Fatigue analysis SS (austenitic) piping

[mylexicon]

I was trying to perfom a dynamic (harmonic analysis) on a piping system of SS austenitic type) material. In order to check my dynamic stresses, I was looking for the appropriate source of reference and the applicable S-N (stress range vs. no. of cycles) curve. So, I did some reading and I am a little lost now. I am having a hard time deciding what curve and what source to use for my fatigue assessment.
Questions:
1) ASME VIII Div 3...
In Article KD-3 of 'ASME VIII-Div 3' S-N curves are provided for different parent material and a safety factor of 2.0 (converting peak to peak stress to zero to peak) is recommended. For the speicific case of Austenitic SS, S-N curve in Fig. KD-320.3M is available and Cycles are limited to 1e6. Does this curve apply to both welded and non-welded SS parts? And what if the fatigue analysis is for cycles higher than 1e6? what do we do then?

2) The other sources I was considering for my analysis are BS5500 & BS7608. BS has a fundamentally different approach...just One S-N curve is used for CS, SS, & Aluminum alloys but the temperature limits of applicability are different for each material. For components which are in service, curves are provided for different 'weld' classes! these curves define a 97.7% probability of survival. What is confusing me is that the stress values which I read off the BS7608 curves are much less (i.e.; more conservative) than that of the ASME VIII curve for austenitic SS!!!
So how about it? how do I get past this dilemma? any guidance is appreciated.
thanks,
Farzad

 

[jte]

Farzad-

Have you considered looking at the old (2006 and earlier) VIII Div. 2 curves? Fig. 5-110.2.2 goes to 10^11 cycles. This curve would apply to both welded and non-welded components - with appropriate SIF's included.

jt

 

[mylexicon]

jte-
you mean I won't find Fig. 5-110.2.2 in more recent editions of VIII Div 2? I only have the 2007 edition and just scanned through it and could not find these curves!
btw, I do have an old copy of Fig. 5-110.1 (from VIII, Div 2) which is the design fatigue curve for CS, low alloy, ...,high alloy,high Tensile steels at T<700F ....for cycles up to 10^6 only. Anyhow, I don't think it is applicable to Austenitic Steel which is the case i am dealing with.
thanks alot though, i'll try to find Fig. 5-110.2.2 and see if i can use that.

regards,

Farzad

 

[jte]

Yes, the fatigue evaluation approach changed from the "old" Div. 2 with the publication of the completely rewritten "new" Div. 2 in 2007.

jt