A semi-analytical model to predict residual stress distribution in thick wall girth weld with narrow gap welding

Abstract

Benefited by its high efficiency and low cost, the narrow gap welding has been widely used in thick wall pressure equipment. Considering the fact that defects in welded joints inevitable, the safety assessments for welding equipment with residual stress are crucial. However, for the thick-wall equipment using narrow-gap welding, the current safety assessment standards specifying the residual stress distribution are not detailed or missing. In this paper, the through-wall residual stress of thick wall girth welds with narrow gap welding is studied. The stress components (bending stress, membrane stress and self-equilibrating stress) at the evaluation point are obtained by stress decomposition. The effects of the heat input, the wall thickness, the radius thickness ratio and the number of welding passes on residual stress are considered, respectively. The results show that the heat input only affects the distribution of bending stress and membrane stress. The axial and hoop bending stresses decrease with the increase of the wall thickness, and the hoop membrane stress is about 0.75 times material yield strength. With the increase of radius thickness ratio, the bending stress decreases while the hoop membrane stress increases. The stress distribution is fluctuating when the number of welding layers is small, which be expressed by trigonometric function. The distribution model of welding residual stress through the wall thickness is proposed. The stress distribution obtained by the proposed prediction model is in good agreement with the finite element calculation results.