Fatigue Modifying Factors in API 579 - FFS

[usecheijk]

Hi there.

For fatigue analysis procedure described in section B-1.5.3 of API 579 ¿In which of equations B1.30, B1.35, F.214 or F.215, fatigue modifying factors (surface finish factor, loading factor, etc.) must be applied?

Thanks!

Jairo

 

[TGS4]

Your question is unclear. Are you asking about Kf (the Fatigue Strength Reduction Factor - or FSRF), which is subsequently defined in Table B1.10 and Table B1.11?

For an evaluation per B1.5.3, the Kf is applied to the stresses to calculate an effective equivalent stress, which is then compared to the S-N curve. The S-N curve is not modified.

 

[usecheijk]

Yes, however Kf defined in table B1.10 and B1.11 is only for welds. ¿What happen with other fatigue reduction factors Ka,Kb,Kc, etc. (Se = Ka.Kb.Kc...Se') commonly used in fatigue analysis?.

Jack

 

[TGS4]

I am not familiar with those terms. They are not contained in API-579/ASME FFS-1.

There is a number of fatigue-related quantities that are not explicitly detailed, but are hidden in the S-N curves, much like the mean stress correction. The quantities that you refer to may fall under such a categorization.