Recently, welded steel pipes have been used to cooling-water inlet-pipes of turbine condenser in power plants.
So we experimented on various methods of corrosion-protection for these pipes mainly by dipping tests to actual sea water, and obtained following results.
(1) Corrosion rates of carbon steel plates in sea water about 0.18mm/year, and ductile cast irons and low-alloy cast irons showed similar corrosion rates, but the casting skin of these cast irons appears to have no long-time effect on corrosion in sea water.
(2) Zinc coatings were highly resistant in sea water and showed also anti-fouling effects.
(3) Coal-tar enamel and asphaltic enamel coatings may be expected long-time effects for applying to steel structures, but anti-fouling properties were very poor, especially in asphaltic enamel, so chlorination methods should be used in case of these coating applied.
(4) Cathodic protection with impressed currents may be effective for these sea water pipes if accurate design are applied.

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This paper is the intermediate report of cathodic protection for ballast tanks of several tankers. Various methods (i. e.: various kinds and types of anode at various current densities) have been applied for several tanks. Tank potential has been measured by tanker crews. The investigation is not completed yet, but some valuable results were obtained. They are as follow:
1) Preliminary electrocoating method was not satisfactory. Coated film was not rigid enough, and disappeared within 6 months.
2) Zinc anode only may be able to use as sacrificial anode for protection of crude oil tank, but magnesium anode is more suitable than zinc anode.
3) Performance of combined use of zinc and magnesium anode is quite excellent.
4) Relation between potential, current density and time is obtained.
5) Polarization of wing tank is a little larger than that of center tank.
6) Ballast period is the controlling factor on the current density to be selected, and suitable current density for Japanese tankers which are usually engaging on the Middle East voyage is 120mA/m².

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