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.
