Development of Guidelines on Corrosion Resistant Steels for Cargo Oil Tanks Available to Purchase

The International Maritime Organization (IMO) adopted new statutory requirements for corrosion protection of cargo oil tanks (hereafter referred to as “COT”) of crude oil tankers in May 2010. It is to be noted that these new requirements allow protection through the use of corrosion resistant steels as well as suitable coatings for COT. Corrosion resistant steels have been developed in Japanese steel mills based on the findings obtained in joint research project undertaken by the SR242 committee established in the Shipbuilding Association of Japan from 1999 to 2001. The project revealed corrosion mechanisms for general corrosion that occurs under the upper deck in inert gas environments and for pitting corrosion that occurs on the inner bottom. Corrosion resistant steels have excellent resistance against corrosion in these COT environments. The concept of protection through the use of corrosion resistant steels is based on the fact that such steels have been shown to better maintain their structural integrity during the target life of the ship by slowing down of the rate at which corrosion occurs compared with conventional steels. The IMO also developed performance standards for corrosion resistant steels together with statutory requirements for protection of COT. However, the maritime industry further seeks detailed guidelines on the unified application of such steels. In reply to their demands, ClassNK developed new guidelines specifying several matters for the suitable application of these steels, including on application range, combined application of corrosion resistant steels and coatings, test procedures for confirming the corrosion resistance of each product, and measures for ensuring the quality of welding work. This paper introduces an overview of the properties of corrosion resistant steels, IMO statutory requirements, and the newly developed guidelines.