Investigation of welded structures on mechanical properties of 304L welded tube-to-tubesheet joints

•Mechanical properties of welded tube-to-tubesheet joints were investigated.•The effects of four types of welded structures on mechanical properties were discussed.•Joints of the extension welded structure have the largest fracture length.•Joints of the extension welded structure have the largest pullout force and fatigue life.

This paper presents an investigation on effects of welded structures on pullout force and fatigue life of welded joints of 304L heat exchanger tube-to-tubesheet. Welded structures including inner-hole with a groove of 45°, extension, inner-hole with a groove of U-shape and plain-end were discussed. Full-size test blocks covering four types of welded structures were used to conduct pullout test and low cycle fatigue test. Furthermore, optical microscopy (OM) and scanning electron microscopy (SEM) were utilized to analyze the failure mechanism. The results show that the joints of the extension welded structure have the largest pullout force and fatigue life because of its largest fracture length, and the undeformed welded zone revealed favorable quality of weld. The cracks originate at the outer surface of tube and striations propagate at an average rate of 50 μm for a loading cycle, finally, the separation commences at the inner surface of the tube, exhibiting equiaxed or hemispheroidal dimples.