Study On The Effects Of Microorganisms On The Metal Corrosion Under Disbonded Coating

Sulfate-reducing bacteria(SRB)was one of the main factors that contributed to the corrosion of buried metal pipeline.For the metal pipeline under disbonded coating,it was more conducive to the survival of SRB when the crevice formed between the anticorrosion coating and the pipeline.Thus destroying the coating performance of the metal pipeline and affecting the corrosion behavior of metal substrate.It was not only caused serious economic losses,but also greatly reduced the safety of oil and gas transmission.The influence of SRB on the corrosion behavior of X80 steel and Q235 steel under disbonded coating in the different disbonded crevice thickness was explored by adopting the self-made device and using the weight loss method in this paper.Based on the study results of weight loss method,the influence of SRB on the corrosion behavior of the metal under disbonded coating was studied deeply by using the wire beam electrode(WBE)experimental device and the microelectrode ionic sensor,then testing the electrochemical parameters of the electrode and detecting the pH value and Cl-concentration of the solution under the crevice at the same time.The study results showed that:(1)From the weight loss method,it can be seen that the corrosion resistance of X80 steel under disbonded coating was stronger than that of Q235 steel with the condition of natural corrosion without SRB.However,the corrosion resistance of Q235 steel under disbonded coating was stronger than that of X80 steel when SRB was presented;the corrosion influence of disbonded crevice thickness on the Q235 steel was greater than X80 steel.(2)For the X80 steel under disbonded coating,when SRB was presented,it can participate in the cathodic reduction process of the electrode and consume H+ in the solution under the crevice,then inhibite the acidification of the solution to a certain extent.So that the corrosion-induced phase of the crevice was 0~18h,extended 12 h than the condition without SRB;with the extension of the soaking time,the crevice corrosion along the depth direction of the crevice in the expansion,the accumulation of SRB metabolites maked the seam continued to block,so the increase period of crevice corrosion was also extended than the condition without SRB;after 11 days of soaking,the corrosion of the electrode under the crevice began to slow down.And after 15 days of soaking,the mass transfer barrier in the seam was removed and the crevice corrosion was corroded into the stable period,both the time was delayed than the condition without SRB.(3)For the Q235 steel under disbonded coating,regardless of whether the solution environment with SRB or without,the corrosion rate of the metal electrode under the crevice was gradually weakened with the increase of the disbonded distance when the disbonded thickness was the same;compared with the corrosion behavior of Q235 steel in the different disbonded crevice thickness,the corrosion degree of the metal electrode under the crevice was the most serious when the thickness was 0.5mm.With the increase of the disbonded crevice thickness,the corrosion effect of SRB on the metal electrode under the crevice was increased,and the corrosion of the metal electrode was gradually extended from the edge of the crevice to the bottom.In conclusion,for the corrosion of the metal under disbonded coating,because of SRB involved in the electrode corrosion reaction and activated the electrode surface metal,the corrosion rate and the corrosion degree of the electrode under the crevice were increased.At the same time,the corrosive area of the electrode under the crevice was further expanded,which reduced the corrosion difference of the electrode both inside and outside the crevice.Therefore,the corrosion was more serious under the condition with SRB.