The Coupled Numerical Simulation Of Pressure Vessel Welding Stress And Work Stress

The presence of residual stress seriously jeopardize the structural safety ofwelded joints of pressure vessel, it’s easy to cause the fatigue crack propagation andearly fracture failure at the joints during long-term use, resulting in a major or fatalaccident.In this paper, the temperature field, stress field and the residual stress field ofthe class II pressure vessel welded joints, take the condensate tank main body forexample, was analysis in a three-dimensional finite element simulation by the largeANSYS finite element analysis software. The paper first discusses the impact of theprogressive activation weld unit method and layer activation weld unit method onwelding stress analysis, and simulation results of experimental testing of these twoelement birth and death methods were compared. The results show that progressiveactivation weld unit method is superior to the method of layer activation.Using progressive weld unit activation method, the welding process of girthweld joints of the tube section and the head, tube section longitudinal weld jointsand the saddle-shaped joint was simulated, the moving heat source along thesaddle-shaped weld trajectory equation was wrote to meet the needs of thethree-dimensional dynamic temperature field, the instantaneous stress field and theresidual stress field analysis at the saddle-shaped joint. Then the internal pressureload was imposed on the three types of connector model, analyzed and comparedthe stress changes in the joints.It can be seen from the results of the temperature field that, weldingtemperature field at the start and end of joint exist a certain length of the transitionsection, it is related to model simplify approach by symmetry, this temperaturedistribution has a certain extent affect to the stress distribution.The stress field in the welding process shows that, it’s mainly compressionstress in the front of the molten pool of metal, and the rear tensile stress, while thelowest stress in the weld pool. After cooling ring weld and longitudinal weldresidual stress in the joints is mainly concentrated in the weld zone and heataffected zone. The peak circumferential stress and axial stress of the girth weldsappear in the inner weld joints. The peak circumferential stress of longitudinal weldjoints appear in the outer weld bead, the axial stress peak is located in the inner weld. The common features of two types of joints in the welding residual stressdistribution are: vertical stress along the weld is higher than the horizontal stressperpendicular to the weld.The circumferential residual stress is significantly higher than the other twodirections along the saddle-shaped joint. There are a certain degree of stressconcentration in the joints of the weld toe and weld root parts, and these area are ina tri-axial tensile stress, and side of the tube section of the weld toe parts iscrack-prone.Three types of joint weld, the stress state of the joints did not change muchafter the superposition of welding residual stress and work stress in the three typesof joint, the circumferential weld and longitudinal weld joints in the peak stressincreased, the internal stress of the saddle-shaped weld joints are released.