Development of Computer-aided nondestructive Evaluation Method of Welding Residual Stresses for Life Extension of Large Plants

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Along and near the bead line of welded structures, there remain eigen-strains, such as thermal strain, plastic strain, and transformation strain. These produce welding residual stresses which have a significant effect on integrity of structures. For the life extension of those components, residual stresses must be evaluated nondestructively. In this study, a computer-aided nondestructive evaluation method was proposed. There, eigen-strain distributions are calculated by the inverse analysis from released elastic strains due to removal of reinforcement of the weld. Then residual stresses are evaluated by the commercial finite element code by imposing eigen-strains as initial strains.Firstly, a basic formulation was attempted for a thin welded plate. Its utility was confirmed by conduction computer simulations as well as experiments. Especially in experiments, results from proposed method were compared with those by the X-ray method, the hole drilling method and the sectioning method. It was shown that all the results obtained agreed very well.Then attempt was made to extend this method to thick welded plates as well as thin welded pipes. Simulations showed that proposed method may have utility for those problems.