Destruction and industrial injuries due to explosions of steam boilers. Causes of steam boiler explosions and their prevention

Kamenskikh A.S.

Safety valve stuck open after tripping

Possible cause: mechanical damage to the valve

Operator actions:

Break of glass or water meter column

Possible reasons: incorrect actions of personnel when purging the water-indicating column (VUS - water-indicating glass), damage to the glass due to its aging

Operator actions:

Operator actions when the water level in the drum drops below the lower permissible level

If the water level has dropped below the lower permissible level, but is still determined by the water indicator glass, the boiler can be recharged by opening the valve on the bypass line around the control valve. Otherwise, the boiler must be immediately turned off (stopped) by protection or personnel. Therefore, if the safety automatic system does not work in this situation, the operator carries out an emergency stop of the boiler. To do this, it is necessary to immediately stop the supply of fuel and related components (air, steam) and sharply reduce the thrust.

Disconnect the boiler from the main steam line and, if necessary, release steam through the raised safety valves.

WATER LEAVE. Possible reasons:

• malfunction or shutdown of automatic power supply
• stoppage or malfunction of feed pumps
• lack of water in the deaerator battery tank
• rupture of the supply pipeline, screen or boiler pipes
• incorrect actions of personnel when purging the boiler
• large leakage of purge or drain fittings

Operator actions:

• Stop fuel supply
• Stop ventilation of the firebox by stopping the smoke exhauster and fan
• If purging was carried out, stop it
• Stop power supply to the boiler by closing the valve on the supply line
• Close the steam shut-off valve of the boiler.

Topping up the boiler is strictly prohibited. Filling the boiler with water in order to determine possible damage due to water leakage can only be done by order of the head of the boiler room and cooling the boiler drum to ambient temperature.

Boiler water boiling

Accompanied by sharp fluctuations in the water level in the water indicator glasses and water hammer in the boiler

Possible reasons:

• a sharp increase in steam consumption and a decrease in pressure in the drum
• increase in salinity or alkalinity of boiler water
• supply of chemical reagents in large quantities to the boiler

Operator actions:

• Stop fuel supply
• Disconnect the boiler from the steam line by closing the main steam shut-off valve
• Stop power supply to the boiler by closing the valve on the supply pipe
• Stop the smoke exhauster and fan
• Blow out the water indicators and determine the water level

Operator actions when the water level of a steam boiler rises above the permissible level

If the water level has exceeded the permissible level, but is still determined by the water indicator glass, the water can be drained through the purge valves, otherwise the boiler must be immediately switched off (stopped) by protective equipment or by personnel. Therefore, if the safety automatic system does not work in this situation, the operator carries out an emergency stop of the boiler. To do this, it is necessary to immediately stop the supply of fuel and related components (air, steam) and sharply reduce the thrust. Fill unburnt solid fuel with water, being careful not to let water get on the heating surfaces of the boiler elements. Disconnect the boiler from the main steam line and, if necessary, release steam through the raised safety valves.

REFUELING THE BOILER

Possible reasons:

• malfunction of water indicators
• sharp decrease in steam consumption
• shutdown or malfunction of the boiler automatic power supply

Operator actions:

If the water level has risen before the protection is set to operate, then it is necessary

If, despite the measures taken, the level continues to rise, then it is necessary

• reduce the boiler power supply, close the shut-off valves on the supply line
• Carefully open the purge line of the lower drum and if after purging the level begins to rise again, then it is necessary
• stop fuel supply
• disconnect the boiler from the steam line
• close the main steam shut-off valve
• ventilate the firebox for 10 minutes
• stop the fan and exhaust fan
• drain the water to the average level by opening the shut-off valves on the periodic purge line.

The basis for the stable functioning and development of any country in the world is the degree of development of its electric power industry. Both the industrial sector and the population directly depend on its sustainable and well-coordinated work. The socio-economic development of the country directly depends.

In Russia there are more than 700 various types power plants, with a total installed production rate of about 225 GW. Most of these power plants are thermal (more than 68%) running on fossil fuels ( natural gas, fuel oil, fossil coals).

