Connection strength and tightness of hydraulically expanded tube-to-tubesheet joints

Abstract Many investigations and practical experience show that most heat exchanger failures occur at the tube-to-tubesheet joints and that they are affected by the geometry of the tube and tubesheet, the manufacturing process and the operating conditions. This paper focuses on the effect of the expansion pressure and operating temperature on the connection capacity of hydraulically expanded joints. Incorporating widely used materials (low carbon steel for the tube and low alloy steel for the tubesheet), the finite element method (FEM) was used to simulate the expansion process and study the connection capacity of the expanded joints. The occurrence and loss of contact between the tube and tubesheet were modeled using contact elements. Furthermore, the effect of a cyclic change in temperature on the connection capacity of hydraulically expanded tube-to-tubesheet joints was investigated. In order to confirm the credibility of the finite element models employed in this study, some specimens were fabricated and joint strength experiments were performed using a MTS 880 testing machine by straining the joints at a set rate while recording the loads. The latter were found to be in acceptable agreement with the FEM calculated values. The results of this study show that the connection capacity of joints can be greatly enhanced by expansion pressure increments, improved at the beginning and lowered gradually with an increase in the temperature. The connection capacity is reduced very little after the first temperature cycle and remains almost unchanged after the second and third cycles. The study also shows that the FEM is a viable method to predict leakage behavior.