The role of sand particles on the rapid destruction of the cavitation zone of hydraulic turbines

Metal surfaces in the cavitation zone of hydraulic turbines working in sandy water are damaged rapidly. The damage is much more severe than that caused either by sand erosion or by cavitation alone. This paper presents an analysis of a worn surface of 18Cr-8Ni steel tested in a Venturi device at a hydroelectric power station in the flood season. Two types of damage were found. The first was a smooth erosion in the area of regular fluid flow. The second was in the regions where cavitation occurred. In the latter regions, the sand particles gain high velocities under the action of cavitation, impinge upon the metal surface and cause severe surface deformation and rapid damage. Embedded sand particles, cavities, cracks, cutting scars and fatigue patterns were found on the sponge-like worn surface.