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.

In ship vapor boilers, corrosion can proceed both on the part of the steam conduit and the fuel combustion products.

The internal surfaces of the steam conduction circuit may be subject to the following types of corrosion;

Oxygen corrosion is the most dangerous type of corrosion. A characteristic feature of oxygen corrosion is the formation of local dotted foci of corrosion, reaching deep yazvin and through holes; The input sections of economizers, collectors and hydrochloride circulation pipes are most susceptible to oxygen corrosion.

Nitritic corrosion - in contrast to oxygen affects the inner surfaces of the heat-stressed lifting tubes and causes the formation of deeper yazvin with a diameter of 15 ^ 20 mm.

Intercrystalline corrosion is a special type of corrosion and occurs in places of the highest metal stresses (welds, roller and flange compounds) as a result of the interaction of the boiler metal with a highly concentrated alkali. A characteristic feature is the appearance on the surface of the metal grid made of small cracks, gradually developing into through cracks;

Underlands corrosion occurs in the deposits of the sludge and in the stagnation zones of circulating circulation of boilers. The process of leakage is electrochemical character at the contact of iron oxides with metal.

On the part of the fuel combustion products, the following types of corrosion may be observed;

Gas corrosion strikes evaporative, overheating and economizer heating surfaces, skin trimming,

Gas-controlling shields and other elements of the boiler exposed to high temperatures of gases .. With an increase in the metal temperature of boiler pipes over 530 ° C (for carbon steel), the destruction of the protective oxide film on the surface of the pipes is beginning, providing unimpeded oxygen access to clean metal. At the same time, corrosion occurs on the surface of the pipes with the formation of scale.

The immediate cause of this type of corrosion is the violation of the cooling mode of the specified elements and increase their temperature above the permissible. For pipes of heating surfaces by reasons RichThe temperature of the walls can be; The formation of a significant layer of scale, violation of the circulation regime (stagnation, tipping, the formation of steam plugs), the omission of water from the boiler, the unevenness of the water distribution and the selection of steam along the length of the steam collector.

High-temperature (vanadium) corrosion affects the surface of heating steamers located in the high temperature zone of gases. When burning fuel, vanadium oxides occurs. At the same time, with a lack of oxygen, vanadium trioxide is formed, and with its excessive - vanadium five-pointed. The corrosion-hazardous is pentolar vanadium U205, having a melting point of 675 0s. The pentoral vanadium, released when combing fuel oil, sticks on the heating surface having a high temperature, and causes active destruction of the metal. Experiments have shown that even the contents of vanadium, as 0.005% by weight composition can cause dangerous corrosion.

Vanadium corrosion can be prevented by a decrease in the permissible metal temperature of the boiler elements and the combustion organization with minimal coefficients of excess air A \u003d 1.03 + 1.04.

Low-temperature (acid) corrosion affects mainly tail heating surfaces. In the combustion products of sulfurous fuel oil, there are always pairs of water and sulfur compounds that form sulfuric acid when connected with each other. When the gases are washed with respect to cold caudal surfaces, the heating pair of sulfuric acid condenses on them and cause metal corrosion. The intensity of low-temperature corrosion depends on the concentration of sulfuric acid in the moisture film settling on the heating surfaces. In this case, the concentration of b03 in combustion products is determined not only by the content of sulfur in the fuel. The main factors affecting the rate of low-temperature corrosion proceedings are;

Conditions of burning reaction in the furnace. With an increase in the excess air coefficient, the percentage of gas B03 increases (with a \u003d 1.15, 3.6% of the sulfur is oxidized, contained in the fuel; at a \u003d 1.7, about 7% sulfur oxidizes). In coefficients of excess air a \u003d 1.03 - 1.04, the b03 sulfuric anhydride is practically not formed;

Condition of heating surfaces;

The power supply of the boiler is too cold water, causing a decrease in the temperature of the walls of the economyzer pipe below the dew toy for sulfuric acid;

Concentration of water in fuel; When burning flooded fuels, the dew point increases due to an increase in the partial pressure of water vapor in combustion products.

Parking corrosion strikes the outer surfaces of the pipes and collectors, the trim, flue devices, fittings and other elements of the gas-air path of the boiler. The soot formed during fuel combustion covers the heating surfaces and the inner parts of the gas-air path of the boiler. Sort hygroscopic, and when cooled boiler, it easily absorbs moisture, causing corrosion. Corrosion is peptic in the formation of a sulfuric acid solution on the surface of a metal when the boiler is cooled and decrease its temperature of its elements below the dew point for sulfuric acid.

