The ship classification company, ClassNK, has issued approval to the global company Nippon Steel & Sumitomo Metal Corporation for its newly developed corrosion resistant steel (NSGP-2) for use on the upper deck and inner bottom of crude oil tanker cargo oil tanks (COT).
This is 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.
In order to reduce COT corrosion and improve crude oil tanker safety, new amendments to the SOLAS Convention were issued in May 2010 requiring oil tankers over 5,000 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)).
ClassNK noted that as the use of corrosion resistant steels would allow shipyards and owners to reduce the time and cost related to coating application development of such steels has been a topic 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, have presented a major challenge to steel makers.