Borzki,

Be careful that if fatigue assessment is performed as per ASME VIII-2 or BS PD5500, ASME B31.3 stresses are not suitable to be employed directly in fatigue assessment.

B31.3 SIFs represent actually 50% from overall Pl+Pb+Q+F peak stress concentration factors. See ASME BPVC III-1/NB considerations regarding Stress Concentration Factors and SIFs inter-dependence.

As a very-rough approximation, B31.3 Von Mises or Tresca stress range (as applicable) should be DOUBLED to be used for ASME VIII-2 fatigue calculation purpose.

Best regards,