LNG低溫軟管“五虎將”（下）

Trelleborg

In April this year, French hose developer Trelleborg became the first company known to qualify a floating cryogenic hose.

Its 20-inch bore hose gained accreditation under European standard EN1474-2. To meet these requirements, Trelleborg tested several full-scale hose prototypes in static and dynamic conditions, mostly in cryogenic conditions using liquid nitrogen at minus 196 degrees Celsius.

Named Cryoline, this product uses a hose-in-hose approach with an outer rubber bonded marine protective hose, surrounding an inner LNG cryogenic composite element, explains marketing manager Vincent Lagarrigue.

The bonded outer hose design is well established in offshore oil loading operations, using rubber, steel rings and reinforcement layers. The inner hose is formed from a mixture of polymer layers sandwiched between two helices of stainless steel wire. Then a layer of insulation shields the outer rubber hose from excessive low temperatures.

Each string is built up in 12-metre sections, and is claimed capable of transferring up to 6000 cubic metres per hour at a working pressure of 20 bar — in a cryogenic burst test on 20-inch line last year it reached 106 bar before failing.

The design has its origins in a multi-year in-house programme by SBM to develop its own cryogenic system of hose and swivel. In 2013, Trelleborg completed a deal with the Monaco company to acquire this technology.

Trelleborg has an established collaboration with Saipem to develop a full tandem offloading system for storing, handling and connecting this pipe. The work has also been supported by Total through a joint industry project between the three organisations that started in 2009.

The vision is that the visiting carrier can set up in tandem at a separation distance of between 100 metres and 150 metres, requiring an overall length of about 200 metres of floating hose. Two hoses would transfer LNG and a third caters for vapour return. They have been designed for operation in sea states up to 5.5 metres significant height.

Dunlop

For the past five years, Dunlop has been making its initial foray into the LNG field by developing a light, strong and flexible largebore hose for aerial use.

The UK company has now reached the point where “we are about 95% on the path to market readiness with our 16-inch bore hose”, says LNG product group manager Simon Bishop. “We are on track to achieve full qualification at the end of this year.”

Dunlop, which became a subsidiary of Continental 12 years ago, has a 60-year history in marine hoses for oil applications. But its move into LNG did not come until 2011.

That was when it acquired the hose technology rights of Bluewater, as the latter terminated its development programme in this area. Before that, the hose had its origins in a 10-year research and development programme executed by patent holder BHP Petroleum in collaboration with UK companies BPP-Tech and Dantec.

The 16-inch bore product Dunlop has now developed appears positively svelte compared with its main rivals. It is of non-bonded composite construction, with very little steel content. It starts with a helix of stainless steel wire on the inside, and then a composite wall of multiple layers of fabrics and films is built up.

This 15-millimetre thick wall includes a highly-engineered braided “sock” of ultra-high molecular weight polyethylene that runs the full length to provide impressive tensile strength. At the outside, another wire helix pushes down at an offset from the inner helix to hold the hose body together.

All this results in a hose that weighs just 45 kilograms per meter and has an overall wall thickness of only about 20 millimeters. “You pretty much double its weight when you fill it with fluid,” remarks Bishop.

“Of course you do get an ice/frost build-up on the outside, where the temperature is something like minus 120 Celsius,” he continues, “but the resulting inch or so of ice works incredibly well as a further insulator and doesn’t affect flexibility.”

As for strength, the tensile load handled under tests at 162 bar equates to 190 tons.

Dunlop has no ambitions towards producing a floating version of its hose at present. It is put off that goal by the pressure drop that comes with the comparatively rough inner bore of all current LNG hose designs, including its own.

These losses can only increase with the longer hose runs that are one of the main drivers towards floating hoses. ”Smoother bores — similar to oil hoses — will be needed if floating hose is to work efficiently enough,” says Bishop. Also, heat in-leak is much more difficult to manage in water than in air.

As for the future, “we recognize there is a growing market in smaller bores for different applications such as bunkering and we are looking into that”, says Bishop. “But that calls for a different design, since we don’t need the very high strength.”