The Synergistic Effect of Cavitation Erosion and Corrosion for Copper and Cupro-Nickel in Seawater

Abstract

Experiments are described in which attempts have been made to investigate the fundamental mechanisms of the synergistic effect of cavitation erosion and corrosion. The design of an all-plastic cavitation tunnel is described which allows specimens to be held under potentiostatic control in a flowing seawater system. Experiments were conducted in a 10 × 20 mm working section with a 60° symmetrical wedge cavitation source at an upstream flow velocity of 14.7 m/s. An extensive test programme has been completed comprising three separate tests: Pure Erosion, Pure Corrosion and Combined Erosion and Corrosion, each conducted at two different cavitation intensities. These tests have concentrated on investigating the erosion/corrosion performance of copper in seawater. Preliminary results using cupro-nickel are also reported. It was found that a clearer indication of the synergistic effect was obtained from depth of penetration measurements than from mass loss measurements. The synergistic effect was found to be most marked when cavitation erosion occurs in the presence of mild corrosion. For the worse case studied, 50 percent of the depth of penetration was caused by synergistic mechanisms.