Box 14.12: Bacteria and Corrosion of Steel
Michel Magot
Bacterial corrosion, biocorrosion, MIC (microbially
Influenced – or Induced – Corrosion), biological corrosion, corrosion by microorganisms: it seems that
there is not much consensus to designate the phenomenon than there is to interpret its mechanisms. But
whatever you call it, it is undoubtly a harmful consequence of bacterial proliferation against which many
industries would like to guard, as it is considered that
its economic weight just in France in this early twentyfirst century is about the billion € per year (Fe ´ron et al.
2002). Under these various names, one usually refers
to a set of special cases of biodeterioration of materials
(Lemaitre et al. 1994), that of the steel corrosion
caused by bacterial growth, and more specifically by
that of sulfate-reducing bacteria. The corrosion of a
metal is a phenomenon of electrochemical nature. In
contact with an electrolyte, the metal atoms can spontaneously move as cations in the aqueous solution (anodic
reaction), and its electrons are used to reduce the elementary particles of the aqueous phase (cathodic reaction). These two half-reactions are associated with
electric currents, namely anodic and cathodic currents.
The net result is the oxidation of the metal, the most
commonly observed form being the rust that occurs
under aerobic conditions, when the metal electrons are
transferred to oxygen. Under anaerobic conditions, the
oxidation reaction of the metal results from electron
transfer to the protons of the electrolyte, and leads to
the formation of hydrogen. In all industries using steel
equipments in contact with water, whether aerated or
not, most cases of bacterial corrosion occur under anaerobic conditions. Indeed, within a biofilm in which aerobic bacteria grow by consuming oxygen, micro-niches
favorable for the development of anaerobic bacteria are
created, including sulfate-reducing bacteria (SRBs) that
are most frequently implicated in cases of bacterial
corrosion listed in the scientific literature.
By the way, their role in this process had been
demonstrated very early in the history of microbiology, since this was in 1934 that Von Wolzogen Kur
and Van der Vlugt proposed a mechanism of bacterial
M. Magot (*)
Institut des Sciences Analytiques et de Physico-chimie pour
l’Environnement et les Mate ´riaux (IPREM), UMR CNRS 5254,
Universite ´ de Pau et des Pays de l’Adour, B.P. 1155, 64013 Pau
Cedex, France
(continued)
Box 14.12 (continued)
corrosion called “the cathodic depolarization theory”.
Briefly, this theory states that SRBs accelerate the spontaneous reaction of steel corrosion in contact with water
(two half-reactions mentioned above) by consuming its
products: metal ions by precipitation as sulfide minerals,
and cathodic hydrogen used as an energy source. This
theory has been, and is still, extremely popular within
the community of microbiologists more than 70 years
after its statement. Actually, some experimental
approaches tended to confirm it, and discoveries made
after its statement, e.g., the hydrogenases of SRBs,
brought new arguments to the concept of cathodic
depolarization. Electrochemists marked nevertheless
less effusive, until they show that advances in the field
of thermodynamics made after the 1930s were not compatible with this theory (Crolet 1992). It thus may still
take many years before the traditional citation of the
cathodic depolarization theory gives way to other
interpretations of the mechanism of corrosion by SRB.
Nevertheless, other tracks have been or are being
explored, among which is the role of sulfides, resulting
from the bacterial reduction of sulfate or thiosulfate.
Their extreme corrosivity, especially in acidic medium,
is well documented in the corrosion literature. Precisely,
the local acidification of the steel surface under a biofilm resulting from SRB metabolic activity is a mechanism that has been hypothesized, and then demonstrated
experimentally (Daumas et al. 1993). The putative role
of phosphorus compounds was also suggested.
The direct or indirect role of bacterial sulfide production was reinforced by the discovery that other
sulfidogenic bacteria could cause unusually fast steel
corrosion in very special circumstances. By analogy,
the acronym TRB, thiosulfate-reducing bacteria, was
proposed to designate this group of strictly anaerobic
bacteria that reduce thiosulfate but not sulfate, to sulfide (see Sect. 14.4). Although thiosulfate-reduction
does not seem to produce energy for these fermentative
anaerobic bacteria, the amount of sulfides that may be
produced in culture could be 2–10 times greater than
sulfide production by SRB. In vitro electrochemical
experiments in anaerobic fermenters showed that
Dethiosulfovibrio peptidovorans can corrode steel
coupons at a rate in the order of 1 cm per year in the
presence of thiosulfate, while SRB, tested under the
same conditions corrode at 5–10 times slower rates. It
seems that the most spectacular industrial cases of
(continued)
586
J.-C. Bertrand et al.
