Which CAESAR stress output to use for DNV/PD5500 high cycle fatigue analysis.

[Winnower]

Hi, I’m looking for some clarification on a point.

I have read around this topic quite extensively and think I have gleaned the knowledge I require but I have not found an explicit answer to my query without getting too bogged down in the theory.

The query is: which stress we should use from CAESAR “stresses extended” output for our input to DNV/PD5500 high cycle fatigue analysis.

I am not using the CAESAR ASME high cycle fatigue module so the stress values in question are those output from the regular CAESAR “stresses extended” load case output.

I am running various different load cases to capture pressure fluctuations, temperature fluctuations, slug loads etc etc to generate stresses for input to our PD5500 analysis.


CAESAR outputs two stress values, the B31.3 “Code Stress” and the “Max Stress Intensity”.

I believe that it is the “Max Stress Intensity” stress value that we should be using (multiplied by some factor (or run an IGE TG12 analysis) to correct the B31.3 SIFS) as our input to PD5500 high cycle fatigue.

I believe that we should not be using the B31.3 “Code Stress” value as our input to PD5500 high cycle fatigue because it does not take account of the radial and hoop stresses that should be considered as part of our fatigue analysis.

Two questions:

1. Is my train of thought correct on this?

2. Given that there is pressure in the pipes, is there any argument or justification for using the B31.3 “Code Stress” values for input to a PD5500 high cycle fatigue analysis?

Your opinions would be gratefully received,
Thanks.

 

[Winnower]

Ok I have had a look at this again and I think I can rephrase the questions.

1) When CAESAR produces a fatigue stress report for the FAT case can anyone confirm that, for the B31.3 piping code the "code stress" listed is based on the "Max Stress Intensity" and that this is the stress that CAESAR has used to calculate the stress range?

2) Following the logic from question 1, If we use PD5500 to do the high cycle fatigue analysis of our piping as per DNV-RP-D101 paragraph 3.12.5(d) then is it correct to use the "Max Stress Intensity" from CAESAR's "Stresses Extended" output and not the "Code stress" (because the codes stress in the "stresses extended" output is the B31.3 code stress which DOES NOT take account of the hoop stress which is required to be considered for fatigue analysis)?

My confusion is that there seems to be two "code stresses" listed, one code stress for the FAT case which is based on the max stress intensity and another code stress for the stresses extended output which is based on B31.3.