Abstract
Maraging steels are particularly well adapted to the making of light-weight, and high-strength propellers necessary to drive super-large tankers of recent design. Drawback of the maraging steel is that it offers far less corrosion-fatigue strength in sea water than in air and is highly vulnerable to local corrosion attack.
Cathodic protection is, therefore, indispensable for the maraging-steel propeller in service, but the potential of the maraging-steel propeller in service, but the potential of the managing-steel propeller must be controlled to closer limits than that of the copper-alloy propeller since excessive cathodic polarization can lead to hydrogen embrittlement of the material. This makes it desirable to use an automatic impressed current system in order to control the potential of the propeller to the optimum level during sea service.
For this system to be applied in cathodic protection of the maraging-steel propeller, it is necessary to know the distribution of electrode potentials over the propeller surfaces.
In this study, the distribution of potentials over the propeller surfaces and ship hull, and the electrode resistances which would occur between the propeller and the ship hull were determined experimentally with a ship model and theoretically by calculation.
The calculation and measurement showed a good agreement as regards the distribution of potentials and currents over the propeller surfaces and ship hull. Electric resistances between the propeller and the ship hull were found to be an important factor to consider in providing cathodic protection for the former.
