Residual stresses in narrow-groove girth welds and applications for fitness-for-service assessment

Abstract

Narrow gap welds have been increasingly used in pressure vessels and pipe components due to their unique advantages. A recent comprehensive investigation into residual stress distributions in narrow gap is presented in this paper, covering component wall thickness from 1” (25.4 mm) to 10” (254 mm), component radius to wall thickness ratio from 2 to 100, and linear welding heat input from low (300 J/mm) to high (18,000 J/mm). By means of a residual stress decomposition technique, two key parameters that govern through-thickness residual stress distributions in terms of their membrane and bending content have been identified. One is component radius to wall thickness ratio (r/t) and the other is a characteristic heat input density (Qˆ) having a unit of J/mm3. With these two parameters, a unified functional form for representing through-thickness residual stress profile in narrow gap welds is proposed for supporting defect assessment. Its adequacy for estimating residual stress distribution trends is further confirmed by comparing with thermomechanical finite element residual stress analyses for a number of selected narrow gap weld cases.