Cathodic Protection Explained: 3 FAQs
Cathodic protection is used as a solution to the common problem of corrosion on metals. In order for cathodic protection to work, the metal to be protected from corrosion must be immersed in an electrolyte. For this reason, cathodic protection is not a viable option for preventing the corrosion of metals exposed to the atmosphere.
How Does Cathodic Protection Work?
Metals get corroded due to an electrochemical reaction that is "anodic" in nature. The anodic reaction results in the loss of electrons from the metal and into the electrolyte. The (now) free-flowing electrons move to the "cathode" side of the metal where the electrons are consumed by a cathodic reaction.
If the electrolyte is acidic in nature, the free-flowing electrons react with hydrogen ions in the electrolyte to produce hydrogen gas.
If the electrolyte is neutral, the cathodic reaction that consumes electrons also consumes oxygen molecules. This reaction leads to the formation of an alkali.
Cathodic protection works under the principle that attaching an external anode to the metal that needs protection and passing DC electricity through the electrolyte will create a cathodic environment on the entire surface the metal to be protected. This prevents occurrence of the anodic reaction that is responsible for corrosion.
What Is Galvanic Protection?
Galvanic protection is among the techniques used in the application of cathodic protection. It refers to a situation in which a more reactive metal is used as an auxiliary anode that has direct electrical connection to the less reactive metal that needs protection. For example, magnesium anode rods are commonly used to protect steel water tanks from corrosion.
Introduction of magnesium anodes into the water tank creates a positive current in the water (electrolyte). The positive current flows to the steel surface of the tank, thereby giving the steel a more negative charge. Thus, steel becomes the cathode and magnesium becomes the anode. Because corrosion takes place on the anode, the steel surfaces of the tank will not corrode.
Galvanic protection is also referred to as sacrificial anode protection. This is because the anode (magnesium) is sacrificed (left to corrode) so as to protect the cathode (steel)
How Is Cathodic Protection Advantageous?
The main advantage associated with cathodic protection in the face of corrosion is that its application is relatively simply. Cathodic protection will work so long as a steady supply of DC electricity to the system is maintained.
Cathodic protection is also preferred for the fact that its effectiveness can be monitored continuously with relative ease.