Cathodic protection consists in protecting the steel gas grid by cancelling out the electrochemical corrosion process that affects metal in contact with an aqueous environment (soil, water, concrete etc.).
To eradicate this electrochemical phenomenon, a “cathodic current” is applied to the metal structure so that the entire surface in contact with the environment is “cathodically protected”, thus cancelling out the corrosion (oxidation) phenomenon. In practice, this (direct) electrical current is generated between the structure you want to protect, the cathode and a structure that you will “sacrifice”, the anode. There are currently two ways to achieve this:
cathodic protection by impressed current: A direct current electrical supply is put in place, which will inject a current between the structure and an anodic mass buried in the same environment.
cathodic protection by galvanic or sacrificial anodes: The structure requiring
protection is connected to a galvanic anode made from zinc or magnesium (for soil), which have less “noble” (or more negative) potentials than steel. This forms a galvanic couple, making the steel anodic because of a current that circulates between the anode and cathode in the environment in question.
Cathodic protection requires professional expertise and is strictly controlled by regulations because it is used to guarantee the integrity of gas and hydrocarbon transport (an distribution) pipelines. This protection against corrosion is said to be “active” and used in conjunction with the passive protection offered by coatings in the context of buried pipelines.