Effects Of Sulfate-reducing Bacteria On The Corrosion Behavior Of 2205 Duplex Stainless Steel In 3.5% NaCl Solution

The ocean contains a large amount of resources such as oil,natural gas,and minerals that are yet to be mined.The development and utilization of marine resources is of great significance for overcoming the shortage of resources.However,the marine environment is a more complex corrosive environment than the terrestrial environment,and its microbial content is high.Therefore,microbial corrosion is an important reason for the corrosion of marine materials.In microbial corrosion,sulfate-reducing bacteria(SRB)under anaerobic environment is one of the most destructive bacteria.2205 duplex stainless steel(DSS)has good comprehensive properties,and gradually replaces austenitic stainless steels with higher alloy contents such as 316 L and 904 L and is widely used in marine and deep-sea fields.Therefore,it is of great significance to study the influence of SRB on the corrosion behavior of2205 DSS in 3.5% NaCl solution,which can provide a theoretical basis for the anti-corrosion measures of stainless steel in the environment containing microorganisms.In this paper,pure SRB strains were obtained through enrichment culture,separation and purification in the China Bohai Sea mud.The growth curve of SRB in 3.5% NaCl solution at different soaking times was measured.The corrosion behavior of 2205 DSS in 3.5% NaCl solution with/without SRB was systematically studied by electrochemical impedance spectroscopy(EIS),potentiodynamic polarization technique,atomic force microscopy(AFM),scanning electron microscopy(SEM),X-ray polycrystalline diffraction(XRD)and X-ray photoelectron spectroscopy(XPS).The influence of SRB in different growth cycles on the pitting behavior of 2205 DSS in 3.5%NaCl solution was studied by electrochemical noise technique and optical microscope.The influence of SRB in different growth cycles on the corrosion behavior of 2205 DSS in 3.5% NaCl solution was studied in detail by using slow strain rate tensile experiment(SSRT)and the corrosion morphology was observed by scanning electron microscopy(SEM).The following conclusions were obtained:(1)SRB growth in 3.5% NaCl solution could be divided into three periods—logarithmic growth(1?3d)SRB rapidly reproduces,stable growth(4?8 d)SRB reproductive and death rates are almost equal,decay phases(9?14 d)the number of SRB has dropped sharply.(2)In 3.5%NaCl solution,SRB was rapidly adsorbed on the surface of 2205 DSS,and the adsorption of SRB on the surface of steel was a dynamic process,with prolonged immersion time for substrate surface coverage,heterogeneity and thickness.The surface pitting pits of 2205 DSS were small and deep when bacteria were present,and large and shallow when sterile.SRB destroys the passivation film by changing the structure and composition of the passivation film,causing defects in the passivation film,resulting in the 2205 DSS being able to significantly enhance pitting corrosion even in low oxygen environments in the presence of SRB.(3)Electrochemical noise results show that the corrosion rate of2205 DSS is greater in 3.5% NaCl bacterial solution containing SRB.The slope K value of the high-frequency linear segment in the sterile solution fluctuates around-20 d B/decade.Although it entered the metastable nucleation stage from the 10 th day,it was still in the metastable nucleation stage on the 14 th day,and local corrosion hardly occurred;in the bacteria solution,K is far away from-20 d B / decade.The 8th day has entered the metastable nucleation area,and K reached the maximum at 10 d.At this time,the surface of the sample has formed stable pitting corrosion.The presence of SRB accelerated the corrosion process of 2205 DSS in 3.5% NaCl solution.(4)2205 DSS is not SCC sensitive in sterile 3.5% NaCl solution.The existence of SRB changed the process of anodic polarization reaction of 2205 DSS in 3.5% NaCl solution,enhanced the thermodynamic tendency of 2205 DSS corrosion,induced pitting corrosion,its metabolites increased the brittleness of steel,and provided an induction point for SCC.The SCC mechanism is a mixing control mechanism of anodic dissolution and hydrogen embrittlement.The SCC sensitivity of 2205 DSS is positively correlated with the concentration of SRB activity.The greater the concentration of SRB activity,the stronger the promotion effect of SRB on SCC.