Creep Behavior of a Bimetallic Welded Joint in a Nuclear Piping System

The information of the creep behavior of a thick welded joint is very important to secure the safety of high temperature service devices. The creep damage development and behavior are very complex; hence it is time consuming to practice the experiment and theoretical analyses. In this paper a simple accurate model was developed to analyze the creep behavior of weld metal and heat-affected zone on a thick bimetallic welded pipe. The pipe was made by welding an A508-class-2 carbon steel pipe to a 304 stainless steel pipe with a shielded metal arcwelding process using INCONEL 182 electrodes. Virtual fabrication technology weld modeling tools (VFT™) developed jointly by Battelle and Caterpillar was used to obtain welding-induced residual stress. The weld residual stress was read into the creep model as initial stress condition for creep analysis. A temperature 1000°F was applied on the bimetallic weld model with inside pressure and axial loading. The simulation results indicated that creep strains were not uniform through the weld joint due to weld residual stresses, materials creep behavior and geometry changes. Some stress and strain concentrations were found on the A508 steel near buttering region, which results in axial cracks.