When laying in a trench insulated pipeline and its subsequent backfilling, the insulating coating may be damaged, and during the operation of the pipeline it gradually ages (loses its dielectric properties, water resistance, adhesion). Therefore, for all installation methods, except above-ground, pipelines are subject to comprehensive protection against corrosion with protective coatings and electrochemical protection (ECP) means, regardless of the corrosive activity of the soil.

ECP means include cathodic, sacrificial and electrical drainage protection.

Protection against soil corrosion is carried out by cathodic polarization of pipelines. If cathodic polarization is carried out using an external direct current source, then such protection is called cathodic, but if polarization is carried out by connecting the protected pipeline to a metal having a more negative potential, then such protection is called sacrificial.

Cathodic protection

The schematic diagram of cathodic protection is shown in the figure.

The source of direct current is the cathodic protection station 3, where, with the help of rectifiers, the alternating current from the along-route power line 1, entering through the transformer point 2, is converted into direct current.

The negative pole of the source is connected to the protected pipeline 6 using connecting wire 4, and the positive pole is connected to the anode grounding 5. When the current source is turned on, the electrical circuit is closed through the soil electrolyte.

Schematic diagram of cathodic protection

1 - power lines; 2 - transformer point; 3 — cathodic protection station; 4 - connecting wire; 5 - anodic grounding; 6 - pipeline

The operating principle of cathodic protection is as follows. Under the influence of the applied electric field source, the movement of half-free valence electrons begins in the direction “anode grounding - current source - protected structure”. Losing electrons, the metal atoms of the anodic grounding pass in the form of ion atoms into the electrolyte solution, i.e. the anodic grounding is destroyed. Ion atoms undergo hydration and are removed into the depth of the solution. At the protected structure, due to the operation of the direct current source, an excess of free electrons is observed, i.e. conditions are created for the occurrence of oxygen and hydrogen depolarization reactions characteristic of the cathode.

Underground communications of oil depots are protected by cathode installations with various types anode grounding. The required protective current strength of the cathode installation is determined by the formula

J dr =j 3 ·F 3 ·K 0

where j 3 is the required value of the protective current density; F 3 - total contact surface of underground structures with the ground; K 0 is the coefficient of exposure of communications, the value of which is determined depending on the transition resistance of the insulating coating R nep and the electrical resistivity of the soil r g according to the graph shown in the figure below.

The required value of the protective current density is selected depending on the characteristics of the soil at the oil depot site in accordance with the table below.

Tread protection

The principle of operation of the tread protection is similar to the operation of a galvanic cell.

Two electrodes: pipeline 1 and protector 2, made of a more electronegative metal than steel, are lowered into the soil electrolyte and connected by wire 3. Since the protector material is more electronegative, under the influence of a potential difference, a directed movement of electrons occurs from the protector to the pipeline along the conductor 3. At the same time, the ion atoms of the protector material go into solution, which leads to its destruction. The current strength is controlled using control and measuring column 4.

Dependence of the bareness coefficients of underground pipelines on the transition resistance of the insulating coating for soil resistivity, Ohm-m

1 — 100; 2 — 50; 3 — 30; 4 — 10; 5 — 5

Dependence of protective current density on soil characteristics

Schematic diagram of tread protection

1 - pipeline; 2 — protector; 3 - connecting wire; 4 - control and measuring column

Thus, metal destruction still occurs. But not the pipeline, but the protector.

Theoretically, to protect steel structures from corrosion, all metals located in the electrochemical voltage series to the left of iron can be used, since they are more electronegative. In practice, protectors are made only from materials that meet the following requirements:

• the potential difference between the tread material and iron (steel) should be as large as possible;
• the current obtained by electrochemical dissolution of a unit mass of the protector (current output) must be maximum;
• ratio of the protector mass used to create protective current to total loss tread mass (utilization factor) should be greatest.

These requirements are best met by alloys based on magnesium, zinc and aluminum.

Tread protection is carried out with concentrated and extended protectors. In the first case, the electrical resistivity of the soil should be no more than 50 Ohm-m, in the second - no more than 500 Ohm-m.

Electrical drainage protection of pipelines

A method of protecting pipelines from destruction by stray currents, providing for their removal (drainage) from the protected structure to a structure that is a source of stray currents or special grounding, is called electrical drainage protection.

Direct, polarized and reinforced drainage are used.

