The sulfidation behavior was investigated of two kinds of the preoxidized Fe-13Cr and Fe-18Cr-3Al alloys for the water wall tubes in oil firing boilers. A McBain balance assembly and CCD sensor were used to determine a sulfidation rate in 1.92% H₂S-H₂ atmosphere. The oxide scale formed on the preoxidized Fe-13Cr alloy was effective to prevent the sulfidation attack at 973K, although it was hardly effective above 873K. On the other hand, the oxide scale on Fe-18Cr-3Al alloy showed remarkable retardation effect on the sulfidation attack at 973K to 1073K. It is concluded that the difference of sulfidation behavior of those preoxidized alloys is attributed to the difference of the scale formation mechanism. The scale on the Fe-13Cr alloy was composed of Cr₂O₃ and Fe₂O₃ which was subsequently sulfidized. On the contrary the scale on the Fe-18Cr-3Al alloy was formed mainly with fine Cr₂O₃ layer which is capable to prevent the sulfidation attack.

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The tinted weldments of stainless steels were investigated on their corrosion behavior in aqueous chloride solution. The oxide scale formed on the simulated HAZ of SUS316L was studied by suface analysis techniques. Generally, the pitting resistance of the HAZ with the scale was deteriorated compared with ones whose scale was removed by polishing with emery paper in all stainless steels tested. The comparison of the pitting corrosion behavior between the TIG weldment and the simulated HAZ showed that the pitting resistance of the HAZ was markedly deteriorated by heating at the temperature between about 600 and 700°C. The secondary ion mass spectroscopy (SIMS) analysis of the simulated HAZ revealed that the scale formed by the heating at the temperature below 800°C consisted of Fe oxide on its surface and Cr-Fe oxide by heating at the higher temperature. The Cr oxide in the surface of the scale was found to be transformed into the oxyhydroxide after pitting potential measurement. And, there was a good correlation between the pitting potential of the simulated HAZ and the Cr content in the outer layer of the scale after the pitting potential measurement. Accordingly, the Cr oxyhydroxide is thought to behave like a passive film in aqueous chloride solution.

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An equation which represents the amount of damage to metallic materials by solid particle impact was derived by comparing the behavior under quasi-static and dynamic indentation. Both the diameter and the volume of the dynamic indentations formed by spherical or angular particles could be described by an exponential function of the material hardness (H_v), K(H_v)^-N. It was found that the constant K and the exponent N in the equation depended upon factors which were related to the aggressiveness of the impact, such as impact velocity, impact angle, and the size and shape of the particles. The relationship between the erosion damage caused by 250μm silica sands and the surface hardness of the material after testing followed this equation for both pure metals and heat-treated alloys, over a wide range of material hardness (H_v 43-1100). The surface hardness gradually changed with the number of particle impacts, reaching a constant value with regular damage on the material surface. Work-hardening was observed in most metals. However, for heat-treated hard steel alloys, not only work-hardening but also softening were observed on the damaged surface.

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Nondestructive technique to estimate the degree of embrittlement in CrMoV steam turbine rotor steel by measuring the open circuit potential change rate in 2, 4-dinitrobenzoic acid solution has been proposed. Five CrMoV rotor steels different in design and service operation condition were tested. Plotting the open circuit potential change rate against the degree of embrittlement, a linear relationship was obtained for only one rotor steel but not for the others. These results suggest that open circuit potential technique could be used to detect temper embrittlement qualitatively, however quantitative prediction is not yet possible. Further investigation is required for accurate estimation concerning the effects of various microstructural change in rotor steel on the open circuit potential.

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The purpose of this paper is to review the recent corrosion incidents and the remedial actions taken by the utility industry. The following corrosion failures and related subjects are presented in this paper. (1) Intergranular stress corrosion cracking (IGSCC) of austenitic stainless steel piping in boiling water reactors (BWRs). (2) Interdendritic stress corrosion cracking (IDSCC) of stainless steel piping weldments in BWRs. (3) Irradiation-assisted stress corrosion cracking (IASCC) in in-core component of nonsensitized austenitic stainless steel. (4) Interganular attack (IGA) of steam generator tube material in pressurized water reactors (PWRs). (5) Corrosion fatigue and erosion corrosion of carbon steel piping. (6) SCC of reactor component materials. (7) Microbial induced corrosion.

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For the environmental protection, the chrolofluorocarbon (CFC) elimination program according to the protocol of Montoreal has started as a world wide activity. Since there is no fluorocarbon which can replace the CFC, it is necessary to accelerate the technical development which is suitable for your needs. This paper deals with the measures of CFC-elimination for the fine cleaning.

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