Latest research progress of marine microbiological corrosion and biofouling, and new approaches of marine anti-corrosion and anti-fouling

Marine resources and industry have become one of the most important pillars in economic development all over the world.However,corrosion of materials is always the most serious problem to the infrastructure and equipment served in marine environment.Researchers have found that microbiologically influenced corrosion(MIC)and marine bio-fouling are two main mechanisms of marine corrosions due to the complicated marine environment and marine organisms.This article summarized the latest research progress about these two mechanisms and indicated that both MIC and marine bio-fouling are closely related to the biofilms on material surfaces formed by the marine microorganisms and their metabolites.As a result,to prevent the occurrence of MIC and bio-fouling,it is important to control the microorganisms in biofilms or prevent the adhesion and formation of biofilms.The traditional method of using chemical bactericide or antifoulant faces the problems of pollution and microorganism resistance.This article introduced four research approaches about the new tendency of applying new materials and technologies to cooperate with traditional chemicals to achieve better and longer effects with lower environment pollution through synergistic actions.Finally,some future research tendencies were proposed for whole marine anti-corrosion and anti-fouling areas.

Study of Microbiologically Induced Corrosion Action on Al-6Mg-Zr and Al-6Mg-Zr-Sc

The corrosion behaviors of Al-6Mg-Zr and Al-6Mg-Zr-Sc in the sulfate-reducing bacteria （SRB） solution in anaerobic environment were studied using electrochemical, microbiological, and surface analysis methods. It was found that the oxide film was more compact owing to the addition of Sc resulting in the open circuit potential shifting by about 100mV positively. On the other hand, it was seen that the pitting sensitivity of Al-6Mg-Zr-Sc alloy in SRB solution decreased and its microbiologically influenced corrosion resistance was improved. Pitting corrosion occurring on the surface of the two alloys under the comprehensive action of the metabolism of SRB was observed by SEM. It was obtained by EDS that the corrosion degree increased with time and corrosion was furthered by deposition of the product.

Electrochemical behavior of microbiologically influenced corrosion on Fe_3Al in marine environment

In this article, microbiologically influenced corrosion behavior of Fe3Al intermetallie compound in microorganism culture medium has been investigated by using weight loss methods, electrochemical techniques, and electron microscopy. Polarization curves showed that a sharp electrical current peak caused by surface pitting could be observed after Fe3Al electrodes were immersed in culture medium for 15 days when the polarization potential was about -790 mV vs SCE. Based on the electrochemical impedance spectroscopy （EIS） and the equivalent circuit parameters of the associated system, the corrosion products were found to exhibit a two-layer structured feature and the microorganisms could induce pitting and erosion corrosion of the inner layer. In addition, the passivating film of the inner layer was absolutely destroyed by microbial metabolic products.

THE ELECTROCHEMICAL BEHAVIOR OF OCEANIC MICROBIOLOGICAL INFLUENCED CORROSION ON CARBON STEEL

The corrosion behavior of carbon steel in the medium of marine microorganisms was investigated by electrochemical impedance spectra, polarization curves, and so on. Experimental results showed that the corrosion potential of carbon steel moved in a negative direction in the unpurified marine microorganism solution, and the polarization style of the cathodic process did not change. The electrochemical impedance spectra showed that the impedance value of the electrode decreased in the medium with bacteria, which indicated that the existence of microorganism could accelerate the corrosion progress of carbon steel.

Microbiologically influenced corrosion of cable bolts in underground coal mines:The effect of Acidithiobacillus ferrooxidans

Reports on corrosion failure of cable bolts,used in mining and civil industries,have been increasing in the past two decades.The previous studies found that pitting corrosion on the surface of a cable bolt can initiate premature failure of the bolt.In this study,the role of Acidithiobacillus ferrooxidans(A.ferrooxidans)bacterium in the occurrence of pitting corrosion in cable bolts was studied.Stressed coupons,made from the wires of cable bolts,were immersed in testing bottles containing groundwater collected from an underground coal mine and a mixture of A.ferrooxidans and geomaterials.It was observed that A.ferrooxidans caused pitting corrosion on the surface of cable bolts in the near-neutral environment.The presence of geomaterials slightly affected the p H of the environment;however,it did not have any significant influence on the corrosion activity of A.ferrooxidans.This study suggests that the common bacterium A.ferrooxidans found in many underground environments can be a threat to cable bolts'integrity by creating initiation points for other catastrophic failures such as stress corrosion cracking.

