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: 3
Supersedes: GS-ENG-06-12, version 2.0

Table of contents

1.0 Scope

The purpose of this document is to provide requirements for the selection and use of natural gas mixtures used in the determination of the performance of gas analyzers (gas chromatograph, calorimeter, densitometer, Therm-Titrator, etc.). This document does not address the selection or initial conditioning of gas cylinders.

2.0 Authority

These requirements have 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 meters, Ancillary Devices and Associated Measuring Instruments

4.0 Natural gas calibration mixture specifications

Unless otherwise authorized by Measurement Canada's Engineering and Laboratory Services Directorate, the natural gas calibration mixtures used to evaluate the performance of gas analyzers 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. The calibration gas must be accompanied by the expression of uncertainty and demonstrate its traceability to the International System of Units (SI). Natural gas mixtures must be 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 k=2 (95%) for gas composition 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.
  3. All gas components must be analyzed for accurate analytical heating value determination, with a target expanded uncertainty of ± 1.5 Btu/ft3 or better.

5.0 Composition of natural gas calibration mixtures

The natural gas calibration mixture composition must comply with the requirements of S-G-03 and any applicable specification that amends it.

Unless otherwise indicated or as may be authorized by Measurement Canada's Engineering and Laboratory Services Directorate, the typical composition of the mixture is outlined in the Typical Composition of Natural Gas Calibration Mixtures table.

Typical composition of natural gas calibration 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

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

6.2 Minimum use pressure

The minimum use pressure must be stated on the 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 cylinder.

7.0 Revisions

The purpose of revision 3 was to amend sections 3.0 and 5.0 to replace the reference to LMB-EG-08—Specifications for Approval of Type of Gas Meters and Auxiliary Devices with a reference to S-G-03. Measurement Canada has integrated the requirements of LMB-EG-08 into specifications S-G-03 (rev. 1). Therefore, LMB-EG-08 has become obsolete.

The purpose of revision 2 was to:

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