Expansion joints: the most inconspicuous cause of refractory damage

5 centimetres — that is how much a 10-metre fireclay wall expands when heated up to operating temperature. Dense high-alumina or magnesite grades expand considerably more. This expansion needs room. If it does not get it, compressive stresses build up — and from them come spalling, bulging and cracks.

From more than 500 projects we know that expansion joints are among the most frequent, yet least considered, causes of damage in refractory construction.

Five principles from practice

• Design the joint width zone by zone — according to material, temperature level and geometry, not by a rule of thumb applied across the whole furnace.
• Prioritise critical points: corners, doors, burner penetrations and material transitions concentrate the stresses.
• Execute joints staggered and in a labyrinth pattern — a continuous joint running through to the insulation becomes a gas duct in operation.
• Do not oversize: joints that are too wide become infiltrated with melt and dust and burn out.
• Document the joint pattern at every inspection: closed-up joints announce damage long before the wall deforms.

Built cold, operated hot

A newly lined burner chamber is handed over cold: bright, clean and true to size. But it has to be judged at operating temperature. We therefore place expansion joints and transitions so that they only close when hot. Burner blocks sit in the wall with a compressible joint so both can expand without spalling each other. The best evidence later is the glow pattern: an even glow indicates a healthy lining, while bright or dark spots are clues we follow up, including from the outside with thermography.

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