Microbiologically Induced Corrosion Action on Al-6Mg-Zr and Al-6Mg-Zr-Sc

The corrosion behaviors of Al-6Mg-Zr and Al-6Mg-Zr-Sc in sulfate-reducing bacteria（SRB） solution in the anaerobic environment were studied by electrochemical, microbiology and surface analysis methods. It is found that the oxide film is more compact resulting in the open circuit potential shifting about 100 mV positively due to the addition of Sc. On the other hand, it is demonstrated that pitting sensitivity of Al-6Mg-Zr-Sc alloy in the SRB solution is decreased and its microbiologically influenced corrosion resistance is improved.

MICROBIOLOGICALLY INFLUENCED CORROSION ON WELD OF STAINLESS STEEL 304L

The influence of welding defects on MIC (microbiologically influenced corrosion) was studied.The open circuit potential (OCP) was measured during MIC test. It was found that OCP shifted to a higher level when the system was inoculated with bacteria and it decreased dramatically when MIC started. Among a series of welding defects golden heat tint was found the most susceptible to MIC. The tubercles over pitting were observed with SEM. Some elements inside of the tubercles were analysed with EDXA. Microbiological analysis of a corroded and a non-corroded sample revealed no significant difference between them with the exception of the number of the manganeseoxidising bacteria.

Infl uence of nitrate concentrations on EH40 steel corrosion aff ected by coexistence of Desulfovibrio desulfuricans and Pseudomonas aeruginosa bacteria

Nitrate addition is a common bio-competitive exclusion(BCE)method to mitigate corrosion in produced water reinjection systems,which can aff ect microbial community compositions,especially nitrate and sulfate reducing bacteria,but its eff ectiveness is in controversy.We investigated the infl uence of nitrate concentrations on EH40 steel corrosion aff ected by coexistence of Desulfovibrio vulgaris and Pseudomonas aeruginosa bacteria.Results demonstrate that only mixed bacteria or nitrate had little eff ect on EH40 steel corrosion,and nitrate could accelerate the corrosion of EH40 steel through the action of microorganisms.The corrosion promotion of nitrate was dependent on its concentrations,which increased from 0 to 5 g/L and decreased from 5 to 50 g/L.These diff erences were believed to be related to the regulation of nitrate in the growth of bacteria and biofi lms.Therefore,care must be taken to BCE method with nitrate when nitrate reducing bacteria with high corrosive activity are present in the environments.

Corrosion Behaviors of Steel A3 Exposed to Thiobacillus Ferrooxidans

The corrosion behaviors of steel A3 in synergistic action of Thiobacillus ferrooxidans （T.f） and electrochemically accelerated corrosion were studied by electrochemical, microbiology and surface analysis methods. The open circuit potential （Eocp） and electrochemical impedance spectroscopy （EIS） of the steel A3 electrodes were measured in leathen culture medium without and with T.f （simply called T.f solution in the following paper） in immersion electrode way at the time of the 2nd, 5th, 10th, 20th and 30th days, respectively. It was found that Eocp of the electrode for immersion in leathen culture medium shifted negatively with the immersion time while that for immersion in T.f solutions shifted negatively, then positively and finally negatively. On the 20th day, the corrosion of steel A3 for immersion in culture medium was in pitting initiation stage while that for immersion in T.f solutions was in pitting growth stage. It was found that the corrosion of steel A3 was accelerated by T.f. The morphology of corrosion product of steel A3 immersion in T.f solutions observed through scanning electron microscopy （SEM） transformed from solid globules to tabular plates and to spongy globules and plates.

