Integrity assessment of interaction of dents with residual stresses of welds using probabilistic design analysis

The interaction of dent with the weld has always been considered a threat to the pipeline. Therefore, Codes and procedure impose more stringent rules than normally applied to plain dents. For example, ASME B31.8 considers dents deeper than 2% and interacting with welds to be injurious and requires an engineering assessment if they are to be left without repair. The objective of this paper is to present a new method of assessment that utilizes finite element analysis couples with probabilistic design analysis. In this paper, the impact of interaction of dent with longitudinal welds and girth welds will be under static and cyclic pressure conditions will be evaluated. The combined effects are included in a single FEA model and the welds will be simulated by imposing initial residual stresses along the weld line. The first part of the paper uses deterministic analysis to present strain and stress contours at the end of indentation stage as well as the stress range and fatigue cycles at the end of pressure cycle stage for a longitudinal weld case as well as girth weld case. The second part uses probabilistic design analysis with variable geometry, material and pressure in addition to the weld location and residual stress value to determine the sensitivity of the strain, stress, and stress range to the input. Two probabilistic design analyses are conducted: one for the interaction of dent with longitudinal welds, the other for the interaction of dent with girth welds.