If the steam velocity is too high, the risk of noise, erosion, and water hammer inside the pipe increases; if it is too low, the pipe will be unnecessarily large and expensive. This tool calculates the velocity in each pipe diameter from the steam flow rate and pressure and selects the smallest diameter that does not exceed the allowable velocity .
Formula
ṁ: steam flow rate (kg/h), vg: specific volume of steam (m³/kg, IAPWS-IF97), d: pipe inner diameter (m).
Recommended speeds
- Saturated steam distribution lines: 25–30 m/s
- Superheated steam lines: 35–50 m/s
- Vent, safety valve outlet, flash steam and condensate return lines: 10–15 m/s
When “line type” is selected, the suggested speed comes automatically; you can change the value as you wish.
Example
With a limit of 30 m/s for 5,000 kg/h of saturated steam at a pressure of 10 bar(g), the choice is DN100 (speed 27.3 m/s). If the same calculation is made with 15 m/s for a 1,000 kg/h vent line at a pressure of 0.5 bar(g), DN200 is obtained: at low pressure, the volume of steam is very large.
Pipe inner diameters are taken from the tables of DIN 2448 / EN 10220 seamless steel pipe and ASME B36.10 Schedule 40/80. Vapor properties are calculated by IAPWS-IF97, viscosity by IAPWS-2008; the coefficient of friction is found by the Swamee-Jain formula, which is the open solution of Colebrook’s equation.
Check the pressure loss in long lines as well. To evaluate your steam system as a whole, you can take a look at our steam boiler guide and get a free quote for your project.