Multi-field Coupling Failure Mechanism in Mountainous CBM Pipelines: Synergistic Effects of Terrain-Induced Gas–Liquid–Solid Separation and Intermittent Operation

This study investigates an internal corrosion-induced failure of a mountainous coalbed methane (CBM) pipeline under intermittent gas supply. The transported medium contained impurities such as H₂S, CO₂, and moisture, which collectively created an acidic corrosive environment. Due to terrain-induced gas–liquid–solid separation, these corrosive components accumulated locally, leading to severe locally uniform corrosion and wall thinning, ultimately resulting in pipeline rupture. A detailed analysis was conducted on the macroscopic morphology of the failed pipeline, corrosion product composition, and underlying corrosion mechanisms. A novel "multi-field coupling" failure mechanism is proposed, that is, the synergistic failure mechanism among the gas-liquid-solid multiphase flow field caused by terrain relief, the alternating stress field caused by periodic start and stop, and the local corrosion field caused by water accumulation in the coalbed methane pipeline in mountainous areas. This study provides important insights for corrosion prevention and safety management in similar pipeline systems operating under complex terrain and intermittent flow conditions.