Overview
EN ISO 12213-2:2009 (identical to ISO 12213-2:2006) defines a standardized method for calculation of the compression factor (z‑factor) of natural gas using a detailed molar‑composition analysis. The method is intended for single‑phase gaseous mixtures (pipeline quality gas) and uses the AGA8‑92DC extended virial‑type equation to compute z from pressure, temperature and mole fractions. Typical uncertainty for pipeline quality gas is about ±0.1%.
Key topics and requirements
- Methodology
- Uses the AGA8‑92DC equation (extended virial form) to determine z by solving the molar density and z simultaneously.
- Numerical solution required - the standard includes guidance and subroutines (Annexes B and F).
- Input variables
- Absolute pressure and temperature.
- Molar composition (mole fractions) of components such as N2, CO2, Ar, CH4, C2H6, C3H8, n‑C4, i‑C4, n‑C5, i‑C5, C6, C7, C8+, H2, CO, H2S, He, O2 and H2O.
- All components with mole fraction > 0.00005 must be represented; sum of mole fractions must equal unity to within 0.0001.
- Ranges of application
- Pipeline quality: 0 to 12 MPa, 263 K to 338 K; relative density 0.55–0.80; calorific value 30–45 MJ·m−3.
- Wider tested ranges (greater uncertainty): up to 65 MPa, 225 K to 350 K, relative density up to 0.90.
- Uncertainty
- ≈ ±0.1% for pipeline quality gases within the specified ranges (validated against GERG and GRI data).
- Uncertainty increases outside these limits (see Annex E).
- Normative content
- Annexes include symbols/units, detailed AGA8 description, worked examples, conversion factors, performance over wider ranges, and example Fortran subroutines.
Practical applications and users
- Who uses it:
- Pipeline and transmission operators, gas metering and custody‑transfer teams, energy traders, gas laboratories, gas network modelers, and software developers implementing thermophysical property libraries.
- Typical applications:
- Accurate z‑factor (real gas factor) calculation for flow metering, custody transfer and billing.
- Pipeline hydraulic modeling and capacity studies.
- Conversion between volumetric and molar/fiscal quantities, energy accounting and quality control.
- Integration into commercial gas property and billing software using the AGA8‑92DC algorithm.
Related standards
- ISO 12213‑1 - Introduction and guidelines to compression factor calculations.
- ISO 6976 - Calculation of calorific values, density and Wobbe index from composition.
- AGA Report No. 8 - Source description of the AGA8 detailed characterization equation.
Keywords: EN ISO 12213-2:2009, compression factor, natural gas, z‑factor calculation, AGA8‑92DC, molar composition, pipeline quality gas, gas metering.
