Overview
EN ISO 6974-1:2012 (ISO 6974‑1:2012) provides general guidelines for determining the composition of natural gas and calculating associated measurement uncertainty using gas chromatography. Part 1 of the ISO 6974 series defines the data‑processing framework for converting chromatographic outputs into component mole fractions (raw and normalized) and sets out the analytical structure for single and multiple operation chromatographic methods.
Key topics and technical requirements
- Scope and purpose: Procedures for calculating component mole fractions from chromatographic data and preparing them for uncertainty assessment (used together with ISO 6974‑2 when uncertainty quantification is required).
- Analysis principles: Definitions of directly measured, indirectly measured and non‑measured components; normalization concepts for processed mole fractions.
- Operational modes: Support for single operation, multiple operation with bridging, and multiple operation without bridging; guidance on when each approach is applicable.
- Calibration approaches: Allowance for multi‑point calibration or a performance evaluation followed by single‑point calibration; treatment of relative response factors (see normative Annex D).
- Data processing and calculation: Stepwise procedure for defining working ranges, selecting equipment, deriving raw mole fractions, and calculating normalized (processed) mole fractions.
- Uncertainty and advanced methods: Conventional normalization is specified; for improved uncertainty assessment the standard references alternative approaches such as generalized least squares (GLS) (Annex B) and methane‑by‑difference (Annex C). ISO 6974‑2 provides the detailed uncertainty calculations.
- Quality assurance: Requirements for routine calibration/QA checks, control charts (Clause 7 and Annex H), outlier testing (Annex E), and test reporting (Clause 8).
- Practical corrections: Includes guidance on pressure correction during calibration and analysis (Annex F).
Applications and users
This standard is intended for:
- Laboratory analysts performing natural gas composition measurements by gas chromatography.
- On‑line process and custody transfer analyser operators and manufacturers.
- Calibration gas producers and metrology laboratories establishing traceable calibrations.
- Pipeline and gas distribution companies needing composition data for calorific value, custody transfer, emissions reporting and physical property calculations.
Using EN ISO 6974‑1:2012 helps ensure consistent, transparent calculation of component mole fractions and provides a structured basis for subsequent uncertainty evaluation (ISO 6974‑2), improving comparability of natural gas composition results across labs and field systems.
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