MIC Myths - Does Pitting Cause MIC?

Abstract It is widely accepted that sulfate reducers, acid producers, metal oxidizers and certain other bacteria can contribute to corrosion. However, it is far from clear how biological activity influences corrosion processes, how much metal loss is caused by bacteria, and most importantly, how microbial attack can be differentiated from other corrosion mechanisms Confusion between Microbiologically Influenced Corrosion (MIC) and other corrosion mechanisms is common. Criteria such as pit “tunneling”, “tiger striping”, pit “terracing”, “high” biological counts, tuberculation and preferential weld attack have frequently been used as diagnostic Rosetta stones solely identifying MIC. Unfortunately, many commonly accepted diagnostic criteria are not unique to MIC, but can also result from numerous corrosion processes unrelated to biological activity. Diagnosis of corrosion mechanisms, whether involving MIC or not, requires critical evaluation of all data, a thorough understanding of fundamental corrosion processes and consistency of both phenomenological observations and theoretical information.