The struggle with parking corrosion is based on the creation of conditions that exclude moisture from entering the surface of the boiler metal, as well as applying anticorrosive coatings on the surface of the elements of the boilers.

With short-term inactivity of boilers after inspection and cleaning the surfaces of heating in order to prevent atmospheric precipitation in the gas pipes of boilers on the smoke pipe, it is necessary to wear a cover, close air registers, viewing holes. It is necessary to constantly control the humidity and temperature in MCO.

To prevent corrosion of boilers during inactivity, various ways of storing boilers are used. Distinguish two ways to store; Wet and dry.

The main way to store boilers is wet storage. It provides for the complete filling of the boiler with nutrient water skipped through electron-ion exchange and adhesive filters, including the steamer and economizer. Keep boilers on wet storage can not more than 30 days. In the case of a longer idle of boilers, dry storage of the boiler is used.

Dry storage provides for a complete drainage of the boiler from water with an accommodation in the collectors of the boilers of the bump bags with a Selikhalia absorbing moisture. Periodically, the collectors are operated, the control measurement of the Selika gel mass in order to determine the mass of the absorbed moisture, and evaporating the absorbed moisture from the Selikahel.

Ministry of Energy and Electrification of the USSR

Main Science and Technology Energy and Electrification

Methodical instructions
For warning
Low-temperature
Corrosion surfaces
Heating and gas pipes boilers

RD 34.26.105-84

Soyucehenergo

Moscow 1986.

Developed by the All-Union Twice Order of the Labor Red Banner Teply Engineering Research Institute named after F.E. Dzerzhinsky

Artists R.A. Petrosyan, I.I. Nadyrov

Approved by the Main Technical Operation Manual Energy Systems 22.04.84

Deputy Head of D.Ya. Shamarakov

Methodical guidelines for the prevention of low-temperature corrosion of heat and gas supplies of boilers

RD 34.26.105-84

The validity period is set
from 01.07.85
until 01.07.2005

These guidelines are applied to low-temperature surfaces of the heating of steam and hot water boilers (economizers, gas evaporators, air heaters of various types, etc.), as well as the gas tract for air heaters (gas ducts, ashors, smokers, flue pipes) and set surface protection methods Heating from low-temperature corrosion.

Methodical instructions are designed for thermal power plants operating on sulfur fuels, and organizations that design boiler equipment.

1. Low-temperature corrosion is the corrosion of the tail surfaces of heating, gas ducts and chimneys of boilers under the action of sulfuric acid vapors condensing on them.

2. Condensation of sulfuric acid vapors, the volumetric content of which in flue gases when burning sulfur fuels is only a few thousandths of the percentage, occurs at temperatures, significantly (by 50 - 100 ° C) exceeding the temperature of the condensation of water vapor.

4. To prevent corrosion of heating surfaces during operation, the temperature of their walls should exceed the temperature point of the flue gases at all loads of the boiler.

For the heating surfaces cooled with a high heat transfer coefficient (economizers, gas evaporators, etc.), the temperature of the medium at the inlet in them should exceed the temperature of the dew point by about 10 ° C.

5. For the surfaces of heating the water boilers when working on a sulfur fuel oil, the conditions for the complete exception of low-temperature corrosion cannot be implemented. To reduce it, it is necessary to ensure the temperature of the water at the inlet to the boiler, equal to 105 - 110 ° C. When using water boilers as peaks, such a mode can be provided with the full use of network water heaters. When using water boilers in the main mode, an increase in water temperature at the inlet to the boiler can be achieved by recycling hot water.

In the installations using the scheme for the inclusion of water heating boilers in the heat carrier through water heat exchangers, the conditions for the reduction of low-temperature corrosion of the heating surfaces are fully ensured.

6. For aircraft heaters of steam boilers, the complete elimination of low-temperature corrosion is provided at the calculated wall temperature of the coldest area greater than the temperature of the dew point at all loads of the boiler by 5 - 10 ° C (the minimum value refers to the minimum load).

7. Calculation of the temperature of the wall of tubular (TVP) and regenerative (RWP) air heater is carried out on the recommendations of the "thermal calculation of boiler aggregates. Regulatory method "(M.: Energy, 1973).

