抄録
Severe corrosion of brass propellers have occurred recently in J. N. R. ferry boats which have been in service between Uno and Takamatsu.
The corrosion is considered to be caused by the following reasons; 1) sea water corrosion, 2) stray current from the railway, 3) sand erosion and 4) cavitation damage. When the cathodic protection with zinc anodes was applied for these propellers, the potential of propellers shifted to more negative values ranging from -580 to -720mV (vs. Ag/AgCl sea water electrode), and the protection current densities ranged from 1 to 1.4A/m2. Thus, the corrosion rate of propeller blades decreased remarkably. Using several kinds of propeller materials, laboratory experiments and field tests were carried out on the following points; 1) cathodic protection against the corrosion of brass by the rotating disk method, 2) cavitation damage by the magneto-strictive vibration and 3) field corrosion tests using the couple of brass and zinc which were dipped in sea water. From the results of these experiments, it was confirmed that the protection potential of propellers in service was suitable as the potential required for the cathodic protection of brass.
