PS-G-18—Provisional specifications for the verification and reverification of gas chromatographs

Category: Gas
Issue date:
Effective date:
Revision number: N/A
Supersedes: N/A


Table of contents


1.0 Scope

These provisional specifications apply to online and laboratory gas chromatographs approved by Measurement Canada (MC) to perform compositional analyses of natural gas samples and calculate their resulting energy density and relative density values for use in trade and custody transfer metering applications.

2.0 Authority

These specifications are issued under the authority of section 18 of the Electricity and Gas Inspection Regulations.

3.0 References

4.0 Definitions

Auxiliary output signal (signal de sortie auxiliaire)

An output signal that supplies information to an auxiliary device other than a dedicated recorder intended for use with the gas chromatograph.

Base pressure (pression de base)

For the purposes of these specifications, the pressure, as expressed in the metric or imperial system of units, to which a particular gas property (e.g. energy density, relative density) is referenced.

Base temperature (température de base)

For the purposes of these specifications, the temperature, as expressed in the metric or imperial system of units, to which a particular gas property (e.g. energy density, relative density) is referenced.

British thermal unit (unité thermique britannique)

A unit of energy established in the imperial system of measurement. One British thermal unit is the amount of energy required to raise the temperature of 1 lb of water by 1 °F. Since the specific heat of water varies with temperature, a British thermal unit is further defined by its reference temperature, for example, BTU(60.5).

BTU(60.5)

The British thermal unit prescribed by the Electricity and Gas Inspection Act as a legal unit of measure for the sale of gas by energy units in Canada. One BTU(60.5) is the quantity of energy that must be added to one pound avoirdupois of distilled water to raise its temperature from 60 °F to 61 °F under standard pressure.

BTU(IT)

The International Table British thermal unit as adopted by the Fifth International Conference on the Properties of Steam (London, 1956). The conference defined one BTU(IT) as being equal to 1055.056 joules.

Energy density (énergie volumique)

The number of energy units per unit of volume at a certain temperature and pressure. Energy density is formally known as calorific power or heating value. It is expressed in British thermal units per cubic foot (BTU/ft³) in the imperial system or in megajoules per cubic meter (MJ/m³) in the International System of Units (SI).

Laboratory gas chromatograph (chromatographe en phase gazeuse de laboratoire)

A gas chromatograph located at a test facility and used to analyze gas samples taken in situ.

Online gas chromatograph (chromatographe en phase gazeuse en ligne)

A gas chromatograph located at a metering station and whose sampling system is connected directly to a flowing gas pipeline to provide for continuous analysis of flowing gas quality. It is capable of transmitting the molecular composition, energy density and/or relative density of each gas sample to one or more auxiliary devices (e.g. flow computer).

Operational location (lieu d'exploitation)

The location (e.g. metering station, test facility, laboratory) at which a particular metering device or piece of equipment is installed and used.

Relative density (densité relative)

The ratio of the density of a gas to the density of air, each referenced to the same conditions of pressure and temperature (e.g. base conditions). Relative density may also be referred to as specific gravity within the natural gas industry.

Relative error (erreur relative)

The ratio of the absolute error of the quantity registered or indicated by the device under test to the actual or conventional true value of the quantity as shown in the following equation:

Relative error = (R - T) ÷ T × 100%

Where,

  • R is the quantity registered or indicated by the device under test
  • T is the actual or conventional true value of the quantity
Reverification (revérification)

The subsequent confirmation of a meter's conformance to legal requirements following the expiration of its initial or subsequent reverification period.

Verification (vérification)

The initial confirmation of a meter's conformance to legal requirements.

5.0 General

5.1 Mandatory verification and reverification

Except where otherwise authorized, all gas chromatographs used in trade or custody transfer applications are subject to mandatory verification and reverification.

5.2 Inspection location

Inspection and testing of the gas chromatograph, for the purposes of verification or reverification, is to be conducted in situ at the chromatograph's operational location.

5.3 Verification triggering events

Any exchange of a verified gas chromatograph's hardware components or its firmware/software versions is deemed to be a verification triggering event and is to be reported by the contractor or device owner to the local Measurement Canada district or regional office.

6.0 Administrative requirements

6.1 Marking requirements

6.1.1 General

The gas chromatograph is to be marked in full accordance with all applicable location, legibility and marking requirements of specification S-G-03 and with any additional marking requirements included in the notice of approval. Where the markings section of the gas chromatograph's notice of approval makes reference to particular clauses of specification LMB-EG-08, these are superseded by the requirements of specification S-G-03.

6.1.2 Notice of approval number

Gas chromatographs manufactured prior to July 1987 are not required to be marked with their applicable notice of approval number.

6.2 Sealing requirements

Verified and reverified gas chromatographs are to be sealed in accordance with the provisions of their notice of approval and specification PS-EG-02, as applicable. Where no sealing provisions are included in the notice of approval, a verification marking is to be applied in a visible location of the gas chromatograph.

6.3 Reverification periods

The initial and subsequent reverification periods for gas chromatographs are as prescribed in bulletin G-18.

7.0 Technical requirements

7.1 General

The gas chromatograph is required to:

7.2 Leakage

Any portion of the gas chromatograph that is intended to contain gas is required to operate without leakage at any pressure up to its maximum rated operating pressure.

7.3 Firmware versions

The gas chromatograph is to be installed with an approved firmware version, as identified in its notice of approval.

7.4 External software versions

As applicable, any external software being used with a gas chromatograph to perform energy density and relative density calculations is required to be approved for that purpose, as identified in its notice of approval.

7.5 Energy density and relative density calculations

The gas chromatograph or the external software identified in its notice of approval is required to calculate energy density and relative density in accordance with an approved standard, as identified in its notice of approval.

8.0 Metrological requirements

8.1 Certified gas mixtures

Performance testing of the gas chromatograph requires two gas mixtures of known composition, energy density and relative density that are:

8.2 Performance requirements

8.2.1 Performance tests

Each of the certified gas mixtures are to be analyzed by the gas chromatograph under test. The gas chromatograph's accuracy and repeatability are to be assessed based on its results for two consecutive analyses of each of the certified gas mixtures.

8.2.2 Accuracy determination

The gas chromatograph's accuracy is to be determined based on its indicated and approved auxiliary output signal values of energy density and relative density for each performance test specified in 8.2.1.

The actual or conventional true values of energy density and relative density, in the same units of measure as calculated by the gas chromatograph, are to be taken from each certified gas mixture's certificate of calibration.

8.2.3 Repeatability determination

The gas chromatograph's repeatability is to be determined based on the differences between the corresponding individual gas component concentrations of the two consecutive analyses for each certified gas mixture.

8.3 Maximum permissible error

8.3.1 Energy density

The accuracy, expressed as a relative error, of the gas chromatograph's indicated and approved auxiliary output signal values of energy density for all performance tests is not to exceed a maximum permissible error of ±0.5%.

8.3.2 Relative density

The accuracy, expressed as a relative error, of the gas chromatograph's indicated and approved auxiliary output signal values of relative density for all performance tests is not to exceed a maximum permissible error of ±1.0%.

8.4 Repeatability limits

The gas chromatograph's repeatability test results are not to exceed the applicable limits specified in Table 1. The applicable repeatability limit is based on the mole percent of the individual gas component, as documented on the particular gas mixture's certificate of calibration.

Table 1: Repeatability limits
Gas component (mole percent) Repeatability limit (mole percent)
0 to 1 0.03
Over 1 to 5 0.05
Over 5 to 25 0.15
Over 25 0.30
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