8. When used in tubular air heaters as the first (by air) the movement of the changeable cold cubes or cubes from pipes with an acidic coating (enamelled, etc.), as well as made of corrosion-resistant materials to the conditions of complete exception of low-temperature corrosion, the following are checked for them (by air) Metal cubes air heater. In this case, the selection of the temperature of the cold metal cubes changeable, as well as corrosion-resistant cubes, should exclude intensive contamination of pipes, for which their minimal temperature of the wall when burning sulfur fuel oils should be lower than the dew point of flue gases by no more than 30 to 40 ° C. When burning solid sulfur fuels, the minimum temperature of the pipe wall under the conditions of the warning of intensive contamination should be taken at least 80 ° C.

9. In RVP, on the conditions of complete exception of low-temperature corrosion, their hot part is calculated. The cold part of the RVP is performed by corrosion-resistant (enameled, ceramic, from low-alloyed steel, etc.) or replaced from flat metal sheets with a thickness of 1.0 - 1.2 mm made of small-carbon steel. The conditions for preventing intensive packing pollution are complied with the requirements of claim. Of this document.

10. As an enameled, a filling of metal sheets with a thickness of 0.6 mm is applied. The service life of the enameled package made in accordance with TU 34-38-10336-89 is 4 years.

Porcelain tubes, ceramic blocks, or porcelain plates with protrusions can be used as ceramic packing.

Given the reduction in the consumption of fuel oil with thermal power plants, it is advisable to apply for the cold part of the RWP, a package of low-alloyed steel 10Hord or 10xst, the corrosion resistance of which is 2- 2.5 times higher than that of small-carbon steel.

11. To protect air heaters from low-temperature corrosion in the starting period, measures set out in the "Guidelines for the design and operation of energy heating calorifications with wire fins" (M.: SPO Uniontehenergo, 1981).

The milling of the boiler on the sulfur fuel oil should be carried out with a pre-enabled air heating system. The air temperature in front of the air heater in the initial period of the extracts should usually be 90 ° C.

11a. To protect air heaters from low-temperature ("parking") corrosion on a stopped boiler, the level of which is about twice the rate of corrosion during operation, before stopping the boiler, it should be thoroughly clean the air heater from outdoor sediments. In this case, before stopping the boiler, the air temperature at the inlet into the air heater is recommended to maintain at the level of its value at the rated load of the boiler.

The cleaning of the TVP is carried out by a fraction with the density of its supply of at least 0.4 kg / pp (paragraph. Of this document).

For solid fuels, taking into account the significant hazard of the corrosion of the aspores, the temperature of the outgoing gases should be chosen above the dew point of the flue gases at 15 - 20 ° C.

For sulfur fuel oil, the temperature of the outgoing gases should exceed the temperature of the dew point at the rated load of the boiler by about 10 ° C.

Depending on the sulfur content in the fuel oil, the calculated value of the outgoing gases should be taken at the rated load of the boiler, indicated below:

The temperature of the outgoing gases, ºС ...... 140 150 160 165

When burning sulfur fuel oil with extremely small excess air (α ≤ 1.02), the temperature of the outgoing gases can be accepted lower taking into account the results of the dew point measurements. On average, the transition from small excess air to the maximum low reduces the temperature of the dew point by 15 to 20 ° C.

The conditions for ensuring reliable operation of the chimney and the prevention of moisture falling on its wall affects not only the temperature of the outgoing gases, but also their consumption. The work of the pipe with load modes is significantly lower than the project increases the likelihood of low-temperature corrosion.

When burning natural gas, the temperature of the outgoing gases is recommended to have no lower than 80 ° C.

13. With a decrease in the loading of the boiler in the range of 100 - 50% of the nominal one should strive to stabilize the temperature of the outgoing gases, not allowing its decline to more than 10 ° C from the nominal.

The most economical way to stabilize the temperature of the outgoing gases is to increase the temperature of the preheating of air in the carriers as the load decreases.

The minimum allowable values \u200b\u200bof the temperature preheating temperatures before RVP are accepted in accordance with clause 4.3.28 "Rules for the technical operation of electric stations and networks" (M.: Energoatomizdat, 1989).

In cases where the optimal temperature of the outgoing gases cannot be provided due to the insufficient surface of the RVP heating, the values \u200b\u200bof the preheating temperatures should be taken, at which the temperature of the outgoing gases does not exceed the values \u200b\u200bshown in these methodical instructions.

