Schematic diagram of pipeline cathodic protection. What is cathodic protection of pipelines and how does it work
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The cathodic protection of the gas pipeline must operate uninterruptedly. For each SKZ, a certain mode is set depending on the conditions of its operation. During operation cathode station a log of its electrical parameters and the operation of the current source is kept. It is also necessary to constantly monitor the anode grounding, the state of which is determined by the magnitude of the RMS current.
| Characteristics of the state of the protective coating and its conductivity. |
The cathodic protection of the gas pipeline must operate uninterruptedly. On sections of the route with interruptions in the supply of electricity for several hours a day, batteries are used that provide protection during a power outage. The capacity of the battery is determined by the value of the protective current RMS.
Cathodic protection of gas pipelines from the effects of stray currents or soil corrosion is carried out using direct electric current external source. The negative pole of the current source is connected to the protected gas pipeline, and the positive pole to a special ground - the anode.
Cathodic protection of gas pipelines against corrosion is carried out due to their cathodic polarization using an external current source.
Influence of cathodic protection of gas pipelines on rail chains of railways.
For cathodic protection of a gas pipeline, standard instruments of electrical installations and special corrosion-measuring and auxiliary instruments are used. To measure the potential difference between an underground structure and the earth, which is one of the criteria for assessing the risk of corrosion and the presence of protection, voltmeters with a large internal resistance by 1 on the scale are used so that their inclusion in the measuring circuit does not violate the potential distribution in the latter. This requirement is due to both the high internal resistance of the underground structure - ground system, and the difficulty of creating a low ground resistance at the point of contact of the measuring electrode with the ground, especially when using non-polarizable electrodes. To obtain a measuring circuit with a high input resistance, potentiometers and high-resistance voltmeters are used.
For gas pipeline cathodic protection stations as a source of electricity, it is recommended to use high-temperature fuel cells with a ceramic electrode. Such fuel cells can operate for a long time on the gas pipeline route, supplying cathodic protection stations with electricity, as well as the houses of line repairers, signaling systems and automatic control of the yards. This power supply method linear structures and installations on the gas pipeline, which do not require high power, greatly simplifies operational maintenance.
Very often, the parameters of cathodic protection of gas pipelines, obtained by calculation, differ significantly from the RMS parameters obtained in practice by measurements. This is due to the impossibility of taking into account the whole variety of factors affecting natural conditions to the security settings.
BUT. G. Semenov, general director, joint venture "Elkon", G. Chisinau; L. P. Sysa, leading engineer on ECP, NPC "Vector", G. Moscow
Introduction
Cathodic protection stations (CPS) are a necessary element of the system of electrochemical (or cathodic) protection (ECP) of underground pipelines against corrosion. When choosing a VHC, they most often proceed from the lowest cost, ease of maintenance and qualification of their service personnel. The quality of the purchased equipment is usually difficult to assess. The authors propose to consider the technical parameters of the CPS indicated in the passports, which determine how well the main task of cathodic protection will be performed.
The authors did not pursue the goal of expressing themselves in a strictly scientific language in the definition of concepts. In the process of communicating with the personnel of the ECP services, we realized that it is necessary to help these people systematize the terms and, more importantly, give them an idea of what is happening both in the power grid and in the VCS itself.
A taskECP
Cathodic protection is carried out when an electric current flows from the RMS through a closed electrical circuit formed by three resistors connected in series:
· soil resistance between pipeline and anode; I anode spreading resistance;
pipeline insulation resistance.
The soil resistance between the pipe and the anode can vary widely depending on the composition and external conditions.
The anode is an important part of the ECP system, and serves as the consumable element, the dissolution of which provides the very possibility of ECP implementation. Its resistance during operation steadily increases due to dissolution, a decrease in the effective area of the working surface and the formation of oxides.
