Orifice Flanges

Specialized Flanges for Orifice Plate Metering and Flow Measurement

What Is an Orifice Flange?

An orifice flange is a specialized weld neck or slip-on flange designed to hold an orifice plate for flow measurement. It features two radial tapped holes (pressure taps) for connecting differential pressure instruments. Orifice flanges are manufactured per ASME B16.36 and are always used in pairs with an orifice plate sandwiched between them.

Key Design Features

  • Two 1" NPT radial pressure tap holes (flange taps) at 180 degrees apart
  • Jack screws for spreading the flanges to insert or remove the orifice plate
  • Raised face with orifice plate recess
  • Available as weld neck or slip-on configurations
  • Matched bore to pipe ID for accurate metering

Common Applications

  • Flow measurement in oil and gas pipelines
  • Process control instrumentation in refineries
  • Custody transfer metering
  • Steam flow measurement in power plants
  • Natural gas distribution metering

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Available Sizes and Pressure Classes

Per ASME B16.36, orifice flanges are available in NPS 1/2 through 24 in Classes 300, 400, 600, 900, 1500, and 2500. Orifice flanges are not typically available in Class 150 because metering accuracy requires tighter tolerances associated with higher pressure classes.

Common Materials

  • Carbon Steel — ASTM A105
  • Stainless Steel — ASTM A182 F304 / F316
  • Alloy Steel — ASTM A182 F11 / F22
  • Low-Temperature — ASTM A350 LF2

Orifice Flanges vs Standard Flanges

Orifice flanges have the same outer dimensions as standard weld neck or slip-on flanges of the same class, but with added pressure tap holes and jack screws. They are always used in pairs. Standard flanges cannot substitute for orifice flanges in metering applications.

Related References