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Case study: Detection of cavitation

Detection of cavitation in the pump area

Occurring cavitation is one of the main reasons for increased wear in turbines and pumps of all kinds. When steam bubbles arise in a liquid at certain points in the system, this is called cavitation. The steam bubbles occur when the static pressure in a system, the temperature and the steam pressure do not match. Physical processes (which will not be discussed in detail here) cause these steam bubbles to burst again and, like micro-explosions, attack and destroy the surfaces of rotating blades in pumps and turbines. This "bursting" of the bubbles emits acoustic emissions in the ultrasonic range, whereby cavitation monitoring can be realised by means of ultrasonic sensors.

Feedwater pumps are a critical part of the infrastructure in CHP plants, as they are used for the continuous supply of water.

Figure 1 - Overview feedwater pumps

As part of a prediction of the remaining service life of the installed roller bearings in motors and pumps, the degree of cavitation was also determined at the pump chamber.

Figure 2 - Measurement at  the pump chamber

The measurement is carried out using Senzoro's Ultrasound Condition Monitoring System, which has combined ultrasonic sensors and artificial intelligence for the first time. The measurement results are displayed directly on the tablet and can be integrated into modern database systems.

Comparison "with" and "without" cavitation

The Ultrasound Condition Monitoring System is equipped with ultrasonic sensors that can measure frequencies in the range of up to 500 kHz. The measuring range is adapted depending on the application. Frequencies up to 120 kHz are sufficient for the detection of cavitation; the erratic occurrence of cavitation is very clearly visible in the spectrogram below.

Figure 3 - Spectrogram of cavitation peaks

Compared to conventional methods (vibration measurement), the presented method has the advantage of measuring cavitation directly (cavitation = ultrasound) and not only indirectly (cavitation causes vibrations). This eliminates false alarms and enables optimised driving. Cavitation monitoring by means of ultrasound thus represents the most advanced and sensitive type of cavitation detection.

Ultrasonic signal over time "with" / "without" cavitation

Author: Dipl. Ing. Mag. Markus Loinig, Senzoro GmbH




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