ISO 5167:2022 Explained: A Guide to All Six Parts

ISO 5167-1:2022 establishes the common foundation: terminology, flow equations, symbols, pressure and temperature measurement, density and expansibility treatment, installation principles and uncertainty methodology. It applies to steady, single-phase flow in a pipe running full. Pulsation, swirl, multiphase flow, deposits and changing composition require additional engineering because they violate or weaken the assumptions behind the standardized correlation.

Part 1 should be read before the device-specific part. It explains how differential pressure, diameter, beta ratio, discharge coefficient, expansibility and density combine to determine flow. It also makes clear that traceability is a system property. A precisely manufactured primary element cannot compensate for incorrect pipe diameter, poor pressure measurement, invalid fluid properties or an unsuitable installation.

ISO 5167-2:2022 covers standardized orifice plates and recognized tapping arrangements. It defines the plate bore, thickness, flatness, upstream-edge condition, concentricity, pressure taps, pipe roughness and validity limits needed to use the standard discharge-coefficient correlation. The familiar simplicity of a plate hides strict dimensional requirements; small damage or deposit at the upstream edge can create a systematic error.

For procurement, specify the exact tapping arrangement and measured pipe bore rather than relying only on nominal diameter. Verify beta ratio and Reynolds number across the operating range. Straight-run requirements depend on beta ratio and the type and spacing of upstream fittings. A calculation that ignores the actual piping configuration is incomplete even if the plate itself is dimensionally correct.

ISO 5167-3:2022 addresses nozzle families, including ISA 1932 nozzles, long-radius nozzles and Venturi nozzles within their respective limits. The rounded inlet provides greater resistance to edge wear than a sharp orifice and suits high-velocity steam, gas and liquid service. Each geometry has its own dimensional definitions, discharge-coefficient treatment and Reynolds-number range.

Engineers must not combine a nozzle name from one family with dimensions or coefficients from another. Confirm inlet profile, throat finish, tap positions and fabrication method. For high-temperature service, the mechanical design must also account for thermal expansion, material strength, welding, pressure boundary rules and transmitter impulse piping; ISO flow correlation does not replace pressure-equipment design.

ISO 5167-4:2022 covers classical Venturi tubes with defined convergent, throat and diffuser arrangements and distinguishes recognized manufacturing forms. Their principal operational advantage is pressure recovery: the diffuser converts part of the velocity head back into static pressure, reducing permanent loss. This makes them valuable in continuously operated, high-flow systems.

A Venturi tube still requires correct upstream piping, throat dimensions, surface condition and pressure-tap construction. Manufacturing form affects the applicable coefficient and uncertainty. Buyers should require an as-built dimensional report and should compare the predicted permanent loss over annual operating hours. A low-loss meter can justify higher initial cost through reduced pump or compressor duty.

ISO 5167-5:2022 covers cone meters, in which the primary body is mounted centrally and the annular opening establishes the differential pressure. The geometry conditions the velocity distribution while generating a measurable signal, supporting installations where conventional straight-run space is limited. The part defines the relevant beta relationship, geometry, tap locations and application constraints.

Standard coverage does not remove the need to examine calibration and the actual disturbance configuration. Cone support geometry, alignment, surface condition and tap construction can influence performance. For custody or contractual measurement, establish the applicable approval route and uncertainty evidence explicitly rather than assuming that a reference to ISO 5167 alone settles legal metrology requirements.

ISO 5167-6:2022 covers wedge meters, whose segmental restriction leaves an open passage favorable for viscous, dirty or solids-bearing fluids. Wedge height and pipe diameter define the effective restriction. The device can remain practical at Reynolds numbers and fluid conditions where a conventional sharp-edged plate becomes difficult to operate.

Installation engineering remains essential. Select orientation to manage gas pockets, sediment and drainage, and protect the pressure connections from plugging. For severe fluids, remote seals, flushing or purging may dominate the measurement design. Calibration can materially improve uncertainty beyond an uncalibrated correlation, so the required performance should be stated together with the calibration scope.

The fundamental discipline remains stable: use verified process properties, stay within the selected device’s limits, manufacture and inspect the defined geometry, provide the required piping, and calculate uncertainty from all significant contributors. The standard does not turn unsteady or multiphase flow into a valid application, guarantee every manufacturer-specific device, or replace pressure-vessel, material and hazardous-area requirements.

A defensible specification cites the exact part and edition—for example, ISO 5167-2:2022—then lists the project conditions, geometry, tapping, piping, inspection, uncertainty and calibration requirements. Writing only “ISO 5167 compliant” is too broad. The six-part structure helps engineers match a device to its technical basis, but compliance is demonstrated through documented details.