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They reliably meet or exceed demanding accuracy standards
H. DECKER, Nafta Krohne Oil & Gas, Houston, Texas
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Due to significant accuracy improvements during the past decade, multipath ultrasonic flowmeters are the fastest growing flowmeter technology, gaining wider usage in the petroleum industry for liquid hydrocarbon custody transfer measurement (Fig. 1). With the introduction of enhanced signal processing and multiple channel design, multipath ultrasonic flowmeters consistently and reliably meet or exceed the demanding accuracy standards required for oil custody transfer metering and fiscal accounting (less than 0.2% of measured value).
Fig. 1
Ultrasonic flowmeters are gaining wider acceptance for liquid hydrocarbon custody transfer measurement.
Unlike traditional technologies such as turbine, Coriolis and positive displacement (PD) meters, ultrasonic flowmeters contain no moving parts and do not require frequent recalibration and maintenance. They also do not need to be protected by expensive and maintenance-intensive strainers that cause pressure drops and necessitate more pumping power. Ultrasonic flowmeters also perform better in large line sizes with high flowrates. Therefore, they require less piping, fewer valves and other components, and reduced maintenance and floor space. Alternative technologies require that large pipelines be split into multiple parallel measuring sections.
A factor inhibiting growth of multipath ultrasonic flowmeters has been the relatively high purchase cost of the meter. However, when all related costs and savings are considered, the ultrasonic technology proves to be not only the most reliable and accurate option, but also the most economical alternative for many oil custody transfer applications.
Measurement theory. Ultrasonic flow measurement by the differential transit-time method is now one of the most universally applied flowmetering processes. It is used for measuring cryogenic liquids, hot liquids, gas and steam up to 500[degree(s)]C and above. The theory of transit-time differential measurement is quite simple. One transducer transmits a signal downstream with the flow, and...