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The influence of microorganisms on the corrosion and protection of metals. An overview
Abstract
Microorganisms are able to drastically change the electrochemical conditions at the metal/solution interface by biofilm formation including bacterial consortia and extracellular polymeric substances (EPS) as the main components. The presence of biofilms generally facilitates the initiation of localized corrosion but this effect can be reversed to corrosion inhibition. Microbial corrosion inhibition and its counter process, microbiologically influenced corrosion (MIC) are rarely linked to a single mechanism or to a single species of microorganisms. In recent years microbial inhibition of corrosion and protection of metals have been attributed to the blocking effect of biofilms and EPS. However, this simplistic approach must be discussed from an electrochemical point of view to understand the complex metal-microbe interactions at the metal surface. With this aim, several practical cases involving sulfate-reducing bacteria (SRB) and other microorganisms are critically discussed. General mechanisms for interpreting the influence of microorganisms on the protection and passivity of metals are presented.
... In addition, the presence of oxygen accelerates MIC of iron, leading to the conversion of the primary iron sulfide product, mackinawite (FeS), to pyrite (FeS 2 ) and elemental sulfur. 5 In the absence of oxygen, anaerobic SRB create a galvanic couplewith the iron surface acting as a cathode and the bio-fouled iron surface as an anode. The open circuit potential of the iron increases and moves to more positive values if the bacteria are active. ...
Microbiologically influenced corrosion is the degradation of a material under the influence of environmental factors complicated by the metabolic activities of microorganisms. Microbiological attack on process equipment used in the petroleum industry results in increased operating expenses and reduced income.
... Specifically, the introduction of oxygen accelerates microscopically induced corrosion of iron leading to the conversion of primary iron sulfide product mackinawite (FeS) to pyrite (FeS 2 ) and elemental sulfur 5 ...
Bacteria population density may provide a viable corrosion control metric for microbiologically influenced corrosion (MIC) in oilfield water handling systems so that the population of the different strains of bacteria such as sulfate reducing bacteria (SRB), acid producing bacteria (APB) [also classified as general aerobic bacteria (GAB)] and general anaerobic bacteria (GAnB) in the operating environment can be kept below a target envelop. Consider, for example, a system that has been experiencing increased corrosion over a period of time. If the trend of increasing corrosion rate versus time parallels the corresponding plot of all bacteria population density over that same period of time, the general assumption is to ascribe the source of increased corrosion to increased bacteria population density. It is because of this empirical correlation that oil companies normally develop in-house guidelines for quantifying bacteria proliferation. There is, however, no generally accepted method for determining such guideline unambiguously. This paper provides a guidance to correlate the effects of bacteria population density on general and pitting corrosion rates with the goal of developing a self-consistent MIC performance indicator. It is based on microbiological and corrosion data obtained from various water handling systems at the Kuwait Oil Company.
Key words: Microbiologically Influenced Corrosion, MIC, SRB, APB, GAB, GAnB
Electrochemical techniques such as: corrosion and critical pitting potential measurements, direct current potentiostatic and potentiodynamic polarization, linear polarization resistance, split-cell current measurements, electrochemical impedance, electrochemical noise, and electrical resistance probes are evaluated for use in investigating microbiologically influenced corrosion. Examples are given to illustrate the capabilities and limitations of each technique.
In batch and continuous fermentations, the reduction in corrosion of SAE 1018 mild steel and 304 stainless steel caused by inhibition of the reference sulfate-reducing bacterium (SRB) Desulfovibrio vulgaris by a protective, antimicrobial-producing Bacillus brevis biofilm was investigated. The presence of D. vulgaris produced a thick black precipitate on mild steel and a higher corrosion rate in batch cultures than that seen in a mono-culture of non-antimicrobial-producing Pseudomonas fragi K upon the addition of SRB to the aerobic P. fragi K biofilm. In continuous reactors, the polarization resistance R
p decreased for stainless steel and increased for mild steel upon the addition of SRB to a P. fragi K biofilm. Addition of either 200 μg/ml ampicillin, chloramphenicol, or ammonium molybdate to batch and continuous reactors after SRB had colonized the metal was ineffective in killing SRB, as inferred from the lack of change in both R
p and the impedance spectra. However, when ampicillin was added prior to SRB colonization, the growth of SRB was completely inhibited on stainless steel in continuous reactors. Prior addition of ampicillin was only able to delay the growth of SRB on mild steel in continuous reactors. External addition of the purified peptide antimicrobial agent gramicidin S prior to the addition of SRB also inhibited the growth of SRB on stainless steel in continuous reactors, and the SRB were also inhibited on stainless steel in both batch and continuous reactors by producing gramicidin S in situ in a protective biofilm when the gramicidin-S-overproducing strain Bacillus brevis 18 was used.
