On Residual Stress and Relief for an Ultra-Thick Cylinder Weld Joint Based on Mixed Hardening Model: Numerical and Experimental Studies

Residual stress distributions as welded and after local postwelding heat treatment (PWHT) of butted weld joint of a huge cylinder with ultra-thick wall were investigated by finite element (FE) simulations and measurement. Sequential coupling thermal-mechanical analyses were conducted with a generalized plane strain two-dimensional (2D) model to simulate the welding procedure bead by bead, combining with three-dimensional (3D) double-ellipsoid moving heat source and mixed isotropic–kinematic hardening plastic model. The simulation was validated by X-ray diffraction (XRD) measurements. Simulation results showed that local PWHT with heated band width of $0.5Rt$ can significantly reduce the residual stress on the outer surface of weld joint, but bring about harmful high tensile stress on inner surface due to bending moment induced by local radial thermal distortion. For the purpose to find out the appropriate heated band width of local PWHT, relations between stress relief and size of heated band were studied. Results show that the stresses on the inner surface reach a maximum value when the heated band width is less than $1Rt$⁠. Based on the simulation results and from the view point of lowering the stress level on the inner surface, the optimum width of 3$Rt$ for heated band was proposed.