Fracture Mechanics Treatment of Residual Stresses in Defect Assessment

Abstract

Over the last decade, as more in-depth understanding of weld residual stresses is being achieved, particularly of their characteristic distributions in pressure vessel and piping components, the residual stress effects on stress intensities at welds are becoming better understood. In this paper, some of the important residual stress characteristics are first identified in the form of either “bending” dominated or “self-equilibrating” dominated types for girth welds. The applicability in other joint configurations in welded structures is then discussed, with a collection of validated residual stress distributions. The characterization of both “bending” and “self-equilibrating” types in residual stress distributions provides a consistent framework for stress intensity factor considerations in either fracture and fatigue assessment. The contribution of weld residual stresses to stress intensities at welds are shown to be in the form of Ksolutions under displacement controlled conditions. The “bending” type residual stresses provide a longer range of influence than “self-equilibrating” type in K solutions. The contribution of “self-equilibrating” type residual stresses to stress intensities is shown to be dominant when crack size is small, while the contribution of the “bending” type dominant for crack size up to a much larger size with respect to wall thickness.