Microbiological Influenced Corrosion, or short MIC is the general term for corrosion, caused by microbiological activities in a liquid or water bearing systems build from metal.
In certain water or liquids one can find either aerobic or anaerobic microbes or bacteria. Some of these microorganism are so nasty, they produce acids or sulfides in their metabolism. These acids, for example H2S or SO4, might cause severe corrosion.
Pipe walls or metallic surfaces, not resistant against such type of corrosion are effected a lot. Resulting in pitting or leaks, which reduces in general the lifetime of the equipment.
If these bacteria or microbes are settling in the so called biofilm, this is worst. The biofilm is not flowing with the water, but stable at one spot. The biofilm is so to say the habitat of the bacteria. The bacteria are even protected from external influence. The acids produced from the bacteria will penetrate always the same spot of the pipe or metallic surface, this can result in serious damage on the metallic surfaces.
One of the most known microbial induced corrosion problems, are the so called sulfur reducing bacteria or short SRB. These are living on the sulfur in the steel. This sulfur is solved and the steel get instable.
See also a case study in a refinery, where corrosion and the microorganism were reduced a lot.