Accidents of steam boilers associated with violation of the water regime, corrosion and metal erosion. Corrosion of steam boilers corrosion in boilers

Owners of the patent RU 2503747:

Technicia

The invention relates to thermal power and can be used to protect against scale heating pipes of steam and water boilers, heat exchangers, boiler plants, evaporators, heating parts, residential houses and industrial systems in the process of current operation.

BACKGROUND

Operation of steam boilers is associated with the simultaneous impact of high temperatures, pressure, mechanical stresses and an aggressive medium, which is boiler water. Boiler and metal surfaces of the boiler are separate phases of a complex system that is formed during their contact. The result of the interaction of these phases is superficial processes arising at the border of their partition. As a result, in the metal surfaces of heating, the phenomena of corrosion and the formation of scale are arising, which leads to a change in the structure and mechanical properties of the metal, and which contributes to the development of various damage. Since the thermal conductivity of the scale is fifty times lower than that of iron of heating pipes, there are a thermal energy loss during heat transfer - with a thickness of 1 mm from 7 to 12%, and at 3 mm - 25%. Strong formation of scale in the system of steam boiler of continuous action often leads to a stop of production for several days a year to remove scale.

The quality of nutrient and, therefore, the boiler water is determined by the presence of impurities that can cause various types of metal corrosion of the inner surfaces of heating, the formation of primary scale on them, as well as a sludge as a source of formation of secondary scale. In addition, the quality of the boiler water depends on the properties of substances resulting from surface phenomena during the transportation of water, and condensate through pipelines, in water processing processes. Removal of nutrient water impurities is one of the ways to prevent the formation of scale and corrosion and is carried out by the methods of preliminary (rot) water treatment, which are aimed at maximum removal of impurities in its original water. However, the methods used do not fully eliminate the content of impurities in water, which is associated not only with the difficulties of a technical nature, but also the economic feasibility of applying methods for water treatment. In addition, since water treatment is a complex technical system, it is redundant for boilers of small and medium performance.

Famous methods for removing already formed deposits are mainly used mechanical and chemical cleaning methods. The disadvantage of these methods is that they cannot be made during the operation of boilers. In addition, methods of chemical purification often require the use of expensive chemicals.

Also known ways to prevent the formation of scale and corrosion carried out during the work of the boilers.

The US 1877389 patent proposed a method for removing scale and prevent its formation in hot water and steam boilers. In this method, the surface of the boiler is a cathode, and the anode is placed inside the pipeline. The method is to pass a permanent or alternating current through the system. The authors note that the mechanism of action of the method is that under the action of electric current on the surface of the boiler, gas bubbles are formed, which lead to the detachment of the existing scale and prevent the formation of a new one. The disadvantage of this method is the need to constantly maintain the flow of electrical current in the system.

In Patent US 5667677, a method is proposed for processing fluid, in particular water, in the pipeline in order to slow down the scale of scale. This method is based on the creation of an electromagnetic field in the pipes, which repels the calcium ions dissolved in water, magnesium walls from the walls of pipes and equipment, not allowing them to crystallize in the form of scale, which allows to operate boilers, boilers, heat exchangers, rigid water cooling systems. The disadvantage of this method is the high cost and complexity of the equipment used.

In the application WO 2004016833, a method for reducing the formation of scale on a metal surface is proposed to exposed to an intersted alkaline aqueous solution, which is capable of forming a scale after a period of exposure, which includes the application of the cathode potential to the specified surface.

This method can be used in various technological processes in which the metal is in contact with an aqueous solution, in particular, in heat exchangers. The disadvantage of this method is that it does not protect the metal surface from corrosion after removing the cathode potential.

Thus, currently there is a need to develop an improved method for preventing the formation of scale of heating pipes, water-heating and steam boilers, which would be economical and highly efficient and provided anti-corrosion protection of the surface for a long period of time after exposure.

In the present invention, the specified problem is solved using the method according to which there is a current electric potential on a metal surface, sufficient to neutralize the electrostatic component of the adhesion of colloidal particles and ions to a metal surface.

Brief Description of the Invention

The objective of the present invention is to ensure an improved method for preventing the formation of water-heating and steam boilers.

Another objective of the present invention is to ensure the possibility of exclusion or a significant reduction in the need to remove scale during the operation of hot water and steam boilers.

Another object of the present invention is to eliminate the need to use flowable reagents to prevent the formation of scale and corrosion of heating pipes of water-heating and steam boilers.

Another object of the present invention is to ensure the possibility of starting work to prevent the formation of scale and corrosion of heating pipes of hot water and steam boilers on the contaminated pipes of the boiler.

