Objective This paper elucidates the root cause of consecutive perforation in a sulfur-bearing natural gas gathering and transportation pipeline.

Method In accordance with the established failure analysis procedure, a comprehensive approach was employed, encompassing macroscopic morphology analysis, physicochemical property testing, metallographic structure examination, microscopic corrosion morphology assessment, and corrosion product composition analysis. By integrating the pipeline's service history, operational conditions, environmental factors, as well as results from intelligent detection and simulation experiments, an in-depth analysis of the causes and mechanisms of the failure was conducted.

Result The physicochemical properties, mechanical properties,and microstructure of the pipeline complied with the standards and design requirements. Both pipeline failures occurred at locally low-lying points, exhibiting a characteristic pattern where the size of the corrosion pits diminished in the direction of corrosion propagation. The failure mode was characterized by localized corrosion leading to perforation. The corrosion products were structurally loose, primarily comprising iron sulfides and oxides. The findings from the intelligent internal inspection revealed that metal loss defects of varying degrees were present throughout the pipeline, with a concentration at the bottom and low-lying areas. Simulation experiments indicated that in the absence of corrosion inhibitors, the corrosion rate of the pipe material reached 0.305 6 mm/year. According to PIPESIM calculations, upon pipeline failure, both gas and liquid phase flow velocities at the failure point were at relatively low levels.

Conclusion The primary failure cause is identified as inadequate dehydration at the single well station, which resulted in liquid accumulation. Without corrosion inhibitors, this accumulated liquid caused severe pitting corrosion. Autocatalytic acidification within these pits exacerbated the corrosion, ultimately leading to pipe perforation.