Cathodic protection of buried pipelines
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Cathodic protection is a corrosion prevention method for protecting the outer walls of buried pipelines, developed based on the principle of galvanic cells. Based on the principle of a galvanic cell, only the anode among the two electrodes is corroded; therefore, cathodic protection involves using artificial methods to make the metal pipeline act as a cathode in order to prevent corrosion. There are two types of cathodic protection: one is the cathodic protection method without external current application. The specific method is as follows: A metal material with a higher reactivity than steel (i.e., more reactive), such as magnesium or zinc, is used as the anode. This anode is buried underground, and wires are used to connect it to the pipeline at regular intervals, thus forming a large circuit in the soil. As a result, the anode metal corrodes, while the steel or cast iron pipeline is protected. This method is often used when the soil resistivity is low, a power source is unavailable, and the pipe coating is of good quality. Another method is cathodic protection using an external direct current. The specific method is to bury scrap iron and similar materials near metal pipes as an anode, connect it to the anode of direct current, and attach the cathode of the power supply to the pipes. Electric current flows from the DC power supply through the cable to the artificial scrap iron anode, then into the protected pipeline via the soil, and returns to the cathode of the power supply through the cable. In this way, the protected pipeline becomes the cathode, thereby preventing corrosion of the pipeline by the soil. This method is more suitable for use when the soil resistivity is high or metal pipes are exposed. In fact, cathodic protection is often used in conjunction with the external coating of pipelines to achieve better corrosion resistance.
How to prevent corrosion in buried pipes? There is a method called cathodic protection, and its principle is quite simple: in electrochemical reactions, only the anode is corroded; therefore, by making the pipeline the cathode, it will not be corroded. There are specifically two methods: The first is one that does not require an external power source, and it is called the sacrificial anode method. For example, use metals that are more reactive than iron, such as magnesium or zinc blocks, bury them underground, and then connect them to the pipes with wires. In this way, a circuit is formed in the soil; the active metal acts as the anode and is gradually corroded, while the pipe, acting as the cathode, remains safe. This method is suitable for situations where the soil resistance is low, there is no power source nearby, and the outer layer of the pipe is coated. The second method is the forced current method, which requires an external DC power supply. Materials such as scrap iron are buried underground as an anode, connected to the positive pole of the power supply, while the negative pole of the power supply is connected to the pipe. Current flows out from the power source, passes through the scrap metal anode and the soil to reach the pipe, and then returns to the power source; in this way, the pipe remains the cathode and is not corroded. This method is suitable for situations where the soil resistance is high, or where the pipes are exposed to a large extent. In practical applications, cathodic protection is usually used in combination with an anti-corrosion coating on the outer layer of the pipeline to achieve a better corrosion prevention effect. .