ISO 9951:1993

Overview

ISO 9951:1993 - Measurement of gas flow in closed conduits - Turbine meters - specifies the requirements for turbine meters used to measure gas flow in closed conduits. The standard covers meter dimensions, construction, performance, calibration and output characteristics, and also addresses installation conditions, leakage testing and pressure testing. Informative annexes A–E provide recommendations for use, field checks and discussion of fluid perturbations. Where local mandatory regulations conflict with ISO 9951, those regulations take precedence.

Key topics and technical requirements

ISO 9951 defines the technical baseline for turbine gas meters, including:

• Meter construction and materials: Shell and internal parts must be suitable for rated pressures and temperatures and resistant to corrosion; exterior protection as necessary.
• Dimensions and interchangeability: Design and tolerances to allow interchangeability of meters of the same size/type; preferred overall length ≤ 5D (D = pipe diameter).
• Flow ranges and performance: Specification of maximum (qmax) and minimum (qmin) flowrates, working range (rangeability) and error limits referenced to specified conditions.
• Pressure and leakage testing:
  • Strength test of pressure-containing parts at minimum 1.5× maximum allowable operating pressure.
  • Assembled meter leakage test pneumatically at minimum 1.1× maximum allowable operating pressure; no visible leakage allowed.
• Pressure tappings and marking:
  • At least one metering-pressure tapping marked “p/” for static pressure measurement at the turbine wheel.
  • Circular tapping bores: minimum 3 mm, maximum 12 mm; slit tappings: 2–10 mm in flow direction.
  • Mandatory badge marking: manufacturer, serial number, qmax, max operating pressure, qmin (at 1.2 kg/m³), etc.
• Calibration and outputs: Calibration data requirements (error at qmin and specified fractions of qmax), methods (test rigs, sonic nozzles), pulse/electrical outputs, counters and mechanical outputs.
• Installation and operational guidance: Annexes include recommendations for installation, field checks and perturbation effects on the measurement.

Applications and who uses this standard

ISO 9951 is used by:

• Meter manufacturers to design and certify turbine meters.
• Calibration and testing laboratories for acceptance and performance testing.
• Gas utilities, pipeline and process engineers for specifying and installing flow metering equipment.
• Regulatory and procurement teams to define technical and safety requirements in tenders and compliance documentation.

Key practical use cases include process gas metering, distribution network metering, and industrial flow measurement where reliable volumetric gas flow data, calibration traceability and pressure/ leakage integrity are required.

Related standards

Relevant normative references cited in ISO 9951 include ISO 4006 (vocabulary), ISO 5167-1 (pressure differential devices), ISO 5208 (pressure testing of valves), ISO 6708 (nominal size), ISO 5168 (uncertainty estimation) and IEC/other industry guides referenced in the document.