The chemical tanker, Sunrise Hope (12,500dwt) is world's first to use a combination of duplex stainless steel and stainless clad steel in construction of its cargo tanks. The ship has recently been delivered to Hiro Naviera by Usuki Shipyard.
Class NK 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."
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.
Related press release: First Chemical Tanker to Use Combination of Duplex Stainless Steel and Stainless Clad Steel Delivered
Duplex stainless steels contain a nearly 50-50 mixture of austenitic and ferritic phases of stainless. Austenitic types of stainless have low strength and a low resistance to stress corrosion cracking and high nickel content. Ferritic forms are magnetic and have low strength, but still a bit higher than austenitic, but they have poor weldability in thick sections and poor low temperature toughness.
Duplex steels solve many of these issues while having greater strength, greater weldability in thicker sections, good low temperature toughness as well as resistance to stress corrosion cracking and, because of the lower nickel content, prices are more stable: important considerations when constructing tanks on a ship.
Stainless clad steel is formed by rolling (compressive bonding) stainless steel and carbon manganese steels into a single plate. The stainless clad steel was also used in the ballast tanks to ensure the coating quality of the tanks is protected. Welding requires a two-step process to bond the backing separately from the stainless facing material to avoid contamination of the weld.
The application of the duplex steels in a ship's cargo tanks resulted from an extensive joint research programme involving steel manufacturers, leading technical universities, a ship designer, as well as ClassNK
Internationally, duplex stainless steel technology has previously been used in shipbuilding, however, this marks the first time that both duplex and stainless clad steels have been used in construction chemical cargo tanks. It is also the first time that duplex stainless steels have been used in a Japanese shipyard.
Application of both stainless steel types in the construction of the Sunrise Hope was achieved as part of a joint research project by ClassNK's Joint R&D for Industry Program, several steel companies and members of academia and consultancies. The team's wealth of specialist knowledge and extensive expertise spanning from material development to ship construction ensured the technology was successfully applied to this first vessel.
Source: http://www.ihsmaritime360.com/