ISO 12213-3:2006

Overview

ISO 12213-3:2006 - Natural gas - Calculation of compression factor - Part 3: Calculation using physical properties - specifies a robust method to calculate the compression factor (Z) of natural gas and similar gaseous mixtures when full molar composition is not available. The method uses physical input properties (superior calorific value, relative density, carbon dioxide content and, when present, hydrogen content) together with pressure and temperature to compute Z using the SGERG‑88 virial equation. The standard is primarily targeted at pipeline‑quality gases and delivers typical uncertainties of about ±0.1 % within the defined operating ranges.

Key topics and technical requirements

• Calculation method: Based on the SGERG‑88 virial equation (derived from the GERG master equation), implemented as a three‑step iterative procedure:
  • Derive an equivalent five‑component composition (equivalent hydrocarbon, N2, CO2, H2, CO) from the physical inputs.
  • Determine virial coefficients B and C from that composition.
  • Solve the virial relation with molar density to obtain Z.
• Required inputs: absolute pressure, temperature, superior calorific value (volumetric, normal conditions), relative density (at 101.325 kPa, 0 °C), mole fraction of CO2 and mole fraction of H2 (if present).
• Ranges of applicability (pipeline quality):
  • Pressure: 0 to 12 MPa (recommended uncertainty limits up to 10 MPa)
  • Temperature: 263 K to 338 K (computer implementations allow down to 250 K)
  • CO2 mole fraction: 0 to 0.20; H2 mole fraction: 0 to 0.10
  • Superior calorific value: 30 to 45 MJ·m−3; relative density: 0.55 to 0.80
• Uncertainty and reporting:
  • Typical uncertainty ±0.1 % (up to 10 MPa) for pipeline conditions; increases outside defined ranges (see Annex F).
  • Report Z to four decimal places and include p, T and method (SGERG‑88).
• Software and implementation:
  • Annexes include algorithm detail, example calculations and a Fortran subroutine (SGERG.FOR). ISO/TC 193/SC 1 can be contacted about available software.

Applications and users

• Practical uses:
  • Metering and custody transfer corrections (volume ↔ standard conditions)
  • Pipeline flow calculation and gas allocation
  • Gas quality verification and network simulation
  • Engineering calculations where full gas composition is unavailable
• Typical users:
  • Pipeline operators and transmission/distribution companies
  • Gas metering and billing engineers
  • Gas analysts, laboratory personnel and regulatory bodies
  • Software developers implementing gas‑property calculators

Related standards

• ISO 12213-1: Introduction and guidelines
• ISO 12213-2: Calculation using molar‑composition analysis
• ISO 6976: Calculation of calorific values, density and Wobbe index
• ISO 80000 (quantities and units) - referenced for units and quantities

Keywords: ISO 12213-3:2006, compression factor, natural gas, SGERG‑88, superior calorific value, relative density, carbon dioxide content, hydrogen content, pipeline quality gas, gas metering.