A long natural gas main from Karikohama to Nihongi in Niigata Pref. was constructed by Teikoku Sekiyu Co. Ltd. in summer of 1959. Its extension is about 37km, and it consists of 8 in pipe line of 16km long and 10 in pipe line of 21km long. One coat of asphalt enamel and one wrap of jute were applied to the pipe and thickness of coatings is about 3mm. The coatings were tested by holiday detector, and fault places in the coatings were repaired in the field before backfilling. The gas main was divided in 3 sections by insulation flanges. A Section is located in sandy coast, and its soil resitivity is about 100, 000Ω-cm. B Section is located in Naoetsu City and in Takata City, and its soil resitivity is about 4, 000Ω-cm. C Section is located in high land district, and its soil resitivity is about 40, 000Ω-cm. Impressed current method was adopted in Section A and C. 5 sets of selenium type rectifiers (each 30V×3A) were installed on electric poles. 70 pieces of 17-D type magnesium anode were installed in Section B. Designed protective current density was 0.2mA/m², but actual protective current density needed was about 0.1mA/m².

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Many works have been made on the corrosion resistance of Zr under various corrosive conditions, but a few attempt have been made to analyze systematically its corrosion resistant property. The authors examined the stabilities of Zr, purified for atomic reactor use, in sulfuric acid solutions of 50, 60, 70, 80 and 90% at 95°, 140°, 185° and 200°C. Two samples were simultaneously tested in autoclave under the previous conditions. No significant change was observed under the concentrations of 50 to 70% through the temperatures tested, while striking increase of corrosion was found under the concentrations of more than 80%. At the temperature from 95° to 200°C, the relationship between corrosion rate and temperature was nearly linear on logarithmic chart.

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