According to studies, the accelerated destruction of underground communications from metal occurs due to the occurrence of electrochemical corrosion. Its cause is the purposeful movement of charged particles, which are stray currents. This situation indicates that in order to ensure the safety of metal structures, it is necessary to figure out how to eliminate stray currents underground in pipes for water supply.
Stray currents are charged electric particles with a certain trajectory of movement that occur in the ground, which is a conductor. The term wandering arose due to the fact that it is impossible to predict the localization of particles and the onset of the process. The influence of stray electrical particles has an extremely negative effect on metal products located above and below the ground.
Similar processes arise due to the growing number of electrified facilities that are the backbone of modern countries. And since the soil is a conductor for electricity, there is an interaction between the elements.
Wandering particles arise like electric ones, for the interaction of which a comparison of the potential difference at 2 arbitrary points is required, only for the wandering variant the conductor is the earth. As a result, the metallic material in the vicinity of the process is destroyed faster due to corrosion.
The reason for the occurrence of stray currents is a large number of equipment operating on electric charge, as a result, the following elements are potential sources:
- the presence of a charger in such facilities as substations, overhead lines with a neutral conductor, distributors;
- the occurrence of activity as a result of the destruction of the insulating layer of wires carrying current in cables and overhead lines, where the neutral is isolated;
- the presence of a connecting technological link between the conductor and the soil in structures with a grounded neutral and rail vehicles driven by current.
The mechanism of the occurrence of spontaneous discharges can be considered on the example of one of the above points.
One end of the neutral wire is connected to the power plant’s charger, and the other end is connected to the power-consuming PEN bus, which has a connection to the charger. It follows that the potential difference of the electrical value between the terminals forms stray currents, since the energy will be transferred to the memory, which in turn will form a circuit.
In this case, the volume of losses does not have a large percentage, since it will pass along the path of the least resistance, however, a certain part will fall into the ground.
Similarly, energy leakage occurs in the case of damage to the insulation of the wiring.
At the same time, a constant uninterrupted leak does not take place, since the system signals about its occurrence and the site is automatically localized, and also, according to the regulations, there is a certain period of time allotted for troubleshooting.
Important! According to statistics, the main places for the formation of electricity leakage and the formation of stray currents fall on urban and suburban areas where there is ground transport that depends on the power grid.
When using urban electrified transport, voltage is supplied from the substation to the traction system, which passes to the rails and makes a reverse cycle. If the rails as an iron base are not sufficiently stable relative to the conductor, this leads to the formation of stray current locations in the soil, then any metal structure that appears in their path, for example, plumbing products, act as a conductor.
Important! This interaction occurs due to the fact that the current, moving, chooses the path of least resistance, which is lower for the metal than for the ground.
All this will lead to accelerated destruction of metal products.
Relationship between currents and corrosion processes
Any water supply system located in the soil is damaged by corrosion due to exposure to moisture and salts, however, if the activity of currents is also connected here, then an electrolytic process occurs. In this case, the rate of the electrochemical reaction is affected by the charge flowing between the anode and cathode. It follows that the activity of damage to metal products will be affected by the resistance of the soil to the movement of charges, as well as the complexity of the currents in the anode and cathode zones.
In such an environment, the water supply system is subject to normal corrosion due to leakage currents. The impact forms a galvanic couple, which accelerates the development of corrosion. There are many moments in history when the laid pipeline was supposed to serve 20 years, but in fact the destruction occurred after 2 years.
Options for possible protection
To protect metal products from harmful effects, various methods are used, which are divided by the nature of their application into passive and active.
This option is the use of a different insulating material that forms a protection between the conductor and the metal. Used as insulation:
- epoxy resin mixtures;
- incorporation into polymers;
- bitumen coating.
But if we limit ourselves only to this option, then full-fledged protection will not work, since the insulating material is not a 100% barrier due to the presence of diffusion permeability. Therefore isolation occurs in a partial way. In addition, in the process of moving pipes, such a layer can be damaged, resulting in significant scratches, cuts, through holes and other flaws.
Important! Therefore, a passive method of protection can only be used as an addition.
Indicates the use of an active method of localizing the source of exposure through the use of cathodic polarization, where the negative charge displaces the natural one.
To implement such protection, it is necessary to use one of two tools:
- Galvanic method — the effect of a galvanic pair, the destruction of the sacrificial anode is performed, thereby ensuring the protection of the metal structure. The method is active when the soil resistance is up to 50 Ohm per meter, if the resistance is lower than the method is not effective.
- Direct current source — provides avoidance of dependence on the resistance of the soil. Cathodic protection is used, the source of which is enclosed in a formed converter connected to an alternating current electrical circuit. Since the source is specially formed by means of its regulation, it is possible to set the required level of current protection, depending on the circumstances.
A similar method can also provide a negative impact:
- overprotection — excess of the required potential, as a result, the destruction of a metal product occurs;
- incorrect calculation of protection — leading to accelerated corrosion destruction near located metal objects.
The above examples can be considered on the protection of such a product as a heated towel rail.
Corrosion processes on such products or other end plumbing products have never occurred, but it was real before the use of metal-plastic pipes, where there is contact with aluminum inside the wall. As a result, the formation of wandering elements occurs not only due to the use of plastic pipes in the immediate room, but also in others, since in an apartment building they can be used by a neighbor from another floor.
Important! To avoid the negative impact of the generated currents on your own design, it is necessary to equalize the potentials by providing a heated towel rail, batteries and water pipes with a grounding element.
At the same time, the use of the much-needed grounding occurs in relation to any communication that is made of metal pipes, for example, a gas pipeline in the ground.
To assess the extent of the current situation with the leakage of electric charges, it is necessary to perform a number of measures:
- measurement of voltage and flow of current along the sheaths of the main cables;
- determination of the potential difference between contact rails and pipelines located in the soil;
- checking the level of insulation of rails from the ground covering, using a section of the track for the experiment;
- estimation of the density of energy leakage from the cable sheath into the ground.
To perform measurements, a special device is used, if activities are carried out on railway tracks, it is necessary to choose the rush hour of traffic.
To check, transformers and substations are used near the line of movement — the electrode connected to the device is connected to the charger and stuck 10 meters from the substation. All the resulting difference is fixed by the device.
If it is necessary to lay a line of pipes for water supply, it is important to identify the location of stray currents, for this purpose the potential difference between two sample points of the earth’s surface, placed perpendicular to each other with an equal distance, is determined. It is important to carry out such a determination systematically with a gap of a kilometer.
In this case, the devices used must necessarily have an accuracy class of at least 1.5, and the resistance of the equipment from 1 MΩ. The use of measuring electrodes with a potential difference above 10 mV. The time of one measurement must pass within 10 minutes, and the gap between the processes is 10 seconds.
The calculation of the potential and the determination of the location of the stray electrical particles should not be neglected, since the quality of the operation of the plumbing system depends on this, in addition, both protection methods should be used simultaneously, which will regulate the resulting voltage and ensure complete protection of the pipeline.