Hydraulic Expansion of Tube-to- Tubesheet Joint

Abstract

Tube-to-tubesheet joints play a sensitive role on the reliability of heat exchangers. The level of positive residual stresses created by the expansion process, which could lead to stress comsion cracking, is the most dominant element for the joint defects.The highest level of these residual tensile stresses usually occurs in the transition zone between the expanded and non-expanded parts of the tube. Consequently, this area becomes the most critical where cracks may initiate leading to leakage of the tubes. Previous experimental and analytical works have been focussed on minimizing tensile residual stresses within a strong enough joint which relies directly on the level of interference pressure between the tube and tubesheet. However, more investigation is needed. In the present paper, nonlinear finite element method is used to investigate the problem. Because there are too many dimensional, manufacturing and material parameters involved, the orthogonal design method is used to minimize the number of analyses besides providing an accurate prediction of the influence of all considered design parameters. An empirical equation is proposed relating the effect of most important parameters on the strength of the joint . This equation could guide the designer and manufacturer of tube-to-tubesheet assemblies.