P-G-18—Procedure for the verification and reverification of gas chromatographs pursuant to the requirements of PS-G-18

Category: Gas
Issue date: 2017-08-01
Effective date: 2017-08-01
Revision number: N/A
Supersedes: Class 12 inspection procedure—Gas Analyzers


Table of Contents


1.0 Purpose

This inspection procedure provides instructions for the verification and reverification of gas chromatographs pursuant to the requirements of PS-G-18. This procedure applies 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 Definitions

Refer to PS-G-18 for definitions of terms that may be relevant to this inspection procedure.

3.0 References

4.0 Safety

4.1 Measurement Canada's health and safety policy

The inspector should be aware of and fully conform to MC's health and safety policy including the provisions specifically relating to the following:

4.2 Contractor's and third party's safety and security requirements

Subject to the policy established in GEN-16, the inspector should be aware of and conform to the contractor's and any third party's safety and security requirements that are applicable to the work site.

4.3 Potential hazards

The inspector should be aware of the following potential hazards which may exist during transport to and from the work site and while at the work site:

4.4 Contractor's responsibilities

The contractor's representative is responsible for the following:

5.0 Inspection apparatus

5.1 Certified gas mixtures

Two MC gas mixtures selected and certified as specified in PS-G-18.

5.2 Additional equipment

The following additional equipment is required:

6.0 Inspection worksheet

The inspection worksheet referred to in this procedure may be obtained by contacting any of MC's electricity and gas regional offices.

7.0 Assessment of conformity with administrative requirements

7.1 General

Obtain and review the gas chromatograph's notice of approval.

7.2 Nameplate information and markings

  1. Examine the gas chromatograph and assess its conformity with the marking requirements of PS-G-18.
  2. Record the gas chromatograph's required markings and any nonconformity with the specified requirements on the inspection worksheet.

8.0 Assessment of conformity with technical requirements

8.1 Device construction and condition

  1. Examine the gas chromatograph and assess its conformity with the construction and condition requirements of PS-G-18.
  2. Record any nonconformity on the inspection worksheet.

8.2 Firmware and external software versions

  1. Confirm that the gas chromatograph's installed firmware version and, where applicable, external software version are approved for use in trade, as identified in the notice of approval.
  2. Record the installed firmware and software versions and any nonconformity on the inspection worksheet.

8.3 Energy density and relative density calculations

  1. Confirm that the gas chromatograph calculates energy density and relative density using an approved standard, as identified in the notice of approval.
  2. Record the standard method of calculation in use and any nonconformity on the inspection worksheet.

9.0 Assessment of conformity with metrological requirements

9.1 General

  1. This assessment involves performance testing of the gas chromatograph's accuracy and repeatability.
  2. Ensure the calibration certificates for the two gas mixtures are still valid and correctly paired with their associated cylinders.
  3. Ensure the gas mixtures have been selected and are used in accordance with the requirements of PS-G-18 and any conditions documented in their calibration certificates.

9.2 Test equipment set-up

  1. Remove the protective cover and fitting from the inlet to the selected gas mixture cylinder.
  2. Inspect the regulator inlet and cylinder valve outlet for foreign matter and ensure that the regulator has the proper connection for the valve outlet.
  3. Inspect the regulator and valve outlet for external corrosion, damaged threads, dirt, dents, gouges and general condition.
  4. Start turning the nut on the regulator inlet by hand to prevent cross threading and keep in mind that the connection has a left-hand thread.
  5. Tighten the regulator inlet connection with a flat-faced wrench, taking care not to force the threads or over tighten.
  6. Ensure that the regulator is shut off by turning the pressure adjusting screw counter-clockwise until it turns freely.
  7. Attach the appropriate fittings to the regulator outlet and connect the low pressure tubing or piping to the regulator outlet.
  8. Instruct the contractor's representative to connect the tubing to route the certified gas mixture to the gas chromatograph's sampling system. Ensure that the tubing is properly purged prior to final connection and tightening.
  9. Instruct the contractor's representative to pressurize the tubing using the regulator's pressure adjusting screw and check for any leaks. Ensure that the pressure does not exceed the pressure rating of the tubing or the gas chromatograph under test.
  10. Instruct the contractor's representative to isolate the gas chromatograph from the line gas supply. It is important to ensure that the gas chromatograph receives an uninterrupted supply of gas during the transition from line gas to the certified gas mixture.

    Note: This step may be omitted for laboratory gas chromatographs used to analyze gas samples in sample cylinders.

9.3 Performance testing

  1. Ensure that the gas chromatograph is in its normal operating mode.
  2. Instruct the contractor's representative to set the gas chromatograph to analyze the certified gas mixture.
  3. Observe the reported nitrogen content in relation to the certified value. The system may not have been sufficiently purged or there may be a leak if the reported nitrogen content fails to stabilize to the certified value. As required, instruct the contractor to make any necessary corrections.
  4. Once the reported nitrogen content is repeatable and compares well to the certified value, proceed with performance testing.
  5. Request the results for the next two consecutive sample analyses.
  6. Record the energy density and relative density from the gas mixture's calibration certificate on the inspection worksheet while ensuring the units of measure match those of the gas chromatograph's indicated and/or auxiliary output signal values being verified.
  7. Record the gas chromatograph's indicated and/or auxiliary output signal values for energy density and relative density from the results of each analysis on the inspection worksheet.
  8. Where the gas chromatograph is approved for multiple systems (e.g. metric, imperial) and units of measure for energy density and relative density, perform steps (f) and (g) for each approved unit of measure that is indicated and/or outputted.
  9. Calculate the relative error of each of the gas chromatograph's indicated and/or auxiliary output signal values for energy density and relative density and record the results to the nearest 0.1% on the inspection worksheet.
  10. Using the gas chromatograph's indicated and/or auxiliary output signal value results from the two consecutive analyzes, calculate the difference between corresponding mole % values for each gas component and compare each result to the applicable repeatability limit specified in PS-G-18.
  11. Record the conformance status (i.e. accepted or rejected) of the gas chromatograph's energy density accuracy, relative density accuracy and repeatability results for the gas mixture on the inspection worksheet. Unacceptable accuracy or repeatability results may indicate problems in the test equipment set-up or a deficiency in the device under test.
  12. Instruct the contractor's representative to return the line gas supply to the gas chromatograph, if applicable.
  13. Repeat the steps in section 9.2 for the second certified gas mixture cylinder and then repeat steps (a) to (l) of this section.
  14. Determine the overall conformance status of the gas chromatograph in relation to all specified requirements and record the result on the worksheet.
  15. Where the gas chromatograph has failed to conform to the specified performance requirements, the contractor's representative may make any necessary adjustments. Repeat all required performance testing in accordance with sections 9.2 and 9.3 and record all As Left results on the same inspection worksheet or a new one.

    Note: Where conformity with specified performance requirements cannot be achieved, the gas chromatograph cannot be used for custody transfer or trade purposes until it has been corrected and reverified.

  16. Upon completion of all performance testing, instruct the contractor's representative to return the line gas supply to the gas chromatograph, if applicable.

10.0 Sealing

Refer to PS-G-18 for the requirements pertaining to the sealing of conforming gas chromatographs.

11.0 Inspection certificate

Complete and issue an inspection certificate in accordance with GEN-27 and section 21 of the Electricity and Gas Inspection Regulations.

12.0 Fees

Charge the fee for the inspection of a chromatograph at the operational location as established in Schedule 1, Part IV, of the Electricity and Gas Inspection Regulations.

13.0 Nonconformity and defect reporting

Report details of any nonconformity or defects identified during the inspection to the regional gas specialist for review and follow-up.

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