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DCCMech (Mechanical) (OP)
26 Apr 11 16:15
Looking to see if I can get some guidance on a fatigue analysis I've been asked to complete on a few pressure absorption swing vessels. I have good data surrounding everything aside from material fatigue properties on 516 grade 70 steel, and have been digging through ASME VIII-2 trying to find s-n curves for your basic pressure vessel carbon steels.

The best I can find is in annex 3.F which details how to produce these curves, but it gets pretty convoluted in finding the number of design cycles. I'd like to simply get the polished endurance limit and cycles at endurance from an s-n curve which is sufficient for me to pop into my FEA program's 'fatigue wizard' add-on and it should do the rest for me.

Anyone have guidance on how to produce these numbers, or material data on SA-516-70? Is it necessary to go through VIII-2's steps, or even worth me trying to obtain specific numbers this way?  
Helpful Member!(2)  TGS4 (Mechanical)
26 Apr 11 17:25
OK - I'm going to stop you right here.  What you are doing is dangerous, and your approach to fatigue is leading you in the wrong direction.  I would highly recommend that you buy this paper which should help guide you through the process.

There is more to fatigue of a pressure vessel than just an S-N curve.  You need to consider the fatigue of the weldments, which will be the limiting factor, especially for a PSA.  You need to understand not only the stress ranges due to pressure cycling, but also thermal cycling.

And with regards to your statement

Quote (DCCMech):

...sufficient for me to pop into my FEA program's 'fatigue wizard' add-on and it should do the rest for me.
Do you actually understand what your black-box is doing?  Unless you understand it COMPLETELY, please get someone who has experience and expertise in this to do it for you.  Otherwise, 5 years from now, the owner of said PSA will likely be contracting me to do a forensic investigation into why it failed after such a short time.  At that point, I will not be kind.  Neither will their lawyers.

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