The present invention relates to a method for preventing the formation of scale and corrosion on a metal surface made of iron-containing alloy and in contact with a steam room, which is capable of forming. The specified method is an annex to the specified metal surface of the current electric potential sufficient to neutralize the electrostatic component of the adhesion force of colloidal particles and ions to the metallic surface.

According to some particular embodiments of the claimed method, the current potential is set within 61-150 V. According to some particular embodiments of the claimed method, the above-mentioned iron-containing alloy is steel. In some embodiments, the metallic surface is the inner surface of the heating pipes of the hot water or steam boiler.

The method disclosed in this specification has the following advantages. One advantage of the method is the reduced formation of scale. Another advantage of the present invention is the ability to use once a purchased operating electrophysical apparatus without the need to use consumables synthetic reagents. Another advantage is the possibility of starting work on the contaminated tubes of the boiler.

The technical result of the present invention, therefore, is to increase the efficiency of water and steam boilers, increased productivity, increase the efficiency of heat transfer, reduced fuel consumption for boiler heating, energy savings, etc.

Other technical results and advantages of the present invention include ensuring the possibility of layer-by-layer destruction and removal of the already formed scale, as well as to prevent its new education.

Brief description of the drawings

Figure 1 shows the nature of the distribution of deposits on the inner surfaces of the boiler as a result of the use of the method according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The method according to the present invention is an annex to a metal surface, subject to the formation of scale, a current electric potential for neutralizing the electrostatic component of the adhesion of colloidal particles and ions forming a scale to a metal surface.

The term "current electric potential" in the sense, in which it is used in this application, means an alternating potential that neutralizing the double electric layer on the metal boundary and a steam room containing salts leading to the formation of scale.

As is known to a person skilled in the art, the electrical charge carriers in the metal, slow compared to the main charge carriers of the electron, are the dislocations of its crystal structure, which carry an electric charge and form dislocation currents. Going to the surface of the heating pipes of the boiler, these currents are part of the double electric layer during the formation of scale. The current, electric, pulsating (i.e., variable), the potential initiates the displacement of the electrical charge of dislocations from the metal surface to the ground. In this respect, it is current dislocation currents. As a result of this current electric potential, the double electric layer is destroyed, and the scale gradually decays and goes into boiler water in the form of a sludge that is removed from the boiler during its periodic purges.

Thus, the term "current potential" is understandable for a person skilled in the art and, in addition, known from the prior art (see, for example, patent RU 2128804 C1).

As a device for creating a current electric potential, for example, a device described in RU 2100492 C1 can be used, which includes a converter with a frequency converter and a pulsating potential regulator, as well as an impulse form controller. A detailed description of this device is given in RU 2100492 C1. Any other similar device can also be used, as will be understood by a person skilled in the art.

The current electric potential according to the present invention can be applied to any part of the metal surface removed from the base of the boiler. The place of the application is determined by the convenience and / or efficiency of the application of the claimed method. The specialist in this field of technology, using the information disclosed in the present description, and using standard test techniques, will be able to determine the optimal place of the current electric potential.

In some embodiments of the present invention, the electric potential is variable.

The current electric potential according to the present invention can be applied during various periods of time. The time of the capacity of the potential is determined by the nature and degree of pollution of the metal surface, the composition of the water used, the temperature regime, and the peculiarities of the heat engineering device and other factors known to those skilled in the art. The specialist in this field of technology, using the information disclosed in the present description and using standard test techniques, will be able to determine the optimal time of the current electric potential application, based on the purposes, the conditions and state of the heat engineering device.

The magnitude of the current potential required to neutralize the electrostatic component of the adhesion force can be determined by a colloidal chemistry specialist on the basis of information known from the prior art, for example, from the book by Dryagin B.V., Churaev N.V., Muller V.M. "Surface forces", Moscow, Science, 1985. According to some embodiments, the value of the current electric potential is in the range of 10 V to 200 V, more preferably from 60 V to 150 V, even more preferably from 61 V to 150 V. The values \u200b\u200bof the current electric potential in the range from 61 V to 150 V lead to the discharge of a double electric layer, which is the basis of the electrostatic component of the adhesion forces in scale and, as a result, the destruction of scale. The values \u200b\u200bof the current potential are lower than 61 V are insufficient for the destruction of the scale, and with the values \u200b\u200bof the current potential above 150 V is likely the beginning of the unwanted electroerosion destruction of the metal of heating tubes.

The metal surface to which the method according to the present invention can be used can be part of the following heat engineering devices: heating pipes of steam and hot water boilers, heat exchangers, boiler plants, evaporators, heating parts, residential houses and industrial objects in the process of current operation. This list is illustrative and does not limit the list of devices to which the method according to the present invention can be applied.

