The impact of gravitational sedimentation on the sulfate-reducing bacterium biofilms formation that induced biocorrosion of X80 steel

Sulfate reducing bacteria (SRB) are considered as one of the main causes for the failures of buried metal pipes. Although many researchers reported that more negative cathodic protection potential was required in environments containing SRB, SRB would increase the concentration of hydrogen adsorbed on steel surface and thus lead to hydrogen embrittlement. In the study, the optimum cathodic protection (CP) potentials of X70 steel in bacterial and sterile media were evaluated with electrochemical impedance spectroscopy. The morphology and composition of corrosion products were characterized by a scanning electron microscope (SEM), an energy dispersion x-ray spectrometer (EDS), and an x-ray photoelectron spectrometer (XPS). The corrosion morphology of X70 steel in NS4 medium was pits and the corrosion in the bacterial medium was more serious than that in the sterile medium. The corrosion products of X70 steel were FeOOH and Fe2O3 in the sterile medium, whereas its corrosion products in the bacterial medium were FeOOH and FeS. When CP potential was −775 mV, SRB growth was promoted and the optimal protection effect on X70 steel was achieved in the bacterial NS4 medium. Pits were still observed under the biofilm and the corresponding corrosion mechanism was extracellular electron transfer (EET). When CP potential was −875 mV, X70 steel realized the optimal protection in the sterile NS4 solution. However, CO2 hydrolysis and SRB metabolism in the bacterial medium resulted in hydrogen-induced pits. When CP potential was −1025 mV, the growth of SRB was inhibited and severe hydrogen evolution corrosion occurred on X70 steel in bacterial and sterile NS4 media. The optimal CP potential for pipeline steel in the sterile medium may lead to hydrogen corrosion in the bacterial medium when H+ concentration was high.

Sulfate Reducing Bacteria (SRB) is a main microorganism in aviation kerosene causing pipelines corrosion. The corrosion regular of SRB in aviation kerosene pipeline (X70 steel) is studied by electrochemical impedance spectroscopy (EIS), potentiodynamic scanning polarization, etc. The results show that SRB participate and accelerate the corrosion of steel pipe. The anodic process of pipeline is blocked and cathodic depolarization promoted. Corrosion reaction is controlled by the cathodic process. The exits of SRB affect the AC impedance characteristics of the pipeline. At the same temperature, with the increasing of the SRB concentration, the corrosion current density increases, the charge transfer resistance decreases and the biofilm resistance first increases and then decreases, which mean the pipeline corrosion will be more serious with bigger SRB concentration. Under the same concentration, when temperature increasing, the corrosion potential is negatively shifted, and the higher the temperature will be, the greater the degree of negative shifts, which results in the decrease of pipeline's corrosion resistance.

Characterization of the biofilm structure and microbial diversity of sulfate-reducing bacteria from petroleum produced water supplemented by different carbon sources

