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Iron (Fe)- and manganese (Mn)-oxidizing bacteria are often cited individually and collectively as putative microorganisms for microbiologically influenced corrosion (MIC). The two groups of microorganisms have in common the ability to attach to surfaces and produce macroscopic accumulations (deposits) of metal oxides/hydroxides/oxyhydroxides that can influence corrosion of some metals and alloys in some environments. In all cases, once initiated, the corrosion is independent of the activities of the colonizing species. Despite the phylogenetic diversity of Fe-oxidizing bacteria (FeOB), the following sections will deal with corrosion mechanisms attributed to neutrophilic, lithotrophic, microaerophilic FeOB. The mineralogy of biologically oxidized Fe is consistent over a wide range of environments. All FeOB produce dense deposits that can cause corrosion of low alloy stainless steels (SS) directly, i.e., under-deposit corrosion. Association of Mn-oxidizing bacteria (MnOB) and other microorganisms may stabil...

Iron (Fe) oxides/oxyhydroxides in drinking water distribution systems (DWDS), produced by electrochemical, chemical, and biological reactions, can adsorb toxic metal ions, including strontium, lead, arsenic, and vanadium that, if desorbed, generate pulses of drinking water with elevated toxic metal ion concentrations. To illustrate that potential, sorption data for strontium (cation) and vanadium (oxyanion) in functioning DWDS are reviewed. In addition, the influence of flow/no flow on adsorption and desorption of strontium in a model DWDS is included. The reactions that influence adsorption and desorption within a DWDS are extremely complicated and poorly understood. The sorption capacity of Fe oxhydroxides varies with surface area, which in turn varies with source water and disinfectant. Desorption and release can be triggered by changes in source water, disinfection chemicals, or flow. Because of the interrelatedness of adsorption/desorption and Fe corrosion products, subtle changes in DWDS operating p...

Microbially influenced corrosion (MIC), is acknowledged to be the direct cause of catastrophic corrosion failures, with associated damage costs ranging to many billions of US$ annually. In spite of extensive research and numerous publications, fundamental questions relating to MIC remain unanswered. The following review provides an overview of current MIC research and stresses the lack of information related to MIC recognition, prediction and mitigation. The review establishes a link between management decisions and root causes. A holistic, proactive approach to MIC is suggested in which an entire system is considered, monitored and improved.

The pioneering work of Dickinson, et al., and other investigators in the Lewandowski research group at the Center for Biofilm Engineering, Montana State University, Bozeman, MT, provided a...

Addition of 1 g/L yeast extract (YE) to sterile, aerobic (approximately 21% dissolved oxygen) and deoxygenated (

The United States Environmental Protection Agency (US EPA) will require some U.S. drinking water distribution systems (DWDS) to monitor nonradioactive strontium (Sr(2+)) in drinking water in 2013. Iron corrosion products from four DWDS were examined to assess the potential for Sr(2+) binding and release. Average Sr(2+) concentrations in the outermost layer of the corrosion products ranged from 3 to 54 mg kg(-1) and the Sr(2+) drinking water concentrations were all ≤0.3 mg L(-1). Micro-X-ray adsorption near edge structure spectroscopy and linear combination fitting determined that Sr(2+) was principally associated with CaCO3. Sr(2+) was also detected as a surface complex associated with α-FeOOH. Iron particulates deposited on a filter inside a home had an average Sr(2+) concentration of 40.3 mg kg(-1) and the associated drinking water at a tap was 210 μg L(-1). The data suggest that elevated Sr(2+) concentrations may be associated with iron corrosion products that, if disturbed, could increase Sr(2+) concentrations above the 0.3 μg L(-1) US EPA reporting threshold. Disassociation of very small particulates could result in drinking water Sr(2+) concentrations that exceed the US EPA health reference limit (4.20 mg kg(-1) body weight).

Field observations and laboratory testing were used to conclude that aggressive localized corrosion of carbon steel pilings in Duluth-Superior Harbor, Minnesota and Wisconsin, is caused by...

