Microbial corrosion involves microbes or bacteria that are omnipresent; in the air, in soils, and in fresh and seawater. Their presence, however, does not necessarily imply a corrosion problem. In fact, even though microbial influenced corrosion (MIC) can be encountered in unlikely geographical regions with ambient temperatures typical of Arctic and Antarctic regions, it is more commonly encountered in temperate, warm and humid climates as far as upstream oil and gas exploration activities are concerned. Also, to put it into perspective, compared with other forms of corrosion that can occur in coiled tubing (CT) strings such as pitting, hydrogen cracking and general (weight loss) corrosion from contact with sour or other low pH wellbore fluids or improperly inhibited acid treatment fluids, MIC represents a rare occurrence. Over the nearly 20 years of CT failure investigations, the author has encountered only a few cases of MIC, one involving coiled tubing manufacturing in southern Texas, USA, and another during CT drilling in southern Australia where the latter involved pre-existing MIC corrosion pits that were suspected of having been incubated during long shipping periods by ocean transport.

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