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 w hich are the standard materials of the International Cavitation Erosio n Test Program which is coordinated by Dr. J. Steller, Institute of Fl uid-Flow Machinery, the Polish Academy of Science, Gdansk, Poland, Thr ee kinds of testing apparatus were used: a vibratory unit, a vibratory unit with a stationary specimen, and a water tunnel. In the two vibra tory tests, the ranking order of the materials according to their dura bility to cavitation attack showed a complete coincidence with each ot her. However, the ranking based on the water tunnel test was different from those of the vibratory units. This was because the damage rate o f some materials was suddenly accelerated in the middle of the water t unnel test. It was revealed that the remote cause of the sudden increa se in erosion rate is the activation of damaged surface in atomic leve l, which promotes corrosion only when a macro-cell of corrosion is for med between the cavitation damaged area (anode) and the undamaged area (cathode). Thus it was pointed out that some undamaged area is some t imes necessary on laboratory test specimens when an accurate simulatio n of the cavitation damage in the filed is demanded.