The specification for orifice flange sets is not particularly clear about ring groove connections for these flange assemblies. Our proprietary CAD flange drawings can give the impression that ring grooves are cut into the face of a flange that may be considered “flat face,” however this is not the case if you review the dimensions. For RTJ orifice flanges, the flange thickness *exclusive* of the depth of the groove must meet the same minimum thickness as that of a standard raised face orifice flange assembly, exclusive of the height of the raised face. Visually speaking, though it may *appear* that the flange groove is cut into a flat face, you can confirm with the dimensions outlined in the B16.36 flange specification that it is more accurately what some would refer to as a “full face” with extra thickness (how much thickness depends on the depth of the groove, just as it would be defined in ASME/ANSI B16.5). Some manufacturers still machine down the should of the face to make it appear similar to the raised portion of a proper RTJ groove flange, in order to avoid initial confusion. Also, note that larger RTJ orifice flanges will require angular taps to ensure proper clearance with the bottom of the groove, which cannot be altered or modified in any way.
In other words: NO, you cannot take a raised face orifice flange, machine down the face, add a groove, and just call it an RTJ orifice flange. Minimum dimensional requirements for flanges must meet the tolerances outlined in ASME / ANSI B16.36 and B16.5 No shortcuts, or else you are out of compliance!