Process Line Sizing & Hydraulics

Q: Which standards or codes apply?

API RP 14E (erosional velocity), ASME B31.3 (process piping), Crane TP-410 (flow of fluids), GPSA for two-phase.

Quick pick (TL;DR)

Liquids: aim ~1–3 m/s (pump discharge), 0.5–1.5 m/s on suction, 0.6–1.2 m/s gravity.
Gas/vapour: 15–30 m/s.
Then check the erosional velocity (API RP 14E: Ve = C/√ρ) and the pressure drop against the line's budget (≈ 0.2–0.5 bar/100 m for liquids).
Pick the smallest standard size that keeps velocity in range, stays below the erosional limit and within the dP budget.

Step 1 — Velocity windows

Service	Typical velocity	Why
Pump discharge	1–3 m/s	Size vs dP
Pump suction	0.5–1.5 m/s	Protect NPSH
Gravity	0.6–1.2 m/s	Self-venting
Gas / vapour	15–30 m/s	Below erosional

Step 2 — Worked example

Process liquid 90 t/h, try 6″

Given mass flow = 90,000 kg/h , ρ = 850 kg/m³ Step 1 — Volumetric flow Q = 90,000 / 850 = 105.9 m³/h Q = 105.9 / 3600 = 0.0294 m³/s Step 2 — Velocity in 6″ A = π/4 × 0.154² = 0.01864 m² v = 0.0294 / 0.01864 = 1.58 m/s 1–3 m/s window → OK Step 3 — Erosional limit Ve = C / √ρ , C = 100 , ρ = 53.1 lb/ft³ Ve = 100 / 7.29 = 13.7 ft/s = 4.18 m/s 1.58 ≪ 4.18 → no erosion risk Answer → 6″ Sch 40 (v 1.58 m/s, dP ~0.18 bar/100 m)

v = Q ÷ area. 6″ gives 1.58 m/s — inside the window, below erosional. 4″ too fast, 8″ wasteful.

Line sizing calculator

Velocity & erosional check → pipe size

Smallest Sch-40 size keeping velocity in window & below erosional limit. Single-phase.

Mass flow (kg/h)

Density (kg/m³)

Service

Erosional C

Velocity screening — long lines are dP-driven; two-phase needs ρv² methods.

Decision flow

1. v = Q ÷ pipe area

Service windowLiquid 1–3 · gas 15–30

ErosionalBelow Ve = C/√ρ

Long lineCheck ΔP/100 m

Pick the smallest size passing all — the largest demanded wins.

Step 3 — Pressure-drop & phase

Check dP/100 m; long lines are dP-driven.
Gas: below erosional & Mach < 0.3.
Two-phase/flare need special methods.

Common mistakes

Velocity only, ignoring dP budget.
High velocity on pump suction.
Ignoring the erosional limit.

Requisition & datasheet

Fluid, flow, density, P, T.
Velocity, erosional, size, dP, schedule.

Frequently asked questions

What should I know about Process Line Sizing & Hydraulics?

Liquids: aim ~1–3 m/s (pump discharge), 0.5–1.5 m/s on suction, 0.6–1.2 m/s gravity. Gas/vapour: 15–30 m/s. Then check the erosional velocity (API RP 14E: Ve = C/√ρ) and the pressure drop against the line's budget (≈ 0.2–0.5 bar/100 m for liquids). Pick the smallest standard size that keeps velocity in range, stays below the erosional limit and within the dP budget.

Which standards or codes apply?