Pipelines running underground are subject to the destructive effects of corrosion. Pipeline corrosion affects metal pipes when conditions arise where metal atoms can become ionic.

In order for a neutral atom to become an ion, it is necessary to give up an electron, and this is possible if there is an anode that will accept it. This situation is possible when a potential difference occurs between individual sections of the pipe: one section is the anode, the other is the cathode.

Reasons for electrolytic reactions

There are several reasons for the formation of a potential difference (the magnitude of its value) in individual sections of the pipe:

• different soil compositions according to physical and chemical properties;
• metal heterogeneity;
• soil moisture;
• meaning operating temperature, transported substance;
• indicator of soil electrolyte acidity;
• the passage of an electric transport line that creates stray currents.

Important! Areas that require protection are determined at the design stage of the facility. All necessary structures are built in parallel with the laying of pipes.

As a result, two types of corrosion damage can occur:

• superficial, which does not lead to destruction of the pipeline;
• local, which results in the formation of shells, cracks, and cracking.

Types of corrosion protection

To protect pipes from destruction, pipeline corrosion protection is used.

There are two main methods of protection:

• passive, in which a protective shell is created around the pipes, completely separating them from the ground. This is usually a bitumen coating, epoxy resin, polymer tape;
• active, allowing you to control the electrochemical processes that occur at the points of contact between the pipe and the ground electrolyte.

The active method is divided into three types of protection:

• cathode;
• tread;
• drainage

Drainage protects pipelines from corrosion caused by stray currents. Such currents are diverted in the direction of the source that creates them or directly into the soil layer. Drainage can be earthen (grounding the anode zones of the pipeline), direct (disconnection from the negative pole of the stray current source). Polarized and enhanced drainage is used less frequently.

Methods for organizing cathodic protection

Cathodic protection pipeline from corrosion is formed if external electric field to organize cathodic polarization of the pipeline, and transfer the damage to the external anode, which will undergo destruction.

Cathode is divided into two types:

• galvanic with the use of protective anodes, for the manufacture of which alloys of magnesium, aluminum, and zinc are used;
• electric, which uses an external direct current source with a connection diagram: minus to the pipe, plus to the grounded anode.

The basis of the galvanic method of cathodic protection: the use of the property of metals to have different potentials when they are used in the form of an electrode. If the electrolyte contains two metals with different meaning potential, then the one with the least value will be destroyed.

The tread material is selected so that certain requirements are met:

• negative potential with a large value compared to the potential of the pipeline;
• significant efficiency;
• high specific current output;
• low anodic polarizability, so that oxide films do not form.

Note! The highest efficiency is for anodes made of zinc and aluminum alloy, the lowest for magnesium.

To increase the efficiency and effectiveness of protection, protectors are immersed in an activator, which reduces the protector’s own corrosion and the amount of resistance to current spreading from the protector, and reduces anodic polarizability.

Protective protective installation consists of a protector, an activator, a conductor connecting the protector and the pipeline, a point for monitoring and measuring electrical parameters.

The effectiveness of tread protection against pipeline corrosion depends on the magnitude of soil resistivity. It works well if this indicator does not exceed 50 Ohm*m, with higher value protection will be partial. To increase efficiency, tape protectors are used.

The limitation for the use of sacrificial protection is the electrical contact of the pipeline and adjacent extended communications.

Cathodic protection stations

More complex to organize, but the most effective is the electric one. To organize it, an external direct current source is constructed - a cathodic protection station. In an electrical station, alternating current is converted into direct current.

Cathodic protection elements:

• anodic grounding;
• DC connection line;
• protective grounding;
• DC source;
• cathode terminal.

The electrical method is an analogue of the electrolysis process.

Under the influence of the external field of the current source, valence electrons move away from the anode grounding towards the current source and the pipe. The grounded anode is gradually destroyed. And near a pipeline from a direct current source, an incoming excess of free electrons leads to depolarization (like a cathode during electrolysis).

To prevent corrosive destruction of several pipes, several stations are constructed and an appropriate number of anodes are installed.

One of the frequently used methods of electrochemical protection various designs Among metals from rusting is cathodic protection. In most cases, it is used in conjunction with the application of special coatings to metal surfaces.

1 General information about cathodic protection

Such protection of metals was first described in the 1820s by Humphry Davy. Based on his reports, in 1824, on the ship HMS Samarang, the theory provided was tested. Iron anode protectors were installed on the copper plating of the ship, which significantly reduced the rate of rusting of copper. The technique began to be developed, and today the cathode of all kinds of metal structures (pipelines, car parts, etc.) is recognized as the most effective and widely used.

In industrial conditions, such protection of metals (it is often called cathodic polarization) is carried out using two main methods.

