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Ultrasonic Meter Accuracy Shifts Resulting From Grime on the Meter Body and Acoustic Transducers
In some applications where ultrasonic flow meters have been inspected and/or removed from service, evidence of a significant buildup of material on the piping and/or meter itself has been observed. This buildup consists of material that has accumulated on the interior surface of the pipe and meter over an extended period.
Previous PRCI research has quantified the accuracy shifts due to grime layers on the adjacent spools of an ultrasonic meter, grime on the flow conditioner, and wear on the flow conditioner. Changes in diagnostic indicators showed effects from grime present upstream of the meter. In general, accuracy shifts were relatively small; however, limited field tests from the past show significant accuracy shifts resulting from grime buildup on the meter body. Some tests suggest that meters with chordal paths respond differently from those with reflective paths. There is also a need to identify meter diagnostic measurements that can be correlated to changes in meter accuracy and to identify the magnitude of changes in the diagnostic measurements that are likely to indicate an unacceptable shift in meter accuracy. The rate of change of the diagnostic measurements may be useful in determining when filter/separation equipment should be added to maintain meter operation within acceptable limits.
The goal of this research was to quantify the ultrasonic meter accuracy shifts, of varying grime thicknesses and grime compositions, on the internal meter body and acoustic transducers, and to correlate any accuracy shifts with the diagnostic indicators of the flow meters. The approach was to evaluate the flow measurement performance of two commercially-available ultrasonic flow meters under conditions in which there were various levels of grime coating, coating types, and coating locations (i.e., transducers coated, meter body coated, and both transducers and meter body coated). The tests were performed under controlled conditions in the Southwest Research Institute Metering Research Facility High Pressure Loop and were designed to compare the baseline (uncontaminated meter) flow measurement performance of each meter to the performance attained with various levels of coating, compositions of coatings, and coating locations. Three compositions of grime simulants were formulated during this project to simulate actual grime buildup that was typically encountered in the field. The final report will be available to the PRCI membership late 3rd quarter of 2012.