Development of automatic measuring system of ultrasonic attenuation using spectrum analysis

近年来，人们对高温核电站的延寿提出了很高的要求，因此对高温核电站的剩余寿命进行准确的评估成为一个重要的问题。本报告提出了一种新的非破坏性评估技术，使用超声波的高温部件的老化劣化损伤（由蠕变和高温疲劳引起）的评估。在以前的工作中，超声衰减是从脉冲回波超声波的第一和第二峰值来评估的。但由于叠加噪声对衰减值的影响较大，用该方法计算的衰减值可能存在一定的误差。本文提出了两种提高频谱分析法测量超声衰减精度的新算法。一种是由原始超声波的包络曲线求取衰减值的方法，另一种是由第一、二次回波求取试件的系统函数求取衰减值的方法。用本文提出的方法和传统的方法对蒙特卡罗模拟和退化试件得到的几种超声波进行了分析。通过比较表明，所提出的方法能更准确地测量超声衰减，且衰减值随剩余寿命的减小而增大。同时也阐明了衰减值作为蠕变和高温疲劳的无损评价参数是有效的。所开发的算法被安装在测量系统，其中包括一台个人计算机，超声波仪器，和数字存储示波器。此外，通过在该系统中加入FFT分析仪，大大缩短了分析时间。最后，所有的检测和分析过程都可以完全自动化，这将使我们能够将上述超声方法应用于真实的结构。

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.