SHIP/SHORE LNG TRANSFER : HOW TO CUT COST ?
SHIP/SHORE LNG TRANSFER˚: HOW TO CUT COST˚?
by
Bernard DUPONT EURODIM Sa,
Michael OFFREDI ITP Interpipe,
Emmanuel FLESCH GAZ DE FRANCE
Chris THOMAS and Bertrand LANQUETIN TOTALFINAELF
Abstract :
THIS PAPER WILL FIRST REVIEW THE EXISTING LNG TRANSFER SHIP/SHORE
SYSTEMS AND THE TYPICAL COST OF THESE FACILITIES.
SIGNIFICANT NOVEL IDEAS TO REDUCE THE COST OF THE TRANSFER FACILITIES
WILL BE REVIEWED.
A NEW DESIGN OF MARINE TERMINAL, CURRENTLY UNDERTAKEN BY A GROUP OF
FRENCH COMPANIES SET UP BY GAZ DE FRANCE AND TOTALFINAELF, WILL BE
UNVEILED :
- THE TRANSFER LINES ON A COSTLY TRESTLE ARE REPLACED BY NEW
CRYOGENIC SUBSEA PIPES DEVELOPED BY ITP INTERPIPE APPLYING PATENTED
TECHNOLOGY FROM HP/HT SEA LINE
- A NEW CONCEPT OF LOADING PLATFORM AND TRANSFER SYSTEM, LINKING
SUBMERGED LINE TO LNG CARRIER IS DEVELOPED BY EURODIM, TAKING
ADVANTAGE, INTER ALIA, OF THE EMERGENCE ON THE MARKET OF RELIABLE
CRYOGENIC FLEXIBLE LINES AS AN ALTERNATIVE TO CONVENTIONAL LOADING
ARMS.
OPERATIONAL AND SAFETY ASPECTS OF THE NEW SYSTEMS WILL BE DEVELOPED
AND TYPICAL COST ELEMENTS ESTABLISHED.
FINALLY, THE PROPOSED PLANS FOR FULL VALIDATION OF THE NOVEL LNG
TRANSFER FACILITIES WILL BE PRESENTED.
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TABLE OF CONTENTS
1 - SUMMARY
2 - EXISTING LNG TRANSFER FACILITIES
2-1 RECEIVING TERMINAL
2-2 LOADING FACILITIES
2-3 TYPICAL COST ELEMENTS
3 - REVIEW OF UNCONVENTIONAL SCHEMES
3-1 SUBSEA CRYOGENIC PIPE
3-2 TRANSFER SYSTEMS
4- NEW LNG TRANSFER CONCEPTS
4-1 DOUBLE WALL PIPE
OBJECTIVES OF THE SUBSEA CRYOGENIC PIPELINE
CONCEPT DEFINITION
COMPONENTS OF CRYOGENIC PIPE
DESIGN PHILOSOPHY
FABRICATION & INSTALLATION
PRECOMMISSIONING
SAFETY
REPAIR
COST ELEMENTS
ON GOING QUALIFICATION PROGRAMME
4-2 TRANSFER SYSTEM ARCHITECTURE
CONCEPT DEFINITION
DESCRIPTION OF THE COMPONENTS
DESIGN CRITERIA AND RESULTS
CONNECTING MODULE
SAFETY AND OPERATION
COST ELEMENTS
FUTURE DEVELOPMENT
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5- CHALLENGES
5-1 CONSERVATISM OF LNG BUSINESS
5-2 TARGET FOR COST REDUCTION
5-3 REGULATORY ASPECT
6- WAY FORWARD
6-1 OVERALL SAFETY ASPECT
6-2 PIPE IN PIPE SPOOL AND CRYOGENIC TEST
6-3 CONNECTING MODULE
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1 -SUMMARY
The existing LNG transfer facilities are robust and safe; over the years the safety level of loading
arms have improved but the weight and the associated cost of the jetty head facilities have increased
as well.
New receiving terminals in emerging countries have to face challenging marine conditions with
monsoon season and no natural harbour. Revamping of existing facilities is often difficult because
of poor access to new larger ships.
Existing LNG transfer facilities were designed for a high gas commodity price; emerging market
will offer lower price for gas hence the whole LNG chain cost must be reduced including the
transfer facilities.
