Turbine Runner T-Joint Welding Residual Stress Simulation And Optimization

In reality, long-term use of large turbine runner blades during the break occurs the situation, this fault is occurring within the design life, it pose a great threat to use of the runner. The welding residual stress of the runner is the main reason which leading to the fault of the runner blades, so the study on the welding residual stresses of the runner blade is necessary.According to the the complexity of the spatial structure of large hydraulic turbine and the feature which the welded joints between runner blades and runner crown or bottom ring are belong to standard T joints, the paper calculates the welding residual stress of large runner with three-dimension thermal elastic plastic finite element, do the Marc finite element software further-development by Fortran, compile the programs of double-ellipsoid moving heat source and filler wire to the welding bead to simulated welding of the T joint and simulated annealing of the whole model. Simulated the single stage and single layer welding of T-joint to calculate the spread and change of welding temperature field and stress field in welding process, and respectively simulated subsection welding,multilayer welding by change the welding sequences, Finally, caluated the temperature field and stress field in the whole process of heating,insulating,cooling of the postweld whole annealing.Through this research, the main results obtained in this paper are as follows:(1) In the single stage and single layer welding, The temperature of welding bead reaches 1725℃when the heat source arrival, the change of temperature in the front of heat source is more obvious than in the rear of heat source, the temperature of region away from welding bead gradually decreased to room temperature.(2) In the single stage and single layer welding, the stress of welding bead in the X, Y, Z three directions are the tensile stress after welding, the peak value of residual tensile stress in the X, Y, Z three directions was 247MPa,511MPa,638MPa. The region away from the weld bead is compressive stress, the peak value of residual compressive stress in the X, Y, Z three directions was 435MPa,430MPa,423MPa, the stress in the region father away from the weld bead is 0. (3) In the subsection welding, the residual tensile stress at the adjacent area between the middle welding section and the end welding section decreased, minimum down to 442MPa, the maximum weld area which residual tensile stress significantly reduced can reach 18.75mm. Subsection welding can reduce the residual tensile stress in the local area of weld bead.(4) In the double layer welding, the residual tensile stress in the Z direction is maximum, in the Z direction, the peak value of residual tensile stress in the first layer welding is 515MPa, the peak value of residual tensile stress in the second layer welding is 571MPa, decreased 20%,10% than single layer welding. Than single-layer, multi-layer welding produce more lower residual stress values.(5) In the process of whole annealing after welding, When the temperature rose up to 600℃, the peak of residual tensile stress is 244MPa, Cooled to room temperature, The peak of residual tensile stress increased to 480MPa. When cooling, the residual tensile stress in the Y direction in the middle of blade increased. The overall annealing can effectively reduce residual stress after welding, but in the cooling, very important to control of the cooling.