GTT Pluto II Subsea Cryogenic Pipeline

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Sheryl Franklin
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GTT Pluto II Subsea Cryogenic Pipeline Approved by As the market is growing continuously, elements of the value chain have to adapt constantly to new needs.

Cryogenic sub sea pipeline offers an opportunity to built terminals in those areas: environmental impact is reduced to a minimum, unloading platform can be moved away from shore line to reach a

1 GTT Pluto II Subsea Cryogenic Pipeline Approved by As the market is growing continuously, elements of the value chain have to adapt constantly to new needs. Some new import and export terminals have to be built near populated areas or have to accommodate with bad soil conditions. Cryogenic sub sea pipeline offers an opportunity to built terminals in those areas: environmental impact is reduced to a minimum, unloading platform can be moved away from shore line to reach a sufficient water depth; pipeline can be laid on a wide range of soil offering a cheaper solution than complex trestles. As pipeline statistics show that accident can always occur, GTT developed a double containment pipeline offering the very high level of safety needed for service during 30 years or more without maintenance. The design philosophy is inspired both by traditional pipeline codes which tends to eliminate very improbable failure modes and by the International Gas Code which focuses more on catastrophic failure chain. Pluto II Pipe structure 6 The pipe structure from the inner element to the outer is: Flow line (1) made of 36% nickel alloy. Primary insulation layer (2). Secondary 36% Nickel alloy Barrier (3). Secondary insulation layer (4). HD Concrete weight lining (5). Carbon steel carrier pipe (6). Foam spacers (S) S A fully redundant pipe structure which offers a very high reliability Double barrier pipe structure

2 Materials and Component detail Materials Materials used in the PLUTO II technology permit to reach a high level of security, to avoid any expansion loop or bellows and to grant a good thermal efficiency: 36% Nickel alloy used for barriers is widely used in GTT s NO96 containment systems. It has a low CTE Value (< / C) and very good mechanical properties at cryogenic temperatures. Expansion loops are avoided, assembly is simplified, space is saved and pressure drops are minimized. The base insulating material is nanoporous silica also called aerogels or nanogels. It is currently the best insulating material for atmospheric pressure applications. This passive insulating material ensures a constant thermal efficiency; it consequently permits to reach an expected lifetime of more than 30 years. The foam used for spacers is a common material for applications. Spacers permit to center components while avoiding significant local thermal leak. They also ensure insulation integrity during pipe in pipe sheathing and field jointing operations. The base design carrier pipe is made of common carbon steel. Its main roles are to act as an armor for internal parts, to prevent any water ingress from surrounding media, and finally to ensure the adequate rigidity and strength for the laying operation. Conventional corrosion protection is applied to prevent any external corrosion; cathodic protection will be used for sub sea applications. Component detail 36% Nickel alloy barriers Low CTE alloy barriers are fabricated using the spiral forming process. For pipes with a high D/t ratio, spirally welded pipes offer: - Better tolerances than LWP. - Higher burst and critical pressures. - Similar weld quality. Moreover SWP are easier to handle and manipulate during the prefabrication stage. Welds on barriers are 100% X-Ray tested and visually inspected. Prototype spirally welded pipes in 36% Nickel alloy have been manufactured using the TIG welding process. Insulating blankets Insulation blankets commercialized by Aspen Aerogels were initially made of 6.4mm thick plies assembled together in a reinforced paper bag in order to reach a given thickness. A new version is currently under approval. A single coated ply is rolled around the pipe to reach the required thickness. Both versions lead to the same thermal and mechanical performances, with the only difference being the insulated barrier prefabrication method. Weighted carrier pipe In the classical design, PLUTO II technology uses a HD concrete lined carbon steel pipe. Concrete liner is manufactured using the centrifugal lining process. A drying line (a simple duct) is molded in the concrete liner. An alternative version has been designed with a standard carbon steel pipe externally weighted or not which is more adapted for onshore applications.

- Detect potential leak or porosity thanks to sweeping gas analysis at the outlet. - Ensure an accurate control of insulation spaces pressure during transient phases.