1. The structure, which is protected from destruction, is connected to an external current source. In this case, the metal product acts as a cathode. And anodes are inert additional electrodes. This technique is usually used to protect pipelines, welded metal foundations, and drilling platforms.
2. Cathodic polarization of galvanic type. With this scheme, the metal structure is in contact with a metal that has a higher electronegative potential (aluminum, magnesium, aluminum alloys, zinc). In this case, the anode refers to both metals (main and protective). The dissolution (meaning a purely electrochemical process) of an electronegative material leads to the flow of the necessary cathode current through the protected product. Happens over time complete destruction"protector" metal. Galvanic polarization is effective for structures that have an insulating layer, as well as for relatively small metal products.

The first technique has found widespread use around the world. It is quite simple and economically feasible, making it possible to protect metal from general corrosion and from many of its varieties - intergranular corrosion of “stainless steel”, pitting, cracking of brass products due to the stresses under which they operate.

The galvanic circuit has found greater use in the USA. In our country it is used less frequently, although its effectiveness is high. The limited use of sacrificial protection for metals in Russia is due to the fact that many pipelines in our country do not have a special coating applied, and this is prerequisite for the implementation of anti-corrosion galvanic techniques.

2 How does standard cathodic polarization of metals work?

Cathodic corrosion protection is achieved through the use of superimposed current. It is supplied to the structure from a rectifier or other source of (external) current, where industrial-frequency alternating current is modified into the required direct current. The object being protected is connected to rectified current (to the “minus” pole). The structure is thus a cathode. The anodic grounding (second electrode) is connected to the “plus”.

It is important that there is good electrolytic and electronic contact between the secondary electrode and the structure. The first is provided by the soil, where the anode and the protected object are immersed. The soil in this case acts as an electrolytic medium. Electronic contact is achieved using conductors made of metallic materials.

Regulation of cathodic anti-corrosion protection is carried out by maintaining the protective potential between the electrolytic medium and the polarization potential indicator (or the structure itself) at a strictly defined value. The indicator is measured with a voltmeter with a high-resistance scale.

Here it is necessary to understand that the potential has not only a polarization component, but also another component - a drop in (ohmic) voltage. This drop occurs due to the flow of cathode current through the effective resistance. Moreover, the quality of cathodic protection depends solely on the polarization on the surface of the product, which is protected from rusting. For this reason, two characteristics of the security of a metal structure are distinguished - the highest and lowest polarization potentials.

Effective regulation of the polarization of metals, taking into account all of the above, becomes possible in the case when the indicator of the ohmic component is excluded from the value of the resulting potential difference. This can be achieved using a special circuit for measuring the polarization potential. We will not describe it within the framework of this article, since it is replete with many specialized terms and concepts.

As a rule, cathode technology is used in conjunction with coating outer surface special protective materials to protect products from corrosion.

To protect uninsulated pipelines and other structures, it is necessary to use significant currents, which is economically unprofitable and technically difficult.

3 Cathodic protection of vehicle elements

Corrosion is an active and very aggressive process. High-quality protection of car components from rust causes many problems for car enthusiasts. All vehicles without exception are subject to corrosive destruction, because rusting begins even when paint coating a small scratch appears on the car.

Cathodic technology for protecting a car from corrosion is quite common these days. It is used along with the use of all kinds of mastics. This technique refers to the presentation electric potential onto the surface of one or another car part, which leads to an effective and long-term inhibition of rusting.

In the described vehicle protection, the cathode is special plates that are placed on its most vulnerable components. And the role of the anode is played by the car body. Such a distribution of potentials ensures the integrity of the machine body, since only the cathode plates are destroyed, and the base metal does not corrode.

Vulnerable spots of a vehicle that can be protected using the cathodic method are understood as:

• rear and front parts of the bottom;
• rear wheel arch;
• areas for fixing sidelights and headlights themselves;
• wing-wheel joints;
• internal areas of doors and thresholds;
• space behind the wheel guards (front).

To protect the car, you need to purchase a special electronic module (some craftsmen make it themselves) and protector plates. The module is mounted in the car interior and connected to the on-board network (it must be powered when the car engine is turned off). Installing the device takes literally 10–15 minutes. Moreover, it takes a minimum of energy, and guarantees very high-quality anti-corrosion protection.

Protective plates may have different size. Their number also differs depending on where in the car they are mounted, as well as on the geometric parameters of the electrode. In practice, the smaller the electrode size, the fewer plates you need.

Car corrosion protection using the cathodic method is also carried out in other relatively simple ways. The most basic one is to connect the positive wire of the car battery to a regular metal garage. Please note that you must use a resistor for connection.

