In order to clarify the roles of cavitation and erosion in the cavitation-corrosion damage of a pump casing used for pumping a corrosive chlorinated fresh water, an electrochemical study has been performed using a one-third scale prototype double-suction volute pump.

Three electrochemical corrosion monitoring electrodes consisting of a medium carbon cast steel test electrode, a stainless-steel counter electrode, and a 0.5 mm diameter stainless-steel capillary, each being separated by epoxy resin, were mounted at different locations of the casing wall. The polarization resistance was determined from the potentiodynamic polarization curves, and the corrosion current density was calculated.

Determination of the corrosion current density as a function of flow quantity revealed that at 10 percent of the normal flow capacity the corrosion current density increased to 50 mA/cm² for the eye area of the casing throat, compared with 0.03–0.08 mA/cm² measured at above 20 percent of the normal flow capacity and for the other locations at any flow range.

It may be suggested that this high corrosion current density results from the synergystic effect of cavitation induced from the reversed flow and corrosion enhancement by chlorine in the water.