Comparison of Heat Input Methods in Welding Residual Stress Analysis

Welding residual stress simulation through finite element analysis is becoming increasingly common in fitness-for-service (FFS) assessments of pressurized equipment. The driving force for the residual stress is non-uniform thermal expansion and plastic strain due to drastic temperature gradients; with this in mind, proper heat transfer modeling is essential to meaningful mechanical predictions. The fundamental input to the heat transfer model is the welding arc power, which is commonly represented as an assigned triple Gaussian function (Goldak double ellipsoid model) or more simply, as a uniform temperature. These two methods are compared in detail, and conclusions drawn about the impact of the heat transfer modeling strategy on the predicted weld residual stress for two detailed cases. This evaluation finds particular significance when the welding power, or more particularly the welding energy per unit length, is used in an attempt to characterize a given weld.