Three groups of CO2 pipeline release experiments were performed using an industrial scale (256 m long

233 mm id) instrumented pipeline with CO2 pre-discharge phase of gas phase

gas-liquid phase and supercritical phase

respectively. The pressure response and the phase transition were recorded and analyzed in the process of CO2 pipeline release. The results showed that when the pressure wave front arrived

the pressure fall and stagnation appeared in the process of gaseous CO2 release. The phase of CO2 in the pipeline during the gaseous CO2 release was mainly in gas state

but the temperature at the end pipe decreased sharply

leading to the formation of gas-liquid homogeneous CO2. The decompression multiple reflection led to multiple pressure fall sharply and rebound in the release of gas-liquid CO2. Gas-liquid layered CO2 transformed to gas-liquid homogeneous CO2 in the phase transition process of gas-liquid CO2

and then the gas-liquid homogeneous CO2 at the top of pipeline transformed to the gas CO2 and consequently the bottom. The pressure fall sharply and rebound appeared near critical region in the release of supercritical CO2. When the pressure passed through the critical pressure line

the pressure change rate could be stagnation and slow down. The discharge of the supercritical CO2

gas-liquid homogeneous CO2 and gas CO2 appeared in the process of supercritical CO2 release.