Microbial corrosion

Microbial corrosion, also called bacterial corrosion, bio-corrosion, microbiologically-influenced corrosion, or microbially-induced corrosion (MIC), is corrosion caused or promoted by microorganisms, usually chemoautotrophs. It can apply to both metals and non-metallic materials.

Bacteria

Some sulfate-reducing bacteria produce hydrogen sulfide, which can cause sulfide stress cracking. Acidithiobacillus bacteria produce sulfuric acid; Acidothiobacillus thiooxidans frequently damages sewer pipes. Ferrobacillus ferrooxidans directly oxidizes iron to iron oxides and iron hydroxides; the rusticles forming on RMS Titanic wreck are caused by bacterial activity. Other bacteria produce various acids, both organic and mineral, or ammonia.

In presence of oxygen, aerobic bacteria like Acidithiobacillus thiooxidans, Thiobacillus thioparus, and Thiobacillus concretivorus, all three widely present in the environment, are the common corrosion-causing factors resulting in biogenic sulfide corrosion.

Without presence of oxygen, anaerobic bacteria, especially Desulfovibrio and Desulfotomaculum, are common. Desulfovibrio salixigens requires at least 2.5% concentration of sodium chloride, but D. vulgaris and D. desulfuricans can grow in both fresh and salt water. D. africanus is another common corrosion-causing microorganism. The Desulfotomaculum genus comprises sulfate-reducing spore-forming bacteria; Dtm. orientis and Dtm. nigrificans are involved in corrosion processes. Sulfate-reducers require reducing environment; an electrode potential lower than -100 mV is required for them to thrive. However, even a small amount of produced hydrogen sulfide can achieve this shift, so the growth, once started, tends to accelerate.

Layers of anaerobic bacteria can exist in the inner parts of the corrosion deposits, while the outer parts are inhabited by aerobic bacteria.

Some bacteria are able to utilize hydrogen formed during cathodic corrosion processes.

Bacterial colonies and deposits can form concentration cells, causing and enhancing galvanic corrosion. [1]

Bacterial corrosion may appear in form of pitting corrosion, for example in pipelines of the oil and gas industry. Anaerobic corrosion is evident as layers of metal sulfides and hydrogen sulfide smell. On cast iron, a graphitic corrosion selective leaching may be the result, with iron being consumed by the bacteria, leaving graphite matrix with low mechanical strength in place.

Microbial corrosion can also apply to plastics, concrete, and many other materials. Two examples are Nylon-eating bacteria and Plastic-eating bacteria.

Susceptible areas in energy industry

The entire oil/gas processing/application system could be susceptible to MIC, e.g. separators, storage tanks, pipelines, etc.

Treatments

Biocides can be batch applied on a periodic basis to remove bacteria buildup in the production and processing facilities and combat microbial corrosion. Formulae based on benzalkonium chloride are common in oilfield industry.

Pigging can help remove biofilm buildup in pipelines.

Surveillance

Bio-coupons can be installed in susceptible spots in the system to monitor bio-mass buildup.

See also

• Microbiologically Influenced Corrosion (MIC) and Other Forms of Corrosion
• Biogenic sulfide corrosion
• Corrosion
• Rusticle

websites

• Dialog to odor and biogenic corrosion in sewage, exhaust air arrangements and fermentation gas arrangements

Further reading

Kobrin, G., "A Practical Manual on Microbiologically Influenced Corrosion", NACE, Houston, Texas, USA, 1993.

Heitz,E., Flemming HC., Sand, W., "Microbially Influenced Corrosion of Materials", Springer, Berlin, Heidelberg, 1996.

Videla, H., "Manual of Biocorrosion", CRC Press, 1996.

Javaherdashti, R., "Microbiologically Influenced Corrosion-An Engineering Insight", Springer, UK, 2008.

D. Weismann, M. Lohse (Hrsg.): "Sulfid-Praxishandbuch der Abwassertechnik; Geruch, Gefahr, Korrosion verhindern und Kosten beherrschen!" 1. Auflage, VULKAN-Verlag, 2007, ISBN 978-3-8027-2845-7.