CAESAR II has the functionality to consider load case combinations to perform fatigue analysis against a defined S-N curve. When considering fatigue due to different expansion stress cases this is fine. When considering pressure cycles there seems to be no capability in CAESAR, nor any clear guidance in B31.3. For piping specified as high pressure, B31.3 K304.8 requires a fatigue assessment in accordance ASME Section VIII Div 2 App5. This requires knowledge of peak stress intensity range which cannot be determined by CAESAR. For normal service piping reference is made to B31.3 301.10 which states that "cyclic loadings shall be considered in the design of piping", but provides no guidance as to how assessment of pressure cycles should be performed. Furthermore, the rules in B31.3 302.3.5(d) only allow for combinations of different displacement stress ranges and not the stress range due to pressure cycles.

I therefore seem to be left with the task of preparing a fatigue analysis and thereby determining a fatigue life utilisation factor for the pressure cycles externally to CAESAR, and then combining it with the that calculated for the expansion stress range from CAESAR manually. Is my interpretation correct?

Steve Baldwin