SU1664874A1 - Subsurface bore hole anode ground conductor - Google Patents

Abstract

This invention relates to cathodic protection of underground structures against corrosion. The purpose of the invention is to increase the service life and reduce operating costs. The anode earthing device contains a current lead 1 in insulation 2, separated by a layer of dielectric 3 from the sheath 4. Outside the sheath 4 is welded by extended steel electrodes 5 so that their surfaces form a protective casing 6 with through longitudinal cavities 7. In the upper part, the earthing switch is provided an additional casing 8 of non-conductive material with a perforated top cover 9. The electrical contact 10 of the current lead 1 with the sheath 4 is protected by a plug 11. The increase in service life and reduced operating costs is achieved by The electrodes are welded to the outer surface of the shell in such a way that their surfaces form a casing, the free space between the current lead and the casing is filled with a dielectric, determined by the ratio of the length of the casing and the casing at the bottom, as well as inserting an additional protective casing and a perforated cover into the device. 1 sp of f-ly, 2 cp of f-ly, 4 ill.

Description

The invention relates to cathodic protection of underground structures against corrosion and the transfer of current over a distance through a wire-to-ground system, specifically to positive polarity earthing devices, and is intended for use in the oil, gas, energy industry, as well as in public utility.

The purpose of the invention is to increase the service life and reduce operating costs.

FIG. 1 shows a grounding conductor; in fig. 2 is a section along A-A in FIG. one; in fig. 3, a, b, c are examples of the use of different extended steel electrode profiles; FIG. 4 shows the bottom portion of the earth conductor at the bottom.

The anode earthing device contains a current lead 1 in insulation 2, separated by a layer of dielectric 3 from the sheath 4. Outside the sheath 4 is welded by extended steel electrodes 5 so that their surfaces form a protective casing 6 with through longitudinal cavities 7. In the upper part, the earthing switch is provided additional casing 8 of non-conductive material, such as polyethylene, with a perforated top cover 9, and this casing protrudes above the ground. Electrical contact 10 current lead

ON O N 00

2

1 with sheath 4 is electrically welded at the top and bottom of the earthing switch and protected by a plug 11. In FIG. 3 shows the working surfaces of 12 electrodes 5.

Grounding works as follows.

In the first period of operation (before the electrochemical dissolution of the protective casing), electrical contact with the ground electrolyte is made only over the surface of the electrodes. Due to the replacement of the conductive backfill (activator) between the current lead and the cladding on the dielectric and the presence of the welded contact connections of the current lead to the cladding, the electrical circuit between the current lead and the electrodes is made only through a metallic connection along the current lead circuit - the welded contact joints - shells - electrodes. The last link in this chain is the electrodes, so only they undergo electrochemical dissolution, and in the shell (before the protective casing dissolves) and at the current lead (before the shell dissolves), the electrode function (i.e., there is no current flowing from the surface into the ground) Thus, due to this, one of the main disadvantages of the known earthing switch, consisting in double electrochemical dissolution of the grounding materials and a significant unproductive waste of materials, is eliminated.

Along the perimeter of the earthing current flows extremely unevenly. Such an uneven current distribution is provided purposefully by imparting a special relief to the working surface of the electrodes — the points or the sections with the maximum radius of curvature (Fig. 3).

The special shape of the working surface of the electrodes provides maximum appearance of edge current draining over the entire length of their effects. The flowing current is concentrated on these working surfaces, the points, and the areas of the electrodes between the points are practically not subject to electrochemical dissolution, i.e., the current density on them is minimal due to the shielding effects, i.e. An automatic redistribution of the density of the current flowing into the ground along the grounding surface occurs depending on the changing electrophysical properties of the soil. In the areas where accelerated dissolution of the working surfaces occurs, - the tips, the effective diameter of the earthing device quickly decreases, which leads to an increase in the electrode-ground transient resistance in this area and

the amount of current flowing. This appears automatically, without additional external influences, and provides for the elimination of local damage (for example,

5 cuts earthing and irretrievable loss of material.

An important role in the work of a grounding conductor is played by ensuring the reliability of contact connections. In order to eliminate the pre-belt output of contact joints, special elements are provided in this earthing switch. The lower contact connection is reliably protected from accelerated destruction caused by

15 by the effect of end current drainage, a screen that is formed by electrodes protruding beyond the shell along the entire perimeter.

