ISO 5167-6:2022

Overview

ISO 5167-6:2022 - "Measurement of fluid flow by means of pressure differential devices inserted in circular cross‑section conduits running full - Part 6: Wedge meters" specifies the geometry, installation and operating conditions, and calculation principles for wedge meters used to determine fluid flow in full, circular pipes. It is part of the ISO 5167 series and is intended for single‑phase, subsonic flows (not suitable for pulsating flows). The standard also contains requirements and guidance for calibration, uncertainty analysis, and practical computation of mass and volumetric flow from differential pressure measurements.

Key topics and technical requirements

• Primary element geometry and manufacture: Defines wedge shape, throat area and related dimensional parameters (wedge gap h, wedge ratio β) and advises on materials and manufacturing quality.
• Field of application limits: Uncalibrated wedge meters are restricted to pipe internal diameters 50 mm to 600 mm, wedge ratios and Reynolds number ranges (Re ≥ 1×10^4); calibrated meters may be used beyond these limits per Clause 7.
• Measurement principle and computation: Flow is obtained from the measured differential pressure across the wedge using a discharge coefficient (C) and an expansibility (expansion) factor (ε); the standard provides formula structure and tables/annexes to support calculation.
• Pressure tappings and instrumentation: Specifies tapping locations and their relation to the primary element for accurate differential pressure measurement.
• Installation requirements: Covers upstream/downstream straight‑run requirements, pipe circularity/cylindricity, internal roughness limits, thermowell positioning and bidirectional meter considerations.
• Calibration and uncertainty: Clause 7 gives requirements for flow calibration programs, test facility considerations, reporting, and uncertainty analysis for the discharge coefficient and expansibility factor.
• Limitations: Applicable to single‑phase, subsonic flows; not for pulsating flow; alternative wedge designs require separate calibration due to limited characterization data.

Practical applications and users

ISO 5167-6 is used by:

• Meter manufacturers designing and certifying wedge meters.
• Calibration laboratories performing type and site calibrations (Clause 7).
• Process and plant engineers in oil & gas, water, chemical, power and HVAC industries specifying or verifying flow measurement systems.
• Metrology and quality assurance teams assessing measurement uncertainty for custody transfer, fiscal metering or process control.

Benefits include improved repeatability in differential‑pressure flow metering, clear guidance for installation and calibration, and consistent uncertainty evaluation.

Related standards

• ISO 5167-1: General principles and requirements for pressure differential devices (must be used in conjunction).
• ISO 4006: Vocabulary and symbols for fluid flow in closed conduits.
• ISO 2186: Secondary device considerations (instrumentation) referenced.