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In-Situ Gas Meter Proving
Due to state and federal regulatory priority for environmental protection,
gas flow in flare lines has been receiving greater attention. Errors in
gas flow rate measurement in industry result from changes in operating
conditions, improper installations, or degradation of meter performance
over time. After installation of flow meters, recalibrating the meter
has to be done one of three ways: remove the meter and send back to the
manufacturer, install another calibrated meter in a bypass arrangement
so that the calibrated meter can check the flow to see if the installed
meter is correct; measure the flow through the in-situ meter with a tracer
gas and compare to the meter reading.
Tracerco has developed an in-situ gas meter proving method that will
reduce errors in flow rate measurements, especially in natural gas transmission
and refinery flare systems. This flow measurement method has been validated
at an independent commercial scale pipeline metering facility using the
Pulse Velocity Technique. The tracer technology was tested on 4-in and
12-in natural gas pipelines at seven gas flow velocities ranging between
1-122 ft/s. The average difference was less than 1%, compared with the
reference velocity of NIST traceable mass flow rate. With the new method
a small amount of isotope tracer is injected into the upstream pipeline,
and one or more pairs of radiation detectors are placed along the line
to measure the tracer time of flight, from which the gas velocity can
be calculated. Different from liquid flow, gas flow frequently involves
faster linear rates and shorter transit times. Properly designed procedures
for the signal capture and analysis plays an important role in the meter
proving accuracy and repeatability. This method can serve as an independent
verification that data reported for environmental or custody transfer
purposes are correct.
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