Refractory Design and Specification
Design responsibilities and specification
API 936 is a quality-control standard for monolithic refractory installation; it does not replace the designer's responsibility to set lining thickness, anchor layout, and service limits. A specification should state material class, test requirements, installation method, curing, and dryout. Design must account for thermal expansion, differential expansion between steel shell and refractory, anchor material and geometry, and corrosion under refractory. Anchors transfer lining load to the shell; their spacing, length, and alloy must match the lining thickness and temperature. Expansion joints relieve compressive stress; missing or misplaced joints cause buckling or spalling. A vapor barrier or breather design may be needed to control steam during dryout. Traps: treating API 936 as a design code; specifying anchors without alloy or length; copying a lining thickness from a similar unit without checking heat flux; and omitting hold points for anchor inspection before casting. Worked example: estimate expansion joint width using ΔL = α L ΔT. For a 2 m long castable panel with α = 8 × 10^-6 /°C and ΔT = 800°C, ΔL = 8 × 10^-6 × 2000 mm × 800 = 12.8 mm. Specify a joint of about 13 mm, or use several smaller joints, and confirm against manufacturer data. Rule of thumb: place expansion joints at regular intervals and around penetrations; never fill them with rigid mortar that prevents movement. The specification should require inspection of anchor welds, spacing, and expansion-joint layout before refractory placement.