The tests of cathodic protection were carried out with regard to the influence of the position of the anodes and the reference electrode on protective effect, potential distribution, protective current, etc. and to the protective current required while running and while stopping, with the automatic protective equipment fitted to a tugboat.
The following are the results obtained:
1) The vessel, while running, requires about double the amount of the protective current required while stopping.
2) It is desirable to set the reference electrode close to the anodes, in view of protecting the painted film.
3) It is adequate for complete protection to arrange the anodes zigzag with the spacing of about 4 meters.

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There have been published few formulae for theoretically calculating the potential distribution on infinite steel plate such as required for designing the anode pitch in the cathodic protection.
This report introduces a theoretical formula for the potential distribution in which the authors assumed the current path from the anode to the cathode taking into consideration the polarization resistance and the paint film resistance.

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In the previous report, the authors introduced a theoretical formula for the potential distribution in the cathodic protection.
This report describes comparison of the calculated values through the formula with the measured values in some actual cases, that is, exemplification of the formula.
In order to make this comparison, the authors experimentally obtained the composite values of the paint film resistance and the polarization resistance as follows:
10³-10⁴Ω-cm² for non-painted steel plate
10⁶-10⁷ Ω-cm² for painted steel plate
Then, the authors made calculation in several cases of cathodic protection by substituting the above values in the theoretical formula, and as the result the calculated values were found in good agreement with the measured ones.

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Cathodic protection by means of an automatic potential controller of motor-driven transformer and rectifier type was applied to steel pipe circulating sea water. This controller regulated automatically the current applied to the pipe to maintain the protective potential within ±5mV under the conditions such as the velocity and the resistivity of sea water changed with time.
But as the result of the experiment, it was pointed out that the reliability of automatic potential control was affected by the location of the reference electrode and the value of the set potential.

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In setting of passivation potential in anodic protection of chemical apparatus, various initial operations, namely, the partial anodic passivation method, the chemical passivation method and the anodic passivation method at room temperature were investigated using type 316 stainless steel and 30% sulfuric acid. These were carried out in order to suppress the dissolution of metal and the pollution of aqueous solution with the metallic ion dissolved and also to minimize the capacity of potentiostat. The effectiveness of these methods were confirmed experimentally; in the practical applications it is desirable to combine these methods properly.

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