Overview
EN ISO 12213-1:2009 (ISO 12213-1:2006) - Natural gas - Calculation of compression factor - Part 1: Introduction and guidelines - provides the introduction and practical guidelines for calculating the compression factor (Z‑factor) of natural gas and similar gaseous mixtures. Adopted by CEN as EN ISO 12213-1:2009, this Part 1 explains the principles behind the calculation methods given in Parts 2 and 3, defines terms and symbols, and sets out the intended scope and limitations for reliable Z‑factor estimation.
Key topics and requirements
- Definition of compression factor (Z): Z = V(real) / V(ideal); the standard explains Z as the ratio of real gas volume to the ideal‑gas volume at specified pressure and temperature.
- Two calculation approaches:
- Part 2 - calculation based on detailed molar composition (component analysis).
- Part 3 - calculation using a more limited set of physical properties (superior calorific value on a volumetric basis, relative density, CO2 content and, if present, hydrogen).
- Applicable conditions: Methods apply when the mixture exists only as a gas (i.e., above water and hydrocarbon dewpoints). Typical pipeline quality gas ranges are supported (temperatures ≈ 263 K to 338 K / −10 °C to 65 °C; pressures up to 12 MPa / 120 bar).
- Accuracy and uncertainty: For pipeline‑quality gases within the normal operating range, predicted Z has an uncertainty of about ±0.1%, provided input data (composition, pressure, temperature) are exact.
- Guidance for broader use: Part 2 can be extended (with increased uncertainty) to wet/sour gases, higher pressures and storage or NGV conditions; Part 3 can be used for gases with higher N2, CO2 or ethane content but with greater uncertainty.
- Practical deliverables: The standard includes equations, symbols, units and plans for verified computer programs (see Annex B).
Applications and users
This standard is essential for:
- Pipeline operators and transmission system managers - custody transfer, flow measurement and energy accounting.
- Metering and gas measurement engineers - converting volume to standard conditions, applying compressibility corrections.
- Gas analysts and laboratories - providing input data (molar composition, calorific values, relative density) for Z‑factor calculations.
- Software developers - implementing compliant calculation routines for SCADA, billing and simulation tools.
- Storage and NGV system designers - when assessing non‑pipeline conditions with adapted uncertainty.
Practical applications include compressibility correction for custody transfer metering, volumetric flow conversion, energy calculations and pipeline hydraulics where accurate Z‑factor prediction is required.
Related standards
- ISO 12213-2 - Calculation using molar‑composition analysis (detailed method)
- ISO 12213-3 - Calculation using physical properties (reduced‑analysis method)
- ISO 6976 - Calculation of calorific values, density and Wobbe index from composition
- ISO 13443 - Standard reference conditions
Keywords: natural gas, compression factor, compressibility factor, Z‑factor, EN ISO 12213-1:2009, ISO 12213, molar composition, superior calorific value, relative density, custody transfer.
