There are five allowable stress need to be checked in flange leakage check in CII.One of these is maximum average stress.In operating condition, the allowable stress for hub,radial,tangential are 1.5Sf, while only 1Sf for maximum average. Why the maximum average doesn't use 1.5Sf? As we know the maximum average is from the average of hub, radial or tangential, why the allowable doesn't use the average of hub, radial of tangential? I feel a little doutful about this...