API 530 or ASME 2 D to determin fatigue life at high temperatures
API 530 or ASME 2 D to determin fatigue life at high temperatures
(OP)
When designing for fatigue life of a pressure vessel at high temperatures, should the allowable be taken from API 530 or from ASME section 2 part D? I have seen this done both ways. In some situations I have seen Larson-Miller calculations that us API 530 to determine a temperature, and then allowable for that temperature is then obtained from ASME sec2 part D. I see that ASME is usually a lower allowable, so maybe this is just a conservative approach. Also, are the allowable stresses in API and ASME for pressure vessels only? For instance would a support system inside a pressure vessel also be designed to the the allowables (Table A-1) or would it be more appropriate to design the support structure using the yield stresses in ASME Table Y-1?





RE: API 530 or ASME 2 D to determin fatigue life at high temperatures
RE: API 530 or ASME 2 D to determin fatigue life at high temperatures
RE: API 530 or ASME 2 D to determin fatigue life at high temperatures
You will need to ensure that you don't have creep-ratcheting, first, before you worry about fatigue.
Fatigue is a totally different beast from creep, and creep-fatigue is an order of magnitude more difficult than either one on its own.
RE: API 530 or ASME 2 D to determin fatigue life at high temperatures
Thank you
steve
RE: API 530 or ASME 2 D to determin fatigue life at high temperatures
RE: API 530 or ASME 2 D to determin fatigue life at high temperatures
The Figure that you refer to (F.12) is a stress-temperature-time graph. Unless I missed something, there is nothing related to number of cycles.
Do you understand the difference between creep (time-dependent) and fatigue (cycle-dependent) and ratcheting (a cycle-dependent failure mechanism)?
RE: API 530 or ASME 2 D to determin fatigue life at high temperatures
I think I need to explain further. The system is designed for 3 different temperatures and a certain amount of time is allowed for each temperature. Solving all 3 equations for 100% life will provide a sort of average design temperature. This temperature is what is then used to determine the allowable. It is at this part that the allowable stress is taken from ASME and not from API. I guess my real question is towards the difference between API and ASME. For some materials the values are basically equal (chrome-moly) and for others (304H), API is significantly higher. Is this due to the brittleness of the material at the higher temperatures? Does 1% creep and 100,000 hours for chrome-moly equal failure because the material is brittle.?