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Pipeline Design & Installation
Systems
Rigid pipeline subsea tie-backs – new operational challenges
Paul Georgeson – Operations Support Manager
Wood Group Kenny
Agenda
- Overview
- Materials
- Inspection
- Monitored data
- Maintenance
and repair
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Assets
Flowlines
820 km
Pipelines
2,400 km
2013-17
2013-17
Source: Douglas Westwood
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Areas
Operational regions
- predominantly Carnarvon
basin
- expanding into:
- Browse
- Bonaparte
- possibly Canning and the
Bight
Source: Geological Survey of Queensland
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Challenges
Considerations for operations
- New depths, cold seawater, hydrates
- Scarp crossings (through, around, over)
- Pipelines passing through new regions
- Design lives > 30 years
- FLNG operating regimes
- Aggressive fluids - CO2, H2S
- High temperatures
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Scarp crossing
Temperature
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Materials
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Material selection - internals
Corrosion
- water (wet gas) + CO2 = carbonic acid (pH 3.8)
- increased temperature and pressure = increased reaction rates
Erosion
- Velocities in excess of 30 m/s
Has led to
- change of materials from carbon steel to a CRA
- chemical injection
- pH stabilisation - change nature of the produced fluid
- corrosion inhibitors - barriers via injected film formers
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Corrosion resistant alloys
Lined and clad pipe and spools, various CRA materials primarily 316L, 625, 22cr
Weld materials, can be driven by contractor experience / preference:
- 622 root, 686 fill and cap
- 625
- 309L
- 22 Cr
Design considerations:
- Qualification / historical design temperatures of CRA material
- Overmatching challenge for some nickel weld consumables at high temperature
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Material selection - externals
Hydrates
- Driving key decisions around external coatings for wet gas flowlines
- Rapid cooling -> hydrates
Wax
- Keep temperatures above wax appearance temperature
Top of line corrosion
- Prevent condensation and water drop out by keeping hot
Has led to
- Keep it hot -> insulated lines, MLPP
- Let it cool -> continuous MEG injection, MEG regeneration plants
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Inspection
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Corrosion / erosion
Operations – In-line inspection (ILI)
- confirm internal pipeline condition via in-line inspection
- work with regulators / licence requirements
- manage challenges with schedule and plant considerations
such as liquids arrival (flow assurance)
- utilise subsea corrosion / erosion monitor data and
production chemistry data to justify ILI timings
Pre operations
- sample during dewatering for water chemistry and
bacteria / biocide residuals
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Source: Rosen
Expansion
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Expansion
Planned buckle ‘design’
- DIs – displacement initiators (dumb or mechanical)
- ZRBs – zero radius bends
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Expansion
Considerations – pre start-up
- Pre start-up inspections, checking for:
- burial around touch down points
- third party interaction
- Possible interventions to remove
seabed material built up around touch
down points
- Recording details of spans either side of
DI
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Expansion
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Expansion
Operations to specify data collection
- global positional data - specifically
buckle shape (x, y, z) survey data
- seabed heights adjacent to pipe and
at set distance from top of pipe
- lateral displacement at DI
- axial movement at DI
- conditions of DI surfaces due to
movement
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Pipeline crossing DI
Expansion
Operations considerations
- global location check campaign to
campaign (drafting, GIS, cloud point
data, etc)
- compare positional data at DI to
operational conditions at the time of
survey / inspection
- run FEA models of buckle shape (x, y, z)
from survey / inspection data – check
stresses and strains
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Axial walking
Asymmetry in the expansion / contraction
Drivers:
- Temperature transient
- Seabed slope
- End tension
- Liquid hold up
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Axial walking
Operations to specify data collection
- check location of structure on
foundation - end terminations
designed to move
- check position of spool / flowline
interface flange / connector
- future intervention if required
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Axial walking
Operations
- record complete operational history of start-up / shut downs and link to
structure locations
- understand spool loads based on position of structure (and associated
connector) and location of spool / flowline connector
- model future movements to ensure they remain within design parameters
or plan for any intervention requirements
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Monitored data
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Data management
Managing data is key, especially with long design lives
Make systems as automated as possible
- Define integrity operating windows (IOWs)
- Production chemistry
- MEG system + pH stabilisation / corrosion inhibitors
- Water chemistry
- Erosion / corrosion monitoring systems
- Velocities / temperatures / pressures
Regular reporting / dash boards summarising data and asset condition
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Data collection from interventions
Data recovered from interventions
- monitoring of spans / structures / spools
- collect data for pipelines / riser motions in operations where there are fatigue
concerns
Understand met ocean conditions
- impact of currents, solitons, tides, cyclones on subsea assets
Understand influence of operations on assets
- impact of production regimes, slugging, flow rates on motions / vibrations
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Maintenance and
Repair
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Pipelines
Reaching critical mass for:
- formation of a ‘repair club’
- equipment sharing
- tool pool
Still CRA repair challenges
Storage and location of CRA and CS pipe will be important
Smaller pipelines may be as critical as the production system (4 - 8” MEG / Utility lines)
Significantly high pressures in smaller lines, worth spending time considering spares /
repairs options
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In summary..
- Number of operational challenges which are pushing industry boundaries
- Pre-start up data capture critical to understanding asset baseline condition and
-
managing future decisions
Management and analysis of inspection and monitored data will be key in early field
life, ensure all calibration work undertaken (project to ops)
Legislative framework to be managed
Longer term larger interventions will be critical and require significant planning
Challenge to industry to ensure Operators get the support and value required
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