Fatigue Analysis 3

[PVGuy]

I have a potential customer who is considering contracting the fatigue calculations on their vessel to me. The end user which is his customer is requiring fatigue calculations to be done per Miner's Rule in Section III (possibly Section II, because the letter was fuzzy). I am fairly familiar with fatigue rules but I am not familiar with this method. Can someone point me to where this is in the Code? Is there another reference that covers this method?

 

[metengr]

I believe that your customer is referring to Design based on Fatigue Analysis in ASME Section VIII, Div 2, Mandatory Appendix 5. Miner's rule is a fatigue analysis method that takes into account cumulative damage by varying stress amplitude ranges/known cycles. This is spelled out in Appendix 5.

 

[PVGuy]

metengr
Thank You, I have access to Division II (though I do not use it often) but I do not have access to Section III so I was concerned when they sent that information. Thanks again.

 

[TGS4]

If the piece of equipment in question is a nuclear component, then it is possible that they were refering to Section III, Division 1, Subsection NB, Article NB-3222.4.

Whether the analysis is Section VIII, Division 2, Appendix 5, or the one that I mention above, proceed with caution - the analysis is not as simple as it may appear.

 

[PVGuy]

TGS4,
Thank you for advising caution. The way I am reading the Div. II version makes me think that the most difficulty is in properly accounting for all of the stresses (membrane from internal and external pressure, bending from uniform edge loads, bending from external loads, thermal induced stresses) and at the correct locations in the vessel wall and inside and outside surfaces of the vessel. You are right it is not as easy as first glance would indicate. Do you know if there is a good guide book that helps explain the Div. II or Nuclear method and perhaps answers some frequently asked questions?

 

[davefitz]

It sounds like the best or most accurate way of ensuring an accurte fatigue anlysis is subcontracting the work to an analyst that has done the same calcualtions in the past, or at least having the final calculations checked and reviewed by a more experienced analyst.

Although I have use sect VIII div 2 app 5 many years ago, my preferred method is to use EN12952-3:2001 ( european boiler code) for standard pressure vessels in boilers.