A heat exchanger made of titanium was used for boiling a solution containing a large amount of NH₄Cl, and crevice corrosion was observed at the gasket of the tube-sheet joint after about two months. The corrosion products were grayish blue, and contained TiO₂ (Rutile), crystalline Ti₂O₃ and amorphous Ti₂O₃⋅nH₂O. The crevice corrosion of Ti was studied in connection with hydrolysis of NH₄Cl in order to investigate the mechanism of the corrosion.
The results obtained were summarized as follows:
1) In the boiling 45% NH₄Cl solution, gaseous NH₃ was expelled from the solution, and the concentration of HCl increased until it finally reached to 0.002mol/kg H₂O. Ti would be dissolved at such a concentration of HCl.
2) However, the crevice corrosion of Ti in a boiling solution of 28% NaCl was observed even at about pH 4. It was, therefore, considered that the crevice corrosion of Ti was caused by the formation of the soluble Ti (III)-complex which was produced in a slightly acidic solution under the lack of oxygen.

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On the test of protective coatings for power transmission towers at the Shiobara 600kV Laboratory of the Central Research Institute of Electric Power Industry, the results of inspection after one and two years were given in the previous reports (Parts 1 and 2). And this report is concerned with the result of inspection done in May 1965 after four-year exposure. Conclusions of the inspection are as follows:
1) Zinc-rich paint system in these coatings showed more excellent result than other kind of coatings at the general atmospheric exposures except that in the industrial environment.
2) The gloss of paint films faded rapidly in early two years, and after that slowly.
3) The states of steel surface have a great influence on the durability of painted films.
4) The test panels agree well with the towers in the deterioration of their paint films.
5) Protective coatings prevent towers from corrosion for four years.

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A study on the stress-corrosion cracking of austenitic stainless steels in high temperature sodium chloride solutions was carried out to estimate the effects of temperature, chloride concentration and dissolved oxygen contents on the susceptibility. Four types of stainless steels of AISI Type 304, 304L, 316 and 347 were corroded in high temperature sodium chloride solutions (temp.: 100°-350°C, Cl^-: 10-500ppm) for 300 hours under a bending stress of 20kg/mm². In deoxygenated solutions, no corrosion cracking was detected in any case. In oxygenated solution, pronounced cracking on 304, 304L and 347 steels was detected at the temperatures between 150°C and 300°C, but no cracking was detected at 350°C. The solution-treated 316 steel indicated no cracking in any case, while, on the contrary, the sensitized one indicated the cracking as well as the other three types of steels.

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