The polarization curves of various galvanic couples, such as mild steel vs. pure zinc, aluminium alloy (NP56) vs. pure zinc, manganese bronze vs. aluminium alloy (NP56), etc. have been measured in diluted sea water, and the following relations have been known.
1) The minimum currents for protection in stagnant water required for steel and aluminium alloy (NP56) become maximum in 1/10 diluted sea water, while such a relation is not seen in the case of manganese bronze.
2) The minimum currents for protection required for the above-mentioned metals in flowing water (containing air bubbles) become larger as the salt concentration of sea water increases.
3) The maximum current density of galvanic couples in flowing raw sea water (containing air bubbles) is always larger than that when measured in stagnant raw sea water. This phenomenon is particularly extensive in the case of aluminium alloy (NP56) being used as a cathode. The current, however, decreases as salt concentration becomes smaller, and in fresh water, becomes almost same as in stagnant water.

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The local corrosion which can not explain the cause by conventional theorys, ununiform material, concentration cell, or erosion, are frequently found actual equipment as petroleum refinery.
And these corrosion has relation with the bubbling.
The author studied the influence of the bubbling on such local corrosion by experience and experiment.
The results obtained were as follows:
(1) Owing to contact with gas phase and liquid phase alternately, distribution of energy are changed on metal surface, and accelerated the corrosion.
(2) The bubbles in the liquid has equivalent energy to heat and mechanical in order to make the bubbles.
(3) Kind of gas, liquid and metal are make change the energy of metal surface.
(4) The name “alternate phase effect” are proposed as new theory.

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For the purpose of improving the performance characteristics of high purity zinc anode in corrosion prevention, the anode behaviors of a number of new zinc alloys, prepared by adding a small amount of indium or related elements to special high grade zinc, were determined under following experimental conditions: anode current density: 1mA/cm²; electrolyte: synthetic sea water at 30°C (no agitation); duration: 300-1, 000hr. Throughout the test anodic potential was regularly observed. At the end of each test, the amount of adherent corrosion product and the weight loss of the anode were measured. The results revealed were:
1) The anodic potential of new zinc alloys containing 0.01-3% of In, Tl, Hg, Cd or Wood's Metal did not increase throughout the tests, whereas that of special high grade zinc increased more or less markedly.
2) The anodic current efficiencies of special high grade zinc was 94-96% and the amount of adherent corrosion products were 10-20% (based on dissolved Zn), while in the case of new zinc alloys they were 97-99% and 2-6% respectively.
3) The decreased corrosion products of new zinc alloys were further characterized by their softness and jelly like appearances; they were removed easily by spraying or mild rubbing. The long sustained anodic potential of new zinc alloys could be ascribed to the properties of their corrosion products.
4) A statistical correlation between anode efficiency and the amount of adherent corrosion product was evident.
An actual shiphull test of the new zinc alloy showed the superior characteristics compared with the usual anode of high purity zinc.

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