The oxidation behaviour of type 430 stainless steel was studied in a range of 1223 to 1373K, in a gas mixture of H₂O (P_H2O=0.006-0.20atm), O₂ (P_O2=0.165atm), and N₂ (P_N2=balance) under atmospheric pressure. Breakaway due to water vapor was found to take place in a manner of localized corrosion. It was also found that the lifetime to breakaway, t_L, is not simply determined by the oxidation conditions, but can be evaluated statistically. An exponential distribution explains the scattering of t_L data. Both the transition probability of breakaway, λ, and the apparent parabolic oxidation rate constant before breakaway, k_p″, increases with an increase in P_H2O, indicating that larger k_p″ in the initial stage leads to earlier breakaway. As the mass gain by oxidation at the breakaway point did not change very much with P_H2O, the accumulation of growth stress in the oxide film will be one of the controlling factors of film breakdown leading to breakaway. The crystalline structure and the surface composition of the oxide film did not change very much with P_H2O before breakaway, suggesting that other structural differences, such as defect concentration, ionic conductivity, or others, can explain the effect of water vapor.

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The relation between the corrosion rate and properties of oxides on iron formed in initial immersion stage was investigated by monitoring corrosion potential (E_corr) and corrosion resistance (R_p) in deaerated 5mol·m^-3 Na₂SO₄ solutions of 473 to 588K. In order to understand electrochemical properties of the oxides, the reactivity of them to cathodic reduction of O₂ also was investigated at room temperature in addition to identification of the oxides. Analyses of iron oxides with X-ray diffraction, laser Raman spectroscopy and SEM showed only magnetite formation, independent of exposure temperature. The temperature dependency of R_p was found to change below and above the exposure temperature of 548-573K. This temperature dependency was maintained in the measurement at room temperature in absence of O₂, whilst being disappeared as changed the atmosphere to O₂. Along with the behaviors in E_corr and the O₂ cathodic reduction, it was considered that the corrosion rate of iron in deaerated high temperature water was markedly dependent of the morphology of the inner oxide layer formed in the initial stage, which being characterized by pore distribution. Further, the corrosion rate below 548-573K was discussed in terms of diffusion processes of Fe²⁺, FeOH⁺ and H₂O through the micropores of inner oxide layer.

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In order to establish the reductive behaviour of oxidizing agents on the surface of titanium in sulfuric acid solution, the polarization characteristics of titanium have been investigated, using potentiostatic and galvanostatic techniques. Many kinds of oxidizing agents, such as oxygen, hydrogen peroxide, persulphate, periodate, ceric, mercuric, cupric, permanganate, and ferric ions were used. They could be classified into two different groups according to the reductive behaviour on the surface of passive titanium. Some of the oxidizing agents, such as Ce⁴⁺, Hg²⁺, Cu²⁺, MnO₄^2-, and Fe(CN)₆^3- ion, were reduced at an appreciable rate on passive titanium as on a platinum electrode. O₂, H₂O₂, S₂O₈^2- and IO₄^- ion, however, could scarecely be reduced on passive titanium, though considerable reduction currents were observed on a platinium electrode. They can also be classified with respect to their sensitivity of response to cathodic pulses and to the restoration rate of potential after interrupting the pulse. From these results, it may be considered that the reduction of oxidant in former group occurs over the whole area of passive film, while only the dissolved points are effective for the reduction of oxidant in latter group.

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Two electrode system, in which the Ag/AgCl electrode serving both as a reference and a counter electrode, has been applied to the potentiostatic polarization in an aqueous solution containing chloride ions. It is experimentally very convenient and useful method in the potentiostatic polarization with small current, such as the cathodic polarization of coated steel for accelerated test of film delamination and the pitting incubation period measurement of stainless steel.

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The “repairing” is becoming an important engineering and technical problem in the maintenance of japanese chemical process equipments which have been operated for last ten years or more. The construction materials in these equipments have suffered various damages such as the embrittlement due to the tempering, hydrogen, creep and the precipitation, and also the corrosion and the cracks. The “weld repairing” involves not only the weld techniques for repairing but also the other important problems such as the assessment of defects, post repair heat treament, evaluation of the reliability of repaired equipments and the estimation of life time. Some of these are also important political problems in relation to the current standards and/or regulations. This report introduces the view and practice of weld repairing, based on the results of subcommittee's activity in the Society of Chemical Engineers, Japan (1981-1984). In this report, the following items are introduced. (1) description of materials damages and degradations, (2) assessment of defects, (3) how the repair welds have been done-from the published literatures and (4) how consider the effect and applicability of post repair heat treatment

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Corrosion behaviors of non-oxide ceramics such as Si₃N₄, sialon, SiC and AlN by high temperature oxygen and water vapor, molten alkali salts, high temperature and high pressure water and acidic aqueous solutions were reviewed. The corrosion rate and the degree of degradation of the mechanical properties greatly depended on the characteristics of the surface film formed by the corrosion reaction.

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