146
♦ ASTM D – 1698, ASTM D – 1744 and ISO/DIS 18436-4 reference different oil testing
methods.
F50.4 Practical Considerations
♦ The majority of the assessments used in determining the type of contaminants and
particles present in oil samples are laboratory based assessments, and as a result require
trained technical staff to undertake these assessments and interpret test results.
F50.5 Advantages
♦ Oil testing can be undertaken as a part of a routine maintenance program to provide a
means of obtaining an early indication of plant failure.
♦ Oil testing can be used to optimize the frequency of oil changes in plant equipment,
preventing premature oil changes and indicating when an oil change is due.
F50.6 Limitations
♦ The majority of the assessments used in determining the type of contaminants and
particles present in oil samples are laboratory based assessments, and as a result require
trained technical staff to undertake these assessments and interpret test results.
Table F-52. Summary Oil Testing.
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Utility
technical
capacity
Economic
factors
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication);
usability
Technology required (level of tool
sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Wastewater/water infrastructure transformers, oil switchgear,
mechanical components requiring oil as lubricant.
Electrical insulant/cooling medium, mechanical lubricant.
Potable and wastewater.
Sample of oil required to be taken. Transformers usually
have tap points, switch gear requires removal from housing.
Mechanical some have sample taps.
None.
None.
Discrete reading.
Non destructive.
Transformers on-line. HV gear off-line. Mechanical
dependent on equipment
Impurities and dielectric strength of oil.
Stand alone.
Fully commercially available.
Standard industry practice.
Accurate results of sample but with electrical equipment are
indicative of condition.
Indicative requiring visual inspection.
Generic approach. Is commercially available.
Skilled operator for dielectric strength. Laboratory for analysis
Specialist equipment for dielectric strength. Laboratory
equipment for analysis.
Method is widely used and documented. ISO/DIS 18436-4.
Many laboratories available.
Depends on tests.
One man sample. Offsite laboratory.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-147
F50.7 Bibliography
1. American Bureau of Shipping, Guidance notes on Reliability Centred Maintenance, 16855
Northchase Drive, Houston, TX 77060 USA, July 2004.
2. ASTM D – 1698, Standard test method for sediment and soluble sludge in service aged
insulating oils.
3. ASTM D – 1744, Standard test method for determination of water in liquid petroleum
products by Karl Fischer reagents.
4. ISO/DIS 18436-4: Condition monitoring and diagnostics of machines - Requirements for
training and certification of personnel - Part 4: Field lubricant analysis. This document is a
Draft International Standard.
F-148
F51.0 On-Line Leak Detection Systems
F51.1 Overview
In the oil and gas sector it is common to have on-line leak detection systems for real
time monitoring of transmission pipelines. All such systems have the same underlying
principle; continuous on-line monitoring of flow parameters (flow and/or pressure) at the
upstream and downstream ends of a pipeline is used to determine if there are any hydraulic
anomalies.
Approaches range from simple comparison of “metered out” volumes with “metered
in” volumes, the monitoring of ‘rate of change’ in parameters of interest, and complex
computational pipeline monitoring.
Computational Pipeline Monitoring (CPM) uses an algorithmic approach to detect
hydraulic anomalies in pipeline operating parameters. The data from sensors is fed into a
computer model that can indicate if there is a new leak within the sensitivity of the algorithm.
The CPM system then provides an alarm and displays other related data to the pipeline
controllers to aid in decision-making.
F51.2 Main Principles
Continuous on-line monitoring of flow and pressure is carried out at the upstream and
downstream ends of a pipeline. The simplest approaches compare “metered out” volumes with
“metered in” volumes. Other relatively straight forward approaches look at the rate of change
in monitored parameters; operating parameters are monitored at various points along the
pipeline and the system reacts when there is a change at an abnormal rate.
More complex approaches utilize complex computational monitoring systems that
simultaneously monitor numerous operating conditions. Flow, pressure and other data are fed
into a mathematical model of the pipeline. The system then continuously compares the
measured values with the values predicted by the model. A discrepancy between measured and
predicted value indicates a change in the operating characteristics of the pipeline; for example,
the presence of a new leak or other hydraulic anomaly.
F51.3 Application
Used as a technique for leak detection in the oil and gas industry by pipeline operators
to protect the public and the environment from consequences of a pipeline failure. There is the
potential to expand use into the water industry for the monitoring of transmission pipes.
F51.4 Practical Considerations
♦ This approach to on-line leak detection is commonly adopted in the oil and gas sector.
The technique relies upon relatively frequent monitoring of at least one flow and one
pressure at opposite ends of the pipeline. A potential difficulty in applying this
technique to the water sector is that pipeline flow needs to be monitored to high degree
of accuracy, which is currently not standard practice.
♦ With an algorithmic approach to detect hydraulic anomalies, the technique can only
indicate the presence of a new leak; any leak existing when the model was first
calibrated will form part of the steady state conditions. A significant leak can, however,
be indicted by the difficulty in making the model fit or in a discrepancy between the
flow into and out of the pipeline.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-149
♦ Operational transients such as pump starts, line fills, valve closures, etc., may be
modeled as well, so that this automatic leak detection system can continue to work
during operational changes that occur in the normal day-to-day operation of the pipeline
system.
F51.5 Advantages
♦ Provides real time assessment of structural condition through detection of new leaks.
F51.6 Limitations
♦ Cost could be prohibitive in the water sector except where there are specific risk and
revenue drivers.
Table F-53. Summary On-Line Leak Detection Systems.
Technical
selection
Technical
suitability
Utility technical
capacity
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
F-150
Assessment
Water pipelines.
N/A
Potable.
None, on-line monitoring technique.
Applicable to structurally sound assets.
None, though only cost-effective for large
mains.
Continuous readings.
Non-destructive.
Asset remains on-line.
Change in flow parameters that indicate a leak.
By definition, integrated software tool.
Developed for the oil and gas sector.
No uptake in the water sector.
Quantitative assessment.
Difficult to validate except by locating new leak.
Would require a high degree of sophistication to
justify.
Automated monitoring.
High level of instrumentation; sophisticated
tools.
N/A
N/A
F52.0 PARMS-Planning
F52.1 Overview
The Pipeline Asset and Risk Management System (PARMS) is a suite of computerbased models developed by CSIRO, designed to assist in the management of water supply
network assets. Two tools have been commercialized to date; PARMS-Planning and PARMSPriority. PARMS-Planning is designed to be used annually for long-term planning and
regulatory reporting, whereas PARMS-Priority is designed to be used on a regular basis to
allow determination of which assets to rehabilitate to meet the water utility’s strategies (see
PARMS-Priority review).
PARMS-Planning is a software tool that allows assessment of both short and long-term
repair and replacement strategies for water pipelines. The PARMS-Planning software can be
used to:
1. Forecast the expected annual number of failures.
2. Assess replacement based upon the predicted number of failures in any one year.
3. Calculate the cost implications of different management and operational scenarios.
PARMS-Planning assesses replacement needs based upon the predicted number of pipe
failures, in conjunction with the policy adopted by the water utility. The failure rates of each
pipe are estimated for each year in the forecast period. The product of the failure rate and the
length of the pipe give the number of failures for that pipe asset. The total number of failures in
the system in any one-year is given by the aggregate of failures for individual assets.
F52.2 Main Principles
The overall approach used by PARMS-Planning is to forecast the expected annual
number of failures for each individual pipe asset over the long term (the next 30 to 100 years),
based on various determinants including the age of each asset, its installation and operating
conditions, and its failure history. The calculation process for each year involves the following:
♦ Estimating the expected number of failures of each pipe for each of the years in the
forecast period using a relevant statistical or physical probabilistic failure model. This
expected number is then converted into an integer number of failures using a negative
binomial probability distribution.
♦ Estimating the cost of each failure. This involves modeling whether the failure was
repaired by clamping; how long the interruption was and when it started; and
consequentially what rebates and penalties applied (where regulators require such
payment); and whether neighboring pipes also experienced an interruption.
♦ Evaluating (in conjunction with a set of policy options) which pipes should be
considered for replacement. Pipes that are identified as replacement candidates are then
either replaced or considered for shut-off valve insertion (inserting a valve to reduce the
number of customers impacted by a pipe failure). The cost of the selected option is
accumulated.
The costs of maintenance are provided within PARMS-Planning per repair, and the cost
of replacement assets are calculated from costs per unit length. Replacements reduce the length
of existing assets and create a new asset in the year of replacement.
The chosen policy options determine when a pipe is a candidate for replacement. This
can be on the basis of the number of failures experienced by the pipe, the number of unplanned
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-151
interruptions, or the net present value of the future costs of the alternatives of maintenance or
replacement.
As noted, the analysis can be tailored to the strategy/policy of individual utilities, but in
general those assets that have multiple failures in any one-year are targeted for replacement
(the number of allowable failures per year depending upon customer preference).
F52.3 Application
PARMS-Planning is used to undertake long term strategic planning for water
distribution networks and model the impact that management strategies will have on
performance.
F52.4 Practical Considerations
♦ PARMS-Planning is a commercial software package that has been implemented in
several authorities in Australia. It is a Windows based application with an easy to use
GUI.
♦ PARMS-Planning requires failure curves to be developed through the analysis of the
utility’s data. These curves are utilized in the forecasting of network performance and
provide the basis for the management modeling scenarios. Generic failure curves are
currently being developed by CSIRO.
♦ Users of the software have reported that it has enabled them to better understand the
long term implications of their management strategies and has provided insight into
how their networks are actually performing.
F52.5 Advantages
♦ The expected failure rate over time can be described for every individual asset in the
network.
♦ PARMS-Planning is able to assess replacement based upon the predicted number of
failures in any one year, and thus is able to include customer preferences for supply
interruptions.
♦ The software allows the modeling of modified asset management strategies that might
occur as a result of regulatory changes or business objective changes.
♦ A combination of graphical and tabular outputs provides users with a detailed
breakdown of network performance by pipe material, pipe age, failure type, etc.
♦ The system incorporates a simple GIS interface that allows network information to be
displayed in an incorporated GIS viewer.
F52.6 Limitations
♦ PARMS-Planning requires good quality asset data as well as failure history data in
order to develop the failure curves.
♦ The failure curve development is normally undertaken by consultants and is an
additional cost to the software package.
F-152
Table F-54. Summary PARMS Planning.
Technical
selection
Technical
suitability
Criteria
Assets covered
Granularity
Service area
Focus of analysis
Scalability of tool/approach
Commercialization
Previous/existing use of the tool
Ease of validation
Flexibility with regard to analysis (asset types) and
granularity (system, asset level)
Integration with other tools/GIS
Utility technical
capacity
Asset management sophistication
In-house skills required
Technology required
Documentation
Data Requirements
Linking to asset data
Availability of software and technical support
Usability
Assessment
Pipes, water pipeline infrastructure.
System and asset level.
Potable
Long term asset management planning using
asset failure curves developed from utility asset
data.
Better suited to medium to large authorities
where good asset data is available; a ‘light’
version is currently in development that could be
more suited to small utilities.
Commercial software.
Used by several large utilities in Australia .
Initial validation is provided in statistical analysis
of failure data and development of failure
curves.
Potable only. Subsystem to system level.
Integrates with most database systems and
requires standard GIS shape files for GIS
implementation.
Aimed at higher level of asset management
where good asset data is available.
Asset manager/engineer.
PC based tool. Windows based operating
system.
Research and development fully documented.
Good quality asset data and asset failure history
data is required.
Linking to utility asset database is provided in
initial setup.
Software available through CSIRO, as is
technical support.
Simple user interface, once data is loaded.
F52.7 Bibliography
1. Burn, L. S., Tucker, S. N., Rahilly, M., Davis, P., Jarrett, R., and Po, M. Asset planning for
water reticulation systems - the PARMS model. Water Science and Technology: Water
Supply, 3(1-2), 55-62, 2003.
2. Burn, S., Ambrose, M. D., Moglia, M., and Tjandraatmadja, G. PARMS - An approach to
strategic management for urban water infrastructure. IWA Leading edge conference on
strategic asset management. San Francisco, 26-27 July, 2004.
3. Burn, S., Ambrose, M. D., Moglia, M., Tjandraatmadja, G., and Buckland, P. Management
strategies for urban water infrastructure. IWA World Water Congress. Marrakech,
Morocco, October, 2004.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
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F53.0 PARMS-Priority
F53.1 Overview
The Pipeline Asset and Risk Management System (PARMS) is a suite of computerbased models developed by CSIRO, designed to assist in the management of water supply
network assets. Two tools have been commercialized to date; PARMS-Planning and PARMSPriority. PARMS-Planning is designed to be used annually for long-term planning and
regulatory reporting (see PARMS-Planning review), whereas PARMS-Priority is designed to
be used on a regular basis to allow determination of which assets to rehabilitate to meet the
water utility’s strategies.
PARMS-Priority is a software tool that assists water authorities to make tactical
renewal and valve insertion decisions for water distribution pipes and networks. The PARMSPriority software can be used to:
♦ Prioritize between pipe assets targeted for potential renewal.
♦ Develop work packages for effective programming of pipe replacement.
♦ Evaluate pressure reduction scenarios.
♦ Analyze shut-off block reduction scenarios (inserting valves to reduce the number of
customers impacted by a failure).
♦ Facilitate information management of water pipe asset and failure information.
♦ Predict pipeline failures and costs for individual assets; including service levels.
F53.2 Main Principles
PARMS-Priority is designed to compliment PARMS-Planning by allowing water
utilities to spend available renewal budgets in an efficient manner by supporting the renewals
prioritization process. The analysis undertaken within PARMS-Priority is based on estimating
risk; risks involved with different scenarios and options are assessed using a standard risk
management approach, as per Australia/New Zealand standards. Risk is calculated by
combining the output of failure prediction models with the output of cost assessment models.
The failure forecasting is developed from a utility’s failure database using statistical
analysis. Depending upon pipe material, failure predictions are based on either statistical NonHomogeneous Poisson models or physical probabilistic models. The predictions provide failure
rates and probabilities for each pipe in the network, taking into consideration the age of the
pipe, material type and diameter, operating pressure, length of pipe, the pipe’s failure history
and where possible soil. The costs and consequences of failures are related to repairs, customer
supply interruptions – rebates, penalties and customer preferences, as well as flooding and
damages.
Costs and failure rates and probabilities are combined to associate risk values with
different scenarios relating to pipeline renewal, pressure reduction and valve insertions.
Scenarios are ranked on various risk and financial indicators such as net-present value of
savings/losses, and payback period.
F53.3 Application
PARMS-Priority is used to prioritize a water pipe renewal program by targeting high
risk assets.
F-154
F53.4 Practical Considerations
♦ PARMS-Priority is a commercial software package that has been used in several
authorities in Australia. It is a Windows based application with an easy to use GUI.
♦ As with PARMS-Planning, PARMS-Priority requires failure curves to be developed
through the analysis of the utility’s data. These curves are utilized in the forecasting of
network performance and provide the basis for the management modeling scenarios.
Generic failure curves are currently being developed by CSIRO.
F53.5 Advantages
♦ Failure predictions are based on rigorous analysis of the failure history of pipe groups.
♦ PARMS-Priority supports the user in identifying renewal clusters, and evaluating the
effects of pressure reduction and valve insertions.
♦ The risk calculation engine can be used to investigate user-specified scenarios and to
prioritize between different actions, which allows for proactive asset management.
♦ A query engine allows authorities to target specific areas of their network to review
performance. A combination of graphical and tabular outputs provides users with a
detailed breakdown of asset performance by pipe material, pipe age, failure type, etc.
♦ The system also incorporates a simple GIS interface that allows asset information to be
displayed in an incorporated GIS viewer.
F53.6 Limitations
♦ PARMS Priority requires good quality asset data to be available as well as failure
history data in order to develop the failure curves.
♦ The failure curve development is normally undertaken by expert consultants and is an
additional cost to the software package.
Table F-55. Summary PARMS-Priority.
Technical
selection
Technical
suitability
Criteria
Assets covered
Granularity
Service area
Focus of analysis
Scalability of tool/approach
Commercialization
Previous/existing use of the tool
Ease of validation
Flexibility with regard to analysis (asset types) and
granularity (system, asset level)
Integration with other tools/GIS
Assessment
Pipes, water pipeline infrastructure.
System, sub-system and Asset level.
Potable.
Decision support system to assist water
authorities make renewal and valve insertion
decisions for water distribution pipes.
Better suited to medium to large authorities
where good asset data is available.
Commercial software.
Used by several large utility in Australia.
Initial validation is provided in statistical analysis
of failure data and development of failure
curves.
Potable only; asset to system level.
Integrates with most database systems and
requires standard GIS shape files for GIS
implementation.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-155
Utility technical
capacity
Criteria
Asset management sophistication
In-house skills required
Technology required
Documentation
Data Requirements
Linking to asset data
Availability of software and technical support
Usability
Assessment
Aimed at higher level of asset management
where good asset data is available.
Asset manager/engineer.
PC based tool. Windows based operating
system.
Users standard asset classification system as
developed by WSSA Australia, but can be
tailored to other regional standards.
Good quality asset data and asset failure history
data is required.
Linking to utility asset database is provided in
initial setup.
Software available through CSIRO, as is
technical support.
Simple user interface, once data is loaded.
F53.7 Bibliography
1. Moglia, M., Burn, S., Meddings, S. Decision support system for water pipeline renewal
prioritisation, ITcon Vol. 11, pp 237 – 256, 2006.
F-156
F54.0 Passive Acoustic Inspection of Pipes (Acoustic Emission)
F54.1 Overview
This technique is a non-destructive method used to detect the release of sound energy
when wires in pre-stressed concrete pipes fail.
During the manufacture of pre-stressed concrete pipes (also known as pre-stressed
cylinder concrete pipe or PCCPs) high strength steel cables (bundles of steel wires) are
wrapped under tension around a central core to apply a compressive stress to the concrete. As
the pipe degrades, the steel cables corrode. Eventually, wires will break releasing the stored
energy, the majority of which is released as sound. This sound propagates along the pipe via
the pipe wall and the water within the pipe.
As deterioration continues, the prestressing cable will continue to corrode and wires
will break releasing more energy in a series of discrete events; these can be detected by
hydrophones or other sensors.
F54.2 Main Principles
Passive acoustic inspection uses acoustic sensors, hydrophones or accelerometers to
detect failures occurring in the prestressing wire of pre-stressed concrete pipes. To locate these
pipe sections, the sensors are placed along the pipeline while the pipe is in service to log when
a wire fails. The location of a failure is determined by using data from the sensors on either
side of the failure. The time difference between the sound reaching the two sensors, the speed
of sound in water, and the distance between the sensors is used to locate where the failure
occurred.
Acoustic sensors can be located in assets on a temporary basis or as a permanent means
of pipeline monitoring.
F54.3 Application
Passive acoustic inspection is used to locate actively deteriorating sections of prestressed concrete pipe.
F54.4 Practical Considerations
♦ The monitoring technique is fully commercialized and used to manage the risk
associated with the catastrophic failure of pre-stressed concrete pipes.
♦ The sensor spacing is limited by the presence of discontinuities in the pipeline between
the failure and the sensors, such as valves or elbows.
♦ Sensor spacing can range from 300 ft to 1500 ft based on the pipeline diameter and
presence of discontinuities.
♦ Inspections are generally used on pipes greater that 30” diameter.
♦ Hydrophones are inserted into the water column through a minimum of a ¾’’ tap.
Accelerometers are installed directly on the pipe surface. Both sensors can be installed
when the pipeline is in service.
F54.5 Advantages
♦ Actively deteriorating sections of pipe can be located without exhuming the pipe or
removing it from service; the rate of deterioration can be determined to prioritize
replacement.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-157
♦ Sensors can be left in place as a permanent means of monitoring asset condition.
♦ Technique can also detect sounds produces during cracking of the concrete.
♦ Inspection is not limited by heavy walled PCCP.
♦ Manhole access is not required.
