Gas Pipeline Flow (Weymouth and Panhandle A)

ScopeReported side by side because the choice between them is a judgment. Both say the same physical thing: flow is driven by the difference of the SQUARES of the absolute pressures, not by the pressure difference. That squared form is the part worth carrying in the field, because it means dropping the outlet pressure buys much more additional flow on a high-pressure line than the same drop does on a low-pressure one. Weymouth suits short, smaller-diameter, high-friction and rough pipe and is generally conservative on large lines; Panhandle A suits long large-diameter transmission at higher flow. They can differ substantially on the same segment, which is why both are shown and neither is presented as the answer. Diameter dominates everything else: capacity goes as diameter to roughly the 2.6 to 2.67 power, so a modest increase in size is a large increase in capacity while doubling the length costs only about 30 percent of the flow. That exponent is why looping a line -- laying a parallel segment -- is such an effective way to add capacity, and why a small restriction anywhere in a run costs more than intuition suggests. Efficiency is where a real line differs from a calculated one: a factor near 0.92 is a clean dry line, and liquid holdup, internal corrosion product, or a partially closed valve show up here and are the usual reason measured flow falls short of predicted. Compressibility is ENTERED because it depends on pressure, temperature and composition, and assuming 1.0 at transmission pressure, where Z runs below 1, UNDERSTATES the flow -- the equations go as about Z^-0.5 (0.85 gives 8% more than 1.0). This is a steady-state, isothermal, single-phase screen at one uniform elevation: it does not handle elevation change, two-phase or liquid-bearing flow, transients and line pack, or compressor station hydraulics, and it does not select the equation for you. The operator's own hydraulic model and the pipeline engineer of record govern.

Formula or tableWeymouth Q = 433.5 (Tb/Pb) [(P1^2 - P2^2)/(G T L Z)]^0.5 d^2.667 E and Panhandle A Q = 435.87 (Tb/Pb)^1.0788 [(P1^2 - P2^2)/(G^0.8539 T L Z)]^0.5394 d^2.6182 E, both in SCF/day with inches, miles, degrees Rankine and psia; the capacity ratio for another diameter is that diameter ratio raised to the equation's own exponent.

Source and editionThe Weymouth and Panhandle A transmission equations as published, at a 14.73 psia and 520 degR base, with gauge pressures converted at 14.7 psi -- the equations require ABSOLUTE pressures and using gauge understates the driving term. Compressibility and pipeline efficiency are ENTERED. A steady-state, isothermal, single-phase screen at uniform elevation: it does not handle elevation change, two-phase or liquid-bearing flow, transients and line pack, or compressor station hydraulics.

Free accessTwo published equations evaluated on entered inputs.

What governsEstimate. AHJ and licensed professional govern.

API field namesequation, id_in, length_mi, inlet_psig, outlet_psig, gravity, flowing_temp_f, z_factor, efficiency, alternate_id_in, inlet_psia, outlet_psia, squared_difference, q_mmscfd, diameter_capacity_ratio

• Absolute pressures the driving term is P1 squared minus P2 squared on psia, not on gaugethe published equations
• Compressibility entered, or computed (added 2026-10-09) from the gravity by Sutton pseudo-criticals and Dranchuk-Abou-Kassem at the average pressure (2/3)(P1 + P2 - P1 P2/(P1 + P2)) and the flowing temperature; flow goes as about Z^-0.5, so 1.0 at transmission pressure understates flow; base pressure 14.73 psiagas-z-factor; the gas analysis
• Uniform elevation elevation change, two-phase flow and line pack are not modelledthe operator's hydraulic model