MIC - Microbial Induced Corrosion
or called as well Microbiological Influenced Corrosion is the general term of corrosion caused by microbiological activities. In some water there are microbes or bacteria, which produce acids or sulfides in their aerobic or anaerobic metabolism. These acids or sulfides can cause severe corrosion at pipe walls or metallic surfaces not resistant against such type of corrosion. Especially if these bacteria or microbes are settling in the so called biofilm, this can result in serious damage on the metallic surfaces.
One of the most known microbial induced corrosion problems are the so called SRB, which are very commonly found in the oil and gas industries and some water systems as well. These SRB are anaerobe bacteria, means they don't need oxygen to multiple. This SRB are "eating" part of the steel from the pipe lines, making the steel weaker and might lead to pitting corrosion. See also case studies, where corrosion or bacteria is reduced a lot.