Fatigue Analysis Advice

[jcoots]

I am charged with designing support lugs for an ASME vessel for about 50,000 cycles of filling. This subject is not one I have any professional practice with but would like to learn. For this case, what would be the best route to take: is there a reference book that may help or would it be necessary to get an outside eng. to look at it, or ...?

Thanks for any input

 

[jte]

I'd recommend posting this to the B&PV forum at forum794.

Having said that, if you are dealing with an ASME VIII vessel, it is most likely to be Div. 1. This Division does not specity how to perform the analysis, so most folks go to a Div. 2 Appendix 5 (2006 ed - I don't know how the 2007 ed handles this) analysis. To answer your question, I'd strongly suggest getting an experienced engineer to check the design. Perhaps you can do it yourself next time, but using the experienced engineer to check your work.

jt

 

[gr2vessels]

jcoots,
As above, the old ASME VIII Div. 2 has had some contribution to the topic of fatigue analysis. It was mostly treated by estimating the need for a fatigue analysis or oversizing the structures for safety. Since the expansion of the FEA techniques in the word, a new era of fatigue analysis has begun, more accurate and capable to streamline the pressure vessel design. The ASME VIII div. 2, ed 2007 is a major re-write of the pressure vessel theory and design. For the first time, the ASME has concluded that in order to remain competitive and somehow relevant in the pressure vessel world, the old recipe book must make room for the design by analysis, including the fatigue analysis based on material stress analysis.
It's no point to waste your time with the old fatigue evaluations, bacause the future is in the stress analysis. Unless you are a professional FEA analyst, you won't be able to handle the stress analysis without specialised software. However, for one off case, you can evaluate the lugs on the basis of ASME VIII Div. 2, even if the vessel was designed for Div. 1. Obviously, you need some corrections for the allowable stresses in Sec II-D, table 1A, rather than 2A.
Cheers,
gr2vessels