Development of automatic measuring system of ultrasonic attenuation using spectrum analysis

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The life extension of high temperature plants is strongly expected recently, so that the accurate remaining life assessment of them has come to be an important problem. This report presents a new non-destructive evaluation technique using ultrasonic waves for the evaluation of aging deterioration damage ( caused by creep and high temperature fatigue ) of high temperature components. In previous works, ultrasonic attenuation is evaluated from the 1st and 2nd peak values of pulse-echo ultrasonic wave. However the attenuation values evaluated by this method may have some error, because those values are greatly affected by the super-imposed noise. In the present work, two new algorithms for the improvement of measuring accuracy of ultrasonic attenuation using spectrum analysis has been developed. One is the method that evaluates the attenuation values from envelope curve of original ultrasonic waves, the other is that evaluates the attenuation values by calculating the system function of specimen from the 1st and 2nd echoes. Several ultrasonic waves obtained from Monte Carlo simulation and degraded specimen are analyzed by using, both the proposed methods and the conventional method. It is shown through the comparison that the proposed methods enable us to measure ultrasonic attenuation more accurately than before, and that the attenuation values tend to increase as decreasing of the remaining life. It is also clarified that the attenuation values is effective as non- destructive evaluation parameter of creep and high temperature fatigue. The developed algorithms are installed on the measuring system which consists of a personal computer, ultrasonic apparatus, and digital storage oscilloscope. In addition the analysis time is very much shortened by incorporating FFT-analyzer in this system. Finally, all of procedures of instrumentation and analysis can be automated fully, and it will enable us to apply the above ultrasonic method to real structures.