Estimation of models for durability of epoxy coatings in water ballast tanks

Abstract

Estimates of the expected life (durability) of protective (organic) coatings for ships are increasingly desired for the rational management of maintenance practices and the setting of asset policies. The life of coatings also has an influence on the prediction of safe remaining structural life, particularly for ships already subject to coating deterioration. Methods for estimating the life of organic protective coatings are briefly reviewed. It is concluded that despite attempts to develop mathematical models of coating deterioration, there is still insufficient unbiased data obtained from actual field experience for sufficiently well-defined vessel areas such as ballast tanks, known to be particularly prone to coating breakdown and poor inspection. Herein a preliminary survey to obtain initial estimates of models for coating durability for water ballast tanks in commercial vessels is described. The survey was conducted using experts from vessel users, coating contractors and suppliers, and an independent expert. As might be expected, the users tended to be more pessimistic and the contractors/suppliers more optimistic in their estimates compared with those of the independent expert. The collective estimates are reasonably consistent with a normal distribution. It was also found that coating life, described as percentage area breakdown, is approximately normal distributed with both increasing mean deterioration and variance.