Various electrochemical methods and approaches adopted by the author's group to analyze corrosion phenomena, corrosion mechanisms and corrosion rate monitoring are introduced. Basic ideas and approaches are described on application of electrochemical impedance for corrosion research and corrosion monitoring system, to apply electrochemistry for simulating and measuring atmospheric corrosion, and to apply channel flow electrode for analyzing anodic dissolution mechanisms. It is clearly shown that zinc ion dissolved from corrosion products on zinc coated steel prevents further corrosion of steel substrate. New hot dipped coating for steel, Al-Mg-Si alloy proposed by the author, has beneficial effect for hydrogen embrittlement of high strength steel during sacrificial action, since its sacrificial potential is much higher than that of zinc as −1.0 V.
Immersion tests of carbon steel were performed in compacted bentonites saturated with simulated groundwater for a 10-year duration under anaerobic condition. The ferrous carbonates were identified as the corrosion product by XRD and XPS analyses in most of the test cases. The amount of corrosion in high carbonate concentration was smaller than those under the other test conditions throughout the test periods. Although the corrosion rate at 50°C was initially smaller than that at 80°C, it resulted in larger value after several years. The effects of carbonate content and temperature on the long-term corrosion rate seemed to be correlated to the behavior of deposition of the iron carbonate on the surface of carbon steel. Additionally, the correlation between initial corrosion rate and the protectiveness of corrosion product film was examined. Except for high carbonate condition, as the initial corrosion rate was larger, the corrosion product film tended to become more protective. The long-term corrosion depth was estimated by the extrapolation of the laboratory test results. The range of the estimated value was in good agreement with that of archaeological analogue data.
Temperature dependency of external stress corrosion cracking (ESCC) of 304 stainless steel was examined with CT specimens. Maximum ESCC propagation rates appeared in the early phase of ESCC propagation. ESCC propagation rates generally became smaller as testing time advance. Temperature dependency of maximum ESCC propagation rate was analyzed with Arrhenius plot, and apparent activation energy was similar to that of SCC in chloride solutions. Temperature dependency of macroscopic ESCC incubation time was different from that of ESCC propagation rate. Anodic current density of 304 stainless steel was also examined by anodic polarization measurement. Temperature dependency of critical current density of active state in artificial sea water solution of pH=1.3 was similar to that of ESCC propagation rate.
In the repair construction work etc. of the buildings the wet fire piping and the wet sprinkler piping are cut by fusion or grinding. In that case, the ignition phenomena at the cutting part are often reported. It is pointed out that the hydrogen generated in piping is the cause of the ignition. To verify these phenomena, we have done two reproduction experiments. In one case, after tap water had been filled to the galvanic couple piping where the galvanized steel pipe was connected with the stainless flexible tube joint , it was sealed up. In the other case, after tap water had been filled to the reactive container where the galvanic couple of stainless steel plate/zinc plate was immersed, it was sealed up. Each device was left sitting for a long duration at the room temperature. The confirmation of gas generation, the componential analysis of the generated gas, the measurement of galvanic current and the pressure change in the reactive container, and the analysis of the water after test were carried out. Those results were theoretically discussed. It is suggested that hydrogen can be generated in the fresh water (tap water) without oxygen by the electrochemical reaction (corrosion reaction) composed of the reduction reaction of hydrogen ion (cathodic reaction) and the oxidation reaction of zinc (anodic reaction).