F54.6 Limitations
♦ Accuracy of section location is affected by discontinuities in the pipeline between the
failure and the hydrophones.
♦ This technique does not quantify the amount of broken wires in the pipe.
Table F-56. Summary Passive Acoustic Inspection of Pipes (Acoustic Emission).
Technical
selection
Technical
suitability
Criteria
Assets covered
Material type
Service Area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Economic factors
F-158
Asset management sophistication required
Skills required (level of tool sophistication);
usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Pipes.
Pre-stressed concrete.
Potable and wastewater.
¾’’ access required for entry of hydrophone into
water column or exposed pipe surface for
accelerometer.
None.
Generally used for 30’’diameter and above.
Continuous.
Non-destructive test.
Inspection requires pipe to be on-line.
Location and number of wire related events
during the monitoring period.
Can be telemetered.
Tool is available from several commercial
suppliers.
Wide use in North America.
Quantitative.
Results can be validated by exposing a pipe
section for visual inspection and/or performing a
RFEC/TC inspection.
Generic approach
Training in use of equipment is required. Analysis
of results conducted by experts.
Specialized equipment is used, can be obtained
from supplier or testing can be conducted by
contractors.
Use documented in the literature.
Tool support available from supplier.
Pipeline specific.
Units are battery powered.
F54.7 Bibliography
1. The pressure pipe inspection company homepage,
http://www.ppic.com/services/aet.asp, accessed 2006.
32H
2. Dingus, M., Haven, J. and Austin, R. Nondestructive None Invasive Assessment of
Underground Pipes, AwwaRF, USA, 2002.
3. Makar, J. M. ; Chagnon, N. Inspecting systems for leaks, pits, and corrosion, National
Research Council of Canada, Institute for Research in Construction, NRCC-42802
(downloaded from www.nrc.ca/irc/ircpubs), 1999.
3H
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
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F55.0 Performance Testing of Rotating Machinery
F55.1 Overview
Performance testing of rotating machinery is a non-destructive method used to assess
whether equipment is operating as per the original specification or manufacturer’s data.
Performance tests are usually conducted in the manufacturer’s shop as part of ‘factory
acceptance testing’ and again on-site as part of ‘site acceptance testing’. Ideally performance
tests should also be carried out periodically to ensure that equipment continues to operate
satisfactorily. Periodic performance tests can reveal deterioration and inefficiencies in
equipment that can lead to significant savings on power bills and maintenance costs.
F55.2 Principles
To undertake a performance test, a rotating machine needs to be run under a range of
operating conditions. For example, the shaft speed or applied load can be altered to give a
range of test results. For each operating condition, data needs to be collected that can be used
to calculate parameters such as efficiency and load capacity. The data collected and parameters
calculated will depend on the particular type of rotating machinery under analysis. The test
results are compared to the specification or manufacturer’s data to determine if the equipment
is operating as required.
Performance testing of pumps is particularly common. For on-site pump testing, a
range of flow conditions can be tested by adjusting the position of a downstream valve to alter
the pump delivery head. Upstream and downstream calibrated pressure gages and a flow meter
are required for this testing. Typically, the flow rate, suction head, delivery head and motor’s
current are measured. The results can be plotted on top of the manufacturer’s pump curves to
show the difference between the actual operating performance and the design (or optimal)
operating performance. The manufacturer will typically guarantee that a pump will operate
within a particular range of the pump curve. Performance testing of pumps can help diagnose
pump problems such as cavitation, impeller damage and case damage. Noise, temperature and
vibrations may also be measured as part of the pump performance test.
F55.3 Application
Performance testing is applicable to all rotating machinery. Applications for the water
and wastewater industry include pumps, fans, motors, screw conveyors, air blowers,
compressors, mixers and centrifuges.
♦ ANSI/HI 1.6-2000 Centrifugal Pump Tests.
♦ ANSI/HI 2.6-2000 Vertical Pump Tests.
♦ ANSI/HI 12.1-12.6 (A128) Rotodynamic (Centrifugal) Slurry Pump Standard.
♦ ISO 9906:1999 Rotodynamic pumps - Hydraulic performance acceptance tests - Grades
1 and 2.
♦ ISO 13380:2002 Condition monitoring and diagnostics of machines - General
guidelines on using performance parameters.
F55.4 Practical Considerations
♦ In order to undertake a performance test the rotating machinery needs to be operated
under a full range of operating conditions.
F-160
F55.5 Advantages
♦ The performance of equipment can degrade significantly with time. Performance
testing can highlight inefficiencies and the need for the repair or replacement of
components, which can lead to cost savings.
F55.6 Limitations
♦ On-site performance tests can be limited by the equipment available to take
measurements. For example, a pump performance test is limited by the location of the
pressure gauge. If a pressure gauge cannot be located close to the pump then the
measurement will be affected by friction head losses in the pipe and fittings giving
unreliable results.
Table F-57. Summary Performance Testing of Rotating Machinery.
Technical
selection
Criteria
Assessment
Assets covered
Pumps, fans, motors, screw conveyors, air
blowers, compressors, mixers and centrifuges.
N/A
Potable and wastewater.
None.
It may be decided that equipment in poor
condition should not be exposed to the full
range of operating loads and conditions.
N/A
Continuous readings over test duration.
Non-destructive.
On-line.
The performance of rotating machinery, e.g.,
efficiency, head, pressure, noise, vibration.
It is possible to use SCADA software to record
the measured data.
Tool is fully developed.
Widespread use throughout the water and other
sectors.
Dependent on the accuracy of the measuring
devices, e.g., flow meters, manometers.
Validation by repetition.
Generic approach.
The operator needs to be able to interpret the
data collected. For instance, they should be
able to read pump curves.
Only basic measurement devices are required.
SCADA may be used to track the results but is
not required.
ANSI/HI 1.6-2000, ANSI/HI 2.6-2000,
ISO 9906:1999, ISO 13380:2002.
Technical support is available from
manufacturers.
Low cost per inspection.
One operator required.
Material type
Service area
Access requirements
Limitations relating to asset condition
Technical
suitability
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Utility technical
capacity
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Economic
factors
Cost per inspection
Resource requirements
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-161
F55.7 Bibliography
1. ANSI/HI 1.6 (M104) American National Standard for Centrifugal and Regenerative
Turbine Pump Tests.
2. ANSI/HI 2.6 (M108) Vertical Pump Tests.
3. ISO 9906:1999 Rotodynamic pumps - Hydraulic performance acceptance tests - Grades 1
and 2.
4. ISO 13380:2002 Condition monitoring and diagnostics of machines - General guidelines on
using performance parameters.
5. ANSI/HI 12.1-12.6 (A128) Rotodynamic (Centrifugal) Slurry Pump Standard.
F-162
F56.0 Phenolphthalein Indicator (Carbonation Testing)
F56.1 Overview
The phenolphthalein indicator test is a quick method used to indicate the presence of
free lime in cementituous materials.
Samples are removed from the structure being tested, such as a pipe section, and stained
with the indicator. Areas with low or no free lime content remain colorless, while areas with
free lime remaining turn pink.
A freshly exposed sample is required. For a pipe section, the sample must be extracted
(see Cut-Out Sampling and/or Core/Coupon Sampling reviews).
F56.2 Main Principles
Phenolphthalein is a pH indicator that changes color, from colorless to pink/red in
alkaline environments where the pH is greater than approximately 9.6; below this pH the
indicator remains colorless. Since free lime has an alkalinity of approximately 12.5, the
phenolphthalein indicator test is a good indicator of free lime. The depth of carbonation and/or
leaching in cementituous materials can thus be detected.
Cementituous materials become carbonated due to the action of carbon dioxide; carbon
dioxide reacts with moisture in the cement/concrete to form carbonic acid. This then reacts
with the free lime to form calcium carbonate. The rate of carbonation is dependent on the
permeability and moisture content of the concrete. Over time, the depth of carbonation will
increase.
Leaching of free lime occurs when water in contact with the concrete/cement surface
dissolves free lime, which is then transported away. This occurs in situations where running
water is in contact with the asset, such as for asbestos cement pipelines.
The service life of concrete assets with steel reinforcement depends on the ability of the
concrete to protect the reinforcement from corrosion. In good quality reinforced concrete, the
steel reinforcement is chemically protected from corrosion by the alkaline nature of the
concrete. The highly alkaline environment promotes the formation of a passive and protective
oxide layer around steel reinforcing bars (Campbell et al, 1991).
The lack of free lime at the surface of the steel reinforcement reduces the alkalinity to
the point where the passive protection layer cannot be maintained. The steel reinforcement is
therefore free to corrode in the presence of moisture and oxygen. This will eventually lead to
spalling of the concrete and failure of the asset.
As above, the tensile strength of a concrete or asbestos cement pipe also falls over time
due to the removal of free lime. Free lime can be leached (washed) out of the cement matrix by
water, or can be chemically converted by carbonation.
F56.3 Application
The phenolphthalein indicator test is used to detect the presence of free lime in
cementituous assets.
F56.4 Practical Considerations
♦ Phenolphthalein indicator is widely used in a number of industries as a general
indicator of alkalinity. For this reason it is readily available from numerous suppliers.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-163
For the purpose of indicating the presence of free lime phenolphthalein indicator is
simple to use and widely used for condition assessment.
♦ When conducting testing all dust created in exposing the surface to be tested should be
removed as this can give false readings. Where holes have been drilled into slabs of
material, the edges of the holes should be chipped at to expose a fresher surface prior to
testing.
♦ The boundary between free lime and carbonated material is blurred due to variations in
material structure. Repeatability in the tests is good; variation of ± 5mm has been found
(Campbell et al, 1991).
♦ The phenolphthalein test can be conducted on-site or in the lab and requires a freshly
exposed surface as carbonation begins immediately on exposure to air.
F56.5 Advantages
•
Phenolphthalein indicator is readily available and easy to use. The test is cheap, fast and
simple to conduct. The test can be conducted in the field or in the lab.
F56.6 Limitations
♦ Test requires some damage to the asset being tested.
♦ Phenolphthalein indicator solution is flammable and appropriate precautions need to be
taken.
♦ Phenolphthalein indicator should not be ingested.
Table F-58. Summary Phenolphthalein Indicator (Carbonation Testing).
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
F-164
Assessment
Any cementituous asset type, civil also.
Cementituous materials only.
Potable and wastewater.
Freshly exposed sample required. For pipes section
must either be extracted or a core sample taken.
No restrictions.
No restriction.
Discreet.
At least part of the asset is damaged/removed to allow
testing.
Non-pressure pipes can remain in use if only a core is
taken above flow. Pressure pipes need to be taken offline for sample removal/testing.
Remaining free lime, used to infer carbonation depth.
Stand alone.
Widely available.
Widely used.
Qualitative indicator; the boundary between
carbonated and non-carbonated areas is some what
blurred, others areas are clearly identifiable.
Direct measurement.
Utility technical
capacity
Criteria
Asset management sophistication required
Skills required (level of tool sophistication);
usability
Technology required (level of tool
sophistication)
Documentation
Availability of technical support
Economic factors
Cost per inspection
Resource requirements
Assessment
Generic approach.
Easy test to conduct by following simple procedure.
No sophisticated tools required to conduct test.
Specialized tools may be required to obtain samples
depending on location and type.
No known standard test methods. Specific chemical
information can be obtained from MSDS,
CAS# 77-09-8.
Knowledge of phenolphthalein is widespread and
easily obtainable.
Low cost.
Resources are required to obtain sample, e.g.,
exposing pipeline and removing sample.
F56.7 Bibliography
1. Dorn, R., Howsam, P., Hyde, R.A. and Jarvis, M.A Water mains: Guidance on assessment
and inspection techniques, CIRIA Report 162, Construction Industry Research and
Information Association, London, England, 1996.
2. Randall-Smith, M., Russell, A. and Oliphant, R., Guidance manual for the structural
condition assessment of trunk mains, WRc, UK, 1992.
3. Campbell, D., Strum, R. and Kosmatka, S., Detecting Carbonation, Concrete Technology
Today, Volume 12, Number 1, 1991.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-165
F57.0 Pipe Potential Surveys
F57.1 Overview
Pipe potential surveys are used to gain an understanding of the electrochemical
interaction between ferrous pipes and the surrounding soil. The pipe-to-soil potential is
measured using a voltmeter and a reference electrode. If electrical connection to the asset can
be made above ground, for example connection to a valve, this does not require exhumation of
the pipe.
The pipe-to-soil potential measured during testing is useful for identifying areas of for
further analysis, including areas where coatings have deteriorated or been damaged. However,
some practitioners consider the application is limited for coal tar enamel coatings due to the
high number of defects generally found in these coatings.
F57.2 Main Principles
There are two main types of pipe potential survey. For pipelines with a high quality
external protective coating, a Direct Current Voltage Gradient (DCVG) survey can be used to
determine the location of gaps in the coating.
The technique involves imposing a direct current on the pipe and measuring the
difference in the pipe-to-soil voltage between two reference electrodes (Cu/CuSO4), which are
gradually moved along the whole length of the main. At gaps in the coating, the imposed
electrical current leaks to earth and there is a significant increase in the voltage gradient
compared to sections of the main where the coating is complete.
The second survey technique determines the pipe-to-soil potential along the length of
the main using a single reference electrode (Cu/CuSO4) and without an imposed current. This
approach is most useful for mains that have either a low quality or no external coating and
where electrical continuity is created by the run lead method of jointing.
In order to convert pipe-to-soil potential into corrosion rate, information is required
about the soil in which it the potential measured. This requires the soil to be sampled every 50
to 100 meters. Sections of the main in different soils are then exposed and their external
condition directly assessed in order to ‘calibrate’ a particular value of pipe-to-soil potential.
A variant of the second form of pipe potential survey should be carried out on a regular
basis where a cathodic protection system is installed. If a pipe’s potential is not suppressed
sufficiently (≤-850 mV Cu/CuSO4 scale) it will continue to corrode. If its potential is
suppressed too much (≈ ≤-1200 mV Cu/CuSO4), excessive alkali can be produced at the pipe
surface leading to the possibility of delaminating of the protective coating.
F57.3 Application
Pipe potential surveys measure the voltage between ferrous pipes and the surrounding
soil. The technique is most applicable to continuously welded steel pipes, which have good
quality external coatings. The voltage can either be the result of an applied current, in the case
of DCVG testing, or electrochemical corrosion cells.
Other techniques are also available which rely on similar techniques, including the
Pearson Survey, the Current Attenuation Survey and the Close Interval Potential Survey. The
Pearson Survey and the Current Attenuation Survey are used to assess the condition of pipe
external linings. The Close Interval Potential Survey is used to determine the level of cathodic
protection throughout a pipeline.
♦ BS 7361 refers to some of these techniques.
F-166
F57.4 Practical Considerations
♦ For the DCVG technique to work, the main has to be electrically continuous. This is
usually the case with steel pipes joined by welding, where the condition of the external
coating is critical for the satisfactory long term performance of the main.
♦ To measure the pipe-to-soil potential, a fine insulated trailing wire is connected to the
pipeline, preferably at an accessible point such as a valve or air valve. The other end is
connected to a voltmeter and then the copper/copper sulfate electrode(s). When in
contact with the ground, the electrodes complete the electrical circuit and allow the
pipe-to-soil potential to be read from the voltmeter.
♦ Pipe potential readings are taken periodically along the pipeline. At any distance, a
constant reading provides some confidence in the results. In contrast, a wildly varying
voltage could indicate the presence of stray current or interference from other pipes.
♦ Water mains coated with coal tar enamel (the default coating in many areas up until the
1980/90’s) will invariably find numerous coating defects, and in some cases continuous
defects where the coating has split due to soil stresses.
F57.5 Advantages
♦ The techniques are non-destructive and can be successful in locating corrosion
hotspots.
♦ Technique may not require a pipe to be exhumed for examination and pipelines can
remain in service.
♦ Locates areas of likely corrosion and indicated if more invasive assessment is required.
F57.6 Limitations
♦ Varying moisture contents in soils over the year will cause variation in results.
♦ Techniques may miss very small isolated areas of corrosion.
♦ Results are affected by the presence of stray currents.
♦ The more advanced techniques require highly specialized equipment and trained
personnel.
Table F-59. Pipe Potential Surveys.
Technical
selection
Criteria
Assets covered
Material type
Service Area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Assessment
Buried pipes.
Externally coated ferrous pipes.
Potable and wastewater.
Electrical contact with asset is required.
DCVG requires pipe to have a good coating
(used for locating flaws in coatings). Not such
requirement for pipe-to-soil testing.
Limited to continuously welded steel pipe.
Discrete.
Non-destructive test.
Inspection can be undertaken on-line.
Measures electrical potential between a pipe.
and surrounding soil to locate areas of corrosion
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-167
Criteria
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Utility technical
capacity
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication);
usability
Technology required (level of tool sophistication)
Economic factors
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
potential.
Stand alone.
Tools are fully commercialized.
Pipe potential surveys are widely used in the gas
industry and to a lesser extent in the water
industry.
Quantitative; techniques are considered to be
reliable.
Results can be validated by exposing of pipe.
Generic approach.
Operators require training; specialized training is
required where electrical currents/potential is
applied to pipes.
Pipe-to-soil technique requires specialized
though widely available equipment. Other
techniques require specialized equipment and
training of personnel.
BS 7361.
From service providers.
Depends on technique used.
Depends on technique used.
F57.7 Bibliography
1. Klechka, E. (2004) Corrosion Protection for Offshore Pipelines, Coatings for Corrosion
Protection, Colorado School of Mines; Accessed November 2006 at:
http://www.mines.edu/outreach/cont_ed/coatings1b.htm.
34H
2. TechCorr (2005) Pipeline Surveys, TechCorr; Accessed November 2006 at:
http://www.techcorr.com/surveys/index.htm.
35H
F-168
F58.0 PiReP/PiReM
F58.1 Overview
The Pipe Rehabilitation Planning System (PiREP) software is a decision support tool
for the management of rehabilitation planning in water supply systems. The software currently
consists of two modules, supporting both long-term strategic rehabilitation management and
mid-term rehabilitation planning.
Strategic planning is undertaken by estimating the annual rehabilitation rates, based on
analysis of failure data for groups of pipes and other operational and environmental parameters.
Mid-term planning is facilitated using a subjective (weighted) risk ranking approach that
provides a priority list of assets.
Pipe Rehabilitation Management (PiReM) is currently under development and is an
enhanced version of the PiReP software.
F58.2 Main Principles
The software was developed as part of a Ph.D. thesis undertaken at the Institute of
Urban Water Management and Water Landscape Engineering at Graz University of
Technology, and has had only limited use within water authorities.
The existing software includes two modules that analyze long-term and medium-term
rehabilitation strategies. These modules are to be revised with further development of the
economic and business management aspects. The addition of GIS functionality is planned.
The main part of the strategic long-term rehabilitation planning is the estimation of
annual rehabilitation rates for groups of pipes considering pipe attributes, existing
environmental influences, aging parameters and failure rates. This requires data from several
years of network operation. The boundaries for the annual planned rehabilitation are given by
calculating pessimistic and optimistic rehabilitation needs.
The medium-term rehabilitation planning module identifies pipes requiring
rehabilitation based on various technical, economical and business management criteria.
Criteria such as high failure rate, potential for corrosion, unusual diameter and unusual material
are considered. The module uses a subjective risk ranking approach to prioritize assets. The
resultant priority list can then be used for the annual planning of future period of five years.
F58.3 Application
♦ The software is designed for the long-term and medium-term rehabilitation planning of
water supply networks.
F58.4 Practical considerations
♦ The software tool is not fully commercialized; though the PiReP software has been
utilized by two Austrian water supply companies.
F58.5 Advantages
♦ The software allows detailed scenario analysis to be undertaken, which permits
authorities to see the results of modifying rehabilitation rates. This allows the financial
needs for long-term rehabilitation to be estimated.
♦ The mid-term rehabilitation module provides a priority list of assets that can be used to
guide annual planning for a future period of five years.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-169
F58.6 Limitations
♦ Non commercial software that has only had limited use in Europe.
