interView QuestiOn
and answer On
‘MicrObiOLOGicaLLy infLuenced
cOrrOsiOn’
icrobiologically Influenced
Corrosion (MIC) can
be addressed as an
electrochemical corrosion
in which the role of micro-
and macro-organisms is undeniable.
Between 20 to 40% of the economic loss
of corrosion is due to MIC. In Canada,
50 % of external corrosion cases of gas
pipelines are attributed to MIC. Being
electrochemical in nature means that MIC
can be treated by conventional ways of
controlling corrosion: coating, CP, use of
chemicals, materials selection and design.
Being microbial in nature, however, adds
more into these measures as well as if
they can be applied with 100% success:
the chemical used are called biocides
(other than inhibiters), Not all coatings are
resistant to MIC, CP may or may not control
MIC and all known engineering materials
(except Titanium and its alloys) have been
reported to be vulnerable to MIC. If MIC
happens in non-metals (such as concrete
or composites), it is more technical to
address it as MID (Microbiologically
influenced deterioration).MIC can be
operate as a pre-commissioning factor
in increasing the risk of corrosion in
M
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PECM Issue 29
common practices such as hydrostatic
test or during inspection practices such
as intelligent pigging. There are two
groups of methods to be used for the
recognition of MIC: Culture-dependent
and culture-independent. Both groups
have serious drawbacks in addition to their
undeniable advantages. Likewise, there
are four ways to treat MIC: physical (use of
coating)/mechanical (pigging, scrubbing)
- Chemical (use of biocides), electrical
(CP) and microbiological (Bacteria against
bacteria). All these treatment methods
also have their own intrinsic limitation and
disadvantages.
1.
W HAT IS MICROBIOLOGICALLY
INFLUENCED CORROSION (MIC) AND
HOW HAS IT ATTRACTED ATTENTION
OVER THE PAST DECADES ?
Microbiologically influenced corrosion
(MIC), or as Europeans mostly prefer to
say microbiologically induced corrosion
is an electrochemical process in nature
where micro-organ isms (such as bacteria
and Archaea) and macro-organisms
(such Barnacles) are capable of affecting
the severity of corrosion by initiation,
acceleration and sometimes deceleration it.
Due to its very high costs, both economic and
ecologic, the interest in MIC always shows an
ever-increasing trend.
2.
W HAT ARE THE KEY TECHNOLOGIES
AVAILABLE IN MARKET TODAY
IN TERMS OF MONITORING AND
DETECTING MIC?
Culture-dependent methods such as MPN
(most probable number) and serial dilution
as well as simple absence/presence cultures
are available. However, these methods
all have the drawback that about 99% of
bacteria are not culturable. Recently, culture-
dependent methods that rely on molecular
microbiology methods, such as PCR, DGGE,
ATPG2 and the like have been developed.
While Culture-independent methods
do have accuracy advantage over their
culture-dependent methods, they also suffer
from serious limitations. In addition, unlike
culture-dependent methods that are the
base for all field tests such as but not limited
to BART, culture-independent methods y
have not been “Field-friendly”…yet!