Study On Corrosion Mechanism And Protection Of Symbiotic Microorganisms In Oil Field Gathering And Transmission Pipeline

As an important part of national energy construction,pipeline transportation,which transports oil and natural gas,is exposed to a variety of complex and changeable environments,and is inevitably corroded in contact with water,soil and air.One of the important reasons for corrosion perforation of pipeline steel is microbial corrosion.In addition to the first discovery of sulfate reducing bacteria involved in corrosion,more and more microorganisms are found to corrode metals,and some microorganisms can enhance corrosion through synergy.Due to the complexity of the environment where the pipeline is located,there is no particularly effective method to solve microbial corrosion.At present,the research on microbial corrosion mechanism mostly focuses on the single sulfate reducing bacteria system,while the corrosion mechanism under the multi bacteria symbiosis system is not clear.In addition,the research on microbial corrosion protection mostly starts from the perspective of microbial inhibition and external protection,and rarely considers the influence of the content of microalloyed elements in metal materials on microbial corrosion.In this paper,sulfate reducing bacteria,saprophytic bacteria and iron oxidizing bacteria were obtained by separating,purifying and enriching microorganisms in oilfield produced water.Laboratory coupon test and electrochemical test were carried out on pipeline steel L360 and pipeline steel L245NS.The corrosion behavior of the two kinds of pipeline steel under different microbial systems was compared and analyzed.The uniform corrosion rate was calculated by weight loss method,the biofilm morphology and pitting morphology of the corroded sample surface were observed by scanning electron microscope,the pitting depth of the corroded sample surface was measured by laser confocal microscope,and the pitting rate was calculated.The corrosion electrochemical behavior of pipeline steel in different systems was studied by electrochemical analysis.The results show that in a single microbial system,the uniform corrosion and pitting corrosion caused by sulfate reducing bacteria are more serious than saprophytic bacteria and iron oxidizing bacteria,and the corrosion effect of the latter two alone is not obvious.In the two bacteria symbiosis system,the combination of sulfate reducing bacteria and two aerobic bacteria produced more serious uniform corrosion and pitting corrosion,while the system combined with saprophytic bacteria and iron oxidizing bacteria did not produce obvious synergistic promotion,which was not different from the corrosion degree under the single bacteria system.In the three bacteria symbiosis system,the corrosion degree of the two pipeline steels reached the maximum.In addition,sulfur resistant pipeline steel L245NS shows better corrosion resistance than pipeline steel L360 in every system containing sulfate reducing bacteria,but there is no significant difference in the degree of corrosion between the two in the system of combination of saprophytic bacteria and iron oxidizing bacteria.The experimental results of this paper can prove that even if the corrosion effect of some microorganisms is not serious,it can enhance the corrosion when cooperating with other microorganisms.Therefore,the corrosion experiment of single microbial system has certain limitations.The results of this study provide a reference for the study of corrosion mechanism in symbiotic system.In addition,the comparison between the two pipeline steels proves that the content of microalloyed elements in metal materials will have an impact on microbial corrosion,and pipeline steel L245NS can alleviate the corrosion caused by H₂S,the metabolite of sulfate reducing bacteria.Compared with other protective measures,appropriate material selection will not produce environmental pollution,drug resistance and high cost,which provides a reference for microbial corrosion protection.