Abstract:
The fracture of water ballast tank (WBT) coatings due to thermal stresses is widely
recognised as an issue. Upon coating fracture, rapid corrosion of the tanker steel
structure will occur, leading to expensive structure repairs or even tanker scrapping. In
this project, the fracture behaviour of two experimental WBT coatings, referred to as A
and B, in the forms of free film and substrated coatings was investigated. Static tensile
tests and fatigue tests of the substrated coatings were performed. A finite element model
of coating cracking was developed. Thermal stress and J-integral of surface cracking
defects in substrated coatings were calculated using the model, in which the effects of
defect size, coating thickness, and thermal strain on coating fracture were investigated.
For the first time, fracture mechanics was used to explain WBT coating fracture
behaviour. The J-integral of surface defects was used to predict the onset strain of
coating cracking under mechanical strains in laboratory and under thermal strains in
service. A theoretical comparison between the cracking drive forces in terms of J -
integrals in WBT coatings under thermal strains and mechanical strains was performed.
