In order to confirm the adsorption of organic corrosion inhibitors on metals by means of back-donation of the metal electrons to an vacant orbital of the inhibitor, the inhibition efficiency of electron-accepting inhibitors was determined for pure iron in a 6.1M HCl solution by polarization measurements. Nitrobenzene derivatives were used as the electron-cacepting inhibitors. They accelerated the cathodic reaction because of their reduction, whereas they inhibited the anodic reaction. The inhibition efficiency of these inhibitors for the anodic reaction was expressed by the Hammett-like equation associated with the Hammett constant, σ. The efficiency of the compounds with an electron-attracting substituent (σ>0) increased with a decrease in the electron density of the nitro group. Since the efficiency of these compounds was closely related to the half-wave potential of reduction, the back-donation of metal electrons to the antibonding π-orbitals was concluded to play an important role in the adsorption of the nitrobenzene derivatives on the iron surface.

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The mechanism of the anomalous corrosion for sensitized Type 304 steel exposed to 28MPa hydrogen at 673K for 57.6ks has been investigated by electrochemical measurements. Anodic current of 10Cr-9Ni steel coupled with Type 304 steel increased by hydrogen charging. And the current density in anodic polarization curve of 10Cr-9Ni steel increased by hydrogen charging, especially at -0.3 and -0.1V vs. SCE. These increases in current density at such potentials result from anodic dissolution, not from the oxidation of the dissolved hydrogen. The increase of intergranular corrosion and intergranular stress corrosion cracking susceptibility of sensitized Type 304 steel by hydrogen charging seemed to be related to the anodic peak at -0.1V vs. SCE. This peak disappeared by heating at 923K, not at up to 873K and the disappearance of this peak was coincided with the discharge of nondiffusible hydrogen. From these results, the degradation of corrosion by hydrogen charging for sensitized Type 304 steel seemed to be due to active corrosion of Cr depleted zone, which was caused by hydrogen trapping.

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The effects of applied stress and strain on the transgranular stress corrosion cracking (TGSCC) susceptibility of low alloy steels have been studied by means of uniaxial constant load tensile test (UCL) and slow strain rate tensile test (SSRT) in 288°C water containing 8ppm dissolved oxygen. The results obtained are summarized as follows:
1) TGSCC can initiate above about 2 S_m of applied stress level, but it is hard to initiate below the stress level of 2 S_m.
2) In SSRT test, the TGSCC susceptibility decreases with increasing pre-exposure time in 288°C water prior to loading.
3) In SSRT test, the TGSCC susceptibility becomes more higher at strain rate of 1.4×10^-6/s than others.
4) No significant difference in the TGSCC susceptibility of A 508 Cl. 2, Cl. 3 and A 533 Gr. B steels are found in this study.
5) The surface finishing such as grinding, machining and paper finishing have no detrimental effect to the TGSCC susceptibility.

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Measurements of initiation and growth of pitting corrosion were carried out for a large number of specimens and machine components in service. The results were discussed in terms of statistics and probability theory and following conclusions were obtained.
1. The number of pit formed is determined by the distribution of pitting susceptibile sites appeared in the surface of metal in a random fashion and can be described by the Poisson distribution.
2. Initiation process of pitting can be given by the Poisson process and the time to pit initiation is described by two different exponential distributions.
3. Growth process of pitting can be given by the proportional model and the distribution of pit depth is described by the log normal distribution.

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