The corrosion products formed on copper in borate-boric-acid solution were examined using the combined method of immersion tests and ESCA, IMMA, electron microscopy and FT-IR spectroscopy. After exposure for a short period, the film was composed of cuprous oxide (Cu₂O) with a small amount of cupric compound. On the other hand, after exposure for a long time, the final product was largely composed of a mixture of anhydrous and hydrous cupric compound (copper borate a material like Cu(BO₂)₂·mH₂O or CuB₄O₇·nH₂O). This cupric compound was a bluish-green fine crystal. The outermost part of the film had a small quantity of impurities and adsorbed contaminations such as H, C, Ca, Na, Mg, Al, Si, P, K, SiO, Ti, Cr and Fe. These contaminators are probably not significant constituents of the corrosion products. In addition, corrosion pits were formed at non-metallic inclusion such as Si.

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The effect of dissolved oxygen, the main factor in SCC of stainless steel in high temperature water, was studied by CERT, and an analysis of the surface film, and by developing potential-pH diagrams. Under a strain rate of 6.67×10^-7sec^-1 in 290°C water, IGSCC occured with more than 0.2ppm dissolved oxygen, while TGSCC occured with less than 20ppb dissolved oxygen. When the strain rate increased from 6.67×10^-7sec^-1 to 3.33×10^-6sec^-1, the IGSCC susceptibility decreased, but the TGSCC susceptibility remained unchanged. IGSCC was accelerated with increasing dissolved oxygen concentration. The increase in oxygen concentration may bring the corrosion potential of stainless steel closer to the transpassive region where the dissolution of chromium is promoted, and SCC more easily takes place. When the concentration of dissolved oxygen is extremely low, the corrosion potential may shift to the active region, thereby rendering the oxidized film unstable and giving rise to TGSCC.

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The electrolyte was needed to control hydrogen content in high strength steel in a fracture experiment. Several buffer solutions such as boric acid-potassium chloride, acetic acid-sodium acetate and sulfuric acid-sodium sulfate were found useful to control hydrogen content. Also the addition of such as urea, thiourea or 3-(N-alkylamino) propionic acid in such electrolytes was found to change the hydrogen content in the range of 1/10 to 10 fold compared with that of no additive. By using such buffer solutions, the hydrogen content could be controlled over one week without regard to presence of cathodic polarization. Also the hydrogen content and its diffusion coefficient of SCM3 were measured as a function of tempering temperature. The increased in tempering temperature brought the decreased content and the increased diffusion coefficient. The activation energy in the diffusion process falled in the range of 6.4-7.4kcal/g.atom.

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The composition and structure of corrosion products formed on copper in phosphate solution were studied by sensitive ESCA, electron microscopy and FT-IR spectroscopy. In an initial stage of corrosion, the product was mainly composed of cuprous oxide with a small amount of cupric compound and, the final product was an anhydrous and/or hydrous cupric complex such as Cu₃(PO₄)₂ or Cu₃(PO₄)₂·3H₂O. This cupric compound was a bluish well developed crystal in the shape of plate. In phosphate solutions of pH less than 6.7, corrosion pits were observed in the copper specimens.

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Based on the stress classification data of stress corrosion cracking failures, we found that 70% to 80% of SCC could be attributed to the residual stress caused by welding or working process. Therefore, it is extremely effective for the prevention of SCC initiation to control residual stress quantitatively. However, there are few reports on the SCC susceptibility in relation to the stress of plant apparatus measured quantitatively.
Here, the role of residual stress was reviewed on the SCC failures of the materials; carbon steel, low alloy steel, stainless steel and Cu alloy. It was emphasized to obtain more correctly the SCC threshold stress and acceptable stress of structure materials in various environments by comparing the laboratory data with the field ones.

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