♦ Requires several years of network failure data. Consequently, the software is not well
suited for small authorities or authorities with only limited data.
Table F-60. Summary PiReP/PiReM.
Technical
selection
Technical
suitability
Criteria
Assets covered
Granularity
Service area
Focus of analysis
Scalability of tool/approach
Commercialization
Previous/existing use of the tool
Ease of validation
Flexibility with regard to analysis (asset types)
and granularity (system, asset level)
Integration with other tools/GIS
Utility technical
capacity
Asset management sophistication
In-house skills required
Technology required
Documentation
Data Requirements
Linking to asset data
Availability of software and technical support
Usability
Assessment
Pipes, water pipeline infrastructure.
System and asset level.
Potable.
Decision support system for the rehabilitation
planning management of water supply systems.
Better suited to medium to large authorities where
good asset data is available.
Non commercial software, although commercial
release is intended.
Only been used by several European water
authorities during its development.
Validation through statistical analysis.
Potable only; asset to system level.
Requires standard GIS shape files and database files
for GIS implementation.
Aimed at higher level of asset management where
good asset data is available.
Asset manager/engineer.
PC based tool. Windows based operating system.
Needs GIS and spatial data.
Only limited documentation available. Has been
based on the German standards DVGW W 401.
Good quality asset data and asset failure history data
is required.
Uses an authorities GIS data base to transfer
information. ESRI shape files and dbf data files are
required. No direct link to GIS is provided.
Only limited support available at this time.
Software still under development.
F58.7 Bibliography
1. Kainz, H., Gangl, G., and Fischer, W. PiReM – Pipe Rehabilitation Management: Decision
Support System for the rehabilitation management of water supply systems, Graz
University of Technology. Website accessed November 2006 at:
http://www.sww.tugraz.at/sww/Projekte/pirem/Offizielle_Beschreibung_PiReM_englisch_
neu_2005.08.01.pdf.
36H
F-170
F59.0 Pit Depth Measurement
F59.1 Overview of Inspection Tool
Pit depth measurement is a manual technique used to infer corrosion rates of ferrous
materials.
Samples are sand blasted and inspected for pitting; the depth of pits are measured using
a pointed micrometer or needle-point depth gauge. The corrosion rate is then estimated, with
care taken not to underestimate results due to corrosion products remaining in the pits (Dorn et
al., 1996). Pit depth measurements can be undertaken as a non-destructive technique in the
field, or a pipe section can be removed for testing in a laboratory.
F59.2 Main Principles
The corrosion of ferrous pipe materials commonly occurs preferentially in localized
areas, resulting in the formation of pits. In order to measure the depth of corrosion pits, the
pipe surface must be sand/grit blasted to remove corrosion products. In situations where a large
number of pits have formed, visual inspection is used to identify the 10 deepest pits for
measuring. However, where only a small number of pits are present they should all be
measured (Dorn et al., 1996).
Pit depth can be measured using several manual instruments, the most appropriate for a
situation depending on the size of the pits found. Larger pits can be measured on site using
pointed micrometer or needle-point depth gauge. Smaller pits need to be examined under a
microscope to determine pit depth (Dorn et al., 1996).
Pit depth alone does not give an indication of asset condition; knowledge of original
wall thickness, general corrosion depth and age are also required to estimate the corrosion rate
and thus remaining life of the asset.
F59.3 Application
Pit depth measurement is relevant only to ferrous materials. Pit depth measurement can
be carried out on site and in the laboratory. More advanced pit depth measurements and those
for small pits require laboratory facilities.
♦ No standards or other documentation found on pit depth measurement, however ASME
B31G-1991 relates to determining the remaining strength of corroded pipelines.
F59.4 Practical Considerations
♦ Detailed knowledge of the original wall thickness and general corrosion depth is
sometimes difficult to obtain.
♦ The age of the pipe may not always be relevant in calculating corrosion rate, as in the
case of coated pipelines, since corrosion begins only after failure/removal of this
coating. For these reasons, corrosion rate estimates should be considered relatively
uncertain and this uncertainty should be considered in decision making
♦ Equipment for manual measurement of pit depth is widely available for a number of
commercial suppliers. Field pit depth measurement equipment is easily portable and
simple to use. Lab-based equipment requires skilled operators and can require difficult
sample preparation. Both field and lab techniques give accurate results, though labbased techniques are more accurate and able to measure smaller pits.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-171
♦ Attention is required to ensure that all corrosion products are removed prior to pit depth
measurement. Corrosion of cast iron results in graphitization which retains the shape of
the pipe disguising locations of corrosion.
♦ Manual measurement in other pipeline sectors has been generally superseded by other
techniques. However, the approach is still used in the water sector.
F59.5 Advantages
♦ Simple technique for field measurements giving accurate results.
F59.6 Limitations
♦ Without knowledge of original pipe wall thickness, pit depth measurement cannot be
used to estimate remaining life of the pipe.
♦ Pit depth will be underestimated if the depth of general corrosion surrounding the pit
measured is unknown and so underestimate the actual corrosion rate.
♦ Coatings will limit the accuracy of corrosion rate estimations, as pitting will only begin
after failure of this coating.
♦ Manual pit depth measurement is time consuming.
Table F-61. Summary Pit Depth Measurement.
Technical
selection
Criteria
Assets covered
Material type
Service Area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Technical
suitability
Interruption to supply/function
Assessment parameters
Integration with software tools
Utility technical
capacity
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
F-172
Assessment
Buried assets.
Ferrous materials only.
Potable and wastewater.
Pipes must be extracted for lab measurements,
field measurements can be preformed in situ.
Any coating and/or corrosion products on the
asset need to be removed prior to
measurements.
No restriction due to size of asset.
Results are discreet.
Field measurements are non-destructive. Lab
based measurements require sections to be cut
from pipe.
No interruption to supply when done in situ.
Pit depth only.
Results need to be used in conjunction with
other data to obtain useful information.
Equipment is widely available.
Wide use in the sector.
Measurement accuracy is high.
Direct measurement.
Generic approach.
Some training is required for field level
measurements. Lab level measurements require
specialists.
Low level technological sophistication required
from field level measurements. For lab level
measurements specialist equipment is required.
No standards or other documentation found on
pit depth measurement, however ASME B31G-
Criteria
Economic factors
Availability of technical support
Cost per inspection
Resource requirements
Assessment
1991 relates to Determining the Remaining
Strength of Corroded Pipelines.
N/A
Can be expensive due to man hours required
Resources are required to obtain sample, e.g.
exposing pipeline, sandblasting asset surface.
Removal of sample may be required.
F59.7 Bibliography
1. Dorn, R., Howsam, P., Hyde, R.A. and Jarvis, M.A Water mains: Guidance on assessment
and inspection techniques, CIRIA Report 162, Construction Industry Research and
Information Association, London, England, 1996.
2. Randall-Smith, M., Russell, A. and Oliphant, R. Guidance manual for the structural
condition assessment of trunk mains, WRc, UK, 1992.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-173
F60.0 Process Control Systems (Integrated)
F60.1 Overview of Tool
An overall Distributed Control System (DCS) network monitors/controls assets and
provides preventative maintenance data. PLCs and PCs servers are typically connected on an
Ethernet ring with all field equipment by a Field bus network.
F60.2 Main Principles
When a DCS is implemented, all the plant equipment, starters, variable frequency
drives, instruments, PLCs etc. are connected together by a field bus network (e.g., Profibus).
This allows on-line diagnostics, field device configuration and predictive maintenance from
one central point.
Intelligent field devices provide a lot of diagnostic information. Usually field devices
offer two kinds of diagnostic information: "on-line" (cyclically retrieved) diagnostic
information and "off-line" (acyclically) retrieved information. On-line information offers
current status of the device; e.g., major status and fault bits stored in the device itself. Off-line
information includes more detailed information about the device. This detailed information
also includes historical information stored in the device itself. Both can be accessed with the
equipment in operation.
F60.3 Application
Motor control centers starters (and connected equipment), variable frequency drives,
instruments and any other plant items that can be connected to the Field bus network.
♦ ISO 13374-1:2003; establishes general guidelines for software specifications related to
data processing, communication, and presentation of machine condition monitoring and
diagnostic information.
F60.4 Practical Considerations
♦ Wide use throughout manufacturing industry. Starting to be used in water industry; the
industry is moving towards fully networked control systems.
F60.5 Advantages
♦ Automatic records can be kept and trends observed.
♦ Fieldbus technologies offer some savings in wiring and cross connections costs and
reduced commissioning costs. Field devices can be tested, commissioned and
configured on-line through the network. Checking device parameters can also be done
through the DCS system on-line.
F60.6 Limitations
♦ Not readily applied to existing plant as requires substantial infrastructure changes and
associated costs. Ideal for green field sites or where major new plant is being installed.
F-174
Table F-62. Summary Process Control Systems (Integrated).
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Technical
suitability
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Economic factors
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
All ‘intelligent’ devices.
N/A
Potable and wastewater.
Field bus network is required with component
parts connected to it.
None.
None.
Continuous.
Non-destructive gathers data from on board
memory device.
On-line.
Current / historical status of component. Status
and condition (faults/healthy), number of trips.
Required to be part of a filed bus system.
Fully developed and off the shelf.
Becoming widespread.
Quantitative.
Depends on application, if for example current
drawn by starter, then this can be validated by
clamp on ammeters.
Aimed at a higher level of sophistication.
Once set up an operator can view condition
status data.
Field bus network.
Tool is documented. Standard ISO 13374.
Yes by supplier of fieldbus technology.
N/A
Overall control system can automatically
produce reports.
F60.7 Bibliography
1. ISO 13374-1:2003 : Condition monitoring and diagnostics of machines - Data processing,
communication and presentation - Part 1: General guidelines.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-175
F61.0 Pull-off Adhesion Testing
F61.1 Overview of Tool
Pull-off adhesion testing measures the adhesive strength of applied coatings to metal,
concrete, masonry, plastic and wood. The strength of epoxies, mortars, plasters, bituminous
coats, paint finishes and metal coatings can be measured. The surface strength of concrete and
other materials can also be tested directly.
The mechanical tensile strength is tested by applying a perpendicular force, either to
destruction or until the applied force reaches a prescribed value. For this reason the test may be
fully non-destructive in certain situations. However, the review below assumes that testing
continues until coating failure.
F61.2 Main Principles
Pull-off adhesion testing involves measuring the mechanical tensile strength of a
coating by applying an increasing stress to the test surface until the weakest path through the
material fractures. Test equipment generally consists of a hydraulic hand pump, an actuator,
test disks or dollies, an abrasive pad, a cutting tool, adhesive, adhesive mixing sticks and
palettes, a drilling template and drill bits for thick coatings.
During testing, the test dolly is attached to the coating surface with an adhesive. Force
is then applied perpendicular to the surface to maximize tensile stress as compared to the shear
stress (Figure F-11). Failure will occur along the weakest path within the system comprised of
the test fixture, adhesive, coating system and substrate. The weakest path could be along an
interface between the test fixture and the coating, the coating and the substrate, a cohesive
fracture within the coating, a cohesive fracture of the substrate (e.g., concrete) or a combination
of these. Test results are generally given as a pressure, psi or MPa, and can be related to the
strength of adhesion to the substrate.
Figure F-11. Basic Pull-Off Test Setup
(Reprinted with permission from: Kolsaker, T., DFD Instruments, 2006).
F61.3 Application
Pull-off adhesion testing can be used to test the surface strength of any asset. This
primarily applies to assets to which coatings have been applied, but the surface strength of
materials such a concrete can also be tested.
F-176
♦ ASTM C4541, ASTM D4541, BS 1881 Part 207 and ISO 4624 (EN 24624) all define
the method and procedures for carrying out pull-off adhesion testing of paints,
varnishes and other coatings.
F61.4 Practical Considerations
♦ Pull-off test equipment is widely available and falls into two general categories,
manually and automatically applied force. The choice of equipment usually depends on
several factors such as the type of coating, the amount of testing required, test
procedure specifications, and personal preferences.
♦ A range of different sized pull-off adhesion testers are available for measuring coating
adhesion on a variety of substrates. For instance a 20mm dolly is ideal for metal, plastic
and wood substrates, while a 50mm dolly is recommended for masonry substrates such
as concrete. Custom dolly sizes are used to meet specific measuring needs.
♦ The testing standards emphasize that the speed of tensile force increase must be
constant and within specified minimum and maximum values and also consistent from
test to test. For these cases, automatic testers are required rather than manual testers.
♦ Pull-off test equipment is portable so that testing can be conducted in a wide variety of
locations.
♦ The measurement range of equipment varies with the specific surface it was designed
for. Many pull-off adhesion-testing pressure systems are calibrated and certified to at
least ± 2% accuracy and 0.01 N/mm2 resolution. The certified stress range will
generally not cover the full stress range possible by the tester.
♦ Test equipment with a self-aligning dolly enables measurement on smooth or uneven
surfaces without adversely affecting the test results.
♦ In order to enable the testing of thick coatings, a drilling template is used for isolating
the test area from the surrounding coating.
♦ Powerful pull-off adhesion testers have been designed particularly for tensile adhesion
testing of the strongest thermal sprayed coatings (e.g., arc, plasma and HVOF sprayed).
These testers have a certified testing range of 19700 psi (136 MPa). This is higher than
the tensile strength of the strongest heat-curing adhesive (used for gluing the test
elements).
F61.5 Advantages
♦ Pull-off testing can be conducted on a wide variety of substrates and coatings.
♦ Testing is not limited to flat surfaces; curved surfaces such as pipes can be readily
tested.
♦ For concrete coatings, there is no need to embed the sample in the concrete substrate
first.
♦ Self-aligning dolly systems enable force to be consistently distributed over the test area,
preventing earlier failure.
F61.6 Limitations
♦ Measurements are limited by the strength of adhesion bonds between the loading
fixture and the specimen surface or the cohesive strengths of the adhesive, coating
layers, and substrate.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-177
♦ This test can be destructive and spot repairs may be necessary.
♦ If the dollies are not cleaned sufficiently, ‘glue failure’ can occur during testing,
resulting in an inaccurate. Self-leveling pull testing devices can produce far too low-test
results if the pull stress is not 100% evenly distributed throughout the pulled coating. If
not, the area where the stress is concentrated will fracture long before maximum stress
has been reached elsewhere resulting in low readings.
Table F-63. Summary Pull-off Adhesion Testing.
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Utility technical
capacity
F-178
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication);
usability
Assessment
Metal, concrete, masonry, plastic and wood assets
which are covered in applied coatings, mortars,
plasters, bituminous coats and paint finishes.
Metal, concrete, masonry, plastic and wood.
Potable and wastewater.
Direct contact with asset coating. If asset is buried
then it must be exposed. Surface coatings should be
cleaned.
Coating must not be too deteriorated.
No limitations relating to size. Small diameter curved
surfaces are more difficult to measure. Specialized
models ‘micro testers’ have been designed for the
testing of small test elements and of fragile material.
Discrete reading.
Overall non-destructive, a small patch of coating is
removed from asset.
The asset can remain in use and does not need to be
taken off-line if the coating being tested is external.
The testing of internal coatings will require for the
asset to be taken off-line in order to allow testing to
occur.
The adhesive strength of applied coatings and the
surface strength of concrete.
Stand alone tool and automatic digital adhesion
testers are available. For digital adhesion testers the
stress increase rate is controlled automatically by a
computer and can be set to comply with the relevant
adhesion testing standard.
Tool is fully developed, exists in manual and digital
forms and is available from a range of commercial
vendors.
Widespread use throughout the water and other
sectors.
Some testers are calibrated and certified to ± 1%.
Generally testers have ± 2% accuracy and 0.01
N/mm2 resolution.
Direct measurement.
Generic approach.
Easy to use by following simple procedure. Basic
training in achieving correct alignment of the testing
machine is recommended. The aim of this is to avoid
substantial unwanted stress concentrations in the
tested material, resulting in premature fracture of the
sample.
Criteria
Technology required (level of tool sophistication)
Documentation
Economic factors
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Low level of technological sophistication is needed for
hand held, manual tools. For digital tools the stress
increase rate can be controlled automatically by
computer.
ASTM D4541, ACI 503-30 USA, ISO 4624 (EN
24624) and BS 1881 Part 207.
Technical support widely available from distributors.
Low cost per inspection.
One operator required. Pneumatic or mains powered.
Resources required can also depend on asset being
inspected. Buried assets need to be exposed.
F61.7 Bibliography
1. ASTM D4541 Standard Test Method for Pull-Off Strength of Coatings Using Portable
Adhesion Testers.
2. ASTM C4541 Pull-Off Strength of Coatings Using Portable Adhesion Testers.
3. ISO 4624 (EN 24624) Paints and varnishes -- Pull-off test for adhesion.
4. BS 1881 Part 207 Testing Concrete Part 207: Recommendations for the Assessment of
Concrete Strength by Near-to- Surface Tests.
5. DFD Instruments, http://www.dfdinstruments.co.uk/topics/Study5-ASTM-D4541.htm,
accessed 2006.
37H
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-179
F62.0 Radiographic Testing
F62.1 Overview
Radiography is the use of radiation to obtain a picture (radiograph) of an object. The
intensity of radiation transmitted through the object is recorded, using a photosensitive film or
digital recorder. The process is very similar to x-ray radiography in a hospital; possible
imperfections are indicated as density changes on the film in the same manner as a medical X
ray shows broken bones.
Radiography is a non-destructive technique that has been used to examine ferrous,
cementituous, and plastic pipes (though not GRP). The radiograph shows variations in material
and structure, including changes in density (such as associated with corrosion products),
inclusion of material ingredients (for plastic pipes), and changes in thickness. It can also be
used for inspection of valves.
F62.2 Main Principles
Traditionally a source of radiation, either gamma or x-rays, was passed through the
material and directed onto a photographic film. There is however a trend to replace
radiography film by non-film type radiation detectors; digital radiography uses radiation
detectors for real time radiographic imaging.
Gamma rays emitted from isotopes (usually Iridium-192, Cobolt-60) are used for
ferrous and cementituous materials. X-rays created by cathode-ray tubes are used for plastic
materials.
According to the WRc Trunk Main Structural Condition Assessment Manual, there are
three variations on the basic technique used in the water sector:
♦ Single Wall Single Image: Here the radiation source is put inside the object under
examination and the photographic film placed on the outside; the radiation passes
through a single wall thickness before reaching the film.
♦ Double Wall Single Image: Here the radiation source is placed outside the object under
examination and the photographic plate positioned externally on the opposing side. The
radiation passes through two walls before reaching the film. However, because of the
intensity of the beam, the features of the wall nearest the source become obliterated and
only those of the wall nearest the film are recorded.
♦ Double Loading: This approach is used to radiograph the features of two adjacent
objects between source and film. Two films with different speeds are placed one on top
of the other and exposed for the same time. The result is that the slow film records the
features of the object closest to the source, with the second object under exposed, and
the fast film records the second object from the source with the one nearest over
exposed.
Details of the material structure can be seen on the radiograph; darker areas correspond
to thinner or less dense material. The features on the film can thus be interpreted in a semiquantitative manner:
♦ For ferrous materials, the technique is suitable for detecting pits, due to the difference
in density between corrosion products and the parent metal. Since corrosion products
are less dense, they appear darker on the radiograph. Calibration is required to estimate
the thickness of the corrosion.
F-180
♦ For cementituous materials, radiography can be used to check for voids. The condition
of reinforcement in pre-stressed concrete pipe has also been examined using these
techniques.
♦ For plastic materials, the radiograph can detect inclusions or manufacturing voids; Xray analysis has been used to determine the distribution of lead stabilizers in PVC-U
pipes.
Gamma radiography has also been used to check welds in pipelines that carry natural
gas or oil. Special film is taped over the weld around the outside of the pipe. A machine carries
a shielded radioactive source down the inside of the pipe to the position of the weld. The
radioactive source is then remotely exposed and a radiographic image of the weld produced on
the film. This film is then developed and examined for signs of flaws in the weld.
