Assessment of design considerations and Field Repair procedures to mitigate cavitation pitting in Hydraulic turbines

Cavitation erosion in hydraulic turbines is of major importance to all members of the hydroelectric community. This erosion is caused by the collapse of vapor bubbles against or very near turbine surfaces. These bubbles are formed in regions where the absolute pressure falls below the vapor pressures of the fluid. Nuclei flowing through these regions experience tension and quickly develop into vapor bubbles. These bubbles then rapidly collapse, creating very high pressure waves emanating from the center of collapse. When the bubble collapse occurs near a material surface, a minute crater may be formed. Over a period of time this can lead to the spalling of material, which will eventually require remedial measures in order to insure continual successful turbine operation