Refractory (castable and brick)

Refractory is heat-resistant lining material used to protect steel shells, ductwork, furnaces, kilns, boilers, cyclones, and vessels from high temperature, abrasion, erosion, slag, and chemical attack. The two broad field forms are pre-formed brick and monolithic castable.

Refractory brick is shaped and fired before installation. Bricks provide predictable properties, controlled joints, and good wear resistance when the geometry suits regular shapes. Castable refractory is mixed with water or another binder and placed by casting, pumping, gunning, or trowelling. It suits complex shapes, repairs, anchors, and areas where brickwork would be slow or impractical.

Selection factors

Refractory is selected by temperature, thermal cycling, chemical exposure, abrasion, slag penetration, alkali attack, mechanical load, installation method, and heat-loss target. Alumina content, calcium aluminate cement, insulating aggregates, silicon carbide, and low-cement formulations all change performance.

Dry-out is critical for castables. Water trapped in the lining must be removed under a controlled heat-up schedule. Heating too quickly can create steam pressure and explosive spalling. Poor curing, wrong water addition, bad anchoring, or rushed commissioning can shorten lining life before the process ever reaches full duty.

Failure modes

Common failures include spalling, cracking, alkali attack, abrasion, slag penetration, anchor failure, thermal shock, shell hot spots, and loss of bond between layers. In rotary kilns, refractory condition also depends on coating stability, ovality, tyre support, and local overheating. In boilers and cyclones, gas velocity and ash chemistry are often decisive.

Inspection uses shell temperature scans, visual checks, sounding, thickness measurements, and outage records. A hot spot is a symptom, not a diagnosis; it may reflect lining loss, poor insulation, coating collapse, or external lagging damage.

Acoustic cleaning context

Sonic horns mounted through refractory-lined walls need proper sleeves, clearances, and temperature protection. Cleaning energy should be aimed at deposits, not at damaging loose refractory. Acoustic cleaning can help prevent dust build-up on refractory surfaces, but it will not fix lining chemistry, anchoring, or dry-out defects.

Selection and failure context

Refractory selection depends on service temperature, thermal cycling, abrasion, alkali attack, slag chemistry, mechanical anchoring, installation method, dry-out schedule, and whether the lining must insulate or conduct heat. Brick linings are often chosen for predictable geometry and repair by replacement. Castables suit complex shapes, anchors, and monolithic linings, but their performance depends heavily on water addition, curing, and first heat-up.

Failure modes include spalling, cracking, anchor failure, chemical corrosion, abrasion, hot-face glazing, alkali bursting, and loss of bond behind the lining. Inspections should record crack pattern, shell hot spots, exposed anchors, missing material, and any process change that made deposits wetter or more corrosive. Acoustic cleaning can reduce deposit load on nearby gas-path surfaces, but it must not be assumed harmless to weak refractory. Repeated pressure pulses, loose linings, and poor anchors should be reviewed before fitting cleaning devices to refractory-lined ducts or vessels.

Cleaning-system interface

When cleaning devices are mounted on refractory-lined equipment, the lining condition should be part of the mechanical review. Loose castable, cracked brick, missing anchors, or hollow-sounding areas can respond badly to vibration or pressure pulses. The nozzle penetration also has to avoid creating a local hot spot, gas leak, or ledge where dust can accumulate.

Outage reports should link refractory condition with deposit history. Heavy build-up can overload linings, but aggressive cleaning can expose weak areas. Acoustic cleaning is most useful when it prevents external dust layers from growing; it should not be relied on to remove material that has reacted into the refractory hot face.

Related terms

• High-alumina refractory
• Rotary kiln
• Furnace
• Waterwall