ClassNK Issues New Welding Guidelines

Classification society ClassNK (Chairman and President: Noboru Ueda) announced that it has released new Guidelines on the Welding of Duplex Stainless Steels. The guidelines have been developed to help shipyards safely and effectively make use of new duplex steels that are increasingly being used in the construction of cargo tanks for chemical carriers. As part of its work to support the safe construction of ships, ClassNK has released the guidelines for free via its website.

Duplex stainless steel has a two-phase microstructure containing grains of both ferritic and austenitic phase, giving it a combination of excellent corrosion resistance and high strength with a lower nickel content than austenitic stainless steels such as SUS304 and SUS316L.

The vast majority of the world’s chemical tankers with stainless steel cargo tanks are built at Japanese shipyards, which have traditionally used austenitic steels for cargo tank construction. Recently however these shipyards are increasingly using duplex stainless steels as an alternative to austenitic stainless steels for their corrosion resistance and high strength properties.

Before shipyards or builders can use duplex stainless steel in the construction of vessels, however, they must first obtain approval for the Welding Procedure Specification (WPS) that will be used when welding duplex stainless steel. It was in order to simplify this process and support the widespread use of these new materials at shipyards around the world that ClassNK released its new Guidelines on the Welding of Duplex Stainless Steels on 14 January 2014.

The new guidelines, which conform to ClassNK rules, provide a comprehensive summary of the requirements for welding procedure specification certification and welding procedure qualification tests, including relevant precautionary measures for the welding of duplex stainless steels.