Thermal power generation plays a huge role in the Eastern part of the country, beyond the Urals, especially in the Arctic zone of Russia, which has difficult natural and climatic conditions for the functioning of industry and the residence of citizens.

In this context thermal power plants, often covering vast areas with a large population, are the most important strategic life support facilities, especially in winter. Based on the fact that one of the most important elements for generating electricity at power plants of this type are high- and ultra-high-pressure steam boilers, the relevance deep analysis factors that negatively affect the operating efficiency of this equipment and the development of measures to prevent accidents in compliance with the rules and regulations of boiler inspection is undoubtedly an urgent scientific and production task.

A modern high-pressure steam boiler, designed to generate steam that has certain physical characteristics and is intended to ensure the rotation of a turbine that generates electricity, is undoubtedly a complex technological production facility of increased danger.

In the harmonious and trouble-free operation of a high-pressure steam boiler, it has great value many factors: the quality of the material from which the boiler and all its elements are made, the quality of the designs of connections and fastenings of the elements, the mode of its operation.

Such a complex mechanism as a high-pressure steam boiler, belonging to group 2 hazardous production facilities, must be serviced by highly qualified personnel and maintained (maintained, repaired and adjusted) exclusively in accordance with the “Rules for the design and safe operation of steam and hot water boilers”. Savings on personnel training, violation of maintenance schedules and repair charts for this equipment, or refusal to support and repair it at all will inevitably lead over time to accidents and damage to boilers, with possible injury to personnel and causing great damage to the power plant and consumers.

Unfortunately, at the moment, at Russian thermal power plants (CHPs), including combined heat and power plants (CHPs), two trends have developed that are negative for maintaining the safe operation of equipment, in particular steam boilers:

Avalanche-like increase in the aging process of the main equipment of power plants;

A sharp reduction in the scientific and technical potential of the industry.

Analysis of factors allows us to state that:

1) at present, there is maximum savings in investments in updating and maintaining thermal power plant equipment at the appropriate technological level;

2) sufficient funds are not invested in the research and development of new methods and instruments that allow not only to detect individual defects, but also to assess the condition and remaining life of the equipment as a whole.

This together causes enormous damage to the safety of boiler inspection facilities at Russian thermal power plants and threatens the stable supply of electricity to consumers over a very large territory.

Currently in scientific literature and journalism, in our opinion, there is not enough analysis of the causes of steam boiler accidents and measures to prevent them from a modern point of view.

In this work, through a cause-and-effect analysis of this issue, we will try to fill this gap to a certain extent.

The reasons leading to accidents of varying severity during the operation of high-pressure boilers can be differentiated into five main groups:

Accidents resulting from certain violations of water treatment and water supply to the steam boiler;

Accidents associated with loss of water during boiler operation;

Accidents of steam boilers associated with excess operating pressure above the specified operating pressure;

Accidents associated with intercrystalline corrosion of structural metals;

Accidents associated with wear of steam boiler elements.

Let us consider each group of reasons leading to certain accidents of high-pressure steam boilers separately.

1. Accidents resulting from certain violations of water treatment and water supply to the steam boiler.

a) the importance of proper water treatment of feedwater for a high-pressure boiler

The reliability of the heating surfaces of boiler units depends on the quality of feed and make-up water. Water is a universal solvent and various mineral impurities enter the boiler with it. These impurities are divided into difficult and easily soluble.

Hardly soluble impurities include Ca and Mg hydroxide salts. The main scale formers are characterized by the fact that their solubility decreases with increasing temperature. Thus, accumulating in the boiler as the water evaporates, these impurities, after passing the saturation point, precipitate in the water. First of all, these are hardness salts - Ca(HCO 3) 2, Mg(HCO 3) 2, CaCO 2, MgCO 2.

Their centers of crystallization are various roughnesses on the heating surface, suspended and colloidal particles located in the boiler water. Substances that crystallize in the volume of water form particles suspended in it, the so-called sludge. Substances that crystallize on the heating surface form dense and durable deposits - scale.

