AGA 3: 1992

Concentric, Square-Edged Orifice Meters

This standard calculates natural gas flow through a flange-tapped, concentric orifice meter.


Corrected Internal Pipe Diameter


Corrected Internal Pipe Diameter

Symbol Description Units
D Corrected internal pipe diameter in
D0 Pipe diameter at calibration> in
λD Linear coefficient of thermal expansion /°F
t0 Pipe/orifice calibration temperature °F
t1 Upstream temperature °F

Corrected Internal Orifice Diameter


Corrected Internal Orifice Diameter

Symbol Description Units
d Corrected internal orifice diameter in
d0 Orifice diameter at calibration in
λD Linear coefficient of thermal expansion /°F
t0 Pipe/orifice calibration temperature °F
t1 Upstream temperature °F

Beta Ratio


Beta Ratio

Symbol Description Units
β Beta ratio -
d Corrected orifice internal diameter in
D Corrected pipe internal diameter in

Velocity of Approach Factor


Velocity of Approach Factor

Symbol Description Units
E Velocity of approach factor -
β Beta ratio -

Expansion Factor


Expansion Factor

Or if the downstream pressure is measured the equation is as follows -

Expansion Factor Downstream

Symbol Description Units
ε Expansion factor -
β Beta ratio -
Δp Differential pressure in H20@60°F
Pf Upstream/downstream pressure Psia
k Isentropic exponent -

Mass Flowrate


Mass Flowrate

Symbol Description Units
qm Mass flowrate lb/hr
Cd Coefficient of discharge -
E Velocity of approach factor -
ε Expansion factor -
d Orifice diameter at the upstream temperature in
Δp Differential pressure in H20@60°F
P1 Upstream pressure Psia

Coefficient of Discharge


Coefficient of Discharge

Note: If meter tube diameter is greater than or equal to 2.8 inches, M, is equal to 0.0. Else if the meter tube diameter is less than 2.8 inches, M, = 2.8 - D.

Coefficient of Discharge

Symbol Description Units
Cd Coefficient of discharge -
Ci Coefficient of discharge at an infinite Reynolds number for a flange-tapped orifice meter -
Ci(CT) Coefficient of discharge at an infinite Reynolds number for a corner-tapped orifice meter -
D Pipe internal diameter at upstream temperature in
β Beta ratio -
ReD Reynolds number -
L1 Flange tapping quotient -
L2 Flange tapping quotient -

Reynolds Number - From Fluid Density


Reynolds Number - Fluid

Symbol Description Units
ReD Reynolds number -
qm Mass flowrate lb/hr
µ1 Dynamic viscosity lb/ft.s
D Internal pipe diameter at the upstream temperature in

Reynolds Number - From Real Gas Relative Density


Reynolds Number - RD

Symbol Description Units
ReD Reynolds number -
qvs Standard Volume flowrate Sft3/hr
Pb Standard Pressure Psia
RD Relative Density -
µ1 Dynamic viscosity lb/ft.s
D Internal pipe diameter at the upstream temperature in
Tb Standard Temperature °R

Constant Description Value Units
Zair Compressibility of Air at 60F 0.99959 -

References