The architecture developed by EURODIM offers a more compliant transfer system based on
cryogenic flexible available today; present development focuses on the load filtering and the
connection of the flexible to the ship manifold. EURODIM is also working on an open sea transfer
system with significant wave height up to 3.5 m.
Replacing costly trestle system by sub-sea pipe will globally reduce the cost of the LNG transfer
facilities. The cryogenic insulated Pipe developed by ITP Interpipe is based on proven weldability
of Invar pipe, Izoflex unique heat insulating characteristics as well as the proven double wall pipe
technology developed for TOTAL by ITP Interpipe (Dunbar , 1992) and then extended to further
projects such as HP/HT SHELL ETAP or ELF TCHIBELI. Feasibility studies have confirmed that
there are neither mechanical nor thermal limitations to the concept and a series of cryogenic tests on
a representative spool of Double Wall Pipe will be launched shortly at Gaz de France testing
facilities.
Full validation of both concepts will require more development work to be carried out within a
project framework
Irrespective of the unmatched quality of these two novel technologies, the project team will have to
convince the LNG community that both concepts are safe and attractive. This may take longer than
expected and this paper is the first step toward this goal.
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2 - EXISTING LNG TRANSFER FACILITIES
LNG transfer facilities are as old as the LNG business with currently some 15 LNG Plants and circa
38 receiving terminals in operation; around 70 LNG transfer facilities are in service world-wide and
this number is expected to grow yearly by a couple of units.
Except for two receiving terminals (COVE POINT in the US and the new OGISHIMA terminal in
JAPAN) the transfer arms are linked to the shore by a trestle or a causeway.
The storage tanks and the transfer facilities for Cove Point and new OGISHIMA are connected via
an underground tunnel.
We will give a brief description of the conventional transfer systems, which comprises two distinct
sub-systems:
- The transfer arms and ship berthing and mooring facilities
- The connection between the tank farm and the jetty head
The following captures the main functionality of the two sub-systems.
2.1 RECEIVING TERMINAL
The transfer facilities usually feature :
- A jetty head with berthing and mooring dolphins associated to a platform equipped with gangway
and loading arms; several process items are also located on this platform (filters, manifolds, drain
drum ). Fire protection equipment (foam, dry powder and firewater) provides adequate safety
coverage. A control booth overlooks the transfer platform. Additionally utilities can be provided to
the Ship.
- Dolphins : 4 berthing dolphins and 6 mooring dolphins are usually required; all the mooring
arrangement is designed in accordance with the acceptable drift of the Loading Arms (usually 3.5 m
fore/aft).
- Loading arms (2 to 4 liquids and 1 vapour) are required to unload the gas carrier at a rate between
3000 to 12000 m3/h. The size of the loading arms are typically 12/16 inch. Most of the loading
arms are fitted with an Emergency Disconnection system.
It should be noted that over time the sophistication of the transfer arms has increased and the safety
level has steadily improved with only a few serious incidents to report.
- The unloading facilities are equipped with filters to avoid contamination of the storage tanks by
undesirable material. All transfer equipment can be drained into a vessel where LNG is either
vented or pumped back to the unloading lines.
- Fire fighting systems include high expansion foam monitors over a spill basin which recovers
LNG spillage; dry powder fire extinguishers and fire water monitors complement the fire protection
hardware.
- Monitoring of the ship berthing and operation of gangway and loading arms is done from a
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technical room. All ship/shore interface electronic equipment is located in this building.
- Nitrogen or inert gas is required for commissioning and decommissioning of the loading arms.
Additional utilities can be provided by the shore to the ship such as bunker, diesel oil, fresh water,
liquid nitrogen
- A connecting trestle (or causeway) supports all necessary pipes (process and utilities) along with
electric and instrument cables. The trestle supports also a maintenance road. The average length
between the storage area and the transfer facilities for the receiving terminals is around 500 meters
but can be much longer when no natural harbour is available.
-
Process pipes
The size of unloading pipes is around 24/30 inches to match the LNG carrier cargo pump
head ,the elevation of the Storage Tanks and the design flowrate set by the duration of the
unloading operation.
Usually two pipes of the same size are used in parallel during unloading operation and in
series to keep the pipe cold in holding mode.
