A study on the effect of weld induced residual stresses and the influence of weld sequencing of centrifugal extractor rotating bowl using numerical simulation and experimental validation

Abstract

Centrifugal Extractors (CE) are the most preferred extraction equipment for the separation of fissile material from radioactive fission products in fast reactor spent fuel reprocessing in order to reduce damage to the solvent by minimizing the residence time. During fabrication of thin section high speed CE rotating bowls, several important factors such as heat input, weld speed, groove geometry, number of passes and weld sequencing are to be considered to control weld induced residual stresses and distortions. The thermal cycles due to concentrated heat input applied during the welding process, generates inhomogeneous plastic deformation and in turn the residual stresses in the weld metal. The presence of tensile residual stresses increase the susceptibility of a weld to fatigue damage, stress corrosion cracking (SCC) and fracture. A 3-D finite element analysis using SYSWELD software, for a three plane GTAW circumferential butt joint is carried out to predict weld induced residual stresses and distortions during fabrication of CE rotating bowls. The GTAW process was simulated using a nonlinear heat transfer analysis with the moving double ellipsoidal heat source model and a sequentially coupled thermo-metallo-mechanical analysis. This study includes temperature dependent thermo-physical, thermo-mechanical properties and isotropic hardening model. The axial and hoop residual stresses on the inner and outer surfaces are computed. Tensile residual stress on the inner surface and compressive residual stress on the outer surface are observed and their impacts on the CE rotating bowl are discussed. The importance of weld sequencing and its inference is investigated and validated against the experimental results.