Hi PKU & Sanok7,

In my opinion, Dave's latest response in clear enough for this issue.

As per my understanding, Coade/Intergraph will never provide design & analysis solutions outside of Codes' applicability. Therefore, Dave's considerations may be regarded as guidelines/recommendations for fatigue assessment of B31 piping.

Please keep in your mind that B31 Codes and DNV RP D101 just refer to ASME VIII-2 Part 5 and/or BS PD5500 Annex G in relation with fatigue assessment, but do not provide "recipes" or specific methodologies for further action.

At the time of his post, Dave's considerations brought to me the latest confirmation regarding some doubts I used to have based upon Paulin Group (PRG) webinars related to fatigue analysis.
So, in my opinion, this approach is the most suitable one to be employed for B31 piping systems' fatigue assessment.

Of course, there are many other "key" issues the engineer should take into account for when he/she performs fatigue analysis on B31 piping piping systems, such as: WHAT KIND OF STRESSES are to be checked against fatigue Curve? or What Fatigue Curve to use?

The first question is very important in my opinion. I believe that Dave's approach is mostly applicable for ASME VIII-2 Part 5 "Smooth Bar" Fatigue Curve. I've seen companies performing fatigue assessment of B31 piping systems using Caesar II peak stress ranges and PD 5500 fatigue curves (e.g. "D", "E", "F" etc.).
In my opinion, such approach is not quite accurate, since PD 5500 Annex G fatigue assessment methodology is not based on Peak stresses but rather on secondary stresses (as per ASME VIII-2 classification). Using "de-rated" PD5500 fatigue curves, the local/peak stress concentration effects are already considered with respect to weld type, weld & loading relative orientation etc.

A good option, many times suggested by our distinguished moderators (Dave and Richard) is to used IGE TD 12 Code within Caesar II environment for fatigue assessment purpose. If you'd have a look on IGE TD 12 fatigue analysis methodology, you'll note that IGE-TD12 SIFs are higher (around 2 times) than the typical B31 SIFs...and Pressure load SIFs are also provided, which you'll not find generally in common piping codes...

It just remains the engineer to employ proper judgement and sound correlations to perform a suitable fatigue assessment.

These are just my thoughts. Any other contribution/clarification would be welcome.

Regards,