Refractory on the tube wall: protecting without blocking the heat

In the combustion chamber of a boiler, the refractory has a different job than in a melting furnace. Behind the lining there are no steel plates but water- or steam-cooled tubes that are meant to absorb the heat. The lining has to protect them without blocking the heat. Too little refractory, and erosion and corrosion attack the tubes. Too much, and the boiler loses output because the heat no longer reaches the tubes.

Principle 1: only as much castable as necessary

On a tube wall, refractory goes only where it is needed: in the zones where ash and particles cause erosion or flue gas causes corrosion. There it is applied thin, dense and cleanly screeded. A thick layer looks solid, but it insulates the tubes and shifts the heat to areas the boiler was not designed for.

Principle 2: openings first

Where tubes are bent apart for burners, nozzles or sight holes, the geometry changes within a small space. Flame, flow and differential expansion meet there, and that is where the castable cracks first. We fit the openings precisely, round off the edges and start with them rather than with the plain surface.

Principle 3: anchors on the fins, never on the tube

The anchors holding the refractory are welded onto the fins between the tubes, never onto a tube. A weld on a pressure-bearing tube is an intervention in the boiler itself. Every weld is inspected before the castable is applied.

• Define the zones: where do erosion and corrosion actually attack? Only those areas are lined.
• Limit the layer thickness: thin, dense, cleanly screeded, with no extra castable as a reserve.
• Openings first: precisely fitted, edges rounded, no step at the transition to the surface.
• Anchors only on the fins, every weld inspected and documented.
• Heat up to the curve: the tube wall heats up faster than the castable, and the mixing water needs time.