直面“恶劣”海况 FLNG技术更迭 逆境求生（上）

The niche field of offloading systems for floating liquefied natural gas (FLNG) projects in exposed seas may not be high profile in today’s low energy price regime. But a small and select band of specialists continues to hold the faith.

With the world’s first two major exposed-ocean offshore liquefaction projects — Malaysia’s Satu and Australia’s mighty Prelude — now well into their development phases and most likely due to start up late this year and sometime in 2018, respectively, the die is cast on this latest frontier.

Further projects like these may be slow to come for a while, reason the offloading specialists, but come they will, and there will be rewards to be reaped.

It is an expensive field to enter. The challenges of transferring LNG from floating platform to visiting carrier vessel out at sea are in an altogether different league from the long-established business of pumping cargoes at traditional sheltered inshore terminals.

Out at sea, the differential movement between platform and carrier becomes too hard to handle using the existing techniques of side-by-side mooring patterns and conventional rigid steel pipe loading arms.

Instead, the need will be for tandem mooring at a safe separation distance, as is done for oil offloading, and for large bore flexible hose that can stand up to the demands of piping a product at minus 162 Celsius. A further question is whether to bridge that gap with hose in an aerial array, or floating.

Names in the game

Three different companies now have a fully-qualified flexible cryogenic hose — Technip, Nexans and Trelleborg — and a fourth, Dunlop, should reach that point by the end of this year.

All four hoses offer much the same throughput of about 5000 cubic metres per hour at up to 20 bar pressure. Three have a 16-inch bore and are aimed at aerial application, hanging in catenary from a deployment frame. Trelleborg’s has a 20-inch bore and is a floating hose.

The first to reach market readiness was Technip. It successfully qualified and demonstrated its aerial ALLS array as long ago as 2008. The company went on to work on a floating variant of its cryohose but no clear news is available about that, with the waters currently muddied by Technip’s impending merger with FMC.

Also qualified — in January 2011 — is Nexans Deutschland with its Cryodyn hose, in partnership with Framo (now OneSubsea) for the deployment system.

Both Technip and Nexans adopt the heavyweight approach of using a stainless steel bellows as their leak-proof barrier inside unbonded composite and steel armour layers. Nexans has a double bellows at its heart with a vacuum in the annulus between the two walls. Both companies build their hoses in single full length sections.

This year, Trelleborg and Dunlop join the market-ready ranks in this field. These two take a more fully-composite approach, and where steel is involved it is chiefly as helices of wire rather than bellows. They also build their hoses in 12-metre long sections and flange these together to form the required length.

In the drive to market readiness for LNG hose and system developers, the most relevant goals to meet are enshrined in EN 1474, the three-part European Standard that specifies design and testing requirements.

For the hose manufacturers, part two is the portion to conjure with, covering transfer hoses in exposed settings. Part three deals with design of the overall system that uses such hoses, while part one covers more conventional inshore transfer arms.

After seven years of development work, Trelleborg has become the first company to announce publicly that it has reached the milestone of qualifying a floating cryogenic hose. In April this year, its 20-inch product gained accreditation under EN1474-2.

Named Cryoline, this product uses a hose-in-hose approach with an outer rubber bonded marine protective hose surrounding its inner LNG cryogenic composite element. Trelleborg is partnered with Saipem for overall system development.

Meanwhile, Dunlop has a five-year effort behind it in this field and believes it should reach final accreditation of its impressively lightweight composite aerial hose by the end of this year.