Investigation of Fatigue Strength of Welded Tube-to-Tubesheet Joint

The tube-to-tubesheet joint of heat exchangers is an important aspect in the design and fabrication process. This paper discusses the fatigue strength of welded tube-to-tubesheet joint under a periodic axial load along the tube by test and by 3D finite element analysis. The testing shows that expanding, in addition to welding, may slightly enhance the fatigue strength of a welded joint. From a microscopic view, the fatigue crack begins at the half melt coarse grain zone of the welded seam on the outer wall of tube and then propagates to the zone of the welded seam on the inner wall of the tube. In the fracture zone, the fracture face is at an angle of 45 deg to the tube wall face and the explicit plastic deformation is present. The analysis, by electronic energy spectrum, shows that there exist many fatigue striations in the fracture face. A 3D finite element analysis correlates with the experimental results.