Cathodic protection-based systems are an electrochemical method applied to prevent the corrosion of metallic materials that remain underground and in liquids caused by corrosive factors in these environments or to carry out the corrosion in a controlled manner, although it cannot be overcome. Its basic principle is based on the theory of electrochemical corrosion. According to this theory, when a current flows through an electrochemical cell, an oxidation reaction takes place at the anode, and a reduction reaction with an equal value with this reaction occurs at the cathode part.
In this type of systems, corrosion does not occur in the cathode part. According to this theory, the anode parts on the surface of the metal are converted into cathodes, thus preventing corrosion.In order to apply cathodic protection, another metal is placed in the same electrolyte to act as an anode. If the anode is a more active material than the material to be protected, a galvanic cell is formed between these materials.
A current occurs and passes spontaneously through this circuit. Since the material to be protected will act as the cathode of this galvanic battery, corrosion does not occur in the material. The material forming the anode part at the same rate as the current passing through the circuit dissolves and separates into its ions. In this case, the galvanic anode cathodic protection system is formed with the galvanic battery logic.
It is also possible to apply cathodic protection with inert anodes. For this type of inert anode cathodic protection application, it is necessary to start the application by adding an external direct current to the system. The positive end of this tool that provides a direct current source added to the system should be connected to the anode, and the negative end should be connected to the material that needs to be protected during application. During this formation, the electrolysis cell takes place.
In this electrolysis cell, oxidation reactions take place at the anode, while reduction reactions take place at the cathode. During the reactions taking place in the anode region, the metal does not dissolve. Since inert metals are used in the anode part, various oxidation reactions such as oxygen output or chlorine output take place depending on the type of electrolyte.
Application areas of cathodic protection systems:
• Steel piles of sea quays
• Fire installation systems
• Internal parts of liquid storage tanks located above or below ground
• To the bottom parts of the underground fuel tanks and the plugs at the ground level.
• Oil and fuel distribution networks
• Drinking water distribution networks
• Natural gas distribution networks
• Compressed air distribution networks
• Sewer systems
• Marine pier steel piles
• Anchors used in the construction of construction column systems
• Boiler boilers
• Heat exchangers and coils
• Systems where refrigerants used in heating and cooling flow
Cathodic protection systems:
In the cathodic protection system, it is essential to prevent the anodic reactions taking place in the metal material structure by turning the metal material to be protected into the cathode of the electrochemical cell to be applied. Thanks to the cathodic protection systems, electron flow is provided to the material to be protected, preventing the ionization of the structure of the material and the material surface is freed from the negative effects of corrosion. Electrons required for cathodic protection systems to protect the material;
• By forming a galvanic couple with the metal material, which has a more anodic structure than the metal material to be protected,
• It can be obtained with an external current supply source with direct current.
In the light of the specified, two types of application are seen in cathodic protection systems;
• Galvanic anode cathodic protection systems
• External current sourced cathodic protection systems
Which of these two types of cathodic protection systems will be used is determined depending on the characteristics of the environment where cathodic protection will be applied, the system and application costs to be used, and the type of structure.
Cathodic protection system mechanism
The reaction that takes place at the cathode during cathodic protection can be made possible by using electrons flowing from the anode. If the electrons flowing from the anode are not used in the cathode region, oxidation reactions cannot occur in the anode part. The conclusion to be reached here is that if there is not enough oxygen in the cathode part, the corrosion event is not expected to occur.
If the electrons required for the cathode reaction to take place are taken from an external current source during cathodic protection, no electron flow occurs with the reaction in the anode part. Thanks to these electrons that cannot be formed, the corrosion situation that progresses from the anode part does not occur. The external current sourced cathodic protection mechanism and the corrosion protection method are realized within the framework of this electrochemical principle.
With the current given to the material to be protected, electrons can move to the surface of the material and stop the anodic reactions completely, while increasing the speed of the cathodic reaction. The reactions taking place in the anode part now take place in the auxiliary anode region, which is connected to the cathodic protection system, instead of taking place on the surface of the protected material. The surface part of the protected material takes its place in the system as a complete cathode.
During the corrosion of the metal in a corrosive environment, if it is connected to a more active metal, namely a galvanic anode, the electrons that will help the cathode reaction take place are met by an oxidation reaction that occurs spontaneously on the galvanic anode metal connected to the system. As a result of this situation, anodic reactions on the surface of the protected metal do not occur. The cathodic protection system with galvanic anode takes place within the framework of this system.
The main purpose of this protection system is to prevent corrosion that may occur from all kinds of corrosion by making the metal more negatively charged than the soil under a fixed potential limit of the metal in the environment against corrosive conditions.