Allowable Stresses in ASME B31.8 Ch VIII Code Operating Case

I am doing a stress analysis using B31.8 Ch VIII code in CAESAR program. As per Table A842.22 in Chapter VIII of B31.8 for combined stress we can use 0.9 as the design factor(F3) to calculate the allowable stress.

B31.8 code based CAESAR operating case allowable stress is 0.9 x SMYS. But B31.8 Ch VIII code based CAESAR operating case allowable stress is only 0.72 x SMYS. I believe 0.72 shall be used only for hoop stress calculation.

I need expert’s advice on this issue.

Thanks

In Chapter VIII, there are three stress equations and three allowable equations. You are correct, the 0.72 factor (F1) is applied for the hoop stress, the 0.8 factor (F2) is applied to the longitudinal stress, and the 0.9 factor (F3) is applied to the combination stress. c2 performs all of these calculations.

The problem here is that there is only room in the stress report for "one Code Stress" and "one allowable stress". So, we generate three ratios: hoop stress/hoop allowable, longitudinal stress/longitdinal allowable, combined stress/combined allowable. Which ever ratio is the largest is the pair of values we display in the stress report.

So if you're seeing an allowable value equal to 0.72*SMYS, then the hoop ratio is governing.

Richard,

Thanks for your quick response. I will compare my results with different ratios to get a clear idea about CAESAR comparison.