Cavitation – Everything you need to know
Cavitation refers to the physical phenomenon in which cavities or steam bubbles are formed at high flow velocities or with fast movement of a body through a fluid such as water. Typical examples for this are impellers in pumps or turbines.
How is Cavitation Developed?
According to the law of Bernoulli, the static pressure of a liquid falls with increasing speed. If the static pressure falls below evaporation pressure, steam bubbles will develop.
Damage caused by cavitation
If the static pressure rises again, the steam bubbles will collapse again. This collapse can be relatively strong, leading to damage, for example on ship propellers. In this case, the surface of the material affected is damaged by shock waves caused by the condensation of the bubble. That is also why cavitation is observed with parts that are used in water, such as pumps. This is also called cavitation erosion. The steam bubbles mostly collapse on neuralgic points, at which the pressure rises again, for example at the pump outlet. At these points, a material abrasion will develop. This can lead to massive damage on the components affected over a long period of time.
Avoidance of Cavitation
Even if cavitation is limited by corresponding structures, it is impossible to prevent its occurrence in many applications. In these cases, only hardening of the steels is recommended. If high demands are placed on erosion resistance, then the BORINOX® process for stainless steel hardening will be suitable. When using the BORINOX® process, the desired properties of stainless steel are maintained. At the same time, the hardness of stainless steel is increased, with a rising resistance to damage by cavitation.
