During the main hull survey of an oil tanker, it was noted that deep spots of grooving corrosion had taken place under the walk ways, which is an almost inaccessible area, when the walkways are in place. The original plate thickness was 15 mm, but several grooved and corroded areas were found with only 5 mm of plate thickness; extending in the transverse direction of the deck.
During survey of cargo centre tanks, cracks were found in some of the deck longitudinals in a amidships. The cracks had penetrated through the flange, into the web of the deck longitudinal, and further into the deck plating at one location. The most probable cause of the cracking was fatigue due to longitudinal hull girder stresses combined with unfavourable location of welding in a knuckle.
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Officer of the Watch 