The Vapour displaced in the shore tanks can be returned to the ship by a dedicated line.
-
Utilities Pipes
Firewater, nitrogen, compressed air complemented by bunker, diesel oil, and fresh water as
required.
-
Maintenance Road
This maintenance road is designed to carry fire truck and maintenance crane necessary to
service the loading arms and other equipment.
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2.2 LNG PLANT LOADING FACILITIES
The description of the LNG loading facilities is very much the same as the unloading facilities
described above.
The platform accommodates larger drain drum designed for the surge protection of equipment at the
Jetty Head.
The longest connection between the tank farm and the jetty head is around 6 km for the LNG Plant.
Because the relative cost of marine facilities is lower for the LNG Plant than for a LNG receiving
terminal, the siteing of LNG plant doesn t always minimise the cost of the transfer facilities.
Unlike the receiving terminals the vapour displaced during loading operation is often flared due to
jetty length and poor economic incentive to recover marginal flared gas.
Figure 2.2 pictures an artistic view of BONTANG 3rd dock.
Figure 2.2 BONTANG 3rd LNG/LPG DOCK
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2.3 TYPICAL COST ELEMENTS
Although there are differences from one project to another in terms of sizing and cost of LNG
transfer facilities, our project has retained the following estimation for reference:
Berthing and
mooring
Jetty head
Trestle
Pipes/ cables
ESTIMATE
($/99)
15 M$
20 M$
15 M$/1000
meter
13 M$/1000
meter
The above in-house estimates for overall project are based on typical productivity and manpower
rates for emerging countries.
3 - REVIEW OF UNCONVENTIONAL SCHEMES
3.1
SUB SEA CRYOGENIC PIPE
Sub-sea cryogenic pipe is not in itself a novel idea; but the current project applies un-common new
design features.
Since the very early days of the LNG industry, cryogenic pipelines have been one of the subject of
choice in world wide conference [1][2][3][4][5]. Subsea cryogenic pipelines have been also
described in some details [6],[7],[10].
The main problems associated with submarine cryogenic pipes are :
- material of construction should be resistant to low temperature;
- shrinkage of the pipe should be accommodated;
- insulation system highly effective thermally, water tight and strong to permit handling;
- fail-safe system i.e. the line should remain operational in case of local damage.
Several solutions have been proposed, out of which the most significant are:
- retrained / pre-strained double pipe system [6] recommending the fabrication of pre-strained
section of pipe with the limit of non-uniform prestrain along the length of the pipe. SHELL tested at
cryogenic temperature sections of pre-strained pipe.
- Modular sections [7] wherein multiple LNG pipe sections utilising expansion joints to
compensate for contraction are connected together by braces to form an integral frame, including
pressure vessels enclosing the expansion joints to permit access for inspection and maintenance .
Patent drawing is shown below (figure 3.1) :
- Concentrical LNG pipe-in pipe with a main transfer conduit and a return conduit both positioned
within an outer jacket [10].
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Figure 3.1 US PATENT 4,826,354 general principle
None of these systems have been applied in projects.
Among current development effort, a company proposing a Poly Urethane Light Foam System
have been working for some time on a cryogenic pipeline that could well be used offshore. Fullscale cycle test at cryogenic temperature have been successfully conducted by this company.
The patented novel cryogenic sub-marine pipe as developed by ITP InTerPipe differs from the
above systems by the following features:
-
Double Wall Pipe technology currently used on sub-sea HP/HT projects.
Internal pipe in INVAR with no loops or expansion joints.
Best insulating material IZOFLEX thus reducing the size of the external pipe.
Continuous annular.
External pipe to handle massive external aggression.
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3.2
LNG TRANSFER SYSTEMS
A number of R&D programs have been launched to develop un-conventional LNG transfer system.
In the past, TOTAL has been associated in the CHAGAL program [8]. This project was based on
the development of a cryogenic Single Point Mooring, which required sub-sea flow lines and
PLEM, flexible hoses and a cryogenic swivel to be designed and tested.
8 cryogenic flexible was designed and tested by COFLEXIP. Patents for the cryogenic 16-inch
swivel initiated by EMH were taken over by SBM. As yet, no LNG transfer project has been based
on this concept.