Consider the metal pipeline itself, which is the protected element of the ECP. The metal pipe is covered with insulation on the outside, in which cracks form during operation due to mechanical vibrations, seasonal and daily temperature changes, etc. Moisture penetrates through the cracks in the hydro- and thermal insulation of the pipeline and the metal of the pipe contacts the ground, thus forming a galvanic couple that contributes to the removal of metal from the pipe. The more cracks and their sizes, the more metal is carried out. Thus, galvanic corrosion occurs, in which a current of metal ions flows, i.e. electricity.
Since the current is flowing, then a wonderful idea arose to take an external current source and turn it on to meet this very current, due to which the removal of metal and corrosion occurs. But the question arises: what is the magnitude of this most man-made current to give? It seems to be such that plus to minus gives zero metal removal current. And how to measure this same current? The analysis showed that the voltage between the metal pipe and the ground, i.e. on both sides of the insulation, must be between -0.5 and -3.5 V (this voltage is called the protective potential).
A taskVHC
The task of the SKZ is not only to provide current in the ECP circuit, but also to maintain it in such a way that the protective potential does not go beyond the accepted limits.
So, if the insulation is new, and it has not had time to get damaged, then its resistance to electric current is high and a small current is needed to maintain the desired potential. As the insulation ages, its resistance decreases. Consequently, the required compensating current from the RMS increases. It will increase even more if cracks appear in the insulation. The station must be able to measure the protective potential and change its output current accordingly. And nothing more, from the point of view of the ECP task, is required.
ModesworkVHC
There are four modes of operation of the ECP:
without stabilization of output values of current or voltage;
I stabilize the output voltage;
stabilization of the output current;
· I stabilization of the protective potential.
Let's say right away that in the accepted range of changes of all influencing factors, the fulfillment of the ECP task is fully ensured only when using the fourth mode. Which is accepted as the standard for the operating mode of the SKZ.
The potential sensor gives the station information about the potential level. The station changes its current in the right direction. Problems begin from the moment when it is necessary to put this very potential sensor. You need to put it in a certain calculated place, you need to dig a trench for the connecting cable between the station and the sensor. Anyone who laid any communications in the city knows what a hassle it is. Plus, the sensor requires periodic maintenance.
In conditions where there are problems with the mode of operation with feedback Potentially, proceed as follows. When using the third mode, it is assumed that the state of the insulation changes little in the short term and its resistance remains practically stable. Therefore, it is enough to ensure the flow of a stable current through a stable insulation resistance, and we get a stable protective potential. In the medium and long term, the necessary adjustments can be made by a specially trained lineman. The first and second regimes do not impose high requirements on the SKZ. These stations are simple in execution and, as a result, cheap, both in manufacture and in operation. Apparently, this circumstance determines the use of such SCs in the ECP of objects located in conditions of low corrosive activity of the environment. If the external conditions (insulation state, temperature, humidity, stray currents) change to the limits when an unacceptable mode is formed on the protected object, these stations cannot perform their task. To adjust their mode, the frequent presence of maintenance personnel is necessary, otherwise the ECP task is partially performed.
CharacteristicsVHC
First of all, the VHC must be selected based on the requirements set out in normative documents. And, probably, the most important thing in this case will be GOST R 51164-98. Appendix "I" of this document states that the efficiency of the station must be at least 70%. The level of industrial noise generated by RMS should not exceed the values specified by GOST 16842, and the level of harmonics at the output should comply with GOST 9.602.
The SKZ passport usually indicates: I rated output power;
Efficiency at rated output power.
Rated output power - the power that the station can deliver at rated load. Typically this load is 1 ohm. The efficiency is defined as the ratio of the rated output power to the active power consumed by the station in the rated mode. And in this mode, the efficiency is the highest for any station. However, most VCSs operate far from the nominal mode. The power load factor ranges from 0.3 to 1.0. In this case, the real efficiency for most stations manufactured today will drop noticeably with a decrease in output power. This is especially noticeable for transformer SKZ using thyristors as a regulating element. For transformerless (high-frequency) RMS, the drop in efficiency with a decrease in output power is much less.
