Proposal of an estimation method of three-dimensional residual stresses for welded pipes by using X-ray diffraction

Abstract

Non-destructive predictions of remaining lifetime, especially for energy plans and chemical plants, are important for assurance of structural integrity. It is necessary to evaluate crack growth rate for each detected crack during the inservice inspection. Today, it is difficult to estimate three-dimensional welding residual stresses for the whole structure on site. Three-dimensional residual stresses can be measured using the neutron diffraction, but the higher energy diffraction method is available only in special irradiation facilities. Therefore, it is impossible to use it as an on-site measurement technique in the in-service inspection. The authors have proposed a non-destructive method to evaluate three-dimensional welding residual stresses using X-ray diffraction and the eigenstrain methodology. In this method, three-dimensional welding residual stresses are calculated on estimated three-dimensional eigenstrains which are evaluated by an inverse analysis on surface elastic strains measured by X-ray diffraction. Numerical simulations were carried out to demonstrate the effectiveness of the proposed method for a welded pipe. Eight kinds of measurement data were made by changing random seeds to evaluate the stability of the proposed method. As a result, residual stresses could be estimated with higher stability. However, further improvements are needed as a future work.