More recently however, COFLEXIP STENA OFFSHORE has promoted a JIP for the development
of a 16 NPS cryogenic flexible to be used for offshore LNG transfer.
Offshore LNG transfer has prompted also extensive R&D programs by FMC (Boom To Tanker),
SBM (single offloading arm) and STATOIL(Offshore Cryogenic Loading System).
While offshore development of LNG Plant on barge or FPSO remains still prospective, several
LNG terminals in emerging countries are at various design stages and are expected to come to
fruition in the near future, probably sooner than LNG offshore transfer from FPSO to LNG carrier.
Hence the approach of our group to appraise if technology developed for the far future (in our case
large cryogenic flexible) could be used to reduce the cost of our current projects.
The architecture as developed by EURODIM is based on existing cryogenic flexibles already tested
or being tested by the industry.
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4- NEW LNG TRANSFER CONCEPTS
Although the novel systems presented in this paper could apply to both export terminals and
receiving terminals, our effort has focused more on receiving terminal because there are currently
more receiving terminals at project phases within the portfolios of the sponsors of this research
program.
Our work has been based on a receiving terminal without vapor return for sake of simplicity. It
should be noted that a vapor return line could be added using the same concepts ;moreover
unloading an LNG carrier without vapor return has been safely achieved in the past and would
require only minor modification to existing LNG carriers re-gasification facilities.
4.1 DOUBLE WALL PIPE
4.1.1 OBJECTIVES OF THE SUBSEA CRYOGENIC PIPELINE
The sub-sea cryogenic pipeline provides the LNG connection between the offloading platform and
the onshore storage facility.
The main criteria that led to the final design for this sub-sea system are the following :
- cost reduction. Operators shall consider the new architecture of interest only if significant cost
savings are associated with it by comparison with the conventional scheme.
- Simple and robust design. With respect to operators requirements, the selected design must
avoid as much as possible complex devices or high technology components which increase the
OPEX (maintenance costs) and the risk of failure of the system. Concepts such as underwater
tunnels or sub-sea expansion loops/ expansion joints were not considered.
- High thermal performances. Due to the length of line targeted by the project (more than 1
mile; typically 3 miles), the heat transfers between the transport pipe and sea environment have to
be reduced as much as possible. The thermal performances of ITP insulated systems with IZOFLEX
material were recently confirmed by full scale thermal tests carried out in Houston by a JIP led by
TEXACO associated with BPAmoco, ExxonMobil and TotalFinaElf.
-
Reliability and safety of the system, during installation and in operation.
4-1-2
CONCEPT DEFINITION
To meet the various requirements listed above, the project team selected a design based on the
Double Wall Pipe technology developed by ITP InTerPipe and already in operation for the
transportation of hot effluent.
ITP double wall pipeline technology consists of two coaxial pipes: an inner pipe is inserted within
an outer pipe and both pipes are linked at their ends. The sealed annular space between the pipes
allows to implement high performance insulation material that reduce significantly the heat transfer
between inner pipe, containing LNG and outer pipe in contact with the seawater.
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The ITP system provides the following main benefits to the project:
-
Capex and Opex reduction;
Safe and simple design for a reduced failure risk;
Environmental friendliness (sub-sea installation);
High insulation capacity to reduce heat ingress.
4-1-3
COMPONENTS OF CRYOGENIC PIPE
The double wall pipe developed by ITP includes:
- Inner pipe
The inner pipe is made of a Nickel alloy with 36% of Ni, commercially named INVAR or Pernifer
36. Because of its very low expansion coefficient, the thermal stresses and strains resulting from the
temperature difference are maintained low (approx. 10 times smaller than stainless steel material).
Combined with its high mechanical strength, high tenacity and good welding properties, the
INVAR material simplifies the design and fabrication of the system. Indeed, there is no need of
artificial expansion device due to the thermal or mechanical length variation.
- Insulation material : IZOFLEX
The selected insulation is the Izoflex, a material developed, patented by ITP and already
implemented to insulate several hot effluent pipeline including pipe with significant temperature
difference between transported multiphase product and outside environment.
