Study On Dynamic Fracture Process And Arrest Toughness Of Supercritical CO₂ Pipeline

CO₂ transport is the key link connecting the CO₂ emission site and Storage site in Carbon Capture,Utilization and Storing-CCUS.Pipeline transport of supercritical CO₂ is currently the most commonly used transportation method in the world.However,once a supercritical CO₂pipeline that has always been in a high-pressure state ruptures,the high-pressure CO₂ can provide a lot of energy for the pipeline to break and expand the crack,which will aggravate the damage of the pipeline and expand the scope of the leakage accident.According to the viewpoint of dynamic fracture mechanics,the research on supercritical CO₂ pipelines mainly focuses on the crack initiation,crack arrest and crack propagation of the pipeline.At present,there are few researches on the dynamic fracture process of CO₂ pipelines,and there is no clear method to calculate the pipeline crack arrest toughness.This article will conduct an in-depth study on this.According to the dynamic fracture mechanics,the fracture research of supercritical CO₂pipeline should be divided into the process of pipeline initiation,crack stop,crack propagation and brittle fracture.Regarding the crack initiation process of supercritical CO₂ pipelines,the calculation method of supercritical crack length is mainly established based on the D-M model.The influence of the pipe wall thickness,the initial pressure and the pipe diameter of the fracture on the critical crack propagation length is analyzed.When the pipeline pressure is large and the pipeline pressure is small,the critical crack growth length is relatively large,and it is not prone to instability growth.Then,based on the improved Battelle two-curve method（BTC）,a calculation method for the ductile crack arrest of the supercritical CO₂ leakage and decompression process is established,and the transmission of the decompression wave of the pipeline and the crack propagation change law are analyzed to determine the supercritical pressure The pipe wall thickness and minimum Charpy energy required for the toughness of CO₂ pipes to arrest cracks.The research results show that the crack arrest pressure of the supercritical CO₂ pipeline can reach the critical pressure.In this case,the minimum pipe wall thickness that meets the strength design generally cannot meet the pipe arrest toughness requirements.To meet the requirements of pipe toughness,it is necessary to improve the toughness of the pipe material or increase the wall thickness.Once the instability expansion occurs,a certain distance of the pipeline will be cracked before the pipeline stops expanding.Limiting the length of the crack expansion can effectively reduce the resulting economic losses.Before this,the crack expansion length of the pipeline under different conditions must be determined first.In this regard,the pressure prediction model of the supercritical CO₂ leakage process is established,and the unsteady crack growth model is established after combining it with the crack growth model.The crack growth length is obtained through discrete integration,and the initial pressure and initial temperature of the pipeline are studied and analyzed.The influence of pipe wall thickness,pipe length and leak size on the crack propagation length of supercritical CO₂ pipes.In addition,the brittle fracture of the supercritical CO₂ pipeline was studied,mainly to calculate the minimum temperature of the CO₂ leakage process with different impurities,and compared with the ductile brittle transition temperature of the pipeline material,and finds that supercritical CO₂ pipeline has the risk of brittle fracture,and if there is more H₂S in CO₂,it will increase the risk of brittle fracture of pipeline,When CO₂ contains a certain amount of N₂ or O₂,brittle fracture of pipeline can be prevented.