BS ISO 20765-1 : 2005

Foreword
Introduction
1 Scope
2 Normative references
3 Terms and definitions
4 Thermodynamic basis of the method
  4.1 Principle
  4.2 The fundamental equation of Helmholtz free energy
  4.3 Thermodynamic properties derived from the Helmholtz
      free energy
5 Method of calculation
  5.1 Input variables
  5.2 Conversion from pressure to reduced density
  5.3 Implementation
6 Ranges of application
  6.1 Pressure and temperature
  6.2 Pipeline quality gas
7 Uncertainty
  7.1 Uncertainty for pipeline quality gas
  7.2 Impact of uncertainties of input variables
8 Reporting of results
Annex A (normative) - Symbols and units
Annex B (normative) - The Helmholtz free energy of the
        ideal gas
Annex C (normative) - The equation for the Helmholtz free
        energy
Annex D (normative) - Detailed documentation for the
        equation of state
Annex E (informative) - Assignment of trace components
Annex F (informative) - Implementation of the method
Annex G (informative) - Examples
Bibliography

Describes a method of calculation for the volumetric and caloric properties of natural gases, natural gases containing synthetic admixture and similar mixtures, at conditions where the mixture can exist only as a gas.