Material Test And Finite Element Analysis Of CO₂ Pipelines Considering Surface Crack Propagation

Pipeline transportation of CO2 is a key part of the CCS implementation.Transporting metal pipes in supercritical CO2 forms a form of corrosion fatigue failure that has the dual role of cyclic stress and corrosion.Accurately estimating and predicting pipeline corrosion fatigue life is the premise of ensuring the safe operation of the pipeline and an important basis for judging whether the pipeline needs to be maintained or replaced.In general,supercritical CO2 high internal pressure delivery conditions of 9 to 15MPa(the general requirements of more than 7.38MPa),and the CO2 pipeline rupture,due to low temperature carbon dioxide leaks,there will be leakage of carbon dioxide pressure loss phase change absorption Thermal phenomena,the local temperature of the pipe is rapidly reduced,so that the pipe in the rupture of local strength and toughness reduction,which led us to study the CO2 pipeline,the need to consider both brittle failure and ductile failure.At the same time,under the influence of cyclic stress caused by fluctuation of internal pressure inside the pipe and complex load outside the pipe,the corrosion fatigue problem of CO2 pipe will be more serious.Carbon dioxide gas belongs to the dangerous goods jointly identified by the United Nations and our country.The second of the nine dangerous goods listed as the second non-natural toxic gas will cause serious consequences and threaten People's health.Therefore,this paper focuses on the key issue-single-point corrosion and double corrosion of CO2 pipe under pressure fluctuations in the pipe surface crack propagation process to carry out research.By using theoretical analysis,the fatigue test of pipe specimen and the numerical simulation of finite element method,the corrosion fatigue failure mechanism of CO2 pipeline is revealed.Through the fatigue test of the pipe specimen under cyclic loading,the crack length at each moment and the corresponding number of lifetimes of the surface crack in the pipe test are obtained.The finite element model of the test pipe is established.The virtual crack closure method and the finite element numerical analysis The stress intensity factor K value of the crack tip is obtained,and the crack propagation curve of the pipe steel specimen is plotted as da/dN-?K curve.The curve is fitted by the method of least squares to obtain the fatigue life of the pipe Based on the prediction formula-Paris formula.Finally,the three-dimensional CO2 pipe model is constructed and the stress intensity factor K at the crack tip is extracted.The K value obtained is brought into the Paris formula and the fatigue life times of the CO2 pipe can be obtained.Based on this,Respectively,explored in the actual land and marine pipelines,under the influence of fluctuations in internal pressure pipeline life of the use of the period.In this paper,finite element modeling method of three-dimensional cracked pipe segment can be used to estimate the fatigue life of CO2 pipeline in various stages of normal use,maintenance,inspection and repair,etc.,For their research provides a technical reserve and learn from.