What Is Anodic Protection?

Anode protection refers to a protection method in which a protected metal is used as an anode and anodization is performed to passivate the metal. The key to anodic protection is to establish and maintain a passive state. Therefore, corrosion systems that do not have obvious passivation characteristics in the anodic polarization curve must be able to achieve anodic protection. The main parameters of anodic protection must also be analyzed.

The protected metal equipment is connected to the positive electrode of an external DC power supply, and the metal is anodic polarized to a certain potential in a certain electrolyte solution. If the metal can establish a passive state and maintain a passive state at this potential, the anode process is inhibited, and the corrosion rate of the metal is significantly reduced, and the equipment is thus protected. This method of protection is called anode protection. ^[1]

Under the action of external anodic direct current, the potential of the metal moves in the positive direction. When it is moved to a blunt potential or the external current density flowing through the metal reaches a blunt current, the metal will undergo anodic passivation and the surface will be generated.

The conditions and characteristics of anode protection are as follows:

(1) Anode protection should not be used in some media with high active anion content, because these active ions, such as chloride ions, can locally destroy the passivation film and cause pitting corrosion at high concentrations.

(2) Like cathodic protection, anodic protection also has a shielding effect. If the layout of the cathode and anode is not reasonable, it may cause passivation in some places, overpassivation in some places, and still in an activated state.

(3) Compared with cathodic protection, anodic protection has high cost and complicated process. Anode protection requires auxiliary cathodes, DC power, and equipment to measure and control the protective potential. ^[1]

1) blunt current density

Generally speaking, when implementing anodic protection, the smaller the value of the blunt current density is, the better, so that a small-capacity power supply device can be selected to reduce equipment investment and power consumption, and also reduce the equipment's The anode is dissolved, and the device is relatively easy to reach a passive state. The composition, temperature, concentration, and pH of metal materials and corrosive media all affect the magnitude of the blunt current density.

2) dimensional blunt current density

The dimensional current density represents the corrosion rate of the metal during anode protection. The smaller the dimensional current density, the smaller the corrosion rate of the equipment, the more significant the protection effect, and the smaller the daily power consumption.

3) Potential range of passivation area

The wider the potential range of the passivation region, the better. The wider the potential range of the passivation zone is, the higher the potential range is allowed to fluctuate without the danger of entering the activation zone. In this way, the electrical equipment and reference electrodes that control the potential need not be too high.

4) Best protection potential

There is also an optimal protection potential during anodic protection. When the anode is at this potential, the dimensional current density is the smallest, the passivation film is the most dense, the anode corrosion rate is the lowest, and the anode protection effect is also the best. ^[1]