Gas Material, Processing and Power Technologies
Purpose of development
Austenitic stainless steel is used for LNG piping, because of its excellent low-temperature characteristics and stable quality. Austenitic stainless steel, however, requires a mechanism, such as bent piping, to absorb thermal contraction, when it is used in LNG facilities. The purpose of this development is to apply Invar alloy, which has a very low coefficient of linear expansion, for LNG piping, in order to reduce the construction cost of LNG piping.
Invar : An alloy of 64% Fe-36% Ni
- Invar has a very low coefficient of linear expansion
which is 1/10th that of austenitic stainless steel
Invar alloy Austenitic stainless steel Coefficient of linear
expansion
1.7~10-6 /K 15~10-6 /K Contraction at LNG
temperature0.3 mm/m 2.8 mm/m - Invar alloy, with its stable austenitic structure,
has excellent strength and ductility at LNG temperature
Invar alloy Austenitic stainless steel 0.2% proof stress
240 N/mm2 205 N/mm2 Tensile strength 440 N/mm2 520 N/mm2 - Examples of present Invar alloy applications
Invar alloy has been used mainly in special applications in which thermal expansion or contraction must be minimized, such as CRT shadow masks and the cargo tank membranes of LNG tankers. However, since Invar alloy has difficulty of welding, it has never been used for thick plate and piping. - Cost reduction of LNG piping by applying Invar
alloy
Application of Invar alloy will reduce the construction cost of LNG piping, because simple straight piping can be used and thus, installation space can be reduced.
(When LNG piping is installed in a tunnel, the large cost reduction for civil work can be achieved)
Conceptual view of Invar alloy LNG piping
Outline of research and developmenti1993-1999j
- Establishing standard values (Setting strength and other properties of Invar alloy including its welded joints)
- Establishing welding technology (Confirming the content of the welding rod and wire and establishing the welding procedure)
- Confirming feasibility to construct Invar alloy LNG piping (Establishing design methods of piping, such as allowable stress and stress analysis on Invar alloy -stainless steel welds)
- Manufacturing test facility
- Evaluating radiographic test procedures for Invar alloy welds Tests on corrosive characteristics of Invar alloy and establishing anti-corrosive measures
Actual on-site Invar alloy LNG piping
Based on the abovementioned developments, in the spring of 2001, an Invar
alloy LNG piping was installed in the Osaka Gas Senboku Terminal II for
the first time in the world and now is in operation.
Invar alloy LNG piping including large diameter one as an interconnection
piping to an LNG tank was installed in the Osaka Gas Himeji Terminal in
August 2003.
The development of Invar alloy LNG piping is recognized as an excellent technology. It received the Award For Technical Achievement 33rd from The Japan Welding Engineering Society in June 2003.
Practical Application in the Undersea Tunnel
In the autumn of 2006, invar alloy LNG transferring piping in the undersea tunnel was installed. This piping connects Osaka Gas Senboku LNG Terminal I and II facing each other across a canal.
Use of Invar alloy allowed the tunnel's inner diameter to be reduced to 2.4 meters compared to 4 meters for stainless steel piping.
