Corrosion-Resistant Steel

Nippon Steel Corporation and Nippon Yusen Kabushiki Kaisha (NYK), have jointly developed a highly corrosion-resistant steel plate, named NSGP-1 (for Nippon Steel's Green Protect-1), to prevent corrosion of the inner bottom of crude-oil tanks of supertankers. NYK has decided to use this steel plate on all new tankers, including those currently on order.

Crude oil contains salt water that has a salt concentration several times higher than seawater, and over time this salt water separates from crude oil and accumulates at the bottom of tanks. The accumulated salt water makes pits on the inner surface of the tanks, and this can then lead to oil leaks. The newly developed steel plate is designed to protect the tanks from such pits. Both NYK and Nippon Steel agreed to work together to jointly develop this highly corrosion-resistant steel plate in order to continue the efforts that both companies have been making to reduce any negative impact that they may have on the environment.

In the process of development, Nippon Steel successfully simulated an environment in which salt water accelerates the corrosion of the bottom of the tank, and discovered the types and amounts of alloy elements that should be combined to create a highly corrosion-resistant steel plate suitable for oil tanks. Building oil tanks using this steel plate requires no special process since conventional steel welding and processing techniques can be used.

To verify the steel plate properties, the two companies used it on the tank bottom of Takamine, a supertanker built in 2004 by Mitsubishi Heavy Industries. Two and a half years later, a regular inspection showed that the steel plate, which was free of any anticorrosion coating, was capable of preventing the occurrence of pits. NYK thus decided to use such steel plates on five supertankers on order from IHI Marine United and Imabari Shipbuilding.

When using NSGP-1 for crude-oil tanks anticorrosion and other coatings are not required. Elimination of coating agents used for building or maintaining oil tanks and will greatly contribute to building environmentally friendly ships. This will also help to improve the safety and reliability of ships.