Ground-beds

The ground bed, for example, of the Russian railway roads used in very tough operating and natural conditions, its defects and deformations present a real threat to the safe trains running and reduce the passage capacity of the railway lines. 

Impressed Current Ground Beds and Interference Problems... 

Current due to the anode effect The potential of the earth near the ground-bed of a cathodic-protection system becomes more positive as the groundbed is approached (see Fig. 10.7, p. 10 10). A structure buried near the ground-bed will pick up current due to this variation in the soil potential and current will flow in the structure in each direction away from a point close to the groundbed (Fig. 10.39). The upper curve AGA in Fig. 10.39 shows how the current in the unprotected structure changes owing to the anode effect. 

A number of methods may be used to reduce the interaction on neighbouring structures. In some circumstances it may be practicable to reduce the current output applied to the protected structure or to resite the ground-bed so that the anode effect on an unprotected pipe or cable is altered as required. The physical separation between the groundbed and nearby buried structures can be increased by installing anodes at the bottom of deep-driven shafts and substantial improvements can be made using this technique. 

Anode materials and their properties along with the recommended uses are noted in Table 1.31. For a number of anodes required for an impressed current ground bed, we calculate the weight required by the equation,... 

GROUND BED - Cathodic protection, an interconnected group of impressed-current anodes that absorbs the damage caused by generated electric current... 

Impressed current anodes must be corrosion resistant and otherwise durable in the environment in which they are used. They must have low consumption rates when coimected to a CP source. All materials used for impressed current anodes are cathodic (more noble) than steel. High silicon cast iron (Fe-0.95C-0.75Mn-14.5Si-4.5Cr) is used for onshore CP applications and in other locations where abrasion resistance and other mechanical damage considerations are important [1]. Graphite anodes are extensively used for onshore pipeline CP applications in which they can be buried in multiple-anode ground beds. However, graphite must be stored and handled carefully because of its brittle nature. 

Design of ICS primarily involves anode selection, rectifier selection, ground-bed selection, and calculation of the I-ground-bed resistance and other main parameters. 

The ground-bed resistance is similar to that of the total circuit resistance calculated for the design of a sacrificial system (Section 15.6.2). In this case, multiple anodes are used and the resistance of anode to ground is calculated from Sunde equation [88]. 

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