The material corrosion test on pH adjustment condition by acid at geothermal field in Japan

Abstract

We carried out a pH adjustment test at the acidic hot water line at Kakkonda geothermal field in November 2017. And we compared the results with the material corrosion prediction equation using a Cr equivalent amount, as proposed by Kurata et al. (1992).
In the field test, the temperature was 145 ° C, the initial base case pH was 5.15, and then the pH was adjusted to 3 and 4 with sulfuric acid or hydrochloric acid. The test duration was 5 hours and K-55, TN80SS, TN80Cr13 and TN110Cr13S were used for the corrosion test. After the corrosion test, antimony and arsenic scales were attached to the test material and the corrosion rate was calculated after removing the scale.
According to the prediction equation, the corrosion rate at pH 4 was about 2 times that at pH 5.15 and 3 to 4 times that value at pH 3. But the measured value at pH 4 was about 1.2 to 1.6 times that at pH 5.15. And at pH 3, carbon steel and low alloy steel showed a high corrosion rate, but stainless steel showed lower values. The corrosion rate in the case of the addition of hydrochloric acid was higher than for sulfuric acid.