The deep well anode ground bed is located at the place where the surface soil resistivity is relatively high and decreases with the depth. This installation form is suitable for local cathodic protection in densely populated areas and small space, small voltage cone and no interference to external structures.
The deep well anode ground bed consists of several single anodes connected in parallel, which are installed in a borehole with a depth of 50-100m and a diameter of 0.3m. Various methods can be used to drill holes, and the commonly used "air lift method" has proved to be particularly suitable.
By testing the natural corrosion potential, power-off potential and ground potential gradient of buried metal structures near the anode ground bed of deep well, it is shown that the buried metal structures near the anode well have been seriously affected, and it is necessary to control the electric field interference generated by the deep well anode well, and the electric pressure should be less than 500 The polarization potential of the anode polarization zone caused by the influence of underground metal structures should be controlled to be less than 100 mV.
In the allowable range of pipeline protection, the voltage offset of anode polarization zone can be eliminated by properly increasing the given potential of power supply, and connecting the protection pipe and anode polarization area (or between insulating flange) by connecting the diode and 0.2 ~ 2 Ω variable resistance to adjust the variable resistance.
Pipeline maintenance should improve the quality of anti-corrosion coating of underground metal structures and regularly detect the pipe to ground potential of anode area, find out the distribution of anode polarization area in the station, and control the interference effect of deep well anode.
The pipeline adopts impressed current cathodic protection, which has the characteristics of high reliability, long service life, adjustable output voltage and current and simple maintenance. Anode ground bed, an important part of impressed current system, can be divided into shallow buried type and deep well type.
At present, deep well anode construction is carried out according to the drawings. Generally, the design is based on the local soil resistivity. The grounding resistance value of the anode ground bed is set first, and then a certain depth is designed. The pre assembled anode is mostly used. After the anode is installed, the grounding resistance of the anode ground bed is measured to compare with the design.
The mathematical model of cathodic protection system of deep well anode to tank bottom plate is established. A typical current density distribution assumption is used to solve the protection potential, and the protection potential of tank bottom plate corresponding to different buried depth of deep well anode is calculated.
1. The relationship curve between buried depth of anode and protection potential can be divided into three parts: when the buried depth is less than 15m, the protective potential increases sharply with the increase of buried depth; when the buried depth is greater than 45m, the protective potential decreases sharply with the increase of buried depth; when the buried depth is between 15-45m, the protective potential decreases slowly with the increase of buried depth.
2. For single tank and single deep well anode, the reasonable buried depth of deep well anode is 25-45m.
3. The influence of the buried depth of anode in deep well on the protection potential of the near positive extreme is greater than that of the far positive extreme, and the influence on the protection potential of the tank center is between the near positive extreme and the far positive extreme.
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