Pure iron sheets, following immersion in artificial city water containing chromate ion as inhibitor, were analysed by the angle-resolved XPS technique. The thicknesses of the surface film and contaminant hydrocarbon layer on the specimens when estimated using a flat, multi-layered surface model were apparently dependent on the take-off angle of the photoelectrons. The origin of this apparent take-off angle dependence of the thickness was attributed to the surface roughness of the specimen rather than the porosity of the surface film. The rough surface was approximated with a simplified model surface consisting of facets with a defined inclination angle. The latter was chosen, by a least squares method, so that the calculated thickness of the surface film became independent of the take-off angle. The compositions obtained using a flat surface model are not affected by the roughness correction procedure. However, the composition is dependent on the take-off angle as the result of a non-uniform in-depth distribution of constituents.

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Erosion-corrosion behaviours of a carbon steel and a stainless steel were studied by electrochemical measurements in “jet-in-slit” sand-erosion testing. The test was conducted under the condition of slurry flow rates lower than 5m/s, pH range 1.5-7.0 and alumina particle of 4×10^-5m diameter. The erosion-corrosion rate was evaluated in terms of the corrosion rate obtained by the electrochemical measurement and the erosion rate. The following results were obtained. (1) The erosion-corrosion rate of the stainless steel increases in proportion to the 4-5 powers of the flow rate. The corrosion rate, which amounts to 10-30% of the erosion-corrosion rate, increases also in proportional to the 4-5 powers of the flow rate. The corrosion is accelerated by the breakdown of passive films due to the slurry flows. (2) The erosion-corrosion rate of the carbon steels is 15-300 times higher than that of the stainless steel, and increases in proportion to the 0.5-1.0 powers of the flow rate. The corrosion rate amounts to almost all of the erosion-corrosion rate. The acceleration of the corrosion is due to the diffusion of disolved oxygen enhancement by the slurry flow. (3) Under the cathodic protection, the erosion-corrosion rate of the carbon steel decreases dramatically resulting about the same rate with the stainless steel.

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Corrosion resistance of stainless steels in nitric acid tends to be decreased by the addition of oxidizing metallic ions, Cr⁶⁺. In this study, the mechanism and condition for the formation of Cr⁶⁺ ions in nitric acid were investigated. The concentration of Cr⁶⁺ ions was measured in the boiling solutions of 3-15N HNO₃+0.2-2.0g/1 Cr³⁺, and oxidation-reduction potentials were measured at various temperatures in 3-11N HNO₃. The results are as follows. (1) Cr⁶⁺ ions accelerate corrosion of stainless steels in nitric acid. (2) Cr⁶⁺ ions were formed from Cr³⁺ ions in nitric acid with the concentration more than 5N. The formation andconsum ption of Cr⁶⁺ ions occurred at the same time while stainless steel was corroding in nitric acid. (3) Thr formation rate of Cr⁶⁺ ions tend to be greater with increasing the concentrations and temperatures of nitric acid, i. e. 5N HNO₃ at the boiling point. (4) The formation condition of Cr⁶⁺ ions was satisfied in the interfacial liquid zones adjacent to the bubbles of nitric acid under boiling condition.

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Effect of temperature on corrosion behavior of steels was evaluated in the range of 150-300°C in high purity water containing about 200ppb oxygen. The exposure tests were carried out in actual and simulated reactor water of BWR plants. Through X-ray diffractometry, SIMS, XPS and chemical analyses, it was clarified that the chemical composition and morphology of oxide films formed on austenitic stainless steel changed above about 250°C. Chromium dissolved easily through corrosion above this temperature, and the oxide films primarily consisted of spinel type oxides containing high concentration of nickel. Further, as the protectivety of oxide films increased with temperature, the corrosion rate had a peak around 250°C after a long exposure period. A major phase of oxide films on carbon steel was magnetite in the whole temperature range. However, as the oxide films formed at high temperatures had very compact structures, the effect of temperature on the corrosion rate was similar to that observed on stainless steel.

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In order to examine the effect of γ phase content on pitting potential of a duplex stainless steel, pitting potentials for type 329 J1 duplex stainless steel with the different α/γ phase ratio prepared by isothermal heat treatment in NaCl and NaCl-H₂SO₄ solutions have been determined by measurements of the anodic polarization curves. The dependence of measured pitting potentials on γ phase content was considered on the basis of the results for the microscopic observation of pit sites on the metal surface and the EPMA analysis of chemical compositions for α and γ phases. When the structure of type 329 J1 steel changed from α single phase to (α+γ) duplex phase, pitting potential in NaCl solution lowered significantly. This lowering of pitting potential corresponded to the change in pitting site from a phase to γ phase. Pitting potentials of type 329 J1 steels with (α+γ) duplex structure decreased slightly with an increase in γ phase content in NaCl and NaCl-H₂SO₄ solutions. It was considered that such decreases in pitting potentials were attributed to the decrease in chromium content of the transgranular precipited γ phase on which pits generated with an increase in γ phase content.

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There are about 600, 000 facilities of hazardous materials such as petroleum and vitriol in Japan. More than 200 leakage accidents in these facilities have been reported every year and about 30% of them are due to corrosion. In this report, tendency of accidents due to corrosion are described from overall view point as follows. (1) Introduction of hazardous materials and facilities in Japan. (2) Tendency of accidents in the last six years. (3) Characteristics of accidents. (4) Causes of corrosion in facilities.

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