What this calculator does
A long pipe run that warms up will grow, and if the growth has nowhere to go it develops enormous force. This calculator converts a material, a length and a temperature rise into the movement in millimetres, and tells you per 100 m so you can compare the figures at a glance.
How to use it
- Enter the length of the straight run and the temperature rise it will see.
- Select the pipe material; plastics expand an order of magnitude faster than steel.
- Read the total movement in millimetres and the equivalent per 100 m.
- Any run with more than about 10 mm of movement at a terminal needs loops, bellows or anchor points.
Governing formula
ΔL = α · L · ΔT Where:
-
α= Coefficient of thermal expansion [1/°C] -
L= Pipe length [m] -
ΔT= Temperature rise [°C]
Derived Equations:
ΔL per 100 m = α · 100 · ΔT Worked example — 30 m of carbon steel warmed by 60 °C
The figures below were produced by running this page's own engine with the example inputs (Pipe run length (m), Temperature rise (°C), Pipe material). If the calculator returns something different for the same numbers, that is a bug, not a rounding difference.
| Expansion over the run | 21.78 mm |
|---|---|
| Expansion per 100 m | 72.6 mm/100 m |
| Material | Carbon steel |
| Compensation needed | Large expansion — provide expansion loops, bellows, or guide/slide anchors; PVC/HDPE need allowance for creep and UV. |
| Assessment | 30 m of Carbon steel grows 21.8 mm for a 60 °C rise (≈ 72.6 mm per 100 m). Large expansion — provide expansion loops, bellows, or guide/slide anchors; PVC/HDPE need allowance for creep and UV. |
- Carbon steel expands about 12.1 mm per 100 m per 10 °C, so 60 °C gives 72.6 mm per 100 m.
- Over 30 m that is about 21.8 mm of movement.
- That is well beyond what a flange gasket absorbs, so plan an expansion loop or a bellows.
Assumptions & limitations
Engineering calculation. Free linear expansion using the coefficient of thermal expansion of the selected material. It ignores restrained stresses, anchor forces and creep.
- Free expansion only — a restrained line develops stress rather than moving, and that case needs a flexibility analysis.
- No allowance for creep in thermoplastics, which roughly doubles their long-term movement.
- Coefficients are averaged over the temperature range; some materials are strongly temperature-dependent.
This tool supports professional engineering work; it does not replace a sealed design. Confirm every result against the applicable standard and a licensed engineer before it is built.
References & standards
- ASME B31.3 — piping flexibility and expansion stress.
- EN 13445 — pressure piping systems, design and manufacture.
- ASME PCC-2 — cold spring and support design for buried piping.