Does stress or deflection govern the support span?

Take the smaller of the two allowable spans. For small-bore lines and water service, deflection often governs; for larger or high-temperature lines, bending stress can govern.

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Piping

Pipe Spacing

Maximum allowable pipe support spacing based on bending stress and mid-span deflection.

When to use this calculator

Use when laying out pipe supports on straight horizontal runs to keep stress and sag within limits.

Required inputs

Pipe size & schedule
Contents + insulation weight
Allowable stress
Allowable deflection

Expected outputs

Maximum support span
Mid-span deflection
Governing limit (stress vs deflection)

Formula overview

Keep units consistent (SI: w in N/m, Z and I in m³/m⁴, S and E in Pa, Δ and L in m).

Stress limit: L = sqrt(0.4 · Z · Sh / w). Deflection limit: L = (Δ · 384 · E · I / (5 w))^(1/4). The allowable span is the smaller of the two.

Worked example

Example: a water-filled line where the stress equation gives L ≈ 6.0 m and the deflection equation (Δ = 13 mm) gives L ≈ 5.2 m.
Governing span = min(6.0, 5.2) = 5.2 m → place supports no more than ~5 m apart.

Common mistakes

Counting only the pipe weight and ignoring contents and insulation.
Using the stress span when deflection actually governs (or vice versa) — always take the smaller.
Applying straight-run spacing across fittings, valves, or other concentrated loads.