Cathodic Protection is a Method Used to Control Corrosion

Cathodic Protection is a Method Used to Control Corrosion

What is cathodic protection meaning for? Generally, Cathodic Protection (CP) is an electrochemical (half electrical and half chemical) method used to control corrosion of buried or submerged metallic structures. Cathodic Protection is a method used to control corrosion. It prevents corrosion by making the protected structure a cathode by installing a more anodic metal (sacrificial or galvanic) anode or a metallic (impressed current) anode connected to a Direct Current (DC) power source. When the proper amount of current is applied to the structure, it becomes a cathode. Since all corrosion occurs at the anode, the structure no longer corrodes. The electrons move in the metallic path (electrical). Reduction (chemical) reactions occur at the surface of the cathode resulting in a hydrogen coating and a more alkaline environment. Oxidation (chemical) reactions occur at the surface of the anode resulting in corrosion and a more acidic environment. After a CP system is installed and adjusted to provide adequate protection, the hydrogen coats the defects in the coating and polarizes in the negative direction (to a copper/copper sulfate reference electrode) over time the current and potentials remain relatively stable; changes in currents or potentials indicate a problem. An error-free measurement of negative 850 millivolts DC or more negative to the copper/copper sulfate reference electrode proves the structure is a cathode and corrosion has been mitigated.

Corrosion
It is convenient to classify corrosion by the forms in which it manifests itself, the basis for this classification being the appearance of the corroded metal. Each form can be identified by visual observation, although, in some cases, magnification is required. Valuable information for the solution of a corrosion problem can often be obtained through careful observation of the corroded test specimens or failed equipment.

Examination before cleaning is particularly desirable. Some of the eight forms of corrosion are unique, but all of them are more or less interrelated. The eight forms of corrosion are:
(1) Uniform Attack,
(2) Galvanic or Two-Metal Corrosion,
(3) Crevice Corrosion,
(4) Pitting Corrosion,
(5) Intergranular Corrosion,
(6) Selective Leaching,
(7) Erosion Corrosion,
(8) Stress Corrosion Cracking.