Microbiologically Influenced Adhesion And Corrosion Of 316L Stainless Steel By Marine Microorganism

Microbiologically influenced corrosion (MIC) has been given severe attention in marine environment concerned of all kinds of structure constructions, such as pipeline, platform for petroleum, etc. In the paper, marine microorganism (nature seawater biofilm, Pantoea which was isolated from seawater and MR-1) influenced corrosion was studied in seawater environments.The microbiologically influenced corrosion behaviors of marine microorganism for 316L SS were studied by the immersing experiments in the nature seawater and in the sterile seawater. The methods used were as follows: electrochemical techniques (the open circuit potential (Eoc), electrochemical impedance spectroscopy (EIS), and polarization curves), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). It was confirmed that the open circuit potential (Eoc) of 316L SS in nature seawater shifted in noble direction nearly 450mV. In sterile seawater, Eoc was stable in experimental period. Marine microorganism and its metabolites were observed on stainless steel surface immersed in seawater after a period of time which changed the superficial properties of 316L SS. Electrochemical experiments showed that the presence of marine biofilms on the stainless steel played a role in inhibiting corrosion according to the decrease in corrosion current densities obtained from the polarization curves, the increase in the resistance of the polarization resistance (Rp) obtained from EIS and the comparison test of SS immersed in nature seawater and sterile seawater. Meanwhile, the element analysis of local position of stainless steel indicated that the corrosion behaviors of stainless steel were due to specific types of bacteria whose metabolism were related to the corrosion in seawater.The influence of Pantoea.sp was studied on the aerobic corrosion of 316L stainless steel using same methods as mentioned above. Within a few hours, the presence of cells induced Eoc decrease around -0.5V compared with Eoc dropped less than -0.1V slowly in sterile medium. Inoculating bacteria 24h later, the number of it can achieve 6.0×108 CFU/mL. The decrease of Eoc was mainly because of the bacterial adhesion and biofilm formation. The electrochemical results indicated that the corrosion of 316L SS was accelerated in the presence of Pantoea.sp according to the increase in corrosion current densities obtained from the polarization curves and the decrease in the resistance of the charge transfer resistance (Rp) obtained from EIS. SEM images showed biofilm attachment that evidenced the effect of bacteria.It was confirmed that MR-1 was one of electrochemical active biofilms. It can result in the drop of open circuit potential quickly and the electrochemical results revealed that it could inhibit the corrosion of 316L SS. We presented that the biofilms which have electrochemical active to transfer electron between the biofilms and 316L SS enabled that 316L SS can accept electron transferred by the biofilms to avoid the corrosion.