Eleven test steels containing P, Cu, Cr, Ni and Al in various combinations were exposed in the atmosphere, tidal and submerged zones up to 5 years. The results show that in the marine atmosphere Cr and Al are beneficial, and at the tidal zone P, Cr, Ni and Al are effective. The slope of the corrosion-time curves decreases in 0.5year. At the tidal zone, moreover, surface rust, local attack and exposure levels have much influence on the corrosion resistance. On the other hand, in the submerged zone the corrosion resistance is increased by the combined additions of Cu, Cr and Al, and the effect is consistent over the whole exposure period. Strongly adherent, hard and Cu, Cr, Al enriched inner rust next to the base metal is formed on such steels and this inner layer increases cathodic polarization remarkably. These results lead to the conclusion that Cu-Cr-Al steels have a good corrosion resistance in marine environments.

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To obtain basic data for development of the ship hull anti-fouling system which utilizes electrolysis of sea water, a pair of long and thin electrodes consisting of lead-silver alloy as anode and iron as cathode was immersed in sea water and study was made on how chlorine resulting from the electrolysis of sea water would be disseminated. Also, an under-water experiment was made with a pair of 36-meter long electrodes fitted longitudinally to the bilge of a 126, 000 tons dead-weight ship under construction. The following results were obtained.
1) The steel wall surface like the ship shell plate lends itself to uniform distribution of chlorine and minute bubbles of hydrogen gas evolved on the cathode assist very effectively in the spread of chlorine.
2) A considerable amount of stray current arising from the anode may be feared to accelerate corrosion of the ship hull steel plate, but this corrosion can be completely prevented by application of the cathodic protection and “drainage” system.

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