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Natural Gas Flow Calibration Service
Name(s) of Calibrations/SRMs/SRD/SRIs and any related programs:
NIST Special Tests for Natural Gas Flow (18080S)
Summary
The Fluid Metrology Group (FMG) maintains the national flow standard for high-pressure natural gas to ensure fairness and transparency in multimillion-dollar transactions involving the purchase and sale of natural gas. In these transactions, flow meters function like cash registers, precisely measuring and recording the flow of gas worth millions of dollars. Even a single inaccurate measurement in a high-pressure natural gas pipeline can result in significant financial losses.
NIST does not have the capacity or infrastructure to calibrate custody transfer flow meters at pipeline pressures of 7 MPa, so calibrations are conducted offsite at the CEESI-Iowa site shown in Fig. 1. The gas flow from a custody transfer station is directed into the CEESI facility, with Fig. 1A illustrating the flow path. Gas entering the facility is directed to the turbine meter building and measured by an array of nine NIST-traceable turbine meters arranged in parallel as shown in Fig. 1B. The flow exiting the turbine meter building is then directed into the calibration building shown in Fig. 1C, where flow meters used for custody transfer of natural gas are installed and calibrated. The facility handles volumetric flow rates ranging from 0.31 m3/s to 10.5 m3/s, or approximate mass flow rates from 12 kg/s to 540 kg/s. The uncertainty in the volumetric flow measurement ranges from 0.16% to 0.21% at the 95% confidence level, depending on the flow rate.
Description
The workhorses of the CEESI Iowa facility are the nine turbine meters in Fig. 1B. Each turbine meter is calibrated in its place of use and at its operating line pressure using a parallel array of critical flow venturis traceable to NIST’s 677 L Pressure-Volume-Temperature-time gas flow standard. The scale-up in flow and pressure results from a collaborative “boot-strapping process” between NIST and CEESI-Iowa, achieving a 12,000-fold increase in mass flow.
FMG monitors calibrations via a secure internet connection, processes the raw data, and generates the calibration reports. Measurements from auxiliary instrumentation (e.g., pressure transducers, temperature sensors, frequency counters) are traceable to NIST, and FMG maintains control charts for them. Flow measurements are periodically compared with those of other national metrology institutes through Key Comparisons to validate our Calibration and Measurement Capabilities.