One of the most negative properties of scale is its very low thermal conductivity (0.1-0.2 W/m*K). Therefore, even a small layer of scale leads to a sharp deterioration in the cooling conditions of the metal of the heating surfaces and, as a result, to an increase in its temperature, which can lead to a loss of strength of the boiler wall and its destruction.

In addition to hardness salts, a harmful factor that creates a danger for trouble-free operation of a steam boiler is the alkalinity of the water. It leads to the phenomenon of foaming water in the drum. In this case, separation devices cannot effectively separate water droplets from steam; accordingly, alkaline water from the drum can enter the superheater, thereby creating the risk of contamination. In addition, increased alkalinity can cause alkaline corrosion of metal and the occurrence of cracks in places where pipes are rolled into collectors and drums.

Another very important factor in water quality that needs to be controlled when used to power high-pressure steam boilers is the content of aggressive gases, such as oxygen and carbon dioxide. They cause corrosion of metals, which in turn leads to a loss of their strength and the creation of a potential emergency situation.

Thus, the main task of water treatment is to combat corrosion and scale. In this case, an effective method for preventing an accident in a high-pressure steam boiler is to take into account chemical composition feed water used for the boiler, since in each region of Russia the water has its own water-alkaline and salt properties.

Taking this circumstance into account, it is necessary to competently select processes that help remove harmful impurities and aggressive gases from water: filtration, water softening by cation exchange, water deaeration.

b) the importance of proper organization of the water regime for efficient work high pressure steam boiler

The water supply mode of a steam boiler must be calculated and maintained at an optimal level depending on its steam output and operating pressure. The boiler must be operated in accordance with the Boiler Operating Rules.

Taking these factors into account will ensure trouble-free and economical operation of high-pressure steam boilers.

2. Accidents associated with loss of water during boiler operation.

According to the rules and requirements given in the work regarding the water level for a steam boiler, there is the following requirement - “... the upper permissible water level in steam boilers is established by the boiler project developer...”. Thus, the water level in steam boilers must be maintained by the boiler equipment operator within the limits specified in the technical documentation for a particular brand of boiler.

A significant percentage of accidents in high-pressure steam boilers occur precisely because of water loss during operation. According to the main reasons for water loss are:

Malfunction (failure to operate) of nutritional devices;

Feed valve malfunction, check valve or automatic regulator of feed water supply to the boiler;

Severe water leakage from the boiler as a result of rupture of pipes, collectors, the appearance of fistulas in drums, etc.;

Failure of shut-off valves on the purge lines during boiler purge;

Inattentive boiler equipment operators;

Violation of production instructions.

Loss of water in a high-pressure boiler can have the most severe consequences, including a boiler explosion. Due to the fact that part of the boiler drum and boiling pipes stop cooling, local overheating of the metal occurs. If, after losing water, you try to continue supplying water to the regulated level, then as a result of thermal overstresses, ruptures of the walls of pipes, collectors, and drums may occur. For liquidation dangerous situation it is necessary to make an emergency stop of the boiler, disconnect the boiler from the steam line and supply pipeline and slowly cool the boiler with the smoke exhauster and fan stopped.

An effective method of preventing accidents in steam boilers for the reason considered is to install an automatic production alarm on the boilers, which records the level of feed water in the boiler. This problem has been partially solved - new designs of high-pressure boilers provide automatic sound and light alarm, triggered when water is lost from the steam boiler. However, most boilers in our country are obsolete, during the operation of which all responsibility for maintaining the water level falls on the installation operator. This subjective factor leads to an increase in accidents and the need to introduce modern equipment.

3. Accidents of steam boilers associated with excess operating pressure above the specified operating pressure.

The main reasons for the increase in pressure in the boiler above the permitted level are:

Sudden decrease (cessation) of steam consumption;

Excessive boost of the firebox (especially this reason relevant when the boiler operates on oil and gaseous fuel).

According to the information given in the work, about 80% of the generating capacities of thermal power plants in the European part of Russia (including the Urals) operate on gas and fuel oil, while at the same time in the Eastern part of Russia more than 80% of the generating capacities of thermal power plants operate on coal.