TYPICAL CRYOGENIC DOUBLE WALL PIPELINE
CONCRETE
LAYER
TM
IZOFLEX
INSULATION 100 MM
OUTER PIPE :
CARBON STEEL
48 /20.6 mm
INNER PIPE :
INVAR
36 / 6 MM
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The high thermal insulation properties of the IZOFLEX enables to design a high thermal
performance double wall pipeline within a reduced annular. The thickness of IZOFLEX to be used
is four times smaller than the one that would have been necessary with Poly Isocyanate Resin (PIR)
insulation for equivalent thermal performances. The resulting compact system contributes to costs
savings.
Mechanical testing in cryogenic environment carried out during the design phase of the project
confirmed the suitability of the material for LNG transport application.
The good mechanical behaviour at any temperature combined with a limited shrinkage effect at low
temperatures and a good annular filling ensures the concentricity of the inner and outer pipes. No
annular spacers are required. Due to the fabrication procedure and insulation material installation
process, thermal-bridging effect along the overall pipeline is reduced to a minimum and overall
thermal performance is optimised.
- Outer pipe
The outer pipe is made of regular carbon steel. This material is designed to protect the internal pipe
& the insulation system. The high weight increases the sub-sea stability of the line. The low cost of
the material contributes to the Capex reduction.
- Concrete
A concrete layer is added for additional protection and pipe stability.
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4-1-4
DESIGN PHILOSOPHY
The pipe system has been designed to withstand:
-
the loads induced by the installation process (string weight and associated tension, hydrostatic
pressure, temperature variations );
the loads in operation (thermal loads, internal and external pressures and differential pressures,
seabed stability, fatigue ) during the life of the pipe.
These various criteria have been reviewed in accordance with the main codes and standards for
refrigeration and sub-sea pipelines. Basically, the inner pipe and the insulation material reduce the
impact of the temperature variations and the outer pipe ensures the integrity of the system. The
continuous annulus all the way through the line allows the placement of additional control devices.
Pressure and temperature control gauges and secondary annular protection increase the safety of the
system and allow the operator to control the system at any time.
4-1-5
FABRICATION & INSTALLATION
A specific fabrication process has been developed for the cryogenic double wall pipeline. This
sequence is driven by the installation procedure based on the towing method.
The fabrication sequence is divided into several fabrication steps. A first step is the pre-assembly of
insulated units (6 or 12 meters long). These pieces are welded together to produce 250 m long
strings or longer.
Once the strings are ready, they are welded onshore before being pulled by suitably adapted means
up to the appropriate location. A double wall insulated riser provides the connection between the
sub-sea pipe and the offloading platform at one end. At the other end, an onshore connecting pipe
will be tied up to the manifold of the storage tanks.
Up to 5000-m long double wall pipeline lay boats or heavy lift crane barge (bottom towing method)
might pull system from the shore to its final position on the seabed.
4-1-6
PRECOMMISSIONING
In order to control the mechanical integrity of the Double Wall Pipe strings, pneumatic testing is
carried out on welded strings before starting the installation.
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4-1-7
SAFETY
Safety issues, as for every new LNG technology, have been particularly addressed. The major
safety issues for the sub-sea cryogenic double wall pipeline are related to a failure of the
containment systems.
-
Water ingress (failure of external pipe):
The risk of occurrence of such an event is reduced to an acceptable level, thanks to proper design of
the pipe external protection (trenching, concrete protection).
Water ingress is monitored by continuous analysis of the annular space normally operating under
reduced pressure; in case of external pipe failure, a large water ingress can be prevented by
pressurisation of the annular space with air.
-
LNG egress (failure of the internal pipe):
Similarly LNG leaks will be detectable by continuous monitoring of the temperature in the annular
space and minor leaks can be reduced by back pressurisation of the annular space by fuel gas while
the system is safely decommissioned for repair.
4-1-8
REPAIR
Various scenarii are considered for repair in case of accidental pipe failure:
- Sub-sea repair, in dry atmosphere in shallow water depth
- Surface repair after pipe recovery by a lifting barge when a section of the pipe needs replacement.
Repair procedure takes into account the corrosive behaviour of sea water on Invar piping.
4-1-9
COST ELEMENTS
For a 2 x 36 inch, our internal evaluation is around 13 000 $/m as direct cost and around 8500 $/m
for a 2 x 30 inch configuration.
