Many vessels and equipment components encounter elevated temperatures during their operation. Such exposure to elevated temperature could result in a slow continuous deformation, creep, of the equipment material under sustained loads. Examples of such equipment include hydrocrackers at refineries, power boiler components at electric generating plants, turbine blades in engines, and components in nuclear plants. The temperature at which creep becomes significant is a function of material composition and load magnitude and duration.

Components under loading are usually stressed in tension, compression, bending, torsion, or a combination of such modes. Most design codes provide allowable stress values at room temperature...