Abstract: The microstructure, mechanical properties and high temperature strength of 12Cr1MoV steel of creep damage has been shown to be completely restored by restoration-heat-treatment. The creep damage rate has no effect on such recovery. Completely recovery of removing cavities include sintering-out of cavities and leaving cavities within the grains. The effect of recovery can be evaluated by the use of equivalent recovery parameter φrc that is related to the creep damage rate. Using the restoration-heat-treatment the service life of main steam pipe will extend when the pipe uses prior to the early stages of the tertiary creep or the ratio of damage not exceeds 0.1 persent.

Key words: Heat-treatment, Main steam pipe, Restoration, Thermal strength