In some embodiments, the iron-containing alloy from which the metal surface is made to which the method according to the present invention can be applied, may be steel or other iron-containing material, such as cast iron, cowar, fahehral, \u200b\u200btransformer steel, Altern, Magnichene, Alnico, Chromium steel, Invar, etc. This list is illustrative and does not limit the list of iron-containing alloys to which the method according to the present invention can be applied. A specialist in the art on the basis of information known from the prior art will be able to such iron-containing alloys that can be used according to the present invention.

An aqueous medium from which scale is capable of forming, according to some embodiments of the present invention, is a tap water. The aqueous medium can also be water containing dissolved metals compounds. Dissolved metals compounds may be compounds of iron and / or alkaline earth metals. The aqueous medium can also be an aqueous suspension of colloidal particles of iron compounds and / or alkaline earth metals.

The method according to the present invention removes previously formed sediments and serves as an unhappy means of purifying internal surfaces during the operation of the heat engineering device, in the future the non-free mode of its operation. At the same time, the size of the zone, within which the prevention of the formation of scale and corrosion is achieved, significantly exceeds the size of the zone of effective destruction of scale.

The method according to the present invention has the following advantages:

Does not require the use of reagents, i.e. environmentally safe;

Easy to implement, does not require special devices;

Allows you to increase the coefficient of heat transfer and increase the efficiency of the boilers, which significantly affects the economic performance of its work;

It can be used as an addition to the methods used by the methods of water treatment and separately;

It allows you to abandon the processes of softening and deaeration of water, which largely simplifies the technological scheme of boiler rooms and makes it possible to significantly reduce costs during construction and operation.

Possible objects of the method can be water-heating boilers, boilers - utilizers, closed heat supply systems, installation of thermal destruction of seawater, steam mills, and so on.

The absence of corrosion destruction, scale formation on the inner surfaces opens up the ability to develop fundamentally new design and layout solutions of the steam boilers of small and medium power. This will allow, due to the intensification of thermal processes, to achieve a significant reduction in the mass and dimensions of steam boilers. Provide a given temperature level of heating surfaces and, therefore, reduce fuel consumption, flue gases and reduce their emissions into the atmosphere.

Example implementation

The method declared in the present invention was tested at the Admiraltey shipyard boiler plants and the Red Chemist. It was shown that the method according to the present invention effectively purifies the inner surfaces of the boilers from deposits. During these works, conventional fuel economy was obtained 3-10%, while the scatter of saving values \u200b\u200bis associated with varying degrees of contamination of the internal surfaces of the boilers. The aim of the work was to evaluate the effectiveness of the stated method to ensure a non-repetitive, non-valuable mode of operation of the vapor boiler aircraft in the conditions of high-quality water treatment, respect for the water-chemical regime and the high professional level of operation of the equipment.

The test of the method declared in the present invention was carried out on a steam boiler number 3 of DCVR 20/13 of the 4th Krasnoselskaya boiler house of the South-Western branch of the State Unitary Enterprise "TEK St. Petersburg". The operation of the boiler unit was carried out in strict accordance with the requirements of regulatory documents. On the boiler there are all necessary means of controlling the parameters of its operation (pressure and consumption of the produced steam, temperature and feed water, the pressure of blowing air and fuel on the burners, discharge in the basic sections of the gas path of the boiler unit). Steam performance boiler was maintained at 18 t / h, steam pressure in the boiler drum - 8.1 ... 8.3 kg / cm 2. Economizer worked in the heat mode. Water of urban water supply was used as the starting water, which corresponded to the requirements of GOST 2874-82 "Drinking water". It should be noted that the number of iron compounds at the input to the specified boiler room, as a rule, exceeds the regulatory requirements (0.3 mg / l) and is 0.3-0.5 mg / l, which leads to intensive ingrowth of the inner surfaces by ferrous compounds.

Evaluation of the effectiveness of the method was carried out at the state of the internal surfaces of the boiler.

Evaluation of the effect of the method according to the present invention on the state of the internal surfaces of the heating of the boiler unit.

Prior to the start of the test, an internal inspection of the boiler unit was performed and the initial state of the internal surfaces was recorded. The preliminary inspection of the boiler was produced at the beginning of the heating season, a month after its chemical cleaning. As a result of the inspection, it was revealed: on the surface of the drums, solid solid dark brown sediments with paramagnetic properties and consisting, presumably, from iron oxides. The thickness of the deposits was up to 0.4 mm visually. In the visible part of boiling pipes, preferably on the side of the furnace addressed to the furnace, are not solid solid sediments (up to five spots per 100 mm of pipe length with a size of from 2 to 15 mm and a thickness of up to 0.5 mm visually).

