Research On Behaviour Of Microbiological Corrosion Of Several Metals Influenced By Sulfate-Reducing Bacteria

With the demand of the economic development,intensive exploitation and effective utilization of marine resource were constantly strengthened.Problems due to microbiologically influenced corrosion(MIC)of metal constructions in marine environment had aroused high concern and extensive study.Metals in seawater suffered MIC,causing severe economic loss to the national economy.Sulfate-reducing bacteria(SRB)are representative anaerobic and corrosive species,and considered to be one of the main culprits among the MIC.Thus,it is very important to research on the effect of SRB on the MIC of different metals.In this paper,the starting SRB strains were incubated in the modified Postgate’s C Seawater(PCS)medium that it was also prepared for the corrosion medium.In hermetic anaerobic condition,effects of SRB on the corrosion behaviour of EQ70 steel,galvanized steel and cupronickel alloy in the simulated seawater without and with SRB were investigated by electrochemical methods(open circuit potential,electrochemical impedance spectroscopy and polarization curve)and surface analysis techniques(scanning electronic microscopy,atomic force microscopy and confocal laser scanning microscopy).The effects of SRB on the corrosion behaviour of the above three metals were discussed and analyzed.The results of electrochemical methods suggest that the corrosion rates of EQ70 steel,galvanized steel and cupronickel alloy were accelerated in the simulated seawater in the presence of SRB under anaerobic condition.The corrosion current densities of anodic polarization in the simulated seawater with SRB are almost one order of magnitude higher than that in the simulated seawater without SRB,the increase in corrosion rate can be attributed to SRB with the conductivity and the generated metal sulphides induced by SRB form a microcell with the metal matrix.The results of SEM shows that the presence of SRB strains and corrosion products attached to the EQ70 steel,galvanized steel and cupronickel alloy surface after 15 days of exposure in the simulated seawater with SRB.Moreover,it can be seen that corrosion of the samples in the simulated seawater with SRB was more serious than that in the simulated seawater without SRB.EDS analysis shows that the S peak was obvious for the samples after exposure for 15 days in the simulated seawater with SRB,and the enrichment of the element of S in the surface of the samples immersed in the simulated seawater with SRB was higher than that immersed in the simulated seawater without SRB.At the same time,the enrichment of the element of matrix in the above three metals immersed in the simulated seawater with SRB was all significantly less than that in the simulated seawater without SRB.The results of CLSM reveal that the pits in the EQ70 steel and cupronickel alloy were obvious and corrosion was more serious than that samples immersed in the simulated seawater without SRB.The results of depth of pits on the sample surface show that the average pit depth on the surface of the EQ70 steel and cupronickel alloy in the simulated seawater with SRB were almost twice than the average pit depth on the surface of samples in the simulated seawater without SRB.