ClassNK Approves Duplex Stainless Steel Tankers
Tankers built by the Japanese shipyards Sasaki Shipbuilding Co., Ltd and Hakata Shipbuilding Co., Ltd were applied with the duplex stainless steel, which was manufactured by Nippon Steel & Sumikin Stainless Steel Corporation. The two domestic vessels, a chemical tanker and an oil tanker, were launched on January 17, 2013.
The cargo tanks for use in chemical tankers built in Japan are generally constructed with austenitic stainless steel SUS304. However, with a nickel content about one quarter of that of SUS304, the newly approved austenitic-ferrite two-phased stainless NSSC2120 can now also be applied to chemical tankers as a substitute for SUS304 for first time in Japan.
Pitting corrosion resistance to sea water and corrosion resistance to acids of NSSC2120 are equal to or greater than those of SUS304. In terms of strength, NSSC2120 is almost twice as strong as SUS304 at 0.2% proof stress under NK Rules. Furthermore, NSSC2120 has weldability equivalent to that of SUS304 when CO2 gas shielded arc welding or submerged arc welding is applied.