Corrosion Test of Casing Steel at High Temperature Acid Condition

Abstract

The authors have been carrying out “development of technologies for utilizing unused acidic hot water in conventional geothermal resources” with the NEDO budget since FY2018. This is to develop a geothermal power plant risk assessment system for high-temperature acidic hot water that has not been used so far by evaluating the material corrosion characteristics of high-temperature acidic hot water at about 300 ° C and above pH3. As one of the evaluation methods, a material corrosion test using a flow type autoclave of New Zealand GNS was conducted. A test piece having a diameter of 8 mm and a length of 13 mm was fixed with zirconia beads inside a flow-type autoclave 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 tests, hydrochloric acid and sulfuric acid, were performed. Three types of specimens, TN125Cr13U steel, TN110Cr13S steel, and 17Cr steel, were used, and a test was conducted at a maximum flow rate of 200 L / min for about 5 hours. The corrosion rate was calculated from 1) the total dissolved amount of iron or the like in the collected solution, and 2) the change in weight before and after the test obtained after removing the coating on the sample surface after the test. The results of the comparison between the corrosion rate obtained in the test and the predicted value by the material corrosion prediction formula by Cr equivalent are introduced.