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Cathodic Rectifiers

How Cathodic Protection works to prevent Corrosion

Corrosion is basically an electrochemical process. That is, it is a process where chemical reactions take place through the
exchange of electrons. By preventing the exchange of electrons, cathodic protection systems prevent the corrosion reactions which would otherwise naturally occur.

Cathodic protection systems are active systems which rely on the application of electric current to control corrosion. Interruption of this protective current will allow corrosion to proceed at a normal rate for the material/environment combination. In order to provide continuous protection the cathodic protection systems require maintenance. This maintenance can be in the form of periodic maintenance of system components such as current rectifiers or anodes in elevated water tanks, or in the form of non-routine maintenance and repair of system components such as anode beds or electrical conductors which are performed to correct system defects revealed by scheduled inspections.

In order to describe the principles of operation of cathodic protection in detail, the nature of the corrosion process must be
described in detail. Corrosion occurs through the action of the electrochemical cell.

Corrosion is the deterioration of a metal through reaction with its environment. The deterioration which occurs can take the form of a uniform wasting away of the metal such as in uniform attack by localized attack such as in pitting corrosion, or by reduction of mechanical strength and ductility such as in hydrogen embrittlement.

All of these forms of corrosion occur through the action of the electrochemical cell. Electrochemical cells all involve a flow of electrical current. At the anode, the area where corrosion occurs, electrons are produced which flow through the metal to a cathodic area where the electrons are consumed in another type of chemical reaction.

The electrochemical cell should be considered as a cyclic phenomenon where each of the components of the electrochemical cell must be present and functioning in order for the overall corrosion reaction to proceed. If anyone of the components of the electrochemical cell are removed or if the individual reactions at either the anode or the cathode can be prevented from occurring
then the entire corrosion process can be prevented. Cathodic protection is based upon this principle.

Cathodic protection is the prevention of corrosion by making a metal, which would ordinarily behave like an anode and corrode, behave like a cathode and be free from corrosive attack. In cathodic protection this is achieved by providing electrons of a higher energy level ( electric potential ) than those which would be produced in the corrosion reaction at the anode.

Impressed current cathodic protection systems a rectifier or other direct current power source is used to increase the potential of the electrons from the anodes in order to provide the desired protective current. Nearly all impressed current cathodic protection systems use alternating current powered rectifiers as a power source.

Rectifiers used for cathodic protection commonly use an adjustable step down transformer, rectifier stacks, meters to indicate output current and voltage, circuit breakers, lightning arrestors and transformer tap connections all in one case. The function of the rectifier is to convert alternating current into controlled direct current.

Common sizes and Common applications

Air Cooled Cathodic Rectifiers
Typically used for small areas. Low maintenance and high reliability for unattended operations

Oil Cooled Cathodic Rectifiers
Specially designed rectifiers that operate under severe heavy-duty, rugged conditions.

Junction Boxes
Cathodic Rectifiers are installed in all types of environments. To provide adequate protection from the elements these boxes protect the electronics.

Silicon Stacks
Silicon stacks (diodes): These stacks are more economical in higher voltage output circuits and in higher current circuits.