4 Protection of pipelines using cathodic polarization method

Depressurization of pipelines of various purposes occurs in many cases due to their corrosion destruction caused by the appearance of ruptures, cracks and cavities. Underground communications are especially susceptible to rust. Zones with different potentials (electrodes) are formed on them, which is caused by the heterogeneity of the soil and the heterogeneous composition of the metals from which the pipes are made. Due to the appearance of these zones, the process of active formation of corrosive galvanic components begins.

Cathodic polarization of pipelines, carried out according to the schemes described at the beginning of the article (galvanization or an external energy source), is based on reducing the rate of dissolution of the pipe material during their operation. Such a reduction is achieved by shifting the corrosion potential to a zone that has more negative indicators in relation to the natural potential.

Back in the first third of the 20th century, the potential for cathodic polarization of metals was determined. Its indicator is -0.85 volts. In most soils, the natural potential of metal structures is in the range of -0.55 to -0.6 volts.

This means that to effectively protect pipelines, it is necessary to “move” the corrosion potential into negative side at 0.25-0.3 volts. With such a magnitude, the practical effect of rusting on the condition of communications is almost completely leveled out (corrosion per year has a rate of no more than 10 micrometers).

The technique using a current source (external) is considered labor-intensive and quite complex. But it provides high level protection of pipelines, its energy resource is not limited by anything, while the resistance (specific) of the soil has minimal impact on the quality of protective measures.

Power sources for cathodic polarization are usually overhead power lines at 0.4; 6 and 10 kV. In areas where there are none, it is allowed to use gas, thermal and diesel generators as energy sources.

The “protector” current is distributed unevenly along the length of the pipelines. Its greatest value is noted at the so-called drainage point - at the place where the source is connected. The greater the distance from this point, the less protected the pipes are. At the same time, excessive current directly in the connection area has a negative effect on the pipeline - there is a high probability of hydrogen cracking of metals.

The method using galvanic anodes demonstrates good efficiency in soils with low resistivity (up to 50 ohm*m). It is not used in soils of the high-resistivity group, since it does not give any special results. It is worth adding here that anodes are made from alloys based on aluminum, magnesium and zinc.

5 Briefly about cathodic protection stations (CPS)

For anti-corrosion protection of pipelines laid underground, SCPs are installed along their route, including:

• anodic grounding;
• current source;
• control and measurement point;
• cables and wires performing connecting functions.

Stations are connected to networks electric current or to stand-alone devices. It is allowed to install several grounding connections and energy sources at the VCS when two or more pipeline lines are laid in one underground corridor. This, however, entails an increase in costs for anti-corrosion measures.

If only one installation is installed on multi-line communications, its connection to the pipes is carried out using special blocks. They do not allow the formation of strong galvanic couples that occur when installing blind jumpers on pipe products. These blocks isolate pipes from each other, and also make it possible to select the required potential on each pipeline element, guaranteeing maximum protection of the structure from rust.

The output voltage at cathode stations can be adjusted automatically (the installation in this case is equipped with thyristors) or manually (the operator switches the transformer windings if necessary). In situations where VSCs operate under time-varying conditions, it is recommended to operate stations with automatic voltage regulation.

They themselves monitor the resistance indicators of (specific) soil, the appearance of stray currents and other factors that have an impact. negative impact on the quality of protection, and automatically adjust the operation of the VCS. But in systems where the protective current and the resistance value in its circuit remain unchanged, it is better to use settings with manual adjustment of the output voltage.

Let us add that regulation in automatic mode is carried out according to one of two indicators:

• protection current (galvanostatic converters);
• according to the potential of the object that is being protected (potentiostatic converters).

6 Information on known cathodic protection stations

Among the popular domestic VCSs, several installations can be distinguished. The station is in great demand Minerva–3000– a powerful system developed by French and Russian engineers for Gazprom facilities. One Minerva is enough to reliably protect up to 30 kilometers of pipelines from rust. The station has the following main advantages:

• unique manufacturability of all its components;
• increased power of the VCS (it is possible to protect communications with very poor protective coating);
• self-healing (after emergency overloads) of station operating modes for 15 seconds;
• availability of high-precision digital equipment for monitoring operating conditions and a thermal control system;
• the presence of protective circuits against overvoltage of measuring and input circuits;
• absence of moving parts and tightness of the electrical cabinet.

In addition, to Minerva–3000 you can connect installations for remote control on the work of the station and remote control her equipment.

Excellent technical indicators systems also have ASKG-TM– modern telemechanized adaptive stations for the protection of electrical cables, city and main pipelines, as well as tanks in which gas and oil products are stored. Such devices are available with different output power ratings (from 1 to 5 kilowatts). They have a multifunctional telemetry complex that allows you to select a specific VCS operating mode, monitor and change station parameters, as well as process incoming information and send it to the operator.