F62.3 Application
In the water sector, the techniques have been used to examine the condition of pipes
and valves in situ. In process industries, radiography has been proven to be very useful in
detecting different kinds of internal deposits in pipes.
F62.4 Practical Considerations
♦ Radiography is one of the most commonly used NDE methods in petrochemical
processing plants. It is understood this technique is not used within the United States
water sector, though it has been used in the United Kingdom water sector.
♦ Radiography has to be carried out by trained staff aware of all the health and safety
issues involved in the use of ionizing radiation. In addition, a certain amount of
experience is required to interpret the radiographs produced.
♦ Exposure times are dependent on section thickness; thicker sections require relatively
longer exposure periods. Similarly, water filled pipes also require relatively longer
exposure times compared to air filled pipes. For pipe diameters greater than 380 mm
(that is, 15”), the main has to be drained down because water is an effective absorbent
of γ-rays. Even for smaller diameters, there is a significant reduction in clarity of the
radiographs if water is present
♦ X-ray sets can only be used when electric power is available and when the object to be
X-rayed can be taken to the X-ray source and radiographed. Radioisotopes have the
advantage that they can be taken to site and no electric power is needed.
F62.5 Advantages
♦ The technique can be applied to most materials in situ. It is a non-destructive inspection
technique, and details of the material structure can be obtained.
F62.6 Limitations
♦ The technique is expensive and there are OH&S issues associated with its use. It
examines only a small area of pipe.
♦ Large diameter mains (> 15”) must be drained down.
♦ Exposing drinking water to ionizing radiation is not approved or sanctioned by any
utility, water industry association, or governmental agency in the United States.
♦ Experience is required to interpret the radiographs produced.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-181
Table F-64. Radiographic Testing.
Technical
selection
Technical
suitability
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Asset management sophistication required
Skills required (level of tool sophistication);
usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Economic factors
Cost per inspection
Resource requirements
Assessment
Pipes, valves.
Ferrous, cementituous, plastics (not GRP)
Potable.
Both sides of the asset must be accessible.
None.
None.
Discrete; small sections only.
Non-destructive.
Generally would require the asset to be off-line,
as water absorbs the radiation.
Changes in material structure, including
inclusions, corrosion, voids, and thickness
changes.
Stand alone tool; images need manual
interpretation.
Tool and service commercially available.
Limited or no use in the United States water
sector; use reported in the United Kingdom water
sector.
Semi-quantitative.
Images can be calibrated; interpretation is a
skilled task.
Generic approach.
High level of skill due to health and safety issues;
would require specialized contractor to
undertake.
Independent of technology.
Standards for use are available; documentation
also available.
N/A; would require specialized contractor to
undertake.
High.
Requires specialist contractor.
F62.7 Bibliography
1. Dorn, R., Howsam, P., Hyde, R.A. and Jarvis, M.A. Water mains: Guidance on assessment
and inspection techniques, CIRIA Report 162, Construction Industry Research and
Information Association, London, England, 1996.
2. Randall-Smith, M., Russell, A. and Oliphant, R. Guidance manual for the structural
condition assessment of trunk mains, WRc, UK, 1992.
3. IAEA Development of protocols for corrosion and deposits evaluation in pipes by
radiography, Industrial Applications and Chemistry Section, International Atomic Energy
Agency,Vienna, Austria, 2005.
F-182
F63.0 Remote Field Eddy Current (RFEC and RFEC/TC Tools)
F63.1 Overview
The Remote Field Eddy Current (RFEC) inspection technique is a non-destructive
method that uses low frequency AC and through-wall transmission to inspect ferrous pipes and
tubes from inside the pipe. The through-wall nature of the technique allows external and
internal defects to be detected with approximately equal sensitivity.
RFEC probes have been successfully adapted for inspection of cast iron and steel water
mains, as well as pre-stressed concrete cylinder pipes (also know as PCCPs).
F63.2 Main Principles
Eddy current testing is often used to find leaks in large u-tube heat exchanger tubes. In
this application, each tube is tested individually. Testing thick walled ferrous pipes from within
using conventional eddy current probes is, however, not practical. Very low frequencies are
necessary to achieve the through-wall penetration required to detect flaws on the outer surface.
This in turn produces low sensitivity. These problems are overcome by the RFEC method. The
RFEC inspection technique measures a different phenomenon; the generated AC magnetic
field.
The RFEC tool uses a relatively large internal solenoid exciter coil, which is driven
with low frequency AC. A detector, or circumferential array of detector coils, is placed near the
inside of the pipe wall, but axially displaced from the exciter. The separation between the two
coils is between two to five times the internal diameter of the pipe.
Two distinct coupling paths exist between the exciter and the detector coils. The direct
path, inside the pipe, is attenuated rapidly by circumferential eddy currents induced in the wall.
The indirect coupling path originates in the exciter fields, which diffuse radially outward
through the wall. At the outer wall, the field spreads rapidly along the pipe with little further
attenuation. These fields re-diffuse back through the pipe wall and are the dominant field inside
the pipe at remote field spacing.
A receiver coil that is placed in the remote field zone of the exciter picks up the field.
Furthermore, because the pipe wall attenuates the through-wall field, the strength of the field is
very sensitive to the wall thickness. Anomalies anywhere in the indirect path cause changes in
the magnitude and phase of the received signal, and can therefore be used to detect defects
such as cracks, pits or wall thinning produced by corrosion.
RFEC tools are used within the pipe. As such, access requires cut-ins at regular
intervals (100 m to 500 m, depending on cable length, pipe alignment, etc). Some tools are
adapted for launching through hydrants. RFEC tools are deployed and propelled through the
pipe by water pressure or by winching. Computerized software is available for signal
interpretation.
When applied to ferrous pipes, the RFEC method is claimed to detect changes in metal
mass, graphitization and wall thinning (the direct field eddy current methods are reported to be
more sensitive for detection of cracks and voids than RFEC).
A modified version of the tool is used for pre-stressed concrete cylinder pipes (also
know as PCCPs) inspection; the RFEC/Transformer Coupling (TC) tool. RFEC/TC testing
uses a combination of the remote field effect and the transformer coupling effect. The remote
field effect acts as a signal attenuator reducing and slowing the signal sent from a detector coil
as is passes out and back in through a metallic pipe wall. The transformer coupling effect acts
to amplify and accelerate the transmitted signal in the presence of continuous prestressing
wires. The electromagnetic field energy produced in the RFEC/TC technique interacts with
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-183
broken pre-stressing wires. Wire breaks interrupt the flow of energy, changing the measured
field and allowing for detection of broken wires.
F63.3 Application
The RFEC method was developed for the inspection of carbon steel components such
as process heat exchangers, tanks and boiler tubes.
It allows for the inspection of pipes and tubes from the inside to check for problems
around the entire circumference and over the entire length.
RFEC probes have been successfully adapted for inspection of cast iron and steel water
mains. A modified version of the tool is used for pre-stressed concrete cylinder pipes (also
know as PCCPs) inspection.
F63.4 Practical Considerations
♦ Tools are commercially available though use requires specialized contractors.
Commercial use of the tools is reported in literature and trade journals.
♦ The sensitivity and resolution of the technique depends on the configuration of the
exciter and detector coils. Detector coils with small footprints improve the resolution,
but reduce the scanning rate.
♦ Inspection speeds with RFEC is significantly lower than conventional eddy current
(Birring, 1999).
F63.5 Advantages
♦ RFEC tools are available to suit a range of pipe sizes 150 mm upwards. The smaller
sizes may be launched through modified fire hydrants. The probes can be used in wet or
dry conditions.
♦ Probes with circumferential array of detectors are capable of examining 100% of the
pipe. Some tools operate through internal cement linings (up to 25 mm), though with a
reduction in sensitivity and resolution.
♦ The RFEC/TC tool is able detect and resolve multiple regions of broken wires at
different axial locations along the pipe.
F63.6 Limitations
♦ Pipe requires internal cleaning prior to inspection. If water is used to propel the tool, it
is necessary to discharge the water to the environment.
♦ There is variability in the success of flaw detection and location by probes supplied by
different companies.
♦ Although capable of giving a good estimate of where the wire break occurs along the
length of the pipe, the technique can give no information at this time as to the
circumferential position of the broken wires.
F-184
Table F-65. Summary Remote Field Eddy Current.
Technical
selection
Criteria
Assets covered
Material type
Service Area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Technical
suitability
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Asset management sophistication
Skills required (level of tool sophistication);
usability
Technology required (level of tool sophistication)
Documentation
Economic factors
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Pipes, water and Wastewater pipeline
infrastructure, tubes.
Iron and steel pipes, PCCPs.
Potable and wastewater.
Tool only for use within pipe (internal use). Tool
access requires cut-ins at regular intervals (100 m
to 500 m, depending on cable length, pipe
alignment). Some adapted for launching through
hydrants.
No limitations relating to asset condition provided
direct contact with the pipe wall is available.
Asset must be of sufficient size to accommodate
wheeled carriage. Devices to suit 150 mm internal
diameter have been produced. These can
negotiate bends up to 15º radius. Tools are tailored
to specific internal pipe diameters, ±5%.
Continuous readings stored in computer memory in
real time and space.
Non-destructive.
Tool application requires pipe to be off-line.
Internal and external defects such as cracks, pits or
wall thinning.
Computerized software is available for signal
interpretation.
Commercialized, availability through specialized
companies.
Commercial use of the tools reported in literature
and trade journals. AwwaRF reports available on
tool sensitivity.
Quantitative assessment; but varied sensitivity to
defects.
Calibration of tool against reference samples
required. Validation possible only by comparison
with manual/direct measurements.
Generic approach.
Professional skills required to interpret output data.
Tool operation typically by a third party.
Specialized equipment and dedicated computer
software.
Tool principles and description of reports generated
by tool will be available.
Tool operation typically by a third party.
Greater than US$5,000 per site, plus civil costs.
Typically two-person crew.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-185
F63.7 Bibliography
1. Birring, A.S. Selection of NDT techniques for inspection of heat exchanger tubing. Proced.
Petroleum Industry Inspection Conference, Texas, USA. June 1999.
2. Burn, L.S., Eiswirth, M., DeSilva D. and Davis P., Condition Monitoring and its Role in
Asset Planning, Pipes Wagga Wagga 2001, Charles Sturt University, Wagga Wagga,
N.S.W., 2001.
3. Dingus, M., Haven, J. and Austin, R. Nondestructive None Invasive Assessment of
Underground Pipes, AwwaRF, USA, 2002.
4. Makar, J. M. ; Chagnon, N. Inspecting systems for leaks, pits, and corrosion, National
Research Council of Canada, Institute for Research in Construction, NRCC-42802
(downloaded from www.nrc.ca/irc/ircpubs), 1999.
38H
5. Rajani, B.; Kleiner, Y. Non-destructive inspection techniques to determine structural
distress indicators in water mains, National Research Council of Canada, Institute for
Research in Construction, NRCC-47068 (downloaded from www.nrc.ca/irc/ircpubs), 2004.
39H
6. Lillie, K., Reed, C. and Rodgers, M. A. R., 2004, Workshop on Condition Assessment
Inspection Devices for Water Transmission Mains, AwwaRF, USA, 2004.
F-186
F64.0 Schmidt Hammer
F64.1 Overview
The Schmidt hammer is a simple hand held device that allows non-destructive
assessment of materials such as brick and concrete. The tool gives an inferred measure of
compressive strength by an assessment of surface hardness.
The hammer consists of a spring loaded mass that is fired at the sample and rebounds,
thereby measuring the ‘rebound number’ for the material. A calibration chart is then used to
give an indication of compressive strength. Digital versions of the tool give direct readouts of
compressive strength.
F64.2 Main Principles
The Schmidt hammer or rebound hammer indirectly measures compressive strength by
measuring surface hardness of materials such as concrete and brick. The original design of the
Schmidt hammer was cylindrical, approximately 55 mm in diameter and 275 mm in length
(Dorn et al., 1996). Several new designs are now available for use on samples of different
geometries, strengths and impact resistances.
In use, the Schmidt hammer is ideally aligned perpendicular to the surface being tested.
A spring loaded mass is then fired at the sample. The distance the mass rebounds from the
surface of the sample is related empirically to the compressive strength of the sample (Proceq,
2005).
F64.3 Application
The Schmidt hammer is used to test the strength and quality of concrete and brick
assets, both civil and pipeline, and is used in a number of international standards:
•
ASTM C 805-97, Svensk Standard SS 13 72 37, Svensk Standard SS 13 72 50, Svensk
Standard SS 13 72 52, BS 1881: Part 202.
F64.4 Practical Considerations
♦ The Schmidt hammer is readily portable and simple and is widely used for testing
concrete assets. The Schmidt hammer is available from many commercial suppliers.
Results obtained from the manual version of the tool are converted to compressive
strength using calibration curves; some digital versions can give compressive strength
readouts directly.
♦ The accuracy of the technique is relatively low for prediction of compressive strength;
between ± 15-20% in well controlled conditions (Feldman, 1977). Due to the
heterogeneity of cementituous materials, multiple readings (~10) should be taken,
although not in exactly the same location.
♦ The result of this technique should only be used as an indication of material strength.
However, it is useful for comparing the relative strengths of different materials or
different areas of an asset (Dorn et al., 1996).
♦ In order to conduct a test using the Schmidt hammer, access to the surface of the asset
is required. This means that buried assets must be exposed and surface coatings must be
removed. The asset surface may also require abrading to provide a smooth surface. The
tool is hand held and so sufficient room is required for personnel.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-187
♦ Depending on the angle of the Schmidt hammer to the vertical during testing,
corrections may need to be made for this angle.
F64.5 Advantages
•
The Schmidt hammer is a quick means of assessing compressive strength of
cementituous or rock like materials, and can provide valuable comparative data
between different parts of a sample, or between different samples (Dorn et al., 1996).
F64.6 Limitations
♦ The accuracy of the technique is relatively low for prediction of compressive strength,
between ± 15-20% in well controlled conditions (Feldman, 1977).
♦ The results are also very dependant on surface conditions (Dorn et al., 1996) and results
can be affected by the smoothness of surface, geometry of sample, moisture content,
type of cement and aggregate and the extent of surface carbonation (Feldman, 1977).
♦ The results obtained are for localized areas of the asset due to the heterogeneous nature
of cementituous materials (Randall-Smith et al, 1992).
Table F-66. Summary Schmidt Hammer.
Technical
Selection
Criteria
Assets covered
Material type
Service Area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
F-188
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Assessment
Manholes, pipes, CSOs, civil.
Concrete, brick.
Potable and wastewater.
Direct contact with asset required. If the asset is
buried, then it must be exposed. Surface
coatings must also be removed. The asset
surface may also require abrading to provide a
smooth surface.
No limitations relating to asset condition.
No limitations relating to size/geometry for
external use on pipes. For internal usage the
asset must be of sufficient size for man entry.
Discrete reading.
Non-destructive.
For man entry, standard safety procedures
should be followed, otherwise the asset can
remain in use.
Equipment gives a reading relating to
compressive strength of asset.
No integration with software tools.
Equipment is widely available from commercial
vendors.
Widely used to assess the quality of concrete
assets.
Quantitative; readings are ± 15-20% accurate.
Results are only indicative of compressive
strength on which can be used.
Generic approach.
Easy to use by following simple procedure.
Tool comes in both manual and digital versions,
manual versions provide rebound numbers only
and compressive strength needs to be obtained
Criteria
Documentation
Availability of technical support
Economic factors
Cost per inspection
Resource requirements
Assessment
by reading calibration curves. Digital versions
calculate compressive strength.
ASTM C 805-97, Svensk Standard SS 13 72 37,
Svensk Standard SS 13 72 50, Svensk
Standard SS 13 72 52, BS 1881: Part 202.
Technical support available from retailers and
from Internet.
Low cost per inspection.
Resources required depend on assets being
inspected.
F64.7 Bibliography
1. ASTM C805-02 Standard Test Method for Rebound Number of Hardened Concrete.
2. BS EN 12504-2:2001 Testing concrete in structures. Non-destructive testing.
Determination of rebound number.
3. Dorn, R., Howsam, P., Hyde, R.A. and Jarvis, M.A. Water mains: Guidance on assessment
and inspection techniques, CIRIA Report 162, Construction Industry Research and
Information Association, London, England, 1996.
4. Feldman, R.F., CBD-187 Non-destructive testing of concrete, Canadian Building Digest,
http://irc.nrc-cnrc.gc.ca/pubs/cbd/cbd187_e.html , accessed 2005.
40H
5. Mastrad: Quality and test systems, http://www.mastrad.com/schmidt.htm , accessed 2005.
41H
6. Proceq, http://www.proceq-usa.com/products/originalschmidt.php , accessed 2005.
42H
7. Randall-Smith, M., Russell, A. and Oliphant, R. Guidance manual for the structural
condition assessment of trunk mains, WRc, UK, 1992.
8. SIS; Svensk Standard SS 13 72 37. "Betongprovning-Hårdnad betong-Studsvärde,"
(Concrete testing - Hardened concrete - Rebound number, in Swedish).
9. SIS; Svensk Standard SS 13 72 50. "Betongprovning-Hårdnad betong- Tryckhållfasthet
skattad med ledning av studsvärden," (Concrete testing - Hardened concrete - Compressive
strength from rebound number, in Swedish).
10. SIS; Svensk Standard SS 13 72 52. "Betongprovning-Hårdnad betong- Tryckhållfasthet,
skattad med ledning av studsvärden och ljudhastighetsvärden," (Concrete testing Hardened concrete - Compressive strength, rated from rebound and sound velocity values,
in Swedish) .
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-189
F65.0 SCRAPS (Sewer Cataloging, Retrieval and Prioritization System)
F65.1 Overview
The Sewer Cataloguing, Retrieval and Prioritization System (SCRAPS) is an expert
system that targets the inspection of critical areas of the sewer network.
The knowledge base of this expert system was assembled with input from a national
group of experts, drawn from both the public and private sectors. Input from the experts was
used to develop the system’s logic, which assesses the overall need to inspect a sewer based on
the pipe’s consequence and likelihood of failure. The inference engine is based on Bayesian
belief network theory, which allows the uncertainty in the experts’ beliefs to be propagated
through the system. The tool was developed with a rapid prototype application process. The
validation of the tool showed it is effective at mimicking the knowledge of experts.
F65.2 Main Principles
SCRAPS assumes sewer collection systems fail when they are unable to convey
wastewater from its origin to its prescribed destination without endangering or inconveniencing
the public. System failures include releases, overflows, and surface collapse. SCRAPS predicts
the criticality of sewer pipelines in terms of how likely the sewer is to fail (likelihood) and the
extent of societal impacts if failure should occur (consequence).
SCRAPS is intended to target CCTV inspections on critical areas of the sewer system,
thereby reducing the potential cost for emergency repair and delaying unnecessary inspections.
The logic in SCRAPS is based on work from the Water Research Centre (WRc, UK), and on a
group of eight mechanisms that define the consequence and likelihood of asset failure. These
mechanisms constitute the tool’s decision making logic. Two of the eight mechanisms, ‘SocioEconomic Impacts’ and ‘Reconstruction Impacts,’ define the consequence of failure. The
remaining six mechanisms define the likelihood of failure, and include ‘Operational Defects’,
‘Structural Defects’, ‘Interior Corrosion’, ‘Exterior Corrosion’, ‘Infiltration’ and ‘Erosion’.
SCRAPS has two primary components: 1) an inference engine and 2) a knowledge
base. The inference engine defines the mathematical algorithm by which a decision is reached.
The knowledge base is the body of information that represents the expert knowledge. The other
components of SCRAPS, a graphical user interface and a database, are developed with
Microsoft Visual Basic and Microsoft Access respectively.
