What can be the reason behind frequent socket weld joint failure in economiser drains and vents (carbon steel tube) in heat recovery steam generator ?
Thermal stresses cause the thermal fatigue failure of the welded joint.
Heat recovery steam generators are continuously exposed to temperature variations and the resulting thermal fatigue weakens the mechanical properties of the weld.
Hope this helps answer your question.
Professor Yehia Khalil, Yale University, USA
Fellow of the University of Oxford, United Kingdom
Hello Professor Khalil:
Certainly, it couldn't be said better! Although, it may be other failure modes (e.g., corrosion under an aggressive local environment, ...), I fully agree that the most frequent failure mode of welds, in the situation at hand, is that of thermal stress/fatigue - assuming that regular and appropriate maintenance is done.
By the way, the study of thermal stresses is, in my opinion, poorly emphasized in more than an engineering school! Thus, if it were of any help, I recommend to Anirban consulting a classic textbook in the field:
Boley, B.A. and J.H. Weiner, "Theory of Thermal Stresses", John Wiley & Sons, 1960.
All the above said, please, Professor Khalil:
Which would be, in your opinion, a practical way to minimize the failure frequency of the foregoing welds, aside - of course - of implementing a sound preventive maintenance program?
I wish you, Anirban, fully success in coping with your technical problem.
Dear Angel,
I appreciate your feedback.
The best way to minimize thermal fatigue is to control the rate of heat up and cool down of such equipment. I've this experience from my past work in the nuclear field and also my work on power electrics circuits that are exposed to temperature fluctuations.
Best wishes,
Prof. Khalil
Thanks for the answers, but it seems the problem in socket joint weld failure is happening only for carbon steel, wherever we are using alloy or stainless steel, it doesn't cause any such issue there. Thermal stress is associated with the material property ?
Exclude the possibility of primary cracks. Low-alloyed warm-strength steels have a tendency to form relaxation cracking. This type of crack is found in the coarse grained area of the heat-affected zone.
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