Natural Gas Pipeline Weymouth Capacity Calculator
Size high-pressure transmission lines and determine gas flow rate in MMCFD and SCFH using the industry-standard Weymouth hydraulic equation.
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The Weymouth Natural Gas Flow Formula
The Weymouth equation is the classic industry benchmark formulation for designing high-pressure, large-diameter natural gas transmission pipelines. It assumes steady-state compressible flow and incorporates a built-in empirical friction factor approximation that makes friction inversely proportional to the sixth root of internal pipe diameter (f ∝ 1 / d^(1/3)).
Mathematical Formulation
Under standard standard base conditions (Base temperature Tb = 520 °R [60°F], Base pressure Pb = 14.73 psia), the Weymouth equation is expressed as:
Where:
- Q = Gas flow rate in Standard Cubic Feet per Day (SCFD)
- P1 = Inlet absolute pressure (psia)
- P2 = Outlet delivery absolute pressure (psia)
- d = Pipe inside diameter (inches)
- G = Specific gravity of gas relative to air (air = 1.00; methane ≈ 0.55 - 0.65)
- Tf = Average flowing gas temperature in Rankine (°R = °F + 459.67)
- L = Pipeline length (miles)
Frequently Asked Questions
When is the Weymouth equation used instead of Panhandle A or B?
The Weymouth equation is primarily used for short to medium high-pressure transmission and gathering pipelines with small to medium diameters (under 24 inches) where relative wall roughness creates fully turbulent flow. For very large transmission lines (30-42 inches) over long distances, Panhandle A/B or Modified Colebrook equations are often compared.
What is MMCFD in gas measurement?
MMCFD stands for Million Standard Cubic Feet per Day. In natural gas commerce, "M" denotes 1,000, and "MM" denotes 1,000,000. One MMCFD of pipeline-quality natural gas (1,020 BTU/SCF) provides approximately 1,020 MMBtu of heating energy per day.
What is the erosional velocity limit in gas pipelines?
Per API RP 14E, the maximum erosional velocity limit is calculated as Ve = C / √(ρ), where C is typically 100 for continuous solid-free service and ρ is the flowing gas density. In practical dry natural gas pipelines, operators maintain operating velocities between 10 and 40 ft/s to avoid noise, valve throttling turbulence, and pipe erosion.
Why must pressures be converted to PSIA?
Compressible gas equations require absolute thermodynamic pressure (psia = psig + atmospheric pressure ∼14.7 psi). Calculating with gauge pressure creates massive errors, particularly when delivery pressures are low.