It is our hypothesis that fermentative, acetogenic, and sulfate-reducing bacteria residing in pipeline facilities can influence corrosion through the production of carbon dioxide and acetate under the prevailing anaerobic conditions. The exacerbation of carbon dioxide corrosion of carbon steel in the presence of acetic acid is a well-known phenomenon in the oil industry. Both chemical compounds can be produced and consumed by microorganisms during the anaerobic biodegradation of organic matter—including hydrocarbons. We contend that the principles governing anaerobic biodegradation activity can be extrapolated to aboveground oil production facilities and that the microbial diversity inherent in petroleum reservoirs largely reflects that in pipelines.

The use of proton exchange membranes (PEMs) in biological fuel cells limits the diversity of novel designs for increasing output power or enabling autonomous function in unique environments. Here we show that selected nanoporous polymer filters (nylon, cellulose, or polycarbonate) can be used effectively in place of PEMs in a miniature microbial fuel cell (mini-MFC, device cross-section 2 cm2), generating a power density of 16 W/m3 with an uncoated graphite felt oxygen reduction reaction (ORR) cathode. The incorporation of polycarbonate or nylon membranes into biological fuel cell designs produced comparable power and durability to Nafion-117 membranes. Also, high power densities for novel larger (5 cm3 anode volume, 0.6 W/m3) and smaller (0.025 cm3 projected geometric volume, average power density 10 W/m3) chamberless and pumpless microbial fuel cells were observed. As an additional benefit, the nanoporous membranes isolated the anode from invading natural bacteria, increasing the potential applications for MFCs beyond aquatic sediment environments. This work is a practical solution for decreasing the cost of biological fuel cells while incorporating new features for powering long-term autonomous devices.

Diagnosing microbiologically influenced corrosion (MIC) after it has occurred requires a combination of microbiological, metallurgical, and chemical analyses. MIC investigations have typic...

Field experiments designed to evaluate deoxygenation of natural seawater as a corrosion control measure for unprotected carbon steel seawater ballast tanks demonstrated decreased corrosion in hypoxic (

Employing electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS), we demonstrate that in both aerobic and anaerobic culture Shewanella oneidensis cells are capable of chromate reduction. No Cr(VI) or Cr(V) species were identified at the cell surfaces in Cr 2p3/2 core photoelectron spectra. More chromium was associated with cell surfaces recovered from anaerobic medium than aerobic. Multiplet-splitting models derived for Cr(III) and Cr(IV) were employed to determine contributions from each ion to Cr 2p3/2 photopeaks collected from the various cell treatments. Whilst in all cases Cr(III) was the major ion associated with cell surfaces, a significant contribution was identified due to Cr(IV) in anaerobically grown cells. The Cr(IV) contribution was far less when cells were grown aerobically. Moreover, when anaerobically grown cells were exposed to oxygen very little re-oxidation of Cr-precipitates occurred, the precipitates were again identified as a mixture of Cr(III) and Cr(IV). A positive relationship was observed between amounts of chromium and phosphorous associated with cell surfaces resulting from the various treatments, suggesting the precipitates included Cr(III)-phosphate. The fact that Cr(IV) remained associated with precipitates following re-oxidation suggests that under anaerobic conditions the intermediate ion is afforded sufficient stability to be incorporated within the precipitate matrix and thus conferred a degree of protection from oxidation. # 2002 Published by Elsevier Science B.V.

A perspective is provided on corrosion inhibition by bacterial biofilms. Inhibition of general corrosion by biofilms has been reported for mild steel, copper, aluminum, and stainless steels. The mechanisms most frequently cited for the inhibition are formation of a diffusion barrier to corrosion products that stifles metal dissolution, consumption of oxygen by respiring aerobic microorganisms within the biofilm causing a diminution of that reactant at the metal surface, production of metabolic products that act as corrosion inhibitors (e.g., siderophores) or specific antibiotics that prevent proliferation of corrosion-causing organisms (e.g., sulfate-reducing bacteria), and formation of passive layers that are unique to the presence of microorganisms. The perspective will review biofilm formation and the processes that make it difficult to predict and control.