The knowledge base of the expert system was developed through a process of
‘‘knowledge acquisition.’’ Knowledge was acquired and incorporated into SCRAPS by
interviewing sewer infrastructure experts, operators, and managers. The knowledge acquisition
process was facilitated by a rapid prototyping process that allowed on-going testing of the
accuracy of the knowledge base.
F65.3 Application
The software is designed to facilitate the management of sewerage networks by
prioritizing CCTV inspections.
F65.4 Practical Considerations
♦ The SCRAPS system is available from WERF.
♦ SCRAPS is principally aimed at small utilities that may not have sufficient system data
to search effectively for potential failures.
F-190
♦ The tool is also usable by utilities that have collected considerable data and performed
condition assessments. In this case, the tool allows prioritization of repair of the sewers
with the highest risk of failure according to the consequences of failure.
♦ The tool may provide insight in to the factors that have had greatest influence on the
current condition.
F65.5 Advantages
♦ SCRAPS can assist small to medium sized utilities develop a strategy to gather
information about their systems by prioritizing their inspection process.
♦ The tool targets critical areas of the sewer system first, thereby reducing the potential
cost for emergency repair and delaying unnecessary inspections.
♦ The tool’s logic is based on the industry paradigm of consequence of failure and
likelihood of failure and extensive input from numerous regional-based experts.
♦ The tool has the advantage of containing the heuristics and understanding of failure and
impact relationships of many experts.
F65.6 Limitations
♦ Large authorities may require more sophisticated approaches.
Table F-67. Summary SCRAPS (Sewer Cataloging, Retrieval and Prioritization System).
Technical
selection
Technical
suitability
Criteria
Assets covered
Granularity
Service Area
Focus of analysis
Scalability of tool/approach
Commercialization
Previous/existing use of the tool
Ease of validation
Utility technical
capacity
Flexibility with regard to analysis (asset types) and
granularity (system, asset level)
Integration with other tools/GIS
Asset management sophistication
In-house skills required
Technology required
Documentation
Data Requirements
Linking to asset data
Availability of software and technical support
Usability
Assessment
Sewer networks.
System level.
Wastewater.
Expert system that prioritizes sewer inspections.
Aimed at small utilities that may not have
sufficient system data to search effectively for
potential failures.
Commercial system available from WERF.
Has been used in the United States.
Validation is possible through comparison with
independent assessments.
Wastewater; system level only.
None.
Aimed at level of asset management where
standard asset data is available.
Asset manager.
PC based tool. Windows based operating
system.
Detailed report available from WERF.
Targets critical assets and requires information
on them.
Through database.
Limited support available.
Windows based software.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-191
F65.7 Bibliography
1. Hahn, M.A., Palmer R.N., Merrill, M.,S. and Lukas, A.B. Sewer inspection prioritization
with a regional expert system. Proc. of the ASCE’s 2000 Joint Conference on Water
Resources Engineering and Water Resources Planning and Management, Minneapolis,
MN, August, 2000.
F-192
F66.0 Slow Crack Growth Resistance of PE Pipes
F66.1 Overview
The Notched Tensile Test is a destructive test that can be used to quantify the resistance
to slow crack growth of a PE pipe material.
The test involves deliberately introducing a razor notch onto a test coupon, which is
then subjected to a pre-defined tensile stress. The time to failure is recorded, which correlates
with the resistance to slow crack growth exhibited by a particular pipe material
Traditionally used to assess performance of new PE materials, this test has also been
used to measure slow crack growth resistance of pipes currently in-service.
F66.2 Main Principles
The test is conducted on a small coupon (50 mm in length and 25 mm in width)
extracted from the pipe wall. The coupon can be extracted so that its longitudinal axis is
aligned with either the pipe longitudinal or circumferential directions. The thickness of the
coupon corresponds to the pipe wall thickness.
A razor notch is deliberately introduced into the coupon specimen using a razor blade.
This razor notch is aligned perpendicular to the longitudinal axis of the specimen. The
specimen is then loaded in tension along its longitudinal axis to a pre-defined nominal tensile
stress and the time to failure is recorded.
The time to failure correlates with the resistance to slow crack growth exhibited by a
particular pipe material. Longer test times correspond to relatively high slow crack growth
resistances.
F66.3 Application
This test is applicable to PE pipe materials only.
•
This test method applies to PE pipes and is described by the American Standard ASTM
F 1473. The American standard ASTM D 3350 specifies a test temperature of 80°C and
a stress of 2.4 MPa. ISO 16241: 2005 also references this test method.
F66.4 Practical Considerations
♦ This test method is primarily used by PE material and pipe producers to rank the slow
crack growth performance of new PE materials. However, some limited studies have
also conducted tests on coupon samples from pipes in service and shown reasonable
correlation with field performance.
♦ Specimen preparation (especially notching) requires skill, but clear guidelines are
provided in the American standard F 1473. Due to the requirement for elevated
temperature, the test method should be conducted in the laboratory.
♦ Different PE material type classifications are listed in the American standard ASTM D
3350. For a particular PE material type, ASTM D 3350 specifies minimum failure times
in the Notched tensile test. Therefore, results from notched tensile tests can be used to
determine the material classification of the pipe under inspection. Furthermore, results
from notched tensile tests on a wide range of PE materials have also been published in
the literature. This provides a basis for comparison in terms of slow crack growth
resistance.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-193
♦ Results from the notched tensile test correlate well with the potential for slow crack
growth failure under normal operating loads. In general, longer failure times correspond
to lower average slow crack growth failure rates in the field. However, the test does not
relate to PE pipe failures that occur under the influence of external factors such as poor
pipe installation practice and third party damage during adjacent excavation.
F66.5 Advantages
♦ The test method should be relatively low cost.
♦ A single coupon test will indicate the resistance to slow crack growth of the pipe under
inspection.
♦ With appropriate expertise, comparisons can then be made with previous literature
studies in which notched tensile test results were compared with slow crack growth
field failures in PE pipes.
F66.6 Limitations
♦ The test method is destructive and coupon samples require careful razor notching.
♦ Test results require comparison with previous studies in the literature to be meaningful.
♦ Tests conducted on new PE materials can result in impractically long test times.
Table F-68. Summary Slow Crack Growth Resistance of PE Pipes.
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Technical
suitability
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Utility technical
capacity
F-194
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication);
usability
Technology required (level of tool
sophistication)
Assessment
Pipes.
Polyethylene.
Potable or wastewater.
Pipe must be exposed and coupon must be extracted
from the pipe wall.
None.
None.
Discrete.
Destructive, but the location of coupon removal on the
pipe can be repaired using an electrofusion coupling.
Tests must be conducted off-line in laboratory.
The resistance of the pipe material to slow crack
growth is measured.
Stand alone.
Test method fully developed and included in
American standards.
Primarily used as a material research tool but has
been applied using coupons extracted from PE gas
pipelines in service.
High degree of accuracy can be achieved in test with
commercially available mechanical test and data
collection equipment.
Direct measurement.
Generic approach.
A medium level of operator skill is required for sample
notching prior to test.
Mechanical test and data collection equipment are
available in many research company test labs.
Criteria
Documentation
Availability of technical support
Economic factors
Cost per inspection
Resource requirements
Assessment
Test method is fully documented in ASTM F 1473.
Threshold values for test times distinguishing different
PE materials classes are covered in ASTM D 3350.
Journal papers quoting typical results for different PE
pipe materials in use are available in the literature.
University or research organizations can offer support
in the use of and interpretation of test results.
Specialist test, so relatively expensive
Laboratory based test.
F66.7 Bibliography
1. ISO 16241: 2005, Notch tensile test to measure the resistance to slow crack growth of
polyethylene materials for pipe and fitting products.
2. ASTM F1473, Standard test method for the notch tensile test to measure the resistance to
slow crack growth of polyethylene pipes and resins.
3. ASTM D 3350, Standard specification for polyethylene plastic pipe and fitting materials.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-195
F67.0 Smart Digital Sewer Pipe Diagnostic System (VTT)
F67.1 Overview
The Smart Digital Diagnostics System for Sewer Pipes is currently being developed. It
is intended to be a new diagnostics system able to interpret digital image data according to
future CEN standard (Visual Inspection Coding System).
When completed, the system will measure and analyze the condition of a sewer pipe
and will support network wide regular condition monitoring and proactive maintenance.
F67.2 Main Principles
The approach is intended to be a replacement for CCTV inspection of sewer pipes. The
technology used differs from CCTV in that it produces very accurate digital side scans of the
pipe wall instead of producing only forward looking continuous images of the pipe. It also
produces very accurate on-line location data with the help of two different measurement
systems.
In use, the system scans the pipe wall, taking one 1mm ring scans, and produces open
folded side scans of the pipe. The image produced is continuous. Besides the side scanning, the
tool captures front view images at discrete intervals.
The scanner’s inclinometer registers vertical movement and a gyroscope registers
horizontal movement. The distance from the starting point is measured from the power cable. If
the x, y and z co-ordinates of the starting point and the ending point are given, the system can
determine the co-ordinates of the centerline of the pipe.
F67.3 Application
When developed, the system will provide automated analysis of defects in sewer
pipelines.
♦ It is intended to interpret digital image data according to a future CEN standard (Visual
Inspection Coding System).
F67.4 Practical Considerations
♦ The system is still in the development stages with the focus of the research and
development being direct defect analysis.
♦ When the software is completed, all the measurements and analyzing work will be
made immediately on-site after the data is collected.
♦ Helsinki Water has utilized the system and field demonstrations have been carried out
in Germany (Hamburg), Denmark (Copenhagen), Sweden (Malmo), Stockholm,
(Gothenburg), Norway (Oslo), Russia (St Petersburg), Latvia (Riga) and Estonia
(Tartu).
F67.5 Advantages
♦ Enables advanced and automatic analysis of sewer pipelines for defects rather than the
manual analysis required with traditional CCTV data. This has the potential in the long
term to reduce the costs associated with sewer inspection.
F67.6 Limitations
♦ The technique is in its development stages and has only been trialed in a number of
European cities.
F-196
♦ The system requires a highly specialized scanner unit.
Table F-69. Summary Smart Digital Sewer Pipe Diagnostic System (VTT).
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Technical
suitability
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Utility technical
capacity
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Economic factors
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Sewer pipelines.
Any material.
Wastewater.
Scanner unit is inserted through manhole
access point.
Assets in very poor condition may cause the
scanner to get stuck.
Scanner unit needs to be inserted into pipeline,
so very small diameter pipes are not suitable,
although the vast majority of sewer pipes will be
covered.
Scanner records continuous data along pie
length.
Non-destructive inspection technique.
No interruption to sewer is needed.
Records high quality digital images with 1mm
accuracy that covers the entire circumference of
the pipe wall.
Requires specialized software to interpret
results.
Non commercial product that is still under
development.
Has been trialed in several European cities only.
Quantitative and qualitative.
Validation is possible through visual inspection.
A high level of sophistication is required using
specialized equipment and software.
Skilled operator required.
Specialized scanner unit is required and
dedicated software to interpret results.
Technique still in development.
Technique still in development.
Initial purchase costs are high.
Skilled operator and equipment is required.
F67.7 Bibliography
1. Welsh School of Architecture (Data Unknown) Case Study: Digital diagnostics system
for sewer pipes. Accessed November 2006 at:
http://www.cardiff.ac.uk/archi/programmes/cost8/case/watersewerage/finlandsewer.pdf.
43H
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-197
F68.0 Smoke Testing
F68.1 Overview
Smoke testing is used to identify faulty or illegal connections to gravity sewer and
storm water systems.
Fans are used to force artificial smoke into the sewer at one or more manholes. The
smoke will then either escape the system at house vent pipes, defective or illegal connections
and other problem areas, allowing them to be identified.
F68.2 Main Principles
Smoke from either smoke bombs or a liquid smoke system is forced into the system at
manholes using specially designed fans. The smoke escapes from the system at house vent
pipes, illegal connections such as down pipes and faulty connections, allowing them to be
identified.
When testing sewer systems smoke should escape from house vent pipes, if smoke
escapes from drain pipes this indicates an illegal connection to the sewer system. The reverse is
true for storm water systems.
F68.3 Application
Smoke testing is used to locate illegal or faulty connections to gravity sewer and storm
water systems, but can also indicate defective connections buried manholes.
F68.4 Practical Considerations
♦ By partially blocking pipes leading away from the test area, smoke is not lost to areas
not being inspected.
♦ Residents and emergency service should be fully informed prior to testing to prevent
unnecessary distress.
F68.5 Advantages
♦ Smoke test systems are inexpensive and provide a fast method for locating illegal and
faulty connections.
F68.6 Limitations
♦ May cause alarm to residents.
F-198
Table F-70. Summary Smoke Testing.
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Economic factors
Cost per inspection
Resource requirements
Assessment
Gravity sewer and storm water.
Any.
Wastewater.
Manhole or similar access to sewer pipes
required.
Not restrictions due to asset condition.
No restriction due to size of asset.
N/A
Testing is Non-destructive.
Inspection can be undertaken while asset is online.
Test indicates connections to sewer pipeline.
Stand alone tool for detecting locations of
inflow.
Equipment is available from a number of
commercial suppliers.
Used in the United States.
Qualitative indication.
Results can be validated by visual or other
inspection methods.
Generic approach.
Low level of operator skill required.
Specialized equipment required to introduced
smoke to assets.
No standards were found on this technique.
Information on testing can be obtained from
equipment suppliers.
Low cost.
Test requires a number of personnel for each
test to locate smoke escape points.
F68.7 Bibliography
1. Hurley, L. Smoke Testing Our Sewer Systems, Pipes Wagga Wagga 2005, Charles Sturt
University, Wagga Wagga, N.S.W., October 17-20, 2005.
2. Ratliff, A. An overview of current and developing technologies for pipe condition
assessment, Pipelines 2003, ASCE 2004.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-199
F69.0 Soil Characterization
F69.1 Overview
Soil characterization involves analyzing soil parameters relevant to the deterioration of
buried assets. Such parameters include pH, sulfide concentrations, moisture content, electrical
conductivity (salinity), shrink-swell capacity and redox potential. Soil characteristics interact
with buried assets of all material types.
Characterization of soil parameters relevant to buried assets allows suitable material
types to be chosen and effective preventative measures to be taken to minimize degradation of
the asset. Soil characterization can also be used with pipe specific information to predict the
working life of the pipe.
F69.2 Main Principles
When collecting samples for lab characterization or in-situ testing the position of the
sample should be relevant to the buried asset. For example, samples should be taken at the
depth of the pipe asset instead of at the surface. Soil parameters of interest include:
♦ Soil resistivity; Soil resistivity is relevant to the corrosion of ferrous materials. Soils
with low resistivity are more likely to have high corrosion rates, while high resistivities
are likely to indicate low corrosion rates (see section on Soil Resistivity).
♦ pH; Low pH values are associated with corrosion of ferrous assets and deterioration of
cementituous assets. However, while a useful indicator of potential corrosivity, the
correlation between pH and corrosion rate is not consistent and can be affected by a
number of factors. Deterioration of cementituous materials will be affected by the type
of acid present, as some react more readily with the cement than others.
♦ Redox potential; the redox potential of soil is a measure of soil aeration and gives an
indication of the suitability of conditions for sulfate reducing bacteria. The presence of
sulfate reducing bacteria can result in the production of corrosive products such as
hydrogen sulfide (as a by-product of metabolism), and can create cathodic areas on
assets due to the consumption of hydrogen. Redox potentials of below 100 mV are most
favorable for sulfate reducing bacteria.
♦ Sulfates also react with cementituous materials forming gypsum and ettringite, which
have significantly higher volumes than the materials they replace causing swelling and
cracking of the pipe wall. Sulfate attack will only occur where the sulfate salt are in
solution.
♦ Chloride content; Chloride ions permeate into cementituous and attack steel
reinforcement. Corrosion of the reinforcement results in a volume increase applying
stress to the asset resulting in spalling.
♦ Moisture content; Soil moisture acts as the electrolyte in electro-chemical corrosion of
ferrous assets. Static water also acts to produce anaerobic conditions suitable for sulfate
reducing bacteria. Static water can also allow sulfates and chlorides to enter solution in
close contact with the asset and permeate into cementituous assets (see above). Flowing
water can act to leach free lime from cementituous assets (Randall-Smith, 1992). Soil
moisture content will also define the degree of saturation of the soil. This will give an
indication of the state of soil drying, which is important for moisture migration and soil
moisture reactivity (see shrink/swell capacity).
F-200
♦ Shrink/swell capacity (soil moisture reactivity); Clay soils change volume depending
on their water content. Clay particles absorb moisture into their crystal lattice causing
them to swell. As the moisture content of the soils reduces due to uptake by plant root
systems, percolation through soil matrix and evaporation, the soil will shrink. Assets
within soils with high shrink/swell capacities are known to have an increased failure
rate, due to the stresses imparted by the soil during the shrink/swell cycle. The basic
properties that characterize shrink/swell capacity are plasticity index, fraction of fine
particles and the mineralogy of the particles. The mineralogy of the particles may be
related to the geologic origin of the soil deposit. Alternatively, direct mineralogical
measurements may be carried out to characterize the soil fractions.
♦ Buffering capacity; Clay soils and soils high in organic matter have high buffering
capacity while sandy soils and soils low in organic matter have low buffering capacity
(Agri-facts, 2005). A soil’s buffering capacity is the degree to which it is able to resist
changes in pH; in particular acidification. The affects of pH are covered above.
♦ Linear polarization resistance; LPR can been used to predict the corrosion rate of
buried ferrous assets; high LPR indicates low corrosion rates. The empirical
relationship between LPR and corrosion rate has been investigated on a number of
occasions, and some doubt has been expressed as to the reliability of the technique
(Heathcote and Nicholas, 1998). (see review on Linear Polarization Resistance)
♦ Contaminants; soil contaminants such as organic compounds can have negative affects
on polymeric materials. Organic compounds such as petrol can migrate through the
polymeric pipes both impacting water quality and remaining in the polymer matrix
causing it to swell and lose strength. Highly levels of acidic continents can also cause
environment stress cracking of polymers dramatically reducing lifetime.
♦ Soil compaction: The susceptibility of the trench filling and the surrounding sediments
for compaction.
These parameters often cannot be used in isolation because of the range of factors
involved in chemical and electrochemical processes that cause corrosion, deterioration and
stress failure (Dorn, 1996). As such, results are often incorporated into scoring systems used to
classify a soil’s potential for corrosion or other mechanisms of deterioration.
F69.3 Application
Soil characterization tests conducted on samples taken at relevant locations can be used
to give an insight into the environment of buried assets without disturbing the asset.
Characterization conducted prior to installation of buried assets can be used to
determine appropriate material type to be used and also establish if any protection measures
need to be included, such as cathodic protection.
F69.4 Practical Considerations
♦ Integration of soil characterization into a GIS system can give a good picture of soil
conditions. Soil information, asset characteristics and depth, and groundwater levels
can be overlayed within a GIS to identify likely interactions between soil, groundwater
and buried assets. This is especially true in cities where the pipe system is in contact
with the ground water table, which is a common occurrence in Europe.
♦ Soil tests are often conducted at failure locations, however, it should be noted that this
may give a skewed picture of soil conditions.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-201
F69.5 Advantages
♦ Samples can be obtained without exposing buried assets.
♦ Characterization can be focused on parameters of interest such as those linked to
corrosion.
♦ Characterization at failure locations can be used to give an indication of the process
involved in failure.
♦ Characterization prior to installation can be used to choose appropriate asset materials
and/or protection.
F69.6 Limitations
♦ As samples are small, tests only give parameters for a small area, which may or may
not be representative of the area of interest.
♦ Analyzes often needs to be conducted in a lab and can be expensive.
♦ Correlation between measured parameters and desired result is not always reliable.
♦ Moisture content of soil sample may not be that seen at the asset location due to
variations in factors such as compaction.
Table F-71. Summary Soil Characterization.
Technical
selection
Technical
suitability
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Utility technical
capacity
Integration with software tools
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
F-202
Assessment
Environmental survey (pipeline assets).
