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. CAESAR II 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.
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Regards,
Richard Ay - Consultant