OFP-CS: The standard Concentric Sharp-Edged Orifice plate is bored and beveled to a 45° angle. Wyatt Engineering’s flow test data, as well as the requirements of most North American and international standards, indicate the cylindrical bore thickness should be limited to a range of 0.5% to 2.0% of the adjacent pipe inside diameter.

OFP-CU: Unlike the standard concentric plate, the Concentric Unbeveled Orifice plate is used for bidirectional flow measurement. This design can also be employed to restrict and limit flow rates, and help minimize cavitation in control valves and other equipment.

OFP-SO: Segmental Orifice plates can be used for the measurement of two-phase or multiphase flow (solids entrained in a liquid and/or gas flow stream; liquids entrained in a gas flow stream). Depending on the process flow, the segmental opening can be placed either at the crown or invert of the adjacent piping. This is a relatively common design in the chemical, pharmaceutical, pulp and paper, and petrochemical industries.

OFP-EO: The bores of Eccentric Orifice plates are not concentric with the pipe in which they are installed. The bore of the eccentric orifice is practically tangent to the inside diameter of the adjacent pipe. Like the segmental orifice plate, the bore can be placed at the top or bottom of the pipe and this design is relatively common in the chemical, pharmaceutical, pulp & paper, and petrochemical industries. Eccentric bore orifice plates are occasionally used when the application requires a very small bore and the process requires a vent or drain hole.

OFP-QE: Quadrant Edge orifice OFP-QE bore is not sharp-edged like the plates described above; rather, it is radiused. This design is for use with viscous process fluids, such as heavy crude or slurries where the pipe Reynolds number is normally less than 10 000. Since the radius of the bore’s upstream edge is a function of the beta ratio, the plate thickness is typically greater than for standard concentric sharp-edged orifice plates.

OFP-CO: Like the quadrant-edge orifice plate, the Conical Orifice plate is designed for use with vis- cous fluids where the pipe Reynolds number is less than 10 000. The bore thickness is limited by counter-boring the downstream face.

The typical materials for orifice plate construction are 304, 304L, 316, 316L stainless steels and carbon steel. Nickel and copper alloys, titanium, duplex stainless steels, PVC, PTFE, and other materials are also available.

The orifice plate thickness is chosen to limit plate deformation by taking into account the magnitude of the differential pressure and other defined stresses. Only under special circumstances will the plate thickness be less than 3 mm (0.120”) nominal.

All Wyatt Engineering orifice plates are finished in accordance with the requirements of the applicable standards. Typically, the surface finish will not exceed 50 microinches, however, special finishes are available.

In order to measure the flow rate accurately, it is essential that the bore of the orifice plate be concentric with the internal diameter of the pipe. It is also necessary that the interior of the pipe be smooth and circular in cross section.

When the nominal pipe size is larger than 65 mm (2½”), commercial pipe, flanges, etc., are typically within tolerance limits for accurate flow measurement. When the pipe diameter is 65 mm (2½”) or less, however, greater care must be taken with the orifice installation smooth run of pipe upstream and downstream from the orifice.