Study On Mic Behavior In The Sediment Of A Product Oil Pipeline In South China

During the transportation of product oil,the local areas where pipelines are prone to deposits are often accompanied by internal corrosion.Microbiologically influenced corrosion(MIC)is one of the causes of corrosion in product oil pipelines.In order to study the microbiologically influenced corrosion behavior in sediments of product oil pipelines,the radial distribution characteristics of microbial communities at different locations in product oil pipelines were analyzed.The corrosion behavior and corrosion characteristics of X65,X70 and X80 grade oil product pipelines were studied.The cause of the corrosion in the pipeline where the deposit is prone to occur is analyzed,and the feasibility of the application of high-grade pipeline steel in the transportation environment of refined oil products under the condition of internal corrosion of the pipeline is discussed.At the same time,based on the above research results,the corrosion status and causes of X65 pipeline steel under the synergistic action of corrosive microorganisms in the sediment environment of product oil pipelines were analyzed.The conclusion provides a basis for controlling corrosive bacteria in product oil pipelines and supports the safe operation of product oil pipelines.The main conclusions are as follows.(1)In the simulated fluid of product oil pipeline sediment,the corrosion tendency and corrosion rate of X65,X70,X80 pipeline steel increase with the increase of immersion time.The results of weightlessness,corrosion morphology and electrochemical analysis show that X80 pipeline steel has better performance and adaptability to the environment,and its aerobic corrosion reaction is slower than that of X65 and X70 pipeline steel.The corrosion products of the three pipeline steels in the simulated liquid are Fe₂O₃,Fe OOH,Fe CO₃,and Fe S.The corrosion mechanism is the same,but the corrosion rate is different.This is because X80 pipeline steel contains more corrosion-resistant trace elements and has a dense structure.In view of the fact that there are few cases of X80 pipeline steel for domestic and foreign product oil pipelines,it is of practical significance to accelerate the development of X80 pipeline steel.(2)An analysis of the radial distribution characteristics of microbial communities at different locations in the product oil pipeline in southern China.A total of 389bacterial genera were detected at 9 sampling sites,including 26 families,41 classes and389 genera.The dominant microbial species in different locations of the pipeline are different,and the radial distribution types are significantly different,and the microbial population richness corresponds to the degree of corrosion of the pipeline.The complexity of the environment makes the actual situation of the MIC of product oil pipelines often more complicated.From the perspective of the radial distribution of the pipeline,the diversity and richness of the microbial community at the relatively low elevation point of the pipeline is significantly higher than the relatively high elevation point,which is much more consistent with the corrosion of the on-site pipeline relative lower elevation point than the higher elevation.The results of the microbial community analysis of the pig products also proved this point,which further explained the cause of the serious corrosion in the low-lying sediments of the pipeline.(3)Regardless of whether it is at the higher or lower point of the relative elevation of the product oil pipeline,microorganisms in the direction of 5/7 o'clock have the highest abundance and diversity,followed by the direction of 6 o'clock,and the least at12 o'clock.Among them,193 genera of 19 phyla of 19 classes were detected in the sediments at the lowest point of relative elevation 5-7 o'clock,and 23 genera with a relative abundance of more than 1%,of which 12 species can trigger MIC.Covered by sedimentary water at 6 o'clock,Sphingomonas,Sphingobium,Citrobacter,Lysinibacillus,Herbaspirillum,Dietzia may be the main causes of corrosion acceleration here.The pipeline is located in the water-oil interface area at 5/7 o'clock,and the corrosive bacteria Brevundimonas and Brucella are relatively high.The difference in the environment,heavy moisture,and oxygen content at 6 o'clock in the pipeline will lead to different mechanisms of MIC corrosion at two points.For the 12o'clock direction where the product oil can be submerged,the corrosion is slight due to the inhibitory effect of Pseudomonas on corrosion.(4)Comparative analysis of OCP,EIS and polarization curves of X65 pipeline steel in natural dilution system(X65-Bacteria)and sterilization dilution system(X65-Asepsis),and found that under the synergy of bacterial communities in the sediment,the corrosion rate of X65 pipeline steel was accelerated.The microbial film growth on the surface of X65 pipeline steel and the microscopic morphology of corrosion products were observed.It was found that bacteria rapidly multiply and metabolize on the electrode surface to produce extracellular polymers(EPS),forming a dense biofilm on the third day.The membrane is mainly composed of organic matter and iron oxide.The density and number of bacteria in the biofilm on the 7th day did not change significantly compared with the third day.Combined with the results of electrochemical analysis,it is believed that due to the porous,loose surface of the electrode,the corrosion product film is easy to fall off,and the combined action of microbial metabolites,the corrosion rate of the metal surface on the 7th day is accelerated.Use finite element analysis to predict the life of the largest corrosion point.The life of the pipeline with the largest corrosion point is calculated to be 5 years,which is consistent with the actual service life.