EN ISO 6974-5:2014 PDF

Overview

EN ISO 6974-5:2014 (ISO 6974-5:2014) specifies an isothermal gas chromatographic method for the quantitative determination of nitrogen (N2), carbon dioxide (CO2), methane to pentanes (C1–C5) and a composite C6+ hydrocarbon pseudo‑component in natural gas. Intended for both online process analysers and laboratory instruments, the method supports composition-based calculations such as calorific value (CV), density and Wobbe index.

Key topics and requirements

• Scope and analytes: Measurement of N2, CO2, CH4, C2–C5 isomers and a composite C6+ representing all hydrocarbons ≥ C6. Working ranges are provided for each component (see Table 1 of the standard).
• Isothermal column switching: A single injection with automated column switching and accelerated backflush of the C6+ fraction. Lighter components are retained while heavier hydrocarbons are eluted and then separated.
• Detector: Thermal Conductivity Detector (TCD) is specified for component detection.
• Composite C6+ handling: C6+ is measured as one “pseudo‑component” peak and calibrated as a composite; detailed extended analyses are used to calculate properties of the C6+ fraction if needed.
• Assumptions & limitations:
  • Oxygen is not expected in source gas; any O2 (air contamination) will be measured with nitrogen.
  • Helium and argon are assumed negligible and not routinely analysed.
  • Samples must be free of liquid hydrocarbon condensate and water.
• Quality control & uncertainty:
  • Establish repeatability through repeated analysis of a reference/test gas and maintain control charts (mean ± standard deviations).
  • Uncertainty treatment aligns with ISO 6974‑1 and ISO 6974‑2 procedures for compositional uncertainty reporting.
• Documentation: Clauses cover apparatus, procedure, control of the apparatus, expression of results and test reporting.

Applications

• Routine online process monitoring of natural gas composition in transmission and distribution systems.
• Laboratory compositional analysis for billing, custody transfer, and quality assurance.
• Input to thermophysical calculations (CV, density, Wobbe index) and to legal or commercial contracts.
• Configuration and performance verification of gas chromatographs used in gas industry operations.

Who should use this standard

• Gas analysis laboratories and technicians
• Pipeline and transmission operators
• Gas utilities and trading companies
• Instrument manufacturers and integrators of gas chromatographs
• Quality managers responsible for composition-based commercial calculations

Related standards

• ISO 6974‑1: General guidelines and calculation of composition
• ISO 6974‑2: Uncertainty calculations
• Other parts of ISO 6974 (Parts 3, 4, 6) for alternative column/analysis configurations
• ISO 6976 for calorific value calculation

Keywords: natural gas, gas chromatography, ISO 6974-5, isothermal method, nitrogen, carbon dioxide, C1–C5 hydrocarbons, C6+ hydrocarbons, calorific value, Wobbe index, thermal conductivity detector, uncertainty, online analysis.