Prediction of residual stress by simulation of the rolled joint manufacturing process for steam generators

Boiler tubes in steam generators are typically installed by a roller expanding process which plastically deforms the tube against the tubesheet to create an interference fit. Such connections necessarily involve residual stresses upon which operating loads are applied. An understanding of the rolling process, and quantitative knowledge of the residual stresses produced by it, are important factors in establishing the integrity of the rolled joint under operating conditions. Previous work has established that 3-D finite element modelling of the rolling process can practically determine the residual stress distribution. The purpose of this work is to develop a detailed numerical model to simulate rolling steam generator tubes into a tubesheet with a triangular hole pattern, and to obtain the resulting residual stress distribution. The boiler tube, tubesheet and three rollers are all modelled as separate components, connected by sliding contact surfaces. Several cases are evaluated, to address variation in key manufacturing tolerances in steam generator rolled joints.