Long-term corrosion of steels exposed to marine environments

This paper presents an overview of the principal features of the recently developed model for the short and the long-term marine corrosion of steels. In marine environments such as immersion, tidal and coastal atmospheric, chlorides conventionally are considered to play a major role in causing corrosion loss. It is shown that the actual corrosion process is considerably more complex and that besides oxidation by dissolved or atmospheric oxygen there is an important influence from the metabolic products of sulphate-reducing bacteria. The model also deals with temperature, oxygen availability, pollution and various other influences. Although the fundamental corrosion processes are all electrochemical in nature, the model does not deal specifically with these. Instead the model is built around the governing corrosion-rate controlling processes. For engineering purposes the rate of loss of material is the critical issue. The main emphasis is on the behaviour of structural and other low alloy steels. The paper closes with some observations about the applicability of the model to stainless and weathering steels and its recent extension to reinforcement corrosion in concrete structures and about current research directions