Gas Flow Rate Calculator (Weymouth)
Unit: psig (Gauge Pressure)
Unit: psig (Gauge Pressure)
Unit: inches
Unit: feet
Natural Gas ≈ 0.6, Air = 1.0
Unit: °F
Estimated Gas Flow Rate
0
SCFD (Standard Cubic Feet per Day)
0
SCFH (per Hour)
0
Pressure Drop (psi)
How to Calculate Gas Flow Rate in a Pipe
Calculating the flow rate of gas through a pipeline is a critical task in engineering, particularly for the oil and gas industry, HVAC systems, and industrial process piping. Unlike liquids, gases are compressible, meaning their density changes significantly with pressure and temperature. This makes the calculation more complex than simply multiplying area by velocity.
The Weymouth Equation
This calculator utilizes the Weymouth Equation, widely accepted for high-pressure gas gathering and transmission lines. It is particularly accurate for pipes with large diameters (typically 6 inches or larger) and high pressure flows, though it provides reasonable estimates for smaller high-pressure lines as well.
The core variables involved in the calculation include:
- Pressure Differential (P₁ – P₂): The driving force of the flow. Gas moves from areas of high pressure to low pressure. The greater the difference, the higher the flow rate.
- Pipe Diameter (D): The internal diameter of the pipe affects flow capacity exponentially. Even a small increase in diameter can drastically increase flow volume.
- Pipe Length (L): Friction acts against the flow. The longer the pipe, the more pressure is lost to friction, reducing the flow rate at the outlet.
- Specific Gravity (G): This compares the density of the gas to air (which is 1.0). Natural gas is typically lighter than air, with a specific gravity around 0.60.
Calculation Logic and Assumptions
To provide a standardized result, the calculation converts all inputs into absolute units (psia for pressure and Rankine for temperature) before processing. The formula assumes:
- Standard conditions of 60°F and 14.73 psia.
- A compressibility factor (Z) of approximately 0.9 (typical for natural gas).
- Pipeline efficiency of 0.92 (standard for new steel pipes).
Example Calculation
Consider a scenario involving a natural gas line:
- Inlet Pressure: 100 psig
- Outlet Pressure: 80 psig
- Pipe Diameter: 4.026 inches (Nominal 4″)
- Length: 1000 feet
Using these parameters, the gas expands as pressure drops, and the friction along the 1000-foot length limits the velocity. The calculator performs the complex integration of these variables to output the flow in Standard Cubic Feet per Day (SCFD).
Note: This calculator is intended for estimation and planning purposes. Critical engineering designs should always verify results with detailed simulations considering elevation changes and specific gas compositions.