港湾における鋼材腐食の研究 (第5報)

鋼矢板構造物の腐食 (1)

抄録

In the previous report it was supposed that steel portion in sea water acted as cathode of macro-corrosion cell, but as a result of further investigation it was confirmed that, at steel sheet piles on sea side, the steel portion above mean low water level served as cathode while that under mean low water level as anode. Moreover, the three kinds of corrosion tendencies of steel sheet piles, which were reported previously, depended considerably on the existence of tidal range, the depth of water, the presence of fresh water, and so on, as follows:
Corrosion tendency (a) was likely to be generated when water level changed every 6 hours and the ratio of cathodic area to anodic area of steel, A_c/A_a, was 0.1 or more and the specific resistance of water, ρ, was greater than 25Ω-cm, especially in the range of several hundreds to a thousand Ω-cm.
Corrosion tendency (b) was likely to be generated when there was tidal level difference and A_c/A_a was 0.1 or more and ρ was nearly equal to 25Ω-cm.
Corrosion tendency (c) was likely to be generated when water level changed every 6 hours and A_c/A_a was 0.1 or less and ρ was nearly equal to 25Ω-cm or when there wasn't daily tidal change.
As mentioned above, it is supposed that corrosion tendencies of steel sheet piles can be explained from the point of view of macro-corrosion.