The metallurgical evidence is given the heaviest
weighting, sufficient to pronounce MIC as
being “very likely” in the absence of any other
evidence from biological or chemical tests. Key
features of the metallurgical fingerprint ascribed
to MIC include corrosion pits composed of several
smaller pits with hemispherical or cuplike
appearance, striations in the direction of rolling
in the steel pit bottom, and tunneling into the
sides of the corrosion pit (Fig. 10). The guides
provide appropriate photographs and methods
for identification of these features. Biological
analyses assess the number of viable SRB, APB,
and anaerobic bacteria present. Chemical analysis
of corrosion products has limited application
in the scorecard and is more fully addressed
later. Commercial kits have been developed for
the analysis of the biological and chemical criteria
used in the guides. Use of these tools is not
confined to pipeline applications or soil environments.
They are generally useful wherever the
corrosion of carbon steel is observed (Ref 64).
A complementary approach to use of an MIC