| 摘要 |
<PICT:1108692/C6-C7/1> Cathodic corrosion protection is provided for an underground structure such as a pipeline 31 by positioning, in a well 27 containing an aqueous electrolyte solution 28, at least one anode 21, 22, 23 at a depth below ground level such that the resistivity of the ground immediately surrounding the solution at said depth is less than the resistivity of the ground at a level 32 intermediate said depth and the ground surface and providing a low resistance electrical connection between the anode and the structure 31, whereby current derived either from a sacrificial anode or from an external D. C. source (shown in Fig. 2 as a rectifier 30) flows from the anode through the solution into the ground and thence to the structure providing cathodic protection for it. Sacrificial anodes may be of Mg. Other anodes may be of platinized Ti wire. Fig. 5 (not shown) illustrates a number of anodes (42) on separate leads whereby the optimum voltage can be applied to the separately connected anodes depending on the resistivity of the ground adjacent them. A typical value is 100 volts. Voltages are used such that gassing at the anodes does not occur. The electrolyte may be a salt water (NaCl) solution or may be based on sulphate. Its concentration may be maintained between predetermined limits. Fig. 4 (not shown) illustrates a well (34) which passes through an underground stream (35). To prevent the stream from washing away the solution within the well, a porous pipe-like liner (36) is installed in a portion of the well.
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