Different studies have been made using conventional electrochemical polarization techniques to establish the mechanism for the action of sulfate reducing bacteria (SRB) in microbiologically influenced corrosion (MIC). Nevertheless, there has been almost no detailed follow-up correlating the corrosive process with time and open circuit potential, corrosion products, sessile bacterial growth and morphological attack, to establish the mechanism of this bacterial action. This research project designed an experimental structure to make these correlations utilizing the hydrogen permeation technique as its principal electrochemical tool to follow the cathodic reaction, coupled with any other electrochemical, microbiological or chemical technique that would permit following the anodic reaction. The study began by reviewing the classic cathodic depolarization theory using an SRB strain identified as Desulfovibrio desulfuricans subespecie desulfuricans ATCC 7775 and an inert palladium sheet as a substrate with and without cathodic polarization. Later, corrodible sheets of carbon steel and iron were used to study the corrosive process, which permitted to establish the mechanism of this SRB on carbon steel when the medium has a high contamination of ferrous ions. © 2011 2002 Revista Técnica. Facultad de Ingeniería. Universidad del Zulia.
The paper presents a review of published literature on the microbiological corrosion of aluminum alloys, copper alloys, iron and mild steels, the higher nickel-chromium stainless alloys, and titanium. All but the higher nickel-chromium alloys and titanium are subject to microbiological corrosion. Suggestions are made for research in this area.
The inhibition of the corrosion of aluminum alloy 2024-T3 in sodium chloride solution was investigated from the view of the chemical species (complexes, compounds) possibly formed with aluminum ion. Four classes of compounds were considered: (I) As a basis for comparison, inorganic oxyanions, chromate, nitrate, perchlorate, and sulfate. (II) The sodium salt of citric acid, a monohydroxy tricarboxylic acid and tartaric acid, a dihydroxy dicarboxylic acid. (III) The sodium salts of acetic, benzoic, and oxalic acids. (IV) Compounds that are known to form stable complexes or compounds with aluminum, such asazelaicacid, benzotriazole, cupferron, oxamide, and quinaldic and rubeanic acids. Inhibitor efficiencies were measured for 14 day immersions and compared with linear polarization measurements. In group I, only chromate gave complete protection, the other anions offering, at certain concentrations, both inhibition and accelerated corrosion (synergistic effect). In group II, both citric and tartaric gave accelerated corrosion at certain concentrations. Of the group III, species, sodium benzoate gave good protection, acetate and oxalate only fair ( ∼ 50% efficiency). Of the group IV compounds cupferron, azelaic acid, and benzotriazole offered fair inhibition. These results are interpreted in terms of the species that are formed with the aluminum ion.
Corrosion fatigue is considered to be one of the most important factors in determining the life of static offshore structures such as platforms for oil and gas production; the combination of corrosive environment and cyclic stress can produce failure of metals by the development and growth of cracks. Seawater provides both the chemical reagent and, through wave action, the source of cyclic fatigue loading. Marine fouling can enhance both factors, first by enhancing the corrosive reactions and secondly by increasing the diameter and surface roughness of platform legs and bracing members. In relation to corrosion fatigue this enhancement is mainly due to the production of hydrogen sulphide by sulphate‐reducing bacteria. Both the effects of loading and hydrogen embrittlement can be independent of anti‐corrosion measures and thus need to be quantified and incorporated into the determination of the design life of the structure. Data are presented on the level of hydrogen sulphide that could be found under marine fouling and on corrosion fatigue crack growth in seawater containing various levels of both biologically produced and abiotic hydrogen sulphide. Crack growth rates are found to be enhanced, even at low levels, by hydrogen sulphide, and there are differences between biological and abiological environments.
Aluminium, zinc and mild steel were subjected to influence of wild strain Bacillus mycoides for 2 years under laboratory conditions at controlled temperature and humidity. The microorganisms were isolated from the metal samples exposed under outdoor conditions in different regions of Lithuania. Electrochemical impedance measurements performed for both biotic and abiotic samples indicated microbially influenced corrosion inhibition for aluminium, corrosion acceleration for zinc and indifference for steel. The microbiological corrosion inhibition implied an environmentally friendly alternative of corrosion protection to toxic chemicals, application of which due to stricter environmental regulations tends to be increasingly restricted.
Bacterial activity at metal surfaces may result in corrosion induction or corrosion inhibition. An important effect of chemoorganotrophic
bacteria under aerobic conditions is the removal of oxygen from the metal surface. This is most effectively done by biofilm-forming
microorganisms and causes corrosion inhibition. Anaerobes promote corrosion if they consume molecular hydrogen, for example
sulfate-reducing bacteria and certain Fe(III)-reducing organisms such as Shewanella putrefaciens. Chemoorganotrophic Fe(III) reducers are of special interest because they remove corrosion products and hence destroy ecological
niches for sulfate-reducing bacteria beneath the deposits. Also, these chemoorganotrophic bacteria may cause passivation of
the metal surface through the consumption of dissolved oxygen, lowering the open circuit potential and the creation of a protective
layer of atomic hydrogen on the metal surface.