Study On Theory And Control Method Of Supercritical Carbon Dioxide Pipe Fracture

Taking the breakage and expansion of supercritical CO₂ pipelines as the research object,the research focuses on the fracture propagation of supercritical CO₂ pipelines.Through investigation and study of relevant theoretical knowledge,the mechanism of the fracture propagation of supercritical CO₂ pipelines was analyzed and combined with the relevant properties of CO₂?T_c=31.2?,P_c=7.38 MPa?,and the phase change law of supercritical CO₂ at cracks.A decompression wave calculation model was established to study the characteristic changes of decompression waves in crack propagation.ANSYS Workbench software was used to simulate and establish a three-dimensional pipe model with cracks.The simulation results were summarized and the corresponding crack control method was proposed.Design a crack arrester suitable for supercritical CO₂ piping.The pressure-decompression wave velocity curve of the CO₂ medium inside the pipe was drawn by calculation of the decompression wave speed to study the influence of impurities,initial temperature and pressure on the propagation characteristics of the decompression wave.The addition of impurities changed the phase boundary of pure CO₂,raised its saturation pressure,increased the pressure plateau in the decompression wave curve,and kept the pressure at a high level for a long time;the temperature caused the supercritical CO₂ to generate two-phase flow earlier.Slowing down the pressure is not conducive to pipeline crack arrest.Although the pressure increases,the critical state CO₂ enters the two-phase state from the single-phase state,but the initial decompression wave velocity also becomes larger,so that the pressure plateau of the decompression wave curve decreases.The pressure drop is accelerated and it is conducive to the arrest of pipelines.The ANSYS Workbench software was used for simulation analysis under different temperatures and pressures to study the effects of temperature and pressure on the pipeline.With the decrease of temperature,the equivalent strain and stress of cracks and extended zones become larger,and the total deformation decreases.Under the influence of different internal pressures,the inner wall of the pipeline is affected far more than the external surface of the pipeline.The pipeline should be fully considered when designing pipelines.The pressure conditions of the inner wall;three stress intensity factors K_I,K_III and K_IIIII were analyzed.During the process of pipeline crack propagation,the effect of K_I on crack propagation is much greater than the effect of K_III and K_IIIII on its expansion,which confirms that the type I crack is the most harmful to the pipeline;the J-integral is analyzed,indicating that the pipeline crack is at both ends and in the middle Location expansion is relatively easy and faster.At the same time,the lower the temperature,the smaller the J-integral value,which means that as the temperature decreases,the resistance to crack propagation is smaller,which is beneficial to the expansion of pipeline cracks.This paper focuses on the study of the fracture mechanism and control method of cracked supercritical CO₂ pipelines,hoping to provide theoretical guidance and technical support for the future development of CCUS projects in China.