Detection of Cavitation with Accelerometers Mounted on Piping Outer Surfaces

Abstract

Cavitation-induced vibration and erosion of pipes is a potentially damaging factor in piping systems. To prevent it, a detection method for cavitation phenomena should be developed. In power plants, especially, it is desirable to detect them from outside pipes during operation. Detection of cavitation phenomena was experimentally investigated in this paper using accelerometers mounted on the outer surface of a pipe upstream and downstream from an orifice. The following results were obtained. (1) With the progression of cavitation, output voltage of the accelerometer varied, and the amplitude and number of the pulse-shaped signals increased. However, it would likely be difficult to distinguish them from noises in an operating plant. (2) It was difficult to recognize the characteristic frequency of cavitation, because the power spectrum density was broad up to the accelerometer limit of 45 kHz. (3) The flow directional distribution of RMS (root mean square) values of accelerometer output voltage varied greatly with the progression of cavitation. Therefore, from comparison of RMS values obtained upstream and downstream from the orifice it seems possible to detect cavitation phenomena in the piping systems of operating plants.

Detection of Cavitation States with Microphone Placed Outside Pipe Components

“…The objective of this study was to develop a detection method of cavitation states at the pipe throats such as valves and orifices in plant piping systems without preparing a data base for judgment of a cavitation state. We have previously carried out vibration measurements using accelerometers mounted on the outer surface of pipes, and we confirmed that cavitation occurrence could be detected by comparing accelerometer outputs upstream and downstream [7] . Moreover, considering applicability to actual plants, we examined a cavitation detection method using microphones as a noncontact technique [8] [9] and confirmed that microphones could detect a developed cavitation state.…”

“…Cavitation erosion rates depend on flow velocity and water temperature, except for the cavitation number, and the pipe damaging risk is different even at the same cavitation number. As strengths of cavitation noises had close relationships with impact forces and erosion rates on the pipe inner surface [7] [14] , the proposed method would be effective to prevent erosion even for different velocities and temperatures with those in this experiment. Although the cavitation detection characteristics would become ambiguous especially at low velocity, pipe damaging risks would become low.…”

Detection of Cavitation with Microphone Placed Outside Piping

“…The objective of this study was to develop a detection method of cavitation phenomena at the valves and orifices in plant piping systems without preparing a data base for judgment of cavitation occurrence. We have previously carried out vibration measurements using accelerometers mounted on the outer surface of pipes, and we confirmed that cavitation occurrence can be detected by comparing accelerometer outputs upstream and downstream [7] . However, in actual plants, there are many pipes where accelerometers cannot be mounted due to high temperatures or pipe locations.…”

“…We confirmed that the microphone measured radiated sounds from the pipe surface in simultaneous measurements using an accelerometer and a microphone. Therefore, we considered it was possible to apply microphones to the cavitation detection method using accelerometers [7] . Figure 8 compares the microphone outputs 90 mm upstream and 75 mm downstream from the orifice when cavitation number was changed.…”

High-pressure emulsion formation in cylindrical coaxial orifices: Influence of cavitation induced pattern on oil drop size

“…In this state, more cavitation bubbles occur and expand, while traveling downstream with the flow, as demonstrated for L/d < 1 by Mizuyama et al (2010) and for L/d > 1 by Sato and Saito (2002). Depending on geometrical aspects and flow velocity, a rapid growth of cavitation bubbles followed by a periodic detachment of those is observed.…”