Microbiologically induced corrosion (MIC) has been identified as a problem in numerous industries where surface water, municipal reclaim water, grey water and even well water is consumed and conditions are right for the formation of biofilms. Water systems with carbon steel, stainless steel and copper piping that are prone to scaling and sludge generation, have high bacterial counts, ineffective biocontrol, experience stagnant or low flow conditions and have moderate operating temperatures are particularly susceptible. That means power plants, refineries, petrochemical facilities, steel mills, pulp and paper mills, and general manufacturing in all geographies may be challenged with MIC issues. (Learn more about MIC in pipelines in the article Testing For Microbiologically Influenced Corrosion in Pipelines.)
Sulfate-reducing bacteria (SRB) are commonly found in anaerobic regions of aquatic and terrestrial environments. In cooling water systems, they are found within the sludges, under deposits and in biofilms. Therefore, heavy industries relying on surface water, reused (gray water), or well water are most at risk, especially power plants, refineries, petrochemical plants, steel mills, and pulp and paper mills.
SRB are generally recognized as playing a major role in MIC. Under deposit attack, which produces shiny, “terraced" or “bullseye” corrosion patterns, is commonly associated with SRB activity.
SRB contribute to corrosion through several mechanisms. The sulfides generated by these organisms are directly corrosive to some metals because they precipitate soluble iron as iron sulfide (FeS). FeS is cathodic to mild steel and accelerates anodic corrosion reactions. Precipitation of iron also stimulates corrosion by accelerating iron removal from the corrosion cell anode. In low pH environments, SRB oxidize hydrogen that has accumulated at the cathode. This depolarizes the cathode and stimulates metal loss in the anode.