SIST EN ISO 9300:2022 PDF

Overview - EN ISO 9300:2022 (Measurement of gas flow by means of critical flow nozzles)

EN ISO 9300:2022 (ISO 9300:2022) defines the geometry, installation and operating requirements for critical flow nozzles (CFNs) used to determine the mass flow rate of single‑phase gases. The standard covers toroidal‑ and cylindrical‑throat CFNs for which sufficient calibration data exist, and it provides the methods and information necessary to calculate flow rate and associated measurement uncertainty. EN ISO 9300:2022 supersedes EN ISO 9300:2005 and was prepared by ISO/TC 30.

Key topics and technical requirements

• CFN geometry and materials: specifies throat shapes (toroidal and cylindrical) and general construction requirements for reliable critical flow behavior.
• Operating limits: CFNs can be used only when the gas reaches critical velocity at the nozzle throat and within defined limits (e.g., throat-to-inlet diameter ratio and Reynolds‑number constraints).
• Installation requirements: guidance for upstream/downstream pressure tapping, temperature and density measurement, piping and chamber configurations, drain holes and downstream conditions.
• Measurement quantities and conversions: procedures to convert measured static pressures and temperatures to stagnation values for use in flow calculations.
• Key calculations: methods to compute mass flow rate, discharge coefficient (Cd), and the critical flow function (C*), plus approaches for viscosity and density inputs.
• Critical back‑pressure considerations: criteria to assess whether back‑pressure affects choked flow performance.
• Uncertainty analysis: practical computation of measurement uncertainty, including correlated uncertainty components and recommended reporting practices.
• Informative annexes: empirical discharge coefficient values, critical flow function tables for common gases, and guidance on calibration and diameter corrections.

Practical applications and typical users

EN ISO 9300:2022 is intended for applications requiring accurate gas mass flow measurement where calibration-free or low‑calibration methods are preferred. Typical users include:

• Flow‑metrology and calibration laboratories
• Custody transfer and billing systems for natural gas and industrial gases
• Pipeline and gas‑distribution operators
• Instrumentation and process engineers specifying flowmeters
• Research and test facilities conducting high‑precision gas flow experiments

Related standards and implementation

• This edition replaces EN ISO 9300:2005 and was developed by ISO/TC 30 (Measurement of fluid flow in closed conduits).
• Organizations implementing EN ISO 9300 should consult their national standards body for purchase, national adoption details and potential patent notices.

Keywords: EN ISO 9300, ISO 9300:2022, critical flow nozzles, CFN, gas flow measurement, mass flow rate, discharge coefficient, critical flow function, uncertainty, toroidal throat, cylindrical throat.