Corrosion-Resistant Steel for VLCC Upper Decks

MOL announced that its newest crude oil tankers, to be launched in 2003, will feature NKK Anti-Corrosion No.5 (NAC5) steel on their upper deck. The new material will ensure longer life for the tankers’ upper decks and protect the marine environment by reducing the risk of oil leakage. The undersides of crude oil tankers’ upper decks are highly susceptible to corrosion caused by high temperatures and humidity. As a result, tankers made of conventional steel have a service life of only about 20 years. MOL and NKK estimate that the use of NAC5 will extend the service life of the vessels by about five years.

The International Maritime Organization (IMO) and other groups have shown growing concern about corrosion on the undersides of upper decks of crude oil tankers, and there have been calls for more stringent inspection of these areas of the vessels. To address the corrosion problem, Nippon Kaiji Kyokai has established a stricter inspection programme including measurement of steel plate thickness. If excessive corrosion is found to have reduced the strength of the hull, ship owners will have to reinforce the weakened plates.
In addition to the use of NAC5, two new crude oil tankers under construction will also use the AX-BOW bow design applied to the Cape-size bulk carrier Kohyohsan, which was awarded Ship of the Year 2001 by The Society of Naval Architects of Japan. The AX-BOW design improves ship propulsion in heavy seas and reduces fuel consumption. Further, the ships will have aerodynamically designed superstructures to reduce wind resistance.