Equilibrium composition of impurity constituents such as H₂, H₂O, CO, CO₂, CH₃, and O₂ in several experimental helium gases simulating the high-temperature gas-cooled reactor coolant was studied. The calculation of equilibrium composition was carried out for the gases of which impurities were equilibrated by only gas-gas reactions and the gases which deposit solid carbon at 800°C and 1000°C. The calculation led to oxygen potential and carbon potential of impure helium at high temperatures. The additions of oxygen or water vapor to some experimental gases abruptly change oxygen and carbon potentials. The oxygen potentials were increased by the addition of 0.2-1vpm of oxygen or 0.2-2vpm of water vapor by a factor of about 10⁷-10⁹. This result shows that an attention should be paid in the gases of which oxygen or carbon potential are affected by the small amount of contaminants such as oxygen or water vapor at an equilibrium state.

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The kinetics of anodic iron dissolution in deaerated and oxygenated distilled water has been studied using a galvanostatic method. In oxygenated water an indirect method was also used. This indirect method is based on determination of the anodic partial potential-current curve from the dependence of the open circuit potential on the concentration of dissolved oxygen. In deaerated water and in oxygenated water containing 0.25m moles O₂/liter or less, an anodic Tafel slope of about 2.3 RT/F was observed; the slope becomes about 2.3_×(2/3) RT/F in water containing higher concentrations of dissolved oxygen. The experimental results in deoxygenated water or water with C_O2-0.25m moles O₂/liter are in agreement with a postulated consecutive dissolution mechanism in which OH^- and adsorbed H₂O molecules participate in the dissolution process via formation of an adsorbed Fe(OH)_ad intermediate. In water containing more than 0.25m moles O₂/liter, the data are explained by assuming that the dissolution reaction is in competition with formation of a “passivating” film formed via reaction Fe(OH)_ad+OH^-→[Fe(OH)₂]_ad+e.

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The selective drainage method is the most common practice for protection of buried pipelines from stray current corrosion, but this method may give over-protection to the pipe along the long area of pipeline. The area that causes stray current corrosion in practice is often limited to the portion of several ten meters of the pipeline on both sides of a railway crossing. Therefore, in order to protect such a short portion of pipeline, it is advisable to eliminate the potential gradient existing around the railway by the use of a intentional anode, as discribed in the previous report.
This method has been found to be applicable to the stray current affected zone which is comparatively large as well as short.
In this report, simplified formulas for calculating the distribution of potential and current in soil are given, and fundamental procedures of the design of this method is discribed.

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The study was carried out to examine the suitability of the electrochemical potentiokinetic reactivation (EPR) method for evaluating the degree of sensitization (DOS) of austenitic stainless steels.
At first EPR test and Strauss test were carried out to establish the relationship between these two test methods using solution-treated Fe-11 Ni-(1-18)Cr steels and Fe-11 Ni-2.5 Mo-(9-16)Cr steels.
Then the DOS of furnace sentitized stainless steels of type 304, 304L and 316L were measured to compare the results of these two tests. The following conclusions were obtained: (i) Reactivation process in EPR method is the formation of etch-pits which were initiated by breakdown of the passive film on chromium depleted zone along grain boundary. The density of etch-pits increases significantly with DOS. (ii) Detectability of EPR method is high enough to evaluate DOS of slightly sensitized stainless steels. (iii) DOS of lower-temperature sensitized steels obtained by EPR method shows a good agreement with that by Strauss test, while the sensitized zone measured by EPR test is found to be broader than that by Strauss test in the specimens sensitized at higher temperature. (iv) This difference can be explained based upon Cr concentration profile near the grain boundary. (v) Reactivation charge in EPR method is also affected by molybdenum alloying.

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The effect of dissolved oxygen on carbon steel corrosion was investigated by immersion tests in a circulating loop, and by measurement of polarization resistance using rotating cylindrical electrodes. Carbon steel is easily passivated by dissolved oxygen in flowing pure water (specific conductivity <0.5μΩ/cm) at room temperature, indicating that the effect of water flow velocity is very remarkable. Passivated steel begins to corrode, if dissolved oxygen is removed from the water or flow is stopped even in the presence of dissolved oxygen. Under such conditions, corrosion intiates locally at weak points of the surface film, and the pits grow gradually and then general corrosion occurs. Once steel has been passivated by oxygen, the passive state can be maintained under a slow water velocity with oxygen rich condition. Even if steel is corroding, it can be passivated easily by the addition of oxygen together with water flow. This phenomenon is reproducible and seems to have a practical significance.

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The mechanism of crevice corrosion of stainless steels has been discussed concerning with its initiation and propagation. The mass transport through the shielding materials, the geometrical condition of the crevice, and the solution chemistry of the anolyte within crevice are emphasized to be important factors for the crevice corrosion. Some quantitative analyses for the geometry of crevice are made using the electrochemical transport theory and the IR-drop through the crevice. The effect of environmental and metallurgical factors on the crevice corrosion processes are also discussed.

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