Refractory linings stresses, allowable

Expansion allowance is often used to reduce the expansion stress in the refractory lining. Expansion allowance is often used in lining systems made of magnesia and silica brick because of their high coefficient of thermal expansion. Approximate methods are used in which a percent of the full expansion displacement is taken for the amount of expansion allowance. Materials such as cardboard and plastic inserts are placed in brick joints that burn out at low temperatures. Compressible blanket of board materials are also used. Typically, low-density (10 to 25 pcf) blankets will compress to about 10 to 20% of their original unloaded thickness. Higher-density (50 to 60 pcf) board materials will only compress to about 80 to 90% of their original unloaded thickness. 

However, it is the combination of design data such as compressive and flexural stress-strain with thermal measurements that allows us to take that extra step from a material test piece to a working refractory lining or component. It allows us to study the thermomechanical behavior of materials. 

Hot lines and equipment are usually thermally insulated to conserve energy and to ensure safe service at temperatures above the oxidation limits of the materials. Care must be taken to ensure that the process stream chemistry is either nonoxidizing or that the process-side surface is protected by an insulating or refractory liner. In such cases, the limiting factor will be the availability of a code maximum allowable stress. 

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