Study On Corrosion Development Of X70 Steel Under The Synergistic Action Of AC And SRB In Marine Environment

With the rapid development of Marine oil and gas industry,the mileage of submarine pipeline construction has been increasing.Therefore,more and more attention has been paid to the safety of submarine pipeline in recent years.However,with the wide application of direct electric heating technology(DEH)and the rapid development of coastal electrified railway and offshore electric power facilities,the submarine pipeline is facing more and more serious AC corrosion risk.In addition,sulfate-reducing bacteria(SRB)living in the Marine environment can also cause microbial corrosion(MIC)of submarine pipelines.It can be seen that AC corrosion and MIC pose a great threat to the safe operation of submarine pipelines.However,most current studies on AC corrosion and MIC do not consider the synergistic effect of the two,and only a few studies are conducted in soil environment.Therefore,this paper takes X70 steel as the analysis object to study the corrosion behavior under the synergistic action of AC and SRB in Marine environment.In this thesis,the corrosion behavior of X70 steel under the synergic action of SRB and AC current with different current density,waveform and frequency was studied by means of electrochemical testing and surface analysis technology in a closed anaerobic device built by ourselves.A self-built real-time image acquisition device and real-time image acquisition software were used to study the corrosion morphology development process of X70 steel under the action of alternating current and SRB,and the image processing technology was used to extract texture features such as energy,contrast,correlation and deficit moment of the corrosion image,and the corrosion development process of X70 steel was quantitatively characterized.The results show that both AC and SRB can promote the corrosion process of X70steel,but the effect of AC on the corrosion rate of X70 steel is significantly greater than that of SRB.The natural corrosion current density of X70 steel is 0.32μA/cm~2,which is lower than that of SRB,0.43μA/cm~2.In addition,under the same AC current density,waveform and frequency,The corrosion current density in sterile environment is much higher than that in bacterial environment.Alternating current can stimulate the life activity of SRB to produce composite biofilm with certain protective effect,which has a significant effect on the corrosion process of X70 steel.Both AC and SRB can promote the occurrence of pitting corrosion.The critical current density from pitting corrosion to local corrosion is 100A/m~2.The synergies of different alternating current densities and frequencies with SRB have significant effects on the electrochemical corrosion process and morphology development process of X70 steel,while different alternating current waveforms have no obvious effects on the electrochemical behavior and morphology development process of X70 steel.