Steam pipe sizing
Velocity and pressure drop in a steam line for every Schedule 40 size — saturated or superheated steam, with IAPWS-IF97 properties.
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The Pipe Sizing and Pressure Drop Excel tool does everything here and more: pressure drop or allowable flow for liquid, gas and steam lines, with fittings, elevation, choked-flow and flashing checks and a size table over every NPS of your schedule. Print-ready report, any units, visible formulas, no macros.
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How this calculator works
Steam lines are sized on two limits: velocity (noise, erosion and, in saturated lines, condensate carried at speed) and pressure drop (the user must still get the pressure it needs). Steam density falls as the pressure falls, so this calculator follows the steam along the line in 40 steps at constant enthalpy (no heat loss), each with the Darcy–Weisbach equation and the Colebrook friction factor, the fittings spread along the length, and the acceleration term at the end. Density, viscosity and wetness come from the IAPWS-IF97 steam tables. The table repeats the calculation for every Schedule 40 size and marks the smallest that meets both your limits.
Example: 5,000 kg/h of dry saturated steam at 10 bar g (184.1 °C) through 100 m of pipe with fittings worth ΣK = 5. A 4-inch Schedule 40 line runs at 30.0 m/s at the inlet and 31.6 m/s at the outlet and loses 0.56 bar, leaving 9.44 bar g. A 3-inch line would run at 52–65 m/s and lose 2.35 bar; a 6-inch line 13 m/s and 0.08 bar. With a 35 m/s limit and a 1 bar allowance, 4 inch is the smallest size that works. The results were checked against an independent 1,000-step calculation with the iapws steam tables and the fluids friction factor for seven lines from 1.5 to 101 bar a, saturated and superheated: pressure drops agree within 0.002 %.
Velocity guidance: Spirax Sarco suggests 25–40 m/s for saturated steam mains and higher velocities, to about 50–70 m/s, for superheated steam; keep exhaust, flash and low-pressure lines slower. Limits: no heat loss or condensate is modelled — drain and trap saturated mains, and allow for start-up loads. References: IAPWS-IF97 (2007); Crane, Flow of Fluids (TP-410); Spirax Sarco, The Steam and Condensate Loop.