Benefits of use ASKG-TM:

• possibility of integration into SCADA complexes due to support of OPC technology;
• backup and main communication channel;
• selection of power value (output);
• increased fault tolerance;
• wide operating temperature range;
• unique accuracy of setting output parameters;
• voltage protection of system power outputs.

There are SKZ and other types, information about which is easy to find on specialized sites on the Internet.

7 What objects can be protected using cathodic polarization?

In addition to protecting cars and pipelines, the polarization techniques under consideration are actively used to protect reinforcement included in reinforced concrete structures (buildings, road facilities, foundations, etc.) from corrosion. Typically, the fittings are a single electrical system, which actively corrodes when chlorides and water enter it.

Cathodic polarization in combination with concrete sanitation stops corrosion processes. In this case, it is necessary to use two types of anodes:

• the main ones are made of titanium, graphite or their combination with a metal oxide coating, as well as silicon cast iron;
• distribution rods – rods made of titanium alloys with an additional layer of metal protection or with a non-metallic electrically conductive coating.

By adjusting the external current supplied to reinforced concrete structure, select the potential of the reinforcement.

Polarization is considered an indispensable technique for the protection of permanent structures located on the continental shelf, in the gas and oil fields. Initial protective coatings It is impossible to restore such objects (they require dismantling and transportation to dry hangars), which means that there is only one option left - cathodic protection of metals.

To protect against sea corrosion, galvanic polarization of civilian ships is used using anodes made of zinc, magnesium, aluminum alloys. On shore (during repairs and moorings), ships are connected to SCZ, the anodes for which are made of platinized titanium.

Cathodic protection is also used to protect against destruction of the internal parts of vessels and containers, as well as pipes that come into contact with wastewater. industrial waters and other aggressive electrolytes. Polarization in this case increases the time of maintenance-free use of these structures by 2–3 times.

Pipelines are by far the most common means of transporting energy carriers. Their obvious drawback is their susceptibility to rust. For this purpose, cathodic protection of main pipelines from corrosion is performed. What is its principle of operation?

Causes of corrosion

Networks of pipelines for life support systems are distributed throughout Russia. With their help, gas, water, petroleum products and oil are efficiently transported. Not long ago, a pipeline was laid to transport ammonia. Most types of pipelines are made of metal, and their main enemy is corrosion, of which there are many types.

The reasons for the formation of rust on metal surfaces are based on the properties environment, both external and internal corrosion of pipelines. Risk of corrosion for internal surfaces based on:

1. Interaction with water.
2. The presence of alkalis, salts or acids in the water.

Such circumstances may arise on main water supply systems, hot water supply (DHW), steam and heating systems. An equally important factor is the method of laying the pipeline: above ground or underground. The first one is easier to maintain and eliminate the causes of rust formation compared to the second one.

With the pipe-to-pipe installation method, the risk of corrosion is low. When directly installing a pipeline outdoors, rust may form due to interaction with the atmosphere, which also leads to a change in design.

Pipelines located underground, including steam and hot water, are most vulnerable to corrosion. The question arises about the susceptibility to corrosion of pipes located at the bottom of water sources, but only a small part of the pipelines are located in these places.

According to their purpose, pipelines with a risk of corrosion are divided into:

• main lines;
• fishing;
• for heating and life support systems;
• for waste water from industrial enterprises.

Susceptibility to corrosion of main pipeline networks

Pipeline corrosion of this type most well studied, and their protection from exposure external factors defined by standard requirements. Regulatory documents discuss methods of protection, and not the reasons for the formation of rust.

It is equally important to take into account that in this case only external corrosion is considered, to which the outer section of the pipeline is susceptible, since inside the pipeline there are inert gases. In this case, contact of the metal with the atmosphere is not so dangerous.

For protection against corrosion, according to GOST, several sections of the pipeline are considered: increased and high danger, as well as corrosion-hazardous.

Exposure to negative factors from the atmosphere for high-risk areas or types of corrosion:

1. Stray currents arise from direct current sources.
2. Exposure to microorganisms.
3. The created stress provokes cracking of the metal.
4. Waste storage.
5. Salty soils.
6. The temperature of the transported substance is above 300 °C.
7. Carbon dioxide corrosion of an oil pipeline.

An installer for protecting underground pipelines from corrosion must know the design of the pipeline and the requirements of SNiP.

Electrochemical corrosion from soil

Due to the difference in voltages formed in individual sections of pipelines, an electron flow occurs. The process of rust formation occurs according to the electrochemical principle. Based on this effect, part of the metal in the anodic zones cracks and flows into the base of the soil. After interaction with the electrolyte, corrosion forms.

One of the significant criteria for ensuring protection against negative manifestations is the length of the line. Along the way you come across soils with different compositions and characteristics. All this contributes to the emergence of a voltage difference between parts of the laid pipelines. The mains have good conductivity, so the formation of galvanic couples with a fairly large extent occurs.

