Compressible Flow Pipe Sizing

Compressible Line Sizing Calculator Guide (PDF)

This calculator determines the pressure drop of a compressible gas or vapour through a pipeline. The calculator can model isothermal and adiabatic flow.

The assumption of compressible flow is reasonable for gases and vapours where the calculated pressure drop is greater than 10% of the upstream pressure.

1. Enter the line number, source and destination of the line
2. Select the flow type - isothermal or adiabatic:
   • Isothermal flow is usually assumed for long pipes
   • Adiabatic flow is usually assumed for short, insulated pipes
3. Enter the fluid details and physical properties
4. Choose the nominal diameter and schedule of the pipe from the drop down lists, or select "Custom" to enter an internal diameter directly
5. The calculator will determine the inside diameter of the selected pipe
6. Enter a length for the pipe
7. Enter an absolute roughness for the pipe. Typical values:
   • Commercial steel: 0.046 mm
   • Drawn tubing (brass, lead, glass): 0.002 mm
   • Asphalted cast iron: 0.122 mm
   • Galvanized iron: 0.152 mm
   • Cast iron: 0.259 mm
8. Enter the quantities of each type of fitting for the pipe if known
9. If the type and quantities of each fitting are unknown, enter a fitting factor. Typical factors for 50 metre long lines:
   • 3" diameter and smaller: 1.5
   • 4" and 6" diameter: 2.0
   • 8" diameter and larger: 2.5
10. Click the "Calculate" button
11. The calculator will determine the outlet pressure and the frictional pressure drop through the line
12. An error will be given if the specified flow rate is too high to be achieved through the pipe with the available pressure drop. In this case:
    • Reduce the flow rate
    • Increase the pipe diameter
    • Increase the inlet pressure