The components of an impressed current cathodic protection system

3 The components of an impressed current cathodic protection system 

The essential elements of a conventional impressed current cathodic protection system are in this section and in Section 7.4. 

Impressed current anodes have very slow or controlled consumption rates when the anodic reaction occurs on the anode surface. As the reaction consumes alkalinity (equation (7.5)) and generates acid (equation (7.6)), it can attack the anode and the concrete. The level of current is therefore important in maintaining a good anode to concrete bond. Types of anode are described later. The function of the anode is to spread the current to all areas to be protected having converted the electrical current from the transformer rectifier (DC power supply) to an ionic current that flows from the anode to the cathode so that the cathodic reaction will occur on the reinforcing steel surface, suppressing corrosion. 

One important requirement is that the interfacial resistance between the anode and the concrete. However, the electrical resistance of the anode system should be proportionately lower than the combination of the interfacial resistance, the concrete cover resistance, and the steel to concrete resistance, otherwise the current will not distribute evenly to the steel. For atmospherically exposed reinforced concrete structures the anode is usually a distributed anode system , such as a paint coating on the surface, an expanded metal mesh across the surface encased in a concrete overlay, strips of anode in slots across the surface or a series of small point or discrete anodes embedded in the concrete cover or among the rebars. 

As gases are evolved at the anode (equations (7.3) and (7.4)) the distributed anodes such as coatings or encased anodes must be gas permeable. 

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THE COMPONENTS OF AN IMPRESSED CURRENT CATHODIC PROTECTION SYSTEM... 

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