| Abstract |
Corrosion and scaling are major problems associated with the geothermal power generation. Material tests in actual geothermal environments, along with laboratory tests, are one of the important measures to evaluate behavior of the material in relation to the corrosion and scaling problems. Since the properties of geothermal steam vary according to geothermal wells, Fuji Electric has been carrying out material tests at various geothermal wells around the world. Recently, Fuji Electric has carried out exposure tests of the turbine materials for the period of one year, using geothermal steam from a deep production well in Japan. One of the purposes of the tests was to examine the effect of the coating to prevent scaling. Six kinds of coating materials to be applied to the blade material were selected with a thickness of approximately 200 Ïm. Test specimens for corrosion tests, SCC tests and corrosion fatigue tests were installed in a test chamber and exposed to the saturated geothermal steam with the pressure of approximately 0.5 MPa. The test specimens for the corrosion tests and SCC tests were examined after 3 months, 6 months and one year of exposure, while the specimens for the corrosion fatigue tests were taken out from the test chamber after one year of exposure and were subjected to the fatigue tests in the air. Along with the coating materials, 2 kinds of rotor materials, 2 kinds of blade materials, one kind of blade material with silver brazed stellite, and one kind of casing material were tested in the same manner as mentioned above. After one year of exposure to the geothermal steam, 5 kinds of the coating materials revealed cracks and/or separation, while one kind of the coating material showed excellent results without any cracks or separation. Only a small amount of scaling was observed on this coating material. The test results show that this coating material is promising to be applied to the geothermal turbines. As for the blade, rotor and casing materials, those currently used for geothermal turbines proved excellent characteristics in the geothermal steam from a deep production well. |