The galvanic current between copper electrodes immersed in solutions of different salt concentration is investigated for the aqueous systems of CuSO₄-Na₂SO₄-H₂O and CuSO₄-H₂SO₄-H₂O. The effect of the liquid junction potential caused by the concentration difference in Na₂SO₄ or H₂SO₄ on galvanic currents were measured quantitatively and elucidated by modified Evans' diagrams. As an extreme case of liquid junction potential effect apparently abnormal phenomena in which the position of higher electrode potential becomes anode against the position of lower electrode potential is demonstrated in galvanic cell. Furthermore the change in polarization resistance due to the difference in salt concentration brings remarkable effect on the amount of galvanic currents.

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With the intention of suppressing the crevice corrosion of austenitic stainless steel used in sea water, the technique of fused coating on stainless steel with thin layer of Ni base alloy which is resistant to crevice corrosion was developed. The effect of Cr and Mo on corrosion resistance of Ni base ternary cast alloy was studied by cyclic polarization method, and two alloys were selected. Fused coating of these alloys were performed with high frequency induction plasma flame.
The following results were obtained: (1) Fused coating layer with power of Ni-31.9% Cr-8.0% Mo-1.9% Si-1.8% B alloy did not reveal desired cyclic polarization behavior in 3% NaCl solution.
In the case of spraying the same amount of Ni-33.7% Cr-19.6% Mo-2.2% B powder as the above one on the former sprayed layer, the fused coating layer revealed good cyclic polarization behavior. Good correspondence was ascertained between cyclic polarizaiton behavior and the results of 6 months immersion test in natural sea water. (2) The difference of the resistance to crevice corrosion between these fused coating layers might be attributed to the Mo content in the matrix of fused caoting layers. Therefore, an enough amount of Mo should be contained in the matrix to maintain the resistance to crevice corrosion.

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The effect of dissolved oxegen on the potential of coated steel was investigated in neutral solutions. The potential difference of coated steel between in aerated solutions and in deaerated solutions was relatively large, for example, 480mV. The value was much larger compared with that of uncoated steel, which suggested that the steel surface beneath paint film had some characteristic behaviors.
The electrochemical behaviors of dissolved oxygen are shown below.
(I) The potential of coated steel in aerated solutions and in reaerated solutions was noble and almost equal, and that in deaerated solutions was less noble. The polarization resistance of coated steel in aerated solutions was largest, and that in both deaerated and reaerated solutions became smaller.
(II) The potential behavior of coated steel was as same as the case (I). The polarization resistance in deaerated solutions was largest, and that in both aerated and reaerated solutions became smaller.
(III) The range of potential difference between in aerated and deaerated solutions was relatively small in the initial stage of immersion or in case of thicker paint film.
These results suggest that passivate film is formed on the steel surface under paint film in neutral solutions.
The model of polarization diagram of coated steel was proposed, considering the effect of dissolved oxygen.

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The influence of the number and the area of specimens used in the extreme value statistical analysis was examined for localized corrosion occurring in a chemical process plant. Two carbon steel tubes were sampled from a heat exchanger in service and sectioned for inspection of corrosion. The size of specimen does not significantly affect the maximum depth of penetration estimated when the total area of the specimens examined and used for prediction are kept constant. However, deviation of the estimated penetration depth becomes larger when the number of specimens is reduced or the return period increases. In conclusion, an average of the several maximum values determined should be used to estimate the maximum depth of penetration. In this case, it is recommended that about 8 maximum depth values should be picked out of those observed in about 16 specimens and the size of each specimen should be determined so as to keep the return period less than 15000.

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On the basis of the previous papers, the resistance to vanadium pentoxide attack and hot corrosion of various heat resisting alloys for practical uses was evaluated. The effects of principal alloying elements such as chromium, molybdenum, titanium, aluminium and rare earth on the corrosion resistance of heat resisting alloys were also discussed.

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