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Pipe Bending Stress Calculator

ASME B31.8 Pipeline Span Design for Unrestrained Piping

Pipeline Span Stress Analysis
Evaluates bending stress and deflection for above-ground (unrestrained) pipeline spans per ASME B31.8 §833.6. Combined longitudinal stress from pressure and bending must not exceed 0.75 × SMYS × T.

Pipe Properties

in
in

Span Configuration

ft

Applied Loads

lbf/ft
Insulation, ice, etc. (besides pipe weight)
lbf
ft from A
psig
For combined stress check

ASME B31.8 Parameters

Design Factor (F): 0.72
°F
—
1.0 for seamless/ERW

Material Strength

ksi
psi
e.g., X52 = 52,000 psi

📘 ASME B31.8 Criteria

Unrestrained Pipe (§833.6):
SL = SP + Sb ≤ 0.75 × SMYS × T

Where:
SP = P×D/(4t) — longitudinal from pressure
Sb = M/Z — bending stress
T = temperature derating factor

Deflection: δ ≤ L/240 (industry)

📚 Engineering Fundamentals

Beam theory, pipe section properties, and ASME B31.8 span design criteria

Read Guide →

Beam Deflection Formulas

Simply Supported: δ = 5wL⁴/(384EI)
Fixed-Fixed: δ = wL⁴/(384EI)
Fixed-Pinned: δ = wL⁴/(185EI)
Cantilever: δ = wL⁴/(8EI)

Design Notes

Support Selection: Fixed-Fixed provides lowest stress/deflection but requires moment-resisting connections. Pinned-Pinned is conservative and easier to detail.

Hydrotest: Water-filled spans have significantly higher loads. Verify support spacing for hydrotest conditions.

Thermal: One support per span should accommodate axial movement. Fixed supports at both ends create high thermal stress.

Code References

ASME B31.8-2020
§833.6 — Unrestrained pipe stress limits
§841.1.6 — Design factors by location class
§841.1.7 — Longitudinal joint factors
§841.1.8 — Temperature derating factors

References:
Roark's Formulas for Stress and Strain
AISC Steel Construction Manual

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