4-1-10 ON GOING QUALIFICATION PROGRAMME
The next step of our development program is the fabrication and testing of a full-scale double wall
pipeline sample. The scope of work includes notably the review of the fabrication process, analysis
of component behaviour during LNG circulation, confirmation of the thermal performances of the
system.
Testing will be done at Gaz de France cryogenic premises at NANTES.
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4-2 TRANSFER SYSTEM ARCHITECTURE
4-2-1 CONCEPT DEFINITION
The architecture and system proposed by EURODIM is based on an equipment that has been
successfully tested or are currently being tested such as cryogenic flexibles lines from M/S
COFLEXIP or M/S COMPOFLEX.
The flexibles lines with their supporting infrastructure are significantly lighter as compared to
traditional articulated arms.
Additionally maintenance of the flexibles and other process items doesn t require a large crane.
Both aspects reduce the overall dimensions and the cost of the transfer facilities.
4-2-2 DESCRIPTION OF THE COMPONENTS
The transfer facilities main components are:
-
-
-
A two level platform with a technical room, a drain drum, compressed air and nitrogen reserves and
a boat landing with utilities connections at the cellar deck; On the main deck, manifolds, filters and
pipes connecting the cryogenic sealines to the flexibles.
A structure supporting in stand-by mode all the flexibles lines and the associated connecting
modules stored separately; a light lifting crane is designed to handle efficiently all connectors and
flexible lines.
Gangway and fire water monitors are located on the same structures
Typical berthing and mooring dolphins as required for the traditional transfer facilities
Firewater connections are located on the closest mooring dolphins.
Figure 4.2.1 pictures a simplified view of the new transfer system for a Receiving Terminal.
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FIG. 4.2.1 NOVEL TRANSFER SYSTEM ARTISTIC VIEW
4-2-3 DESIGN CRITERIA AND RESULTS
For the LNG transfer system and architecture, our group has focused on a Receiving Terminal for
standard LNG carriers ranging from 70 000 m3 to 135 000 m3.
The LNG unloading rate considered is 10 000 m3/hour.
As for the present terminals, the berthing site is considered as relatively sheltered (in the first phase
of development) and loading/mooring environment corresponds to significant wave heights of 1.5
to 2 meters. In these conditions, the safe operating envelope of movements of the ship manifold axis
during loading is typically 11 meters fore/aft, 6 meters transversally and 8 meters vertically.
In order to achieve our objective to reduce cost while maintaining or even improving the safety
level of the new transfer system, we have taken a very conservative stand for the working
conditions of the flexible lines.
The newly developed large size cryogenic flexible hoses coming to the market are somewhat
’overdone’ for the present application — since they are designed and built to permit offshore LNG
transfer (from FPSO to LNG carrier) in sea states of some 5 meters significant wave.
Notably we have based the conceptual design and architecture on a minimal bending radius of 10
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meters for the catenary suspended cryogenic lines. The catenary suspension of the cryogenic hose
has been chosen because it is ideal in order to keep excellent internal working conditions in the
flexible even in the case of large 3-D motions of the offshore transfer.
The flow rate of 10 000 m3/hour requires 3 x 16" diameter lines for a length of 45 meters each. We
have developed a system able to cope with 3 to 4 x 16" diameter lines (possibility to include one
spare flexible) or even with 20" diameter flexible lines, should it be interesting economically.
With regards to safety, the transfer system design also integrates the mandatory requirement of a
safe and reliable emergency disconnection system for the LNG lines.
The reliability and simplicity of the system for normal operations such as connection/disconnection
and storage are also participating to the safety of the concept, for which user friendliness has been a
governing design factor.
This, combined with the very limited acceptable load on the flanges of the ship manifold, has led to
a design based on a flexible line attached at one end to the fixed platform and on the other end on a
Multi-function Cryogenic Connection Module (MCCM) , interfacing the ship manifold flange and
flexible line mobile extremity, which serves all the complex functions of the transfer system.
4-2-4
CONNECTING MODULE
Thus, for each flexible, the Multi-function Cryogenic Connection Module (patent pending) has the
following functions:
-
-
Normal connection (flexible hot);
Filtering of the stresses induced by the physical motions and the loads induced by the flexible
line at cryogenic temperature in order to cope with the limited stress permissible at the ship
manifold flanges;
Normal disconnection (flexible cold);
Emergency closure of the valves;
Emergency disconnection of the flexible assembly from the ship manifold.
