Gas & Liquid Custody Transfer Measurement
Typical: 0.55-0.70 (sweet gas), 0.70-0.90 (rich gas)
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Understand turbine meter principles, AGA 7 requirements, K-factor linearity, and installation best practices
Turbine meter sizing for natural gas involves converting standard flow (MMSCFD) to actual cubic feet per minute (ACFM) at operating pressure and temperature, then selecting a meter size whose capacity range encompasses the minimum and maximum flows. The flow velocity through the meter should be 15-70 ft/s for gas service per AGA Report No. 7.
The optimal velocity range for gas turbine meters is 15-70 ft/s. Below 15 ft/s, the meter may not spin reliably and linearity degrades. Above 70 ft/s, bearing wear accelerates and measurement accuracy decreases. Custody transfer meters should operate in the 20-50 ft/s range for best accuracy.
Rangeability (turndown ratio) is the ratio of maximum to minimum flow rate at which the meter maintains its specified accuracy. Standard turbine meters achieve 10:1 rangeability, while high-performance meters can achieve 20:1 or better. Higher rangeability means the meter can accurately measure a wider range of flow rates.
AGA Report No. 7 requires minimum 10 pipe diameters (10D) of straight pipe upstream and 5 pipe diameters (5D) downstream of the turbine meter. If fewer than 20D upstream is available, a flow conditioner (tube bundle or plate type) should be installed to remove swirl and velocity profile distortion.