The erosion-corrosion of steel by nonaqueous coal slurry in kerosene was investigated by measuring the weight loss in a stirring flow system. The corrosion rate of SS 41 steel by the nonaqueous coal slurry was less than that of 304 stainless steel, but this relationship was reversed even if the slurry contained only 0.2% water, and then the weight loss of SS 41 steel was increased with increasing water content. Further, the weight loss was seen to be effected by the use of different kind of coal.

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Nitric acid of 98% is very acidic and oxidizing, and therefore is severely corrosive for commercial anti-corrosive materials. In order to develop new stainless steel resistant to such corrosive media, several electrochemical measurements and corrosion tests were carried out. The results obtained in these tests are as follows.
(1) Platinized-platinum electrode potential was more noble by ca. 100mV in 98% concentrated nitric acid solution than in 65% nitric acid solution containing 10g/l CrO₃ (so-called “accelerated Huey Test Solution”) at boiling temperatures.
(2) SUS 304L was more noble than aluminum in 98% nitric acid. Therefore corrosion of SUS 304L at transpassive corrosion potential was inhibited by contacting with less-noble aluminum.
(3) Addition of aluminum to stainless steel was resulted in inhibition of corrosion for stainless steels in liquid phase, but no inhibition effect in vapor phase of nitric acid was obtained.

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The effects of flow rate on crevice corrosion were studied in terms of repassivation potential, E_R, for metal/metal-crevice of Type 316 steel in 3% NaCl solution at 25°C. Crevice conditions are provided by the two disks in contact with each other having inner and outer diameters of 2r=10 and 2R=20mm, respectively. The relation of E_R with flow rate (V) obtained is
E_R2(V.SCE)=0.045V(ft/s)-0.29
=0.148V(m/s)-0.29
where E_R2 is the repassivation potential for growing crevices and V is the flow rate, rω. “r” is the inner diameter and “ω” is the angular velocity of the metal disks being rotated in the solution. E_R became more noble with increasing flow rate but did not exceed 0 V. SCE in the range of flow rates studied lower than 6ft/s (1.83m/s). At a flow rate of 13ft/s (4m/s) extrapolated E_R value attains to 0.30 V. SCE which is more noble than (0.1-0.2) V. SCE, the potential of Type 316 steel reported in flowing sea water. In these situations it is expected that there would occur no crevice corrosion. Metal/metal-crevice of Type 444 steel behaved similarly to that of Type 316 steel. In comparison with metal/metal-crevices of Type 316 and Type 444 steels mentioned above, metal/asbestos-crevices of Type 316 steel did not show much increase in E_R values with increasing flow rate. In this type of crevice flowing condition of its environment would not only remove occurrence of corrosion but accelerate it through increase of cathodic reactions.

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Relation between the fluctuations of corrosion potential and the corrosion rate has been investigated for aluminum immersed in NaCl solutions for 24-240 hours at 30°C. The fluctuations of corrosion potential were recorded with a strip chart recorder for a minute, and were expressed as a number of waves (n). The corrosion rate was expressed in two forms, one is the rate of pit growth (v) determined by the calibrated microscope technique, and the other is the mean corrosion rate (r) determined by the weight loss measurement. It was found that time dependence of the value of n corresponded to the variation of v, when a specimen was immersed in 5×10^-1M NaCl solution, 5×10^-2M NaCl solution containing 20mg/l Cu²⁺, and in 5×10^-2M NaCl solution containing 20mg/l Cu²⁺ and 10^-1M NaNO₃. Time dependence of the value of n also corresponded to the variation of r for a specimen immersed in 5×10^-2M NaCl solution containing 20mg/l Cu²⁺. It was also demonstrated the mean value of n (n) was approximately proportional to v and r in NaCl solutions with and without Cu²⁺.

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Macro-galvanic effects of steel reinforcements in mortar structures on corrosion of underground steel pipes in electric contact with the reinforcements have been studied in the laboratory using a simulated system. It is demonstrated for the first time that the liquid junction potential takes part in the driving force of the corrosion cell. This suggests that the galvanic current depends on the chemical properties of the mortar as well. The anode specimen shows the electrode potential higher than that of the cathode under the short-circuited condition. This phenomenon apparently conflicts with the statements in textbooks, and provides a typical example of the liquid junction potential effect (LJP-effect) reported by the authors previously.

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