Research On Corrosion Failure Rule And Control Method Of Buried Pipeline Under SRB

In recent years,with the rapid development of oil and gas industry in China,the construction of buried pipelines has gradually expanded,but affected by soil moisture,corrosive anions(Cl^-,SO₄^2-,HCO₃^-),soil microorganisms and other factors,then cause leakage of oil and gas pipeline prone to local corrosion.Among them,sulfate reducing bacteria?SRB?is one of the main causes of microbial corrosion and stress corrosion cracking?SCC?in buried pipelines.It is necessary to explore the corrosion failure rule and control technology under the action of SRB.In this paper,SRB strains were enriched and purified from the soil around the service pipeline in southwest China by microbial culture.The growth curve of SRB in soil simulation fluid in southwest China was plotted to study the influence of SRB growth process on the surrounding corrosion environment.The results showed that the amount of SRB significantly changed the pH,conductivity and sulfide content of the corrosion environment,which had a great impact on the corrosion environment.The corrosion behavior of steel base materials and welds of X52,X70,X80,and X100buried pipelines in simulated soil solution of SRB in southwest China was studied by means of corrosion weight loss,electrochemical test combined with metallographic microscopic observation,XRD,and SEM surface analysis techniques.The results show that the corrosion weight loss trend of base material and weld of X52,X70,X80 and X100 pipeline is basically the same in southwest SRB soil simulation solution.At the initial stage of corrosion,the average corrosion rate is relatively high,but as the number of SRBs increases,the corrosion rate of each grade of base metal and welds decreases slightly.As the corrosion time increases in thelater stages of corrosion,a large amount of H2S and extracellular polymers?EPS?makes the surface FeS of the substrate transform to Fe1-x S and other sulphur-iron compounds,At the same time,due to the continuous accumulation of corrosion products,the stress in the corrosion product film increases,and the corrosion products are stimulated by corrosive anions such as SO4^2-,Cl^-,S^2-The film ruptured and fell off,and the corrosion rate of the welds of the base metals of various steel grades increased to varying degrees.The average corrosion rate is higher due to uneven weld structure,segregation,and high surface activity.From the weight loss results,it can be seen that the X52 base metal and weld,X70 weld and X100 base material and weld are all moderately corroded,and the X70 base material,X80 base material and weld are mildly corroded at 30 days of corrosion.It can be seen from the electrochemical test that the polarized electrodes of X52 and X70 are activated,while X80 undergoes an activation-passivation transition,and X100 steel undergoes significant passivation.With the increase of the strength of the steel grade,the passivation characteristics are strengthened..The comprehensive analysis results show that the base material and welds of X80 pipeline steel have the best corrosion resistance in the Southwest SRB soil simulation fluid.The effect of SRB concentration on the stress corrosion behavior of X52,X70,X80,and X100 pipeline steels in the southwestern soil simulation solution was studied by slow strain rate tensile test?SSRT?,and the fracture morphology of the samples was characterized by scanning electron microscopy?SEM?.The results show that with the increase of SRB concentration,the stress-corrosion sensitive evaluation parameters?fracture life,fracture strength,and section shrinkage?of X52,X70,X80,and X100 series pipeline steels in southwest soil simulation fluid have better consistency.Judging from the loss of area shrinkage factor,X100 pipeline steel has the strongest sensitivity to stress corrosion in Southwest SRB soil simulation fluid,followed by X52 and X70,and X80 is the smallest.The increase in SRB concentration has a significant effect on the stress corrosion cracking of series pipeline steels.In view of the particularity of the service environment of buried pipelines,the application of bactericides and other methods cannot protect the SRB corrosion process of the soil environment outside the pipeline.The most effective method at present is to adopt the anti-corrosion layer+cathodic protection joint protection method.Protective coating is the focus of future research,and it is very necessary for online monitoring research of microbial activity in high-consequence areas and special soil environments.