An increase in the rate of pipeline corrosion provokes high density electron flow. The depth of the lines is no less important, since it retains a significant percentage of humidity and the temperature is not allowed to fall below the “0” mark. Mill scale also remains on the surface of the pipes after processing, and this affects the appearance of rust.

By conducting research work A direct relationship has been established between the depth and area of ​​rust formed on the metal. This is based on the fact that the metal is larger area surfaces are most vulnerable to external negative manifestations. Special cases include the occurrence of significantly smaller amounts of destruction on steel structures under the influence of the electrochemical process.

The aggressiveness of soils to metal is, first of all, determined by their own structural component, humidity, resistance, alkali saturation, air permeability and other factors. The installer for the protection of underground pipelines from corrosion must be familiar with the pipeline construction project.

Corrosion under the influence of stray currents

Rust can arise from an alternating and constant flow of electrons:

• Rust formation under the influence of constant current. Stray currents are currents located in the soil and in structural elements located underground. Their origin is anthropogenic. They arise as a result of exploitation technical devices direct current spreading from buildings or structures. They can be welding inverters, cathode protection systems and other devices. The current tends to follow the path of least resistance, as a result, with existing pipelines in the ground, it will be much easier for the current to pass through the metal. The anode is the section of the pipeline from which the stray current exits to the soil surface. The part of the pipeline into which the current enters acts as a cathode. On the described anodic surfaces, currents have an increased density, so it is in these places that significant corrosion spots form. The corrosion rate is not limited and can be up to 20 mm per year.
• Rust formation under the influence of alternating current. When located near power lines with network voltage over 110 kV, as well as parallel arrangement pipelines under the influence of alternating currents, corrosion forms, including corrosion under the insulation of pipelines.

Stress Corrosion Cracking

If the metal surface is simultaneously affected by external negative factors and high voltage from power lines that create tensile forces, rust formation occurs. According to the research carried out, the new hydrogen-corrosion theory gained its place.

Small cracks are formed when the pipe is saturated with hydrogen, which then ensures an increase in pressure from the inside to levels higher than the required equivalent of the bond of atoms and crystals.

Under the influence of proton diffusion, hydrogenation of the surface layer occurs under the influence of hydrolysis at increased levels of cathodic protection and simultaneous exposure to inorganic compounds.

After the crack opens, the rusting process of the metal accelerates, which is provided by the ground electrolyte. As a result, under the influence of mechanical influences, the metal undergoes slow destruction.

Corrosion due to microorganisms

Microbiological corrosion is the process of rust formation on a pipeline under the influence of living microorganisms. These can be algae, fungi, bacteria, including protozoa. It has been established that the proliferation of bacteria most significantly influences this process. To maintain the vital activity of microorganisms, it is necessary to create conditions, namely nitrogen, humidity, water and salts. Also the conditions are:

1. Temperature and humidity indicators.
2. Pressure.
3. Availability of lighting.
4. Oxygen.

When selected acidic environment organisms can also cause corrosion. Under their influence, cavities appear on the surface, which are black in color and bad smell hydrogen sulfide. Sulfate-containing bacteria are present in virtually all soils, but the rate of corrosion increases as their numbers increase.

What is electrochemical protection

Electrochemical protection anti-corrosion protection of pipelines is a set of measures aimed at preventing the development of corrosion under the influence of an electric field. Specialized rectifiers are used to convert direct current.

Protection against corrosion is carried out by creating an electromagnetic field, as a result of which a negative potential is acquired or the area acts as a cathode. That is, a section of steel pipelines, protected from the formation of rust, acquires a negative charge, and the grounding becomes positive.

Cathodic protection of pipelines against corrosion is accompanied by electrolytic protection with sufficient conductivity of the medium. This function is performed by soil when laying metal underground highways. Contacting of the electrodes is carried out through conductive elements.

The indicator for determining corrosion indicators is a high-voltage voltmeter or corrosion gauge. Using this device, the indicator between the electrolyte and the soil is monitored, specifically for this case.

How is electrochemical protection classified?

Corrosion and protection of main pipelines and tanks from it are controlled in two ways:

• A current source is connected to the metal surface. This area acquires a negative charge, that is, it acts as a cathode. Anodes are inert electrodes that have nothing to do with design Dont Have. This method is considered the most common, and electrochemical corrosion does not occur. This technique is aimed at preventing the following types of corrosion: pitting, due to the presence of stray currents, crystalline type of stainless steel, as well as cracking of brass elements.
• Galvanic method. Protection of main pipelines or sacrificial protection is carried out by metal plates with high levels of negative charges, made of aluminum, zinc, magnesium or their alloys. Anodes are two elements, so-called inhibitors, while the slow destruction of the protector helps maintain the cathode current in the product. Protective protection is used extremely rarely. ECP is performed on the insulating coating of pipelines.

