API 936 cheat sheet

Calcium oxide classification by weight: conventional castable >2.5% CaO; low-cement 1.0–2.5%; ultra-low-cement 0.2–1.0%; no-cement <0.2%.

Increasing bulk density and reducing apparent porosity generally raise cold strength, abrasion resistance, and thermal conductivity while lowering insulating value.

For dense monolithic refractories, thermal conductivity typically decreases as service temperature rises; insulating castables and ceramic fiber remain low-conductivity at all temperatures.

Hot modulus of rupture and refractoriness under load quantify load-bearing capacity at temperature; both generally fall as CaO, silica, and flux content increase.

Abrasion resistance depends on aggregate hardness, matrix bond strength, porosity, and temperature; dense high-alumina castables outperform lightweight insulating materials in erosive FCC service.

FCC refractory selection must address catalyst erosion, thermal cycling, and vanadium/sodium attack; high-alumina, spinel, and chrome-bearing materials resist these, while silica-rich refractories are vulnerable to fluxing.

Thermal shock resistance improves with lower thermal expansion, higher thermal conductivity, lower elastic modulus, and controlled porosity rather than maximum strength alone.

Common castable aggregates include tabular alumina, fused alumina, mullite, bauxite, spinel, and zircon; each trades cost against density, refractoriness, and chemical resistance.

Selection inputs include hot-face temperature, atmosphere, chemical species, erosion severity, thermal cycle frequency, anchor system, and allowable shell temperature.

Typical anchor alloys: type 304 stainless steel for oxidizing service to about 1500°F, type 310 stainless steel to about 1900°F, and nickel-based alloys for higher-temperature or reducing service.

Hexmesh anchors are commonly specified on 2-inch centers, 3/4 to 1 inch deep, and 12 to 14 gauge; mesh depth is matched to lining thickness and must be completely filled.

Anchor tips should terminate roughly 1/2 to 1 inch below the hot face so the refractory cover protects the metal from overheating and oxidation.

Refractory and insulation thickness are selected to keep the steel shell below its design temperature, often about 500 to 650°F in FCC service.

Expansion or control joints are placed at regular intervals and at shell discontinuities; castable linings commonly use joints spaced about 4 to 6 feet apart.

Anchor welds are fillet welds sized per drawing; inspection includes 100% visual examination plus bend testing of sampled welds.

Shell surfaces are cleaned of scale, oil, rust, and moisture before anchor welding so that welds and refractory bond are sound.

Installed monolithic lining thickness is commonly checked to plus or minus 1/4 inch unless the project specification requires tighter tolerance.

Design must account for differential thermal expansion between steel shell and refractory and must provide paths for moisture and steam to escape.

Mixing water must be clean and potable, typically 50 to 80°F; water is measured by weight or calibrated volume and never exceeds the manufacturer's maximum.

Use a mechanical forced-action mixer; mix for the manufacturer's specified time, commonly 3 to 5 minutes after the last water is added, and keep batch size within mixer capacity.

Working time is commonly about 30 to 60 minutes at 70°F; it shortens as mix and ambient temperature rise and lengthens in cold conditions.

Place castable continuously to avoid cold joints; if placement stops beyond working time, form a keyed joint rather than bonding fresh material to set material.

Consolidate castable with internal vibrators until air bubbles stop and the surface turns glossy; under-vibration leaves voids and over-vibration causes segregation.

Gunning is performed perpendicular to the surface at the manufacturer's recommended distance; rebound material must never be reused or worked back into the lining.

Low-cement castables are typically moist-cured about 24 hours at 65 to 85°F before dryout to allow hydraulic bond development.

Test panels are cast from the same mix and at the same time as field placement, then cured and dried alongside the lining for quality testing.

Installation should not proceed when shell or ambient temperature is below 50°F unless heating and enclosures maintain proper mixing and curing conditions.

Cold crushing strength and modulus of rupture are measured per ASTM C133 on cured and dried specimens, commonly 2-inch cubes and bars.

Bulk density and apparent porosity are measured on field samples; bulk density is commonly required to be within about 5% of the manufacturer's published value.

Abrasion resistance is evaluated by ASTM C704, which blasts a specified abrasive at the refractory surface and measures volume loss.

Permanent linear change is measured after reheating a specimen to a specified temperature and cooling; it indicates irreversible dimensional change.

Hammer tapping detects voids, delamination, and unbonded refractory by a change from a sharp ring to a dull thud.

Test frequency is typically at least one sample panel per mix, per shift, or per lot, with additional panels for each significant change in materials or conditions.

Anchor welds receive 100% visual inspection plus bend testing of sampled welds; failed welds are repaired and re-inspected before lining placement.

Pre-installation quality control verifies material certificates, shelf life, dry storage, and freedom from caking or contamination.

Residual moisture in a new lining is checked and documented before dryout because excess water can cause steam spalling during heat-up.

Free water is removed near 212°F; a typical dryout holds at about 250 to 300°F to drive off water slowly and avoid steam spalling.

Dense castable linings are commonly heated at 25 to 50°F per hour during initial dryout, with slower rates for thick or low-permeability sections.

Chemically bound water in cement-bonded refractories is released roughly between 500 and 900°F, so a controlled hold in that range is specified.

Vents or weep holes in the lining allow steam and water vapor to escape during dryout, reducing pressure buildup and spalling risk.

Repairs require removal of all cracked, spalled, or unbonded material back to sound refractory, with square edges and clean exposed anchors.

Anchors that are severely oxidized, deformed, or have failed welds are replaced rather than embedded in new refractory.

Cracks wider than about 1/8 inch, or deep cracks reaching anchors, are typically cut out and repaired during turnaround maintenance.

Emergency or hot repairs may use ceramic fiber modules or gunning mixes, but permanent repair follows the same preparation and curing rules as new installation.

Post-turnaround inspection documents lining condition, crack maps, repair areas, and dryout records for future maintenance planning.