Research On Corrosion Mechanism And Control Method Of Microbial Corrosion In Gasoline And Diesel Transportation System

The corrosion failure of metal materials not only results in huge loss to our national economy.More importantly,it also directly threatens the safety of human production and life and brings resources waster,environmental hazards,and hinders the development of new technologies.Corrosion could be influenced by various factors,and microorganisms,especially sulfate reducing bacteria(SRB)has been viewed as one of the main factor for water system corrosion.Microbioloically influenced corrosion accounts for 50%of the total corrosion.With the rapid increase in urban energy market demand in our country and the continuous expansion of the underground pipeline network of the refined oil transportation system,the surrounding microbiologically influenced corrosion environment of pipeline materials has also become more and more serious.Therefore,the study on corrosion problem of the refined oil transportation system and the corresponding protect measures is of great significance for safe transportation for gasline and diesel.In this thesis,we systematically studied X60 corrosion mechanism of pipeline steel under simulated working conditions and monitor the formation process of bacterial biofilm through on-site investigation,analysis of corrosion deposits in oil products and pipelines,and the enrichment,separation,purification,and identification of corrosive bacteria,combined with electrochemical methods,corrosion weight loss,and material surface analysis methods.Moreover,this work developed different biocides and evaluated their long-term protection effect aiming at the current MIC problems.The main findings are as follows:1.Composition analysis of corrosion sediments in refined oil pipelinesThe sediments of the refined oil pipeline are composed of Fe₃O₄,Fe S,Fe₂O₃ and Fe OOH.The SRB content in the sediment was as high as 10⁶ cells/m L,and a small amount of IOB bacteria was also detected.Desulfovibrio was demonstrated by species identification using 16Sr DNA sequencing method.The test results of the critical water content of gasoline and diesel show that the critical water content is 2.4 mg water per litre gasoline,and 2 mg water per litre diesel.2.Corrosion behavior of X60 steel by aqueous and bacteria-containing refined oilWith the increase of water content,the corrosion of refined oil gradually intensified.The corrosion is mainly localized corrosion and the corrosion rate is 0.04 mm/a under the condition of critical water content(2.4 mg water per litre gasoline).Corrosion products were mainly Fe OOH and Fe₂O₃,indicating that the corrosion in the pipeline is not simply caused by stagnant water.In the oil containing bacteria,SRB can be adsorbed and aggregated on the metal surface,forming biofilm in a short time and then cracking to aggravate the corrosion of X60.The corrosion products contain high contents of Fe,O and S,which are consistent with the actual elemental analysis of the sediment in the pipeline,the content of S is higher in the corrosion products in refined oil containing the bacterial liquid system.The weight loss experiment shows that the corrosion rate in the bacterial liquid is as high as 0.15 mm/a,and the maximum local corrosion pit is as high as 25.1?m/14d when the volume ratio of diesel and SRB bacterial liquid is 1.The type of corrosion is local corrosion.3.Study on X60 corrosion behavior in simulated pipeline sediment corrosion environmentThe corrosion rate of X60 under SRB-containing sediments is 0.48 mm/a,which is an order of magnitude higher than that of the sterilization system.The the maximum corrosion hole depth on the surface of the test piece is as high as 34?m/21 d,which is 1.5 times that of the blank sterilization group,and much higher than the corrosion rate in the bacterial liquid containing refined oil.In the system containing SRB,the corrosion products on the surface of the test piece are mainly Fe₃O₄ and Fe S,which are basically the same as the analysis results from on-site deposits,indicating that the Fe S results from SRB corrosion and the corrosion in the pipeline is due to the corrosion process of bacteria and water in the sediment.4.Performance evaluation of screening fungicides to prevent MICThe biocide 3,5-Dimethyl-(2H)-tetrahydro-1,3,5-thiadazine-2-thione(DMTT)was screened out.The results show that 100 mg/L DMTT can effectively kill the SRB in the sediment and possesses a certain inhibitory effect on the SRB in the solution.Resistance probe corrosion rate detection,surface analysis technology and corrosion product analysis all show that the addition of 100 mg/L DMTT can slow down the corrosion process of SRB under sediments,and inhibit or even kill bacteria.After the addition of biocides,the corrosion inhibition rate calculated by the corrosion rate of resistance probe was 63.5%,the peak value of corrosion rate and the number of corrosion peaks decreased,and the XRD did not detect the corrosion product components produced on the metal surface,indicating that DMTT can be used as a long-term biocides under the sediment.