Investigation of detection method of cavitation behavior using microphone outside of piping

Cavitation induced vibration and the consequent erosion of pipes are one aspect of the potential damaging factors in the piping system. In order to prevent such trouble, it is demanded to develop a detection method of cavitation. Especially, in a plant system such as nuclear power plants, it is preferred to detect them measuring outside of pipes during plant operation. In this paper, the detection method of cavitation using a microphone was experimentally examined comparing with an accelerometer, as a result, (1) Output of the microphone varied with the cavitation number, and output voltage of the microphone increased with development of cavitation, and the measurement result with the microphone was similar to that of the accelerometer, qualitatively. (2) When cavitation occurred, a pulse shaped signal was clearly detected by carrying out 8 kHz high path filter processing to the microphone output waveform. (3) When cavitation occurred, frequency distributions of microphone output waveform differed from those without cavitation and the frequency component of an output waveform with a microphone became large mainly in the range of 1 kHz to 3 kHz. (4) The result of the simultaneous measurement by the accelerometer and the microphone, both of sensors detected the shockwave considered to generate at the same time. Using the characteristics of the results, it turned out that cavitation detection using microphone without contacting pipes could be performed like an accelerometer mounted on the pipe surface. (author)