煉油廠冷卻系統碳鋼材料之細菌微生物腐蝕研究

Study on the Microbiologically Influenced Corrosion (MIC) of Carbon Steel Used for the Cooling System in a Petroleum Refinery

本研究探討煉油廠冷卻系統碳鋼材料細菌微生物腐蝕（microbiologically influenced corrosion, MIC）之行為，內容包括以細菌微生物技術分析現場冷卻水中的微生物活力，並進行實驗室模擬現場環境的碳鋼MIC加速試驗（含菌類培養及電化學交流阻抗頻譜量測）。結果顯示，循環冷卻系統不同位置的菌落數有所不同。當一般嗜氧性菌類（黏稠性細菌膜生成菌）數量愈多時，厭氧性菌類數量亦有增多的趨勢。實驗室進行的MIC加速試驗可迅速評估細菌對碳鋼腐蝕的影響。在有菌的環境中，穩定的生物膜（biofilm）會迅速在材料表面形成，此時材料的電化學阻抗值會隨之增加，而生物膜中的硫酸還原菌（sulfate-reducing bacteria, SRB）會造成碳鋼表面生成Fe-S化合物。此外，即使環境條件不利於生物膜的生成，原先已存在於材料表面的生物膜仍可繼續成長。本研究探討了碳鋼材料發生MIC的初期行為，有關MIC對材料長期的影響，則需持續性的監測及研究。

This study investigated the microbiologically influenced corrosion (MIC) behavior of carbon steel used for the cooling system in a petroleum refinery in Tao-Yuan, Taiwan. The microbiological techniques were used to analyze the microbiological characteristics of the on-site cooling water. The accelerated MIC tests, including the bacteria culture and electrochemical impedance spectroscopy measurement, in the simulated on-site environments were carried out in the laboratory. Results showed that the amounts of bacteria were different at the different locations in the cooling system. The amounts of the anaerobic bacteria might increase on raising the amounts of the aerobic bacteria, namely the slime forming bacteria. The accelerated MIC tests could rapidly evaluate the effect of bacteria on the corrosion resistance of carbon steel. In the bacterium-containing or polluted environments, the stable biofilm could quickly form onto the carbon steel, leading to an increase in the electrochemical impedance of the metal. The sulfate-reducing bacteria (SRB) inside the biofilm would interact with the carbon steel, resulting in the formation of Fe-S-containing compound. Even though the environment was unsuitable for the formation of biofilm on the metal surface, the pre-existing biofilm on the metal could still apparently continue to grow. In this study, the initial MIC behavior of carbon steel was investigated. An ongoing study is required to understand the long-term MIC behavior of metals.