Experiment research on crack propagation and gas decompression characteristics during the fracture process of CO2 pipelines

: To reveal the coupling mechanism between decompression phase transition and crack propagation in fractured CO 2 pipelines, full-scale supercritical CO 2 pipeline rupture tests were carried out, and a decompression wave prediction model was built using an isochoric thermodynamic framework and the GERG-2008 equation of state. The model accurately reproduces the pressure plateau induced by CO 2 phase change. Combined with the Battelle Two-Curve Method (BTCM), the study identifies dynamic crack initiation and physical arrest under fluid-structure interaction. Within 2 s after rupture, pressure near the crack dropped by 36.3% with an obvious axial gradient; internal temperature plunged to −52.60°C, forming axial and radial thermal stratification exceeding 80°C relative to initial conditions. The initial gas cloud spread at 68.67 m/s, followed by high-pressure-driven crack tearing with a peak propagation velocity of 372.02 m/s. Severe Joule-Thomson cooling caused local material cold embrittlement at 0.20 s and triggered physical crack arrest. Fracture micromorphology evolves sequentially: ductile-brittle mixed fracture dominates crack initiation and growth, then shifts to brittle cleavage at arrest, and finally forms shear ductile fracture due to curled pipe wall losing geometric constraints. This work offers key experimental data for crack arrest design and safety evaluation of CO 2 transmission pipelines.