What the standard covers
B16.36 defines weld-neck and threaded orifice flanges built on the same body dimensions as the equivalent B16.5 pressure-class flange, with two additions specific to orifice service:
- Radial pressure-tap holes machined into the flange body, at a defined size and location relative to the flange face
- Provision for jack-screw holes on some configurations, so the flanges can be parted without a full bolt breakout
Because the body dimensions and bolt circle match the corresponding B16.5 flange of the same size and class, an orifice flange bolts up to standard pipe flanges and fittings on either side without any special transition piece.
B16.36 vs. the plate-sizing standards
This is the point people most often mix up. B16.36 is a hardware standard — it says nothing about what bore diameter belongs inside the flange. The bore comes from a separate flow-equation standard, typically ISO 5167-2 or ASME MFC-3M, applied to your actual pipe size, fluid and flow range. A flange set built correctly to B16.36 with the wrong bore inside it will fit perfectly and measure — or restrict — incorrectly. See our orifice calculator for the plate side of that equation, and the standards comparison on our blog for how ISO 5167 and ASME MFC-3M relate to each other.