A general view of the change in efficiency for SKZ of different designs can be seen in the figure.
From fig. it can be seen that if you use the station, for example, with a nominal efficiency of 70%, then be prepared for the fact that you have spent another 30% of the electricity received from the network uselessly. And this is in the best case of rated output power.
With an output power of 0.7 of the nominal, you should already be prepared for the fact that your energy losses will be equal to the useful energy spent. Where is so much energy being wasted?
ohmic (thermal) losses in the windings of transformers, chokes and active elements of the circuit;
· energy costs for the operation of the station control circuit;
Loss of energy in the form of radio emission; energy losses of the output current ripple of the station at the load.
This energy is radiated into the ground from the anode and does not produce useful work. Therefore, it is so necessary to use stations with a low ripple coefficient, otherwise expensive energy is wasted. Not only that, at high levels of ripples and radio emission, power losses increase, but besides this, this uselessly dissipated energy interferes with normal operation. a large number electronic equipment located in the vicinity. The required total power is also indicated in the SKZ passport, let's try to deal with this parameter. The SKZ takes energy from the power grid and does it in every unit of time with such intensity as we have allowed it to do with the adjustment knob on the station control panel. Naturally, it is possible to take energy from the network with a power not exceeding the power of this network itself. And if the voltage in the network changes sinusoidally, then our ability to take energy from the network changes sinusoidally 50 times per second. For example, at the moment when the mains voltage passes through zero, no power can be taken from it. However, when the voltage sinusoid reaches its maximum, then at this moment our ability to take energy from the network is maximum. At any other time, this possibility is less. Thus, it turns out that at any time the power of the network differs from its power at a neighboring time. These power values are called instantaneous power at a given time and it is difficult to operate with such a concept. Therefore, we agreed on the concept of the so-called effective power, which is determined from an imaginary process in which a network with a sinusoidal voltage change is replaced by a network with a constant voltage. When we calculated the value of this constant voltage for our electrical networks, we got 220 V - it was called the effective voltage. And the maximum value of the sinusoid of the voltage was called the amplitude voltage, and it is equal to 320 V. By analogy with the voltage, the concept of the effective value of the current was introduced. The product of the effective voltage value and the effective current value is called the total power consumption, and its value is indicated in the RMS passport.
And the full power in the SKZ itself is not fully used, because. it has various reactive elements that do not waste energy, but use it, as it were, to create conditions for the rest of the energy to pass into the load, and then return this tuning energy back to the network. This energy returned back was called reactive energy. The energy that is transferred to the load is active energy. The parameter that indicates the ratio between the active energy that must be transferred to the load and the total energy supplied to the RMS is called the power factor and is indicated in the station passport. And if we coordinate our capabilities with the capabilities of the supply network, i.e. synchronously with a sinusoidal change in the voltage of the network, we take power from it, then such a case is called ideal and the power factor of the RMS operating with the network in this way will be equal to one.
The station must transmit active energy as efficiently as possible to create a protective potential. The efficiency with which the VHC does this is evaluated by the efficiency factor. How much energy it spends depends on the method of energy transfer and on the mode of operation. Without going into this vast field for discussion, we will only say that transformer and transformer-thyristor SKZs have reached their limit of improvement. They do not have the resources to improve the quality of their work. The future belongs to high-frequency VMS, which every year become more reliable and easier to maintain. In terms of efficiency and quality of their work, they already surpass their predecessors and have a large reserve for improvement.
Consumerproperties
The consumer properties of such a device as SKZ include the following:
1. Dimensions, the weight and strength. Probably, it is not necessary to say that the smaller and lighter the station, the lower the cost of its transportation and installation, both during installation and repair.
2. maintainability. The ability to quickly replace a station or node on site is very important. With subsequent repairs in the laboratory, i.e. modular principle of construction of SKZ.
