Estimation of residual stress in the rolled joint and its effect on its pull-out strength at different temperatures

Abstract

The rolled joint between pressure tube and end-fitting in a pressurized heavy water type reactor is critical from integrity and performance point of view as significant magnitudes of residual stresses are generated during the rolling process. The distribution of residual stress in the rolled joint is required for assessment of operational performance and integrity of the same. The 3D FE simulation of the rolling process considering material, geometric and contact nonlinearities are very scarce in literature. Moreover, the discussion regarding development of residual stress in the joint during the rolling process and its subsequent relaxation at higher temperatures and corresponding data are not available in literature. The pull-out strength of the rolled join is an important operational parameter which ensures a leak tightness (due to presence of compressive contact stresses) and other functional requirements of the joint. The strength of the joint also changes significantly with temperature due to change in material properties and release of residual stresses. Especially at the severe accident regime, the strength may reduce to such as extent that the tube may get disassembled from the end-fitting due to joint pull-out. The objective of this work is to evaluate the residual stresses that are present in the joint during the rolling process and also estimate the pull-out strength of the joint at different temperatures using finite element analysis. These results shall be useful to the engineers involved in study of severe accident in Indian pressurized heavy water reactors.