About the features of electrochemical protection

The main cause of pipeline destruction is the result of corrosion of metal surfaces. After the formation of rust, cracks, ruptures, and cavities form, which gradually increase in size and contribute to the rupture of the pipeline. This phenomenon occurs more often near highways laid underground or in contact with groundwater.

The principle of cathodic protection is the creation of a voltage difference and the action of the two methods described above. After carrying out measuring operations directly at the location of the pipeline, it was found that the required potential to help slow down the destruction process should be 0.85V, and for underground elements this value is 0.55V.

To slow down the corrosion rate, the cathode voltage should be reduced by 0.3V. In this situation, the corrosion rate will not exceed 10 microns/year, and this will significantly extend the service life of technical devices.

One of the significant problems is the presence of stray currents in the soil. Such currents arise from the grounding of buildings, structures, rail tracks and other devices. Moreover, it is impossible to make an accurate assessment of where they may appear.

To create a destructive effect, it is enough to charge steel pipelines with a positive potential in relation to the electrolytic environment, these include pipelines laid in the ground.

In order to provide the circuit with current, it is necessary to supply an external voltage, the parameters of which will be sufficient to break through the resistance of the soil foundation.

As a rule, such sources are power lines with power ratings from 6 to 10 kW. If electric current cannot be supplied, then diesel or gas generators can be used. The installer for the protection of underground pipelines from corrosion must be familiar with the design solutions before performing work.

Cathodic protection

To reduce the percentage of rust on the surface of pipes, electrode protection stations are used:

1. Anode, made in the form of grounding conductors.
2. Converters of constant electron flows.
3. Equipment for process control and monitoring of this process.
4. Cable and wire connections.

Cathodic protection stations are quite effective; when directly connected to a power line or generator, they provide an inhibitory effect of currents. This ensures protection of several sections of the pipeline simultaneously. Parameters can be adjusted manually or automatically. In the first case, transformer windings are used, and in the second, thyristors are used.

The most common in Russia is the high-tech installation - Minevra -3000. Its power is sufficient to protect 30,000 m of highways.

Advantages of the technical device:

• high power characteristics;
• updating the operating mode after overloads in a quarter of a minute;
• using digital regulation, operating parameters are monitored;
• tightness of highly critical connections;
• connecting the device to remote process control.

ASKG-TM are also used, although their power is low, their equipment with a telemetry complex or remote control allows them to be no less popular.

A diagram of the insulation main of the water supply or gas pipeline must be available at the work site.

Video: cathodic protection against corrosion - what is it and how is it performed?

Corrosion protection by installing drainage

The corrosion protection installer for underground pipelines must be familiar with the drainage system. Such protection against rust formation of pipelines from stray currents is carried out by a drainage device necessary to divert these currents to another section of the ground. There are several drainage options.

Types of execution:

1. Executed underground.
2. Straight.
3. With polarities.
4. Reinforced.

When carrying out earthen drainage, electrodes are installed in the anode zones. To ensure a straight drainage line, an electrical jumper is made connecting the pipeline to the negative pole of current sources, for example, grounding from a residential building.

Polarized drainage has one-way conductivity, that is, when a positive charge appears on the ground loop, it automatically turns off. Enhanced drainage operates from a current converter additionally connected to electrical diagram, and this improves the removal of stray currents from the main line.

The increase for pipeline corrosion is carried out by calculation, according to the RD.

In addition, inhibitor protection is used, that is, a special composition is used on the pipes to protect against aggressive environments. Standstill corrosion occurs when boiler equipment is idle for a long time; to prevent this from happening, equipment maintenance is necessary.

An installer for the protection of underground pipelines from corrosion must have knowledge and skills, be trained in the Rules and periodically undergo a medical examination and pass exams in the presence of an inspector from Rostechnadzor.

M. Ivanov, Ph.D. n.

Corrosion of metals, especially iron and unalloyed steel, causes great harm to devices and pipelines operated in contact with water and air. This leads to a reduction in the service life of equipment and additionally creates conditions for water contamination with corrosion products.

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As is known, corrosion is an electrochemical process in which the oxidation of a metal occurs, that is, the release of electrons by its atoms. This process takes place in a microscopic part of the surface called the anodic region. It leads to a violation of the integrity of the metal, the atoms of which enter into chemical reactions, especially actively in the presence of atmospheric oxygen and moisture.

Since metals are good conductors of electricity, the released electrons flow freely to another microscopic region, where reduction reactions occur in the presence of water and oxygen. This region is called the cathode.

