Microbial corrosion

Microbial corrosion, or bacterial corrosion, is microorganisms, usually chemoautotrophs. It can apply to both metals and non-metallic materials. The phenomenon is also referred to as Bio-corrosion, Microbiologically Influenced Corrosion, Microbially Induced Corrosion or MIC.

Bacteria

Some sulfate-reducing bacteria produce ammonia.

In presence of oxygen, biogenic sulfide corrosion.

Without presence of oxygen, 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; the electrode potential of at least -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 galvanic corrosion. [1]

Bacterial corrosion may appear like graphite matrix with low mechanical strength in place.

Various corrosion inhibitors can be used to combat microbial corrosion. Formulae based on benzalkonium chloride are common in oilfield industry.

Microbial corrosion can also apply to concrete, and many other materials.

Aviation fuel

Hydrocarbon utilizing microorganisms, mostly Cladosporium resinae and Pseudomonas aeruginosa, colloquially known as "HUM bugs", are commonly present in FSII, which is added to the fuel, acts as a growth retardant for them. There are about 250 kinds of bacteria that can live in jet fuel, but fewer than a dozen are meaningfully harmful.

Recent events

In response to increased awareness of the nature and danger of microbial corrosion, a two-day international symposium was held in Perth, Western Australia in February 2007. It attracted speakers and attendees from as far as Argentina, Brazil, New Zealand, Singapore, the UK and the US in addition to Australian representatives. The symposium primarily focussed on the identification of Microbial Corrosion in marine, mining and industrial environments and the best course of action to remove and prevent further attacks.