Combination of simulation and experiment in designing repair weld strategies A feasibility study

Numerical simulations, based on an off the self commercial finite element FE code and experimental tests using the neutron diffraction ND technique, are combined in an attempt to evaluate post weld heat treatment PWHT of a letterbox type repair weld in respect of its effect on the residual stress field. 21 4CrMo steel plates with an 18 pass repair weld were heat treated at various temperature levels and for different durations. Due to the prohibitive cost of a complete residual stress mapping, ND tests were performed only at selected specimen locations. In this sense, FE simulation acts as a supplement to ND, since it predicts the complete residual stress field. Uncoupled quasi static thermoelasticity in conjunction with an element activation deactivation technique, simulating deposition of new weld material, are combined in a 3D FE analysis. Grouping of the 18 weld beads in lumps, following a sensitivity analysis, reduces computational costs to feasible levels, whereas a creep strain hardening law is used to simulate stress relaxation during PWHT. Computed residual stresses are compared to ND measurements for verification purposes. Comparison of heat treated specimen measurements to heat treated and untreated specimen predictions illustrates that PWHT has a strong effect on the residual stress field, achieving significant stress relaxation