Dryout, Repair, and Maintenance of Refractory Linings
Dryout, repair, and maintenance
Dryout removes free water and decomposes or drives off chemically bound water without causing explosive spalling. A controlled schedule specifies heating rate, hold temperatures, hold duration, and maximum skin temperature. Thin linings dry faster than thick ones; thick linings and dense castables need slower ramps and longer holds. Traps: treating dryout as a simple bake-out, skipping holds because steam is not visible, heating the shell unevenly, and repairing a failed area without removing all damaged material. Repair requires removing refractory to sound material, usually with square or slightly undercut edges, cleaning and roughening the surface, inspecting anchors, and using a compatible patch material. A patch that is stronger or stiffer than the parent lining can crack at the interface. Maintenance inspection should look for cracks, spalling, hot spots, anchor exposure, and corrosion at the shell. Worked rule: for a thick castable lining, hold at about 110°C until steam evolution stops, then ramp slowly through the chemically bound water release range; follow the manufacturer's curve and record shell temperatures. Never speed up dryout to meet a schedule-cracking and spalling often appear after startup, not during the hold. A useful rule of thumb is to repair only after the unit is cool enough to inspect, and to re-inspect the patch during the next shutdown.