The device for creating a current potential described in RU 2100492 C1 was attached at a point (1) to the hatch (2) of the upper drum from the back side of the boiler (see figure 1). The current electric potential was equal to 100 V. The current electric potential was maintained continuously for 1.5 months. At the end of this period, an autopsy of the boiler was made. As a result of the internal examination of the boiler unit, almost complete lack of deposits (not more than 0.1 mm visually) on the surface (3) of the upper and lower drums in the range of 2-2.5 meters (zone (4)) from the drums of the drums (device attachment points To create a current potential (1)). At the removal of 2.5-3.0 m (zone (5)) from deposit luchkov (6), preserved in the form of separate tuberculos (spots) with a thickness of up to 0.3 mm (see figure 1). Further, as it moves to the front, (at a distance of 3.0-3.5 m from the hatches), continuous sediments begin (7) to 0.4 mm visually, i.e. On this distance from the connection point of the device, the effect of a cleaning method according to the present invention practically did not appear. The current electric potential was equal to 100 V. The current electric potential was maintained continuously for 1.5 months. At the end of this period, an autopsy of the boiler was made. As a result of the internal examination of the boiler unit, almost complete lack of deposits (no more than 0.1 mm visually) on the surface of the upper and lower drums within 2-2.5 meters from the drum luchkov (device attachment points to create a current potential) were established. At the removal of 2.5-3.0 m from the hatching of the deposition, in the form of separate tubercles (spots) with a thickness of up to 0.3 mm (see FIG. 1). Next, as we move to the front (at a distance of 3.0-3.5 m from the hatch), continuous deposits begin to 0.4 mm visually, i.e. On this distance from the connection point of the device, the effect of a cleaning method according to the present invention practically did not appear.

In the visible portion of boiling pipes, within 3.5-4.0 m from the drums, there was almost a complete absence of deposits. Next, as it moves to the front, there are not solid solid sediments (up to five spots per 100 pm with a size of from 2 to 15 mm and a thickness of up to 0.5 mm visually).

As a result of this test stage, it was concluded that the method according to the present invention without the use of any reagents makes it possible to effectively destroy previously formed deposits and provides a non-free operation of the boiler.

At the next stage, the test device for creating a current potential was attached at the point "B" and the tests continued for another 30-45 days.

Another opening of the boiler unit was produced after 3.5 months of continuous operation of the device.

An inspection of the boiler unit showed that the remaining sediments were completely destroyed and only in minor quantities were preserved in the lower sections of boiling pipes.

This made it possible to draw the following conclusions:

The size of the zone, within the limits of which the boiler's non-free operation is ensured, significantly exceed the size of the zone of effective destruction of deposits, which allows the subsequent transfer of the point of connection of the current potential to clean the entire inner surface of the boiler unit and further maintain the non-free mode of its operation;

The destruction of previously formed deposits and the prevention of education is provided by various processes in nature.

According to the results of the inspection, it was decided to continue testing until the end of the heating period in order to final purification of drums and boiling pipes and clarify the reliability of providing a non-free operation of the boiler. Another opening of the boiler unit was produced in 210 days.

The results of the internal inspection of the boiler showed that the process of cleaning the internal surfaces of the boiler within the upper and lower drums and boiling pipes ended with almost complete deletion of deposits. On the entire surface of the metal, a thin dense coating was formed, having a black color with blue party, the thickness of which is even in the moistened state (almost immediately after opening the boiler) did not exceed 0.1 mm visually.

At the same time, the reliability of providing a non-free operation of the boiler unit was confirmed when using the method of the present invention.

The protective effect of the magnetite film was preserved up to 2 months after disconnecting the device, which is enough to ensure the conservation of the boiler unit with a dry way when it is transferred to the reserve or for repair.

Although the present invention has been described in relation to various specific examples and embodiments of the invention, it should be understood that this invention is not limited to them and that it can be implemented in practice within the scope of the claim below

1. A method of preventing the formation of scale on a metal surface made of iron-containing alloy and is in contact with a steam room from which a scale is capable of forming an application to the specified metal surface of the current electric potential in the range from 61 V to 150 V to neutralize the electrostatic component of force Adhesion between the specified metal surface and colloidal particles and ions forming the scale.

