In the previous report, based on the results of corrosion survey of steel sheet pile structures, corrosion tendencies of steel sheet piles have been divided into three types, (a), (b) and (c), according to the condition of corrosion under H. W. L. But due to the further corrosion surveys, it has been proved that there are other two types of corrosion tendencies of steel sheet pile structures. Namely, the tendency in which corrosion concentrates only at concave surface of steel sheet piles directly under residual water level is called corrosion tendency (d), while another tendency in which concentrated corrosion occures both at convex and concave surfaces of steel sheet piles directly under L. W. L. is called corrosion tendency (e). Corrosion rates (both sides) at the portion in which corrosion concentrated were 0.5 to 1.0mm/yr.
On the other hand, investigating the relations between corrosion tendencies and conditions of steel sheet pile structures based on the corrosion survey results of 83 examples, it is supposed that corrosion tendencies of steel sheet piles are affected by water depth, tide level difference, presence of fresh water, kind of backfill, shape of cross section of steel sheet piles, residual water level difference, and so on. Damage caused by concentrated corrosion are flow-out of backfill and settling or subsidence of superstructures of steel sheet pile structures.

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The performance of magnesium galvanic anode, which has been used to protect and earth the pipeline, is affected by alternating current induced on coated steel pipelines from high voltage electric distribution line. The effects of alternating current on the potential and corrosion of magnesium galvanic anode were examined in back fill solution at 30°C. With an increase in AC current density up to 10.0mA/cm², the potential of magnesium anode shifted more noble than its rest potential by 0.3-1.8V. Corrosion rate of magnesium anode increased at AC current density of 1.0mA/cm², and at 10.0mA/cm², an extraordinary increase in corrosion rate was observed. The effect of AC on the potential of magnesium anode can be explained by polarization curves measured by using a synchroscope.

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Erosion corrosion of brass in water containing 3% sodium chloride with relative velocities of 1-7m/sec at 30°C were studied by using a rotor-type testing apparatus. The results obtained were summarized as follows: 1) The corrosion rates of brass increased with increasing relative velocity, but they increased little at higher velocities than 4m/sec. 2) The corrosion rates of brass increased markedly when sand particles were added to the solution, and the effect of sand particles was promoted with an increase in relative velocity. 3) At relative velocity of 3m/sec brass was protected almost completely by supplying cathodic current even in the case of containing sand particles in the solution, but the cathodic protection was not sufficient when the relative velocity was higher than 5m/sec, because of the mechanical characteristics of sand erosion. 4) Erosin of brass increased makedly with increasing relative velocity.

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Severe corrosion of brass propellers have occurred recently in J. N. R. ferry boats which have been in service between Uno and Takamatsu.
The corrosion is considered to be caused by the following reasons; 1) sea water corrosion, 2) stray current from the railway, 3) sand erosion and 4) cavitation damage. When the cathodic protection with zinc anodes was applied for these propellers, the potential of propellers shifted to more negative values ranging from -580 to -720mV (vs. Ag/AgCl sea water electrode), and the protection current densities ranged from 1 to 1.4A/m². Thus, the corrosion rate of propeller blades decreased remarkably. Using several kinds of propeller materials, laboratory experiments and field tests were carried out on the following points; 1) cathodic protection against the corrosion of brass by the rotating disk method, 2) cavitation damage by the magneto-strictive vibration and 3) field corrosion tests using the couple of brass and zinc which were dipped in sea water. From the results of these experiments, it was confirmed that the protection potential of propellers in service was suitable as the potential required for the cathodic protection of brass.

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