3-D Elastic And Plastic FEM Analysis Of Hydraulically Expanded Tube-to-Tubesheet Joints With Tubesheet Hole Groove

For shell-and-tube heat exchanger, There are welding and expanding two methods used for connecting tube to the tubesheet. In expanding method, the tube is expanded either by rollers or by hydraulical pressure. Though the hydraulical expansion method was developed much later than roller expansion, it is developed more quickly for its important advantages. It is promising to be mainstream. The aim of the study on hydraulically expanded tube-to-tubesheet joints is to obtain knowledges of the effects of joint geometry, materials properties and expansion load on expanded joint tightness and pulling-out strength. In traditional study on hydraulically expanded tube-to-tubesheet joints, the methods used, whether theoretical or experimental, all have some limitations. Firstly, theoretical analysis is mostly limited to two-dimensional axisymmetric model and the material is assumed to be linear elastic-perfectly plastic. It is then difficult to consider the effects of the actual properties of engineering materials and the effect of the actual dimension and shape of the joints. Secondly, the experimental method costs too much, and also the experimental solutions are verydifficult to generalized as design guidelines. The main purpose of this paper is to exploit a 3-D F.E.M to overcome the shortages mentioned above.In this paper a 3-D elastic-plastic parametrization flnit element model of hydraulically expanded joint has been established including the following aspects, which have rarely been found in the previous reference: (1) the effects of the surrounding holes; (2) the effects of the strain hardening properties; (3) the effects of the tube portions extended outside the tubesheet hole; (4) the effects of the width, depth and location of the groove. The geometry, material properties and the loads are included in model as parameters. By assigning different value to each of the parameters, the geometry, the material properties and the loads of the joint can be changed. Thus, with such a joint model, it is easy to study systematically and quantitatively the influences of many joints parameters. The study can give us a better understanding on the mechanism and provide a basis for optimization design of the hydraulically expanded joint.As a study of reliability of expansion joints, in this paper the distribution of the change of equivalent stress, contact pressure, and the residual contact pressure with expanding pressure were investigated. The effects of groove geometry (including the width, depth and location) in the tubesheet hole on joint tightness are also investigated. A comparison of joint tightness is also made between expanded joints with and without groove in the tubesheet hole. The tube head effect is also presented.Several conclusions drawn from this paper could be used as reference for formulating the standard of groove of hydraulically expanded joint in the future.