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

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1.1 ORIFICE PLATE INSTALLATION REQUIREMENT
1.2 INTRODUCTION
An orifice plate is a thin square-edged plate with a machined circular bore, concentric with
the meter tube ID, when installed.
1.3 General
The orifice meter shall consist of the following elements:
1.3.1 A thin, concentric, square-edged orifice plate – the faces of the plate shall always be
flat and parallel.
1.3.2 An orifice plate holder consisting of a set of orifice flanges (or an orifice fitting)
equipped with the appropriate differential pressure sensing taps;
1.3.3 A meter tube consisting of the adjacent piping sections (with flow conditioners).
1.4 Flange taps
1.4.1 The upstream tap center shall be located 1 inch. (25.4 mm) upstream of the nearest
plate face.
1.4.2 The downstream tap center shall be located 1 inch. (25.4 mm) downstream of the
nearest plate face
1.4.3 The upstream and downstream taps shall be in the same radial direction

1.5 Temperature measurement
The flowing fluid temperature (Tf) shall be measured at the designated downstream
location (as specified in API MPMS Ch. 14.3, Part 2/AGA Report No. 3, Part 2. by placing a
temperature sensing device in the middle of the flowing stream to obtain the flowing
temperature in deg. Celsius. The thermowells shall be placed on the downstream side of the
orifice and neither closer to the plate than dimension DL and farther from the plate than
dimension 4DL as shown in table 7, 8a and 8b in API MPMS 14.3.2/AGA report No.3 Part 2.
Adequate sections of the meter run upstream and downstream of the thermowell should
be thermally isolated to ensure that indicated temperature readings reflect the temperature
of the flowing fluid and not the effects of the ambient conditions of the pipe surrounding
the thermowell.
Thermowell length shall not be longer than the length obtained by the formula below and
not shorter than 1/3 of the pipe ID.
𝐿= {𝐹𝑚. 4.38 𝑋 𝑂𝐷 𝑋 10
𝑆 𝑋 𝑉
√[𝐸
𝜌(𝑂𝐷2 + 𝐼𝐷2)]}
1
2

Where

L =
Probe length in mm
Fm =
virtual mass factor; a constant to take account of the extra mass of the cylinder due
to the fluid surrounding it and vibrating with it, for gas, Fm=1.0, for water and other liquids,
Fm=0.9
OD = Outside diameter of the probe in mm