Vinyl paint is superseding oil paint as ship's bottom paint. The characteristics of vinyl paint film are better than those of oil paint film. However, there is a fear that, when some part of paint film happens to be defective, heavy local corrosion develops intensively at the defective part, as is often experienced on ships in service. In order to prevent the hull from corroding, cathodic protection is widely adopted along with the use of anti-corrosive paint. This method has proved effective, but there still remains a problem of deterioration of paint film as blistering and peeling. We investigated this problem by making immersion and rotation tests for 6 to 7.5 months in the sea and a continuous cathodic protection test for 5 months.
This article deals with the effect of oil and vinyl paints applied on steel plates upon corrosion of the plates and the effect of cathodic protection upon paint film damage and deterioration.
The durability of paint film of vinyl paint in sea water was good, but corrosion was apt to concentrate on the defective part of paint film. The pitting of vinyl painted plate was about two times as deep as that of oil painted plate. However, the application of cathodic protection with the use of vinyl paint even when the protected supply potential is as less noble as -1.0V (vs. S. C. E.), had little possibility of blistering and peeling of paint film. Another advantage was that the required current density was only about 3mA/m².

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Protective current in earth, which flows from anode to cathode for cathodic protection, causes potential gradient in ground, and metalic foreign structures in the field will be affected by the current.
The phenomenon is called interference, and it causes sometimes damages on the foreign structures.
In this paper, theoretical equations for the potential gradient in the field are discussed, and some methods of applying the equations for analyzing measured potentials, and for finding suitable method to reduce the interference, are explained including practical remarks to be at tended.

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Researches were made on the cause and mechanism of the pitting corrosion on the surface of gas cooler tubes. We conducted a series of electrochemical tests in sea water containing free chlorine. The test results showed that the cause of pitting corrosion lies in a local dissolution of mill scales on the surface of the tube which were formed in the process of hot-working and that free chlorine is concerned in the dissolution velocity of mill scales.

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