Two types of laboratory corrosion tests of intermittent immersion in synthetic sea water and marine exposure tests were carried out in order to study the effects of alloying elements on the corrosion resistance of low alloy steel in the splash zone.
Effects of alloying elements were found to depend upon the frequency of the dry-and-wet cycle. In relatively dry environments, such as marine atmosphere or upper splash zone, addition of Mn, Cu, P and Cr improved the corrosion resistance of steel.
In wet environments, such as lower splash zone or tidal zone, addition of P improved the corrosion resistance considerably, whereas Cr affected adversely.
X-ray diffraction of the rust layer formed on the steel specimen revealed that these alloying elements affected the corrosion resistance by changing the particle size of magnetite, which was the main constituent of the rust layer formed in the marine atmosphere. Thus, addition of alloying elements that resulted in the rust layers of finer magnetite particles improved the corrosion resistance of the steel.

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The corrosion of mild steel and the protective effect of cathodic current were studied in water containing 3% sodium chloride with the relative velocities of 3-6.5m/sec at 35°C, by using high speed rotor test apparatus.
The results obtained were summarized as follows: (1) The corrosion rates of mild steel increased markedly in moving condition as compared with stagnant one. The corrosion potential was more noble in moving condition than in stagnant condition. (2) The corrosion rates of mild steel in moving condition were different from that under stagnant condition and were almost constant in a range of pH less than 3.3. (3) Mild steel was protected almost completely by supplying cathodic current even under moving condition. Protective potential for mild steel with the relative velocities of 3-6.5m/sec was -0.6V (SCE) at pH6, and was -0.8V (SCE) at pH 3.3 and 2.

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