Most of the examination regarding corrosion of steel structures at harbors has been conducted from point of the so-called general corrosion of steel buried in a single zone, for example, in sea water or in mud zone, and so on.
However, since long steel contacts nearly with several different zones in field, for example, sea water, mud zone unsaturated with sea water and mud zone saturated with sea water, it may be supposed that another corrosion unlike general corrosion will occur along the surface of long steel passing through different zones.
Accordingly, to distinguish corrosion tendencies of steel in a single zone and in different zones, in this report the former was called micro-corrosion, and the latter macro-corrosion.
To obtain a clue to the elucidation of steel corrosion problem at harbors, the relation between macro-and micro-corrosion rate of steel was investigated at laboratory and in field, and the following results were obtained:
(1) When steel contacted with both mud zones unsaturated and saturated with sea water, steel in unsaturated mud zone served as cathode and steel in saturated mud zone as anode, and then potential difference was about 150 to 200mV. In this case, macro-corrosion rate was directly proportional to the ratio of cathodic to anodic surface areas of steel, A_c/A_a. So, steel may become more dangerous due to macro-corrosion with increasing of A_c/A_a, and macro-corrosion rate may be neglisible at reduced A_c/A_a.
(2) When steel contacted with flowing sea water and mud zone saturated with sea water, there was such tendency that macro-corrosion cell occurred, whose cathode was steel in sea water and whose anode was steel in saturated mud zone. Then, potential difference was about 50mV, and contrary to the case (1), macro-corrosion occurred only when A_c/A_a was less than 0.3 to 0.6.
(3) When steel contacted with flowing fresh water and saturated mud zone, tendency of macrocorrosion was similar to that in the case (1).
(4) When steel contacted with flowing sea water, unsaturated and saturated mud zones, steel in sea water and unsaturated mud zone acted as cathode and steel in saturated mud zone as anode.
Therefore, it seems that such structures constructed with steel sheet pile as quay must be the using example of steel at harbors which is effective to diminish the danger resulting from corrosion because A_c/A_a in quay becomes about 0.3 in general.

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The change of the surface state of iron during corrosion in sulfuric acid solution was investigated by using an ellipsometer in the presence and absence of stannous ions.
No optically stationary state of surface was observed for corroding iron in the solution. To obtain reproducibility, electropolishing followed by electrochemical polarization appeared to be the best surface treatment for the optical investigation.
Results of ellipsometric measurements indicate that during immersion of iron in the solution an absorbing film was formed on the surface without appreciable change of the electrode potential. In 1hour immersion the film grew up to about 150Å, which was assumed to be a kind of precipitated solid film.
When stannous ions were added, the surface state of iron changed slowly to the optically reverse direction and reached a steady state, while the potential initially rose rapidly to a noble value and then fell gradually. This can be explained by assuming some structural change of the film resulting in the formation of an iron-tin compound leading to the inhibition of iron corrosion.

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The corrosion behaviors of austenitic stainless steels in high-temperature boric acid solutions were studied to estimate the effect of boric acid on the general corrosion rate in high-temperature water and on the stress-corrosion cracking in high-temperature chloride solution. The general corrosion rate in static or dynamic water was not so much affected by the existence of boric acid, and the average corrosion rate for 10, 000 hours was about 2mg/dm². month at 300°C. The stress-corrosion cracking in sodium chloride solution was diminished by the existence of boric acid. The general corrosion rate and the stress-corrosion cracking were suppressed by the addition of a small amount of potassium hydroxide.

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