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Concerns over Microbiologically Influenced Corrosion
(MIC) Increasing
Adapted from Concern Over MIC
Expanding Among Corrosion Engineers, D.P. Pope, Pipeline & Gas Industry February
1997, pp 23-25.
Piping and pipeline systems are often great places to grow microbes that can produce corrosive conditions. MIC often works in combination with other forms of corrosion such as crevice corrosion and under-deposit corrosion on in the pipe. It can also accelerate corrosion produced by impurities in the system environment such as H2S and/or CO2.
For example, MIC can occur in the crevices produced by disbonded coatings on the outside of the pipe that are shielded from cathodic protection. Internally, sites for MIC are where water, debris and other nutrients accumulate on the pipe wall. Both sites provide the local conditions conducive to colonization of microbes which can further exacerbate corrosion problems by producing organic acids or acid producing gases. There is a long list of microbes that can participate in the corrosion reaction which include aerobic or anaerobic types (depending on whether they require oxygen or lack of oxygen to survive). They can also metabolize nutrients in the environment (sulfates, nitrates, iron) to produce corrodants or otherwise accelerate the attack of steel.
Detection of MIC can be accomplished by a variety of methods. Sampling and culturing can be performed for identification of the magnitude of the infection and the active strain(s) of organism present. For these methods to be most effective, they should be applied on-site immediately following sampling. This procedure can also be used to assess the efficacy of preventative or remedial treatments. Chemical analysis and pH of corrosion products can also give important information relative to the nature of the problem. Evidence taken from the metal surface (sessile surveys) has a better chance of properly assessing the situation versus sampling of the liquids (planktonic survey).
MIC Survey Check List
Internal Environment:
External Environment:
Prevention or remediation of MIC is usually accomplished by application of either physical or chemical methods. One of the most effective actions to mitigate MIC is pigging which physically removes standing water and accumulated debris in the line. Biocides and inhibitors can also be used to fight MIC. However, significant incompatibilities between the various types of chemicals can exist and they should be checked using a planned regiment of laboratory or field testing for both chemical compatibility and performance prior to widespread field or plant application.
Adapted from Concern Over MIC Expanding Among Corrosion Engineers, D.P. Pope, Pipeline & Gas Industry February 1997, pp 23-25.
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