Development of Modified 304 Stainless Steel Resistant to Stress Corrosion Cracking in Chloride Environment

The influence of water pollution and welding defects on MIC (microbiologically influenced corrosion) was studied. The open circuit potential (OCP) was measured during MIC test. It was found that OCP shifted to a higher level when the system was inoculated with bacteria while the OCP of those samples in water without bacteria was kept at a low level. The OCP decreased dramatically when MIC started in polluted water. Combination of weld defect heat tint, polluted water and adding bacteria causes MIC happen at high rate. Some elements inside the tubercle were analyzed with EDXA. The pits and biofilm were observed with SEM. Microbiological analysis revealed the difference of bacteria between corroded and uncorroded samples.

Effect of Sulfate-reducing Bacteria on Corrosion Behavior of Mild Steel in Sea Mud

Microbiologically influenced corrosion （MIC） is very severe corrosion for constructions buried under sea mud environment. Therefore it is of great importance to carry out the investigation of the corrosion behavior of marine steel in sea mud. In this paper, the effect of sulfate-reducing bacteria （SRB） on corrosion behavior of mild steel in sea mud was studied by weight loss, dual-compartment cell, electronic probe microanalysis （EPMA）, transmission electron microscopy （TEM） combined with energy dispersive X-ray analysis （EDX） and electrochemical impedance spectroscopy （EIS）. The results showed that corrosion rate and galvanic current were influenced by the metabolic activity of SRB. In the environment of sea mud containing SRB, the original corrosion products, ferric （oxyhydr） oxide, transformed to iron sulfide. With the excess of the dissolved H2S, the composition of the protective layer formed of FeS transformed to FeS2 or other non-stoichiometric polysulphide, which changed the state of the former layer and accelerated the corrosion process.

Effect of exogenous flavins on the microbial corrosion by Geobacter sulfurreducens via iron-to-microbe electron transfer

Microbes can cause or accelerate metal corrosion,leading to huge losses in corrosion damages each year.Geobacter sulfurreducens is a representative electroactive bacterium in many soils,sediments,and wastew-ater systems.It has been confirmed to directly extract electrons from elemental metals.However,little is known about the effect of electron shuttles in G.sulfurreducens corrosion on stainless steel.In this study,we report that exogenous flavins promote iron-to-microbe electron transfer,accelerating micro-bial corrosion.G.sulfurreducens caused 1.3 times deeper pits and increased electron uptake(with 2 times increase of i_(corr))from stainless steel when riboflavin was added to the culture medium.OmcS-deficient mutant data suggest that G.sulfurreducens utilizes riboflavin as a bound-cofactor in outer membrane c-type cytochromes.The finding that,in the presence of microbes,riboflavin can substantially accelerate corrosion highlights the role of flavin redox cycling for enhanced iron-to-microbe electron transfer by G.sulfurreducens and provides new insights in microbial corrosion.

Microbiologically Influenced Corrosion Behavior of Fe_(40)(CoCrMnNi)_(60) and Fe_(60)(CoCrMnNi)_(40) Medium Entropy Alloys in the Presence of Pseudomonas Aeruginosa

In this work,the microbiologically influenced corrosion(MIC)of Fe_(40)(CoCrMnNi)_(60) and Fe_(60)(CoCrMnNi)_(40) medium entropy alloys(MEAs)induced by Pseudomonas aeruginosa(P.aeruginosa)was investigated.Corrosion behaviors during 14 days of immersion in sterile and P.aeruginosa-inoculated culture media are presented.Under sterile conditions,both MEAs exhibited good corrosion resistance against the culture medium solution.In the presence of P.aeruginosa,the pitting corrosion of MEAs was promoted.The results of inductively coupled plasma‒mass spectrometry(ICP‒MS)and potentiodynamic polarization tests showed that the presence of P.aeruginosa promoted the selective dissolution of passive film and accelerated the corrosion of MEAs.The results of X-ray photoelectron spectroscopy(XPS)and Mott-Schottky measurements further demonstrated the degradation effect of P.aeruginosa on the passive film.Compared with Fe_(60)(CoCrMnNi)_(40),Fe_(40)(CoCrMnNi)_(60) manifested better resistance to the MIC caused by P.aeruginosa,which may be attributed to more Cr oxides and fewer Fe oxides of the passive film.

