What is the Use of Ground Beds in Cathodic Protection?

What is the Use of Ground Beds in Cathodic Protection?

The cathodic protection type determines how the cathodic current is supplied to the structure. Cathodic protection can be applied by either an impressed current system or by a sacrificial anode system. Impressed current cathodic protection systems use an external DC current source and a variety of anode materials to supply the cathodic current. Sacrificial anode CP systems generate the cathodic current from the corrosion of metals less noble than the metal to be protected.

Metallic structures in contact with water, soil, concrete, and moist air are subject to corrosion. Cathodic protection (CP) is one of the few methods that successfully mitigates corrosion. It can be applied in any situation where the environment surrounding the metal acts as a conductor for electric current. It has been successfully applied to offshore structures, ships, boats, propellers, moorings, pipelines, storage tanks, piers, jetties, bridges, aquaria, instrumentation etc.  

Anode ground beds are used to increase the anode current output in soils in cathodic protection. They typically comprise an excavation which is filled with low conductance carbonaceous material into which the anode(s) are placed. The total resistance of the system then becomes the resistance of the anode to the carbonaceous backfill plus the resistance to earth of the backfill itself. The anode resistance is reduced by the low resistance of the backfill (typically 50 ohm-cm for coke breeze), and the resistance of the backfill to earth is reduced by the large surface area of the backfill in contact with the soil. Standard anode to ground resistance formulae are used to obtain the resistance values.

Because of the variables involved in ground bed sites, experience is invaluable in attaining competence in their design. They are designed with regard to the current demand of the structure to be protected, to the soil resistance, and to other structures and stray current effects.