The Effect of the Welding on the Residual Contact Stress in the Expanded Zone of Expanded-Welded Tube-to-Tubesheet Joints

The fabrication of stainless steel tube-to-tubesheet joints of heat exchangers consists of welding after hydraulic expansion. Here, this process is simulated by use of the finite element method, which is carried out in a sequentially decoupled analysis: the welding temperature field is solved by a transient thermal analysis, and subsequently, a nonlinear elastic plastic stress analysis is carried out. The effect of the unexpanded zone length with reference to the expanded zone of the joints is investigated. The results indicate that welding after the expansion will produce a shrinkage deformation in the tube end. This further reduces the magnitude of the contact stress in the expanded zone and moves it toward the tubesheet secondary surface. The percentage reductions of the contact stress and the contact area are introduced to quantitatively describe the effect of the welding on the expansion zone of the joint. The results show that these reductions decrease linearly with change in the unexpanded zone length, and that the effect of the welding on the contact stress in the expanded zone cannot be neglected. Therefore, a reduction of the influence of the welding on the structural integrity of tube-to-tubesheet joints should be taken into account when utilizing the technique of welding after hydraulic expansion.