16. Due to the lack of reliable acid-resistant coatings to protect against low-temperature corrosion of metal gas ducts, their reliable operation can be achieved by careful insulation, ensuring the temperature difference between the flue gases and the wall of no more than 5 ° C.

At present, insulation materials and designs are not sufficiently reliable in long-term operation, therefore it is necessary to conduct periodic, at least once a year, control over their condition and, if necessary, carry out repair and restoration work.

17. When used in an experimental order to protect the gas ducts from low-temperature corrosion of various coatings, it should be borne in mind that the latter must provide heat resistance and gas content at temperatures exceeding the temperature of the outgoing gases at least 10 ° C, resistance to sulfuric acid concentration 50 - 80% In the temperature range, respectively, 60 - 150 ° C and the possibility of their repair and recovery.

18. For low-temperature surfaces, structural elements of RVP and boiler gas supplies, it is advisable to use low-alloyed steels of 10HNDP and 10XD, which are 2 - 2.5 times in corrosion resistance.

The absolute corrosion resistance is only very deficient and expensive high-alloy steel (for example, EI943 steel, containing up to 25% chromium and up to 30% nickel).

application

1. Theoretically, the temperature of the flue gas dew point with a predetermined content of sulfuric acid and water can be determined as a boiling point of a solution of sulfuric acid of such a concentration, at which there is the same content of water vapor and sulfuric acid.

The measured temperature point of the dew point depending on the measurement methodology may not be coincided with theoretical. In these recommendations for the temperature of the dew point of flue gases t R. The temperature of the surface of a standard glass sensor with apart at a distance of 7 mm is taken one from the other platinum electrodes with a length of 7 mm, at which the resistance of the dew film is the electrodes in the steady state equals10 7 ohm. In the measuring circuit of the electrodes, an alternating current of low voltage is used (6 - 12 V).

2. When burning sulfur fuel oils with excess air 3 - 5% temperature point of dew flue gases depends on the sulfur content in fuel S P. (Fig.).

When burning sulfur fuel oils with extremely low air excess (α ≤ 1.02), the temperature of the flue gases dew should be taken according to the results of special measurements. The conditions for the transfer of boilers in the mode with α ≤ 1.02 are set forth in the "Guidelines for the transfer of boilers operating on sulfur fuels, into combustion mode with extremely small excess airs" (M.: SPO SoyuceCenergo, 1980).

3. When burning sulfur solid fuels in the dust-shaped state temperature of the dew point of flue gases t P. It may be calculated according to the sulfur and ash content in the fuel S r Pr., A R PR and condensation temperature of water vapor t Kon. according to the formula

where a un - Share of ash in charge (usually received 0.85).

Fig. 1. The dependence of the temperature of the dew point of flue gases from the sulfur content in the combustion fuel oil

The value of the first term of this formula a un \u003d 0.85 can be determined in fig. .

Fig. 2. The difference in temperature points of the dew of flue gases and condensation of water vapor in them depending on the sulfur contents ( S r Pr.) and ash ( A R PR) In the fuel

4. When burning gaseous sulfur fuels, the dew point of flue gases can be determined in fig. Provided that the sulfur content in the gas is calculated as the above, that is, in a percentage by weight by 4186.8 kJ / kg (1000 kcal / kg) heat combustion of gas.

For gas fuel, the size of the sulfur content in percentage by weight can be determined by the formula

where m. - the number of sulfur atoms in the sulfur component molecule;

q. - bulk percentage of sulfur (sulfur component);

Q N. - heat combustion of gas in KJ / M 3 (kcal / nm 3);

FROM - coefficient equal to 4,187, if Q N. It is expressed in KJ / m 3 and 1.0, if in kcal / m 3.

5. The corrosion rate of the replaced metal packing of air heater during the combustion of the fuel oil depends on the temperature of the metal and the degree of corrosion activity of flue gases.

When burning sulfur fuel oil with an excess of air 3 - 5% and blend the surface of the corrosion (from two sides in mm / year), the RVP packing can be estimated according to Table. .

