This paper describes the outline of hydrogen embrittlement（HE）of metallic materials in corrosive environments in terms of corrosion reaction, entry and penetration of atomic hydrogen, the effects of atomic hydrogen on material properties and HE mechanisms already reported. In addition, the issues on HE in corrosive environments and a unified concept of HE mechanism are also discussed.

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Considering that Cl^－ influences corrosion rate of girders of steel bridges, precipitation rate of air-born salt is used to discuss the stability of steel bridges in a corrosion environment. While precipitation rate of Cl^－ is one of the factors in residence time of Cl^－, residence time of Cl^－ on girder is considered to directly affect the corrosion of that of steel bridges. So this study examines the residence time of Cl^－ on inside-ward web of the girder of the bridge, based on the precipitation rate of Cl^－ on girder and removing rate of Cl^－ from web by rinsing with dewdrop. Exposed period of the examined web are 1 month, 3 months, and 1 year. The residence time of Cl^－ on inside-ward web exposed during 1 month or 3 months is calculated to be 30 to 700 days. The residence time is long during winter and spring, short during summer and fall. This fluctuation of residence time infers that Cl^－ is accumulate during winter and spring, and rinsed during summer and fall. The residence time of Cl^－ obtained from web exposed during 1 year is 250 days, suggesting that Cl^－ on the inside-ward web is replaced within period of 1 year.

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Atmospheric corrosion behaviors of carbon steel and corrosive environmental factors were investigated at three exposure test sites in Fukui prefecture, which is located on the coast of Sea of Japan and at just about the middle of the main island of Japan. Corrosion rate of carbon steel coupon exposed at a rural site for one year（Jan.2010 ～Dec.2010）was measured to be 0.022 mm/y. Mean value of monthly precipitation rate of airborne salt analyzed by dry gauze method was 8.2 mgNaCl/（m²d）, and the time of wetness（TOW）was 3900 h. The corrosivity of the atmosphere in Fukui was classified as medium in the categories of corrosivity of the atmosphere in Japan by these measurement values.
Monthly corrosion rate of carbon steel decreased in the spring and summer of February to July and increased in winter of November to January. It was confirmed that the corrosion rates of each month were correlated with the amount of deposited salt, Ws, and daily average electricity, Q, measured by ACM（Atmospheric Corrosion Monitor）type corrosion sensor.

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In the construction of the weathering steel bridges, it is important to accurately evaluate the environmental characteristics of the local region. It is well-known that the salt accumulation affects corrosion of the weathering steels, because the protective rust layer is difficult to be generated under the high salinity condition. In order to evaluate the corrosion durability for the bridge, the precipitation rate of air-borne salt is investigated monthly for a year prior to construction of bridge. However, climate change makes it difficult for engineer to evaluate the corrosion durability for the weathering steel bridges over 100 years. In this study, the authors focused on the relations between the precipitation rate of air-borne salt and the wind-force energy coefficient. We discuss the estimation feasibility of corrosive environment considering climate change by means of these relations developed in this study.

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Galvanic corrosion has been observed in galvanized steel pipes and steel pipes connected to stainless steel, copper and copper alloy in building piping systems. However, the influence of pipe diameter on galvanic corrosion has not been investigated either theoretically or in the laboratory. We installed four galvanic couples（SUS304 stainless steel and galvanized steel）having different pipe diameters into a circulation loop in order to simulate a buildingʼs air-conditioning and other piping systems. Test results show that galvanic current increases as the pipe diameter increases, while the current density does not, which means that the anode area also increases. Moreover, because large-diameter pipes are thicker, corrosion of their pipe joints are likely to progress more slowly than the pipe joints of small-diameter pipes.

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Type 310S stainless steel cathodically treated in a nitric acid - nitrate solution in anticipation of formation of conductive nitrides has been evaluated in terms of contact resistance against gas diffusion layer（GDL）, polarization behavior, surface chemical state and PEFC performance when used as bipolar plate. The contact resistance between the treated stainless steel and GDL did decrease to the demanded level. XPS analysis indicated formation of thin nitride layer on stainless steel among oxides. The thickness of the nitride layer was within a few nanometers but was stable even after anodic polarization at 0.6 V vs. SCE. The cathodic treatment was applied to stainless steel bipolar plates for operation of a single cell. The cell performance was comparable to that with graphite bipolar plates, suggesting great promise as a convenient surface treatment for stainless steel bipolar plates.

