Select an active metal (alloy) whose electrode potential is more negative than that of the protected metal, and electrically connect it with the protected metal in the electrolyte environment from the outside. This kind of active metal with negative potential will be preferentially corroded and dissolved as an anode in electrochemical cells, so it is called sacrificial anode. The released current will polarize the cathode of the protected metal to the required potential range, thus inhibiting corrosion and realizing protection. This is sacrificial anode cathodic protection.
(A) electrochemical corrosion principle
Metal pipes have a surface layer to prevent corrosion. When the surface layer is in danger of corrosion, after the exposed surface layer of the metal pipeline is wetted by rain or wet soil, oxygen groups and hydrogen ions in the soil form batteries, which are oxidized into anode iron, so the iron will corrode in a very short time and then rust.
The three main electrochemical corrosion components are as follows:
1, the metal dissolves at the cathode, and turns into metal ions flowing into the solution;
Me → Male+Female
2. Electrons flow from anode to cathode.
3. After flowing to the cathode, X in the solution that can absorb electronic substances will receive electrons.
X+ne → X ne
(2) Analysis of relevant protection schemes
Learn the electrochemical principle to analyze the causes of metal corrosion, and customize the relevant protective measures for the three main reasons of electrochemical corrosion, which can follow the following three criteria;
1, slow down or prevent financial dissolution
The first method is to choose a suitable metal, or to study and customize a basically insoluble metal.
The second method is to separate the substance that will cause corrosion from the metal.
The third method is to change the PH value or other properties of the metal.
2. Prevent electrons from flowing to the cathode.
The first method is to change the metal potential.
The second method is to change the flow direction of electrons.
3. Removing electronic substances that can be absorbed by the cathode;
Because oxygen will continuously flow into the soil from the air, there is no relevant measure to clean the substance that can absorb electrons on the cathode.
Second, the detailed plan to prevent electrochemical corrosion
Three causes of electrochemical corrosion were studied and five schemes were synthesized. The following criteria can be adopted to finally achieve anti-corrosion.
(a) Select an appropriate metal or research and customize a basically insoluble metal.
Make it a truly corrosion-resistant metal. When making metal, other substances will be added to improve the anti-corrosion level of metal. When refining steel, manganese, chromium and other components should be added to refine it into stainless steel.
(2) Separate the substance that will cause corrosion from the metal.
Several schemes can be used to separate corrosive substances from metals. First, paint, asphalt, plastic or enamel, tin, zinc, chromium, nickel, silver and gold are applied to the metal surface. Apply it to the surface of the metal to be rusted by electroless plating or electroplating to prevent the inner layer from being corroded.
(3) changing the properties of metals
Try to add corrosion inhibitor to the system that can form batteries, change the properties of the medium and reduce the corrosion rate.
(4) Change the metal potential.
Cathodic protection measures are taken, and the electrolyzer is composed of power supply. Set the metal to be protected as cathode, waste metal as anode, and the metal to be protected as cathode for protection.
(5) Change the flow direction of electrons.
Anode protection measures are taken, and the protected metal is anodized by external power supply to make it become anode. When the positive value of correlation is reached, there is a new phase layer or adsorption layer on the surface to passivate the metal.
Third, explore new methods.
As an oilfield ground construction unit, the engineering construction company undertakes the maintenance work of various oil production plants and the reconstruction project of old areas all the year round. In actual construction, many aged and corroded pipes pass through the hole because of the strong corrosiveness, alkalinity and acidity of the pipeline medium. On the other hand, the transported medium contains relatively high oxygen and hydrogen ions, which are higher than those in soil, and the electrochemical corrosion is more serious.