Microbial Influenced Corrosion (MIC) is a process influenced by various microorganisms especially by sulfate reducing bacteria (SRB) which affects the kinetics of corrosion procedure under anaerobic conditions. About 20% of the annual corrosion damages of metals may be produced by microbial activities especially due to anaerobic corrosion influenced by SRB. MIC is the main contributor of corrosion problems and a leading cause of pipeline failure in oil and gas industries. SRBs are main microorganisms that can anaerobically generate sulfide species causing biocorrosion in the injection networks. Moreover, the produced H2S gas is toxic, corrosive, and responsible for a variety of environmental problems. Additionally, the presence of SRB can result in health and safety risks to workers due to sulfide production. In order to prevent this, oil-producing companies use high concentrations of biocides to disinfect the water and inhibit excessive biofilm formation caused mainly by (SRB). However, traditional biocides may be harmful to environment by forming harmful disinfection byproducts. Also the biocide treatment having other disadvantages like low efficiency against biofilms, release of disinfection byproducts and its high cost. Theses disadvantages can be solved by the use of green biocides including nanomaterials which has very low toxicity, environmental acceptability, safety and ease of use etc. Several nanomaterials have been utilized to inhibit the growth of different microorganisms and can be a possible alternative for controlling SRB biofilm and its corrosion. Here, we introduced an environmentally benign approach to use a green biocide; chitosan-ZnO nanocomposite against SRB induced MIC towards carbon steel. The nanoparticles of chitosan and ZnO were prepared independently and treated together to form the chitosan-ZnO nanocomposite. The nanocomposite was synthesized with different percentage of ZnO initial content and characterized by SEM, TEM, FTIR, TGA etc. The average size of chitosan nanoparticles were in between 40-60 nm and it clearly shows the distribution of ZnO NPs in the chitosan nanoparticles matrix. The particles in chitosan-ZnO nanocomposite were found with almost spherical morphology. The electrodes were made of carbon steel S150 was used for all the experiments. S150 carbon steel electrode of exposed area of 8 mm diameter used for the corrosion experiments after hot mounting process followed by polishing and grinding process. The electrodes were incubated with SRB containing media with and without nanocomposites and kept in a shaking incubator at 37° under inert atmosphere. The effect of the chitosan-ZnO nanocomposite on corrosion inhibition was studied by varying the concentrations of nanocomposites under optimized bacterial concentration and experimental conditions. The surface features and the elemental analysis of the biofilm and corrosion product were evaluated by SEM as well as XPS in different time intervals and compared with the control samples. The surface features of the corroded electrodes was investigated by SEM and profilometry after removing the corrosion product by using a simple chemical treatment procedure. The effect of chitosan-ZnO nanocomposite on corrosion behavior of carbon steel against SRB was investigated by electrochemical impedance spectroscopy, corrosion potential, polarization resistance and polarization curve measurements at different time intervals. It was found that the chitosan-ZnO nanocomposite inhibits the SRB biofilm formation and corrosion. The results of the electrochemical analysis showed that the chitosan-ZnO nanocomposite (10% ZnO content) at 250 ppm concentration having highest corrosion inhibition and can be used an effective corrosion inhibition agent against SRB induced MIC. References Wang, H. F., et al. Materials Chemistry and Physics 124, 791-794, (2010).Vanaei, H. R., et al. International Journal of Pressure Vessels and Piping 149, 43-54, (2017). Xu, D. et al. Engineering Failure Analysis 28, 149-159, (2013).

Synergistic effect of sulphate-reducing bacteria and external tensile stress on the corrosion behaviour of X80 pipeline steel in neutral soil environment

The effect of SRB and applied potential on the stress corrosion sensitivity of X80 pipeline steel was analyzed in high-pH soil simulated solution under different conditions using a slow strain rate tensile test, electrochemical test, and electronic microanalysis. The experimental results showed that X80 pipeline steel has a certain degree of SCC sensitivity in high-pH simulated solution, and the crack growth mode was trans-granular stress corrosion cracking. In a sterile environment, the SCC mechanism of X80 steel was a mixture mechanism of anode dissolution and hydrogen embrittlement at −850 mV potential, while X80 steel had the lowest SCC sensitivity due to the weak effect of AD and HE; after Sulfate Reducing Bacteria (SRB) were inoculated, the SCC mechanism of X80 steel was an AD–membrane rupture mechanism at −850 mV potential. The synergistic effect of Cl− and SRB formed an oxygen concentration cell and an acidification microenvironment in the pitting corrosion pit, and this promoted the formation of pitting corrosion which induced crack nucleation, thus significantly improving the SCC sensitivity of X80 steel. The strong cathodic polarization promoted the local corrosion caused by SRB metabolism in the presence of bacteria, whereby the SCC sensitivity in the presence of bacteria was higher than that in sterile conditions under strong cathodic potential.

