The corrosion rate monitoring of SUS 304 and Fe in deaerated autoclave water of 250°C and 50kg/cm² was attempted through overvoltage measurements by using the galvanostatic linear polarization method. It was found that the overvoltage due to solution resistance could be separated from the total overvoltage without using a compensation circuit for solution resistance and 10min as the polarization time was adequate enough to estimate the corrosion rate. The large corrosion rate of Fe in initial period decreased with time up to about 50h to attain an apparent steady value, while the transient period for SUS 304 was remarkably short. The electron diffraction and IMA analyses of corrosion products on SUS 304 gave spinel-type oxides corresponding to NiO·Fe₂O₃ at the outer layer and NiO·(Fe, Cr)₂O₃ at the inner layer as main products, and corrundum (Fe, Cr)₂O₃ as minor one. Further, it was found that the spinel consisted of outer iron rich layers and inner chromium rich ones.

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Until now copper tube has been used as heat exchanger tube for saltmaking evaporator, but at present for economical reason austenitic stainless steel tube is used for evaporator. Because SCC of austenitic stainless steel in chloride solution is anxious, SCC tests with some electro seam-weld stainless steel tubes and plates in boiling salt water were investigated. The microstructure of weld joint of seam-weld tube is similar to that of mother metal and corrosion behaviour of seam-weld tube is equal to that of seamless tube in acid corrosion test. At U-bend SCC test of any material SCC not occurred in boiling salt water, but at SCC test by constant load in boiling salt water SCC occurred in Type 304 and 304L at stress above 15kg/mm² and in Type 316L at stress above 25kg/mm². In conclusion, Type 316L is recommended for the material of saltmaking evaporator.

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As a series of study to develop a procedure to make a quantitative evaluation of corrosion data, it was demonstrated that the extreme value statistical analysis can be applied to various actual localized corrosion data acquired from presently operating machine components and that corrosion life prediction can be done by examining the time dependence of estimated maximum depth of penetration. At first a procedure to perform quantitative evaluation of pitting corrosion data was briefly described. Plots of corrosion data on extreme value probability paper were explained and followed by description of linear fitting of the plot, a test for goodness of fit and rejection of an isolated value, and determination of control limits for observed values.
Finally attempts were made to demonstrate the usefulness of this analysis for performing quantitative evaluation of various actual localized corrosion data. The following actual localized corrosion data were obtained from the operating machine components: tuberculation of carbon steel feed water pipes for hydroelectric power stations, pitting and crevice corrosion of cupro-nickel heat exchanger tubes employed for a water cooled chilling machine, and crevice corrosion of joints for type 316 stainless steel capillary tubes used for high speed liquid chromatography.

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Stress corrosion cracking test of Type 310S steel was conducted potentiostatically in 25% MgCl₂ solution at 80°C. Notched round-bar specimen made it possible to study the stress corrosion crack initiation at the base of notch as a corroding crevice under an application of fracture mechanics. Cracking occurred at the potential range from -380 to -340mV (SCE) and when stress intensity, K_I, was over K_ISCC≅7.5kg·mm^-3/2. In the region II where K_I was larger than 10kg·mm^-3/2 crack growth l_II, did not depend on K_I and was insensitive to changes in electrode potentials. The lower limit of the potential range for cracking is the potential just more noble than the repassivation potential for crevice, E_R.CREV, and the upper is regarded to correspond to that where l_II is equal to the dissolution rate at the crevice-bottom.

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The formation of macro-cells that cause premature failure in underground utility pipes by localized corrosion has been demonstrated by field measurements of the pipe-to-soil potentials and the corrosion currents flowing in the pipes that suffered from this type of corrosion. The potential of a pipe which is in electric contact with rebars in the concrete wall of a building is noble, e. g., -450mV vs. Cu/CuSO₄, indicating danger of corrosion. On insulating the pipe from the rebars, the potential shifts to a normal value more negative to -700mV. The corrosion current associated with the formation of the macrocells is large; 12mA in one case and 5.4mA in another case. The results show the importance of insulating pipes from the structure of the building.

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The designs and performances of various internal and external reference electrodes for high temperature high pressure aqueous solutions are reviewed. The application of these electrodes to the studies on the stress-corrosion cracking of Type 304 stainless steel in simulated light water reactor environments is described.

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