3. Convenience in service. Ease of maintenance, in addition to ease of transportation and repair, is determined, in our opinion, as follows:
the presence of all necessary indicators and measuring instruments, the possibility of remote control and monitoring the operation of the SKZ.
conclusions
Based on the foregoing, several conclusions and recommendations can be drawn:
1. Transformer and thyristor-transformer stations are hopelessly outdated in all respects and do not meet modern requirements, especially in the field of energy saving.
2. A modern station must have:
· high efficiency in all range of loadings;
power factor (cos I) not less than 0.75 in the entire load range;
output voltage ripple factor no more than 2%;
· current and voltage regulation range from 0 to 100%;
lightweight, durable and small-sized body;
· modular principle of construction, i.e. have high maintainability;
· I energy efficiency.
Other requirements for cathodic protection stations, such as protection against overloads and short circuits; automatic maintenance of a given load current - and other requirements are generally accepted and mandatory for all SKZ.
In conclusion, we offer consumers a table comparing the parameters of the main manufactured and currently used cathodic protection stations. For convenience, the table shows stations of the same power, although many manufacturers can offer a whole range of manufactured stations.
METAL STRUCTURES»
Cathodic protection of underground metal structures
The principle of operation of cathodic protection
Upon contact of the metal with soils related to electrolytic media, a corrosion process occurs, accompanied by the formation of an electric current, and a certain electrode potential is established. The magnitude of the electrode potential of the pipeline can be determined by the potential difference between the two electrodes: the pipeline and the non-polarized copper sulfate element. Thus, the value of the potential of the pipeline is the difference between its electrode potential and the potential of the reference electrode with respect to the ground. On the surface of the pipeline, electrode processes of a certain direction and stationary in nature change in time proceed.
The stationary potential is usually called the natural potential, implying the absence of stray and other induced currents on the pipeline.
The interaction of a corroding metal with an electrolyte is divided into two processes: anodic and cathodic, which take place simultaneously on different parts of the interface between the metal and the electrolyte.
When protecting against corrosion, the territorial separation of the anode and cathode processes is used. A current source with an additional grounding electrode is connected to the pipeline, with the help of which an external direct current is applied to the pipeline. In this case, the anode process occurs on an additional grounding electrode.
The cathodic polarization of underground pipelines is carried out by applying an electric field from an external direct current source. The negative pole of the direct current source is connected to the protected structure, while the pipeline is a cathode in relation to the ground, an artificially created grounding anode is connected to the positive pole.
A schematic diagram of cathodic protection is shown in fig. 14.1. With cathodic protection, the negative pole of the current source 2 is connected to the pipeline 1, and the positive one is connected to the artificially created anode-ground electrode 3. When the current source is turned on, it flows from its pole through the anode ground into the ground and through the damaged sections of the insulation 6 to the pipe. Further, through the drainage point 4 along the connecting wire 5, the current returns again to the minus of the power source. In this case, the process of cathodic polarization begins on the bare sections of the pipeline.
Rice. 14.1. Schematic diagram of pipeline cathodic protection:
1 - pipeline; 2 - external source of direct current; 3 - anode grounding;
4 - drainage point; 5 - drainage cable; 6 - cathode terminal contact;
7 - cathode output; 8 - pipeline insulation damage
Since the voltage of the external current applied between the ground electrode and the pipeline significantly exceeds the potential difference between the electrodes of the corrosion macropairs of the pipeline, the stationary potential of the anode ground does not play a decisive role.
With the inclusion of electrochemical protection ( j 0a.add) the distribution of currents of corrosion macropairs is disturbed, the values of the potential difference "pipe - earth" of the cathode sections approach each other ( j 0k) with the potential difference of the anode sections ( j 0а), the conditions for polarization are provided.
Cathodic protection is regulated by maintaining the required protective potential. If, by applying an external current, the pipeline is polarized to an equilibrium potential ( j 0к = j 0а) dissolution of the metal (Fig. 14.2 a), then the anode current stops and corrosion stops. Further increase of the protective current is impractical. With more positive potential values, the phenomenon of incomplete protection occurs (Fig. 14.2 b). It can occur during cathodic protection of a pipeline located in a zone of strong influence of stray currents or when using protectors that do not have a sufficiently negative electrode potential (zinc protectors).
