Introduce the principle of anodic protection
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Using the equipment as the anode and applying a current from the outside generally accelerates corrosion, and the corrosion current increases with anode polarization. However, for metals that can be passivated, a different situation occurs: as the potential increases with current, once it reaches the passivation potential, the corrosion current drops sharply, by as much as tens of thousands of times; thereafter, as the potential continues to rise, the current remains constant until the passivation region is reached. Using this principle, with the device to be protected as the anode and an electric current being applied to keep the potential in the middle of the passivation region, the corrosion rate can be kept very low; the magnitude of the applied current indicates the corrosion rate of the device.
Anodic protection is an electrochemical protection method that utilizes the passivation properties of metals to prevent corrosion. The core principle is that when the device acts as an anode and a certain amount of anodic current is applied from the outside, corrosion is generally intensified. However, for metals that can form a passivation film, when the anode potential reaches a certain specific value (known as the passivation potential), a strong and stable passivation film is rapidly formed on the metal surface, resulting in a sharp reduction in the corrosion current – by as much as tens of thousands of times. Upon further increasing the potential, the current does not increase significantly; instead, it remains at a low and stable level over a wide range, and this region is known as the passivation region. In engineering practice, the anodic protection technique is utilized: the equipment to be protected is used as the anode, and an appropriate current is applied via an external power source to keep its surface potential stable at a midpoint in the passivation region. At this point, the surface of the device remains in a passivated state for an extended period, effectively suppressing the corrosion rate. At the same time, by measuring the current introduced, the actual corrosion condition of the equipment can also be reflected. .