A full-field residual stress estimation scheme for fitness-for-service assessment of pipe girth welds: Part I – Identification of key parameters

Abstract

In this two part series of papers, a recent comprehensive investigation of residual stress distributions in pipe and vessel girth welds is presented, covering component wall thickness from 6.35 mm (1/4″) to 254 mm (10″), radius to wall thickness ratio from 2 to 100, weld preparation from single “V” to double “V” to narrow-gap welds, and welding linear heating input from low (300 J/mm) to high (7,500 J/mm). Through the use of a residual stress decomposition technique, two key parameters that control through-thickness residual stress distributions in terms of their membrane and bending content have been identified by examining a large number of parametric residual stress analysis cases. One is component radius to wall thickness ratio (r/t) and the other is a characteristic heat input (Qˆ) having a unit of J/mm3. With these two parameters, a unified functional form for representing through-thickness residual stress profiles, along with its solution scheme, is proposed and demonstrated in this paper (Part I) for applications in weld region. A shell theory based analytical procedure is then introduced in Part II for estimating through-thickness residual stress profile at any axial distance away from weld regime. The effectiveness of the analytical estimation procedure is then confirmed by finite element residual stress solutions on a large number of component configurations and welding conditions.