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Economic pipe diameter

Enter flow, length, fittings and prices to see velocity, head loss, pumping energy and total yearly cost for each commercial size, and the payback of upsizing.

Pre-sizing and estimating tool: results do not replace design, calculations or reports signed by a licensed professional, nor verification against the applicable codes and standards.

Pre-sizing
Flow
Pumping
Pipe and comparison

Installed cost per meter = mass per meter (Sch 40) × steel price × installation factor (supports, welding, erection, painting).

Economic analysis
—Lowest total-cost size
—

Total yearly cost by pipe size

Investment annualized at the MARR and service life plus pumping energy. The shortest bar is the economic size.

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Velocity and head loss

Usual range for water in discharge lines: 3 to 10 ft/s (1 to 3 m/s).

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Results by size

Project payback

Cash flow of the improvement: investment in year 0 and annual savings escalated at the rate entered, discounted at the MARR.

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The report gathers this page's inputs, results, equations, assumptions and references, with fields for project, engineer and revision. In the print dialog, choose Save as PDF.

Method, assumptions and references

Equations used

Darcy–Weisbach: hf = (f · L ÷ D + ΣK) · v² ÷ (2g)
Colebrook–White: 1 ÷ √f = −2 log10(ε ÷ (3.7 D) + 2.51 ÷ (Re √f)); laminar (Re < 2300): f = 64 ÷ Re
Hazen–Williams (water option): hf = 10.67 · L · Q^1.852 ÷ (C^1.852 · D^4.8704) + ΣK · v² ÷ (2g), SI units
Oil: ν(T) from the Walther equation (ASTM D341) with ν40 of the ISO VG grade and typical ν100; ρ(T) = 870 · [1 − 0.00065 (T − 15)]
Re = ρ v D ÷ μ; v = Q ÷ (π D² ÷ 4)
Electric power: P = ρ g Q (Hs + hf) ÷ (ηpump · ηmotor)
Investment = mass per meter (Sch 40, steel 7,850 kg/m³) × L × steel price × installation factor
Total yearly cost = investment × CRF(i, n) + energy × price

Assumptions and limits

  • Inside diameters of Sch 40 pipe per ASME B36.10M; other schedules or materials have different inside diameters.
  • Water density and viscosity from IAPWS (IF97 and IAPWS 2008) at the temperature entered.
  • Constant flow and efficiencies through the year; sizes with velocity between 1 and 20 ft/s (0.3 to 6 m/s) are compared.
  • Pump and motor cost is taken as equal across sizes (simplification); for large head differences, add the pump change to the investment.

Standards and technical documents

  • Colebrook, C. F. (1939). Turbulent flow in pipes, with particular reference to the transition region. J. Inst. Civil Eng.; Moody, L. F. (1944). Friction factors for pipe flow
  • Crane Co., Technical Paper No. 410 (TP-410): Flow of Fluids Through Valves, Fittings and Pipe
  • ASME B36.10M: Welded and Seamless Wrought Steel Pipe; ABNT NBR 5590: tubos de aço carbono com ou sem solda
  • IAPWS R12-08: Release on the IAPWS Formulation 2008 for the Viscosity of Ordinary Water Substance
  • Hydraulic Institute & Europump, Pump Life Cycle Costs: A Guide to LCC Analysis for Pumping Systems
  • Peters, Timmerhaus & West, Plant Design and Economics for Chemical Engineers (economic pipe diameter)

U.S. regulations

  • DOE 10 CFR Part 431, Subpart Y: energy conservation standards for clean water pumps (Pump Energy Index)
  • DOE 10 CFR Part 431, Subpart B: electric motor efficiency standards
  • ASME B31.1 (power piping) and B31.3 (process piping): design codes adopted by states and owners

Frequently asked questions

What is the economic pipe diameter?

The size with the lowest total cost over the line’s life: bigger pipe costs more to buy and install but uses less pumping energy. The calculator adds both costs per year for each commercial size.

What velocity should I use for water?

Discharge lines are usually sized for 3 to 10 ft/s (1 to 3 m/s). Below that the line tends to be oversized; above it, head loss, noise, erosion and water-hammer risk grow.

How do I estimate the sum of K?

Add each fitting’s coefficient: long-radius 90° elbows about 0.3, open gate valves 0.15, check valves 2, tank entrance 0.5 and exit 1. Crane TP-410 lists values by type and size.