Leakage electrochemical corrosion can be counteracted by applying a voltage from an external direct current source to shift the electrode potential of the metal to values ​​at which the corrosion process does not occur.

On this basis, cathodic protection systems for underground pipelines, tanks and other metal structures have been built. If an electric potential is applied to the protected metal, such potential values ​​are established on the entire surface of the metal structure at which only reduction cathode processes can occur: for example, metal cations will accept electrons and transform into ions of a lower oxidation state or neutral atoms.

Technically, the method of cathodic protection of metals is carried out as follows ( rice. 1). A wire is supplied to the metal structure to be protected, for example a steel pipeline, which is connected to the negative pole of the cathode station, as a result of which the pipeline becomes the cathode. At some distance from the metal structure, an electrode is located in the ground, which is connected with a wire to the positive pole and becomes the anode. The potential difference between the cathode and anode is created in such a way as to completely eliminate the occurrence of oxidative processes on the protected structure. In this case, weak currents will flow through the moist soil between the cathode and the anode in the soil thickness. Effective protection requires the placement of several anode electrodes along the entire length of the pipeline. If it is possible to reduce the potential difference between the protected structure and the soil to 0.85-1.2 V, then the rate of pipeline corrosion is reduced to significantly low values.

So, the cathodic protection system includes a source of direct electric current, a control point and anode grounding. Typically, a cathodic protection station consists of an AC transformer and a diode rectifier. As a rule, it is powered from a 220 V network; There are also stations powered by high (6-10 kV) voltage lines.

For the cathode station to operate effectively, the potential difference between the cathode and anode it creates must be at least 0.75 V. In some cases, about 0.3 V is sufficient for successful protection. At the same time, as technical parameters Cathodic protection stations use the nominal values ​​of the output current and output voltage. Thus, usually the rated output voltage of stations is from 20 to 48 V. When long distance between the anode and the protected object, the required value of the station output voltage reaches 200 V.

Auxiliary inert electrodes are used as anodes. Anode grounding electrodes, for example, the AZM-3X model manufactured by JSC Katod (Razvilka village, Moscow region), are castings made of a corrosion-resistant alloy, equipped with a special wire with a copper core in reinforced insulation, as well as a sealed coupling for connection to the main cable of the cathodic protection station. It is most rational to use grounding conductors in environments with high and moderate corrosive activity when resistivity soil up to 100 Ohm.m. For optimal distribution of field strength and current density throughout the equipment body, around the anodes there are special screens in the form of a backfill of coal or coke.

To assess the efficiency of a cathodic protection station, a system is required that consists of a measuring electrode and a reference electrode and is the main part of the control and measuring point. Based on the readings of these electrodes, the cathodic protection potential difference is regulated.

Measuring electrodes are made of high-alloy steel, silicon cast iron, platinized brass or bronze, and copper. Reference electrodes are silver chloride or copper sulfate. According to their design, reference electrodes can be submersible or remote. The composition of the solution used in them must be close to the composition of the medium, from harmful effects which the equipment needs to be protected.

One can note the long-acting bimetallic reference electrodes of the EDB type, developed by VNIIGAZ (Moscow). They are designed to measure the potential difference between an underground metal object (including a pipeline) and the ground to automatically control a cathodic protection station under heavy load conditions and at significant depths, that is, where other electrodes cannot ensure constant maintenance of a given potential.

Equipment for cathodic protection is supplied mainly by domestic manufacturers. Thus, the mentioned CJSC “Kathod” offers the “Minerva-3000” station ( rice. 2), designed to protect main water supply networks. Its rated output power is 3.0 kW, output voltage is 96 V, protection current is 30 A. The accuracy of maintaining the protective potential and current value is 1 and 2%, respectively. The ripple value is no more than 1%.

Another Russian manufacturer, Energomera OJSC (Stavropol), supplies modules of the MKZ-M12, PNKZ-PPCh-M10 and PN-OPE-M11 brands, which provide effective cathodic protection of underground metal structures in areas of high corrosion hazard. The MKZ-M12 module has a rated current of 15 or 20 A; rated output voltage is 24 V. For models MKZ-M12-15-24-U2, the output voltage is 30 V. The accuracy of maintaining the protective potential reaches ±0.5%, the specified current is ±1%. Technical resource- 100 thousand hours, and service life - at least 20 years.

LLC "Electronic Technologies" (Tver) offers cathodic protection stations "Tvertsa" ( rice. 3), equipped with a built-in microprocessor and a telemechanical remote control system. Control and measuring points are equipped with non-polarizing long-acting comparison electrodes with electrochemical potential sensors, which provide measurement of polarization potentials on the pipeline. These stations also include an adjustable source of cathode current and a block of sensors for electrical parameters of the circuit, which is connected through a controller to a remote access device. The transformer of this station is made on the basis of ferrite cores of the Epcos type. A voltage converter control system based on a UCC 2808A microcircuit is also used.

