Abstract: Aiming at the problem of oil and gas long-distance pipeline being prone to corrosion failure, this paper conducted macroscopic and corrosion product analysis, metallographic analysis, chemical analysis, mechanical property testing, hardness determination, scanning electron microscopy and energy spectrum testing of the failure area and surrounding soil analysis of the natural gas longdistance pipeline. The results show that external mechanical damage first led to great damage defects and thickness thinning of the pipe wall, and also caused breakage of the external anti-corrosion coating of the pipe. Then the damage site was directly exposed to the electrolyte environment of the soil, and chemical or electrochemical corrosion occurred in the damaged site until the occurrence of the pipeline failure due to local wall thickness reduction. The above analysis demonstrates the general phenomenon of pipeline failure induced by mechanical damage during installation and subsequent corrosion during operation. According to the failure causes, this paper puts forward relevant recommendations and measures for the procurement, construction and installation, and operation and maintenance stages, which are of certain reference value for the handling of similar problems.

Key words: L360, long-distance pipeline, external corrosion, failure analysis, mechanical damage, chemical corrosion, electrochemical corrosion