This article is based on the JSCE Society Award Lecture delivered at the ceremony of the Award presentation in recognition of the author's contribution to diffusion and development of corrosion science and engineering. The first part reviews the history of research and development in corrosion as affected by the change of society during the last one third of the century, in which the author served as a research engineer at the corrosion laboratory of a steel company. Then follow author's concepts, developed through experiences, of the significance of corrosion societies, “old boys network”, research work in industries, corrosion education, corrosion consultants, international cooperation, and intellectual property. Recent contribution to the diffusion of corrosion protection technology of buried utility piping, through which the author thinks he benefited society most, is described in some details.
NKK has developed a system in which waste plastics are pulverized by crushing and granulating of lumpy one or agglomerating of film type plastics and injected into a blast furnace. The plastics are used as a substitute for the coke used in ironmaking. The system with an annual capacity of 30, 000 ton, has been operated from October, 1996. It was found that the total recycling ratio of waste plastics reached as high as 76%, with 51% and 25% of material and thermal recycling respectively.
To clarify the acidic Intergranular Stress Corrosion Cracking (IGSCC) mechanism of alloy 600, some metallurgical factors were extracted from the various IGSCC contributing factors, and several kinds of experimental studies were conducted. Acidic IGSCC susceptibilities of mill-annealed, sensitized and thermally treated (TT) alloy 600 which have different grain boundary characteristics were examined using C-ring and SSRT tests. Grain boundary characteristics, such as chromium depletion, intergranular slipping behavior and electrochemical dissolution, were examined in detail using a modified Huey test, a Transmission Electron Microscope (TEM) study, and an electrochemical measurement, respectively. The C-ring and SSRT results showed that the IGSCC resistance of the sensitized material which had the chromium depletion zone was the least, and the TT material was the most resistant. TEM analysis showed that the slips at the grain boundary were easy to detect in the mill-annealed and sensitized materials. In the TT materials, however, slips were suppressed by its intricate dislocation morphology. Electrochemical study showed that the preferential dissolution of nickel tended to occur with an increase in temperature and decrease in pH under the acidic condition. From these metallurgical and electrochemical test results, it was concluded that the slipping behavior and the nickel dissolution at the chromium depletion zone worked together as the influencing factor to acidic IGSCC.
Corrosion behaviours of mild steel were investigated by measurement of corrosion loss and stress corrosion cracking tests in methanol and its solutons containing formic acid. In methanol solution containing 0.5% formic acid, corrosion rate was maximum at the composition of approximately 98% methanol with 2% water and was minimum at 85 to 90% methanol with 10 to 15% of water. General corrosion and pitting corrosion were found in these solutions. Especially at temperatures of 40 to 50°C, many pits were observed. In methanol solution containing 0.05 and 0.5% formic acid, corrosion loss increased proportionally square root of immersion time. Addition of acid to 85 to 85.5% methanol with 14.5% water increased corrosion rate in the order of hydrochloric acid, formic acid and acetic acid. Sodium chloride addition to about 85% methanol solution containing 0.5% formic acid decreased corrosion rate in comparison with non addition. Stress corrosion cracking was not found before 140 hours in U-bend and 3 point bending tests in methanol solution containing formic acid.
The oxidation resistance and degradation process were investigated in air at 1173K for up to 1.44 Ms for the TiAl alloy, which has been pre-sulfidized at 1173K in a H2-H2S gas mixture to form a TiAl3 (+TiAl2) layer with 20 micron thickness on the alloy surface. And the reaction diffusion process of the TiAl3-TiAl2-TiAl system was computer-simulated. The TiAl3 layer with very good oxidation resitance changed quickly into a TiAl2 at 80ks, which agreed well with the calculated one. The TiAl2 layer transformed slowly to a TiAl, indicating good oxidation resitance for up to 810ks, while with further oxidation it degraded singnificantly at 1.44 Ms, in contrast to the calculated time of 4 Ms. This is due to a locallized oxidation along alloy grain boundaries, and the degradation mechanism was proposed.
The applicability of extreme value statistics to localized corrosion was studied based on a actual case. The localized corrosion under tubercles on inner surface of the steel channel in which river water flowed was investigated. Their depths obeyed the distribution of exponential type, while the maximum depths did the double exponential distribution. When the similar data appeared in the previous papers, extreme value statistics was often assumed to be applicable. However, according to the theory of extreme value statistics, the maximum depths are necessary to be sampled from a single population. Then, it was evaluated by calculating the confidence intervals for the population mean whether the data belong to the same population or not. Moreover, the theoretical distribution of maximum depths was calculated and was compared with the measured one. The results of these analyses showed that extreme value statistics was inapplicable to the present case. Thus, the present case study demonstrates that extreme value statistics is not always applicable to the maximum depths of localized corrosion, even if the depths obey the distribution of exponential type and the maximum depths do the double exponential distribution.