orificeplate

An orifice plate is a flat, rigid disk with a precisely sized circular bore placed perpendicular to a pipeline. The bore creates a constriction that causes a measurable pressure drop between upstream and downstream faces. By applying conservation of mass and Bernoulli’s principle, the differential pressure is related to the flow rate, enabling flow measurement or control in a variety of fluids.

Typical orifice plates are installed between pipe flanges and can be standard thin plates or thicker variants. The bore diameter d, pipe diameter D, and the beta ratio β = d/D characterize the geometry. Concentric (central) alignment with a sharp-edged bore is common, though alternative edge geometries and tap configurations exist to suit different fluids and installation conditions. Materials include carbon steel, stainless steel, and alloys, chosen for fluid compatibility and temperature.

Operationally, for incompressible flow, the volumetric flow rate Q is approximated by Q = Cd A2 sqrt(2 ΔP / ρ), where A2 is the orifice area (π d^2/4) and Cd is a discharge coefficient that depends on β and Reynolds number. For gases, compressibility is accounted for with an expansion factor Y, yielding Q = Cd Y A2 sqrt(2 ΔP / ρ).

Orifice plates are standardized in many regions under ISO 5167, which provides methods to compute correction factors for different β, Reynolds numbers, and installation conditions. They require straight lengths of pipe upstream and downstream to develop reliable flow profiles and proper tapping arrangements to minimize measurement error. Orifice plates are widely used in chemical processing, water supply, oil and gas, and power generation for metering and control.