Identifying microbially influenced corrosion on surfaces contacted by mill waters

This introduction to microbiologically influenced corrosion (MIC) describes how bacteria can cause MIC where inadequate disinfection of mill water or white water allows biofilms to grow on metal surfaces. Although planktonic bacteria (that float in solution) rarely cause corrosion, sessile bacteria (that adhere to surfaces) can produce corrosive chemicals or promote under-deposit corrosion. The diagnosis of MIC requires knowledge not only of corrosion processes, but also of microbiology, water treatment, and plant operations. Although the presence of bacteria does not prove that the corrosion was caused by MIC, factors such as the presence in the corroded area of bacteria that can cause MIC, of chemical indicators of MIC, of features of the corrosion damage that are characteristic of MIC, and recent operational changes that could have enhanced the activity of microorganisms can combine to provide compelling evidence. Because of the complexity of mill water environments, test data must be reviewed with care because of the possibility that other components of the water could have interfered with the analytical results.