Marine Corrosion Solutions
How Electro-Guard Impressed Current Cathodic Protection Systems work
Impressed Current Cathodic Protection systems have five basic components: the anode, the reference cell, the electronic controller, the monitoring station, and the vessel's underwater metal structures.
The protective current for cathodic protection of the boat's underwater metal structures is provided by the vessel's DC electrical power system. Electrical current flows from the DC source into the metal structures being protected. The metal structures emit electrical current into the water surrounding the boat. The current flows through the water by ionic conduction and is absorbed out of the water at the system's anodes and is subsequently delivered back to the power source through the system's controller.
The amount of current (in amperes) delivered to the underwater metals is controlled by an electronic circuit that measures the voltage difference between a stable external reference electrode (reference cell) and the structures being protected by the controller. This voltage difference measurement is known as the solution potential and is the key measurement for determining the level of cathodic protection. The controller regulates the current being delivered to the metal structures so that the external reference voltage matches a calibrated internal reference voltage. The internal reference voltage is calibrated for the type of metal the system is designed to protect.
As long as sufficient anode current is available and there are no strong external electrical influences -- such as stray electrical currents -- the controller will always supply the amount of anode current necessary to match the solution potential of the metal structures being protected to that of the internal calibrated reference voltage. As stated above, the term "solution potential" refers to the voltage difference between the stable reference electrode and the protected metal structures.
The controller is calibrated to maintain a solution potential for a boat's metal structures at which all electrochemical reactions will be cathodic -- hence the term "cathodic protection". Cathodic reactions are reduction reactions which are noncorrosive. Anodic reactions are oxidation reactions and are corrosive. By regulating the electrical current, the controller changes the solution potential of a boat's metals from their natural potential, where the electrochemical reactions are both anodic and cathodic, to the calibrated internal reference potential at which all reactions are cathodic. Since there are no longer any anodic (oxidation) reactions occurring on the boat's underwater metal surfaces, corrosion is prevented.