Fungal influenced corrosion is reviewed for carbon steel and aluminum fuel tanks; carbon steel cables; and painted and unpainted ship holds containing wet and dry cargos, including wood, molasses, fatty oils and cereal. Deterioration of fiber-reinforced composites and glass has also been attributed to fungal species.

Sulfur and sulfur compounds can produce pitting, crevice corrosion, dealloying, stress corrosion cracking, and stress-oriented hydrogen-induced cracking of susceptible metals and alloys. Even though the metabolic by-products of the biological sulfur cycle are extremely corrosive, there are no correlations between numbers and types of sulfur-related organisms and the probability or rate of corrosion. Determination of specific mechanisms for corrosion caused by microbiologically mediated oxidation and reduction of sulfur and sulfur compounds is complicated by the variety of potential metabolic/energy sources and by-products; the coexistence of reduced and oxidized sulfur species; competing reactions with inorganic and organic compounds; and the versatility and adaptability of microorganisms in biofilms. The microbial ecology of sulfur-rich environments is poorly understood because of the association of aerobes and anaerobes and the mutualism or succession of heterotrophs to autotrophs. The physical...

Microbial colonization of metals (zirconium, chromium, niobium, tantalum, molybdenum, tungsten, and type 4340 steel [UNS G43400]) and susceptibility of these metals to microbiologically influenced corrosion by sulfate-reducing bacteria was investigated. Environmental scanning electron microscopy characterization after 12 months and 21 months showed patchy biofilms on all metals except tungsten. Weight loss after 24 months for zirconium and niobium were either nonexistent or negligible, indicating that these metals did not experience MIC under the test conditions.

Effects of mass transport, corrosion products and biofilm formation on corrosion kinetics of five copper alloys, four stainless steels and titanium grade 2 exposed to natural and artificial seawater were determined. Corrosion current density (icorr), anodic (ba) and cathodic (bc) Tafel slopes were determined from analysis of polarization curves recorded in the vicinity of the corrosion potential (Ecorr) under controlled mass transport conditions as a function of exposure time. Rotating cylinder electrode experiments demonstrated that Ecorr and corrosion rate for stainless steels and titanium were independent of mass transport. For copper alloys icorr depended linearly on rotation speed r0.7, while Ecorr was independent of mass transport. These results indicate that both cathodic and anodic reactions for stainless steels and titanium are under charge transfer control, whereas these reactions are under mass transport control for copper alloys. Corrosion rates of copper alloys were also obtained using linear polarization and weight loss. Corrosion rates obtained with the two methods agreed for exposures in artificial seawater. In natural seawater, corrosion rates determined with linear polarization underestimated corrosion rates from weight loss data by a factor of two or more. Environmental and traditional scanning electron microscopy coupled with energy-dispersive X-ray analyses were used to document surface topography, bacterial colonization and form of corrosion after removal of corrosion products. De-alloying of all copper alloys occurred in natural seawater. Intergranular corrosion was observed for 70Cu-30Ni alloy under elliptical deposits of embedded diatoms. De-alloying and intergranular corrosion did not occur in artificial seawater. Sulfides produced by bacteria may have accelerated attack of nickel in grain boundaries of 70Cu-30Ni alloy.

Polyaspartate, a polyanionic peptide analog of an oyster-shell protein fraction, inhibited corrosion of AISI 1018 mild steel (UNS G10180) in seawater in a dose-dependent manner. A maximal ...

Samples of three stainless steels and titanium grade 2 were exposed to flowing seawater at Port Hueneme, California under natural and reduced light environments. A total of four sets of samples were exposed for times up to 120 days. Open-circuit potential ( E corr ) and electrochemical impedance data as a function of exposure time were used to monitor the electrochemical behavior of the four materials. Surface examination showed a gradual increase in coverage by the biofilm as a function of exposure time. A small increase of E corr was observed, independent of exposure conditions and similar in magnitude to that observed in an abiotic, synthetic salt solution. Impedance data remained capacitive over the entire test period. Capacitance values were similar in natural and synthetic seawater. Localized corrosion was not observed for any sample. Pitting scans in 3.5% NaCl, performed as a function of pH, showed that the pitting potential of 304 stainless steel (SS) reached a value of about 0 mV at pH = 2.