3 Peripheral systems Nitrogen sweeping During line service, gaseous nitrogen is swept in both insulation spaces. The roles of sweeping are to: - Avoid presence of oxygen to eliminate risks of explosive mixture due to potential porosities. Removing oxygen also ensures internal corrosion inhibition. - Detect potential leak or porosity thanks to sweeping gas analysis at the outlet. - Ensure an accurate control of insulation spaces pressure during transient phases. Fiber optic sensor is deployed using the floating technique: small stainless steel ducts are inserted in the secondary insulation during prefabrication; they are jointed during section assembly. The fiber is finally floated in this duct using a low viscosity liquid which density is slightly higher than fiber s average density. Cryogenic Flanges / Abutments At both line extremities, special flanges are needed to retain the three pipes. This flange described on the figure below is mainly composed of an internal low CTE alloy flange (1) to which Low CTE alloy barriers (4) are welded. This internal flange is maintained in an outer flange (2) connected to the carrier pipe thanks to densified wood rings (3) which can withstand thermal and pressure loads. 2 Nitrogen sweeping Temperature monitoring During transient phases and service, temperatures of the secondary insulation space are monitored thanks to a distributed temperature sensor (fiber optic & Raman effect based sensor). Temperatures can be measured every 1 meter along the line. It permits to: - Detect any change in temperature due to potential porosity ( leak & water ingress). - Detect, localize and monitor any anomaly in insulation. 4 Cryogenic flange / abutment Redundant monitoring system, no maintenance needed 3 1

4 Design basis / System efficiency Thermal efficiency PLUTO II technology s main interest is to replace traditional trestles. The maximum requested length for lines is probably ranging between 15 and 20km. Overall thermal efficiency is divided in two parts: pressure drops and thermal flux through the pipes. Classical diameters (~ ) allow a reduction of pressure drop contribution to a low enthalpy increase in cargo (~50W/m). The thermal contribution is reduced thanks to the thermal insulation and is of the same order of magnitude (50 to 100W/m depending on surrounding media temperature and nature). The overall heat transfer coefficient in 30 C water is lower than 0.21W/m 2.K. (The average value is 0.17W/m 2.K) Service Leak Radius Radius Pressure containment Pluto II pipeline has been designed under the following assumptions: Water - Design pressure: 30 Bars - Service pressure : 15 Bars - Shortest valve closure: 5s Double barrier principle As shown in the figure on the right, the double barrier pipe principle relies on the total redundancy of tightness and insulation. During service, the temperature gradient is divided between the two insulation layers (Service graph). In the Leak scenario ( Leak graph), the secondary barrier remains tight and the secondary insulation prevents the carbon steel pipe from cooling down. That is the reason why carbon steel pipe can be used as carrier pipe avoiding the use of expensive alloys. Water Ingress Radius Temperature profiles Vs Scenarios In the water ingress scenario (Water Ingress graph), while the secondary insulation loses part of its efficiency, the primary insulation remains fully operational. High thermal and tightness performances ensured by the double barrier principle

Tests, studies and prototypes Characterization of materials: Fabrication tests: - CTE

Sea water compatibility - Fiber optic validation - Mechanical tests on spacers - 36% Ni

welding speed has been increased from 30cm/min to 250cm/min) Cryogenic tests on concrete

transfer - Thermo mechanical study - Collapse pressure evaluation For the cryogenic

validation tests Full scale tests done on the prototype: - Sections fabrication validation

validation. - Validation of sweeping procedures - Loss of containment.

FEM analyses on the flange and pipe Mock-up tests: - Fabrication procedures validation -

5 Tests, studies and prototypes Characterization of materials: Fabrication tests: - CTE Measurements - Conductibility Measurement - Mechanical test - Thermal shocks & cycling - Sea water compatibility - Fiber optic validation - Mechanical tests on spacers - 36% Ni alloy SWP fabrication - Orbital welding on barriers - Welding processes improvements (The welding speed has been increased from 30cm/min to 250cm/min) Cryogenic tests on concrete FEM analyses: For the pipeline itself: - Steady state heat transfer - Transient heat transfer - Thermo mechanical study - Collapse pressure evaluation For the cryogenic flanges: - Steady state heat transfer - Thermo mechanical validation Welding process validation tests Full scale tests done on the prototype: - Sections fabrication validation - Jointing procedures validation - Flanges fabrication - Steady state & transient thermal validation. - Validation of sweeping procedures - Loss of containment. - The pipe has been tested in cryogenic conditions during more than 110 days. FEM analyses on the flange and pipe Mock-up tests: - Fabrication procedures validation - Thermal model validation - Tolerances validation - Collapse behavior of the assembly ~30 m Artist view of the test bench Collapse tests and first mock-up

6 GTT Pluto II prototype Barriers sheathing Installation on the test bench Concrete Abutments Abutments prefabrication Pipe under water Assembled prototype

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