boiling

Cavitation erosion (and the related erosion or impingement corrosion) is an infrequently discussed yet frequently misunderstood phenomenon that can lead to metal damage and failure. It can afflict everything from engines and generators to plumbing systems and propellers. Cavitation is the formation of voids or bubbles in a liquid that are a result of forces that act upon the liquid. It’s important, however, to distinguish these voids from common bubbles as the latter contain a gas, often air, while the former contain nothing. That is, they are vacuum bubbles. Interestingly, the formation of the cavitation void is tantamount to boiling because the boiling point of a liquid drops as the pressure drops. (It’s why mountaineers use pressure cookers; at a high altitude and therefore lower atmospheric pressure, water boils at a temperature lower than 212°F.) Thus, cavitation bubbles are essentially a result of low temperature boiling induced by low pressure. Cavitation may occur as liquid moves swiftly around constrictions and through orifices, particularly when such orifices change shape from small to large, as in water moving past a gate valve, or worse, through a partially opened valve. These conditions create a Venturi effect and the rapid change in pressure is conducive to the formation of cavitation bubbles.