Time-variant reliability analysis of steel plates in marine environments considering pit nucleation and propagation

Corrosion is a severe threat to the integrity of ships and other steel structures in marine environments due to material loss and the associated reduction in their load-carrying capacities. Most existing studies on corrosion of steel plates in marine environments dealt only with general corrosion. However, laboratory experiments and field tests have shown that pitting corrosion can occur and even dominate the material loss of corroded structures, especially for plates with local coating failure, metal with mill scale surfaces, and alloys with special compositions. In this paper, a cellular automata-based model with both numerical and categorical attributes is proposed to analyze steel plates subjected to general and pitting corrosion. The proposed model can depict various corrosion behaviors including uniform loss of plate thickness, pit nucleation, and pit propagation. The parameters of the model are calibrated based on results from existing exposure tests. The calibrated model is then used to evaluate the time-variant reliability of a steel plate in corrosive environments. It is found that the general corrosion model with a time-invariant corrosion rate cannot realistically predict the long-term corrosion material loss and the thickness of corroded plates may show considerable spatial variability due to pitting corrosion.