Cathodic protection is nothing but method used to reverse the flow of current between the two dissimilar metals under surrounding environment. There by reversing the action of metals in contact. This is achieved by applying the external circuit and forcing the anodic metal to behave as cathode.
Impressed Current Method
Current is applied in opposite direction to that of the corrosion current, thereby nullifying the effect of the later one on the base metal i.e. converting the base metal to cathode from an anode.
Such impressed current obtained by using dc source such as battery or dry cell along with an insoluble anode such as platinum, stainless steel, graphite, etc.
In this method as shown in figure the insoluble metal used is normally embedded underground to this with the help of dc current source.
The impressed current is applied and whole of this assembly is connected to the metallic structure to be protected. The connection is done by using wires.
The insoluble anodes are kept inside backfill made up of gypsum or any such material which can help in increasing.
The electrical contact with soil such an anode can be single if the area of the metallic structure to be protected is small or there can be many such anodes which can be connected in series if the area of the metallic structure to be protected is wider i.e. a long pipeline.
Due to application of impressed current anode deteriorates and hence it is to be replaced from time to time. Application of this method are seen in care of water tanks, buried pipelines, carrying water or oil condenser and transmission lines and ships.
This method is highly useful because it can protect the long length structure for longer time. Thereby reducing the frequency if monitoring as well as maintenance cost. This both method are widely used because protection provided to the base metal is long term and maintenance is easy.