Thus, taking this reason into account when analyzing the industrial safety of a high-pressure steam boiler (boiler inspection) is most relevant for heat and power enterprises in the European part of Russia.

An effective measure to mitigate the danger in the operation of the boiler, which can be caused by an uncontrolled increase in pressure, are safety valves installed on the boiler and adjusted to the pressure in accordance with the instructions of the Rules.

These valves are required to protect boilers and superheaters from exceeding their pressure by more than 10% of the design pressure. Operation of boilers with faulty or unadjusted safety valves is prohibited. Failure to comply with these requirements leads to boiler explosions due to excess pressure.

4. Accidents associated with intercrystalline corrosion of structural metals.

Corrosion is one of the main causes of failures in steam boilers. According to the conclusions given in the work, even high-alloy and austenitic steels are subject to intense corrosion. As noted above, in the analysis of proper water treatment of feed water for a boiler, water, or rather the impurities it contains and its pH, negatively affect the condition of the metal structure of the boiler equipment.

The chemical effect of alkaline water on the boiler metal leads to corrosive attacks, which significantly weaken the boiler structure. The integral effect of thermochemical and mechanical influences leads to the appearance of intercrystalline corrosion (corrosion) cracking and other defects in the metal structure in the metal of the boiler drum.

Intercrystalline corrosion occurs in metal under the influence of mechanical and tensile stresses close to the yield point. As a result, the metal becomes brittle and microcracks appear in it, which over time transform into through ones. This type of corrosion can occur in rolling, riveting, and welded joints of drums and boiler manifolds. As a rule, initially detect this type corrosion is very difficult, since, firstly, it occurs in places inaccessible to direct inspection, and secondly, during an internal inspection of the boiler, corrosion can only be detected by clearly visible cracks.

Thus, intercrystalline corrosion is a factor that negatively affects the boiler design and can create a danger for it. stable operation. An effective preventive measure in this case is thorough water treatment, preventive work, inspections, as well as the development of new methods and devices for the timely detection of intercrystalline corrosion.

5. Accidents associated with wear of steam boiler elements.

These accidents can be divided into two types: technical and organizational. Organizational reasons include the following: 1) poor quality of scheduled and routine repairs, internal inspections and diagnostics; 2) failure to comply with boiler inspection requirements.

The number of accidents for this reason is relatively small; it should be noted that they are accompanied by great destruction and injury to operating personnel.

Thus, summing up the cause-and-effect analysis of accidents of steam boilers and effective methods their warnings, we can conclude that compliance with the requirements and rules of boiler inspection and the development of new devices and methods for diagnosing boiler problems are the key to their reliable operation and trouble-free operation.

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7. Vasiliev A.A., Dromiadi A.A., Ivanov D.S., Irdyncheev G.L., Tolstoy K.V. Intercrystalline corrosion and its development on the main elements of the boiler using the example of a double-drum steam boiler of type DE-25-24-380-GMO // Scientific works of Kuban State Technical University. – 2015. – No. 9. – P. 1-8.

Great attention is paid to the safe operation of steam boilers.

As a result of the replacement of obsolete structures (vertical-cylindrical, heat turbine, etc.), the accident rate of steam boilers for lately decreased sharply. However, accidents have not yet been completely eliminated, especially due to loss of water. In some cases, the loss of water led to explosions of steam boilers with the destruction of the boiler room and human casualties.

For recent years Due to the equipping of steam boilers with a nominal steam output of 0.7 t/h or more with automatically operating sound alarms for the upper and lower limit positions of water levels, water loss accidents on such boilers have sharply decreased. Water leaks occurred only on boilers that did not have alarms or, due to poor maintenance, were faulty and inactive at the time of the accident.

In some cases, the consequences of the accident were aggravated by the incorrect actions of the maintenance personnel who recharged the boiler after detecting a water leak in violation of the requirements of the “Standard Instructions for Boiler House Personnel” approved by the USSR State Mining and Technical Supervision on July 12, 1979.

