Transient early and longer term influence of bacteria on marine corrosion of steel

There are essentially two periods when microbiological activity is important for the corrosion of steel coupons in marine environments. The first commences soon after first exposure but becomes ineffective after some months, for reason(s) not yet elucidated. The second period commences when sufficient rust layers have built-up on the corroding surface to permit new microbiological activity under suboxic and anoxic conditions. Since microbiological activity depends on the availability of appropriate micro-environments and on the rate of supply of necessary nutrients, it is argued that the first period concludes as a result of the changing microenvironment caused by the build-up of corrosion products. This interferes both with the metabolite flux and the availability of iron as a necessary nutrient for bacterial metabolism. A model consistent with field observations is proposed.