nondestructive measurement of degradation in aged plants and remaining life evaluation system

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Degradation mechanisms which can take place in aged energy plant components are widely varied depending on material of the component, service environment, and operating conditions. For plant life management and extension, prediction of remaining lives of the plants which is based on detection and quantitative evaluation of in-service degradation of the components.(1) development of nondestructive inspection methods for various types of degradation which are respectively based on the degradation mechanisms, and (2) development of a prototype system which can specify the dominant deterioration factors for a aged plant components under given operation conditions, have been in the scope of this research project.For defect-type degradation, Induced Current Focused Potential Drop method has been successfully applied to determine shape and size of three dimensionally shaped surface cracks. For material-type degradation, Electrochemical Materials Characterization methods have been developed for the following degradations which no nondestructive inspection methods have been available for ; creep damage in directionally solidified Ni-base super alloy for gas turbine applications, creep damage in W-modified heat-resistant ferritic steels, high-temperature low-cycle fatigue damage in Ni-base superalloys, thermally aging embrittlement of duplex stainless cast, and aging embrittlement of type 310S stainless steel.With respect to the life evaluation system, genetic algorithm has been introduced to develop the prototype system which supports identifying dominant factors for in-service degradation and helps to predict remaining lives of components. The system has been successfully applied to corrosion damage evaluation of heat-exchanger tubes of chemical plants.