Length I of the protruding part of the electrodes

20 satisfies the ratio

I 3d,

where d is the diameter of the shell (Fig. 4). This size is chosen from those structures that it is necessary to completely eliminate current drainage from the shell to the ground. For this, the angle a must be less than 10 °. On the other hand,

30 a arctg (y). therefore arctg (-),

where the ratio between the length of the protruding part of the electrodes and the diameter of the shell.

In the upper part, the earthing switch is equipped with an additional protective cover of non-conductive material. This casing completely prevents current from flowing into the ground from the top of the earthing, which prevents the electrochemical dissolution of the contact connection 40, and also reduces the amount of electric potential on the earth's surface, increases the effect of the deep current spreading

Reliable contact connections in

Combined with automatic redistribution of current along the length of the electrodes, you can avoid irretrievable loss of materials and increase the utilization rate of the electrode material and the shell to almost 100%. Indeed, the shell itself generally begins to undergo electrochemical dissolution only after the% of electrodes have been dissolved. Then, even if for some exceptional reason the shell is destroyed, the earthing switch does not go out of service and continues to work in the form of two Electrodes fed from one current lead until complete electrochemical dissolution of the shell material.

In this grounding device, the elements of steel extended profiles form longitudinal through cavities along the entire length of the shell (Fig. 3). These cavities are channels for venting gases to the surface of the earth. Emitted gases accumulate under the additional casing and are removed to the surface of the earth due to the fact that the casing protrudes above the surface of the earth and has a perforated top cover. Freedom of gassing is ensured at all stages of the work of the earthing switch.

During the first period of operation of the earthing switch, for example, from cylindrical hollow electrode-tubes (Fig. 3 Sv), gases are removed through various openings, which are formed in an obligatory order due to the weakness of the ground adjoining to the complex, relief surface of the electrodes around the perimeter. As the electrochemical dissolution of the sections with the maximum radius of curvature, gases begin to move through the cavities formed by the working surfaces of the electrodes and the casing. After the sheath begins to undergo electrochemical dissolution, gases are released through the cavities between the sheath and the shell.

Another advantage of the proposed earthing design is the absence of contact joints from dissimilar materials. All elements located in the ground are made of the same material (steel), which excludes the emergence of galvanic couples and the accelerated release of compounds.

The table shows the results of the tests of the grounding of the proposed design, analogue and prototype, carried out in the ground with non-uniform electrical conductivity.

The results obtained demonstrate the advantages of the proposed earthing device. The earthing device was cut in a layer with high electrical conductivity after 1.7 years, the prototype served almost a year longer, and the proposed earthing switch even had a fairly stable resistance to current spreading even for the 5th year of operation, i.e. term

its service is not less than 2 times higher than that of the known earthing.

The utilization of the material of the grounding

14 Mo

where Мр is the mass of the working part of the electrodes, which undergoes electrochemical dissolution during the service life; M0 is the total mass of the earth conductor. In the proposed design of the earthing, this coefficient is 24% higher, and the average irretrievable metal loss per year is 1.5 times less than that of the known earthing.

20

Claims (4)

1. A deep borehole anode earthing, comprising a current lead located in a filler, electrodes and a shell, characterized in that, with In order to increase service life and reduce operating costs, the electrodes are welded to the outer surface of the shell with the possibility of forming a casing that isolates the shell from the ground and forms between the inner surface of the housing and the shell are through longitudinal cavities, with the longitudinal protrusions on the outer surface of the housing, and the free space between the current lead and the shell is filled with a dielectric. 2. The earthing device according to claim 1, characterized in that, at the bottom, the casing is made longer than the length of the shell, and the length of the protruding part satisfies the inequality: where d is the outer diameter of the shell. 3. The earthing device according to claim 1, characterized in that in the upper part it is equipped additional protective casing of non-conductive material, and this casing protrudes above the ground and is provided with a perforated cover. 4. The earthing device according to claim 1, characterized in that the electrodes and the shell are made in the form of pipes mainly of steel. l-gpts, 01 W.8W91 Fig.Z