Prediction of the residual stress fields in mechanically rolled and hydraulically expanded steam generator tube plugs

The work presented in the following pages addresses the residual stresses in plastically deformed steam generator tube plugs. Both hydraulically expanded and mechanically roll expanded plugs are modeled and analyzed. The ANSYS finite element code is employed to mathematically simulate the expansion processes through the use of both two dimensional axisymmetric and three dimensional solid models. The displacements known to exist after roll expansion are utilized as a guide in establishing equivalent forces and displacement loading conditions for the finite element analysis. The stress results from the axisymmetric model and the three dimensional model are utilized to predict the residual hoop and axial stresses at the conclusion of the expansion processes. In addition, the results clearly indicate that both expansion techniques create a predominant residual hoop stress that could be expected to lead to axial cracking in a primary water stress corrosion cracking environment. Recommendations are included to modify the current processes in order to reduce both the residual hoop and axial stresses in roll expanded tube plugs.