This conceptual approach concentrating all the complex mechanical functionalities of the transfer
system in a modular unit which can be loaded, with the system integrated crane, onto a supply
vessel for possible inspection/maintenance, is an additional attractive point serving reliability and
consequently system availability and safety. The flexible line, is nicely suspended in catenary
configuration out of reach of any ’aggression’ in all conditions, i.e. storage or fluid transfer and is
not very sensitive to wind loads.
Our analyses confirm that the new transfer system developed is technically feasible and economical.
Notably loads and cyclic movements imposed to the flexible lines are acceptable for the various
existing technologies of cryogenic flexible hoses (one manufacturer has confirmed in depth our
analyses) and the loads induced by the flexible lines movements and loads are acceptable for
standard Emergency Release Couplers and/or Quick Connect Disconnect Couplers. Further, it
should be noted that thanks to the flexible lines configuration, sophisticated and costly LNG swivel
joints can be saved and the system is ideally pure and simple.
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4-2-5
SAFETY AND OPERATION
The main safety requirements of the new system are comparable to the safety requirement of the
traditional articulated arm as in fact in both cases the major risk occurrence is located in the area of
ship manifold at the level of the connectors.
In addition, one should note the extreme ’comfort’ in which the flexible hoses are working thanks to
:
a) Benign environment.
b) There is a great margin in the utilization ratio of the flexible lines as the maximum movement
envelope considered is based on acceptable cyclic loading criteria.
An accidental excursion out of the working envelope will not lead to an alteration of the flexible
hose (such as for instance the yield stress of the stainless steel liner). Only minor leakage can be
expected in case of major incident. Naturally available cascade margins of multiple layers flexible
pipe with regard to acceptable ship movement are an interesting feature of the solution.
Further, all transfer flexible lines can be disconnected at once in case of emergency (in case of ship
movements risking to overstretch flexible lines).
Commissioning and decommissioning of the flexibles will follow the standard practices outlined by
the SIGTTO for the articulated arm; in particular, the flexibles shall be self-drainable and shall be
inerted. Cool-down procedures relevant for cryogenic flexible lines shall be developed.
Between two consecutive cargo transfer, all operations to achieve the optimum readiness for the
next loading (basic maintenance and supply of utilities) will be done with a support vessel berthed
at the main transfer platform.
During LNG transfer operation, the supply vessel will be moored at a mooring dolphin for fire
water supply and readiness to evacuate personnel in case of emergency.
Major maintenance activities such as replacement of flexible will be done by simple winching and
only a basic working barge or supply vessel is required for these operations.
In terms of operation, the proposed facilities have the same functionality that the base case; in our
estimation of the OPEX, we have included an additional supply boat, a contract for diving services
on subsea lines and regular replacement for re-certification of the transfer flexibles.
As for the Safety aspect, all the criteria of traditional transfer facilities are met or exceeded.
4-2-6
COST ELEMENTS
Cost reduction for the transfer facilities have been estimated at some 5 M$ in terms of direct cost.
The lower cost of the flexibles versus articulated arms and the simpler transfer platform both
participate equally to this cost reduction.
Further studies on the simplification of the berthing and mooring pattern to fully use all the
potential of the flexibles in terms of drifting should further reduce the cost of the transfer facility.
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4-2-7
FUTURE DEVELOPMENT
The current efforts to develop this novel transfer system focus on:
-
-
finalisation of the MCCM and industrialisation with manufacturers of cryogenic equipment;
modification of the berthing pattern in order to fully utilise the potential of the flexibles with a
direct objective to reduce the cost associated with the dolphin arrangement in a traditional
terminal;
research and screening of more compliant transfer systems to match near shore open sea
conditions up to Hs = 3,5 m (see fig 4.2.7).
Fig 4.2.7 COMPLIANT LNG LOADING SYSTEM
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5- CHALLENGES
5.1 CONSERVATISM OF LNG BUSINESS
Traditionally, the LNG business has been very conservative but, by the end of the last decade, novel
designs have been applied to cope with the necessary cost reduction to increase LNG market share.
