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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:
- Water accumulation
- Water quality (pH, salts, CO2,
- Temperature
- Flowing or shut-in condition
- Nature of chemical treatments
- Coupon studies
External Environment:
- Soil composition
- Coating conditions
- Cathodic protection levels
- Coupon studies
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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