Refinery Pipe Size Calculator

Inputs

Example data table

These examples show typical inputs and the resulting nominal size using common schedules.

Flow and velocity basis

Pipe size begins with continuity: Q equals velocity times area. The calculator converts the entered flow to m³/s, applies your design velocity, and computes internal diameter as D = √(4Q/(πV)). In refinery liquid lines, 1–3 m/s is common for transfer and circulation, while 0.6–1.5 m/s often suits suction and viscous services. Validate velocities against erosion, noise, and cavitation limits always.

Safety margin for future duty

The safety margin increases the computed diameter by a chosen percentage before selecting a nominal size. Use 5–10% when duty is well defined, and 10–20% when routing, fouling, or product slate may change. A modest margin can reduce later tie-ins and helps preserve pump head during debottlenecking.

Reynolds number interpretation

Reynolds number Re = ρVD/μ indicates flow regime and friction sensitivity. Below Re 2,300, laminar flow produces higher friction dependence on viscosity and may justify a lower velocity target. Most refinery process lines are turbulent, where friction depends more on diameter and roughness than on viscosity changes. Tracking Re also supports heat-transfer assumptions and helps flag unusually high shear rates in sensitive products.

Roughness and schedule effects

Absolute roughness ε affects turbulent losses. New carbon steel is often approximated near 0.045 mm, while aged or scaled pipe can be higher. Schedule selection changes inside diameter; thicker walls reduce ID, raising velocity and pressure drop for the same nominal size. Use the schedule that meets pressure and mechanical needs, then confirm hydraulics remain acceptable. If corrosion allowance is large, treat the reduced end-of-life ID as the controlling case.

Pressure drop screening and design follow-up

Pressure drop is estimated with Darcy–Weisbach: ΔP = f(L/D)(ρV²/2). The calculator uses laminar f = 64/Re and a fast turbulent correlation (Swamee–Jain) for screening. For detailed design, add equivalent length for elbows, valves, strainers, and control elements, then include elevation changes, vapor pressure margin, and pump curve checks. Fittings can contribute 20–60% of total loss on congested pipe racks, so confirm with a line list and isometric count.

FAQs

1) Which flow unit should I choose?

Use the unit from your datasheet. The calculator converts inputs to m³/s internally, so results remain consistent across m³/h, L/s, L/min, gpm, and bbl/h.

2) What design velocity should I start with?

For many liquid services, 1–3 m/s is a common starting range. Use lower targets for suction, viscous products, or erosion-prone streams, and verify against your project specification.

3) Why does the recommended NPS change with schedule?

Different schedules have different inside diameters. A smaller ID raises velocity and pressure drop at the same flow, which can move the selection to the next larger nominal size.

4) Does this include fittings and valves?

No. The pressure drop uses straight length only. Add equivalent lengths or K-values for elbows, tees, valves, strainers, and control devices during detailed hydraulic calculations.

5) What roughness value should I enter?

0.045 mm is a typical screening value for clean new carbon steel. Increase it for aged, scaled, or internally corroded lines, or follow your company’s standard roughness assumptions.

6) When should I download the report?

Download CSV or PDF after a successful calculation. Attach it to line sizing notes, then update inputs as routing, fittings, and operating conditions become better defined.

Standard nominal size reference

Inside diameters shown are typical values used for quick selection.