Soil characterization can be related to any
material depending on tests conducted.
Potable and wastewater.
Access to soil at point of interest.
None.
Results are discreet.
Non-destructive.
Inspection does not affect assets.
Soil parameters.
None.
Equipment is widely available, although most
tests need to be conducted in a lab.
Wide use.
Results should be viewed as a qualitative
assessment of the general soil properties.
None.
Results can be validated through other tests.
Generic approach.
Operator training is required; the level is
dependant on testing being conducted.
Specialized equipment required for most tests.
Techniques described well in literature and
standards.
Information available in literature and for
contractors supplying the services.
Economic factors
Criteria
Cost per inspection
Resource requirements
Assessment
Cost depends on number and type parameters
being tested.
Resources required is dependant on testing
being conducted.
F69.7 Bibliography
1. Agri-facts: Practical Information for Alberta’s Agriculture Industry,
http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex3684/$file/5341.pdf?OpenElement , accessed 2005.
4H
2. Dorn, R., Howsam, P., Hyde, R.A. and Jarvis, M.A. Water mains: Guidance on assessment
and inspection techniques, CIRIA Report 162, Construction Industry Research and
Information Association, London, England, 1996.
3. Heathcote, M. and Nicholas, D. Life Assessment of Large Cast Iron Watermains, Urban
Water Research Association of Australia, Research Report No 146, 1998.
4. Matti, M.A. and A. Al-Adeebt Sulphate attack on asbestos pipes, The international journal
of cement composites and lightweight concrete, 1985.
5. Randall-Smith, M., Russell, A. and Oliphant, R. Guidance manual for the structural
condition assessment of trunk mains, WRc, UK, 1992.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-203
F70.0 Soil Corrosivity
F70.1 Overview
The predominant deterioration mechanism for ferrous pipes is electro-chemical
corrosion. Soil corrosivity tests use one or more soil characteristics to predict the likely rate of
corrosion.
A soil’s corrosivity to ferrous pipe materials can be assessed in different ways; some
methods predict only that corrosion is likely, while others predict a likely rate of corrosion.
F70.2 Main Principles
Najjaran (2006) reports several different methods that incorporate multiple soil
characteristics:
♦ The 10- point DIPRA method uses soil resistivity, pH, redox potential, sulfide content
and moisture content to classify soils as either corrosive or non-corrosive.
♦ The Metalogic method uses twelve soil factors; soil type, soil resistivity, water content,
pH, buffering capacity, chloride and sulfide concentrations, ground water level,
horizontal and vertical homogeneities and electro-chemical potential to rate corrosivity
at four levels from highly corrosive to virtually non-corrosive.
♦ The Spickelmire method uses a twenty-five point method and includes soil properties
as in the DIPRA method and pipe factors such as pipe location, size, maximum surge
pressure, design life, and leak repair difficulty. This method ranked corrosivity at four
levels from mild to severe.
♦ Linear Polarization Resistance (LPR) is a soil characteristic used to predict the
corrosion rate of buried ferrous assets. LPR has a negative correlation with corrosion
rate in ferrous assets, meaning that soils with high LPR values will exhibit low
corrosion rates. Heathcote and Nicholas (1998) reported that LPR (Also see LPR
review) showed significant correlation with pitting rate of cast iron when measured
manually.
F70.3 Application
Soil corrosivity gives an indication of the likelihood that corrosion will occur. It can
generally be used to qualitatively rank soil types, such as on a scale from non-corrosive
through to very corrosive. Soil corrosivity tests are relevant for buried ferrous assets. Soils can
be categorized into broad corrosivity categories that identify areas where corrosion potential is
highest.
F70.4 Practical Considerations
♦ LPR measure using automated systems showed very limited correlation with corrosion
rate and so should not be used unless technique correlations to pit rate have been
improved.
♦ Methods for measurement of soil characteristics, such as pH, resistivity, redox potential
and moisture content, are available either from standards or literature. Companies are
available to conduct all of the required soil characterization work if needed.
♦ Prediction of pipe condition requires additional information such as pipe age and wall
thickness.
F-204
F70.5 Advantages
♦ Techniques used in predicting soil corrosivity can be conducted prior to laying pipe
allowing appropriate corrosion control measures to be undertaken. Categorization of
soil types into corrosivity classes can be useful in focusing attention on assets where
more detailed monitoring and inspection of buried ferrous assets may be justified.
♦ Outputs from soil corrosivity tests can be linked to soil layers within a geographic
information system, in order to provide a spatial overview of likely areas of high
corrosivity.
F70.6 Limitations
♦ Most techniques only indicate the corrosion rate qualitatively.
♦ Corrosion rate does not allow the condition of an asset to be assed on the rate of its
degradation.
Table F-72. Summary Soil Corrosivity.
Technical
selection
Technical
suitability
Criteria
Assets covered
Material type
Service Area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Economic factors
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Environmental survey (pipeline assets).
N/A
Potable and wastewater.
Access to soil required.
None.
None.
Results are discreet.
Non-destructive.
Inspection does not affect assets.
Technique predicts corrosion from soil
characteristics.
Knowledge of corrosion rate requires knowledge
of pipe wall thickness and age in order to
provide pipe condition information.
Approaches to soil corrosion assessment are
available from commercial suppliers.
Widely used.
Qualitative assessments.
Results can be validated through inspection of
pipes.
Generic approach.
Operator training is required.
Lab based testing procedures.
Information available from literature.
Information available in literature.
Cost varies depending on technique employed
Dependent on technique applied
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-205
F70.7 Bibliography
1. Heathcote, M. and Nicholas, D. Life Assessment of Large Cast Iron Watermains, Urban
Water Research Association of Australia, Research Report No 146, 1998.
2. Najjaran, H., Sadiq, R. and Rajani, B. Fuzzy Expert System to Assess Corrosion of Cast/
Ductile Iron Pipes from Backfill Properties, Computer–Aided Civil and Infrastructure
Engineering, 21, pp. 67-77, 2006.
3. Sadiq, R., Rajani, B. and Kleiner, Y. Fuzzy-Based Method to Evaluate Soil Corrosivity for
Prediction of Water Main Deterioration, Journal of Infrastructure Systems, 10, 4, pp. 149 –
156, 2004.
F-206
F71.0 Soil (Electrical) Resistivity
F71.1 Overview of Inspection Tool
The predominant deterioration mechanism for ferrous pipes is electro-chemical
corrosion. Soils with low resistivity are more likely to have high corrosion rates, while high
resistivities are likely to indicate low corrosion rates. As such, measuring soil resistivity gives
an indication of the rate at which corrosion will occur. Soil resistivity can be measured in situ
or in the lab using a number of techniques.
F71.2 Main Principles
A number of factors influence the rate at which corrosion of ferrous assets will occur
including resistivity, pH, redox potential, moisture content and sulfide levels. Of these factors
soil resistivity is considered to be most representative of the likelihood of corrosion (Najjaran
et al, 2006). Resistivity varies with changes in soil moisture and salt content, lower moisture
content resulting in higher resistivity; lower salt content resulting in higher resistivity.
Field measurements of soil resistivity are conducted using the Wenner technique. This
involves inserting four equally spaced electrodes into the soil. An electrical potential is then
impressed between the outermost electrodes, and the potential drop between the two central
electrodes measured. Several measurements are taken and used to calculate the soil resistivity
(Lillie et al, 2004).
Lillie et al (2004) state that the electrodes should be located directly above the pipe and
along its axis; however other sources (ASTM G57-95a (2001) indicate that electrodes should
be placed perpendicular to the axis of the pipe.
The Wenner technique measures the average resistivity from the soil surface to a depth
equal to the pin spacing, in particular the spacing between the two central electrodes, so this
distance should be chosen to coincide with pipe depth.
Laboratory measurements of soil resistivity can be conducted using a variation of the
Wenner technique (ASTM G57-95a (2001), AS 1289.4.4.1 - 1997) or a two electrode method
(ASTM G187-05)
F71.3 Application
Soil resistivity is an environmental indicator of the corrosivity of soils. In conjunction
with other environmental information, the corrosion rate of materials in the soil can be
estimated. Reference standards include:
♦ AS 1289.4.4.1 -1997: Determination of the electrical resistivity of soil.
♦ ASTM G187-05 Standard Test Method for Measurement of Soil Resistivity Using the
Two-Electrode Soil Box Method.
♦ ASTM G57-95a(2001) Standard Test Method for Field Measurement of Soil Resistivity
Using the Wenner Four-Electrode Method.
F71.4 Practical Considerations
♦ These techniques are widely used in the sector, and services are provided by a number
of companies.
♦ As resistivity can change with depth due to the effect of the water table, when using the
Wenner technique, the spacing between each pin should be equal or greater than the
pipe depth.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-207
♦ Measurements should be taken to the side of the line of the pipe, to avoid the pipe from
being included in the conduction path.
♦ Due to differences in the degree of compaction, the results obtained in the laboratory
tend to be lower than the corresponding values measured in situ.
♦ Soil resistivity should not be measured on soil at below-freezing temperatures.
F71.5 Advantages
♦ Low cost technique.
♦ Gives an indication of soil corrosion potential.
♦ Widely used technique.
F71.6 Limitations
♦ Soil resistivity is only indicative of corrosion rate for buried ferrous assets; further
detailed analysis is required to actually determine corrosion rate and asset condition.
Table F-73. Summary Soil (Electrical) Resistivity.
Technical
selection
Technical
suitability
Utility technical
capacity
Economic factors
F-208
Criteria
Assets covered
Material type
Service Area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication);
usability
Technology required (level of tool
sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Environmental survey (pipeline assets).
Soil.
Potable and wastewater.
Access to soil surface required.
None.
None.
Results are discreet.
Non-destructive.
Inspection does not affect assets.
Soil electrical resistivity.
None.
Equipment is widely available but generally
superseded.
Widespread use.
Quantitative, but qualitative interpretation.
Results can be validated though other soil test.
Generic approach.
Operator training is required.
Low level technological requirements, specialized
equipment required.
AS 1289.4.4.1 -1997, ASTM G187-05, ASTM G5795a(2001).
Information available in literature.
Low cost .
Measurements can be undertaken by a single
person.
F71.7 Bibliography
1. Dorn, R., Howsam, P., Hyde, R.A. and Jarvis, M.A. Water mains: Guidance on assessment
and inspection techniques, CIRIA Report 162, Construction Industry Research and
Information Association, London, England, 1996.
2. Lillie, K., Reed, C. and Rodgers, M. A. R., 2004, Workshop on Condition Assessment
Inspection Devices for Water Transmission Mains, AwwaRF, USA, 2004.
3. Najjaran, H., Sadiq, R. and Rajani, B. Fuzzy Expert System to Assess Corrosion of
Cast/Ductile Iron Pipes from Backfill Properties, Computer-Aided Civil and Infrastructure
Engineering, 21, pp 67-77, 2006.
4. Randall-Smith, M., Russell, A. and Oliphant, R., Guidance manual for the structural
condition assessment of trunk mains, WRc, UK, 1992.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-209
F72.0 Thermographic Testing
F72.1 Overview
Thermographic testing uses infrared (IR) imagery to locate defects and potential
failures in electrical equipment by scanning for thermal abnormalities. As IR energy is emitted
from objects due to their thermal properties, thermographic testing enables the early detection
of electrical problems that are associated with a thermal signal, such as overheating. This nondestructive test allows for the early identification and repair of defects before they potentially
cause unscheduled power losses, equipment damage, or even catastrophic equipment failures.
F72.2 Main Principles
Thermographic testing detects thermal properties using IR imaging. IR imaging allows
invisible IR radiation to be converted into a visible image so that objects are viewed on the
basis of their heat emissions rather than light properties. Images can be instantaneously viewed,
photographed, video recorded or if required can be downloaded to provide reports and
historical records for future comparison. By locating thermal abnormalities in images, such as
hot or cold spots, deteriorating and defective components can be identified and repaired or
replaced before failure.
F72.3 Application
Thermographic testing is an effective method of locating problems in all electrical
equipment that carries a current. Thermographic testing is potentially applicable to the
following: Substations, Switchgear, Motor Control Centers, Motors, Bearings, Transformers,
Circuit Breakers, Cables, Terminators, Bus Bars, Bus Plugs, Overhead Distribution Lines,
Starters Contactors, Transmission Lines, Power Panels, Lighting Panels, High Voltage
Equipment, Switches, Controls and Low Voltage Equipment. IR can also be used for roads and
roofs.
♦ ASTM-E1934-99a and ISO/DIS 18436-8 are applicable to thermographic testing.
ISO/DIS 18436-8 is a Draft International Standard (DIS) with no specific standard for
this test method.
F72.4 Practical Considerations
♦ Thermographic testing is widely applied for the testing of electrical systems; there are
numerous commercial organizations that provide specialist skills.
♦ The testing equipment consists of handheld camera that is battery powered, so it is
readily portable.
♦ Thermographic testing allows rapid scanning of electrical equipment and the results are
repeatable. The equipment must be under load conditions during testing.
♦ Comparison of images taken from regular thermographic testing may show changes in
heat emissions, which enables early detection of possible faults.
F72.5 Advantages
♦ Thermographic testing allows rapid scanning of equipment and can be used at a
distance, meaning that no direct contact or intrusion is required.
♦ The results are reliable, can be recorded in different formats and sensors can be
sensitive to 0.1 °C.
F-210
F72.6 Limitations
♦ A temperature difference is required to identify electrical faults. Some operator
experience is necessary as sensitivity and resolution can be reduced with distance to
object and angle of view.
♦ As most thermographic testing is performed on "live front" energized equipment
precautions must be taken to ensure no direct contact with live parts.
Table F-74 Summary Thermographic Testing.
Technical
selection
Technical
suitability
Utility technical
capacity
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Economic factors
Cost per inspection
Resource requirements
Assessment
Wastewater/water electrical infrastructure substations, switchgear, motor control centers,
motors, bearings, transformers, circuit breakers,
cables, terminators, bus bars, bus plugs,
overhead distribution lines, starters contactors,
transmission lines, power panels, lighting
panels, high voltage equipment, switches,
controls and low voltage equipment.
N/A
Potable and wastewater.
Hand held battery operated.
None.
None.
Discrete.
Non-destructive.
Equipment is required to be on-line/under load.
Heat generated.
Stand alone.
Commercialized, can be used off the shelf.
Standard industry practice.
Qualitative.
Direct observation.
Generic approach
Field service engineer, HV authorized (in HV
areas)
None, is a stand alone portable tool
Is well documented. ISO/DIS 18436-8; ASTME1934-99a
Sufficient suppliers of equipment, training and
services.
Low.
One operator needed.
F72.7 Bibliography
1. ISO/DIS 18436-8: Condition monitoring and diagnostics of machines - Requirements for
training and certification of personnel - Part 8: Thermography (Under Development).
2. ASTM-E1934-99a (2005) Standard Guide for Examining Electrical and Mechanical
Equipment with Infrared Thermography.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-211
F73.0 Transformer Circuit Protection Coordination and Protection Relays
F73.1 Overview of Tool
Transformer circuit protection coordination and protection relays are designed to
prevent damage to valuable electrical equipment from short circuits or other faults.
Coordination of protection relays aims to minimize disruption to network operations by
ensuring that only equipment impacted by the fault is isolated and shutdown.
This review outlines the testing and analysis of electrical protection systems that should
be undertaken to ensure adequate protection and the reliable performance of protection relays.
This type of protective device co-ordination review should be done as part of any
comprehensive maintenance program at least every five years.
F73.2 Main Principles
Coordination of relay protection is designed to ensure that only the equipment
threatened with damage is isolated and removed from service. Relay settings determine when a
relay sends a control signal to a circuit breaker. A review of transformer circuit protection
coordination and protection relays should include analysis of fault levels, equipment ratings,
protection installed and protection settings to ensure faults such as short circuits will not cause
damage to electrical equipment.
Tests are designed to provide inputs to relay protections that simulate faults, such as
short circuits. Tests include primary and secondary injection tests sets for HV/MV distribution
switchboards and motor control centers for establishing the protection operates at the right
settings and includes motor protection relays. Primary injection testing involves injecting a
high current on the primary side of the transformer, which means the whole system is covered
by the test and requires the equipment to be off-line. Secondary testing involves disconnecting
protective relays from the transformers and circuit breakers, with current and voltage fed
directly to relay protection, which means that equipment can stay on-line. Primary injection
testing is generally only used in the case where new equipment is being commissioned or when
secondary circuits are not accessible.
F73.3 Application
Analysis of circuit protection coordination and protection relays can be applied to the
following: LV switchboards, HV switchgear, transformers and cabling. Relevant standards
include:
♦ AS/NZ 3000 wiring rules. Various standards for equipment types (fuses, breakers,
MCCBs, etc.).
♦ AS 3851-1991: The calculation of short-circuit currents in three-phase alternating
current systems.
♦ AS 3865-1991: Calculation of the effects of short-circuit currents.
♦ IEC 60865- Short-circuit currents - calculation of effects.
♦ IEC 60909- Short-circuit currents in three-phase alternating current systems.
F73.4 Practical Considerations
♦ Testing of electrical protective systems is standard, particularly in organizations such as
power and water utilities.
F-212
♦ The analysis of relay protection and coordination requires an experienced and specialist
engineer. There are a number of companies that specialize in providing the expertise to
design and test electrical protection systems.
F73.5 Advantages
♦ The design and testing of electrical protection systems is critical in preventing damage
to important and expensive electrical equipment.
♦ If adequate information is available there is the potential for non-invasive desktop study
of electrical protection systems.
F73.6 Limitations
♦ If data on the electrical protection system is lacking, a desktop analysis is not possible.
Therefore, direct access to components may required, which in some cases will result in
power shutdowns. Plant has to be off-line to enable the tripping of breakers.
Table F-75. Summary Transformer Circuit Protection Coordination and Protection Relays.
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Utility technical
capacity
Economic factors
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Electrical protection systems; fuses, overload
units, CTS, protection relays.
N/A
Potable and wastewater.
Access to HV authorized areas.
None.
None.
Gives time co-ordination with other devices for
fault currents.
Non-destructive.
For testing of equipment reaction it is necessary
to trip feeder units with resultant power outages.
Time for protection system to react and its
interaction with other protection devices.
Stand alone.
Fully developed.
Standard industry practice.
Within tolerances of supplied equipment e.g.,
tripping times may have a 10% margin.
Direct measurement.
Generic approach.
Requires experienced and qualified engineer.
N/A
Standard design in accordance with AS/NZ
3000; AS 3851-1991: AS 3865-1991 ; IEC
60865 ; IEC 60909.
N/A
N/A
Site survey and offsite desktop study.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-213
F73.7 Bibliography
1. AS/NZS 3000:2000 Electrical installations (known as the Australian/New Zealand Wiring
Rules).
2. AS 3851-1991 : The calculation of short-circuit currents in three-phase alternating current
systems.
3. AS 3865-1991 : Calculation of the effects of short-circuit currents.
4. IEC 60865- Short-circuit currents - Calculation of effects - Part 1: Definitions and
calculation methods.
5. IEC 60909- Short-circuit currents in three-phase AC systems - Part 3: Currents during two
separate simultaneous line-to-earth short circuits and partial short-circuit currents flowing
through earth.
6. Thorp, J.S. The Protection System in Bulk Power Networks, Power System Engineering
Research Centre, 2003.
F-214
F74.0 Transient Earth Voltage (TEV)
F74.1 Overview of Tool
The detection of transient earth voltage (TEV) is an indicator of partial discharge. In
general terms, partial discharge is a minute electrical pulse or discharge occurring in a gas
filled void or on a dielectric surface of a solid or liquid insulation system. This can occur upon
insulation breakdown due to aging, damage or contamination. The pulse or discharge only
partially bridges the gap between the phase to ground insulation. This is an early indicator of
insulation failure. Emissions from a partial discharge are electromagnetic, radio up to 80 MHz,
light, heat, acoustic ultrasonic and gases.
