Pitting corrosion of mild steel in marine immersion environment - Part 2: Variability of maximum pit depth

A recent study has shown that in marine conditions micro-pitting in mild steel is present very early after first immersion and that macro-pitting usually does not become significant until anaerobic conditions set in. The overall pitting behavior with time was represented by a multiphase phenomenological model. This was calibrated to data from a variety of sources but with approximately consistent steel exposure area. The maximum pit depth model was shown to be a function of seawater temperature. Herein that model is developed further to deal with uncertainty in maximum pit depth information. Consistent with an earlier empirical application, it is argued that extreme value probability theory for maximum pit depth is appropriate. It is shown that when calibrated to statistical data the model evolves with time. The model presented for dealing with the uncertainty inherent in maximum pit depth represents a major departure from conventional techniques.