The criteria for protecting metal from corrosion are the protective current density and protective potential.
Cathode polarization non-isolated metal structure up to the value of the protective potential requires significant currents. The most probable current densities required for steel polarization in various media to the minimum protective potential (-0.85 V) with respect to the copper sulfate reference electrode are given in Table. 14.1
Rice. 14.2. Corrosion diagram for the case of full polarization (a) and
incomplete polarization (b)
Usually cathodic protection used in conjunction with insulating coatings applied to the outer surface of the pipeline. The surface coating reduces the required current by several orders of magnitude. So, for the cathodic protection of steel with a good coating in the soil, only 0.01 ... 0.2 mA / m 2 is required.
Table 14.1
Current density required for cathodic protection
bare steel surface in various environments
The protective current density for insulated main pipelines cannot become a reliable protection criterion due to the unknown distribution of damaged pipeline insulation, which determines the actual metal-to-ground contact area. Even for an uninsulated pipe (cartridge at an underground passage through railways and highways), the protective current density is determined by the geometric dimensions of the structure and is fictitious, since the portion of the surface of the cartridge remains unknown, covered with constantly present passive protective layers (scale, etc.) and not participating during the process of depolarization. Therefore, the protective current density as a protection criterion is used for some laboratory research performed on metal samples.
With cathodic protection of the pipeline, the positive pole of the DC source (anode) is connected to a special anode ground electrode, and the negative (cathode) is connected to the protected structure (Fig. 2.24).
Rice. 2.24. Pipeline cathodic protection scheme
1- power line;
2 - transformer point;
3 - cathodic protection station;
4 - pipeline;
5 - anode grounding;
6 - cable
The principle of operation of cathodic protection is similar to electrolysis. Under the influence of an electric field, the movement of electrons from the anode ground electrode system to the protected structure begins. Losing electrons, the metal atoms of the anode ground electrode pass in the form of ions into the soil electrolyte solution, that is, the anode electrode is destroyed. An excess of free electrons is observed at the cathode (pipeline) (recovery of the metal of the protected structure).
49. Tread protection
When laying pipelines in hard-to-reach areas remote from power sources, tread protection is used (Fig. 2.25).
1 - pipeline;
2 - protector;
3 - conductor;
4 - control column
Rice. 2.25. Protective protection scheme
The principle of operation of the sacrificial protection is similar to that of a galvanic couple. Two electrodes - a pipeline and a protector (made of a more electronegative metal than steel) are connected by a conductor. In this case, a potential difference arises, under the action of which there is a directed movement of electrons from the protector-anode to the pipeline-cathode. Thus, the protector is destroyed, not the pipeline.
The tread material must meet the following requirements:
Provide the greatest potential difference between the protector metal and steel;
The current at the dissolution of a unit mass of the protector should be maximum;
The ratio of the tread mass used to create a protective potential to the total tread mass should be the largest.
The requirements are best met magnesium, zinc and aluminum. These metals provide almost equal protection efficiency. Therefore, in practice, their alloys are used with the use of improving additives ( manganese, which increases the current output and India- increasing the activity of the protector).
50. Electric drainage protection
Electrical drainage protection is designed to protect the pipeline from stray currents. The source of stray currents is an electric transport operating according to the “wire-to-ground” scheme. The current from the positive rail of the traction substation (overhead wire) travels to the motor and then through the wheels to the rails. The rails are connected to the negative bus of the traction substation. Due to the low transition resistance "rails-ground" and the violation of jumpers between the rails, part of the current flows into the ground.
If there is a pipeline with broken insulation nearby, current flows through the pipeline until conditions are favorable for returning to the negative bus of the traction substation. At the point where the current exits, the pipeline is destroyed. Destruction occurs in a short time, since the stray current flows from a small surface.
Electrical drainage protection is the diversion of stray currents from the pipeline to a source of stray currents or special grounding (Fig. 2.26).
