Internal localized corrosion of X65-grade crude oil pipeline caused by the synergy of deposits and microorganisms

•An X65 pipeline suffered from severe localized corrosion after short time service.•A large amount of SRB was detected in the pigging solids and products/deposits.•The deposits comprised silicon dioxide, calcium carbonate, ferrous carbonate, and oil sludge.•Significant localized corrosion resulted from the under-deposit microbial corrosion. A case study of an X65-grade crude oil pipeline suffering from severe internal localized corrosion after short-time service was presented. The causes were analyzed via thickness measurement, microbial analysis, SEM, EDS, and XRD analysis. The results showed that a large number of corrosion pits were distributed in the area of 4–8 o'clock at the bottom of the pipeline, and severe localized wall thickness reduction was observed. Around the corrosion pits, extremely thick (∼3 mm) and complex products/deposits can be seen at the edge of the pit, while relatively thinner ones can be seen at the bottom of the pit. In addition, a large amount of SRB was detected in the pigging solids and products/deposits scarped from the inner pipe. Based on the results, the under-deposit microbial corrosion was proposed as the leading cause for the significant localized corrosion of the pipeline in a short-term service.