INFLUENCE OF GALVANIC MACROCELL CORROSION ON THE CAVITATION EROSION DURABILITY ASSESSMENT OF METALLIC MATERIALS INTERNATIONAL CAVITATION EROSION TEST OF GDANSK

Cavitation erosion tests were carried out on five metallic materials which are the standard materials of the International Cavitation Erosion Test Program which is coordinated by Dr. J. Steller, Institute of Fluid-Flow Machinery, the Polish Academy of Science, Gdansk, Poland, Three kinds of testing apparatus were used: a vibratory unit, a vibratory unit with a stationary specimen, and a water tunnel. In the two vibratory tests, the ranking order of the materials according to their durability to cavitation attack showed a complete coincidence with each other. However, the ranking based on the water tunnel test was different from those of the vibratory units. This was because the damage rate of some materials was suddenly accelerated in the middle of the water tunnel test. It was revealed that the remote cause of the sudden increase in erosion rate is the activation of damaged surface in atomic level, which promotes corrosion only when a macro-cell of corrosion is formed between the cavitation damaged area (anode) and the undamaged area (cathode). Thus it was pointed out that some undamaged area is some times necessary on laboratory test specimens when an accurate simulation of the cavitation damage in the filed is demanded.