A study on the influence of seawater temperature on corroding ship structural steel in extreme marine exposure conditions

Corrosion in offshore steel structures in deeply influenced by several environmental factors, seawater temperature and chemical compositions in particular. This research paper is to determine the influence of seawater temperature on the corrosion mechanism in the ship structural steels by performing series of corrosion experiments at two different seawater temperatures. The corrosion conditions in the laboratory experiments were maintained o simulate the extreme saline conditions in the Arabian Sea for maximum durations up to 321-365 days using artificial seawater. Corrosion deposits were characterised with the help of various analytical techniques whereas corrosion losses were measured using two methods (i) mass loss method (ii) dimensional metrology method involving various statistical parameters and measurement tools. Furthermore, Melchers corrosion model basically derived for corrosion in field seawater conditions was pitched with the corrosion results performed in this research using artificial seawaters; without biological factors. Interestingly, the corrosion trends observed during this study were found to be similar to those reported in Melchers’ model for steels under natural seawater exposure conditions. Furthermore, characterisation of rust deposits revealed traces of sulphide containing compounds and anaerobic corrosion were observed only on the steel coupons exposed to artificial seawater at higher exposure temperature i.e., 40 OC. Despite similar corrosion conditions other than the seawater surface temperature, significantly varying corrosion rates/losses and patterns (uniform/ pit depths) were observed in the two different corrosion conditions, where corrosion loss was found to be proportional to the seawater temperature, similar to trend previously reported in literature during exposure of steels in the natural seawater conditions.