Schematic diagrams of electrical drainage protection

a - direct drainage; b — polarized drainage; c - enhanced drainage

Direct electrical drainage is a drainage device with bilateral conductivity. The direct electrical drainage circuit includes: rheostat K, switch K, fuse Pr and signal relay C. The current strength in the pipeline-rail circuit* is regulated by the rheostat. If the current value exceeds the permissible value, the fuse will burn out, current will flow through the relay winding, which, when turned on, turns on a sound or light signal.

Direct electrical drainage is used in cases where the potential of the pipeline is constantly higher than the potential of the rail network, where stray currents are discharged. Otherwise, the drainage will turn into a channel for stray currents to flow into the pipeline.

Polarized electrical drainage is a drainage device that has one-way conductivity. Polarized drainage differs from direct drainage by the presence of a one-way conductivity element (valve element) VE. With polarized drainage, current flows only from the pipeline to the rail, which eliminates the flow of stray currents onto the pipeline through the drainage wire.

Enhanced drainage is used in cases where it is necessary not only to remove stray currents from the pipeline, but also to provide the required protective potential on it. Enhanced drainage is a conventional cathode station, connected with the negative pole to the protected structure, and the positive pole - not to the anode grounding, but to the rails of electrified transport.

Due to this connection scheme, the following is ensured: firstly, polarized drainage (due to the operation of valve elements in the SCP circuit), and secondly, the cathode station maintains the necessary protective potential of the pipeline.

After the pipeline is put into operation, the operating parameters of the corrosion protection system are adjusted. If necessary, taking into account the actual state of affairs, additional cathodic and drainage protection stations, as well as protector installations, can be put into operation.

Until now, when constructing long industrial pipelines, the most popular pipe material is steel. Possessing many remarkable properties, such as mechanical strength, the ability to function at high internal pressure and temperature and resistance to seasonal weather changes, steel also has a serious drawback: a tendency to corrosion, leading to the destruction of the product and, accordingly, the inoperability of the entire system.

One of the methods of protection against this threat is electrochemical, including cathodic and anodic protection of pipelines; The features and types of cathodic protection will be discussed below.

Definition of electrochemical protection

Electrochemical protection of pipelines from corrosion is a process carried out under the influence of a constant electric field on a protected object made of metals or alloys. Since alternating current is usually available for operation, special rectifiers are used to convert it to direct current.

In the case of cathodic protection of pipelines, the protected object acquires a negative potential by applying an electromagnetic field to it, that is, it becomes a cathode.

Accordingly, if a section of pipe protected from corrosion becomes a “minus”, then the grounding connected to it becomes a “plus” (i.e. an anode).

Anti-corrosion protection using this method is impossible without the presence of an electrolytic medium with good conductivity. In the case of underground pipelines, its function is performed by the soil. The contact of the electrodes is ensured by the use of elements made of metals and alloys that conduct electric current well.

During the process, a constant potential difference arises between the electrolyte medium (in this case, soil) and the element protected from corrosion, the value of which is controlled using high-voltage voltmeters.

Classification of electrochemical cathodic protection techniques

This method of preventing corrosion was proposed in the 20s of the 19th century and was initially used in shipbuilding: the copper hulls of ships were sheathed with anode protectors, which significantly reduced the rate of metal corrosion.

Once effectiveness has been established new technology, the invention began to be actively used in other areas of industry. After some time it was recognized as one of the most effective ways protection of metals.

There are currently two main types of cathodic protection of pipelines against corrosion:

1. The easiest way: to a metal product that requires protection from corrosion, it is supplied external source electric current. In this design, the part itself acquires a negative charge and becomes the cathode, while the role of the anode is performed by inert, design-independent electrodes.
2. Galvanic method. The part in need of protection comes into contact with a protective (tread) plate made of metals with high values ​​of negative electric potential: aluminum, magnesium, zinc and their alloys. In this case, both become anodes metal element, and the slow electrochemical destruction of the protector plate guarantees the maintenance of the required cathode current in the steel product. Through more or less for a long time, depending on the parameters of the plate, it dissolves completely.

Characteristics of the first method

This method of ECP of pipelines, due to its simplicity, is the most common. It is used to protect large structures and elements, in particular, underground and above-ground pipelines.

The technique helps to resist:

• pitting corrosion;
• corrosion due to the presence of stray currents in the area where the element is located;
• corrosion of intercrystal type stainless steel;
• cracking of brass elements due to increased stress.

Characteristics of the second method

This technology, unlike the first one, is intended, among other things, to protect small-sized products. The technique is most popular in the USA, while in Russian Federation rarely used. The reason is that to carry out galvanic electrochemical protection of pipelines, it is necessary to have an insulating coating on the product, and in Russia main pipelines are not treated in this way.

