2501 Proposal of an Estimation Method of Welding Residual Stresses in Welded Pipes for Risk-Analysis-Based Assurance of Structural Integrity

It is indispensable to evaluate welding residual stresses for assurance of structural integrity in welded structures. Since residual stresses have to be estimated nondestructively for operating plants, the bead flush method, which is based on the eigen-strain evaluation, has been proposed. In this method, welding residual stresses are calculated by an elastic analysis from eigen-strains that can be estimated by the inverse analysis from measured elastic strain changes when the reinforcement of the weld is removed. Although the accuracy of this method have been proved in welded plates and pipes with relatively high bead height, it is difficult to estimate reasonalby accurate residual stresses because absolute values of experimental errors usually become higher as the bead height decreases down to the actual level. Further problem is lack of statistical point of view for the risk assessment. In this study, to solve these difficulties, stabilizing methods are applied to the inverse analysis to restrict the space of solution and the released raw strain data are pretreated according to the foresight information.