Simulation Study On Residual Stress And Fatigue Performance Of Welded Joint Of Two-phase Large Strain Pipeline Steel

Due to the effect of cyclic stress in the service of pipeline steel pipe,the fatigue failure of pipeline caused by fatigue crack at the weld joint is one of the most important failure forms of pipeline steel pipe.In the process of forming,the residual stress concentration at the welding joint will have a certain impact on the fatigue performance of pipeline steel.Therefore,it is of great significance to study the residual stress of weld joint of steel pipe and its influence on fatigue performance for the service safety design of pipeline.In this paper,the physical simulation and numerical simulation method are used to study the structure and properties of the weld joint in the actual welding process,and the numerical simulation model of the weld joint sample is established.The residual stress of plate weld joint is studied by pre deformation,and then the influence of residual stress on fatigue performance is studied.On this basis,a three-dimensional simulation model of steel pipe is established to simulate the influence of steel pipe expanding on the residual stress and fatigue performance of weld joint.The results of welding thermal simulation experiment of X80 pipeline steel show that the performance of FGHAZ is weakened obviously,the lowest point of strength is also in CGHAZ,but the lowest point of fatigue life is in CGHAZ.At the same time,the material property parameters of numerical simulation are also obtained through the thermal simulation experiment.For the plate weld joint specimen,the residual stress is mainly concentrated in the coarse-grained area of welding due to the change of microstructure and properties in the heat affected zone of welding and the effect of weld reinforcement after simulating the pre deformation,and the maximum value appears at the toe of welding.With the increase of pre deformation,the residual stress also increased.When the pre deformation is increased from 0.5%,1%,2%to 4%,the maximum residual stress at the inner weld toe is increased from 429MPa,449MPa,479MPa to 481MPa.The increase of residual stress significantly reduced the fatigue life from 9.959×10~4N,8.184×10~4N,6.402×10~4N to 5.317×10~4N.The three-dimensional simulation results of steel tube show that the expanding amount has little influence on the distribution of residual stress,but has great influence on the maximum residual stress.When the expanding capacity increases from 0.5%,1%,2%to 4%,the maximum residual stress of weld toe in the welded joint of steel pipe increases from 372MPa,430MPa and 434MPa to 454MPa,and its fatigue life decreases from 9.889×10~4N,3.431×10~4N,2.680×10~4N to 2.297×10~4N.