PS-G-16—Provisional specifications for the verification, reverification, installation and use of conditioning orifice plates

Category: Gas
Specification: PS-G-16 (rev. 1)
Issue date:
Effective date:
Supersedes: PS-G-16

Table of contents

1.0 Scope

These specifications apply to the verification, reverification, installation and use of conditioning orifice plates (COPs) and related meter run assembly components.

2.0 Authority

These specifications are issued under the authority of sections 12 and 18 of the Electricity and Gas Inspection Regulations.

3.0 References

4.0 Definitions

Conditioning orifice plate (plaque à orifices tranquillisante)

A multi-hole orifice plate designed to simultaneously function as a differential pressure element and as a flow conditioner. Conditioning orifice plates are designed for use with meter tubes that are shorter in length than those used with conventional orifice plates.

Deviation (relative error) écart (erreur relative)]

The difference between the volume or flow rate measured by the meter under test and the volume or flow rate measured by a reference meter. Corrections must be made for the differences in gas pressure, temperature and compressibility between the two meters. The deviation shall be calculated as follows:

(Deviation i %) = [[(Q i) - (Q ref i)] × 100] ÷ (Q ref i)Footnote 1

Flow algorithm (algorithme d'écoulement)

The mathematical relationship used to transform the measured pressure differential in the meter to a mass flow or volumetric flow rate at metering conditions.

Linearity (linéarité)

The maximum difference between the meter's mean deviations and any of the error deviations for test points between the maximum and minimum rated flow rates, calculated as follows:

(Linearity i %) = [(Deviation i %) ÷ (Mean deviation %)] × 100%

Maximum flow rate (Qmax) (débit maximal)

The maximum rated flow rate of a meter, as specified in the meter's Notice of Approval (NOA).

Minimum flow rate (Qmin)

The lowest flow rate at which the meter's deviation is less than the maximum permissible error and the linearity is less than the maximum values prescribed in clause 5.1.3, as specified in the meter's NOA.

Maximum permissible error (erreur maximale tolérée)

The largest allowable deviation within the specified operational range of the meter.

Mean deviation (écart moyen)

The mean error of a meter, calculated as follows:

(Mean deviation %) = (1 ÷ n) x [(uppercase d1) + (uppercase d2) + … + (uppercase dn)]

Repeatability (répétabilité)

The largest spread of errors of a given meter when several successive measurements are performed at the same flow rate under the same operating conditions.

Reynolds number (Re) (nombre de Reynolds)

The dimensionless number equalling the ratio of inertial forces to viscous forces in closed pipe flow.

Specification limit (limite de specification)

The maximum error permitted for a meter's performance characteristic.

Test limit (limite d'essai)

The limit established when the specification limit is adjusted for the associated measurement uncertainty.

5.0 Metrological requirements

5.1 Accuracy tests

5.1.1 Subject to clause 5.1.3, initial verification tests shall be conducted on a suitable test mediumFootnote 2 at Reynolds numbers which are representative of the meter's intended use. Where Qmax cannot be achieved because of limitations of the test facility, the upper test flow rate shall be at least 0.4Qmax, and the meter shall be tested at least five flow rates approximately equally spaced between 0.1Qmax and the maximum flow rate attainable by the test facility.

5.1.2 When tested at a test facility, the COP shall be flow calibrated together with a metering section (i.e. upstream and downstream meter tubes, flow conditioner and any required plate carrier) supplied either by the test facility (laboratory) or the meter owner (customer). If the metering section is supplied by the test facility, the test facility shall provide an attestation that the components comply with the specification requirements set out in AGA Report No. 3, Part 2, 4th Edition (2000).

5.1.3 The maximum permissible error of the meter shall not exceed the following tolerances:


Where the meter's Qmax cannot be achieved, the errors of the meter shall not exceed the following tolerance limits:

Maximum permissible deviation = TL x Q attained ÷ Q max

5.2 Verification requirements

Subject to the requirements of section 6.2, the meter tubes, flow conditioner and plate carrier (used with conventional/universal type plates) or flange union (used with paddle type plates) shall be inspected to verify conformance with the specification and installation requirements of the AGA's Report No. 3, Part 2, 4th Edition (2000).

