Ultrasonic non-destructive testing measures: regulation of technical requirements

Abstract

The current regulatory documents for measures in the form of standard samples CO-2, CO-1 used in ultrasonic non-destructive testing are analyzed. The normalized metrological characteristics of measures are considered. It is shown that the normalized metrological characteristics do not ensure the reliability of the control in the proper volume. Differences in the normalized characteristics of measures of the same type produced by different organizations and shortcomings in the normalization of acoustic characteristics are noted, leading to different values of instrument parameters on measures of the same type and a significant error in the evaluation of control results. The necessity of normalizing the ultrasound velocity for the types of waves actually used in the measures and reducing the permissible error of measuring the velocity in the measures to ±(0.2–0.5) % is shown. It is noted that the attenuation of ultrasound in the measures is normalized only for a longitudinal wave at one frequency of 2.5 MHz and does not provide the claimed error of ± 1 dB when adjusting to the sensitivity of the devices and assessing the size of the detected defect. It is proposed to determine the attenuation of ultrasound in measures by comparing the amplitudes of ultrasonic echo signals in these measures with the amplitude of the ultrasonic echo signal in the initial measure. At the same time, the initial measure should have a simple geometric shape that allows it to be certified according to the absolute value of the attenuation coefficient. It is noted that the current State verification scheme for measuring the propagation velocities and attenuation coefficient of ultrasonic waves in solid media requires improvement, since it does not provide for the transfer of a unit of attenuation coefficient for shear waves and it does not fully take into account the real state of affairs with the measuring instruments already used in practice. To ensure the comparability and reliability of measurement results with the help of measures in full, it is proposed to develop a unified regulatory document for the general requirements for the standardized metrological characteristics of measures, methods of their measurement and a local verification scheme for transmitting units of speed and attenuation of ultrasound.