Microbiologically Influenced Corrosion (MIC)
Microbiologically influenced corrosion (MIC) refers to corrosion caused by the presence and activities of microorganisms. While microalgae, bacteria, and fungi do not produce unique types of corrosion, they can accelerate corrosion reactions or shift corrosion mechanisms. Microbial action has been identified as a contributor to rapid corrosion of metals and alloys exposed to soils; seawater, distilled water, and freshwater; crude oil, hydrocarbon fuels, and process chemicals; and sewage.
MIC can occur as an independent corrosion mechanism or in conjunction with other corrosion mechanisms. These characteristics present challenges to implementing effective corrosion management of systems in which MIC is an applicable threat.
Rarely can a case of suspected MIC be confirmed without evidence from multiple analysis techniques and sciences. When trying to justify MIC as a contributing or root cause of corrosion it is recommended that biological, chemical, metallurgical, and operational lines of evidence all need to be examined.
Although microbiological conditions are only one piece of the MIC puzzle, the counting of viable bacteria has historically received the most emphasis. Serial dilution using liquid culture media, despite its limitations, has been the predominant method used to identify viable bacteria
There are no definitive tests or accepted standardized methodologies that can be applied to directly implicate MIC as the probable cause rather, it is often determined through a process of deduction of the facts and elimination of other mechanisms.