Ultrasound investigations of the samples of a steam pipe elbow containing micro flaws have been performed, cut at different distances from the crack that appeared as a result of long-term operation. Changes in the velocities of longitudinal acoustic waves are determined depending on the porosity of the samples. The parameters of acoustic noise caused by multiple scattering of waves on microdefects in the samples are investigated. It is shown that the width of an estimated distribution of the probability density function of instantaneous values of an acoustic noise signal can be used as an informative parameter for microdamage ultrasonic monitoring of a medium. At the same time, accurate measurement of the velocity of ultrasonic wave is not required. Acoustic noise measurements can be performed using standard ultrasonic flaw detectors.
Rinkevich et al. (Thu,) studied this question.