The Kurs-OP company (Moscow) produces Elkon cathodic protection stations, the output voltage of which varies in the range from 30 to 96 V, and the output current in the range from 20 to 60 A. Output voltage ripple - no more than 2% . These stations are designed to protect single-strand pipelines from soil corrosion, and with the use of a joint protection unit, multi-strand pipelines in areas without stray currents in moderate climate conditions (from -45 to +40 ° C). The stations include a single-phase power transformer, a converter with stepwise regulation of the output voltage, high-voltage equipment, a two-pole manual disconnector and surge suppressors.

One can also note cathodic protection installations of the NGK-IPKZ series manufactured by NPF Neftegazkompleks EKhZ LLC (Saratov), ​​the maximum output current of which is 20 or 100 A, and the rated output voltage is 48 V.

One of the suppliers of cathodic protection stations from the CIS countries is Hoffmann Electric Technologies (Kharkov, Ukraine), which offers equipment for electrochemical protection against soil corrosion of main pipelines.

Electrochemical corrosion protection consists of cathodic and drainage protection. Cathodic protection of pipelines is carried out by two main methods: the use of metal protector anodes (galvanic protector method) and the use of external direct current sources, the minus of which is connected to the pipe, and the plus is connected to anode grounding (electrical method).

Rice. 1. Operating principle of cathodic protection

Galvanic tread protection against corrosion

The most obvious way to carry out electrochemical protection of a metal structure that has direct contact with an electrolytic medium is the galvanic protection method, which is based on the fact that different metals in the electrolyte have different electrode potentials. Thus, if you form a galvanic couple from two metals and place them in an electrolyte, then the metal with a more negative potential will become an anode-protector and will be destroyed, protecting the metal with a less negative potential. Protectors essentially serve as portable sources of electricity.

Magnesium, aluminum and zinc are used as the main materials for the manufacture of protectors. From a comparison of the properties of magnesium, aluminum and zinc, it is clear that of the elements under consideration, magnesium has the greatest electromotive force. At the same time, one of the most important practical characteristics of protectors is the efficiency factor, which shows the proportion of the protector mass used to obtain useful electrical energy in the circuit. Efficiency protectors made from magnesium and magnesium alloys rarely exceed 50% in, in contrast to protectors based on Zn and Al with efficiency. 90% or more.

Rice. 2. Examples of magnesium protectors

Typically, protector installations are used for cathodic protection of pipelines that do not have electrical contacts with adjacent extended communications, individual sections of pipelines, as well as tanks, steel protective casings (cartridges), underground tanks and containers, steel supports and piles, and other concentrated objects.

At the same time, tread installations are very sensitive to errors in their placement and configuration. Incorrect selection or placement of tread units leads to a sharp decrease in their effectiveness.

Cathodic corrosion protection

The most common method of electrochemical protection against corrosion of underground metal structures is cathodic protection, carried out by cathodic polarization of the protected metal surface. In practice, this is realized by connecting the protected pipeline to the negative pole of an external direct current source, called a cathodic protection station. The positive pole of the source is connected by a cable to an external additional electrode made of metal, graphite or conductive rubber. This external electrode is placed in the same corrosive environment as the object being protected, in the case of underground field pipelines, in the soil. Thus, a closed electrical circuit is formed: additional external electrode - soil electrolyte - pipeline - cathode cable - DC source - anode cable. As part of this electrical circuit, the pipeline is the cathode, and an additional external electrode connected to the positive pole of the direct current source becomes the anode. This electrode is called anode grounding. The negatively charged pole of the current source connected to the pipeline, in the presence of external anodic grounding, cathodically polarizes the pipeline, while the potential of the anode and cathode sections is practically equalized.

Thus, the cathodic protection system consists of a protected structure, a direct current source (cathodic protection station), anode grounding, connecting anode and cathode lines, the surrounding electrically conductive medium (soil), as well as elements of the monitoring system - control and measuring points.

Drainage corrosion protection

Drainage protection of pipelines from corrosion by stray currents is carried out by directed drainage of these currents to a source or to the ground. Installation of drainage protection can be of several types: earthen, direct, polarized and reinforced drainage.

Rice. 3. Drainage protection station

Earth drainage is carried out by grounding pipelines with additional electrodes in the places of their anode zones, direct drainage is carried out by creating an electrical jumper between the pipeline and the negative pole of a source of stray currents, for example, the rail network of an electrified railway. Polarized drainage, unlike direct drainage, has only one-way conductivity, so when a positive potential appears on the rails, the drainage is automatically turned off. In enhanced drainage, a current converter is additionally included in the circuit, allowing the drainage current to be increased.