| Abstract |
In order to increase the competitiveness of the geothermal energy against the conventional energy resources, there is a great necessity for improving the geothermal systems; reducing the costs of the geothermal power plant construction and providing secure energy exploitation. One of the major obstacles that affects a stable and continuous energy production is the corrosion of constructional materials and equipment due to their interaction with an aggressive environment. Among all of the existing electric power generation facilities, corrosion is considered to be the most severe on geothermal power plants. This can be attributed to the extreme high temperature and pressure conditions present in geothermal systems, as well as the existence of almost an entire periodic system of elements in form of corrosive salts. This study has sought to understand the impact of different factors on the corrosion performance of carbon steel, the most widely used engineering material, and its integrity. This way the probability of the material failure would be minimized and a safer operating window of power plants would be established. The focus was put on the geothermal fields Sibayak and Lahendong - hotspots of Indonesia, the country with the highest geothermal potential in the world. The main objective was to evaluate the corrosion performance of carbon steel API Q125 at different temperature (70 °C, 100 °C, 175 °C), pressure (100 kPa, 900 kPa), pH (2, 4) and chloride concentration (20 mg/L, 1,500 mg/L) conditions. The investigations were performed under stagnant conditions by means of electrochemical measurements and long term exposure tests in the artificial geothermal brines, simulating the conditions present on Sibayak and Lahendong geothermal sites. The results showed active uniform corrosion in all of the investigated conditions. The most detrimental effect was attributed to the high solution acidity (pH 2) at 100 °C (100 kPa) that caused the corrosion rates to exceed 1 mm/y. The mildest surface activity (corrosion rates less than 0.01 mm/y) was measured at 175 °C (900 kPa) in the solution pH 4 containing 1,500 mg/L chlorides, implying to the possible suitability of the carbon steel API Q125 for power plant construction in the former conditions. |