1) The hub is the back ring, integral with flange ring, that's used to make a stronger flange. It's applicable to both slip on and welding neck flanges. See fig.2-4(3).
2) No, this is normally referred to as a pad flange
3) No: for soft type full face gaskets there is no calculation method provided by ASME VIII. App.Y deals with flanges with full face metal to metal contact. prex
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