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Fast-Tracking LNG Carriers
LNG carriers are being built today in a record time of just 8 to 12 months.
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The tanks that hold the LNG at temperatures of -163° C are lined with low-expansion nickel alloys.
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The cold rolling mill at Imphy where coils of low-expansion nickel alloy are produced.
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Cold rolling gives tight dimensional tolerances and a high quality finish.
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Requirement for faster, better welding met by variant of Invar 'workhorse.'
Nickel magazine, May 5, 2003 -- France’s Imphy Ugine Precision (IUP) has
developed a variant of K93600, more commonly known as Invar(R), that meets the new weldability requirements for carriers using the
Gaztransport Technigaz (GTT) design. The revised alloy, Invar M93, allows for faster, better-quality welding,
an important feature now that liquefied natural gas (LNG) carriers are being constructed in a record 8-12
months.
Over the past decade, IUP has become a key player in the growing market for LNG tanker liners by
providing an affordable solution to the thermal stresses the tanks endure as they transport their cryogenic
cargo to ports around the world.
Since 1963, shipbuilders designing LNG carriers to the specifications of GTT of France, one of the main
suppliers of LNG containment systems, have used IUP’s Invar, an iron-nickel alloy, to line the carrier’s gas
tanks.
Using the GTT design, the tanks are fully integrated into the hull of the ship. The cargo containment
system, which is fitted inside the tanks between the inner hull and the gas cargo, has a liner consisting of
two separate metallic membranes about 0.7 millimetre thick and 500 millimetres wide. The membranes are made
of Invar, a special 36%-nickel iron steel alloy with an extremely low coefficient of thermal
contraction. At temperatures of -163° C (the temperature of liquid methane, the main component of natural
gas), Invar provides a high level of ductility.
The chief advantage of the variant alloy is that it reduces the total cost of lining a tank.
Using Invar M93 to line a tank is less costly than using other liner materials such as stainless steel
because the strips can be made thinner and don't need to be corrugated before they are applied to
the tanks. Invar M93 is also leak-proof.
As a result of these factors, the market share for LNG carriers using Invar technology has doubled to 60%
today from 30% in the mid-1990s, according to IUP.
"IUP has supplied Invar for 68 LNG carriers, including 42 in operation and 26 under construction, since 1963
thanks to its know-how and special finishing equipment," says the company’s communications manger, Sylvie
Gindre.
Since natural gas is relatively clean to burn, compared to coal or oil, its popularity is increasing
worldwide. According to Gindre, world consumption of LNG is expected to grow by 10% between 2000 and 2005,
including a 45% jump in consumption in the United States. There is a corresponding boom in the LNG
shipbuilding business.
GTT recently launched a new containment system that can carry up to two million cubic metres of LNG. The
system uses an Invar primary membrane for quick assembly and reinforced polyurethane foam panels for
insulation. The second membrane is made of a composite aluminium-glass fibre called triplex.
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