304不銹鋼在含鉬酸根與氯離子溶液中之連續性電化學監測

Continuous Monitoring on the Electrochemical Behavior of 304 Stainless Steels Immersed in Chloride Solutions

本研究目的在模擬海水入侵下，電廠冷卻水機組之不銹鋼材料，可能遭受局部孔蝕之監測試驗。研究方法首先採用現場連續監測法，以電化學腐蝕監測系統針對電位、極化阻抗及零電阻電流進行量測，繼而配合試片SEM觀察，動態極化曲線分析等，找出SS304遭受孔蝕所需之臨界氯離子濃度，並建立資料庫。將所建立之資料庫鍵入監測系統中，經由連續監測，一旦電廠冷卻水機組系統遭遇海水洩入之異常狀況下，藉由電化學訊號之急遽變化，立即發出警示，提醒運轉人員機組材料（不銹鋼SS304）將開始遭受孔蝕之侵害，迅速採取緊急應變措施，防止腐蝕發生。本連續式監測系統顯示SS304不銹鋼試片在氯離子濃度高於400 ppm時，腐蝕電位發生急劇震盪，且零電阻電流上升，開始遭受孔蝕。

The purpose of this study was to establish a monitoring system that is available for continuous in-situ monitoring on the cooling system of a boiler in a fossil power plant. Data bases such as the corrosion potential, polarization resistance, and zero-resistance current density, in combination with the SEM morphology of corrosion pits and potentiodynamic polarization analyses obtained from laboratory tests, were built together in the monitor system. In this work, the data of potentiodynamic polarization correlated to the SEM morphology of a pitting corrosion crack, initiated under a critical concentration of chloride, were built in the system. This system is useful for providing a warning of pitting risk on 304 stainless steels, a major material used in the cooling system where seawater was present. Abrupt changes simultaneously appearing in more than two electrochemical measurements would lead to an alarm. This alarm would prompt the operators to take emergency actions for preventing the initiation of pitting corrosion. With our developed monitoring system, pitting corrosion could be detected when there are abrupt changes in corrosion potential and zero-resistance current density, resulted from a chloride concentration of higher than 400 ppm.