Michel Magot
Bacterial corrosion, biocorrosion, MIC (microbially
Influenced – or Induced – Corrosion), biological corrosion, corrosion by microorganisms: it seems that
there is not much consensus to designate the phenomenon than there is to interpret its mechanisms. But
whatever you call it, it is undoubtly a harmful consequence of bacterial proliferation against which many
industries would like to guard, as it is considered that
its economic weight just in France in this early twentyfirst century is about the billion € per year (Fe ´ron et al.
2002). Under these various names, one usually refers
to a set of special cases of biodeterioration of materials
(Lemaitre et al. 1994), that of the steel corrosion
caused by bacterial growth, and more specifically by
that of sulfate-reducing bacteria. The corrosion of a
metal is a phenomenon of electrochemical nature. In
contact with an electrolyte, the metal atoms can spontaneously move as cations in the aqueous solution (anodic
reaction), and its electrons are used to reduce the elementary particles of the aqueous phase (cathodic reaction). These two half-reactions are associated with
electric currents, namely anodic and cathodic currents.
The net result is the oxidation of the metal, the most
commonly observed form being the rust that occurs
under aerobic conditions, when the metal electrons are
transferred to oxygen. Under anaerobic conditions, the
oxidation reaction of the metal results from electron
transfer to the protons of the electrolyte, and leads to
the formation of hydrogen. In all industries using steel
equipments in contact with water, whether aerated or
not, most cases of bacterial corrosion occur under anaerobic conditions. Indeed, within a biofilm in which aerobic bacteria grow by consuming oxygen, micro-niches
favorable for the development of anaerobic bacteria are
created, including sulfate-reducing bacteria (SRBs) that
are most frequently implicated in cases of bacterial
corrosion listed in the scientific literature.
By the way, their role in this process had been
demonstrated very early in the history of microbiology, since this was in 1934 that Von Wolzogen Kur
and Van der Vlugt proposed a mechanism of bacterial
M. Magot (*)
Institut des Sciences Analytiques et de Physico-chimie pour
l’Environnement et les Mate ´riaux (IPREM), UMR CNRS 5254,
Universite ´ de Pau et des Pays de l’Adour, B.P. 1155, 64013 Pau
Cedex, France
(continued)
Box 14.12 (continued)
corrosion called “the cathodic depolarization theory”.
Briefly, this theory states that SRBs accelerate the spontaneous reaction of steel corrosion in contact with water
(two half-reactions mentioned above) by consuming its
products: metal ions by precipitation as sulfide minerals,
and cathodic hydrogen used as an energy source. This
theory has been, and is still, extremely popular within
the community of microbiologists more than 70 years
after its statement. Actually, some experimental
approaches tended to confirm it, and discoveries made
after its statement, e.g., the hydrogenases of SRBs,
brought new arguments to the concept of cathodic
depolarization. Electrochemists marked nevertheless
less effusive, until they show that advances in the field
of thermodynamics made after the 1930s were not compatible with this theory (Crolet 1992). It thus may still
take many years before the traditional citation of the
cathodic depolarization theory gives way to other
interpretations of the mechanism of corrosion by SRB.
Nevertheless, other tracks have been or are being
explored, among which is the role of sulfides, resulting
from the bacterial reduction of sulfate or thiosulfate.
Their extreme corrosivity, especially in acidic medium,
is well documented in the corrosion literature. Precisely,
the local acidification of the steel surface under a biofilm resulting from SRB metabolic activity is a mechanism that has been hypothesized, and then demonstrated
experimentally (Daumas et al. 1993). The putative role
of phosphorus compounds was also suggested.
The direct or indirect role of bacterial sulfide production was reinforced by the discovery that other
sulfidogenic bacteria could cause unusually fast steel
corrosion in very special circumstances. By analogy,
the acronym TRB, thiosulfate-reducing bacteria, was
proposed to designate this group of strictly anaerobic
bacteria that reduce thiosulfate but not sulfate, to sulfide (see Sect. 14.4). Although thiosulfate-reduction
does not seem to produce energy for these fermentative
anaerobic bacteria, the amount of sulfides that may be
produced in culture could be 2–10 times greater than
sulfide production by SRB. In vitro electrochemical
experiments in anaerobic fermenters showed that
Dethiosulfovibrio peptidovorans can corrode steel
coupons at a rate in the order of 1 cm per year in the
presence of thiosulfate, while SRB, tested under the
same conditions corrode at 5–10 times slower rates. It
seems that the most spectacular industrial cases of
(continued)
586
J.-C. Bertrand et al.