Corrosion survey of lock gate and sluice facilities at Amagasaki Harbor has been carried out, and the following results were obtained.
There was such tendency at gate leaves of the lock gate and the sluice that corrosion was concentrated at protruding parts of members (i.e., edges of reinforcement) in the area directly under L. W. L. as at steel sheet pile structures, and at extreme places corrosion rates exceeded 1mm/yr (one side), while material thicknesses reduced were not more than 0.1mm/yr (one side). Furthermore, such corrosion tendency could be seen at screens of pump houses for regulating water level inside the lock gate and the sluice. On the other hand, in the case of jet pipes of the gate leaves, corrosion was concentrated at the parts covered by drifting objects and the sides embedded in mud deposits.
However, the concentrated corrosion phenomena mentioned above could be explained by the same action of macro-corrosion cell as in the case of other steel structures at harbors.
Besides the above, corrosion survey method of lock gate and sluice facilities was also investigated and it was found that for grasping the true situation in corrosion of lock gate and sluice facilities, corrosion rates of members should be measured not only in the direction of thickness but also in the direction of width.

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A mechanistic aspect of passivation of stainless steels in reducing ammonium sulfate solution was studied.
When a reducing agent such as sulfur dioxide, thiosulfate or sulfite was added in ammonium sulfate solution, the redox potential of Fe²⁺/Fe³⁺ and the corrosion potential of stainless steels moved to less noble direction, and then steels were severely corroded. When the ammount of such reducing additives exceeded the critical value, the rest potential of the stainless steels shifted to noble direction into passive region and corrosion was protected, while the redox potential of Fe²⁺/Fe³⁺ remained at a constant base level, and Fe³⁺ in solution were strongly reduced to Fe²⁺. The critical value corresponds to the condition that the limiting diffusion current density of reduction of HSO₃^- to S is beyond a anodic peek current density in active region. In this case, the corrosion behavior was strongly controlled by cathodic diffusion process. Investigation was also made on various factors related to the critical value.

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