Streptomyces lunalinharesii 235 prevents the formation of a sulfate-reducing bacterial biofilm

This study describes the biofilm formation by sulphate-reducing bacteria (SRB) on different materials, which has implications for the biomedical, pharmaceutical, food and chemical process industries. SRB was chosen as a model organism being an anaerobic bacterium. Biofilm formation on different materials and corrosion of titanium by SRB were monitored with time using confocal laser scanning microscopy and fluorescent FISH probes were used to authenticate the SRB strain. The thickness of the mono-culture SRB biofilm has ranged from 4 to 24 µm during thed 12–84 hr; however, the maximum biofilm thickness (24 µm) was recorded after 60 hr of growth. Planktonic growth of the SRB strain showed a log phase up to 48 hr and the sulphide production ranged from 2 to 14 mg l−1. For a comparative account, the SRB biofilm formation on copper was chosen as a positive control. Finally, the putative role of extracellular electron transfer by SRB in the biocorrosion process and the plausible mechanism of pitting corrosion of titanium is described in detail.

Effect of CO2 on the SRB-induced corrosion behavior of X65 steel in oilfield-produced water.

Recent findings showed severe localized corrosion of submerged steel bridge piles in a Florida bridge and was associated with microbial activity in presence of marine foulers (Permeh et al, 2017;2018). Microbiologically Influenced Corrosion (MIC) can cause severe degradation of civil infrastructure. MIC has often associated with the formation of biofilm (including the complex interaction of microbe communities and development of extracellular polymeric substances (EPS)) that can influence the corrosion process either by creating oxygen differential aeration cells or generating acidic substances and cathodic reactant depending on the type of bacteria. Sulfate reducing bacteria (SRB) has received much attention in the study of MIC of steel developed in natural waters (Melchers and Wells, 2006; Castaneda and Benetton, 2008). Reactions associated with SRB causes cathodic depolarization of steel leading to the reduction of sulfates to sulfides and promoting steel corrosion (Borenstein,1994). Coatings have been developed to mitigate MIC and marine fouling. Studies have shown that coating blistering and disbondment can occur as a result of microbial attack due to the production of metabolites that degrade coating chemical and physical properties (Mansfield et al.,1998; Muntasser et al.,2002). Recent work evaluated the corrosion mitigation properties of a commercially-available, water-based, self-polishing, antifouling coating in environments that supported SRB as part of a larger research program to identify susceptibility of steel degradation in natural waters due to MIC (Permeh et al.,2019). In the work described here electrochemical impedance spectroscopy (EIS) was conducted to identify microbial activity and degradation of an antifouling coating. EIS was conducted on steel coupons coated with an antifouling coating (with and without coating defects) exposed to SRB inoculated modified Postgate B solution. The exposed coating surface area was ~19.6 cm2 and the coating thickness was ~0.17-0.35 mm. A three-electrode configuration was used for EIS measurements where the coated steel plate was the working electrode, an activated titanium rod was used as a reference electrode, and an activated titanium mesh was used as a counter electrode. EIS measurements were made at OCP condition with 10 mV a.c. perturbation voltage and at frequencies 1Mhz>f>1Hz. The measurements resulted in impedance with multiple loops in the Nyquist diagram (as shown in Figure 1) associated with processes relating to the polymeric coating, development of surface layers (biofilm), and the steel interface. Fitting of the impedance response to equivalent circuit analogs were made to identify coating characteristics and surface layer formation during the experimental exposure in inoculated and non-inoculated solutions. The results revealed near-ideal capacitance for the polymeric coating and a decrease in coating pore resistance. In samples inoculated with SRB, a second high frequency loop developed indicating formation of surface films. The results from EIS indicated degradation of the coating due to its self-polishing characteristics and that formation of surface layers associated with SRB can form as biocide components of the coating become depleted. Continued SRB growth may allow development of marine fouling if the antifouling coating components become less effective and allow possible shelter for SRB to promote MIC. Further work to verify these characteristics in field settings are in progress. References Borenstein, S. (1994). Microbiologically influenced corrosion handbook. Elsevier.Castaneda, H., & Benetton, X. D. (2008). SRB-biofilm influence in active corrosion sites formed at the steel-electrolyte interface when exposed to artificial seawater conditions. Corrosion Science, 50(4), 1169-1183.Mansfield, F., Lee, C. C., Han, L. T., Zhang, G., & Little, B. (1998). The Impact of Microbiologically Influenced Corrosion on Protective Polymer Coatings. University of Southern California Los Angeles Dept of Materials Science And Engineering.Melchers, R. E., & Wells, T. (2006). Models for the anaerobic phases of marine immersion corrosion. Corrosion Science, 48(7), 1791-1811.Muntasser, Z., Al-Darbi, M., Tango, M., & Islam, M. R. (2002, January). Prevention of microbiologically influenced corrosion using coatings. In CORROSION 2002. NACE International. Permeh, S., Boan, M. E., Tansel, B., Lau, K., & Duncan, M. (2019, February). Update on Mitigation of MIC of Steel in a Marine Environment with Coatings. In Coatings+, SSPC 2019. Permeh, S., Li, B., Boan, M. E., Tansel, B., Lau, K., & Duncan, M. (2018, July). Microbially Influenced Steel Corrosion with Crevice Conditions in Natural Water. In CORROSION 2018. NACE International.Permeh, S., Reid, C., Echeverría Boan, M., Lau, K., Tansel, B., Duncan, M., & Lasa, I. (2017, April). Microbiological Influenced Corrosion (MIC) In Florida Marine Environment: A Case Study. In CORROSION 2017. NACE International. Figure 1

