Analytical estimation of residual stresses in the transition zone of hydraulically expanded tube-to-tubesheet joints

The “tube-to-tubesheet” joint expanded hydraulically plays a key role in many industrial applications, such as heat exchangers and boilers. These joints consist of three zones: Expanded zone, unexpanded zone, and a transition zone. This process generates residual stresses in the transition zone, influencing the durability, tightness, and reliability of these joints. The transition zone constitutes the weakest link of this joint, due to the presence of high axial residual stresses produced during the expansion process which, coupled with other service loads can lead to its failure. Hence, estimating the residual stresses in the transition zone caused by the expansion process is crucial for optimal joint design. The analytical model developed in this paper has shown that the equivalent residual stresses can reach 76% of the yield stress of the tube material and that the residual axial stresses reach 88% of the yield stress and the hoop stresses can reach 55% of the yield stress. It has also been shown that the stresses are maximum at the inner diameter of the tube. This study has provided an analytical model capable of predicting the residual stresses in this joint as a function of the expansion pressures, which is important for optimal sizing of the joint. A finite element analysis will be used to validate the analytical model.