Gas pipeline flow capacity
Gas flow rate from the inlet and outlet pressures — the general isothermal flow equation with the Colebrook-White friction factor; gas velocity, average pressure, Reynolds number.
Q_st = (π · d² / 4) · (T_st / P_st) · √[(P₁² − P₂²) · d · R / (λ · L · Z · T · M)]M = 28.96 · γ_g g/mol; Re = 4 · ṁ / (π · d · μ); λ: Colebrook-WhiteP_avg = (2/3) · (P₁ + P₂ − P₁ · P₂ / (P₁ + P₂))Steady isothermal flow on a horizontal line; the kinetic energy change is neglected (negligible for sections longer than about 1 km). Z and T are section averages. Elevation matters for gas only in hilly terrain. With liquids in the gas (associated gas with condensate and water) the capacity is overstated.
Source: General flow equation (Menon E.S., Gas Pipeline Hydraulics, 2005); Colebrook-White formula
Inputs
You can change a field's unit: the value is converted to the formula's units automatically.
For gauge pressure choose the MPa(g) unit; it is converted automatically.
Dry gas 0.56–0.65, associated gas 0.7–1.0.
At the average pressure P_avg (see the results) and average temperature.
Natural gas 0.011–0.014 mPa·s.
New pipe 0.02–0.05 mm, internally coated about 0.01 mm.
Unit converter for this formulaPressure · Length · Temperature · Viscosity · Gas rate · Velocity
- MPa1
- kPa1,000
- bar10
- atm9.86923
- kgf/cm²10.1972
- mmHg7,500.62
- MPa(g)0.898675
- barg8.98675
- psi145.038
- psia145.038
- psig130.342
- ksi0.145038
psi and psia are absolute pressure; gauge units (barg, MPa(g), psig) are above atmospheric (101.325 kPa = 14.696 psi). Pressure differences in the formulas do not depend on this.
- v₂ — Gas velocity at the outlet–
- P_avg — Average pressure in the section–
- Re — Reynolds number–
- λ — Darcy friction factor–
More in Pipelines
Design wall thickness by Barlow's formula with the factors of ASME B31.4 (liquid pipelines) and B31.8 (gas pipelines), the corrosion allowance, and the allowable pressure of the selected pipe.
Weight per metre of steel pipe and of the whole section, the internal (line fill) volume and the mass of the product in the line.
Friction loss by Darcy-Weisbach (friction factor from Colebrook-White, 64/Re in laminar flow) plus the elevation change; the flow velocity and Reynolds number.
Hoop stress and its percentage of SMYS at the test pressure — at the gauge and at the lowest point of the section, where the water column adds to the pressure.
Free expansion of a section with a temperature change, and the longitudinal stress in a pipeline restrained by the soil, including the internal pressure (Poisson effect); the axial force.
Results are engineering estimates from standard formulas; for design decisions check them against the codes, project documents and specialists' calculations. The formulas carried over from the original set are unchanged, and their errors are described in the notes.