Anaerobic microbiologically influenced corrosion mechanisms interpreted using bioenergetics and bioelectrochemistry： A review

Microbiologically influenced corrosion （MIC） is a major cause of corrosion damages, facility failures, and financial losses, making MIC an important research topic. Due to complex microbiological activities and a lack of deep understanding of the interactions between biofilms and metal surfaces, MIC occurrences and mechanisms are difficult to predict and interpret. Many theories and mechanisms have been pro- posed to explain MIC. In this review, the mechanisms of MIC are discussed using hioenergetics, microbial respiration types, and biofilm extracellular electron transfer （EET）. Two main MIC types, namely EET-MIC and metabolite MIC （M-ME）, are discussed. This brief review provides a state of the art insight into MIC mechanisms and it helps the diagnosis and prediction of occurrences of MIC under anaerobic conditions in the oil and gas industry.

Microbiologically influenced corrosion of Cu by nitrate reducing marine bacterium Pseudomonas aeruginosa

The microbiologically influenced corrosion(MIC) mechanisms of copper by Pseudomonas aeruginosa as a typical strain of nitrate reducing bacteria(NRB) was investigated in this lab study.Cu was immersed in deoxygenated LB-NO3 seawater inoculated with P.aeruginosa and incubated for 2 weeks.Results showed that this NRB caused pitting and uniform corrosion.The maximum pit depths after 7 d and 14 d in125 mL anaerobic vials with 50 mL broth were 5.1 μm and 9.1 μm,accompanied by specific weight losses of 1.3 mg/cm2(7 d) and 1.7 mg/cm2(14 d),respectively.Electrochemical measurements corroborated weight loss and pit depth data trends.Experimental results indicated that extracellular electron transfer for nitrate reduction was the main MIC mechanism and ammonia secreted by P.aeruginosa could also play a role in the overall Cu corrosion process.

Microbiologically influenced corrosion of 304 stainless steel by halophilic archaea Natronorubrum tibetense

The corrosion behavior of 304 stainless steel(SS)in the presence of aerobic halophilic archaea Natronorubrum tibetense was investigated.After 14 days of immersion,no obvious pitting pit was observed on the SS surface in the sterile medium.By contrast,the SS exhibited serious pitting corrosion with the largest pit depth of 5.0μm in the inoculated medium after 14 days.The results of electrochemical tests showed that the barrier property of the passive film decreased faster in the inoculated medium.The X-ray photoelectron spectroscopy results indicated that the detrimental Fe2+and Cr6+increased in the passive film under the influence of archaea N.tibetense,which resulted in the accelerated deterioration of passive film and promoted the pitting corrosion.Combined with the energy starvation tests,the microbiologically influenced corrosion mechanism of 304 SS caused by halophilic archaea N.tibetense was discussed finally.

Enhanced resistance of 2205 Cu-bearing duplex stainless steel towards microbiologically influenced corrosion by marine aerobic Pseudomonas aeruginosa biofilms