Rice. 2.26. Scheme of electrical drainage protection
1 - pipeline; 2 - drainage cable; 3 - ammeter; 4 - rheostat; 5 - knife switch; 6 - valve element; 7 - fuse; 8 – alarm relay; 9 - rail
Electrochemical protection – effective method protection of finished products from electrochemical corrosion. In some cases, it is impossible to renew the paintwork or protective wrapping material, then it is advisable to use electrochemical protection. Covering an underground pipeline or bottom sea vessels it is very time-consuming and expensive to renew, sometimes it is simply impossible. Electrochemical protection reliably protects the product from, preventing the destruction of underground pipelines, ship bottoms, various tanks, etc.
Electrochemical protection is used in cases where the potential for free corrosion is in the region of intensive dissolution of the base metal or overpassivation. Those. when there is an intensive destruction of the metal structure.
The essence of electrochemical protection
to finished metal product a direct current is connected externally (DC source or protector). Electric current on the surface of the protected product creates cathodic polarization of the electrodes of microgalvanic pairs. The result of this is that the anodic areas on the metal surface become cathodic. And as a result of exposure to a corrosive environment, not the metal of the structure is destroyed, but the anode.
Depending on which direction (positive or negative) the potential of the metal is shifted, electrochemical protection is divided into anode and cathode.
Cathodic corrosion protection
Cathodic electrochemical corrosion protection is used when the protected metal is not prone to passivation. This is one of the main types of protection of metals from corrosion. The essence of cathodic protection is the application of an external current from the negative pole to the product, which polarizes the cathodic sections of corrosion elements, bringing the potential value closer to the anode ones. The positive pole of the current source is connected to the anode. In this case, the corrosion of the protected structure is almost reduced to zero. The anode is gradually destroyed and must be replaced periodically.
There are several options for cathodic protection: polarization from an external source of electric current; decrease in the rate of the cathode process (for example, electrolyte deaeration); contact with a metal that has a more electronegative potential for free corrosion in a given environment (the so-called sacrificial protection).
Polarization from an external source of electric current is used very often to protect structures located in the soil, water (bottoms of ships, etc.). Besides this species corrosion protection is used for zinc, tin, aluminum and its alloys, titanium, copper and its alloys, lead, as well as high-chromium, carbon, alloy (both low and high alloy) steels.
An external current source is cathodic protection stations, which consist of a rectifier (converter), a current supply to the protected structure, anode ground electrodes, a reference electrode and an anode cable.
Cathodic protection is applied both independently and additional view corrosion protection.
The main criterion by which one can judge the effectiveness of cathodic protection is protective potential. The protective potential is the potential at which the corrosion rate of the metal in certain conditions environment takes the lowest (as far as possible) value.
There are disadvantages to using cathodic protection. One of them is danger overprotection. Overprotection is observed with a large shift in the potential of the protected object in the negative direction. At the same time, it stands out. The result is destruction protective coatings, hydrogen embrittlement of metal, corrosion cracking.
Tread protection (tread application)
A type of cathodic protection is cathodic protection. When using sacrificial protection, a metal with a more electronegative potential is connected to the protected object. In this case, not the structure is destroyed, but the tread. Over time, the protector corrodes and must be replaced with a new one.
Tread protection is effective in cases where between the tread and environment small transitional resistance.
Each protector has its own radius of protective action, which is determined by the maximum possible distance at which the protector can be removed without losing the protective effect. Protective protection is used most often when it is impossible or difficult and expensive to bring current to the structure.
Protectors are used to protect structures in neutral environments (sea or river water, air, soil, etc.).
For the manufacture of protectors, the following metals are used: magnesium, zinc, iron, aluminum. pure metals do not fully fulfill their protective functions, therefore, in the manufacture of protectors, they are additionally alloyed.
Iron protectors are made of carbon steels or pure iron.
