Papers by Keyword: Backward Radiated Ultrasound

Abstract: This work investigates the relationship between the creep-fatigue life and ultrasonic test of creep-fatigue damage. Under the creep-fatigue interaction, the main cause of life reduction is the initiation and growth of microvoid with increasing hold time. The number/size of microvoid/cavity, the fraction of cavity area varied with the hold time. Therefore, the life evaluation using the microvoid with the variation of hold time is very informative for safety of components in power plants. In this study, using the heat resisting alloy, P122 steel for USC (ultra super critical) power plant, the creep-fatigue tests with various hold times and their ultrasonic inspection were carried out for the purpose of evaluation for creep-fatigue life. The results obtained by Rayleigh surface wave of backscattered ultrasound were compared and analyzed with the experimental parameters. The good agreement between the experimental life and the predicted life was obtained.

Abstract: Generally, as the hold time of static load increases, the degradation of material becomes more rapid and the creep-fatigue life decreases. Under the creep-fatigue interaction, the cause of life decrease was mainly the initiation and growth of microvoid with increasing hold time. In this study, using the newly developed alloy of P92, the artificial creep-fatigue degradation tests and its ultrasonic inspection were carried out to evaluate creep-fatigue life. From the relations between the creep-fatigue life and the nondestructive degradation assessment by backscattered ultrasound inspection, the new nondestructive life evaluation parameter, SDA (Slope of Decaying Amplitude) was proposed. Also, to verify the nondestructive life evaluation ability, the life evaluation results by SDA were compared with those of the destructive life evaluation obtained through the fraction of cavity area. From the test result of backscattering Rayleigh surface wave, the linear relationship between SDA and experimental life could be obtained. The good agreement between the experimental life and the predicted life by SDA was also obtained. Finally, it can be stated that the new life evaluation/degradation parameter, SDA (Slope of Decaying Amplitude) could be utilized for the evaluation of the material degradation under creep-fatigue interaction.

Abstract: The application of nondestructive evaluation to creep-fatigue damage was examined in this paper. Generally, as the hold time of static load increases, the degradation of material becomes more rapid and the creep-fatigue life decreases. Therefore, in the evaluation of creep-fatigue strength and life of high-pressure vessel such as main steam pipe at high temperature is very important in power plants. In this study, the creep-fatigue behavior of P92 steel was evaluated nondestructively by the backscattered ultrasound using the creep-fatigue specimens. The results obtained by Rayleigh surface wave of backscattered ultrasound were compared and analyzed with the experimental parameters. Also, the relation between the SDA (slope of degraded area) and creep-fatigue life was examined. From the result of nondestructive test, we suggest that SDA would be used as the new parameter for the evaluation of creep-fatigue damage. As the degradation increased, the SDA decreased and also the creep-fatigue life decreased.

Abstract: The initiation and growth of internal defects usually cause the failure of long term operated structural components at high temperature. Therefore, by investigating the internal defects of material, the integrity of the system can be maintained and the unexpected failure can be prevented. The main purpose of this study is to investigate the possibility of the application of ultrasound to the measurement and estimation of the creep damage. In this study, the phased array ultrasound and backward ultrasound were employed to detect the internal defects caused by creep. Using the newly developed P92 steel, both creep and NDE ultrasound tests were performed. The results of defect inspection were checked by microstructure examination. Reliable information on the size and position of crack were obtained and successful estimation of the amount of micro-voids and their distribution proved to be obtainable by the ultrasound inspection technique. The width of the creep degraded zone was confirmed by the width of ultrasonic signal, and the severity of degradation was confirmed by ultrasonic amplitude.