© 2019 Department of Petroleum Resources. All rights reserved Department of Petroleum Resources (DPR) PROCEDURE GUIDE

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Maximum Peak to Peak Error: ±1 .0% for qt ≤qi ≤qmax
±1 .4% for qmin ≤qi ≤qt
qt is the transition gas flow rate below which the expanded error limit is applicable
qi is the actual gas flow rate passing through a UM under a specific set of test conditions
qmin is the minimum gas flow rate through the UM that can be measured within the
expanded error limit
qmax is the maximum gas flow rate through the UM that can be measured within the
expanded error limit.

1.15.8 ULTRASONIC METER INSTALLATION REQUIREMENT

1.15.8.1 Pressure taps
At least one pressure tap shall be provided for measuring the static pressure in the meter.
Each pressure tap hole should be between 1/8” and 3/8” nominal in diameter and cylindrical
over a length at least 2.5 times the diameter of the tapping, measured from the inner wall
of the meter body. The tap hole edges at the internal wall of the meter body should be free
of burrs and wire edges and have minimum rounding. For a meter body with a wall thickness
less than 5/16”, the hole should be 1/8” nominal in diameter. Pressure taps may be located
at the top, left side and/or right side of the meter body.
1.15.8.2 Piping installation
Both the upstream and downstream piping configuration (with or without flow
conditioners) shall be installed in such a way that the additional flow rate measurement
error shall not be more than ±0.3% due to the installation configuration.
1.15.8.3 Protrusions
No part of the upstream gasket or flange face edge shall protrude into the flow stream more
than 1% of the internal diameter to minimize flow disturbances especially at the upstream
flange. However, thermowells are excluded from the protrusion limit.
1.15.8.4 Meter body length and bores
The UM bore and the adjacent upstream pipe along with the flanges should have the same
inside diameter to within 1% of each other.
1.15.8.5 Thermowells
For unidirectional flow, the thermowell should be installed downstream of the meter. The
thermowell should be located at least 6 inches from the flange weld or 2 ND whichever is
larger, and no farther than 5 ND from the downstream USM flange face.
The recommended insertion length for thermowells and sample probes is between 1 /3 ND
to 1 /2 ND for line sizes NPS 2 to NPS 1 0 and 1 /5 ND to 1 /3 ND for line sizes NPS 12 and larger.
Special thermowell design may be required for insertion lengths greater than 1 /3 ND.
1.15.8 Environmental consideration
Factors such as temperature, vibration and electrical noise shall be taken into consideration.
Appropriate measures should be taken to mitigate extreme temperatures and excessive/
unnecessary vibration and electrical noise should be avoided