Engineering tool
Thermal Expansion & Joint Gap Calculator
Work out how much a refractory run grows on heating, and the expansion joint needed to absorb it, from the coefficient of thermal expansion and the temperature rise.
Expansion — mm
Recommended joint — mm
Linear strain — %
Pick a material for a typical α, or enter it directly. Lengths in millimetres.
Formulas used
- Length increase ΔL = α × L₀ × ΔT
- α in 10⁻⁶ per K
- Expansion joint ≈ ΔL × 1.1 per uninterrupted run
Practical notes
- The recommended joint carries a 10% margin over the calculated growth, which is normal practice for a run that must not go into compression.
- Too little joint spalls the hot face; too much lets slag and metal into the gap. Both fail, in different ways.
- α varies with temperature; the values offered here are means over roughly 20–1000 °C.
Frequently asked questions
Should each brick have a joint?
No. Joints are placed at intervals along an uninterrupted run. The calculation gives the growth of whatever length you enter, so enter the distance between joints.
Why does magnesia need so much more joint than fireclay?
Its expansion coefficient is more than twice as high, so the same run grows more than twice as much for the same temperature rise.