Table 1

Table 2 Up to 0.1. Contents in sulfur fuel oil S p,% Corrosion rate (mm / year) at the wall temperature, ° C 75 - 95 96 - 100 101 - 110 111 - 115 116 - 125 Less than 1.0 0,10 0,20 0,30 0,20 0,10 1 - 2 0,10 0,25 0,40 0,30 0,15 More than 2. 131 - 140 More than 140. Up to 0.1. 0,10 0,15 0,10 0,10 0,10 St. 0.11 to 0.4 incl. 0,10 0,20 0,10 0,15 0,10 St. 0.41 to 1.0 incl. 0,15 0,25 0,30 0,35 0,20 0,30 0,15 0,10 0,05 St. 0.11 to 0.4 incl. 0,20 0,40 0,25 0,15 0,10 St. 0.41 to 1.0 incl. 0,25 0,50 0,30 0,20 0,15 Over 1.0 0,30 0,60 0,35 0,25 0,15 6. For coal with a high content of calcium oxide, the dew point temperature is lower than those calculated according to claims of these methodical instructions. For such fuels, it is recommended to use the results of direct measurements.

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.

Low-temperature corrosion is subjected to surface heating of tubular and regenerative air heaters, low-temperature economizers, as well as metal gas ducts and chimneys at metal temperatures below the flue gas dew point. The source of low-temperature corrosion is SO 3 sulfuride, forming a seam-acid pair in flue gases, which is condensed at temperatures of the dew point of flue gases. Several thousandths of the percentage of SO 3 in gases are sufficient to cause metal corrosion at a speed greater than 1 mm / year. Low-temperature corrosion slows down when organizing a foil process with small excess airs, as well as when using additives to fuel and increasing the corrosion resistance of the metal.

High-temperature corrosion is subjected to eaves of drum and direct-flow boilers when burning solid fuels, steamers and their attachments, as well as the screens of the lower radiation part of the supercritical pressure boilers when combing sulfur fuel oil.

Corrosion of the inner surface of the pipes is a consequence of the interaction with the metal of oxygen gas and carbon dioxide gas) or salts (chlorides and sulfates) contained in boiler water. In modern boilers of supercritical pressure of steam, the content of gases and corrosionactive salts as a result of deep desalting of nutritious water and thermal deaeration is slight and the main cause of corrosion is the interaction of metal with water and steam. Corrosion of the inner surface of the pipes manifests itself in the formation of OSPIN, Yazvin, shells and cracks; The outer surface of damaged pipes may not differ from healthy.

Damage as a result of internal corrosion of pipes also include:
Oxygen parking corrosion affecting any sections of the inner surface of the pipes. The most intensively affected areas covered with water-soluble sediments (pipe steamers and the transition zone of the forwarding boilers);
submissive alkaline corrosion of boiling and on-screen pipes, occurring under the action of concentrated alkali due to evaporation of water under the layer of sludge;
Corrosion fatigue manifested in the form of cracks in boiling and screen pipes as a result of the simultaneous effect of the corrosion medium and variable thermal stresses.

Okalo is formed on pipes due to overheating them to temperatures significantly exceeding the calculated one. Due to the increase in the productivity of the bootaggers, there were increasing cases of the failure of pipeline pipes due to insufficient loan resistance to the fuel gases. Intensive scale is most often observed when combing fuel oil.

Wearing pipe walls occurs as a result of an abreasting action of coal and shale dust and ash, as well as jets of steam coming out of damaged adjacent pipes or sniffing vehicles. Sometimes the cause of wear and stagnation of the pipe walls is the fraction used to clean the heating surfaces. Places and degree of wear of pipes are determined by outer inspection and measurement of their diameter. The actual thickness of the pipe wall is measured by ultrasonic thickness gauge.

Warning of screen and boiling pipes, as well as individual pipes and sections of wall panels of the radiation part of the direct-flow boilers occurs when the installation of pipes with unevenly tension, the cliff of fastening of pipes, water lunch and due to lack of freedom for their thermal displacements. Change the coils and shirm of the steamer occurs mainly due to the burning of suspensions and fasteners, excessive and uneven tension allowed when installing or replacing individual elements. Change the coil of the water economizer is due to the brave and displacement of supports and suspension.

Fistulas, foiling, cracks and breaks may also appear as a result: deposits in the pipes of scale, corrosion products, technological scale, welding graph and other foreign objects that slow down the circulation of water and contributing to the overheating of the pipes; stagnant fraction; The inconsistencies of the brand became parameters of steam and the temperature of the gases; external mechanical damage; Violations of operating modes.