Proposal of an Estimation Method of Welding Residual Stresses in Welded Pipes for Risk-Analysis-Based Assurance of Structural Integrity (1st Report: Improvement of Accuracy by Pre-Treatment of Strain Data)
In welded structures, it is indispensable to evaluate welding residual stresses for assurance of structural integrity.
Today, several nondestructive evaluation methods of residual stresses have been proposed, however measured results
can not be applied to the FEM (Finite Element Method) analysis. For the FEM applications, all the 6 components of
stresses in the whole structure must be estimated and those solutions should satisfy the self-equilibrium condition.
From this view point, authors have proposed the bead flush method. In this method, welding residual stresses are
calculated nondestructively by a simple elastic FEM analysis from eigen-strains which are estimated by the inverse
analysis from released strains during removal of reinforcement of the weld. By now, the effectiveness of this method
has been proved for welded plates and pipes with relatively high bead height. As decreasing bead height down to below
one mm level, however, it is difficult to satisfy both high accuracy and stability because of higher effect of measurement
error. In this study, to obtain multiple residual stress distribution from a single measurement, released raw strain data
were pre-treated in consideration of a prior knowledge before conducting the inverse analysis.
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