Classification societies Lloyds Register and ClassNK have approved Nippon Steel & Sumitomo Metal Corporation's newly developed corrosion resistant steel (NSGP-2) for use on the upper deck and/or inner bottom of crude oil tanker cargo oil tanks (COT). Following earlier approvals of steels for the inner bottom plating of COTs, this marks the first time that approval has been granted for corrosion resistant steels for both the top and bottom parts of the COT, providing owners and shipyards with a practical alternative to coating systems.
"While coated conventional steel meets IMO regulations, the additional costs associated with coating application can be high," said Yasushi Nakamura, ClassNK EVP. "This approval of NSGP-2 means that owners now have a practical alternative to meet IMO regulations for COT corrosion protection, and we expect the use of this kind of steel will increase in the future."
To reduce COT corrosion and improve crude oil tanker safety, amendments to the SOLAS Convention, issued in May 2010, required oil tankers (over 5000 dwt contracted after January 2013) to adopt appropriate corrosion protection measures for their COTs in line with either the IMO Performance Standard for Protective Coatings for COT (MSC.288(87)) or the IMO Performance Standard for Alternative Means of Corrosive Protection for COT (MSC.289(87)).
As the use of corrosion resistant steels would allow shipyards and owners to significantly reduce the time and cost related to coating application, development of such steels has been the target of intense research over the past several years. However, differences in the corrosion mechanism found in the top portion of the COT, which is exposed to gases released from crude oil during transport, and the inner bottom, which is in direct contact with the crude oil cargo, posed a major challenge to steel makers.
Nippon Steel & Sumitomo Metal Corporation released the world's first corrosion resistant steel (NSGP-1) for use on the inner bottom of COTs in 2011. The approval of NSGP-2 marks the first time that class-approved steels for both the top and bottom of the COTs will be available on the market.
Photo credit: Amtec corrosion