The invention relates to thermal power and can be used to protect against scale and corrosion of heating pipes of steam and water boilers, heat exchangers, boiler installations, evaporators, heating parts, residential house heating systems and industrial objects during operation. The method of preventing the formation of scale on a metal surface made of iron-containing alloy and is in contact with a steam room from which scale is capable of forming the application to the specified metal surface of the current electric potential in the range from 61 V to 150 V to neutralize the electrostatic component of the adhesion force between The specified metal surface and colloidal particles and ions that form scale. The technical result is to improve the efficiency and productivity of the operation of hot water and steam boilers, an increase in the efficiency of heat transfer, ensuring layer-by-layer destruction and removal of the resulting scale, as well as the prevention of its new education. 2 Z.P. F-lies, 1 pr., 1 yl.

a) oxygen corrosion

Most often, steel water economizers of boiler aggregates suffer from oxygen corrosion, which, with unsatisfactory deaeration, nutritious water fail out of 2-3 years after installation.

The immediate result of oxygen corrosion of steel economizers is the formation of fistulars in tubes, through which water flows at high speed. Such jets aimed at the wall of the neighboring pipe are able to wear it up to the formation of through holes. Since the economizer pipes are located quite compactly, which the resulting corrosion fistula is able to cause massive damage to pipes if the boiler unit remains for a long time in working with a fistula that appears. Cast-iron economizers of oxygen corrosion are not damaged.

Oxygen corrosion Economic sectors are often exposed. However, with a significant concentration of oxygen in nutrient water, it penetrates into the boiler unit. Here, oxygen corrosion is mainly subjected to drums and squeezed pipes. The main form of oxygen corrosion is the formation of in-depth metal (ulcers), leading to their development to the formation of fistulas.

An increase in pressure intensifies oxygen corrosion. Therefore, for boiler aggregates with a pressure of 40 Ata and above, even the "spocks" of oxygen in deaerators are dangerous. An essential value is the composition of water from which the metal comes into contact. The presence of a small amount of alkali enhances the localization of corrosion, the presence of chlorides disperses it over the surface.

b) parking corrosion

Boiler units that are in simple are affected by the electrochemical corrosion, which was called the parking. Under the operating conditions, boiler aggregates are often removed from work and put on a reserve or stop for a long time.

When you stop the boiler unit to reserve, the pressure in it begins to fall and in the drum there is a vacuum that causes the penetration of the air and the enrichment of the boiler water with oxygen. The latter creates conditions for the appearance of oxygen corrosion. Even if the water is completely removed from the boiler unit, the inner surface does not happen dry. The fluctuations in temperature and humidity of the air cause moisture condensation phenomenon from the atmosphere enclosed inside the boiler unit. The presence on the surface of the metal film enriched with oxygen access creates favorable conditions for the development of electrochemical corrosion. If there are deposits capable of dissolving in the moisture film, the intensity of corrosion increases in the inner surface of the boiler unit. Such phenomena may be observed, for example, in superheatters, which often suffer from parking corrosion.

If there are deposits capable of dissolving in the moisture film, the intensity of corrosion increases in the inner surface of the boiler unit. Such phenomena may be observed, for example, in superheatters, which often suffer from parking corrosion.

Therefore, when the boiler unit is derived from the work in a long-term simple, it is necessary to remove the existing flushing deposits.

Parking corrosion It may cause serious damage to boiler aggregates, if special measures will not be adopted. Her danger is also in the fact that the corrosion foci in the period of downtime continue to act in the process of work.

To protect boiler aggregates from parking corrosion produce their conservation.

c) intercrystalline corrosion

Intercrystalline corrosion It occurs in rivet seams and roller compounds of steam boiler units, which are washed off by boiler water. It is characterized by the appearance of cracks in metal, initially very thin, imperceptible to the eye, which develops, turn into large visible cracks. They pass between metal grains, why this corrosion is called an intercrystalline. The destruction of the metal at the same time occurs without deformation, so these destruction is called fragile.

Experience has been established that intercrystalline corrosion occurs only with the simultaneous presence of 3-conditions:

1) high tensile stresses in metal close to the yield strength.
2) looseness in rivet seams or roller connections.
3) aggressive properties of boiler water.

The absence of one of the listed conditions excludes the emergence of fragile destruction, which is used in practice to combat intercrystalline corrosion.

The aggressiveness of the boiler water is determined by the composition of the salts dissolved in it. The content of the caustic natra is important, which at high concentrations (5-10%) reacts with the metal. Such concentrations are achieved in non-rotating riveting seams and rolling compounds in which the boiler water is evaporated. That is why the presence of looseness may determine the appearance of fragile destruction under appropriate conditions. In addition, an important indicator of the aggressiveness of the boiler water is the relative alkalinity - a shry.

d) conducting conducting corrosion

Conductive corrosion called metal destruction as a result of chemical interaction with water vapor: ZFE + 4N20 \u003d FE304 + 4N2
The destruction of the metal becomes possible for carbon steels with increasing temperature of the pipe wall to 400 ° C.

