Subsea cryogenic pipelines are emergenging technologies that are essential for the new generation of offshore LNG loading and receiving terminals. Current LNG product transfer systems use short runs of rigid or flexible pipe. As terminals move further offshore, there is a need to develop longer runs of insulated rigid pipeline LNG transfer systems.
A major issue for these systems is the pipe contraction due to the low temperature of the LNG. At present, there are mainly two methods to accommodate this contraction:
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Use of INVARTM or other alloy with ultra-low thermal expansion coefficient, or
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Use of bellows, one in each segment (about 50 ft long) of the pipeline, which is a self-contained pipe-in-pipe segment with vacuum insulation.
While technically feasible, both methods suffer major disadvantages in cost, reliability, durability, or maintenance requirement.
A new pipeline configuration has been developed to address these disadvantages. This configuration uses a highly efficient thermal nano-porous insulation in the annular space between the inner and outer pipes. This material is kept in an ambient pressure environment, which is produced through sealing by metal or non-metal bulkheads. The bulkheads transfer the contraction induced axial compression load on the inner cryogenic carrier pipe(s) to the external jacket pipe. The resulting pipeline bundle is a structural element, which addresses the thermal contraction & expansion loads without resorting to expansion bellows or ultra-low thermal contraction alloys.
As an example, a LNG carrier pipe that would be rated for cryogenic service and be configured to transfer thermal loads imparted through the bulkheads would be a 9% Nickel steel, while the jacket pipe is carbon steel. The thermal insulation used in the configuration is a high performance nano-porous aerogel product, approximately 2" thick, in blanket form installed within the annular space without vacuum and under ambient pressure.
This paper will discuss the techical details of the configuration, and the Phase I test performed in April 2004 using a cryogenic pipe specimen under flowing LNG conditions.
LNG is currently the fastest growing hydrocarbon fuel in the world to date. While gas as a primary fuel source is forecast to grow at 3% in the coming two decades, LNG is forecast to grow at double that rate over the same period [1]. This growth will result in the need for additional facilities for the production and transportation of LNG in the foreseeable future, and as a result new technologies will emerge to address cost, safety and reliability issues that this expansion may create.
For example, LNG loading into the tankers and the offloading thereof, require the use of terminals designed to handle the LNG. Terminals at the loading site are normally close to the liquefaction plant and traditionally on the offloading end, the terminal is situated near a storage facility and re-gasification plant. Proximity of the onshore terminals to water access has prompted a review of increased shipping traffic in congested waterways [2].
