Overview
ISO 12213-1:2006 - Natural gas - Calculation of compression factor - Part 1: Introduction and guidelines - provides the introductory framework and practical guidance for calculating the compression factor (Z‑factor) of natural gas and similar mixtures that exist only as gases. Part 1 explains the scope, terminology and general principles used in the calculation methods detailed in ISO 12213-2 and ISO 12213-3. It also documents input-data requirements, expected accuracy and operational limits for the recommended equations.
Key topics and requirements
- Compression factor (Z): defined as the ratio of real gas molar volume to ideal-gas volume (Z = pV/RT). Synonymous with compressibility factor.
- Two calculation approaches:
- Part 2 (detailed molar-composition method) - uses a full molar analysis and the AGA8-92DC equation.
- Part 3 (physical-properties method) - uses superior calorific value, relative density and CO2 content and the SGERG-88 equation (derived from MGERG-88).
- Input-data requirements:
- For Part 2: all constituents with mole fraction > 0.00005; mole fractions must sum to unity within 0.0001.
- For Part 3: superior calorific value (volumetric), relative density, CO2 and, if applicable, hydrogen content.
- Applicable conditions and accuracy:
- Typical transmission/distribution range: temperatures ~263 K to 338 K (−10 °C to 65 °C) and pressures up to 12 MPa (120 bar).
- Within these ranges for pipeline-quality gas, predicted Z uncertainty ≈ ±0.1% (assuming exact input data).
- Gas must be above water and hydrocarbon dewpoints for validity.
- Pipeline-quality guidance:
- Predominantly methane (mole fraction > 0.70).
- Superior calorific value typically 30–45 MJ·m−3.
- Nitrogen and CO2 may each be up to ≈0.20 mole fraction; ethane up to ≈0.10; hydrogen and CO up to typical ranges when synthetic admixtures are present.
Applications and users
ISO 12213-1 and its companion parts are essential for:
- Gas transmission and distribution engineers performing volumetric calculations and pipeline flow analysis.
- Custody transfer and metering specialists who need Z-factor for accurate volume-to-mass conversions.
- Laboratory analysts and gas quality teams implementing calculation software.
- Storage, LNG/UGS, and NGV system designers who require reliable compressibility data at specified P–T conditions.
- Developers of gas‑properties and custody-transfer software (Annex B notes planned verified computer programs).
Related standards
- ISO 12213-2 (molar-composition calculation)
- ISO 12213-3 (physical-properties calculation)
- ISO 6976 (calorific values, density, Wobbe index)
- ISO 13443 (standard reference conditions)
- AGA Report No. 8 (AGA8-92DC); GERG technical references (SGERG/MGERG)
Keywords: ISO 12213-1:2006, natural gas, compression factor, Z-factor, AGA8-92DC, SGERG-88, molar composition, calorific value, relative density, pipeline quality.
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