Introduction of large single shaft gas turbine driving refrigeration compressor can be regarded in
many respects as more challenging than a sub-marine cryogenic pipe and/or a transfer system based
on cryogenic flexibles.
Constant pressure for cost reduction pushes all operators to select innovative design.
5.2 TARGET FOR COST REDUCTION and IMPACT ON THE LNG PRICE
Clearly for a grass roots LNG Plant, the target of cost reduction when applying both concepts would
be at best a couple of percent of the overall project cost. Cryogenic sub sea pipe offers a large
choice for the location of additional LNG berths in the case of expansion projects.
For a receiving facility, the cost reduction can be in the range 10-15% of the project cost when a
breakwater and/or major dredging is mandatory.
Altogether, the cost reduction in terms of saleable LNG in the range of 3/5 cents/Mmbtu is modest
but more cost reduction can be expected if the siteing of the LNG receiving facilities is optimised
with regards to the location of large existing consumers (reduced interconnecting cost to bring the
gas to the market).
5.3 REGULATORY ASPECT
For the Double Wall Pipe, governmental agencies will challenge the safety aspect of the sub-sea
LNG pipe and the effect of a plausible loss of containment. Specific programs to address this issue
are currently under development.
For the transfer facilities, the use of flexible is not forbidden but their use is currently limited to
very specific applications such as emergency transfer of cryogenic cargo. Hoses have been
traditionally compared to articulated arms and papers presented at SIGTTO panel [9] have
advocated that hose operations are less risky than hard-arms or at least not more risky.
Indeed, the use of large bore hoses is limited because of the uneasy operation of the flexible
compared to balanced hard arms. In our project, a specific architecture with manipulating crane will
be used for all the operation related to connection / disconnection.
Thus, the issues raised in the codes and procedures can be successfully addressed by our proposed
system but full recognition of both novel concepts by regulatory/government agencies is expected
to require some time.
6- WAY FORWARD
In order to get wider acceptance, additional work is required.
6-1 OVERALL SAFETY ASPECT
Both concepts must be carefully designed and detailed Quantitative Risk Assessment study is prerequisite prior to the full endorsement of the concepts by operators.
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6-2 DOUBLE WALL PIPE SPOOL AND CRYOGENIC TEST
A spool of Double Wall Pipe will be fabricated by ITP Interpipe and tested at GAZ de FRANCE
cryogenic test premises; detailed procedures for fabrication and installation will also be developed
to better assess the cost of installed pipe.
6-3 CONNECTING MODULE
A detailed design of the connecting module based on full scale simulation and typical lay-out of
LNG carriers manifolds will be carried out shortly. This will confirm the feasibility of the
connecting module for all operating scenarios.
The partners with a specialised manufacturer will develop a detailed mechanical design for the
module and confirm cost estimation.
ACKNOWLEDGMENT : this project is partly funded by the French Ministry of Industry.
REFERENCES:
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
LNG PIPELINES by P Herv Air Liquide LNG 1 1968 Paper 29b
LIQUEFIED NATURAL GAS MAINS by O Ivan TZOV LN2 1970 Paper 3.7
TECHNICAL FEASIBILITY AND COST OF LNG PIPES by TE Hoover LNG 2 1970 Paper 3.8
PIPELINE AND GAS JOURNAL , June 1975
LES PIPELINES CRYOGENIQUES by Mr Mialon PETROLE & TECHNIQUES May 1984
A SUBMARINE OFFSHORE LOADING LINE FOR LNG by CWN Veeling (SHELL) LNG 3
paper II-8 1972
US PATENT 4,826,354 dated May 2sd 1989 UNDERWATER CRYOGENIC PIPELINE SYSTEM
Inventor A Adorjan EXXON.
OFFSHORE LOADING SYSTEMS FOR LIQUEFIED GAS by P Branchereau EMH LNG 8 Paper
IV-7 1986.
HARD ARMS versus HOSES SIGTTO PANEL 29/07/93;
US PATENT 6,012,292 dated Jan,11,2000 by Alan SILVERMAN (MOBIL).
CONTACTS
For more details on the project, please contact :
- double pipe wall for [email protected]
- transfer system : [email protected]
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