Procedure for life assessment of degraded steam turbine components and life diagnosis system.

An investigation of steam turbine components retired after long-term service at elevated temperatures has clarified that one of the most typical characteristics of material degradation in Cr-Mo-V steel is softening, and that the mechanical properties necessary for life prediction such as creep and low cycle fatigue are affected by material degradation (softening).As a typical example, this paper shows the quantitative relationships between the material hardness and these degraded mechanical properties for Cr-Mo-V rotor forgings. Creep and fatigue life assessment for steam turbine rotors could be more accurately made through the nondestructive measurement of hardness and the evaluation of the degraded creep and fatigue properties.A life diagnosis system was developed based on the present procedure with a 32 bit super mini-computer and man-machine interfaces.This system helps us perform easier and more sophisticated life diagnosis and maintenance of steam turbine main components used at high temperatures such as rotors, casings, valves, blades and bolts.