To develop a geothermal power plant risk assessment system for high-temperature acidic hot water, we carried out the material corrosion tests using a flow-through autoclave at GNS Science, New Zealand. A test piece, having a diameter of 8 mm and a length of 13 mm, was isolated with zirconia beads inside a pressure vessel having a length of about 15 cm. The test temperature was 250, 300, 350° C., the pH of the fluid was 3 at room temperature, and two types of acid, hydrochloric acid and sulfuric acid, were used. Three types of specimens, TN125Cr13U steel, TN110Cr13S steel, and 17Cr steel were used, and the tests were conducted to a maximum flow rate of 10 L/ min for about 1,3 and 8 days. The corrosion rate was calculated from the change in weight before and after the test, obtained after removing the corrosion product present on the sample surface. And we estimated corrosion rate from the metal concentration of dissolved water. The results of the comparison between the corrosion rate obtained in the tests and the predicted values by the material corrosion prediction formula by Cr equivalent, are introduced.

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