Lowering the Cost of LNG Piping
THE MAGAZINE DEVOTED TO NICKEL AND ITS APPLICATIONS
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PIPELINES THAT carry liquified natural gas, at minus 199°C, from ship to shore must be capable of
withstanding significant swings in temperature.
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IF STAINLESS STEEL is used, bends in the pipe are needed to allow them to flex during expansion or
contraction.
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IF K93600 IS USED, no bends are required. Therefore the amount of pipe needed is significantly less and
the tunnel containing the pipe can be much smaller.
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Using a more expensive alloy allows for a low-cost design.
By John Milne
Nickel Magazine, March 2005 -- A piping system engineered by Osaka Gas, of Japan, for handling liquified natural gas (LNG) has resulted in significant cost savings. The pipe is made of K93600 (an alloy of 36% nickel, the balance being mostly iron), rather than less expensive austenitic stainless steel. However, the system requires fewer meters of pipe and a smaller-diameter underwater tunnel, so the total cost of the system is lower than that of conventional designs.
The K93600 pipe used has an outside diameter of 31.8 centimetres (cm) with a wall thickness of 6 millimetres (mm).The piping is contained in an concrete tunnel 2.4 meters in diameter.
Natural gas, when cooled to minus 199°C, becomes a liquid, which causes the volume to be reduced about 600 times. One benefit of this is that LNG is economical to transport from far-flung sources such as Liberia to markets in Japan or North America, where it is re-gasified for use as regular natural gas. LNG is transported in ocean-going ships, contained in nickel alloy stainless steel S30400 or K93600 tanks (see 'More Info' below). Once delivered to a port, the LNG must be off-loaded into stationary shore storage tanks. This is normally done through underwater or underground pipelines from the tanker.
Owing to the extremely low temperatures involved, the thermal expansion and contraction of the pipeline are major factors in the design and construction of the piping system. Normal LNG piping construction uses S30400 stainless steel with loops or bends to allow it to flex with the expansion or contraction of the pipe when gas flows through it.
The Osaka design permits straight runs of piping because the coefficient of expansion/contraction of K93600 is low over a wide range of temperatures. K93600 contracts at a rate of 0.3 mm per meter of length between 20°C and LNG temperatures compared to 2.8 mm per meter for S30400 stainless. The total length of piping required is less, as the bends or loops needed with stainless steel are not required with K93600.
Since bends or loops in the piping system are eliminated using K93600, the underwater tunnel that contains the piping can be of smaller in diameter and is therefore less expensive to construct.
John Milne is a consultant to the Nickel Institute.
PHOTOS: Osaka Gas
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