An antibacterial 2205-Cu duplex stainless steel （DSS） was shown to inhibit the formation and growth of corrosive marine biofilms by direct contact with copper-rich phases and the release of Cu^2＋ ions from the 2205-Cu DSS surface. In this work, the microbiologically influenced corrosion （MIC） resistance of 2205- Cu DS5 in the presence of the corrosive marine bacterium Pseudornonos aeruginosa was investigated. The addition of copper improved the mechanical properties such as the yield strength, the tensile strength and the hardness of 2205 DSS. Electrochemical test results from linear polarization resistance （LPR）, electrochemical impedance spectroscopy （EI5） and critical pitting temperature （CPT） measurements showed that 2205-Cu DSS possessed a larger polarization resistance （Rp）, charge transfer resistance （Rct） and CPT values, indicating the excellent MIC resistance of2205-Cu DSS against the corrosive P. aeruginosa biofilm. The live]dead staining results and the SEM images of biofilm confirmed the strong antibacterial ability of 2205-Cu DSS. The largest pit depth of 2205-Cu DSS was considerably smaller than that of 2205 DSS after 14d in the presence ofP. aeruginosa （2.2 μm vs 12.5 μm）. 2205-Cu DSS possessed a superior MIC resistance to regular 2205 DSS in the presence of aerobic P. aeruginosa.

Effect of sulphate-reducing bacteria on the electrochemical impedance spectroscopy characteristics of 1Cr18Ni9Ti

The electrochemical characteristics of 1Cr18Ni9Ti in sulphate-reducing bacteria （SRB） solutions and the biofilm of SRB on the surface of the 1Cr18Ni9Ti electrode were studied by electrochemical, microbiological, and surface analysis methods. Electrochemical impedance spectroscopy （EIS） of 1Cr18Ni9Ti was measured in the solutions with and without SRB at the culture time of 2, 4, 8 d, respectively. The measurement used two test methods, the nonimmersion electrode method and the immersion electrode method. It was found that the polarization resistance （Rp） of 1Cr18Ni9Ti in the solutions without SRB is the greatest for each test method. When using the nonimmersion electrode method, Rp shifts negatively at first and then positively, and the time constant is only one. Although using the immersion electrode method, the Rp shifts positively at first and then negatively, and the time constant also changes when the biofilm forms. The biofilm observed through SEM is with pores. It was demonstrated that SRB has accelerated corrosion action on 1Cr18Ni9Ti. The protection effect of the biofilm on the electrode depends on the compact degree of the film.

Electrochemical studies of microbiologically influenced corrosion of X80 steel by nitrate-reducing Bacillus licheniformis under anaerobic conditions

In this work, the impact of a wild-type nitrate-reducing Bacillus licheniformis strain on the corrosion behavior of X80 steel under anaerobic conditions was studied by electrochemical tests and biofilm characterization. The bioelectrochemical, electrochemical, and chemical reactions between X80 steel and microorganisms were investigated comprehensively. The results show that B. licheniformis can accelerate the corrosion of X80 steel substrate in early immersing by two ways: biocatalytic cathodic nitrate reduction and acidification induced by bacterially-secreted acids. However, the corrosion rate of X80 steel decreased after immersing for ca. 1 week in B. licheniformis culture due to iron biomineralization. This work provides direct insights into the mechanism of microbiologically influenced corrosion of carbon steel by the nitrate-reducing bacterium.

Microbiologically influenced corrosion behavior of S32654 super austenitic stainless steel in the presence of marine Pseudomonas aeruginosa biofilm

S32654 super austenitic stainless steel（SASS） is widely used in highly corrosive environments. However,its microbiologically influenced corrosion（MIC） behavior has not been reported yet. In this study, the corrosion behavior of S32654 SASS caused by a corrosive marine bacterium Pseudomonas aeruginosa was investigated using electrochemical measurements and surface analysis techniques. It was found that P. aeruginosa biofilm accelerated the corrosion rate of S325654 SASS, which was demonstrated by a negative shift of the open circuit potential（EOCP）, a decrease of polarization resistance and an increase of corrosion current density in the culture medium. The largest pit depth of the coupons exposed in the P.aeruginosa broth for 14 days was 2.83 m, much deeper than that of the control（1.33 m） in the abiotic culture medium. It was likely that the P. aeruginosa biofilm catalyzed the formation of CrO_3, which was detrimental to the passive film, resulting in MIC pitting corrosion.