F74.2 Main Principles
If a partial discharge occurs in the phase to earth insulation of an item of high voltage
plant, a small quantity of charge is transferred capacitively to the earthed metal cladding. An
electromagnetic wave is generated at the discharge site which propagates away in all
directions. By escaping through an opening in the metal cladding, such as a gasketed joint, this
can be detected on the outer surface as a TEV. The TEV has a nanosecond rise time and
amplitude that varies widely from millivolts to volts.
F74.3 Application
TEV can be used to inspect HV switchgear, transformer cable boxes and tappings for
the detection of electrical insulation breakdown.
F74.4 Practical Considerations
♦ Inspection of HV switchgear is best carried out in conjunction with ultrasonic emission
inspection to detect problems between phases, terminations and switch tank spouts (see
Ultrasound Emissions review).
♦ HV authorized personnel only to undertake testing of HV electrical equipment.
F74.5 Advantages
♦ TEV is non-destructive and components are monitored while in normal operation.
♦ This method is easy to use and provides instantaneous information. It is a compact and
user-friendly tool that is also very durable.
♦ There is no requirement to expose electrical live parts. No requirement for directs
contact.
F74.6 Limitations
♦ Detects discharges to earth through voids or insulation breakdown. It does not detect
discharge between phases or into air. It therefore cannot, on its own, be used for all HV
switchgear or fault applications.
♦ It is best used in a device that uses a combination of ultrasound and electromagnetic
detection.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-215
Table F-76. Summary Transient Earth Voltage (TEV).
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Technical
suitability
Utility technical
capacity
Economic factors
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication); usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
HV switchgear, transformer cable boxes and
tapping selector switches.
Electrical insulation.
Potable and wastewater.
HV authorized person usually required to
access plant areas.
None.
None.
Continuous during test.
Non-destructive.
On-line
Electrical discharge to earth.
Stand alone.
Commercialized, can be used off the shelf.
Industry standard practice.
Validity confirmed on insulation testing of unit
(requires power down) and physical inspection.
Is an indicative tool.
Direct measurement.
Generic approach.
Field service engineer, HV authorized.
None is a stand alone portable tool.
Is well documented.
N/A
Low cost test.
One operator needing only time required to
access plant item.
F74.7 Bibliography
1. EA technology, http://www.eatechnology.com, accessed 2006.
45H
F-216
F75.0 Ultrasonic Emission Inspection
F75.1 Overview of Tool
The use of audible sound has long been part of the information gathering process to
diagnose the operating condition of plant and machinery.
Audible sounds generated by individual bearings, electrical arcing, or leaks are difficult
to differentiate in a noisy environment where components operate within close proximity of
one another. Machinery also generates sound above the range of normal human hearing in the
ultrasound region. Due to the properties of ultrasound, the sounds made by individual parts can
be differentiated. Any physical changes in equipment will produce resultant sound changes.
Theses sound changes will often first appear within the ultrasound spectrum before the audible
spectrum, giving the opportunity for early diagnosis.
Ultrasonic emission inspection is a non-destructive method for maintenance
diagnostics, safety, and quality control.
F75.2 Main Principles
Machines and equipment generate both audible sound and ultrasound when in
operation. Ultrasound is sound that occurs above the normal range of human hearing, the upper
range of human hearing is typically 20 kHz. Defects such as electrical arcing and bearing
damage can be identified by their ultrasound signature.
Inspection is undertaken using a portable sensor. The ultrasound signal is converted
into the audible region with the normal audible signals being filtered out. The reproduced noise
retains recognizable characteristics such that a bearing sounds like a bearing and electrical
arcing sounds like arcing. This permits detection even in extremely noisy environments.
Ultrasound is very directional and attenuates much faster than audible sound. Therefore
it stays close to its source allowing for easier location. Detection can be improved by making
direct contact with the plant item using a solid probe so eliminating air gap attenuation.
In the case of bearings and gears, ultrasound will be emitted prior to mechanical failure,
thus giving the end-user of the ability to perform maintenance before breakdown occurs.
Ultrasonic emission inspection can also be used to detect and pinpoint electrical arcing,
tracking (partial discharge) or corona discharge on high voltage and medium voltage electrical
systems.
F75.3 Application
Ultrasonic emission inspection can be used to inspect plant mechanical defects within
motor bearings and gearing. Electrical faults that involve arcing, tracking over insulation
(partial discharge) or air discharge (corona) can also be detected. Acoustic ultrasonic can also
be used to check steam trap performance and to find air leaks.
♦ Ultrasonic emission inspection is referenced in ISO-10375 - Non-Destructive Testing Ultrasonic Inspection - Characterization of Search Unit and Sound Field.
F75.4 Practical Considerations
♦ Ultrasonic emission inspection is widely used throughout industry due to ease of use
and instantaneous results it obtains.
♦ Ultrasonic emission detectors are compact, user-friendly and very durable. They can be
hand carried. The method can be implemented for routine predictive and preventive
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-217
maintenance inspections, for identification of failed components when a problem is
suspected, and for confirmation of repairs.
♦ This method cannot be used in isolation for all HV switchgear applications. Inspection
of HV switchgear is best carried out with in conjunction with transient earth voltage
inspection (see transient earth voltage review). HV authorized personnel only to
undertake testing of HV electrical equipment.
F75.5 Advantages
♦ Ultrasonic emission inspection is non-destructive and components are monitored while
in normal operation.
♦ There is no requirement to expose electrical live parts or for direct contact. This method
is easy to use and provides instantaneous information.
♦ This inspection method can be used in hazardous areas with suitably rated detectors.
F75.6 Limitations
♦ Ultrasonic's will show problems with air switches, insulators and bushings in outdoor
structures only where direct air passage is available, for example, through the skin of
the cable box.
♦ It cannot, on its own, be used for all HV switchgear applications. Inspection of HV
switchgear is best carried out with in conjunction with transient earth voltage inspection
(see Transient Earth Voltage Review).
Table F-77. Summary Ultrasonic Emission Inspection.
Technical
selection
Criteria
Assets covered
Material type
Service area
Access requirements
Technical
suitability
Utility technical
capacity
F-218
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation
Asset management sophistication required
Skills required (level of tool sophistication);
usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Assessment
Wastewater/water motor bearings, HV/ MV
switchgear. All components from main
switchboards to individual motors.
N/A
Potable and wastewater.
No portable battery operated. Physical contact
required via probe to outer casing.
None.
None.
Continuous during test.
Non-destructive test.
Can be on-line.
Mechanical condition, electrical discharges.
Stand alone.
Commercialized; can be used off the shelf.
Standard industry practice.
Indicative measure.
Requires inspection of asset.
Generic approach.
Field service engineer
Tool only.
Well documented. ISO-10375.
Is well documented.
Economic factors
Criteria
Cost per inspection
Resources required
Assessment
Relatively low cost
One operator needing only time required to access
plant item and listen.
F75.7 Bibliography
1. ISO-10375 - Non-Destructive Testing - Ultrasonic Inspection - Characterisation of Search
Unit and Sound Field.
2. CTRL, http://www.ctrlsys.com/library/faq/faq_ut.php, accessed 2006.
46H
3. EA technology, http://www.eatechnology.com, accessed 2006.
47H
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-219
F76.0 Ultrasonic Measurements; Continuous (Guided Wave)
F76.1 Overview
Ultrasonic inspection is a non-destructive test conducted by sending high frequency
sound into an asset and evaluating any echoes detected. Ultrasonic examination procedures are
widely used for thickness measurement, corrosion monitoring, delamination checks and flaw
detection in welds, forgings, castings and pipes.
In the material, the ultrasonic pulses travel in straight lines, until they hit an interface
between two different materials (steel and air for example), or a flaw, when most of the energy
of the vibration will be reflected. A small amount of the energy is reflected back to the probe,
where it is detected.
This section applies to continuous techniques used for the rapid screening of pipes for
corrosion/erosion. Discrete ultrasonic inspection techniques are considered in a separate
section (see Ultrasonic Measurements; Discrete).
F76.2 Main Principles
In recent years much work has gone into the development of ultrasonic techniques for
the rapid screening of pipes for corrosion/erosion. This has resulted in systems that make use
of low frequency guided waves. Systems were originally designed for use on above-ground
exposed or insulated pipes, but are now used on buried pipes, though the range of inspection
can be shorter.
Depending on the type of guided wave used, the number of transducers can range
between two and four. Torsion waves require only two transducers, while longitudinal waves
required three or four transducers. Torsion wave systems were first introduced in 1998 and can
be used in pipes filled with water. Longitudinal waves are not used for water filled pipes as the
signal is partially propagated through the water and also reenters the pipe wall, making signal
interpretation very difficult even in simple situations. Longitudinal systems that use three
transducers can only operate on a single frequency, while four transducer systems can operate
using more frequencies, improving results.
During testing a unit using piezoelectric transducers is clamped around the pipe and
ultrasound is sent simultaneously in both directions along the pipe. The signal obtained is
similar to a conventional ultrasonic A-scan, where the horizontal axis represents distance along
the pipe and the vertical axis represents signal amplitude, which is indicative of the severity of
the corrosion. Unlike conventional A-scans, the signals are displayed from three different wave
modes, namely symmetrical, horizontal flexural and vertical flexural. The relative intensities
and characteristics of these three signals are important in identifying different distributions of
corrosion.
Electro-magnetic acoustic transducers (EMATs) have also been used in some
applications. EMATS give relatively consistent results in comparison to piezoelectric
transducers since they do not need any couplant. Other methods are available which do not
require direct contact with the pipe, however these techniques suffer from increased noise in
the signal, reducing accuracy and the length of pipe which can be inspected.
F76.3 Application
Continuous ultrasonic measurement is used to obtain an understanding of corrosion
along a pipeline, above and below ground pipes can be assed. This technique is suitable for use
on pipe diameters above 50mm (2.0") and on wall thicknesses up to 40mm (1.6").
F-220
•
ASTM E1816-96(2002); Standard Practice for Ultrasonic Examinations Using
Electromagnetic Acoustic Transducer (EMAT) Techniques.
F76.4 Practical Considerations
♦ While this technique is relatively new, commercialized tools and services are available,
although generally from specialized consulting companies.
♦ Recent advances in these systems allow focused guided waves to be used. These allow
the location of circumferential corrosion and improved signal to noise ratio. Although
propagation distances vary according to pipe geometry, contents, coating/insulation and
general condition, it is not unusual that a range of up to 30m (100') in either direction
from the transducer can be inspected. The technique is equally sensitive to internal and
external corrosion, but cannot distinguish between them.
F76.5 Advantages
•
The principal advantage of this technique is that it provides 100% initial screening
coverage, and only requires local access to the pipe surface (i.e. exposure of small
section of buried pipe or removal of a small amount of insulation) at those positions
where the transducer array is to be attached.
F76.6 Limitations
♦ Continuous ultrasonic measurement is more expensive than discrete ultrasonic
measurements. While the technique is equally sensitive to internal and external
corrosion, it cannot distinguish between them.
♦ Only very limited pipe lengths can be inspected when the pipe is heavily coated in a
very alternative material such as fresh bitumen. Surface deposits such as scale and
corrosion products also limit the length pipe which can be inspected.
Table F-78. Summary Ultrasonic Measurements; Continuous (Guided Wave).
Technical
selection
Criteria
Assets covered
Material type
Service Area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Technical
suitability
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Assessment
Pipes, water and wastewater pipeline
infrastructure.
Iron and steel pipes.
Waste and potable water.
Direct contact with pipe wall required.
No limitations relating to asset condition
provided direct contact with the pipe wall is
available.
Pipe diameters above 50mm (2.0") and on wall
thicknesses up to 40mm (1.6").
Continuous readings.
Non-destructive. External tool require exposure
of pipe surface.
Does not require interruption.
Level of wall thickness or corrosion pit depths in
iron and steel pipes.
Tool integrated with software; some systems
upload results via mobile phones.
Commercialized.
Some use reported in the literature.
Quantitative.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-221
Criteria
Ease of validation of results
Utility technical
capacity
Asset management sophistication required
Skills required (level of tool sophistication);
useability
Technology required (level of tool sophistication)
Documentation
Economic factors
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Validation possible only by comparison with
manual /direct measurements.
Generic approach.
Professional skills to interpret output data. Tool
operation typically by a trained technician.
Specialized equipment and dedicated computer
software.
Tool principles and description of reports
generated by tool will be available.
Service provided by special operator.
Variable. Staff time will be the highest cost.
Equipment cost US$1,000-10,000.
Typically one person.
F76.7 Bibliography
1. Lowe M.J.S., Alleyne D.N., Cawley P., Defect detection in pipes using guided waves,
Ultrasonics Vol. 36, p147-154, Elsevier Science, 1998.
2. Wassink, C.H.P., Robers M.A., de Raad J.A, and Bouma T. (2000) Condition Monitoring
of Inaccessible Piping, 15th World Conference on Nondestructive Testing, Roma (Italy)
15-21 October 2000. Accessible at:
http://www.ndt.net/article/wcndt00/papers/idn075/idn075.htm.
48H
F-222
F77.0 Ultrasonic Measurements; Discrete
F77.1 Overview
Ultrasonic inspection is a non-destructive test conducted by sending high frequency
sound into an asset and evaluating any echoes detected. Ultrasonic examination procedures are
widely used for thickness measurement, corrosion monitoring, delamination checks and flaw
detection in welds, forgings, castings and ferrous pipes.
An ultrasonic flaw detector has an oscillator circuit that sends electrical pulses to a
probe. The transducer in the probe produces ultrasonic vibrations when it receives the electrical
pulse. A range of vibration frequencies can be chosen between 1 MHz and 15 MHz depending
on the specific application. For example, typical frequencies used in weld examination are
between 2 MHz and 5 MHz.
The ultrasonic vibrations leave the probe and are conducted into the material to be
tested by a couplant, usually grease, oil, water, paste or gelatin.
In the material, the ultrasonic pulses travel in straight lines, until they hit an interface
between two different materials (steel and air for example), or a flaw, when most of the energy
of the vibration will be reflected. A small amount of the energy is reflected back to the probe,
where it vibrates the piezoelectric crystal, generating an electric current. This current returns to
the flaw detector, where it is amplified, rectified, filtered and displayed.
This section applies to discrete techniques used for screening of pipes for
corrosion/erosion at discrete locations. Continuous ultrasonic inspection techniques are
considered in a separate section.
F77.2 Main Principles
Several methods are available to produce the ultrasonic signals, piezoelectric ceramics
being the most common. Other methods include electromagnetic acoustic transducers
(EMATs), magnetosctrictive sensors (MSS), lasers and piezoelectric polymers.
When measuring wall thickness, the crystal is aligned perpendicular to the wall. The
waves propagate to the back wall and are reflected back towards the transducer. The transit
time from initial pulse to reception of back wall reflection is recorded. Knowledge of the
material’s ultrasonic velocity then gives the distance traveled by the wave. Calibration targets
of known thicknesses and materials are normally used to make these determinations
Figure F-12 illustrates a simple set-up using the pulse-echo principle and a twin crystal
probe. In this configuration, one crystal acts as transmitter and the other as the receiver.
Figure F-12. Simple Set-Up Using the Pulse-Echo Principle and a Twin Crystal Probe.
(Reprinted with permission from: Drury, J., 1996)
Figure F-13 shows a more complicated situation where the ultrasonic signal passes
through three materials the cement lining, pipe wall and corrosion products respectively. Four
echo signals are generated in this case, at the air-cement lining, cement lining-pipe wall, pipe
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-223
wall corrosion products and corrosion products-air interfaces. It should be noted that the
situation below is a schematic only, the transducer and detector both need to be in contact with
the surface of the asset being inspected. Also field experience indicates that ultrasonic
techniques are unable to detect flaws in cement mortar linings.
Figure F-13. Multiple Interfaces on Cement-Lined Water Pipe Create Multiple Ultrasonic Reflections
(Shown with a Probe Located Internally).
Wall thickness measurements are performed using a conventional flaw detector and a
compression wave probe, which sends longitudinal waves into the component at normal
incidence to the surface. Signals are displayed on the flaw detector screen in the form of an Ascan, in which the horizontal axis represents time and the vertical axis represents signal
amplitude. When a 0° compression probe is being used, the horizontal axis is equivalent to the
depth of the discontinuity (flaw or other interface) from the scanning surface.
The use of an A-scan display allows the operator to distinguish more easily between
signals originating from embedded plate flaws and the nominal back wall response. Also, the
dynamics of the back wall echo can be observed on the A-scan display to detect the presence of
pitting.
Conventional twin-crystal 0° compression probes are generally used to detect hidden
corrosion. However, where pitted surfaces are being assessed for remaining thickness, pencil
probes are used. These have a pointed tip which is designed to fit into the pits, so that the
remaining thickness can be measured where pitting is at its most severe.
F77.3 Application
Use for thickness measurement, corrosion monitoring, delamination checks and flaw
detection in welds, forgings, castings and ferrous pipes.
•
ASTM E1816-96(2002); Standard Practice for Ultrasonic Examinations Using
Electromagnetic Acoustic Transducer (EMAT) Techniques.
F77.4 Practical Considerations
♦ The technique is fully commercialized, with widespread use of the probes reported in
literature and trade journals. Accuracy of results can be high, but depends upon
application and calibration.
♦ When ultrasonic tools are used for condition assessment, the ideal reflector of the
ultrasonic sound energy is a flat, smooth, surface parallel to the scanning surface and
F-224
larger in area than the beam at that range. These characteristics are not found in
corroded pipes.
♦ An eroded pipe surface with a gradual gradient over most of the length of the eroded
area is a reasonable reflector (the surfaces are nearly parallel and relatively smooth). An
ultrasonic probe placed anywhere in the eroded region is therefore likely to give a
reasonable echo amplitude. Reasonable measurement accuracy can be expected as long
as the beam circumference is smaller than the eroded area. Drury (1996) showed that in
most cases corrosion measurements are accurate to within 0.5mm. If, however, the
erosion is uneven and with corrosion pits the accuracy is limited. Corrosion pits can
have a variety of shapes, but may be generalized into two forms, lake type and cone
type (Drury, 1996).
Figure F-14. Types of Corrosion Pits.
♦ In lake type pitting the major part of the reflecting target is relatively parallel to the
scanning surface and will give adequate echo amplitude, provided the ultrasonic probe
is placed over the "flat" region.
♦ Cone type pits are the most difficult to detect as the major reflecting surfaces are not
favorably orientated, the surfaces are rough and often ridged, and the target area is often
small in relation to the beam cross section. The latter is true particularly of the base of
the pit. For this reason cone type pits are the least likely to be detected and have the
greatest inherent inaccuracy in their measurement.
♦ The likelihood of detecting corrosion pitting using the ultrasonic method is dependent
on many factors. Until recently, it was common practice to use spot checks on a grid
pattern. Area scanning is however now preferred and can be applied manually using
contact scanning or via automated scanning.
♦ As noted above, the reflecting surface that is offered by typical corrosion pitting is
often poor for ultrasonic purposes and the operator needs to be able to see the character
of the signal to avoid errors. For this reason simple digital thickness meters are not
suitable for corrosion detection. Equipment with an A-Scan presentation is preferred
and this can be complimented by B-Scan (through wall view) and C-Scan (plan view
image) facilities.
♦ The curved outer surface of pipe causes the incident ultrasonic beam to diverge. The
effect becomes more severe as the diameter of the pipe decreases. The effect is
overcome by making the circumferential dimension of the beam focus on the surface of
the test material small compared with the diameter of the pipe being inspected. For this
reason, probes with small beam focus are more suited for small diameter pipe.
F77.5 Advantages
♦ Probes are available in a wide range of sizes, measurement accuracies and costs.
♦ Simple to use. User manuals supplied with instruments sufficient for operator training.
♦ The external units can be used without supply interruption.
♦ Wall thickness reductions detected with a reasonable degree of accuracy.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-225
F77.6 Limitations
♦ Inspection requires pipe cleaning prior to inspection to remove material, which would
affect the readings. For internal inspection, the pipe has to be off-line and dry as
inspection units are generally not waterproof.
