The reason for the corrosion attack is considered to be that the thin aluminium film on the surface is depolarised and locally broken down, in connection with the formation of chlorine released from the hypochlorite. The filling and emptying of the tank is not sufficient to remove all the corrosion products. Once pitting corrosion has started, it may continue to develop for a certain period if the tank is not properly washed with water after the application of hypochlorite. In addition, the shore-supplied water was frequently chlorinated, which meant that the tanks were frequently exposed to chlorides.Įven small amounts of hypochlorite can be very dangerous for aluminium, irrespective of the Al-alloy chemical composition, resulting in the development of serious pitting. The fresh water tanks were sterilised annually, which exposed the tanks to a solution of hypochlorite for 12-24 hours. The process for cleaning the fresh water tanks was considered to have been a major factor in the corrosion process. Transverse bulkheads and deckhead Bottom plating The corroded areas in the fresh water tank had to be partly renewed and repaired to an acceptable standard.
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