軟鋼の腐食疲労に対する防食の効果

抄録

The propeller shaft of ship is normally insuarated electrically from ship's hull while in running. Under such condition the effect of galvanic anode on ship's hull can not be expected act to prevent galvanic corrosion on propeller shaft. It is the fact that most of all damages of propeller shaft commonly caused by the corrosion fatigue, and this kind of damage was mostly caused by such electrically insurating effect. On this point of view, we tried some torsional fatigue tests on mild steel pieces immersed in salt water which protected cathodically with impressed currents. With our results, the effect of protection showed increasing in corrosion fatigue strength than the one without protection.
The rate of current density which need for complete prevention of corrosion for steel plate statically immersed in salt water is commonly agreed with about 150mA/m². To compare with this, our results of torsional fatigue tests showed much more current, say 700-800mA/m² were needed.
With such point of view, we can expect that the damage of propeller shaft and corrosion of propeller can be prevented mostly with the application of cathodic protection directly on the shaft under the current density of some little above 800mA/m².