Fatigued containers -- How to address excessive cycle counts beyond the limits specified in JB4732?
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This post was last edited by FORREST_GUMP on 2015-6-3 at 18:43. It is a vertical container made of Q345R material; the design temperature is 50°C, with pressure fluctuations ranging from 0.1 to 0.3 Mpa. The total number of cycles over its design life is 5.92x10^6, which exceeds the value of 10^6 specified in Figure C-1 of Appendix C of JB4732. How should the design take this into account?
Either reduce the service life or reduce the number of cycles. There is no other way.
JB4732 is based on ASME 8-2; you can refer to version 04 of ASME 8-2 for the allowable stress variation range after the number of cycles exceeds 10^6. PS: If the design life of this container is 20 years, that means there would be a stress variation once every less than two minutes. What is this container used for, if it experiences such frequent variations? These are just my personal opinions; I welcome everyone’s feedback
This is the case with most design institutes; by using stainless steel, the number of cycles can reach one million!
There is a provision in 4732 stating that fatigue analysis can be omitted when the pressure fluctuations are less than 20% of the design pressure; this might be helpful. Another point mentioned on the third floor is that, according to the fatigue analysis rules in ASME VIII-2, it is possible to reach ten million cycles
Is it an adsorption tank? With such a high frequency of alternation, could the original poster provide some information on this?
Thank you for your answer: handshake
Thank you for your reply. The equipment in question is the buffer tank of a pressure swing adsorption unit. The main purpose is to seek advice on how to design containers that have experienced fatigue due to exceeding the specified number of cycles. This number of cycles represents an extreme value estimated for such cases; in reality, the actual number of cycles for the equipment might be slightly lower (not yet finalized), but it will certainly exceed 10^6 cycles.
Thank you for your answer. I have seen the method you mentioned before, but I am more interested in knowing the solutions when carbon steel and low-alloy steel are still used :)
Thank you for the reply. I had thought of that as well, since the operating pressure of the equipment isn’t very high. But can the method of increasing the design pressure to avoid fatigue analysis completely replace it? I have little experience; have you actually used it?
The equipment in question is the buffer tank of a pressure swing adsorption unit. The main purpose is to seek advice on how to design containers that have experienced fatigue due to exceeding the specified number of cycles. This number of cycles represents an extreme value estimated for such cases; in reality, the actual number of cycles for the equipment might be slightly lower (not yet finalized), but it will certainly exceed 10^6 cycles.