PRCI

Recent Results

Evaluation of Clamp-On Ultrasonic Meters as In-Situ Meter Verification Tools

A variety of meter types is used by the natural gas industry to measure the volume of gas transported through pipelines. To ensure accurate measurement and avoid costs associated with lost-and-unaccounted-for gas, these meters must be verified (or proved) periodically. Field proving of a meter, however, requires measurements with a highly precise reference device, as well as correct installation of the meter and related test instrumentation.

Ultrasonic flow meters were introduced to the natural gas industry for custody transfer measurements a decade ago.  Attributes of ultrasonic flow meters include a relatively broad flow rate range compared to more traditional metering technologies, low pressure drop (when a flow conditioner is not used), and reasonably good measurement accuracy and repeatability. A more recent development in ultrasonic metering technology has been the clamp-on ultrasonic meter, which can be mounted on the outside of a pipe and sends and receives ultrasonic waveforms through the pipe wall. This device offers several advantages over the wetted sensor ultrasonic meters, including portability, the ability to be installed without shutdown and disassembly of the pipeline, and the use of electronic parameters to help determine the condition of the flowing gas and the accuracy and repeatability of measurements. Because of these features, clamp-on ultrasonic meters are being considered for their potential as diagnostic tools.

The objectives of this project were to:

  • Evaluate the reproducibility of measurements made with the clamp-on ultrasonic meter through repeated removals and re-installations of the meter.
  • Evaluate the ability of a commercially-available clamp-on ultrasonic flow meter to accurately diagnose natural gas flow conditions that can produce measurement errors in traditional natural gas meters.
  • Evaluate the ability of the clamp-on ultrasonic meter to quantify the errors in measurements made with traditional metering technologies under such adverse conditions.
Key Results

PRCI evaluated the accuracy and repeatability of commercially available clamp-on ultrasonic meters (USMs) when installed in a meter run incorporating another metering technology so as to verify the accuracy of the meter under test.

PRCI recommended that a performance baseline be established first in any conventional meter run in which a clamp-on ultrasonic flow meter is to be used for diagnostic purposes. The test should account for flow conditions specific to the conventional meter and more accurately track changes from these conditions. The baseline flow test should be performed under optimal flow conditions in the conventional meter run. The configuration of the clamp-on meter should be recorded as part of the baseline process.

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