Refer to ASME Section VIII, Division 1 - Appendix 2 Figures 2-4(1) and 2-4(2). In the second figure this value the flange face bevel size is the dimension for the material removed on the flange face the contacts the back of the lap. In the first figure there is a note indicating that the gasket reaction diameter, G, is determined as the mid-point of contact between the flange and the lap. Therefore, this value will result in G being calculated as the (OD Lap Face + 2*Bevel + B)*0.5. For the example below, the G value will come out to 32.8125 in.
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