Study of Orifice Flow Metering for SCADA in Compact Natural Gas Regulator Stations

Flow measurement is a key part of Pacific Gas & Electric Company (PG&E) gas distribution SCADA implementation plan. It will help build accurate hydraulic models for Gas Planning enabling simulation and analysis of complex existing hydraulic systems and predict failure scenarios. Installing flow metering equipment in existing below ground regulator stations with short pipe runs is a challenge as most meters require several diameters of straight pipe. For our application; accuracy, reliability, water resistance and reasonable maintenance cycles are key criteria in choosing the right meter. These limiting requirements made the Emerson 405C flow conditioning orifice meter with its compact profile and short pipe runs a good candidate, the challenge was to install the flow meter in very compact stations that do not meet the minimum pipe run requirements for the meter and achieve the required accuracy established by PG&E Gas Control on the SCADA system. This paper will focus on analyzing the accuracy under specific conditions of an Emerson 4” 405C Beta 0.65 orifice meter in two configurations established by the research team, the first located at 2 pipe diameters downstream of a 4” gas filter and the second close coupled downstream of the filter, both configurations are tested with a clean filter and partially plugged. The results obtained are under the maximum percent error established and provide the flexibility to install this type of meters in most of existing below ground PG&E regulator stations with minimum piping modifications.