Cathodic Protection Types
At CP Solutions, Inc.®, a wide variety of engineered corrosion-control applications are possible using either sacrificial (galvanic) anodes or impressed current (rectified) anodes for cathodic protection of municipal, industrial and commercial infrastructure.
Sacrificial Anode Cathodic Protection
Sacrificial anodes are most often made of an alloy of magnesium, zinc or aluminum, although different alloys are available for different electrolytes including seawater, soil and concrete. Each different type of sacrificial anode will be the source of cathodic protection current because of higher electrical potential anode of the anode versus the protected structure.
The Practical Galvanic Series provides guidance in selecting the proper anodes to use in corrosion control through sacrificial anode protection for various metals. Selecting an alloy for the process requires a great amount of consideration for the electrolyte the anode and structure are placed in, as well as considering factors such as size, shape, and protective coatings or wrappings applied to the structure. One must also consider the intended life span of the system.
Impressed Current Cathodic Protection
Inert anodes are used in impressed current protection and powered by an external source of DC current. These anodes can be made of graphite, cast iron, mixed-metal oxide-coated titanium, or platinum-niobium clad metals. There are many sizes and shapes of impressed current anodes, including wires, rods, tubes, sticks, plates, and disks.
It is very important to consider the composition of the electrolyte when selecting the best impressed current anode for your needs. The most common DC current source is a rectifier, although other sources like solar energy systems are available.
In these systems, anodes are installed within the electrolyte around the structure to be protected and connected to the positive output terminal of the rectifier. The structure is connected to the negative terminal. The current will flow from the anodes, through the electrolyte, and onto the structure. The metallic connection between the structure and the rectifier will complete the DC circuit. These systems offer a variety of anode configurations that are dependent upon the electrolyte and the structure being protected.