Corrosion products are hydrogen gas and magnetite. Watering corrosion has both uniform and local (local) character. In the first case, a layer of corrosion products is formed on the metal surface. The local nature of corrosion has the type of ulcers, grooves, cracks.

The main cause of steam corrosion is the heating of the tube wall to the critical temperature at which the metal oxidation is accelerated by water. Therefore, the fight against steam corrosion is carried out by eliminating the causes of metal overheating.

Watering corrosion It is impossible to eliminate by some changes or improvement of the water-chemical mode of the boiler unit, since the causes of this corrosion are linked in the furnace and intracerene hydrodynamic processes, as well as operating conditions.

e) submissive corrosion

This type of corrosion occurs under the layer of sludge formed on the inner surface of the pipe of the boiler unit, due to the nutrition of the boiler is not sufficiently purified water.

Metal damage arising during submissive corrosion has a local (peptic) character and are usually located on the half-version of the pipe traveled to the furnace. The resulting ulcers have a look of shells with a diameter of up to 20 mm and more, filled with iron oxides that create "tubercles" under ulcers.

Corrosion of hot water boilers, heating systems, heat systems are much more common than in parokoness systems. In most cases, this provision is explained by the fact that when designing a water-heating system, less attention is paid, although the factors of education and subsequent development of corrosion in boilers remain exactly such as for steam boilers and all other equipment. Dissolved oxygen, which is not removed by the deaeration method, rigidity salts, carbon dioxide entering the water-heating boilers with nutrient water, cause various types of corrosion - alkaline (intercrystalline), oxygen, chelated, subwind. It must be said that chelate corrosion in most cases is formed in the presence of some chemical reagents, the so-called "complexons".

In order to prevent the occurrence of corrosion in the hot water boilers and its subsequent development, it is necessary to seriously and responsibly consider the preparation of the characteristics of water intended for feeding. It is necessary to ensure the binding of free carbon dioxide, oxygen, output the pH value to an acceptable level, take measures to protect against corrosion of aluminum, bronze and copper elements of heating equipment and boilers, pipelines and heat equipment.

Recently, special chemical reagents are used for high-quality correctional thermal networks, water boilers and other equipment.

Water at the same time is a universal solvent and inexpensive heat carrier, it is beneficial to be used in heating systems. But its insufficient preparation can lead to unpleasant consequences, one of which is corrosion of hot water boilers. Probable risks are primarily associated with the presence of a large number of unwanted impurities. It is possible to prevent the education and development of corrosion, but only if you clearly understand the reasons for its appearance, as well as to be familiar with modern technologies.

For hot water boilers, however, as for any heating systems using water as a coolant, three types of problems due to the presence of the following impurities are characteristic of:

• mechanical insoluble;
• sedimentary dissolved;
• corrosionactive.

Each of the species listed impurities can cause the formation of corrosion and failure of the water boiler or other equipment. In addition, they contribute to a decrease in the efficiency and productivity of the boiler.

And if for a long time to use water in heating systems in the heating systems, this may lead to serious consequences - breakage of circulation pumps, decrease in the diameter of the water pipeline and subsequent damage, failure of regulating and shut-off valves. The simplest mechanical impurities are clay, sand, ordinary dirt - are present almost everywhere, both in tap water and in artesian sources. Also in coolants in large quantities there are corrosion products of heat transfer surfaces, pipelines and other metal elements of the system that are constantly in contact with water. It is not worth it and say that their presence over time provokes very serious problems in the functioning of water boilers and all the heat and power equipment, which are mainly associated with corrosion of boilers, the formation of lime deposits, the damage to salts and the foaming of boiler water.

The most common reason, in connection with which arises corrosion of hot water boilers, these are carbonate sediments arising from the use of increased rigidity water, the removal of which is possible. It should be noted that as a result of the presence of stiffness salts, scale is formed even in low-temperature heating equipment. But this is not the only cause of corrosion. For example, after heating of water to a temperature of more than 130 degrees, the solubility of calcium sulfate is significantly reduced, as a result of which a layer of dense scale is formed. At the same time, the development of corrosion of metal surfaces of hot water boilers is inevitable.

For the first time, the outer corrosion of the screen pipes was found at two power plants in high-pressure boilers TP-230-2, who worked on the AC and sulfur coal and sulfur fuel oil and were in operation of about 4 years. The outer surface of the pipes was subjected to corrosion corrosion from the side facing the furnace in the zone of the maximum temperature of the torch. 88.

Mainly destroyed pipes of the middle (width) part of the furnace, directly above the incendiary. belt. Wide and relatively shallow corrosion ulcers had an irregular shape and often closed each other, as a result of which the damaged surface of the pipe was uneven, buggy. In the middle of the deepest ulcers, fistulas appeared, and through them jets of water and steam began to escape.

