Cavitation

Cavitation occurs in high velocity, variable pressure situations and in waters containing dissolved or entrained gas. Pockets of vapor form at low-pressure regions, and as the water flows to zones of higher pressure, the pockets collapse (implode), causing shock pressures as great as several thousand psig. These high shock pressures physically destroy protective oxide films and dislodge metal grains from the surface.

The evidence of cavitation is often deep, circular pits, without tuberculation. The attack occurs in many areas, including the suction side of pump impellers, sharp bends in piping systems and the discharge side of globe or gate valves. It may also occur in diesel engines, caused by the pressures created by piston slaps. High dissolved nitrogen concentrations have been found to aggravate the condition. The use of a suitable film-forming corrosion inhibitor can aid significantly in retarding the attack.