In the field of engineering, what are the reasons for cathodic protection? How much do you know about it? In this regard, let's learn about it together, hoping to help you.
1. Corrosion potential or natural potential
Corrosion potential (natural potential): Each metal immersed in a certain medium has a certain potential, which is called the corrosion potential (natural potential) of the metal.
Corrosion potential can indicate the relative ease of a metal losing electrons. The more negative the corrosion potential, the easier it is to lose electrons.
We call: the part where electrons are lost the anode area.
The part where electrons are obtained is the cathode area.
The anode area is corroded due to the loss of electrons (for example, iron atoms lose electrons and become iron ions that dissolve into the soil), and the cathode area is protected by electrons.
2. Reference electrode
In order to compare the electrode potentials of various metals, there is a common reference electrode.
The saturated copper sulfate reference electrode has good repeatability and stability of electrode potential, simple structure, and is widely used in the field of cathodic protection.
3. Cathodic protection
The principle of cathodic protection: it is to add a large amount of electrons to the metal, so that the protected metal is in a state of excess electrons as a whole, so that each point on the metal surface reaches the same negative potential, and the metal atoms are not easy to lose electrons and become ions and dissolve into the solution.
There are two ways to achieve this goal:
1) Sacrificial anode cathodic protection: it is to connect the metal with a more negative potential to the protected metal and place it in the same electrolyte, so that the electrons on the metal are transferred to the protected metal, so that the entire protected metal is at a relatively negative and the same potential.
Features: This method is simple and easy, does not require an external power supply, and rarely produces corrosion interference.
Application: Protect small metal structures or those in low soil resistivity environments (soil resistivity is less than 100 ohms. meters). Such as: urban pipe networks, small storage tanks, etc.
2) Impressed current cathodic protection: through an external DC power supply and an auxiliary anode, the current is forced to flow from the soil to the protected metal, so that the potential of the protected metal structure is lower than that of the surrounding environment.
Application: Protect large metal structures or those in soils with high soil resistivity, such as: long-distance buried pipelines, large tank groups, etc.