ISO 5167-2:2022

Overview

ISO 5167-2:2022 - part of the ISO 5167 series - defines how to measure fluid flow in full circular conduits using orifice plates as differential-pressure primary devices. The standard specifies orifice-plate geometry, allowable pressure-tap locations, installation and operating conditions, and the calculation background (discharge coefficients, expansibility factors and uncertainty). It applies only to subsonic, single‑phase flows and is intended to be used together with ISO 5167‑1 (general principles).

Key topics and technical requirements

• Orifice plate geometry and manufacture: required shapes, edge forms, thickness limits and material/manufacture considerations for reliable measurement.
• Pressure tappings covered: flange tappings, corner tappings, and D / D/2 tappings. (Other tappings such as “vena contracta” and pipe tappings are excluded.)
• Calculation basis: mass and volumetric flow are derived from the measured differential pressure together with the discharge coefficient (C), expansibility factor (ε), fluid density (ρ), orifice diameter (d) and beta ratio (β).
• Limits of use: not applicable for pulsating flow; pipe sizes < 50 mm or > 1 000 mm are excluded; Reynolds numbers below 5 000 are excluded; flow must remain subsonic and single‑phase.
• Installation requirements: minimum upstream/downstream straight lengths, pipe circularity/cylindricity, carrier rings and gasket/fixing methods to minimise measurement errors.
• Flow conditioners: guidance on acceptable flow straighteners (e.g., tube bundles, Zanker-type plates) to stabilise upstream profiles where required.
• Calibration and uncertainty: procedures for flow calibration of orifice meters, test-facility and meter installation guidance, and methods for uncertainty analysis.
• Supplementary material: informative annexes provide tables of discharge coefficients/expansibility factors and details about flow conditioners.

Practical applications and who uses this standard

ISO 5167-2 is used by:

• Flow metrology and instrumentation engineers specifying or verifying orifice‑plate meters.
• Calibration laboratories conducting flow calibrations and uncertainty analysis.
• Process, petrochemical, water/wastewater, and utility engineers requiring standardized differential‑pressure flow measurement.
• Procurement and QA teams ensuring installed meters meet recognized international measurement requirements.

Using ISO 5167-2 helps achieve repeatable, traceable flow measurements, reduce installation-related errors, and support coherent uncertainty estimates for process control, custody transfer and regulatory reporting.

Related standards

• ISO 5167-1 (general principles and requirements)
• ISO 4006 (vocabulary and symbols)
• ISO 5168 (uncertainty evaluation procedures)
• ISO/IEC Guide 98-3 (GUM - expression of uncertainty)

Keywords: ISO 5167-2:2022, orifice plate flow measurement, differential pressure devices, discharge coefficient, flow calibration, pressure tappings, Reynolds number, installation requirements, flow conditioners.