Creepin refractories is the slow, time-dependentdeformation of a material under constant stressand high temperature. It is critical in applications like reformers and furnaces where the refractory is under load for extended periods. The amount of deformation is typically measured over 50–100 hours in standardized tests such as ASTM C832.

Creep is not the same as thermal expansion (which is reversible), or cracking (a sudden failure).