Microbiologically Influenced Corrosion on A106 Carbon Steel in Water Cooling System of Thermal Power Plant

• Main Authors: Chien-Ken Hung, 洪健根
• Other Authors: Shiow-Kang Yen
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/99514432729148987187

碩士 === 國立中興大學 === 材料工程學研究所 === 91 === The volume capacity of cooling water used in Taichung thermal power plant was about 300 m3. The amount of microorganism was increasing with increasing time and the microbiologically influenced corrosion (MIC) was also getting serious. Therefore, increasing the inhibitor concentration and/or adding some bactericide is a feasible method to control MIC. Various kinds of bacterial were found in the cooling water. In general, two categories including medium temperature germs and high temperature germs were separated. The corrosion characteristics were evaluated by potentiodynamic polarization tests, AC-impedance tests, corrosion potential trends, and SEM observation. It was found that the molybdate inhibitor and the bactericide was effective for medium temperature bacteria on controlling the corrosion of A106 carbon steel tubes but was not effective for high temperature bacteria. After corrosion test, the oxide film on carbon steel was degraded gradually with increasing corrosion time. With inhibitor and bactericide added, the oxide film was sustained in medium temperature bacteria environment but it was degraded and the steel was pitted in high temperature bacteria. Corrosion potentials of carbon steel were maintained at noble region for effective controls but shifted to active region for ineffective controls. Also, the much higher electrical resistance of germ layer, oxide layer, and double layer was found on effective controls and much lower on ineffective controls.