Most metals are corroded on contact with air and water. It is briefly chewed, ie oxidized or corroded by other chemical effects. For example, corrosion of iron, oxidation of aluminum. The risk of corrosion is a great risk, especially for metal pipes under the ground that pass through the water. Different protection methods have been developed in order to prevent corrosion of the metal from which such pipes are made. One of these methods is to place a more active metal near the pipes in contact with these pipes. This method is called cathodic protection. There are many different areas where cathodic protection is used. Of these, this method is mostly used in oil drilling rigs. Cathodic protection method is also used to prevent corrosion on ships' surfaces. Briefly, cathodic protection is a kind of metal protection method.
In the cathodic protection method, the metal structure to be protected is turned into a cathode of an electrochemical cell and the reactions that stop developing on the metal surface are stopped. In order to achieve this, a cathodic external flow is applied to the metal structure to be protected.
Cathodic protection method was first used in 1930 years. However, in parallel with the great advances in technology in recent years, new high performance anodes have been found and cathodic protection method has been the most economical and effective method for combating corrosion. There are also several types of cathodic protection.
A corroded metal is chemically acting as an anode. If the potential of this metal is changed and forced to act as cathode, corrosion is avoided. This is the application principle of cathodic protection method. This protection is called cathodic protection from external current.
Another form of cathodic protection method is to use a more active metal as an anode and to create an artificial battery circuit, by transferring electrons to the metal to be protected against corrosion, to convert this metal into cathode. The protection made in this way is also called galvanic anode cathodic protection.
Importance of Cathodic Protection Measurement
The purpose of the cathodic protection method is to polarize the metal to be protected negatively against the soil and protect it against all kinds of corrosion. In the Annex of the Regulation on Health and Safety in the Use of Work Equipment, issues related to maintenance, repair and periodic checks (Annex-III), the subject of cathodic protection is discussed under the installations. According to the principles in this article, cathodic protection method should be performed once a year under regular checks unless otherwise stated in the relevant standards. In addition, these checks must be performed by electrical engineers, electrical technicians or high technicians.
In cathodic protection method, four different measurements are made: three potential measurements and one current measurement:
- System / Soil potential measurement: Cathodic protection measurements are usually made with reference to the copper or copper sulfate electrode. A rod of the avometer is connected to the reference electrode and the potential is read. This potential value should be the lowest 850 mV.
- Anode / Earth potential measurement: One rod of the avometer is connected to the poles in sequence. The pole with a high potential value is the pole to which the cable from the anode is connected. This value must be between 1300-1500 mV.
- Pipe / Earth potential measurement: One rod of the avometer is connected to the poles. The pole with a low potential is the pole to which the cable from the pipe is connected. This value must be between 400-650 MV.
- Measurement of current drawn from the anode: One end of the avometer is connected to the poles to which the cable from the anode is connected and the current drawn from the anode is read. This value must be between 5-100 mA.
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