Calculation of Hydraulically Expanded Tube-to-Tubesheet Joints

Abstract

Tubular heat exchangers are basic components in chemical plant engineering. Due to the fundamental importance of heat transfer in chemical processes, fail-safe behavior of the heat exchangers is a decisive prerequisite for reliable performance of plant complexes. Most of the nonoperating periods of tube bundle apparatus are induced by damages at tube-to-tubesheet joints. In the case of expanded tube connections, irrespective of being rolled or hydraulically fitted, the residual interfacial pressure generated by the expansion process was not sufficiently high and/or additional weakening of the joints by service loadings had happened. Therefore, careful design of tube-to-tubesheet joints requires detailed knowledge about the interaction between an expanded tube and the surrounding tubesheet. In 1976, Krips and Podhorsky, therefore, used finite circular rings for structural representation of the tubesheets. These rings are denoted as equivalent sleeves. Comparison with finite element results led to the introduction of a corrective factor by the same authors to adapt the equivalent sleeve diameter. This paper discusses a formula for the equivalent sleeve diameter, which is based on an analytical treatment of the mechanical properties of multiholed sheets. In the first part of the paper, an elastic-plastic computation of the residual contact pressure is presented. In themore » second part, the sleeve diameter is derived by an analytical treatment of finite perforated disks. The final part consists of checking the analytical results with nonlinear finite element analyses.« less