The application of the duplex steels in the 12,500 dwt ‘Sunrise Hope’s’ cargo tanks was made possible by a joint research programme involving steel manufacturers, leading technical universities and the ship’s designer, as well as ClassNK, which supported the project as part of its Joint R&D for Industry Programme.
The chemical tanker will be operated by Nippon Marine. The eco-ship design vessel is equipped with 14 cargo tanks, all which employ duplex stainless steel technology.
Construction of the vessel was carried out in accordance with ClassNK’s Guidelines on Welding of Duplex Stainless Steels, which were released in January 2014, marking the first time the guidelines have been used in the construction of an actual vessel.
Duplex stainless steel provides not only significantly greater strength and excellent corrosive resistance in comparison with the commonly used austenitic stainless steel SUS316LN, but also its low nickel composition makes it economical.
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, ClassNK said.
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.
On the ‘Sunrise Hope’, duplex stainless steel KSUS329J3L replaced 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 were compression bonded together into a single plate.
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 vessel’s construction was achieved as part of a joint research project carried out as part of the ClassNK Joint R&D for Industry Programme by JFE Steel Corp, Nippon Steel & Sumikin Stainless Steel Corp (NSSC), Taseto 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.