LNG
Subsea LNG loading systems are ready to be put to the test
LNG loading goes subsea
S Colin McKinnon
addresses delegates at Gastech
ubsea LNG loading pipelines from shore could become a cost effective way of re-
placing loading jetties for LNG vessels.
Colin McKinnon, technical
director at JP Kenny, said subsea LNG loading pipelines are feasi- ble and a system designed by Technip is ready for deployment. McKinnon said: “Subsea LNG lines are feasible. Onshore buried LNG lines are being de- veloped. The technology has been qualified on a number of subsea LNG loading lines. There has been extensive testing and weld qualification of the welding needed for the exotic materials. “The regulators are being
engaged. Projects can be deliv- ered in three years, so the ques- tion is which project is going to
be the first to use this subsea technology.”
McKinnon said a typical loading jetty can be 1-3km long and as they get longer they get more expensive. The benefit of the subsea system is the cost associated with eliminating the trestle. “There are also safety issues at play, with the vessel able to remain further out to sea so you can put the loading facilities further away. “As for the loading of the car-
rier, you can adopt a dolphin at the end of the subsea loading line or you can have a single point mooring. There are a number of technology building blocks avail- able to designers to decide which is the best solution.”
He said the typical system will consist of two loading lines, typically 32-inch for the LNG and a vapour return line,
The Arctic
Discoverer LNG vessel
typically 24-inch. McKinnon estimated the cost for such a line at between $100-190m in- cluding installation. “They are quite substantial diameter pipelines and the tech- nology developed is either a pipe- in-pipe technology where you have got the 36-inch inner pipe, which can be stainless steel, invar or 9% nickel and you have an insulation layer and then an outer pipe which can either be carbon steel or stainless. “If you want to go triple pipe,
you have the inner pipe, insula- tion, then you have got a stain- less steel intermediate pipe which provides an additional barrier, secondary containment if you like, and then an outer pipe of carbon steel.”
McKinnon said that pipeline codes need to be revised to cover LNG service, and a system ap- proach to design needs to be taken to help move the subsea loading lines forward. Currently an amalgamation of codes is used for LNG loading lines, with the DNV-OS-F101 used for offshore sections. This is supplemented with
material requirements for cryo- genic pipelines from ASME B31.3 and B31.5, and also sup- plemented with the onshore pipeline gas and hydrocarbon liquid requirements of ASME B31.8 and B31.4.
He said that because of the quality of the material used there would typically be no need to in- spect the pipes internally for maintenance purposes, while ex- ternally normal ROV inspections could be carried out.
22 November/December 2012 Offshore Technology
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