Effects of cathodic polarization on X65 steel inhibition behavior and mechanism of mixed microorganisms induced corrosion in seawater

Biocorrosion in marine environment is often associated with biofilms of sulfate reducing bacteria (SRB). However, not much information is available on the mechanism underlying exacerbated rates of SRB-mediated biocorrosion under saline conditions. Using Desulfovibrio (D.) vulgaris and Desulfobacterium (Db.) corrodens as model SRBs, the enhancement effects of salinity on sulfate reduction, N-acyl homoserine lactone (AHL) production and biofilm formation by SRBs were demonstrated. Under saline conditions, D. vulgaris and Db. corrodens exhibited significantly higher specific sulfate reduction and specific AHL production rates as well as elevated rates of biofilm formation compared to freshwater medium. Salinity-induced enhancement traits were also confirmed at transcript level through reverse transcription quantitative polymerase chain reaction (RT-qPCR) approach, which showed salinity-influenced increase in the expression of genes associated with carbon metabolism, sulfate reduction, biofilm formation and histidine kinase signal transduction. In addition, by deploying quorum sensing (QS) inhibitors, a potential connection between sulfate reduction and AHL production under saline conditions was demonstrated, which is most significant during early stages of sulfate metabolism. The findings collectively revealed the interconnection between QS, sulfate reduction and biofilm formation among SRBs, and implied the potential of deploying quorum quenching approaches to control SRB-based biocorrosion in saline conditions.

Sulfate-reducing bacteria (SRB) have a unique ability to respire under anaerobic conditions using sulfate as a terminal electron acceptor, reducing it to hydrogen sulfide. SRB thrives in many natural environments (freshwater sediments and salty marshes), deep subsurface environments (oil wells and hydrothermal vents), and processing facilities in an industrial setting. Owing to their ability to alter the physicochemical properties of underlying metals, SRB can induce fouling, corrosion, and pipeline clogging challenges. Indigenous SRB causes oil souring and associated product loss and, subsequently, the abandonment of impacted oil wells. The sessile cells in biofilms are 1,000 times more resistant to biocides and induce 100-fold greater corrosion than their planktonic counterparts. To effectively combat the challenges posed by SRB, it is essential to understand their molecular mechanisms of biofilm formation and corrosion. Here, we examine the critical genes involved in biofilm formation and microbiologically influenced corrosion and categorize them into various functional categories. The current effort also discusses chemical and biological methods for controlling the SRB biofilms. Finally, we highlight the importance of surface engineering approaches for controlling biofilm formation on underlying metal surfaces.

