Overview
ISO 12213-2:2006 specifies a rigorous method for calculating the compression factor (Z) of natural gas and similar gaseous mixtures when a detailed molar-composition analysis is available. The standard adopts the AGA8-92DC detailed-characterization (extended virial-type) equation to compute Z and molar density from absolute pressure, absolute temperature and mole fractions of gas components. It is intended primarily for pipeline quality gas and provides stated uncertainties and ranges of application for reliable volumetric property calculations.
Key topics and requirements
- Calculation method: Uses the AGA8-92DC equation (extended virial form) and requires solving coupled equations for Z and molar density by numerical methods.
- Input variables: Absolute pressure, absolute temperature and mole fractions of components (N2, CO2, Ar, CH4, C2–C10 hydrocarbons, H2, CO, H2S, He, O2, H2O, etc.). All components with mole fraction > 0.00005 must be represented.
- Ranges of application (pipeline quality):
- Pressure: 0 to 12 MPa (tested up to 65 MPa for wider ranges)
- Temperature: 263 K to 338 K (wider: 225 K to 350 K)
- Superior calorific value: ~30 to 45 MJ·m^-3 (wider: 20 to 48 MJ·m^-3)
- Relative density: 0.55 to 0.80 (wider: up to 0.90)
- Uncertainty: Typical uncertainty for pipeline-quality gas is ±0.1% (within specified ranges); Annex E discusses extended-range performance.
- Reporting precision: Report Z to four decimal places and molar density to five decimals; include p, T and method (ISO 12213-2, AGA8-92DC).
- Supporting material: Normative annexes provide symbols/units, full AGA8-92DC description, example calculations, unit conversions and Fortran subroutines; informative annexes discuss broader performance.
Applications and practical value
- Accurate calculation of volumetric properties for pipeline operations, transmission and distribution custody transfer, flow measurement, billing and energy accounting.
- Use in gas quality control, engineering simulations, custody metering verification and software tools for gas property calculations.
- Useful for laboratories and gas analysis teams that produce mole-fraction compositions from chromatographic or analytical methods.
- Enables consistent, traceable results for regulatory compliance and commercial transactions where precise Z-values are required.
Who should use this standard
- Pipeline operators and transmission companies
- Metering and custody transfer engineers
- Gas analysis laboratories and QA/QC teams
- Energy traders, regulators and standards developers
- Software developers implementing gas property calculation modules
Related standards
- ISO 12213-1 - Introduction and guidelines
- ISO 12213-3 - Calculation using physical properties
- ISO 6976 - Calculation of calorific value, density and Wobbe index from composition
- AGA Report No. 8 (AGA8-92DC) - detailed characterization method referenced by ISO 12213-2
Keywords: ISO 12213-2, compression factor, natural gas, molar composition analysis, AGA8-92DC, pipeline quality gas, gas metering, uncertainty ±0.1%
