| Title | CORROSION RATE ESTIMATION OF Cr CASING STEELS AT HIGH TEMPERATURE ACID CONDITIONS |
|---|---|
| Authors | N. Yanagisawa, M. Sato, K. Osato, Y. Yamamoto, K. Lichti, B. Mountain, and L. Sajkowski |
| Year | 2021 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Material corrosion, Acid fluid, High temperature |
| Abstract | To develop a geothermal power plant risk assessment system for high-temperature acidic hot fluid, 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. Measurement of the corrosion rate under the conditions from 150 to 350 ºC was carried out for the two chromium (Cr) type materials, Super 13Cr, and 17Cr. The test brine had a pH of 3.0 at room temperature and contained non-condensable gases (Total 3%, CO2: 96%, H2S: 4%) and chloride ion (10,000 ppm). 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. We estimated corrosion rates from the dissolved metal concentrations in the experimental effluents, and we estimated corrosion rates using Cr equivalent, pH and temperature using models proposed by Kurata et al. (1992). With brine and pH adjusted to 3.0 by addition of sulfuric acid at room temperature, the measured corrosion rate from weight change and dissolved metal concentration showed the highest value at 250 ºC and was higher than the testing at 350 ºC. The reason for this result was hypothesized to be the change of pH at higher temperature, for example, 3.38 at 250 ºC and 4.5 at 350 ºC based on geochemical simulator modelling. Comparing the results for the two alloys tested, the relative corrosion rate of Super 13Cr/17Cr was lower in the higher temperature exposure testing than the 1.6 ratio value that would be predicted based on Cr equivalent. Analysis results suggest that that the Super 13Cr performed better than predicted by the Cr equivalent because of the better formation of adherent and protective corrosion products on this alloy at the higher pH encountered at the higher temperature. |