Pitting Mechanism of X60 Pipeline Steel under the Action of SRB

Pitting in the body of underground pipelines and the failure during their service period will result in serious security incidents and huge economic loss. There appeared pitting in the body of X60 pipeline with the thickness of 7.1mm after 13 months of service, which resulted in air leakage. The corrosion mechanism of the pipeline body pitting was researched through site investigation and sample analysis by SEM and XRD. The results showed that all corrosion holes were located in the bottom of the pipeline in a straight line shape, plenty of S and Cl elements were found in the corrosion product around the holes, which was confirmed as FexSy through EDS and XRD analyses. A plenty of FeO(OH)were found in the scales beside the pipeline body. The cause of the corrosion holes was confirmed with the combination analyses of site environment, corrosion morphology and corrosion products to be microbiological corrosion due to SRB. Improvement measures were proposed according to the corrosion characteristic and site condition.