Abstract

Offshore production of LNG will soon be a reality as several oil companies are working on projects aimed at building large floating LNG production units in the near future. Tandem loading has been used to transfer crude oil between two floating vessels for several decades worldwide and the time has now come to transfer of LNG in a similar manner. In areas with harsh weather, the vessel motions will require the loading to be performed in a Tandem configuration and flexible pipes / hoses are required as transfer arrangement between the two vessels to accommodate the relative vessel movements. Framo Engineering has together with Aker Pusnes, Kongsberg Oil&Gas Technologies (KOGT), Nexans and MIB developed a tandem loading system for LNG named the " Offshore Cryogenic Transfer System (OCT)??. This paper describes the successful development, manufacture, testing and approval of the double walled corrugated, stainless steel vacuum insulated flexible pipe designed for offshore transfer of Liquefied Natural Gas in the OCT system.

The Goals and the Challenges

Offshore transfer of LNG has been discussed for decades. The obvious solution is to " copy?? the methods and procedures that have been developed and refined by the crude oil loading industry in more than 20.000 offloading operations in areas such as the North Sea. One main challenge with a offshore offloading system for LNG is the need for a flexible hose that can maintain its functions and integrity at a temperature of −164 degrees C. Bonded reinforced rubber hoses are used to transfer crude oil and are also used for LPG transfer, however, the exposure temperature is limited to approximately - 50 degrees C. None of the conventional hose materials will offer the required mechanical properties at -164 degrees C. However, some metals maintain or even improve their properties at cryogenic temperature and 316 Stainless Steel is one such material. Nexans in Hanover has manufactured and supplied corrugated stainless steel vacuum insulated pipes to the cryogenic industry for many decades and have developed extensive know-how on the manufacturing process.

A Joint Industry Project was carried out in 2000–2004 to develop, manufacture and test a 10.5?? ID flexible pipe. The pipe design was based on Nexans manufacturing technology and KOGT riser technology. The project was successful, but in the years to come it became clear that a larger pipe with higher flow capacity would be required. A second JIP was carried out in 2007–20010 with the purpose to design, build and test a 16?? ID flexible pipe, based on the experiences gained in the first JIP.

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