By far, the microbiological species most associated with corrosion has been Sulphate-Reducing Bacteria (SRB). Majority of Microbiologically Influenced Corrosion (MIC) research has focused on the activities of this type of bacteria. One of the primary reasons for this has been the presence of iron sulfides in corrosion products associated with MIC. SRB reduce sulfates to sulfides, which then react with iron and steel. However, an accepted fact is that MIC is also caused by the action of the biofilm produced by bacteria, in a similar way to under-deposit corrosion.
The primary method used to prevent MIC in the oil and gas industry is by use of biocides. The criteria used for selection of biocides is often their proficiency to kill SRB. The danger with this is that one can neglect the ability of other bacteria frequently found in oil and gas environment, such as general aerobes and general anaerobes to cause corrosion by biofilm production. This became evident when severe general & pitting corrosion was observed in two oil and gas separators in one of the facilities in Kuwait Oil Company (KOC), where SRB levels were zero but significant numbers of sessile and planktonic general aerobes and general anaerobes were found to be present in the process.
Using microbiological and chemical analysis, the mechanism of this type of MIC, specially the relationship between the quantity of various biofilm-forming bacteria and nature and magnitude of corrosion has been studied and the findings are presented in this paper.