Mineralogical data, thermodynamic stability (Pourbaix) diagrams, and the simplexity principle for precipitation reactions were used to evaluate corrosion product mineralogy on copper alloy...

A critical review of the literature concerned with the application of electrochemical techniques in the study of microbiologically influenced corrosion (MIC) is presented. The electrochemical techniques covered in this review include measurements of the corrosion potential, the redox potential, the polarization resistance, the electrochemical impedance, electrochemical noise, and polarization curves including pitting scans. For each experimental technique some discussion concerning experimental procedures, advantages and disadvantages of the technique for the study of MIC is presented. Applications range from studies of the corrosion of steel pipes in the presence of sulfate reducing bacteria to investigations of the formation of biofilms and calcareous deposits on stainless steels in seawater and the destruction of concrete pipes in sewers by microorganisms producing very low pH solutions. For each experimental technique at least one example for typical experimental data is presented.

Dynamic templating as a result of cathodic hydrogen gas production is suggested as a possible mechanism for the formation of tube-like corrosion products on an unlined cast iron pipe in a drinking water distribution system. Mounds of corrosion product, with protruding tubes and freestanding tubes, were observed within a single 30 cm section of piping. Internal morphologies for all shapes were texturally complex although mineralogically simple, composed of two iron oxide/oxyhydroxides minerals: α-FeOOH (goethite) and Fe3O4 (magnetite). Static templating by either microorganisms or minerals was rejected as a possible mechanism for tube formation in this study.

Methods for handling and storing natural coastal seawater, particularly methods for deaeration over time, influenced the chemistry and microflora. Bubbling nitrogen into natural seawater t...

Mackinawite, a tetragonal iron sulfide mineral, is generally a major corrosion product when iron alloys are corroded by sulfate-reducing bacteria (SRB). The experimental database for the m...

In the following section, B.D. Craig (Metallurgical Consultants Inc.) discusses the technical note by M.B. McNeil (Naval Coastal Systems) and B.J. Little (Naval Research Laboratory), “Mackinawite Formation During Microbial Corrosion,” which was published in Corrosion 46, 7(July 1990): p. 599. In the Reply section, McNeil and Little respond to Craig's comments.

The apparatus described in this paper, consisting of a two-compartment cell in which the compartments are biologically isolated and electrolytically continuous, is ideally suited for the study of microbiologically induced corrosion (MIC). The electrochemical impact of three bacterial isolates on three metal substrata has been quantified using this apparatus. In addition, three proposed mechanisms for MIC have been evaluated.

A rapidly proliferating obligate thermophilic bacterium with an optimum temperature range of 60 to 70 C was isolated from a failed nickel 201 brazed joint. Corrosion experiments have demonstrated that the isolate is responsible for the (1) in situ production of acidic metabolites and (2) creation of differential aeration cells, resulting in a significant corrosion current.

Starvation, growth phase, and carbon source influenced bacterial cell surface hydrophobicity. Both the number and kind of microorganisms that colonized metal surfaces depended on the type of metal and the presence of an imposed electrical potential. No significant differences in attachment and growth of a pure culture were observed when metal surfaces were dipped in an exogenous energy source. The chemical composition of naturally occurring adsorbed organic films on metal surfaces was shown to be independent of surface composition and polarization.

The following article discusses “Effect of Seawater Biofilms on Corrosion Potential and Oxygen Reduction of Stainless Steel,” by S.C. Dexter and G.Y. Gao, which was published in Corrosion 44,10(1988): p. 717. A reply from Dexter follows.

Dissolved oxygen (DO) and pH were measured at metal/artificial seawater interfaces using microelectrodes in biotic and abiotic systems. Measurements in a closed system proved that presence of electrochemical and/or biological reaction products substantially influence the conditions at the metal surface. For long-term studies, only open (e.g., continuous flow) reactors should be used. An open channel flow reactor suitable both for microbiological and electrochemical measurements has been constructed and successfully tested.