Ground systems, buried structures

For reinforced-concrete structures buried in soil or immersed in water, cathodic areas may be due to noble metals present in the environment and electrically connected with the steel embedded in the concrete. For example, this is the case with copper grounding systems. 

Figure 10.235 illustrates the proper way to bond the tower base ground leads to the buried ground system [9]. Dress the leads close to the tower from the lowest practical structural element at the base. Keep the conductors as straight and short as possible. Avoid any sharp bends. Attach the ground wires to the tower only at one or more existing bolts (or holes). Do not drill any holes into the tower. Do not loosen any... 

Any radial that comes within 2 ft of a conductive structure must be tied into the ground system [9]. Bury the interconnecting wire, if possible, and approach the radial at a 45° angle, pointing toward the expected surge origin (usually the tower). Cadweld the conductor to the radial and to the structure. 

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. 

Before mechanical refrigeration systems were introduced, people cooled their food with ice and snow, found or made on-site or gathered in the mountains. This practice survives today in the Taurus Mountains of Turkey. Ice was stored in icehouses usually partially buried in the ground and lined with straw or sawdust. Remains of these structures survive on many farms in Europe and North America. Ice has long been used for space comfort conditioning. In the early nineteenth century, ice was placed in air ducts to cool and dehumidify warm air blown by fans. 

The successful commissioning and effective use of a cathodic protection system is usually monitored by measuring the spatial distribution of the cathode potential on the structure. This may be achieved via regular ground stations in the case of a buried pipeline (Fig. 10.30) or a portable, heavy-duty reference electrodc/digital voltmeter probe (Fig. 10.31) in the case of offshore rigs and platforms. 

It has been shown above that there must be a source of current to supply electrons to the areas of the metal which is corroding. In a metal buried in ground, anodic areas corrode by release of electrons and if an equal number of electrons are not introduced from an external source, the metal would continue to corrode. An external anode which supplies such current is called auxiliary anode in the electrochemical cell and referred to as anode in a cathodic protection system. Electrodes of graphite, cast iron, platinum and titanium act as conductors of electricity and supply the desired current to the structure to be protected. The conductors are energized by a DC source. The rate of consumption of anode electrodes... 

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