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Creep and Fatigue (Ratchet) interaction
3

Creep and Fatigue (Ratchet) interaction

Creep and Fatigue (Ratchet) interaction

(OP)
Dear All

I was hoping to find some method according to ASME BPVC VIII-2 in order to find a way of evaluating some equipment for their fatigue strength in high temperatures. However, I failed in the first step by reading the article 5.1.1.3.

Quote (ASME BPVC VIII-2 5.1.1.3)

The design-by-analysis procedures in Part 5 may only be used if the allowable stress from Annex 3-A evaluated at the design temperature is governed by time-independent properties unless otherwise noted in a specific design procedure. If the allowable stress from Annex 3-A evaluated at the design temperature is governed by time-dependent properties and the fatigue screening criteria of 5.5.2.2 are satisfied, the elastic stress analysis procedures in 5.2.2, 5.3.2, 5.6, 5.7.1, 5.7.2, and 5.8 may be used.

What can I do in this situation?

Warm Regards

RE: Creep and Fatigue (Ratchet) interaction

3
Find an expert. Engage them. Pay them.

RE: Creep and Fatigue (Ratchet) interaction

Agree with TGS4. Don't mess about if you ain't got the knowledge!!!

RE: Creep and Fatigue (Ratchet) interaction

(OP)
Thank you TGS4.

Quote (TGS4)

Find an expert. Engage them. Pay them.

This can be an answer to all questions here. I mean if I have the knowledge then why would I even ask any questions? We are all here to learn.
Anyway I think by this sentence you mean this issue is far more complicated than I could even imagine but do not worry about it I am not going to design a pressure vessel in creep condition and fabricate it. In these situations even my manager will outsource such a design. I was just trying to get familiar with this kind of design. You have previously answered many of my questions regarding fatigue but this does not make me a fatigue designer. Thanks anyway.

RE: Creep and Fatigue (Ratchet) interaction

I give this advice to folks with much experience in non-creep analyses. There is so much about creep, creep-ratcheting, and creep-fatigue that are non-intuitive, that they can quickly overwhelm even the most experienced analyst.

Go to API 579-1/ASME FFS-1 Part 10. Even something seemingly as simple as material properties gets complicated in creep. Reference your recent post about average vs min properties.

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