Microbial induced corrosion
(MIC) occurs when corrosion exists due to microorganisms.
The two most commonly tested
groups of microorganisms are SRB's and APB's.
SRB is the
acronym for Sulphate Reducing Bacteria. Formations that have
natural occurring sulphate form corrosive Hydrogen Sulphide (H2S)
with the aid of SRB's. Corrosive H2S then reacts
(corrodes) with iron to form iron sulphide. SRB's are removed by a
wide variety of available biocides. The best biocides are those
that are also corrosion inhibitors (leave a protective film).
One of the waste products of
SRB's is Hydrogen Sulphide (H2S). This toxic and
corrosive chemical reacts with metallic iron (Fe) to form the
potentially explosive product called Iron Sulphide (FeS). Iron is
removed from the pipeline wall molecule-by-molecule until a pit
eventually perforates the wall and forms a hole.
APB is the
acronym for Acid Producing Bacteria. Almost all acids are
corrosive to metals. By controlling the population of these
bacteria, the concentration of aggressive acids are lowered.
MIC is best controlled with
a combined batching and pigging program. Other variations include
batching only, and various types of pigging.
The presence of APB's and
SRB's are determined by convenient tests that are inoculated at the
Most MIC is induced by
symbiotic means. Symbiosis is mutually dependent situations.
For example: Most yeasts found in oilfield lines are Slime Formers
(they form a layer between the pipeline fluids and the pipeline wall).
SRB populations lower significantly decrease at very low pH values.
SRB's proliferate in between the layer of yeast and the pipeline wall.
SRB's then excrete nutrients that the yeast metabolizes to increase its
growth rate, which provides a larger protective layer for the SRB's...and
Identification of SRB's and
APB's are subcategorized as Sessile and Planktonic. Sessile
microbes are those attached to linings and pipe surfaces, where
Planktonic microbes are floating in the liquid.
MIC is usually controlled
with biocides that have been batched and pigged.