GS-ENG-06-12 — Requirements for the selection and use of natural gas mixtures used by Measurement Canada

Category: Gas
Issue date:
Effective date:
Revision number: 4
Supersedes: GS-ENG-06-12, (rev. 3)


Table of contents


1.0 Scope

This document outlines the requirements for the selection and use of natural gas mixtures to evaluate the performance of gas analysis devices. It does not address the selection or initial conditioning of gas cylinders.

2.0 Authority

This document has been issued under the authority delegated to the Senior Engineer, Gas Measurement.

3.0 References

API 14.1, The American Petroleum Institute (API), Collecting and Handling of Natural Gas Samples for Custody Transfer

GPA 2198, Gas Processors Association: Selection, Preparation, Validation, Care and Storage of Natural Gas and Natural Gas Liquids Reference Standard Blends

S-G-03—Specifications for the Approval of Type of Gas Metering Devices

4.0 Natural gas mixture specifications

Unless otherwise authorized by Measurement Canada's Engineering and Laboratory Services Directorate (ELSD), natural gas mixtures used to evaluate the performance of gas analysis devices must meet the following specifications:

  1. Natural gas mixtures must be:
    • highly accurate, sufficiently stable and homogenous, and traceable by weight to a national metrological institute such as the National Research Council of Canada or the National Institute of Standards and Technology;
    • accompanied by a certificate indicating the expression of uncertainty and demonstrating traceability to the International System of Units (SI); and
    • gravimetrically blended with full analysis of high purity raw materials and/or confirmed by direct comparison to reference material.
  2. The target relative expanded uncertainty with a coverage factor of k = 2 (95% confidence level) for the gas composition of a mixture must be:
    • equal to or less than 1% relative for component concentrations within the concentration range of 10 mol % to 100 mol %;
    • equal to or less than 2% relative for component concentrations less than 10 mol %; and
    • equal to or less than 0.2% relative for methane (if determined directly).
  3. All gas components must be analyzed for accurate heating value determination, with a target expanded uncertainty of ± 0.15% or lower.

5.0 Composition of natural gas mixtures

Unless otherwise indicated or authorized by the ELSD, the typical composition of natural gas mixtures is as indicated in Table 1.

Note: If the device's Notice of Approval authorizes the capability to detect components that are not listed in Table 1, then mixtures must be selected such that they are composed of all of the components that the device is approved to analyze. The appropriate concentrations must be selected to be within the approved upper and lower detection limits.

Table 1: Typical composition of natural gas mixtures
Component name Component concentration range in mol %
High calorific value mixture Low calorific value mixture
Methane 78 to 88 90 to 100
Ethane 6 to 9 0.7 to 3.7
Propane 4.35 to 4.45 0.05 to 0.15
Isobutane 0.65 to 1.05 0.01 to 0.4
N-butane 0.9 to 1.3 0.01 to 0.4
Isopentane 0.25 to 0.35 0.05 to 0.15
N-pentane 0.2 to 0.3 0.05 to 0.15
N-hexane 0.25 to 0.35 0.05 to 0.15
Carbon dioxide 0.01 to 4 0.01 to 2.5
Nitrogen 0.01 to 0.82 0.05 to 2.5

The gas mixture's certificate must indicate the mixture's hydrocarbon dew point temperature and pressure.

6.0 Conditions of use

6.1 Minimum storage and use temperature

The gas mixture must be stored and used at a temperature of at least 20 °F (11.1 °C) above the dew point. The gas cylinder must be heated before use when it was shipped or stored below its stated dew point temperature.

6.2 Minimum use pressure

The minimum use pressure must be stated on the gas mixture's certificate. The minimum pressure being the limiting pressure value below which the gas mixture must no longer be used, as below this pressure deviation from certified composition may occur.

6.3 Certification period

The certification period is the period in which the composition of the gas mixture is guaranteed to be stable and within the limits of expanded uncertainty and/or tolerance. Measurement Canada recommends a maximum three-year certification period for a gas cylinder.

7.0 Revisions

The purpose of revision 4 was to:

  • amend section 5.0 to account for gas components that are not included in Table 1;
  • revise the specifications for mixtures;
  • update terminology.

The purpose of revision 3 was to amend sections 3.0 and 5.0 to replace the reference to LMB-EG-08 with a reference to S-G-03.

The purpose of revision 2 was to:

  • amend section 6.1 to remove the word "rolled";
  • amend section 5.0 to remove the recommended maximum value for hydrocarbon dew point.