The Practical Application of 36% Ni Steel Piping in LNG Plants Available to Purchase

Conventionally, 18-8 stainless steel has been used for the facility of cryogenic service in LNG plant because of the excellent toughness. Although 18-8 stainless steel piping requires pipe looping to relax thermal expansion in the cryogenic piping of LNG plant, 36% Ni steel (generally called as Invar) piping does not require pipe looping due to its low coefficient of linear expansion of about one-tenth of that of 18-8 stainless steel. Elimination of pipe looping makes significant reduction of the piping cost by reducing the number of elbows, welding points and adoption of small diameter of piping. Furthermore, it is possible to reduce the tunnel diameter, when the piping is installed in a tunnel. However, conventionally, it has been known that there is a difficulty in adopting the material from the viewpoint of weldability, which is reheat cracking at the weld metal in multi-layer welding. So, we have developed an excellent welding technology for 36% Ni steel with a new welding consumable. In order to adopt 36% Ni steel to the cryogenic piping in LNG plant, comprehensive experiments to find out the properties such as mechanical properties, corrosion resistance, weldability, nondestructive inspection and thermal stress analysis were conducted. By using the results the appropriate welding procedures were established and 36% Ni steel was used for the Ohgishima LNG receiving terminal of Tokyo Gas Company.