♦ If the pipe is inspected from the inside, care needs to be taken because the surface of the
specimen (concave rather than convex) will make the beam converge rather than
diverge.
Table F-79. Summary Ultrasonic Measurements; Discrete.
Technical
selection
Criteria
Assets covered
Material type
Service Area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Technical
suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Utility technical
capacity
Asset management sophistication required
Skills required (level of tool sophistication);
useability
Technology required (level of tool sophistication)
Documentation
Economic factors
Availability of technical support
Cost per inspection
Resource requirements
F-226
Assessment
Pipes, tanks, etc.
Iron and steel.
Waste and potable water.
Direct contact with asset wall required. Pipe
surface must be clean. The asset surface may
also require shot blasting abrading to provide a
smooth surface.
Poor coupling on excessively pitted surfaces
can cause inaccuracies.
Internal tools: generally limited to pipes 250 mm
and greater. External tools: no limit, but small
diameter pipes require probes with small
footprint to minimize curve effect.
Discrete.
Non-destructive. External tool require exposure
of pipe surface. Internal tool requires access by
cut-ins or other methods.
External tool does not require interruption.
Internal tool application requires pipe to be offline.
Wall thickness or corrosion pit depths in iron
and steel pipes.
Stand alone.
Commercialized, availability widespread.
Widespread commercial use of the UT probes
reported in literature and trade journals.
Quantitative.
Validation possible only by comparison with
manual/direct measurements. Calibration of tool
against reference samples required.
Generic approach.
Tool operation typically by a trained technician.
User manual sufficient for operator training.
Specialized equipment and dedicated computer.
software.
Tool principles and description of reports
generated by tool will be available
Service provided by special operator.
Variable. Staff time will be the highest cost.
Equipment cost US$1,000-10,000.
Typically one person to carry out test, but pipe
must be excavated.
F77.7 Bibliography
1. Drury, J.C. Corrosion monitoring and thickness measurements – what are we wrong?, IIR
Bulk Liquid Storage Tank Conference London 22nd /23rd January 1996, accessed at:
http://www.silverwinguk.com/en/technical%20pdfs/ultrasonics_corrosion_pitting.pdf.
49H
2. Saka, M. and Salam Akanda, M. A. Ultrasonic Measurement of the Crack Depth and the
Crack Opening Stress Intensity Factor under a No Load Condition, Journal of
Nondestructive Evaluation, Vol. 23, No. 2, pp 49-63, 2004.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-227
F78.0 UtilNets
F78.1 Overview
UtilNets is a prototype software-based decision-support system intended to help
manage the preventative maintenance of water distribution assets. It performs current condition
assessments and reliability-based life predictions for pipes, and analyzes the consequences of
maintenance decisions.
UtilNets uses a GIS-based user interface, and results are presented as thematic maps
and tables. The tool provides a forecast on the aggregate structural, hydraulic, water quality,
and service reliability of the network, together with an assessment of the required rehabilitation
expenditures. It also provides support to rehabilitation planning by ranking each pipe segment
in the whole network on a basis of its need for rehabilitation.
Currently, the software is in a prototype phase and can only be used in the assessment
of cast-iron water mains.
F78.2 Main Principles
UtilNets is based on physical models of asset degradation. The life expectancy of pipe
segments is determined based on known asset performance data and the permanent, seasonal
and variable loads to which a pipe segment is subjected. This life expectancy is then used in
conjunction with budgetary figures for the prioritisation of asset rehabilitation measures such
as lining or replacement. While still in the prototype phase UtilNets has been implemented for
cast-iron water pipes, it is extendable to other pipe materials, and includes the following:
♦ Probabilistic models that give a measurement of the likelihood of structural, hydraulic,
water quality and service failure of pipe segments over the next several years.
♦ Assessment of both the quantifiable and qualitative consequences of various
rehabilitation options, including the ‘do nothing’ option, over time.
♦ Selection of the optimal rehabilitation policy for each failed pipe segment.
♦ An aggregate structural, hydraulic, water quality and service profile of the network
together with an assessment of the required rehabilitation expenditures.
♦ An assessment of network reliability in terms of demand point connectivity and flow
adequacy.
UtilNets optimizes the individual rehabilitation policy for each segment and the ranking
of rehabilitation within the whole network.
F78.3 Application
The software is designed to facilitate maintenance management of water distribution
assets. A prototype of UtilNets has been implemented for cast-iron water pipes, but is
extendable to other pipe materials
F78.4 Practical Considerations
♦ UtilNets has been used by several European water authorities during its development,
but is not yet commercialized.
♦ Since most utilities have in general incomplete information about the state of their pipe
network, a complex Default Manager has been incorporated to yield forecasts even
F-228
where data is incomplete. Probability curves are provided to assist the Default Manager
where applicable.
♦ A data dictionary has also been prepared as part of UtilNets to assist users. The data
dictionary sets out the way in which data is held, by both type and units.
F78.5 Advantages
♦ A data dictionary has been prepared as part of UtilNets to assist the user in setting up
the system.
♦ The software comes with an import manager which can be used to import data into the
UtilNets database from a number of sources such as Oracle and Access databases, text
files and Excel.
♦ The software provides defaults that allow analysis when there are data gaps.
F78.6 Limitations
♦ UtilNets in its current prototype form is rigid, complex and requires large amounts of
data that may be unaffordable to collect and to enter on to the system. For this reason
more utilities are being involved from across Europe to help the developers in
designing the commercially available version of UtilNets.
♦ Currently only grey and ductile cast-iron water mains can be assessed.
Table F-80. Summary UtilNets.
Technical
selection
Technical
suitability
Criteria
Assets covered
Granularity
Service Area
Focus of analysis
Scalability of tool/approach
Commercialization
Previous/existing use of the tool
Utility technical
capacity
Ease of validation
Flexibility with regard to analysis (asset types) and
granularity (system, asset level)
Integration with other tools/GIS
Asset management sophistication
In-house skills required
Technology required
Documentation
Data Requirements
Linking to asset data
Availability of software and technical support
Usability
Assessment
Pipes, water pipeline infrastructure.
Sub system level.
Potable.
Reliability-based, decision-support system for
the maintenance management of pipes.
Better suited to medium to large authorities
where good asset data is available.
Currently prototype software.
Only been used by several European water
authorities during its development.
Via statistical means only.
Potable only; designed for assessment at a
segment level, utilizing a cluster of pipes.
None.
Aimed at higher level of asset management
where good asset data is available, though
defaults are provided.
Asset manager/engineer.
PC based tool. Windows based system.
Only limited documentation available.
Good quality asset data and asset failure history
data is required.
No direct link.
Only limited support available at this time.
High skill levels may be required.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-229
F78.7 Bibliography
1. Hadzilacos, T.; Kalles, D.; Preston, N.; Melbourne, P.; Camarinopoulos, L.; Eimermacher,
M.; Kallidromitis, V.; Frondistou-Yannas, S.; and Saegrov, S. UtilNets: a water mains
rehabilitation decision-support system, Computer, Environment and Urban Systems,
Volume: 24, Issue: 3, pp. 215-232, 2000.
F-230
F79.0 Valve Exercising
F79.1 Overview
The operation of valves is critical to the function of a water distribution system. In the
event of a pipe failure, valves are used to minimize the impact and to allow repair work to be
carried out. Boundary valves can also be operated in an emergency to rezone areas. As such,
valve locations should be known and operation checked intermittently, although the impact of
the disturbed flow must be considered before doing this (change in flow conditions can disturb
sediments and cause discoloration events).
Valve exercising is a non-destructive test used to ensure the function of valves by
moving them through their full range of motion. Periodic operation gives a measure of
operability, which in turn can be used as an indicator of condition. A valve exercising program
is thereby used as a means of identifying faulty or broken valves needing replacement.
F79.2 Main Principles
Valve exercising is generally performed as a program where all valves in a network are
assessed. A valve exercising program consists of four main components; 1) locating the valve,
2) exercising the valve, 3) maintaining up-to-date records for each valve and 4) scheduling
repairs as required.
When conducting a valve exercising program, each valve should be operated through a
full cycle and returned to its original position on a regular basis. The time frame can vary
between authorities, depending on local experience, but should be often enough to prevent a
build-up of corrosion products and any other deposits that could render the valve inoperable or
prevent full closing. The time interval between valve exercising for more critical valves should
be shorter than for other less important valves.
When conducting the program, a detailed record of valves should be maintained
including the number of turns required to close or open the valve, torque required to operate
valve (if possible), valve location, valve condition, maintenance required etc. This data should
be compared with previous records to identify any changes to valve operation.
If when exercising valves the action is tight (requires more torque than previously), the
operation should be repeated until the opening and closing actions are smooth and free.
Equipment is now widely available to operate valves reducing the effort required by operators.
F79.3 Application
Valve exercising is conducted in order to maintain an up-to-date record of valve
condition, schedule repair work as required and to extend valve life through preventative
maintenance. The following documents provide guidance on valve exercising:
♦ ANSI/AWWA G200-04, Distribution Systems Operation and Management, American
Water Works Association
♦ AWWA Manual M44 Distribution Valves, American Water Works Association
F79.4 Practical Considerations
♦ Equipment is now widely available to operate valves reducing the effort required by
operators, reducing back problems and improving the efficiency of operation.
♦ A program of flushing may be undertaken first in an attempt to minimize the risk of
water quality issues associated with changed flow conditions when valves are operated.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-231
♦ The torque used to operate a valve should be the lowest required. This torque should be
maintained throughout as too much torque on closing will mean significantly more
torque will be required to reopen the valve. Too much torque can also force the valve
and a higher percentage of broken valves will result.
F79.5 Advantages
♦ Valve exercising can increase the lifetime of a valve, removing build-up on the action
that can prevent operation.
♦ Allows valves requiring repair to be identified.
F79.6 Limitations
♦ Cost of introducing the program may seem prohibitive to some authorities.
♦ Changed flow conditions could result in disturbance of sediments and discoloration
events.
Table F-81. Summary Valve Exercising.
Technical
selection
Technical
suitability
Utility technical
capacity
Economic factors
F-232
Criteria
Assets covered
Material type
Service Area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication);
useability
Technology required (level of tool
sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Valves.
N/A
Potable.
Valve must be accessible.
No restrictions, if the valve cannot be exercised in its
current condition then it should be repaired or
replaced.
Depends on equipment being used to operate valve.
Discrete.
Non-destructive.
Inspection can be conducted on-line.
Valve condition and operability.
N/A
Equipment for valve exercising is fully commercialized
Not used historically, but is now being undertaken.
Direct assessment of operability.
N/A
Generic approach.
Operator needs training in procedure of equipment
use and data recording.
Require specific equipment to operate valves, where
not operated by hand.
Tools and related documentation are available from
equipment suppliers.
Tool supported from equipment supplier.
Low cost.
Requires only single person, equipment to operate
valve and to record relevant data.
F79.7 Bibliography
1. Blakely, D. Why bother with a valve exercising program, On Tap Magazine, National
Drinking Water Clearinghouse, 2004. Accessed October 2006 at:
http://www.nesc.wvu.edu/ndwc/articles/OT/WI04/valve.html.
50H
2. Hurley, L. (2005) Water Main Valve Exercising Program, Conference Proceedings of
Pipes Wagga Wagga 2005, Charles Sturt University, Wagga Wagga, N.S.W., October 1720, 2005.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-233
F80.0 Vibration Analysis
F80.1 Overview of Tool
Vibration analysis is used to monitor the condition of assets and for fault diagnosis.
Vibration is typically measured using hand-held (can be permanently positioned)
accelerometers placed on the equipment at key measurement points, with portable data
collectors and software for vibration analysis. Vibration analysis is commonly used on large
items of rotating equipment, such as turbines, centrifugal pumps, motors, gearboxes etc.
F80.2 Main Principles
All machines vibrate; over time the pattern of this vibration changes as the asset
condition changes. By measuring the displacement at different points of an asset over time
using transducers, the pattern of the vibration can be established.
The pattern of the vibration provides a great deal of information about the asset, such as
RMS level (imbalance and misalignment), shock pulse (bearing condition) and spike energy.
This information can then be analyzed using Fast Fourier Transform techniques. Once broken
down into component frequencies, patterns can be observed that relate to plant operation. An
example of this is a fan’s rotation with its resultant signature frequencies and the additional
frequency caused by an imbalance on one of the blades.
Analysis can be preformed by experience and knowledge of the equipment,
manufacturer’s guidelines, or by using proprietary software. In the example given above, the
number of fan blades and speed will directly relate to observed frequencies so allowing the
cause to be determined. A severity number can then be assigned, to act as a benchmark. The
number is chosen either by experience or the proprietary software. If the number increases,
each time the asset is tested, the condition of the asset has deteriorated. The importance of
changes will be different for differing assets. Understanding when to take action requires
experience, training, manufacturer’s guidance and Standards.
F80.3 Application
Vibration analysis can be used on any vibrating machinery, but is most commonly used
on machinery with rotating parts such as gearboxes, drive shafts, motor bearings, rotors in
electric motors, pumps and fans.
The ISO 10816-1:1995 and BS ISO 18436-2:2003: reference vibration analysis.
BS ISO 18436-2:2003 specifies the general training requirements for personnel who
perform condition monitoring and diagnostics on assets using vibration analysis. Certification
to this standard will provide recognition of the qualifications and competence of individuals to
perform machinery vibration measurements and analysis using portable and permanently
installed sensors and equipment. However, ISO certification is only necessary if a utility is ISO
certified; the Vibration Institute provides various levels of certification from technician to
expert and is generally used by most industries in the United States.
F80.4 Practical Considerations
♦ Vibration analysis is in wide use throughout manufacturing industry, using both
permanent and portable transducers. While it is relatively easy to record vibration data,
proper analysis requires experienced and trained personnel.
F-234
♦ Vibration analysis should be used as part of routine assessment to allow for developing
trends in the equipment to be identified. Vibration analysis assessments are often
carried out on a monthly basis.
♦ Vibration can be measured using a number of different types of transducers;
accelerometers, velocity transducers and displacement transducers. Accelerometers are
the most common and versatile transducers in use and the only type capable of
measuring high frequency vibration such as that produced by bearing and gear
problems. However, accelerometers have reduced accuracy at low frequencies.
♦ Repeatability is key to worthwhile comparisons. If the plant is operated at different
speeds, the frequencies generated and their amplitude may be changed. The plant must
therefore be operated in the same manner and the same load as previous samples.
During a sample the load and speed must remain constant.
♦ Block/washers are normally installed on equipment to provide a stable source for the
vibration probe and to provide repeatability of results.
F80.5 Advantages
♦ Vibration analysis is non-destructive. Portable measuring devices can be used. Assets
can remain on-line subject to repeatability issues noted above.
F80.6 Limitations
♦ Must form part of a monitoring program to allow comparison with previous results.
Table F-82. Summary Vibration Analysis.
Technical Selection
Criteria
Assets covered
Material type
Service area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Suitability
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Assessment
Rotating machinery such as gearboxes,
misalignment of couplings on drive shafts, motor
bearings, out of balance rotor in electric motors,
pumps, and fans.
N/A
Potable or wastewater.
Fixed test points required to ensure same
measuring point used.
None.
None.
Can be either. More usually discrete
measurement.
Non-destructive.
Must be on-line with same load conditions as
previous test.
Vibration.
Stand alone.
Fully developed and of the shelf.
Widely used.
Good accuracy of measurement
Alignment checks, ultrasound measurement.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-235
Utility technical
capacity
Economic factors
Criteria
Asset management sophistication required
Skills required (level of tool sophistication);
usability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Generic approach.
Requires training.
Standard PC.
Well documented. ISO 10816; ISO 18436.
Widely available.
No information.
One person no more than a few minutes per
load once test points are established.
F80.7 Bibliography
1. ISO 10816-1:1995: Mechanical vibration—Evaluation of machine vibration by
measurements on non-rotating parts—Part 1: General guidelines.
2. BS ISO 18436-2:2003: Condition monitoring and diagnostics of machines—Requirements
for training and certification of personnel.
3. Vibration School.com, http://www.vibrationschool.com/index.htm, accessed 2006.
51H
F-236
F81.0 Visual Inspection (Pipes)
F81.1 Overview
Visual inspection is a low-tech inspection method of structural condition assessment
that requires no specialized equipment and can provide a great deal of useful information about
buried assets.
Visual inspection can be carried out as an opportunistic approach to condition
assessment when assets are unearthed for operational reasons. Visual inspection is also
undertaken as a precursor to other condition assessment techniques.
After exposing the asset, visual observations should be recorded using written
descriptions, photography and/or video recordings. Exposing buried assets also allows the
quality and condition of back fill to be assessed.
F81.2 Main Principles
Visual inspection of the external surface of a buried asset requires the asset to be
exposed. Once exposed and cleaned, the condition of any external protective measure such as
PE sleeving or bitumen coating can be inspected.
The spread and pattern of any deterioration on the asset can then be assessed. This may
provide an indication of the cause of the deterioration, and the likelihood of it being more
widespread.
Unearthing the asset also allows the quality and condition of backfill to be assessed.
The quality and condition of back fill is a critical factor for polymeric pipe lifetime, and can
also strongly affect the condition of external coatings on ferrous mains. In particular:
♦ Plastic materials are subject to fracture resulting from point loading. For this reason the
presence of stones and other similar materials in the surround media should be noted.
♦ Pitting concentrated at the crown of a ferrous pipe may be caused by rocks in the
backfill damaging the external coating when the pipe was originally buried. Such
effects are likely to occur wherever the system is in rocky soils (Dorn, 1996).
F81.3 Application
This technique is used commonly onsite and should be undertaken whenever a pipe is
exposed and as a precursor to other condition assessment techniques.
F81.4 Practical Considerations
♦ Visual inspection is a widely applied approach to condition assessment and can be
applied by operators with a basic knowledge of asset deterioration.
♦ Standard inspection record forms should be used to ensure all relevant data are
collected and is available in a standard format (Dorn, 1996). Training of
maintenance/service personnel in the requirements of completing inspection forms can
increase data available for analysis.
♦ Digital photographs can be taken to provide a permanent record of points of interest.
F81.5 Advantages
♦ Physical observation can be conducted when the asset is exposed for other reasons
enabling useful information to be obtained at minimal cost.
Condition Assessment Strategies and Protocols for Water and Wastewater Utility Assets
F-237
♦ The technique is simple and requires no specialized equipment, although a camera and
welding hammer can be useful. When undertaken as an opportunistic inspection it is
low cost. Results can be used to indicate any further tests which might be useful.
F81.6 Limitations
♦ Results are qualitative only; depending on operator experience and detail included in
inspection reports. Results are also limited to the section observed.
Table F-83. Summary Visual Inspection (pipes).
Technical
selection
Technical
suitability
Utility technical
capacity
Economic factors
Criteria
Assets covered
Material type
Service Area
Access requirements
Limitations relating to asset condition
Limitations relating to asset size/geometry
Continuous/discrete
Destructive/non destructive
Interruption to supply/function
Assessment parameters
Integration with software tools
Commercialization of tool
Previous/existing use of the tool in sector
Accuracy/reliability
Ease of validation of results
Asset management sophistication required
Skills required (level of tool sophistication);
useability
Technology required (level of tool sophistication)
Documentation
Availability of technical support
Cost per inspection
Resource requirements
Assessment
Pipes.
Any.
Wastewater and potable.
Physical access to the asset is required.
None.
None.
Results are discreet.
Non-destructive.
Inspection does not affect assets.
Visual condition of pipe, and quality of backfill.
None.
Framework approach.
Widespread use.
Qualitative only.
Results can be validated through other
assessment techniques.
Generic approach.
Operator training is required for consistent
results.
None.
Technique described well in literature.
Information available in literature.
Low cost.
Can be undertaken by a single person.
F81.7 Bibliography
1. Dingus, M., Haven, J. and Austin, R. Non-destructive None