Succeeding the hydrogen states in solid solution, interactions of hydrogen with various defects such as dislocations, vacancies, precipitates, grain boundaries and voids have been reviewed. The binding energies of hydrogen with defects are collected with emphasis on experimental methods and assumptions in the theoretical analyses. The origins of the interactions are briefly described in terms of electron theories on the states of hydrogen.

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Initial stage of rust formation behavior of carbon and weathering steels was investigated under wet/dry cycles with spraying of Na₂SO₄ solution and dripping of NaCl or MgCl₂ solution. With spraying of Na₂SO₄ solution, the weight loss of both steels increased directly with increasing time during the dripping of either NaCl or MgCl₂ solution. On the other hand, in the absence of spraying, the rate of weight loss decreased with time. The weight loss with dripping of MgCl₂ solution was smaller than with NaCl solution after 28 days regardless of spraying. X-ray analyses of the rusts showed that the amount of α-FeOOH was greater with dripping of NaCl solution than with MgCl₂ solution, and with spraying than without spraying. The amount of X-ray amorphous phase was greater with dripping of MgCl₂ solution than with NaCl solution, without spraying than with spraying, and for weathering steel rather than carbon steel. Without spraying a dense inner dark layer, including a black region, was formed in the rusts on both carbon and weathering steels subjected to the dripping of NaCl or MgCl₂ solution after a test period of 28 days. On the other hand, with spraying the rusts formed were all porous and not dense. The surface potential measured by Kelvin probe showed that the rusts on both steels after 28 days exposure without spraying are more protective than those with spraying.

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The corrosion monitoring of carbon steel in moderate corrosive environments was carried out using electrochemical noise impedance. For correct electrode impedance estimation, it was emphasized that data to be analyzed have a good correlations between the potential and current noises both in time and frequency domains. An ordinary three-electrode method, three identical electrodes were used for electrochemical noise measurement in aerated and deaerated 0.5M NaCl solutions. The impedance calculated from the noise data was compared with that measured by an ordinary AC impedance method. The correlation between potential and current noises in the time domain was calculated by the correlation coefficient, and their correlation in the frequency domain was calculated by the coherence function. When both the correlation coefficient and the coherence function were high enough, the impedance at very low frequency obtained by the electrochemical noise agreed well with that obtained by AC measurement. Based on this, the measurement and calculation procedure for corrosion monitoring by electrochemical noise impedance was proposed. The procedure proposed was successfully carried out for continuous monitoring of steel corrosion rate in a moderate corrosive medium.

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The water quality change under an anaerobic condition was examined in the 30m³ steel tank. Measuring items were the concentrations of dissolved oxygen (DO), of total sulfides, of ferrous ion, the number of sulfate reducing bacteria (SRB), redox potential (ORP), and pH. The measurement was started from January, and its period was 394 days.
DO decreased to 0ppm in about a half year. At this moment, the SRB started to be detected. Sulfides concentration increased rapidly, reaching 1.38ppm. It fell to 0.03ppm from January to March. The strong correlation was obtained between log. of total sulfides concentration and ORP. The correlation coefficient was -0.88. It was shown that ORP were near to equilibrium redox potentials (S/H₂S), (FeS₂/FeS, H₂S), (S/HS^-). The ferrous iron was dissolved through epoxy coating.
It can be expected that these results are useful to elucidate the corrosion mechanism and to develop its protection technology.

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This paper describes results of exposure test by using the test pieces which simulate cathodically protected marine steel structure. The cathodic current density in tidal zone had maximum value according to the reduction of rust formed at the time of low water, when immediately after immersion. The cathodic current density in tidal zone decreased gradually toward high water, and increased gradually after the time of high water. The reason of change in cathodic current density is considered the periodically exposure in the different concentration region of dissolved oxygen by tide.

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