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Effects of an inhibitor on the corrosion of Al and Al alloys in Cl^－ and Cu^2＋ solutions at 363 K have been investigated by gravimetry and analyses of surfaces and vertical cross sections of specimens with a scanning electron microscope and an energy dispersive X-ray spectrometer. Addition of the inhibitor to the Cu^2＋ solution inhibited effectively the corrosion of Al and Al alloys, while inhibitor addition to the Cl^－ solution didnʼt at all. The inhibitive effect in the Cu^2＋ solution can be explained in terms of the SiO₂ film formation on the specimen, leading to the suppression of Cu deposition.

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Stress corrosion cracks in steel specimen under high temperature and high pressure were monitored using an optical fiber AE monitoring system. The AE monitoring system was composed of an optical fiber interferometer, a feedback circuit and a digitizer. The optical fiber sensor was coated with a polyamide, which has high heat resistance. A sensing portion of the optical fiber was wound over a cylinder type sensor holder that acted as a wave guide for AE connected to a CBB jig. A sample was fabricated by welding a low alloy steel plate with a carbon steel plate. AE signals were monitored for 28 days（2.4 Ms）under a CBB test at 180℃ and 1.0 MPa. 119,460 AE signals were detected. Noise signals caused by the heater and autoclave were reduced by utilizing the correlation coefficient of AE waveforms and their frequency spectra. The characteristics of the waveform propagated along the wave guide were also utilized for eliminating noise signals. Only 96 AE signals were extracted after the noise reduction process. These AE signals were detected 1.2 Ms after start of AE monitoring. It was estimated that SCC was initiated during this time.

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This paper was investigated the effects of nitrate, sulphate and bicarbonate ions, NO₃^－, SO₄^2－ and HCO₃^－, which are components of the tap water, on occurrence and repassivation for creviced corrosion of flat healds, 13Cr stainless steel components used for a water jet loom（WJL）, in 0.11-5.6 mM chloride ion, Cl^－, solution when the electrode potential of test piece was kept at 570 mV vs. SHE.
An occurrence of creviced corrosion in Cl^－ solution was inhibited by presence of more than an equimolar amount of NO₃^－ to Cl^－, or in excess of an equimolar amount of SO₄^2－ to Cl^－. A growth creviced corrosion in Cl^－ solution was passivated by presence of more than an equimolar amount of NO₃^－ to Cl^－, or more than six molar amount of SO₄^2－ to Cl^－. The term required to repassivate crevice corrosion completely after NO₃^－or SO₄^2－ was added to Cl^－ solution decreased with increasing NO₃^－ or SO₄^2－ concentration. HCO₃^－ did not inhibit an occurrence of creviced corrosion and not repassivate a growth creviced corrosion for flat healds in Cl^－ solution. This is because that HCO₃^－ exists in H₂CO₃ as non-dissociation form in the pH 2.2 acidic solution in corroding crevice on test piece, due to dissociation equilibrium. A growth creviced corrosion on test piece was repassivated in Cl^－ solution, as a result of the addition of NO₃^－, SO₄^2－. This results that corrosion current decreases with increasing pH_C.C., and then the pH of solution inner the crevice corrosion, the pH_C.C., exceeds depassivation pH, pH_d, irrespective of the type of anion.

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At Mt.Oyama in the southwest of Kanto Plains, acid fog has occurred frequently and the dieback of virgin fir forest has been observed. In this study, we placed the metal samples of galvanized steel and stainless steel at Mt. Oyama mountaintop and in Yokohama and analyzed the characteristics of their surfaces by SEM every three months to assess the effect of acid fog on the metal corrosion. We also investigated the effects of simulated fog water on the corrosion of metal samples. For the galvanized steel, the corrosion was induced by the chloride ion with high concentration in acidic solution. For the stainless steel, the progress of corrosion was observed under neutral pH condition with chloride ion, and furthermore, the corrosion was accelerated under acidic condition.

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