Proposal of an Estimation Method of Welding Residual Stresses in Welded Pipes for Risk-Analysis-Based Assurance of Structural Integrity (2nd Report: Application of the L-Curve and the Artificial Noise Methods)

Abstract

To assure structural integrity for operating welded plants, it is required to evaluate welding residual stresses without crippling the functions of the parts. As a nondestructive method, the bead flush method has been proposed. By applying this method, all the 6 stress components that satisfy the self-equilibrium condition in whole structure can be computed, since solutions are calculated by the FEM analysis from eigen-strains that are estimated from released strains during removal of reinforcement of the weld. In the previous report, a new approach to apply this method to welded pipes with relatively low height of reinforcement was proposed. In there, released raw strain data were pre-treated in consideration of a prior knowledge before conducting the inverse analysis. In this study, to improve statistical estimation accuracy, the L-curve method and the artificial noise method are introduced as well as “the truncated singular value decomposition method”. By using these methods, it is shown stable solutions of multiple residual stress distributions can be obtained from a single measurement of released elastic strains.