Impact of Bauschinger Effect on the Residual Contact Pressure of Hydraulically Expanded Tube-to-Tubesheet Joints

The level of the contact pressure and the stresses induced during the hydraulically expanded tube-to-tubesheet process are the key factors for the integrity of a leak free expanded joint. The modelling of this type of joint requires an adequate representation of the material behavior in order to accurately evaluate important joint parameters such as the residual contact pressure and induced residual stresses. Maintaining a lower bound safe limit of the initial residual contact pressure over the lifetime of the expanded joint insures its durability. A design tool that addresses a proper material-geometry combination in conjunction with the required expansion pressure is developed. The proposed model is based on strain hardening material behavior of the tube and the tubesheet. The interaction of these two components is simulated during the whole process of the application of the expansion pressure. Particular emphasis is put on influence of reverse yielding and Bauschinger effect on the residual contact pressure. The results from the analytical model are confronted to those of the numerical FEA model. Two joints of different geometries and materials are considered to demonstrate the importance of considering the real material behavior in both models.