Investigation of stress corrosion crack propagation characteristics and life prediction for thick-walled double U-groove pipe welds in PWR steam generator

Abstract

Stress corrosion cracking (SCC) is a critical concern in evaluating the structural integrity of pressurized water reactor (PWR) primary pressure boundaries. Material mismatch and welding-induced residual stresses introduce significant challenges in predicting crack propagation paths and service-induced defect lifetimes. This study examines the influence of welding residual stress on SCC in a thick-walled double U-groove pipe dissimilar steel welded joint of a PWR steam generator (SG), and assesses the propagation life of SCC from an engineering standpoint. First, the distribution and stress state of residual stresses in complex SG dissimilar steel joints were analyzed using the two-way thermal coupling finite element method to establish initial stress boundary conditions for simulating SCC propagation influenced by residual stresses. Next, the extended finite element method combined with the maximum principal stress criterion was employed to investigate the propagation direction and path of cracks originating from various initial positions due to welding residual stresses. Concurrently, the J-integral method was used to calculate the stress intensity factors of cracks at different depths along the propagation path. Finally, based on the modified Shoji model, the relationship between the stress intensity factor and SCC propagation rate was examined, allowing for predictions of crack propagation rates and service life for SCC with varying initial defects.