Coating Life Prediction for Water Ballast Tank

Corrosion is the key factor responsible for the degradation of ship structures and in no place is this truer than water ballast tanks. Coating protection system is a continual research interest for classification societies and coating industries. Up to now, most coating performance analyses are qualitative not quantitative. Coating life prediction is almost always based on experience and various assumptions, due to unavailability of practical data support systems. This paper describes a preliminary impartial investigation of coating life carried out with interviewees from the Australian Defence Science and Technology Organization (DSTO), shipyards, coating supplier and an independent expert. Plate surface, edges and welds in ballast tank were considered and the influences of dry film thickness (DFT) and surface preparation (SP) are addressed. The investigation gives some insight into the life of practical coating systems for water ballast tanks. Coating life is proposed to be representable by a normal distribution when corrosion breakdown is below 10% of plate thickness, which is of practical implication.