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Long pipe runs, thermal expansion and the movement you must allow

How far a run grows, why plastics move far more than steel, and when expansion loops stop being optional.

The engineering question

A long pipe run is anchored at both ends. What movement must be allowed, and at what point does the restraint itself become the problem?

Worked example

The figures below were produced by running the Pipe Thermal Expansion Calculator with the same inputs — during the build, from its authoritative engine.

Results
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.
  1. Movement is the coefficient of expansion times length times temperature rise.
  2. Steel moves roughly 12 mm per 100 m per 10 °C; uPVC moves several times that.
  3. Beyond about 10 mm of movement at a terminal, loops or bellows are needed.

Sanity check

If a plastic line is being restrained like a steel one, the material selection is wrong before the expansion design is.

Tools for this problem

These are the EngiMetric calculators that compute the numbers in this topic. Each one shows its formula, its units and its limits rather than returning a bare result.

Engineering review required

This topic supports professional engineering work; it does not replace a sealed design. The result depends on site data, the governing standard and engineering judgement, and should be confirmed by a competent engineer before it is built.

References & standards

  • ASME B31.3 — piping flexibility
  • EN 13445 — pressure piping systems
  • ASME PCC-2 — support design

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