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Orifice Calc — Help Guide
Overview
Orifice Calc is designed to estimate natural gas flow rate (MCFD) using standard orifice-meter
calculations. The app incorporates compressibility corrections, flowing conditions, gas
composition inputs, and meter geometry to produce a reliable engineering estimate.
This tool is intended for field reference, troubleshooting, and estimation purposes.
Meter / Tap Setup
Meter Tube ID (inches)
Enter the internal diameter of the meter tube.
This value is used to calculate Beta ratio, which is required for orifice flow calculations.
Orifice Plate Bore (inches)
Enter the bore size of the installed orifice plate.
Together with Meter Tube ID, this determines:
Beta = Orifice Bore ÷ Meter Tube ID
Tap Location Type
Select the tap configuration used by the meter run:
● Flange taps
● Pipe taps
This affects expansion, Reynolds, and discharge-related corrections.
Tap Orientation
Select:
● Upstream
● Downstream
This selection impacts the Y-factor expansion correction.
Beta Section
Beta
The app automatically calculates:
Beta = bore ÷ meter tube ID
Beta Range
Recommended ranges:
● Flange taps: 0.15 – 0.70
● Pipe taps: 0.20 – 0.67
Operation outside these ranges may reduce accuracy.
Base / Gas Properties
These inputs define gas composition and base conditions used for compressibility and
correction factors.
Atmospheric Pressure (psia)
Local atmospheric pressure at the meter location.
This may be adjusted for elevation if desired.
Base Pressure (psia)
Standard base pressure used for measurement conversion.
Typical value: 14.73 psia
Base Temperature (°F)
Standard base temperature.
Typical value: 60°F
Gas Specific Gravity (air = 1.0)
Gas gravity relative to air.
Typical pipeline gas: 0.55 – 0.70
CO2 (mole %)
Carbon dioxide concentration in the gas stream.
N2 (mole %)
Nitrogen concentration in the gas stream.
Compressibility at Base (Z)
Compressibility factor at base conditions (Zb).
This value is used in the supercompressibility calculations.
Flowing Conditions
These represent real-time operating conditions.
Static Pressure (psig)
Line pressure measured at the meter.
Differential Pressure (inH2O)
Orifice differential pressure.
The app assumes inches of water column (inH2O).
Flow Temperature (°F)
Gas flowing temperature at the meter.
Calculation Button
Press:
Calculate Gas Rate (MCFD)
The app performs:
● AGA NX-19 supercompressibility calculations
● Expansion factor calculations
● Reynolds corrections
● Meter factor calculations
● Final volumetric flow computation
Results
The result field displays:
● Gas flow rate in MCFD
If required inputs are missing or invalid, the app will display:
“Waiting for input...”
Accuracy and Intended Use
Orifice Calc is designed to provide engineering-grade estimates using recognized calculation
methods. However, results depend on the accuracy of:
● Meter geometry
● Gas composition
● Pressure measurements
● Temperature measurements
Disclaimer
This application is provided for estimation and reference purposes only. Results should be
verified against company measurement standards, calibrated equipment, and official flow
calculation systems. The developer assumes no responsibility for decisions made using this software.
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