5. Conclusions
In summary, the collected evidence suggests that the failure mechanism of the tube-to-tubesheet in the shell-tube heat exchanger was fatigue fracture. The fracture surfaces showed obvious crack propagation traces. Fatigue striations, which were the micro-evidence of fatigue, were observed clearly. The fatigue crack initiated from the defects at the tube-totubesheet welded joint. The periodic load might come from the resonant vibration of the tube or the changes in temperature and pressure of the fluid inside the heat exchanger. Bad welding and unsuitable expansion position of the tubes at the tubeto-tubesheet might give rise to the formation of initial cracks. In future, prevention of failure of the shell-tube heat exchanger would still be an important topic. Improving the quality of welding and expansion processes were effective way to reduce the failure problems of the tube-to-tubesheet welded joint in such heat exchangers.
