A reaction area selected electrochemical corrosion test methods, which are used a focusing pulse YAG laser beam irradiation (laser machining) technique and micro-electrochemical cell techniques, were applied to investigate the re-passivation kinetics of metals, atmospheric corrosion behavior of coated steels and hydrogen entry behavior of coated steels. In this paper, the applications of the techniques for evaluation of post welded heat treatment on electrochemical behavior of low C-13%Cr welded joints, re-passivation behavior of titanium in artificial saliva, detection of atmospheric corrosion generated hydrogen and hydrogen permeation efficiency at scratched areas are described.
Stress Corrosion Cracking (SCC) in stainless steel specimens under a high temperature and a high pressure water environment was monitored in the Crevice Bent Beam (CBB) test using an optical fiber AE sensor. Type 304 stainless steel was monitored during 294 ks under 513 K and 4.0 MPa, respectively. 5227 AE signals were detected. AE event rate was increased after 155 ks from start of the experiment. AE signals were extracted using AE waveforms and their frequency spectra in all time. 4 AE signals were extracted. Those AE were estimated to be occurred by large cracks that occurred after 155ks.
In order to make a quantitative evaluation of degradation in coatings by the electrochemical impedance spectroscopy method, it is necessary to be able to understand the relationship between each coating method and coatings’ degradation phenomena and the behavior of the impedance. In this research, using test pieces for different coating methods, salt slay test, sunshine weather meter test and combined cyclic corrosion test were performed, and evaluations were made by means of the electrochemical impedance spectroscopy method and surface observations. As a result, though it was difficult to determine the corrosion resistance from the impedance prior to the test, from impedance measurements performed over time, it was found that it was possible to detect the presence of cracks and blistering. As a simple method of determining the degradation, investigations were performed observing the time rate of change of the impedance. From variations in the time rate of change of impedance, it was found that it would be possible unambiguously to detect degradation regardless of the coating method employed.
In the boiling water reactors (BWRs), reactor cooling water is maintained in high purity condition by controlling of a deionizing and deaerating apparatus, however H2O2 contains by water radiolysis. In order to determine the corrosive condition in high-temperature pure water containing H2O2, the electrochemical impedance spectroscopy was performed in this study. To simulate BWR condition precisely, the measurements were performed without any electrolyte. The obtained impedance responses were changed with the H2O2 concentration. The solution resistance and polarization resistance were determined by the equivalent circuit analyses. The conductivity was determined by the obtained solution resistance and the calculation of the current flow between the working electrode and the counter electrode by the 3-demensional finite element method. The value, 4.4×10−6 S/cm, was obtained as the conductivity of the pure water at 288°C. The reciprocal of the obtained polarization resistance increased in proportion with H2O2 concentration. This indicates that the corrosion current density was determined by the diffusion limiting current density of H2O2. The diffusion coefficient of H2O2 at 288°C was determined using the relationship between the reciprocal of the polarization resistance and H2O2 concentration. The obtained diffusion coefficient was 1.5×10−4cm2/s. This is about twice larger than that of the reported value of O2.