Features of ECP of pipelines

The main reason for pipeline failure (partial depressurization or complete destruction) individual elements) is metal corrosion. As a result of the formation of rust on the surface of the product, micro-tears, cavities and cracks appear on its surface, gradually leading to system failure. This problem is especially relevant for pipes that run underground and are constantly in contact with groundwater.

The principle of operation of cathodic protection of pipelines against corrosion involves the creation of an electrical potential difference and is implemented in the two ways described above.

After carrying out measurements on the ground, it was found that the required potential at which any corrosion process slows down is –0.85 V; for pipeline elements located under the earth layer, its natural value is –0.55 V.

In order to significantly slow down the processes of destruction of materials, it is necessary to reduce the cathode potential of the protected part by 0.3 V. If this is achieved, the corrosion rate of steel elements will not exceed 10 μm/year.

One of the most serious threats to metal products is stray currents, that is, electrical discharges penetrating into the ground due to the operation of grounding power lines (power lines), lightning rods, or movement on train rails. It is impossible to determine at what time and where they will appear.

The destructive effect of stray currents on steel structural elements appears when these parts have a positive electrical potential relative to the electrolytic medium (in the case of pipelines, soil). The cathodic technique imparts a negative potential to the protected product, as a result of which the risk of corrosion due to this factor is eliminated.

The optimal way to provide the circuit with electric current is to use an external energy source: it guarantees the supply of voltage sufficient to “break through” the soil resistivity.

Typically, overhead power transmission lines with powers of 6 and 10 kW act as such a source. If there are no power lines in the pipeline area, mobile generators operating on gas and diesel fuel should be used.

What is needed for cathodic electrochemical protection

To ensure a reduction in corrosion in pipeline areas, special devices called cathodic protection stations (CPS) are used.

These stations include the following elements:

• grounding acting as an anode;
• DC generator;
• control, measurement and process control point;
• connecting devices (wires and cables).

Cathodic protection stations quite effectively perform their main function, when connected to an independent generator or power line, simultaneously protecting several nearby sections of pipelines.

You can adjust the current parameters either manually (by replacing transformer windings) or in an automated mode (in the case where there are thyristors in the circuit).

Minerva-3000 is recognized as the most advanced cathodic protection station used in the Russian Federation (the SKZ project commissioned by Gazprom was created by French engineers). One such station makes it possible to ensure the safety of about 30 km of underground pipeline.

Pros of "Minerva-3000":

• high level power;
• opportunity quick recovery after overload occurs (no more than 15 seconds);
• equipped with the digital control units of the system necessary for monitoring operating modes;
• absolutely sealed critical components;
• the ability to control the operation of the installation remotely when connecting special equipment.

The second most popular SKZ in Russia is “ASKG-TM” (adaptive telemechanized cathodic protection station). The power of such stations is less than those mentioned above (from 1 to 5 kW), but their automatic control capabilities are improved due to the presence of a telemetry complex with remote control in the original configuration.

Both stations require a 220 V voltage source, are controlled using GPRS modules and are characterized by fairly modest dimensions - 500x400x900 mm and a weight of 50 kg. The service life of the SCP is from 20 years.

Parameter name	Meaning
Article topic:	Cathodic protection
Rubric (thematic category)	Industry

Cathodic protection ta is the most common type of electrochemical protection. It is used in cases where the metal is not prone to passivation, that is, it has an extended region of active dissolution, a narrow passive region, high values ​​of passivation current (i p) and passivation potential (p p).

Cathodic polarization can be carried out by connecting the protected structure to negative pole external current source. Cathodic protection is carried out by external current. .

The cathodic protection diagram is shown in Fig. 4. The negative pole of the external current source 4 is connected to the protected metal structure 1, and the positive pole is connected to the auxiliary electrode 2, which works as an anode. During the protection process, the anode is actively destroyed and is subject to periodic restoration.

Cast iron, steel, coal, graphite, and metal scrap (old pipes, rails, etc.) are used as anode materials. The sources of external current for cathodic protection are cathodic protection stations, the obligatory elements of which are: a converter (rectifier) ​​that generates current; current supply to the protected structure, reference electrode, anode grounding conductors, anode cable.

Cathodic protection of factory equipment (refrigerators, heat exchangers, capacitors, etc.) exposed to an aggressive environment is carried out by connecting an external current source to the negative pole and immersing the anode in this environment.

Cathodic protection with external current is impractical in conditions of atmospheric corrosion, in a vaporous environment, in organic solvents, since in this case corrosive environment does not have sufficient electrical conductivity.

