Approved versions:
Basic (uncorrected), ETC (temperature compensated), PTZL (Pressure, Temperature, and Z
compensated) or Mini Max (integral
Mercury Mini Max corrector)
Orifice Metering Systems
Orifice
metering is approved for billing purposes, provided that the requirements
listed below are met and the utility submits an acceptable
In-Service Performance Plan to the Commissions Engineering Division.
Acceptable Engineering Standards:
üAmerican Gas Association Report No. 3: Orifice Metering of Natural Gas and Other Related Hydrocarbon Fluids,
Part 1: General Equations and Uncertainty
Guidelines
üAmerican Gas Association Report No. 3, Part 2: Specification and Installation Requirements
üAmerican Gas Association Report No. 3, Part 3: Natural Gas Application
Applicability:
Orifice meters shall be permissible in
applications where the uncertainty of the orifice meter is less than 1.0% for
all historical and/or expected sustained demand levels of gas flow. The uncertainty
of the orifice meter shall be calculated as specified by the American Gas
Association Report Number 3 (AGA 3), Part 1.The utility must demonstrate the uncertainty calculation result is less
than 1.0% for all expected sustained demand levels of flow. To ensure the
uncertainty requirements are met across the expected flow range, a stacked
differential pressure transducer arrangement may be used.
Installation and Specifications:
Each orifice meter
installation shall meet the geometrical, dimensional, and installation
requirements as specified by the AGA 3, Part 2 standard in effect at the time
of construction. Note that earlier editions of AGA 3 may have requirements that
affect the uncertainty of the orifice meter adversely, resulting in greater uncertainty.
Therefore, the AGA 3, Part 2 edition number must be greater than or equal to
the AGA 3, Part 1 edition number used to calculate uncertainty.
Calculation of flow
through the orifice meter shall be performed as specified by AGA 3 using
real-timedata for differential pressure, static pressure, and
flowing temperature. Specific gravity shall be measured and representative of
the gas flowing through the orifice meter. Orifice bore diameter and meter tube
diameter shall be used in calculating flow as specified by AGA 3.
