On the Residual Stress Profiles in New API 579/ASME FFS-1 Appendix E

Abstract

In this paper, the mechanics basis underlying the parametric through-thickness residual stress profiles proposed for the new joint fitness for service document referred to as API 579/ASME FFS-1 Appendix E is presented. The proposed residual stress profiles are described to a large extent by a unified parametric function form valid for a broad spectrum of pipe and vessel welds. The functional relationship is established based on the comprehensive knowledge base developed within a recent major international joint industry project (JIP) under the auspice of Pressure Vessel Research Council (PVRC) and a large amount of residual stress measurement data from recent literature. One of the most important features associated with the proposed revision is that residual stress profile is uniquely determined by two important sets of governing parameters: (1) parameters relevant to pipe geometry, i.e., r/t and t; (2) a parameter related to welding linear heat input Q (J/mm), referred to as the characteristic heat input \(\hat Q\)which has a dimension of J/mm3. As a result, the corresponding through-wall residual stress distribution exhibits a continuous change as a function of r/t, t, and \(\hat Q\), instead of falling into a few discrete and unrelated profiles, as seen in the current Codes and Standards.