Study on Application of Cathodic Protection in Atmospheric Environment

在宽度为-50 mm、长度为1m的碳钢试片上设置铂阳极流动阴极保护电流，涂覆不同的亲水涂层。在钢阳极之间施加一定的电压，在不同施加电压、海盐沉淀量、相对湿度和涂层亲水性的条件下，测量直径为2 mm的人工缺陷处的阴极电流和电极电位。证实了这种阴极保护方法在一定条件下是有效的，因为人工缺陷的电极电位随着外加电压、海盐沉积量和PH的增加而降低，这种阴极保护方法的优点是在腐蚀性较高的条件下有效。给出了阳极下绝缘层的电流分布和电阻、涂层上的水膜和极化电阻作为PH的函数，从而可以估计缺陷处的电极电位，得到如下结论：1)当涂层条件良好且只存在一个缺陷时，阴极保护电流可达3-5m2)当存在两个缺陷时，虽然阳极附近的缺陷可以得到保护，但很难同时保护两个缺陷。3)由于几乎所有的电压降都施加在阳极下的绝缘层上，因此应该减小该层的电阻。

Platinum anode to flow cathodic protection current was set on the carbon steel coupon-50mm width and lm length with various hydrophile coatings. A determined voltage was applied between steel and anode, then cathodic current and electrode potential at artificial defect with diameter of 2mm were measured under conditions with various applied voltage, amount of deposited sea salt, relative humidity (RH), and hydrophile property of coating. It was confirmed that this cathodic protection method was effective under some conditions, because the electrode potential of artificial defect decreased with incrcasing applied voltage, amount of deposited sea salt and PH.And it is advantage of this cathodic protection method to be effective such conditions with higher corrosivity.Distributions of current density and electrode potential were analyzed based on measured results by using 1-dimensional model with equivalent electric circuit. Current distribution and resistance's of insulation layr under the anode, water film on the coating, and polarization resistance were given as functions of PH.Thus it was possible to estimate electrode potential at defects, and it was known as follows ;1)When coating condition is good and there exists only one defect, cathodic protection current reaches as far as 3-5m.2)When there exist two defects, it is difficult to protect both of them, though the defect near the anode can be protected. Arrangement of Anodes should be considered in this case.3)Because almost all voltage drop is applied to insulating layr under the anode, resistance of this layr should be decreased.