Fatigue Analysis in a Bellow Expansion Joint Installed a Heat Exchanger

Abstract

In this work, the failure analysis of a bellows expansion joint installed in a heat exchanger is shown. The analysis was performed using the techniques of visual inspection, chemical analysis, mechanical tests, metallographic and fractographic examination. The results show that the chemical composition, mechanical properties and microstructure correspond to the material design specification. While the macroscopic fractographic analysis revealed the presence of circumferential cracking, adjacent to the weld bead and expansion joint. The trajectory of the crack is simple without secondary ramifications or cracks, nor was plastic deformation associated with the fracture observed. The scanning electron microscopy results, show the presence of thin lines in the form of grooves, parallel to the crack propagation front, that are identified as microscopic striations, typical of fatigue fractures. Thus, the bellows expansion joint failure was identified as a fatigue fracture, due these accessories work in the presence of fluctuating loads. Although, fatigue failure is common in this type of components, after a long time of service; However, the results of this research demonstrate that the movements and vibrations in the heat exchanger, in combination with the expansion joint installation by fillet welding in the overlapping sleeve and misalignment of the joint, are able to generate the level of stress required to drive the fatigue failure, even though the heat exchanger was not in service.