Microbiologically influenced corrosion (MIC) is one of the most aggressive forms of corrosion leasing to infrastructure and equipment damage in various industries, including oil and gas, water systems, medical devices, marine environments, nuclear waste storage facilities, and aviation fuel systems and storage. During the last 10 year, PHMSA estimates that MIC has caused 503 internal corrosion incidents at a reported property damage of $188 million and a loss of 53,000 barrels of oil. Some common bacteria associated with MIC are sulfate-reducing bacteria (SRB), iron and CO2 reducing bacteria and iron and manganese oxidizing bacteria. SRB are generally considered the most aggressive group of bacteria in pipeline systems that causes MIC and pitting, especially of carbon steel in the oil and gas industry. SRB are facultative anaerobes and thrive in anoxic environments, using sulfate as a terminal electron acceptor and producing hydrogen sulfide (H2S) as a metabolic byproduct. Furthermore, SRBs also can reduce both nitrate and thiosulfate and obtain their energy from organic nutrients, such as lactate.Electrochemical techniques to monitor for MIC focus on studying the electrochemical characteristics of the interface or mass transport properties of a system that are modified by the microbiological activities. Polarization sensors, such as the BIOX system or BioGeorge, use polarization based on a galvanic couple between a stainless steel electrode and a sacrificial anode. The measured galvanic current is proportional to biofilm that has grown on the electrode surface. Other electrochemical sensors use electrochemical impedance spectroscopy (EIS) or amperometry to measure biofilm thickness by comparing the electrochemical signatures of a reference channel (without bacteria) to a measurement channel (exposed to bacteria); while sensors based on electrochemical resistance use linear polarization measurements to determine the amount of biofilm on an electrode surface. Electro hydrodynamical impedance has also been used to measure the diffusion coefficient in a biofilm and correlate to biofilm growth and thickness. While these approaches can accurately predict the presence and/or thickness of a biofilm on a metal surface, they cannot determine the risk of MIC associated with biofilm formation, as the presence of a biofilm does not necessarily mean that a surface experiences MIC. Additionally, many of the techniques are destructive or require visual examination of the surface after analysis.This work presents a split-chamber zero resistance ammetry (SC-ZRA)-based approach to overcome the limitations to MIC monitoring described above and serve as a screening system to determine the risk of MIC associated with certain microorganisms or groups of microorganisms. Previous work using a split-chamber approach to assess MIC was used by Daumus for the study of stainless steel corrosion in the presence of sulfate reducing bacteria, and subsequently used by Miller et al to evaluate MIC under aerobic, Fe (III)- and nitrate-reducing conditions. In this approach, two identical electrochemical cells (chambers) are separated by an ion-transport membrane. Each chamber contains an identical electrode of the same material which are electrically connected through a zero-resistance ammeter. When one of the chambers is inoculated with microorganisms, the galvanic current between the two electrodes is measured through the zero ammeter. This configuration mimics the microbiologically induced development of localized anodic and cathodic patches on a metal surface that leads to corrosion. The flow of electrons (difference in corrosion current between the two chambers) depends solely on the microbiological activities of bacteria in one of the two chambers, so the influence of the microorganisms on MIC, as well as the extent of corrosion, can be quantified.Using the SC-ZRA technique we were able to characterize the mechanism and electrochemical signatures of SRB corrosion. Specifically, we found that in split-chamber incubations containing an electron donor, electrons flow from the inoculated to the uninoculated chambers. While the current direction could be interpreted as electron transfer such as in a microbial fuel cell, these systems deploy inert graphite electrodes. When used for MIC characterization, the SC-ZRA uses reactive carbon steel electrodes. Indeed, when positive current was detected, greater corrosion was detected on WE1, which is consistent with redox couples, as well as previous work to characterize MIC using SC-ZRA measurements. After depletion of an electron donor, SRB uses electrons from the metals surface as an electron donor reversing the flow of electrons from the uninoculated to the inoculated chamber. In future work, this technique can be used to provide a mechanistic understanding and a monitoring tool for corrosion of metals that are exposed to SRB under a variety of redox regimes.

Stress Corrosion Cracking Behavior of X80 Pipeline Steel in Acid Soil Environment with SRB