Ultrasonic Flowmeters for Liquid Hydrocarbon Custody Transfer ...

ARC Insights, Page 4
lems associated with temperature stability. In order to ensure API’s recommended
10,000 pulses per run, pulse interpolation is used to compensate
for the relatively small volume of product displaced in this type of prover.
Precise time determination and pulse counting provide high accuracy with
fewer pulses. The small proof volume of compact provers limits its applicability
to proving small ultrasonic meters in the plant and is unlikely to be
used for larger custody transfer pipeline applications.
Turbine Master Meters
Master Meter
Proving with a master meter involves using an alternate technology to
prove repeatability using a meter whose calibration has been previously
determined against a standard. This approach enables proving over any
length of time. A turbine metering run, for instance, would be incorporated
into the prover and calibrated on the specific process fluid. The output of
the ultrasonic meter is then synchronized with the pulses
from the turbine using the appropriate number of pulses to
provide adequate repeatability. Master meters are seldom
used for custody transfer applications since they may have
the same inherent problems as the meters proved. The master
meter adds another dimension of uncertainty to the
system that must be accounted for however the overall size
of the prover can be reduced.
Recommendations
• Oil industry users must decide if the benefits of ultrasonic technology
for custody transfer applications outweigh any additional time and cost
required to prove it according to the API standard. A cost-benefit
analysis may be required to make this determination.
• Suppliers need to lessen the burden of proof on their customers by developing
more efficient proving methods.
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