5.3 Reverification requirements

5.3.1 Dimensional reverification The requirements of section 5.2 shall apply. Where permitted by a NOA, the COP may be dimensionally reverified, provided that:

  1. The COP has been initially flow calibrated.
  2. The dimensions of the COP were measured and recorded at the time of initial verification.
  3. The measured dimensions are within the tolerances specified in the NOA.

5.3.2 Reverification interval

COPs shall be reverified in accordance with the applicable initial reverification period and subsequent reverification period prescribed in MC's bulletin G-18.

6.0 Technical requirements

6.1 Design, composition and construction

6.1.1 The COP shall be used in conjunction with an industry-approved standard orifice fitting.

6.1.2 The COP shall conform in every technical respect to the approved type as documented in the NOA.

6.2 Installation and use

6.2.1 General Unless otherwise stated in the NOApproval, the meter shall be installed either vertically or horizontally. In a vertically-installed meter, the gas shall flow downward. Where conditions of reverse flow may occur during meter usage, the installation shall include features to prevent reverse flow through the meter. The COP shall be installed such that the high and low pressure taps are located directly between two of the bore holes, perpendicular to the plane of the pipe. Where a meter is subject to flow pulsations and it has been shown that the meter's accuracy is affected by such disturbances, appropriate provisions shall be made to reduce the intensity of disturbances to a level that will not induce a measurement error greater than the MPE specified in clause 5.1.3. The meter shall not be used outside the range of ambient temperature for which it is approved. Where necessary, shelter and heaters or other arrangements shall be provided to ensure that this requirement is met. In the case of orifice fittings that include a second set of telemetry taps for redundant pressure measurements, these taps are not to be used. Plate carriers shall include a method to prevent the COP from rotating within the plate carrier during insertion. Methods may include tabs in the seal ring or a setscrew installed through the plate carrier.

6.2.2 Meter installation

The meter shall be installed in a manner consistent with the manufacturer's installation requirements and any other special installation requirements shall be set out in the NOA for the type of service that the meter is intended to be used.

6.2.3 Upstream meter tube length

Unless otherwise authorized by the NOA, a straight pipe equal in length to two times the nominal meter diameter shall be installed upstream of the meter.

6.2.4 Downstream meter tube length

Unless otherwise authorized by the NOA, a straight pipe equal in length to two times the nominal meter diameter shall be installed downstream of the meter. In cases where the thermowell is permanently installed in the downstream meter tube, the entire meter run, which includes the upstream and downstream straight pipes, must be calibrated as an integral system.

6.2.5 Meter alignment

The meter shall be installed in a manner consistent with the manufacturer's maximum permissible meter / meter tube step change and maximum permissible meter non-axial alignment as specified in the NOA.

6.2.6 Thermometer well

Unless otherwise authorized by the NOA, the thermometer well used for measuring the flowing gas temperature shall be installed between two and five diameters downstream of the metering element.

6.2.7 Flow computer

The flow computer used to calculate mass flow through the COP must be a model which has been type approved for use of the algorithms listed in the NOA.

7.0 Administrative requirements

7.1 Nameplate marking

The COP shall be marked in full accordance with the markings section of the NOA, without distorting the plate.

7.2 Verification marks

7.2.1 Upon verification and reverification, the COP, tubes and plate carrier shall each be marked with a verification mark, without distorting the plate. This may be done using a special steel punch designed to produce an imprint that uniquely identifies the meter verifier and the year of verification.

7.2.2 For paddle type plates, the verification mark shall be applied to the downstream side of the paddle handle. For conventional/universal type plates, the verification mark shall be applied on the downstream face, near the outer edge of the plate.

7.2.3 For orifice plate carriers, the verification mark shall be applied near the nameplate.

7.2.4 For meter tubes, the verification mark shall be applied on the outer edge of either flange or near the nameplate.

8.0 Revisions

The purpose of this revision is to move all approval requirements into S-G-03—Specifications for the approval of type of gas meters, ancillary devices and associated measuring instruments, supersede the reference to LMB-EG-08—Specifications for approval of type of gas meters and auxiliary devices by the reference to S-G-03. LMB-EG-08 has become obsolete. This revision also reformates to new formatting requirements.

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