Tread protection. Sacrificial protection is a type of cathodic protection. The pipeline protection scheme is shown in Fig. 5. A more electronegative metal, protector 3, is attached to the protected structure 2, which, dissolving in the environment, protects the main structure from destruction.

Once the protector has completely dissolved or lost contact with the structure being protected, it is extremely important to replace the protector.

Figure 5 Pipeline sacrificial protection scheme

The protector works effectively if the transition resistance between it and the environment is low. During operation, a protector, for example zinc, can become covered with a layer of insoluble corrosion products, which isolate it from environment and sharply increase the contact resistance. To combat this, the protector is placed in filler 4 - a mixture of salts, which creates a certain environment around it that facilitates the dissolution of corrosion products and increases the efficiency and stability of the protector in the ground.

In comparison with cathodic protection by external current, it is advisable to use sacrificial protection in cases where obtaining energy from the outside is difficult or if the construction of special power lines is not economically profitable.

Today, tread protection is used to combat corrosion. metal structures in sea and river water, soil and other neutral environments. Use of tread protection in acidic environments limited high speed self-dissolution of the protector.

Metals can be used as protectors: Al, Fe, Mg, Zn. In this case, use pure metals It is not always advisable to use them as protectors. To give protectors the required performance properties, alloying elements are introduced into their composition.

Cathodic protection - concept and types. Classification and features of the Cathodic Protection category 2017, 2018.

Protection of pipelines from corrosion can be carried out using a variety of technologies, the most effective of which is the electrochemical method, which includes cathodic protection. Often, anti-corrosion cathodic protection is used in combination with the treatment of steel structures with insulating compounds.

This article examines the electrochemical protection of pipelines and studies its cathodic subtype in particular detail. You will learn what the essence of this method is, when it can be used and what equipment is used for cathodic protection of metals.

Contents of the article

Types of cathodic protection

Cathodic corrosion protection of steel structures was invented in the 1820s. For the first time, the method was used in shipbuilding - the copper hull of the ship was sheathed with protective anode protectors, which significantly reduced the rate of copper corrosion. The technique was adopted and began to actively develop, making it one of the most effective methods of anti-corrosion protection today.

Cathodic protection of metals, according to technology, is classified into two types:

• method No. 1 - an external current source is connected to the protected structure, in the presence of which the metal product itself acts as a cathode, while third-party inert electrodes act as anodes.
• method No. 2 – “ galvanic technology“: the protected structure is in contact with a tread plate made of a metal having a higher electronegative potential (such metals include zinc, aluminum, magnesium and their alloys). The function of the anode in this method both metals perform, while the electrochemical dissolution of the metal of the tread plate ensures that the required minimum cathode current flows through the protected structure. Over time, the tread plate is completely destroyed.

Method No. 1 is the most common. This is an easy-to-implement anti-corrosion technology that effectively copes with many types of metal corrosion:

• intercrystalline corrosion of stainless steel;
• pitting corrosion;
• cracking of brass from increased stress;
• corrosion under the influence of stray currents.

Unlike the first method, suitable for protecting large structures (used for underground and above-ground pipelines), galvanic electrochemical protection is intended for use with small-sized products.

The galvanic method is widespread in the USA; in Russia it is practically not used, since the technology for constructing pipelines in our country does not provide for treating pipelines with a special insulating coating, which is prerequisite for galvanic electrochemical protection.

Note that without the corrosion of steel increases significantly under the influence of groundwater, which is especially typical for spring period and autumn. In winter, after water freezes, corrosion from moisture slows down significantly.

The essence of technology

Cathodic anti-corrosion protection is carried out through the use of direct current, which is supplied to the protected structure from an external source (rectifiers that convert alternating current into direct current are most often used) and makes its potential negative.

The object itself, connected to direct current, is a “minus” - a cathode, while the anode grounding connected to it is a “plus”. The key condition for the effectiveness of cathodic protection is the presence of a well-conducting electrolytic medium, which is soil when protecting underground pipelines, while electronic contact is achieved through the use of metal materials with high conductivity.

In the process of implementing the technology, the required current potential difference is constantly maintained between the electrolytic medium (soil) and the object, the value of which is determined using a high-resistance voltmeter.

Features of cathodic protection of pipelines

Corrosion is the main cause of depressurization of all types of pipelines. Due to damage to the metal by rust, ruptures, cavities and cracks form on it, leading to the destruction of the steel structure. This problem is especially critical for underground pipelines that are constantly in constant contact with groundwater.

Cathodic protection of gas pipelines against corrosion is carried out using one of the above methods (using an external rectifier or galvanic method). The technology, in this case, makes it possible to reduce the rate of oxidation and dissolution of the metal from which the pipeline is made, which is achieved by shifting its natural corrosion potential to negative side.

