ISO/TR 12767:2023

Overview - ISO/TR 12767:2023 (Measurement of fluid flow by pressure differential devices)

ISO/TR 12767:2023 is a Technical Report that provides practical guidance for estimating flowrate when pressure differential devices (mainly orifice plates and, to a lesser extent, Venturi tubes) are constructed or operated outside the strict requirements of the ISO 5167 series. It explains how departures from the ISO 5167 specifications affect measured flowrate and measurement uncertainty, and gives users a way to assess the likely magnitude and direction of resulting errors. This edition (third, 2023) updates and consolidates existing guidance for manufacture, installation and maintenance of differential-pressure flowmeters.

Key topics and technical requirements

• Scope and intent: Guidance applies where installations cannot fully conform to ISO 5167; it does not apply to cone or wedge meters.
• Main device focus: Predominantly orifice plates; includes an example for Venturi tubes.
• Error assessment approach:
  • Treats each variation individually (interactions between multiple deviations can be unpredictable).
  • Provides methods to estimate discharge coefficient changes and additional uncertainty.
• Construction deviations covered:
  • Orifice-plate edge sharpness and thickness
  • Condition of upstream/downstream faces
  • Position and condition of pressure tappings
  • Carrier ring and joint ring dimensions, protruding welds, eccentricity
• Pipeline and layout effects:
  • Upstream/downstream pipe conditions, steps and tapers, pipe diameter, and layout disturbances
  • Recommendations on discharge coefficient compensation and limits to applying corrections
• Operational deviations and maintenance:
  • Plate deformation (elastic/plastic), deposition on faces and in meter tube, surface roughness changes
  • Pipe roughness impacts and mitigation/maintenance strategies
• Uncertainty guidance: How to estimate additional uncertainty when ISO 5167 conditions are not met.

Practical applications - who should use it

• Flow measurement engineers, process and pipeline engineers
• Metering contractors, manufacturers and calibration labs
• Operations and maintenance teams managing retrofit or constrained installations
• Custody transfer and thermal/hydraulic system auditors assessing measurement risk

ISO/TR 12767:2023 is useful where full compliance with ISO 5167 is impossible or costly; it helps stakeholders make informed decisions about acceptable errors, possible corrective actions, and maintenance priorities.

Related standards

• ISO 5167 series (primary normative reference; methods and requirements for differential-pressure flowmeters)
• ISO 5167-1 (general principles and requirements) - referenced directly in this report

Keywords: ISO/TR 12767:2023, ISO 5167, pressure differential devices, orifice plates, Venturi tubes, flowrate measurement, discharge coefficient, meter installation, measurement uncertainty, pipe roughness.