UFC 3 -430-11
14 February 2001
in a horizontal run cannot be avoided then use a segmental or eccentric
orifice plate.
Use a concentric, square-edge orifice plate located in a vertical run with flow
in the upward direction for liquids containing gas or vapor. Use a segmental
or eccentric orifice plate with the opening at the top if locating the orifice
plate in a horizontal run cannot be avoided.
5-2.8.2.1 Design. Meter runs should be a minimum pipe diameter of 5.08 centimeters
(2 inches). Do not use an orifice bore diameter of less than 12.7 millimeters (0.5 inch)
due to the possibility of plugging. Do not locate orifices where a liquid is subject to
flashing.
Select the orifice plate maximum design flow and meter differential to give a
scale reading of approximately 70 percent at normal flow. Use a meter differenti al of
2.54 meters (100 inches) of water unless not practical.
The orifice plate beta ratio should be between 0.25 and 0.70 and preferably
between 0.4 and 0.6. The beta ratio must never be less than 0.20. Do not exceed a
beta ratio of 0.70 for gases or steam and 0.75 for liquids.
5-2.8.2.2 Mounting. Mount the transmitter near the orifice flanges. Use flange taps
whenever practical. Specify orifice flange and taps in accordance with ASME B16.36,
Orifice Flanges. Flange taps are well suited for pipe sizes of 5.08 centimeters (2
inches) and larger. Provide meter taps at the top of the flange for gas service in
horizontal lines. Provide meter taps on the sides of the flange for steam, vapor and
liquid service in horizontal lines. Mount the meter below the orifice taps for liquid and
steam service and above the orifice taps for gas service. Provide a separate three-
valve type manifold for each meter. Provide condensate traps for both the high and low
pressure sensing lines for steam and condensate service lines.
5-2.8.2.3 Construction. Use 304SS material as a minimum for the orifice plate.
Provide an identification tab projecting beyond the orifice flange. Show the following
minimum information on the tab.
Actual measured orifice bore
Pipe i nside diameter
Orifice plate material
Orifice plate orientation to flow
Type of fluid
5-2.8.3 Flow Nozzles. Use flow nozzles for applications where a higher accuracy is
required than using orifice plates.
5-2.8.4 Venturi Tubes. Use venturi tubes for applications where higher accuracy,
lower pressure drop and shorter meter run are required than using orifice plates or flow
nozzles.
5-5
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