Deep anodes

The first anode installation for the cathodic protection of gas pipelines in New Orleans consisted of a 5-m-long horizontal cast-iron tube. Later old tramway lines were used. Since in downtown New Orleans there was no suitable place to install impressed current anodes and to avoid detrimental effects on other pipelines, Kuhn recommended the use of deep anodes which were first installed in 1952 at a depth... 

Fig. 1-13 The first deep anode for cathodic protection in Germany.

With deep anodes, a tube that allows gases to escape must be included to avoid a build-up of gas (see Section 9.1.3). The anode chains are supplied with cable, a centering device and a gas escape tube. 

Deep anodes are installed where the resistivity is high in the upper layers of soil and decreases with increasing depth. This type of installation is recommended for densely populated areas and for local cathodic protection (see Chapter 12) on account of the small space needed and the smaller voltage cone, which avoids interference with foreign structures. 

Deep anodes consist of parallel-connected single anodes which are set in boreholes 50 to 100 m deep with a diameter of 0.3 m. The boreholes can be produced by a variety of boring methods, but the air lift method has proved particularly suitable (see Fig. 9-10). The borehole is filled with water to ground level according to the principle of a mammoth pump. Compressed air is fed via a pipe to... 

Fig. 9-10 Drilling for a deep anode bed with the air lift method.

Fig. 9-12 Increase in grounding resistance of a deep anode due to formation of a gas pocket.

A significant rise in temperature AT is calculated in a volume of soil at a distance up to 3 from the anode, where is the anode radius. Factors are the thermal conductivity of the soil, k, length of the anode, L, the grounding resistance, Rq, and the current, I. The rise in temperature can be calculated from these parameters [10]. For deep anodes it amounts to ... 

Fig. 9-13 Voltage cone of 30-m-long deep anodes with various depths of earth coverings t.

In urban districts, installation of impressed current anodes near the surface is usually very difficult because of the interference of nearby installations. Here the installation of deep anodes in suitable soils is recommended these also have the advantage of being able to be installed in the track of the supply line (see Section 9.1.3). 

Deep anodes are mainly used for injecting such high protection currents (see Section 9.1). The advice given in Section 9.1 on resistances and potential distribution relates to anodes in homogeneous soils. Large deviations are to be expected in soil used as backfill and in the neighborhood of structures [2]. This is generally the case with local cathodic ( hot-spot ) protection. 

Fig. 12-2 Local cathodic protection in a power station. deep anodes O horizontal anodes Potential readings Ccu-cuso4 volts (A) free corrosion potential before commissioning the cathodic protection (B) 4 months after switching on...

Cathodic protection with impressed current anodes is used predominantly with cables or steel casing in which the cable is inserted, outside built-up areas where it is possible to build large anode installations without damaging interference with other lines. In densely populated areas, protection with impressed current anodes is often only possible with deep anodes, with surface anodes or locally at individual problem points (local cathodic protection, see Chapter 12). 

Deep anode installation 20-m cable trench, including cable and laying DM 1600... 

The model shown in Figure 13 considers three parallel pipelines of approximately 70km in length sharing the same CP system which consists of 11 ICCP deep anodic beds delivering 10A each. The distance between pipelines is 10m in the local normal direction. The model considers two soil layers (0.02 S/m from ground level to -35m, and 0.005 from -35m to -100m). 

T.H. Lewis Jr., Replaceable deep anode design and installation, in Proceedings of the Corrosion and Prevention, LORESCO International, Australia, 1998, pp. 352-357. 

Tufram TFE aluminum Deep anodizing process followed by TFE impregnation used on aluminum alloys... 

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