Chemical Tanker First to Use New Duplex Stainless Steel Cargo Tanks

MT Sunrise Hope. Photo: ClassNK
MT Sunrise Hope. Photo: ClassNK

The new chemical tanker built in Japan is the first to use a new type of steel cargo tanks said to be cheaper and stronger that existing tanks.

The tanker, MT Sunrise Hope, was successfully delivered to Oita-based Hiro Naviera S.A. recently by Usaki Shipyard Co. and will be operated by Nippon Marine Co.. The ship is the first to be built with cargo tanks made from a combination of duplex stainless steel and stainless clad steel.

The 12,500 metric ton Sunrise Hope is designed with 14 cargo tanks, built with the duplex stainless steel combination developed by joint research program involving steel manufacturers, technical universities, ship designers, and ship classification society ClassNK through its Joint R&D for Industry Program. Construction of the vessel was carried out in accordance with ClassNK’s Guidelines on Welding of Duplex Stainless Steels, released in January 2014, marking the first time the Guidelines have been used in the construction of an actual vessel.

According to ClassNK, duplex stainless steel provides not only significantly greater strength and excellent corrosive resistance in comparison with the commonly used austenitic stainless steel SUS316LN, but its low nickel composition also makes it economical. ClassNK notes that although duplex stainless steel technology has been used previously in shipbuilding internationally, this marks the first time in the world that a combination of both duplex and stainless clad steels have been used in the construction of a chemical tanker’s cargo tanks. It is also the first time that duplex stainless steels have been used in a Japanese shipyard, while the lean duplex stainless steel which contains lower nickel compared to duplex stainless steel have been used in some cases.

Duplex stainless steels consist of a mixture of both of austenite and ferrite phases and offer enhanced strength and corrosion resistance superior to that of commonly used austenitic stainless steels, ClassNK says. On the Sunrise Hope, duplex stainless steel KSUS329J3L replaces the commonly used SUS316LN for the bulkheads inside the cargo tanks, while the bulkheads adjacent to the cargo tanks were constructed using stainless clad steel, in which stainless steel and carbon manganese steels have been compression bonded together into a single plate, ClassNK says. The stainless clad steel of the ballast tanks also ensures the coating quality of the tanks is protected.

The application of the steels in the construction of the Sunrise Hope was achieved as part of a joint research project carried out as part of the ClassNK Joint R&D for Industry Program by JFE Steel Corporation, Nippon Steel & Sumikin Stainless Steel Corporation (NSSC), Taseto Co., Ltd, and ClassNK, with the support of Professor Hiroshi Yajima and Associate Professor Tadakazu Tanino from Nagasaki Institute of Applied Science and Toshiaki Mori from Consultancy Juk Fnadyke.