Abstract
A large and growing portion of electricity is produced by aging thermal power plants. Although excellent, high quality materials such as CrMoV steel and 12% Cr steel, etc. are used for the steam turbines, various forms of metallurgical degradation, due to creep and fatigue, etc. affect the parts and components during long-term operation at high temperature. Extending the life of steam turbines and ensuring high reliability requires life assessment technology, scheduled repairing, conversion, modification and upgrading of components in order to provide a stable power supply. As the high temperature parts and components of aged steam turbines are mainly metallurgically damaged by creep, fatigue and the interaction of both, life assessment combined with analytical and nondestructive methods is essential for realizing strategic plant life extension. We have developed a life assessment technology that takes material degradation into consideration, and have applied the procedure to more than 650 units and 2500 components since 1983. A rotor bore replication device was developed in 1989 for the purpose of nondestructive observation of creep voids and supporting the validity of life prediction results. This paper describes the technical features and applied experience of recent life assessment technology for existing high temperature steam turbines.
Highlights
INTRODUCTIONThe destructive method can directly evaluate the metallurgical property in laboratory testing devices, sample taking is extremely limited as operations because of the shape and construction of parts and components, and in addition, the analytical method must be used in combination in order to establish the test conditions
Valves and blades, etc. are made of high strength materials such as CrMoV steels and 12% Cr steels, but these materials are metallurgically degraded under long-term operation at high temperature
The destructive method can directly evaluate the metallurgical property in laboratory testing devices, sample taking is extremely limited as operations because of the shape and construction of parts and components, and in addition, the analytical method must be used in combination in order to establish the test conditions
Summary
The destructive method can directly evaluate the metallurgical property in laboratory testing devices, sample taking is extremely limited as operations because of the shape and construction of parts and components, and in addition, the analytical method must be used in combination in order to establish the test conditions. The combined method with the analytical and nondestructive methods is the most effective and useful in order to evaluate residual life as well as the cumulative damage due to creep, fatigue and the interaction of both, in combination with the numerous destructive examination results that are obtained from actual retired rotors, casings, valves and so on
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