Through practical tests it was found that the potential cathodic polarization metals, at which all corrosion processes slow down, is equal to -0.85 V, whereas for underground pipelines in natural mode it is -0.55 V.

For anti-corrosion protection to be effective, it is necessary to reduce the cathode potential of the metal from which the pipeline is made by -0.3 V using direct current. In this case, the rate of corrosion of steel does not exceed 10 micrometers over the course of a year.

Cathodic protection is the most effective method protection of underground pipelines from stray currents. The concept of stray currents means electric charge, which enters the ground as a result of the operation of grounding points of power lines, lightning rods, or the movement of trains along railway lines. It is impossible to find out the exact time and place of the appearance of stray currents.

The corrosive effect of stray currents on metal occurs if the metal structure has a positive potential relative to the electrolyte (for underground pipelines the electrolyte is the soil). Cathodic protection makes the metal potential of underground pipelines negative, which eliminates the risk of their oxidation under the influence of stray currents.

The technology of using an external current source for cathodic protection of underground pipelines is preferable. Its advantages are unlimited energy resources that can overcome the resistivity of the soil.

Overhead power lines with a power of 6 and 10 kW are used as a current source for anti-corrosion protection; if there are no power lines on the territory, mobile generators running on gas and diesel fuel can be used.

Detailed overview of cathodic corrosion protection technology (video)

Cathodic protection equipment

For anti-corrosion protection of underground pipelines, special equipment is used - cathodic protection stations(SKZ), consisting of the following units:

• grounding (anode);
• DC source;
• control, monitoring and measurement point;
• connecting cables and wires.

One SCP connected to the power grid or to an autonomous generator can perform cathodic protection of several nearby underground pipelines. Current adjustment can be done manually (by replacing the winding on the transformer) or automatically (if the system is equipped with thyristors).

Among cathodic protection stations used in domestic industry, the most technologically advanced installation is considered to be Minerva-3000 (designed by engineers from France at the request of Gazprom). The power of this VS is sufficient for effective protection 30 km of underground pipeline.

The advantages of the installation include:

• increased power;
• overload recovery function (update occurs in 15 seconds);
• availability of digital control systems to control operating conditions;
• complete tightness of critical components;
• possibility of connecting equipment for remote control.

ASKG-TM units are also widely in demand in domestic construction; in comparison with Minerva-3000, they have a reduced power (1-5 kW), however, in the stock configuration, the system is equipped with a telemetry complex, which automatically controls the operation of the SCP and has the ability to be remotely controlled .

Cathodic protection stations Minerva-3000 and ASKG-TM require power from a 220 V power supply. Remote control of equipment is performed using built-in GPRS modules. SKZ have quite larger dimensions - 50*40*90 cm and weight - 50 kg. Minimum term The service life of the devices is 20 years.

One of the frequently used methods of electrochemical protection of various metal structures from rust 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, the theory provided was tested on the ship HMS Samarang. 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 elements, 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 found wide application all over the world. It is quite simple and economically feasible, making it possible to protect the metal from general corrosion and from many of its varieties - intergranular corrosion of stainless steel, pitting, cracking of brass products caused by 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 of metals in Russia is due to the fact that many pipelines in our country do not have a special coating applied, and this is a 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 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 rusting of car components causes many problems for car enthusiasts. All vehicles without exception are subject to corrosive destruction, because rusting begins even when a small scratch appears on the paintwork of 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 application of electrical potential to the surface of a particular 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.

Under vulnerabilities vehicles that can be protected using the cathodic method understand:

• 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 fewer plates you need, the more larger size has an electrode.

Car corrosion protection using the cathodic method is also carried out by other comparatively in 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 damage 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 begins active formation corrosive galvanic components.

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 to the negative side by 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 a high level of protection for pipelines, its energy resource is not limited by anything, and 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 negative influence 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 electrical networks or to autonomous 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 the 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 of (specific) soil, the appearance of stray currents and other factors that affect 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 – 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 over the operation of the station and remote control of its equipment.

The systems also have excellent technical performance ASKG-TM– modern telemechanized adaptive stations for the protection of electrical cables, city and main pipelines, as well as containers in which gas and oil products are stored. Such devices are produced with different indicators(1 to 5 kilowatts) power output. 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. The original protective coatings on such objects cannot be restored (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, and 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 internal parts vessels and containers, as well as pipes that come into contact with industrial wastewater and other aggressive electrolytes. Polarization in this case increases the time of maintenance-free use of these structures by 2–3 times.