Reference
Line sizing usually starts from a target velocity, then confirms the pressure drop. These are common process rules of thumb, not code requirements — gas and steam lines are ultimately limited by allowable pressure drop, noise, and erosion, and two-phase lines by the API RP 14E erosional velocity.
| Service | m/s | ft/s |
|---|---|---|
| Liquid — pump suction | 0.3–1.5 | 1–5 |
| Liquid — pump discharge | 1–3 | 3–10 |
| Liquid — general/gravity line | 0.5–2 | 1.5–6 |
| Gas / vapor line | 15–30 | 50–100 |
| Saturated steam | 25–40 | 80–130 |
| Superheated steam | 35–60 | 115–200 |
| Compressed air | 10–30 | 30–100 |
Guidance bands, not limits. Keep pump-suction velocity low to protect NPSH; keep liquid lines below ~4 m/s to limit erosion, noise, and water hammer.
Around 1–3 m/s (3–10 ft/s) for pump-discharge lines and 0.3–1.5 m/s for pump suction. Staying below about 4 m/s limits erosion, noise, and water-hammer risk.
Low suction velocity keeps friction loss small, which protects the available NPSH and helps avoid cavitation. Discharge lines can run faster because head is available to overcome the extra friction.