Some actual data of cathodic protection by long life Al anode system applied to marine steel structures (sheet piling wharf, steel pile, pier, dolphin, etc.) were analysed and compared with impressed current system, from the viewpoint of economy and maintenance practice.
The conclusions are summarized as follows.
1) In common submarine environments, Al anodes giving initial current density for steel of 0.1A/m² in sea water, and 0.02A/m² in mud, polarize steel structures to the potential of Ca. -900mV (vs. Ag-AgCl half cell) within short periods and are expected to maintain this condition for the whole life of the anodes.
Anode current density in this steady state is supposed to be 0.2-0.3mA/cm², and it is recommended to keep the anode current density larger than 0.1mA/cm², since the current efficiency of anode is larger.
2) Long life Al anode systems are capable of sufficient protection to marine steel structures for longer than 10 years, and cathodic protection using these anodes are compatible with the impressed current system on an economic point even in the case of large structures.
3) Judging from the weight losses of test pieces, it was confirmed that, for steel structures fitted with Al anodes, the protective effects in tidal zone, even in about 50% submerged portion, were practically equal to those in fully submerged portion.

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In the previous report, it was found that the corrosion rates measured by cell voltage-current curves were in good agreement with those found by weight loss measurements at the stagnant condition, if the sweep velocity of cell voltage was less than 100mV/min and the area ratio of cathode to anode was more than 1.
In this report, cell voltage-current curves were measured under the condition that the sweep velocity of cell voltage was 100mV/min and the area ratio of cathode to anode was 1.
In the first time, the effects of the concentration of chloride ion and flow rate on corrosion rates of mild steel were investigated in 0.3-30g/l sodium chloride solution recycling at the rate of 0-2m/sec at 20-22°C.
Then, corrosion rates of mild steel in the industrial waters at Kawasaki City were measured, and it was indicated that their corrosion rates in these waters were greatly affected by two factors: concentration of chloride ion and flow rate.

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The corrosion resistance of iron-molybdenum alloys has been investigated in maleic acid solution and the results are summarized as follows:
(1) The polarization behaviour of α phase alloys does not substantially differ from that of pure iron in H₂SO₄ and NaOH solutions. A similar behaviour was also found in maleic acid solution.
(2) The critical current density of α+Fe₃Mo₂ two phase alloys is greater than that of α phase alloys.
(3) With regard to anodic passivity, it was found that 60% Mo-Fe alloy attains it easily. But the alloy dissolves in the form of hexavalent molybdenum ions at the potential E_p higher than about +0.3 volt.
(4) On decreasing the potential, the two stages, the dissolution of the intermetallic compound Fe₃Mo₂ and the dissolution of α phase alloy, can be distinguished in the polarization of α+Fe₃Mo₂ two phase alloys.
(5) The rise of temperature was found to increase remarkably the anodic dissolution and the corrosion weight loss.

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