Natural Gas Flow Calibrations
NIST provides calibration services for flow meters used in high pressure natural gas. The calibration flow range extends from 0.125 m3/s (7.5 × 103 L/min or 1.6 × 104 acfh) to 9 m3/s (2.7 × 105 L/min or 5.7 × 105 acfh) at a nominal pipeline pressure of 7500 kPa (1088 psi) and at ambient temperatures. Corresponding mass flow calibrations extend from 6 kg/s (13 lbm/s) to 585 kg/s (1290 lbm/s). The uncertainty for volumetric flow calibrations is 0.22% (k = 2) at the highest flow with increased uncertainties at lowest flow.
Flow calibrations are performed offsite at the Colorado Engineering Experimental Station Incorporated (CEESI) in Garner, Iowa. All calibrations are performed using turbine meter working standards that are traceable to NIST primary flow standards. The calibration process is under NIST's metrological control, meaning the turbine meters as well as all other auxiliary measurements (e.g., temperature, pressure, frequency, gas composition) are routinely calibrated by NIST using suitable transfer standards. To read more about the Natural Gas Flow Calibration Service, see NIST Special Publication 1081.
Ultrasonic flow meters are the most common meter type that is calibrated; however, many other flow meter types can also be calibrated (e.g., turbine meters, critical flow venturis, coriolis flow meters). Flow calibrations are performed in pipe sizes ranging from 30.48 cm (12 inches) to 76.2 cm (30 inches). In cases where the flow meter is installed in upstream and downstream piping lengths supplied by the customer, the associated flanges should be rated to withstand a minimum pressure of 10 MPa at ambient temperatures (i.e., flange ratings must be 600 lb or higher). Additionally, for safety reasons, customers must have all flange welds x-rayed and hydrostatically tested before shipping their flow meters for calibration.
We deliver a calibration report that includes an uncertainty analysis for the flow meter calibration factor. This uncertainty includes the uncertainty of the flow standards given above as well as uncertainties related to instrumentation associated with the meter under test and its reproducibility. A normal flow calibration includes five flow set points. For example, for an ultrasonic flow meter these five set points include five flows at 10%, 25%, 40%, 70%, and 100% of the meter full scale as well as a single point at the minimum flow (i.e., typically 0.76 m/s or 2.5 ft/s depending on meter type). At each of the five flows rates, five (or more) measurements are gathered to assess the flow meter repeatability. As a result, the tabulated data for the calibration are averages of five or more individual measurements. It is helpful if the customer specifies the flow set points and the instrumentation requirements of the meter (pressure, temperature, and full scales required). After completing the five set points three verification points are taken, typically between 20% and 80% of the full scale. Verification points compare the meter reported values after calibration coefficients have been installed to the flow measured by the turbine meter working standards. (Note, if the flow set points shown above are inadequate, the customer can select to distribute the five set points and verification point as desired).
Calibration fees for this and other services can be found in the Fee Schedule available online from the NIST Calibrations Website.
This calibration service must be scheduled in advance due to testing schedules at CEESI’s Iowa Facility.
To have your flow meters calibrated: