Study On Corrosion Behavior Of EH40 Steel Induced By Extracellular Polymeric Substances

The presence of microorganisms in marine environment can significantly affect the corrosion process of metals.Extracellular polymeric substances(EPS),as a typical metabolite of microorganism,are important corrosion influencing factors.In addition,studies have confirmed that the corrosion process of metals in the actual environment is related to the community formed by a variety of microorganisms.However,there are few studies on the mechanism of metal corrosion induced by EPS metabolized by typical corrosive microorganisms.As a result,EPS produced by Desulfovibrio vulgaris,Methanococcus maripaludis,Pseudomonas aeruginosa and Amphidinium carterae Hulburt,four typical corrosion microorganisms in marine environment,have been selected in this paper.The mechanism of its influence on corrosion behavior of EH40 steel in 3.5wt.%NaCl solution was investigated by electrochemical and surface analysis techniques.This study has important guiding significance for in-depth understanding of MIC mechanism in marine environment and corrosion protection of steel used in marine engineering.The main results are as follows:(1)The adsorption of D.vulgaris and P.aeruginosa EPS on the surface of EH40 steel is mainly protein,and the adsorption of P.aeruginosa EPS is more uniform than that of D.vulgaris EPS.The adsorption of M.maripaludis and A.carterae EPS on the surface of carbon steel was mainly polysaccharide and more uniform.In 3.5wt.%NaCl solution containing four kinds of EPS alone,uniform corrosion occurred in EH40 steel under aerobic environment.Among them,D.vulgaris,M.maripaludis and A.carterae EPS promote corrosion of EH40 steel,while P.aeruginosa EPS inhibits corrosion of EH40 steel.The corrosion of EH40 steel is mainly localized in anaerobic environment,and each EPS promotes the corrosion of EH40 steel,which is mainly caused by the non-uniform distribution of EPS film on the surface of carbon steel,but the corrosion degree is smaller than that in aerobic environment.(2)In the case of synergistic EPS of pairings of microorganisms,the EPS membrane layer of the three groups was mainly protein.In aerobic environment,three groups of EPS films are uniformly distributed on the surface of EH40 steel,and the corrosion characteristics are uniform corrosion.The three groups of synergistic EPS films inhibited the diffusion of dissolved oxygen and inhibited the corrosion of carbon steel 7 days before immersion.After soaking for 7 days,the corrosion of the EPS film with the coordination of D.vulgaris and M maripaludis and the coordination of D.vulgaris and P.aeruginosa lost its protective effect and accelerated.The main reason is that the excessive complexation between EPS functional group and Fe2+/Fe3+ causes the loose porous EPS film layer to no longer isolate the dissolved oxygen.However,the EPS films synergistic with D.vulgaris and A.carterae are less affected by the complexation of functional groups and still inhibit corrosion.(3)The three groups of EPS all promoted the corrosion of EH40 steel in the anaerobic environment with the cooperation of EPS and the corrosion characteristic was local corrosion.The non-uniform distribution of EPS film on the surface of carbon steel was the main cause of local corrosion and accelerated the corrosion of carbon steel.At the same time,the corrosion degree of EH40 steel in anaerobic environment under the action of each synergistic EPS is smaller than that in aerobic environment,and the corrosion of EH40 steel in the synergistic condition is faster and more serious than that under the single action of four kinds of microorganisms EPS in anaerobic environment.