It was characteristic of the complete absence of such corrosion on the on-screen pipes of the average pressure boilers of these power plants, although medium pressure was there in operation significantly "for a longer time.

In subsequent years, the outer corrosion of the on-screen pipes appeared on other high-pressure boilers worked on solid fuel. The zone of corrosion destruction spread sometimes at a considerable height; In some places, the thickness of the pipe walls as a result of corrosion decreased to 2-3 mm. It was also observed that this corrosion is practically absent in high-pressure boilers working on fuel oil.

The outer corrosion of the on-screen pipes was found in the boilers of TP-240-1 after 4 years of operation working at a pressure of 185 at the drums. In these boilers, the suburbs of brown coal, having humidity of about 30%; The fuel oil was burned only during crossing. These boilers have corrosion destruction also arose in the zone of the highest heat load of the screen pipes. The peculiarity of the corrosion process was that the pipes were destroyed both from the side facing the furnace and from the side facing the smelting (Fig. 62).

These facts show that the corrosion of the on-screen pipes depends primarily on the temperature of their surface. In the mid-pressure boilers, water evaporates at a temperature of about 240 ° C; In boilers, calculated on the pressure of 110 AT, the estimated boiling point of water is 317 ° C; In TP-240-1 boilers, water boils at a temperature of 358 ° C. The temperature of the outer surface of the screen pipes usually exceeds the boiling point of about 30-40 ° C.

Can. Assuming that intensive outer corrosion of the metal begins with an increase in its temperature to 350 ° C. In the boilers designed for pressure 110 AT, this temperature is achieved only with the firing side of the pipes, and in boilers having a pressure of 185 AT, it corresponds to water temperature in pipes . That is why the corrosion of the on-screen pipes by the clutch was observed only in these boilers.

A detailed study of the issue was produced at TP-230-2 boilers working on one of the above-mentioned power plants. There were taken samples of gases and hot

A torch particles from a torch at a distance of about 25 mm from the on-screen pipes. Near the front screen in the zone of intense outer corrosion of pipes, the furnace gases almost did not contain free oxygen. Near the rear screen, in which the outer corrosion of the pipes was almost absent, free oxygen in the gases was significantly more. In addition, the test showed that in the area of \u200b\u200bcorrosion education, more than 70% of the samples of gases

It is possible to "assume that in the presence of excess oxygen, hydrogen sulfide burns and corrosion does not occur, but in the absence of excess oxygen, hydrogen sulfide enters into a chemical connection with the metal of the pipes. At the same time, iron sulfide FES is formed. This corrosion product was indeed found in sediments on screen pipes.

Outdoor corrosion is subject not only carbon steel, but also chromolibdden. In particular, in boilers TP-240-1 corrosion struck onto the on-screen pipes made of steel brands 15xm.

There are still no proven activities for a complete prevention of the described type of corrosion. Some decrease in the speed of destruction. Metal was achieved. After adjusting the combustion process, in particular with an increase in the excess air in the furnace gases.

27. Corrosion of screens for ultrahigh pressure

In this book, briefly described on the conditions of metal of steam boilers of modern power plants. But the progress of energy in the USSR continues, and now a large number of new boilers are built, designed for higher pressure and pair temperature. Under these conditions, the practical experience of operation of several TP-240-1 boilers operating from 1953-1955 is of great importance. With a pressure of 175 at (185 AT in the drum). Very valuable,\u003e in particular, information about corrosion of their screens.

The screens of these boilers were subject to corrosion both with outdoor and inner side. Their external corrosion is described in the previous paragraph of this chapter, the destruction of the inner surface of the pipes does not seem to be one of the types of metal corrosion described above

The corrosion occurred mainly from the fire side of the upper part of the inclined pipes of the cold funnel and was accompanied by the appearance of corrosion sinks (Fig. 63, a). In the future, the number of such shells increased, and a solid strip occurred (sometimes two parallel. Bands) of the metal (Fig. 63,6). The absence of corrosion in the welded joint zone was also characteristic.

Inside the pipes there was a flip of loose sludge with a thickness of 0.1-0.2 mm, which consisted mainly of iron and copper oxides. The increase in the corrosion destruction of the metal was not accompanied by an increase in the thickness of the sludge layer, therefore, corrosion under the layer of the sludge was not the main cause of corrosion of the inner surface of the on-screen pipes.

In boiler water, a clean-phosphate alkalinity mode was maintained. Phosphates were introduced into the boiler is not. It is not possible, and periodically.

