Definition - What does Cavitation Corrosion mean?
Cavitation corrosion is a specific type of erosion which results from gas bubbles' implosion on metal surfaces. It is usually connected with abrupt pressure variations associated with a fluid's hydrodynamic parameters, such as in propellers, stirrer blades and turbine blades.
Areas of low and high pressure have a tendency to become induced under specific conditions such as high velocity. In areas with low pressure, vapor bubbles and gas can be produced. When such bubbles shift to high-pressure areas, they cave in and produce pressure waves, which can erode protective films, leading to heightened levels of corrosion.
Corrosionpedia explains Cavitation Corrosion
Cavitation may take place when liquid moves quickly through orifices and constrictions, such as when the shape of the orifice abruptly changes size. This is usually the case with water that moves past a valve or gate through a slightly opened valve. Such conditions result in a quick pressure change which is conducive to cavitation bubbles' formation.
Cavitation may also take place when liquids pass beneath a tall vacuum. This can happen when the fuel supply or pump hydraulic fluid is restricted leading to the high vacuum. Cavitation corrosion may also take place on the back portion of propeller blades when they are overloaded or the surface is not sufficient.
The formation of gas bubbles within a liquid can result in local film damage that serves as protection to corrosion. When local corrosion has been established, this can be a new spot for further cavitation attack and turbulence. This phenomenon is commonly seen in high-speed blade propellers and pumps. It is intensified in the case of entrained air seen in high-velocity systems. This could also take place on sound generators with high intensity. Substances like nickel and titanium alloys and stainless steels have high resistance to cavitation corrosion. However, these are not exempted from attack, especially under severe conditions.
Cavitation can be confirmed with the aid of hydrodynamic analysis, which is used to minimize and locate the formation of bubbles or shift the bubble collapse to a certain area where there will be a minimal effect. There is no standard test for this type of corrosion, but this can be avoided through experience and actual scale tests.
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