Zinc protectors
Zinc protectors contain about 0.001 - 0.005% lead, copper and iron, 0.1 - 0.5% aluminum and 0.025 - 0.15% cadmium. Zinc projectors are used to protect products from marine corrosion (in salt water). If the zinc protector is used in slightly saline, fresh water or soil, it is quickly covered with a thick layer of oxides and hydroxides.
Protector magnesium
Alloys for the manufacture of magnesium protectors are alloyed with 2–5% zinc and 5–7% aluminum. The amount of copper, lead, iron, silicon, nickel in the alloy should not exceed tenths and hundredths of a percent.
The protector magnesium is used in slightly saline, fresh waters, soils. The protector is used in environments where zinc and aluminum protectors are ineffective. An important aspect is that magnesium protectors must be used in an environment with a pH of 9.5 - 10.5. This is explained high speed dissolution of magnesium and the formation of sparingly soluble compounds on its surface.
Magnesium protector is dangerous, because. is the cause of hydrogen embrittlement and corrosion cracking of structures.
Aluminum protectors
Aluminum protectors contain additives that prevent the formation of aluminum oxides. Up to 8% zinc, up to 5% magnesium and tenths to hundredths of silicon, cadmium, indium, and thallium are introduced into such protectors. Aluminum protectors are used in the coastal shelf and flowing sea water.
Anode corrosion protection
Anode electrochemical protection is used for structures made of titanium, low-alloy stainless, carbon steels, high-alloy ferrous alloys, dissimilar passivated metals. Anode protection is used in highly conductive corrosive environments.
With anodic protection, the potential of the protected metal is shifted to a more positive side until a passive stable state of the system is reached. The advantages of anodic electrochemical protection are not only a very significant slowdown in the corrosion rate, but also the fact that corrosion products do not enter the product and the medium.
Anode protection can be implemented in several ways: by shifting the potential to the positive side using an external electric current source or by introducing oxidizing agents (or elements into the alloy) into the corrosive environment, which increase the efficiency of the cathodic process on the metal surface.
Anode protection with the use of oxidizers is similar in its protective mechanism to anodic polarization.
If passivating inhibitors with oxidizing properties are used, then the protected surface passes into a passive state under the influence of the current that has arisen. These include dichromates, nitrates, etc. But they pollute the surrounding technological environment quite strongly.
With the introduction of additives into the alloy (mainly doping with a noble metal), the reduction reaction of depolarizers occurring at the cathode proceeds with a lower overvoltage than on the protected metal.
If an electric current is passed through the protected structure, the potential shifts in the positive direction.
An installation for anodic electrochemical protection against corrosion consists of an external current source, a reference electrode, a cathode, and the protected object itself.
In order to find out whether it is possible to apply anodic electrochemical protection for a certain object, anodic polarization curves are taken, with the help of which it is possible to determine the corrosion potential of the structure under study in a certain corrosive environment, the region of stable passivity and the current density in this region.
For the manufacture of cathodes, low-solubility metals are used, such as high-alloy stainless steels, tantalum, nickel, lead, and platinum.
In order for anodic electrochemical protection to be effective in a certain environment, it is necessary to use easily passivated metals and alloys, the reference electrode and cathode must always be in solution, and the connecting elements must be of high quality.
For each case of anode protection, the layout of the cathodes is designed individually.
In order to anode protection was effective for a certain object, it is necessary that it meets some requirements:
All welds must be of high quality;
In the technological environment, the material from which the protected object is made must pass into a passive state;
The number of air pockets and slots should be kept to a minimum;
There should be no riveted joints on the structure;
In the device to be protected, the reference electrode and cathode must always be in solution.
To implement anode protection in the chemical industry, heat exchangers and cylindrical units are often used.
Electrochemical anode protection stainless steels applicable for industrial storage of sulfuric acid, ammonia-based solutions, mineral fertilizers, as well as all kinds of collections, tanks, mernikov.
Anode protection can also be used to prevent corrosion damage in chemical nickel plating baths, heat exchangers in the production of artificial fibers and sulfuric acid.
