Corrosion and protection tests of steel in marine environments were done, and the following results have been obtained.
1) Mean corrosion rates of steel piles calculated from thickness measured by using ball type micrometer in laboratory approximated to the values obtained from weight decreases.
2) Mean corrosion rates (one side) of 6th year steel piles were 0.07 to 0.08 mm/yr in tidal zone, 0.06 to 0.10 mm/yr in sea water, 0.02 to 0.05 mm/yr in sea mud zone, 0.065 to 0.16 mm/yr in atmospheric zone and 0.01 to 0.03 mm/yr in soil.
3) Protective current densities in sea water at Niigata port were larger than the standard value in ordinary sea water, 50 mA/m2. It is considered that such tendency is mainly due to increasing of specific resistance of sea water by flowing of fresh water.