Orifice Flanges are used with orifice meters for the purpose of measuring the flow rate of either liquids or gases in the respective pipeline. Pairs of pressure "Tappings", mostly on 2 sides, directly opposite each other, are machined into the orifice flange. This makes separate orifice carriers or tappings in the pipe wall unnecessary.
Orifice Flanges generally come with either Raised Faces or RTJ (Ring Type Joint) facings. They are, for all intensive purposes, the same as weld neck and slip-on flanges with extra machining.