The fact that the temperature of the metal pipe temperature is periodically sharply, and sometimes it was above 600 ° C (Fig. 64). The zone of the most frequent and maximum temperature increase coincided with the zone of the greatest destruction of the metal. Reducing the pressure in the boiler up to 140-165 AT (i.e., before the pressure in which new serial boilers operate) did not change the nature of the temporary increase in the temperature of the pipes, but was accompanied by a significant decrease in the maximum value of this temperature. The reasons for such a periodic increase in the temperature of the fire side of the inclined pipes are cold. The funnels have not been studied in detail.

This book discusses specific issues related to the work of steel parts of the steam boiler. But to study these purely practical issues, it is necessary to know the general information relating to the structure of steel and its "properties. In the schemes showing the structure of metals, atoms are sometimes depicted in the form of contacts in contact with each other (Fig. 1). Such schemes show the alignment of atoms in the metal But it is difficult to clearly show the location of the atoms relative to each other. Erosion is the gradual destruction of the metal surface layer under the influence of mechanical exposure. The most common type of erosion of steel elements - a steam boiler is their abrasion of solid ash particles moving along with smoke gases. With long abrasion, there is a gradual decrease in the thickness of the walls of pipes, and then their deformation and gap under the action of internal pressure.

A number of boilers use river and tap water with low pH and low rigidity to feed thermal networks. Additional river water treatment on a tap station usually leads to a decrease in the PN, a decrease in alkalinity and an increase in aggressive carbon dioxide. The appearance of aggressive carbon dioxide is also possible in the connection schemes used for large heat supply systems with direct hot water waterborne (2000h3000 t / h). Water softening according to the Na-cation scheme increases its aggressiveness due to the removal of natural corrosion inhibitors - stiffery salts.

With a poorly established deaeration of water and possible increasing concentrations of oxygen and carbon dioxide due to the lack of additional protective measures in the heat supply systems of the internal corrosion, Heatinglery equipment of the CHP.

During the examination of the feed tract by one of the CHP of Leningrad, the following data was obtained by corrosion velocity, g / (m2 · 4):

Corrosion Indicator Installation Place

In the pipeline of the feeding water after heaters of the heating system before the deaerators of the pipe with a thickness of 7 mm climbed over the year of operation in places up to 1 mm in some sections, through fistulas were formed.

The causes of ulcerative corrosion of water boilers are as follows:

insufficient removal of oxygen from feeding water;

low pH value due to the presence of aggressive carbon dioxide

(up to 10h15 mg / l);

the accumulation of products of oxygen corrosion of iron (Fe2O3;) on heat transfer surfaces.

Operation of equipment on network water with iron concentration Over 600 μg / l usually leads to the fact that several thousand hours of operation of hot water boilers are observed intensive (over 1000 g / m2) by iron-oxide deposits of their heating surfaces. At the same time, often emerging leaks in the pipes of the convective part are noted. In the composition of deposits, the content of iron oxides usually reaches 80ch90%.

Especially important for the operation of hot water boilers are starting periods. In the initial period of operation on one CHP, the removal of oxygen was not ensured to the norms installed by the PTE. The content of oxygen in the feed water exceeded these norms 10 times.

The concentration of iron in the feeding water reached - 1000 μg / l, and in the reverse water of the heating network - 3500 μg / l. After the first year of operation, cutting from pipelines of the network water were made, it turned out that the contamination of their surface with corrosion products was over 2000 g / m2.

It should be noted that on this CHP, before turning on the boiler, the internal surfaces of the on-screen pipes and the pipes of the convective beam were subjected to chemical cleaning. By the time the screening of samples of the on-screen pipes, the boiler worked 5300 hours. The sample of the on-screen pipe had an uneven layer of yellow-pointed sediments of black and brown color, firmly related to the metal; The height of the tubercles 10h12 mm; Specific contamination 2303 g / m2.

The composition of deposits,%

The surface of the metal under the layer of deposits was amazed by ulcers with a depth of 1 mm. A convective beam tubes from the inside were brought by deposits of iron oxide type of black and brown color with a height of tubercles up to 3h4 mm. The surface of the metal under deposits is covered with ulcers of various sizes with a depth of 0.3 h1.2 and a diameter of 0.35h0.5 mm. Separate tubes had through holes (fistulas).

When the water-heating boilers are installed in the old systems of centralized heat supply, in which a significant amount of iron oxides have accumulated, there are cases of depositing these oxides in the heated boiler pipes. Before turning on the boilers, it is necessary to make a thorough flushing of the entire system.

A number of researchers recognize an important role in the occurrence of submissive corrosion of the rusting process of water boilers under their downtime, when not taken proper measures to prevent parking corrosion. Corrosion foci arising from atmospheric air to the wet surfaces of the boilers continue to function when the boilers are working.