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How It Works
Pipes lengthen and shorten with temperature changes. If unrestrained, the change in length is ΔL = L × α × ΔT. If the pipe is anchored and cannot move, the thermal expansion creates internal stress: S = E × α × ΔT. Expansion joints or loops accommodate the movement in long runs.
Example Problem
A 100-ft (1,200 in) steel pipe (α = 6.5×10−6) sees a 100°F temperature rise.
- ΔL = 1,200 × 6.5e−6 × 100 = 0.78 in
If restrained (E = 29×106 psi): S = 29e6 × 6.5e−6 × 100 = 18,850 psi.
Frequently Asked Questions
Which pipe materials expand the most?
HDPE expands about 18 times more than steel per degree. PVC expands about 5 times more. Metallic pipes (steel, ductile iron) expand the least. Always use the correct α for the pipe material.
How are expansion joints sized?
Calculate ΔL for the expected temperature range and pipe length. The expansion joint must accommodate at least that movement plus a safety margin, typically 10–25% extra.
What happens if thermal stress exceeds the yield strength?
The pipe may buckle, crack at welds, or push fittings apart. For restrained pipes, the thermal stress must stay below the allowable stress for the material and design code in use.
Related Calculators
- Steel Pipe Design Calculator — pressure rating using Barlow's formula.
- Plastic Pipe Design Calculator — pressure class equations for plastic pipe.
- Pipe Hydrostatic Pressure Calculator — external water pressure on buried pipe.
- Thermal Expansion Calculator — calculate material expansion from temperature change.
- Pipe Flow Calculator — compute flow rate and velocity in the pipe system.
- Length Unit Converter — convert pipe lengths between feet, meters, and inches.
National Resources Conservation Service. National Engineering Handbook. 1995. USDA.