LNG低溫軟管“五虎將”（上）

Four of the five groups that have worked seriously in this field have developed a flexible hose as the heart of their proposed LNG transfer system. Here is a run-down on all five.

FMC Technologies

The undisputed dominant presence in liquefied natural gas offloading systems at present is FMC Technologies. It has half a century of experience using rigid stainless steel pipe and intermediate swivels.

This articulating array, known as Chiksan, works well with the short distances and small differential movements that occur for carriers at shore terminals or in benign environments generally. That line has been successfully extended for side-by side loading in ever more demanding environments. Currently, it has reached the heights of being adopted on board Shell’s mighty Prelude platform off Australia’s north-west coast, and for Malaysia’s Satu and Rotan.

However, beyond that, FMC has for the last seven years also been engaged in developing a tandem system. This is still based around use of rigid smooth bore steel pipe, with its claimed superior pressure-drop performance.

At its French base in Sens, to the south of Paris, the company has conducted extensive work with a one-fifth scale model of its articulated tandem offshore loader (Atol) offering.

That 24-inch concept has now reached a “technology readiness level high enough for its deployment on field”, according to sales director Renaud Ledevehat, speaking at the Offshore Technology Conference (OTC) in May. “An execution plan has been developed, detailing a 30- month delivery time,” he said.

A large tubular truss gantry cantilevers from the stern of the floating platform. Pipes spring from there to connect at a skid mounted on the bow of the carriers at a separation distance of as much as 115 metres. The system is fit for operation in waves up to 5.5 metres significant height.

Technip

As the first of the major companies to investigate flexible pipe for LNG, Technip had a fully developed aerial system ready for commercial take-up by spring 2008. Its Amplitude LNG Loading System (ALLS) was demonstrated in trials at the Montoir import terminal in France at that time.

The system used a 50-metre length of free-hanging cryohose with a stainless steel bellows forming its 16-inch inner bore. Outside that, a series of nonbonded synthetic fibres, thermal insulation and thermoplastic layers brought the outer diameter to 27 inches.

The ALLS system remains the company’s base-case offering for tandem offloading. And in an OTC paper this year it aired a variation that incorporates the HiLoad mooring unit as a means to connect to a carrier at mid-ships manifold even in open seas.

After its aerial hose became market-ready, Technip moved on to work on floating versions. By 2013 it was talking of a “Mark 2” flexible. This could include a floating variant for deployment to either bow or midships manifold in lengths of 300 metres or more and was billed as “expected to be ready in the short term”.
No real detail about its current status is being volunteered at present, because of apparent restraints during Technip’s ongoing merger with FMC Technologies.

The company is known also to have recently begun developing a new smaller-diameter cryogenic flexible pipe (with bores from four to six inches) for small to mid-scale transfer.

Nexans

Nexans Deutschland started developing its high-tech flexible hose for LNG service well over a decade ago, including joint industry projects with Chevron, Shell and Statoil. In January 2011, it reached the qualification stage for its robust 16-inch Cryodyn pipe.

That pipe was adopted in the offshore cryogenic transfer project with OneSubsea and others. “By 2014,” says Christian Frohne, who was Nexans’ director for LNG transfer solutions at that time, “we had a more or less fully qualified tandem transfer system for harsh dynamic environments.” Since then, the project has been on hold.

The hose is novel in using a vacuum for heat insulation. This is held in a sandwich of two corrugated stainless steel bellows that form the inner barrier of the hose. Held apart by spacer rings, each bellows can handle full operating pressure by itself. “For LNG, the vacuum requirement is not high,” says Frohne, “it doesn’t need to be much below a hundredth of a millibar.”

The Cryodyn hose can be formed in a continuous manufacturing process with no limit on the length produced. In 2009, Nexans went as far as building a dedicated manufacturing machine, which produced several prototypes for various internal and customer qualification projects, including specific tests by “a major operator”.

As for a floating variant of Cryodyn: “We have not gone into that in much detail,” says Frohne, “chiefly because those who have asked us for qualification and engineering work have always voted for aerial or submerged. But we are doing some study for floating hoses, although for smaller sizes.”