An analysis of accidents of steam boilers that do not have automatic power regulators installed shows that accidents due to water loss occur mainly as a result of weakened personnel attention, mainly in the evening and at night. Thus, in the period from 0 to 8 a.m. the number of accidents reaches 50%, from 8 to 16 a.m. - up to 20%, and from 4 to 24 p.m. - up to 30%.

As a result of violations of personnel's production discipline, about 80% of accidents occur due to loss of water.

Loss of water in a steam boiler can occur not only due to the fault of personnel who did not refuel the boiler in a timely manner, but also due to technical malfunctions of water indicating devices, purge and feed fittings, feed devices, insufficient productivity and pressure of feed devices, rupture of the screen, boiler or economizer pipe. Let's give a few examples.

At the thermal power plant, due to a deep loss of water, an accident occurred in the TGME-454 boiler with a capacity of 500 t/h (pressure in the drum "16.2 MPa). In this case, four screen pipes ruptured, fistulas appeared in two pipes, the entire screen system was deformed with amplitude up to 250 mm (gas-tight firebox).

Material damage from the accident amounted to about 200 thousand rubles. The investigation established that the cause of the accident was: operation of the boiler with the automatic safety system turned off (cutting off the fuel supply to the boiler when the water level drops below the permissible level), incorrect actions of the boiler operator in an emergency situation.

At the thermal power plant, due to a deep loss of water, an accident occurred in the TP-35 steam boiler with a capacity of 45 t/h (pressure in the drum 3.9 MPa). In this case, two screen pipes ruptured, 40% of the screen pipes were deformed. Material damage from the accident amounted to 10 thousand rubles.

Causes of the accident: operation of the boiler with gas supply to the burners through the bypass line, excluding automatic shutdown fuel when water is lost. The boiler operator intervened in the operation of the automatic control system by influencing the control key of the supply control valve, and manually closed the valve on the boiler water supply unit when the water level was at an emergency low. The boiler began manual feeding, thereby violating the requirements of the job description and instructions for the prevention and elimination of accidents. Due to changes in the operating mode of the boiler, the shift manager of the thermal power plant did not ensure that his subordinate personnel complied with the requirements of production instructions, and did not take measures to emergency stop the boiler. There was an unsatisfactory state of production discipline among maintenance personnel and engineering personnel, which was expressed in failure to comply with the requirements of current safety rules and instructions.

In the third case, in the boiler room, due to a deep loss of water, an accident occurred with the steam boiler DKVR-2.5/13. As a result of the accident, the boiler screen and boiler pipes were damaged.

Causes of the accident: the driver left the boiler running without supervision; the boiler was operating with faulty safety automatics; maintenance personnel violated production instructions.

In the boiler room, due to a deep loss of water, an accident occurred with the steam boiler DKVR-10/13. As a result of the accident, the boiler screen and boiler pipes were damaged and the rolling connections were damaged. Damaged pipes have also been completely replaced.

Causes of the accident: incorrect actions of the driver who purged the boiler without proper control over the water level in the upper drum of the boiler; faulty state of automatic safety and alarm systems for water loss from the boiler; acceptance of a shift by a senior driver without checking the status and automatic safety; admission to servicing steam boilers of personnel who have not passed the test of knowledge of current safety rules and production instructions.

To prevent water loss in steam boilers, it is necessary:

Do not allow persons to service boilers who have not completed training in the scope of the relevant program and do not have a certificate from a qualified commission for the right to service the boiler;

Do not allow the operation of boilers with faulty water indicator, purge and feed fittings, as well as automatic safety systems that ensure normal operation of the boiler from the monitoring and control panel;

Check the serviceability of all feed pumps by briefly putting them into operation (for boilers with an operating pressure of up to 2.4 MPa within the time limits established by the production instructions, check water indicators by blowing out for boilers with an operating pressure of up to 2.4 MPa at least once per shift, for boilers with operating pressure from 2.4 to 3.9 MPa - at least once a day, and over 3.9 MPa - within the time limits established by the instructions);

Prohibit leaving the boiler during operation without constant supervision by personnel and prohibit the operator from performing any other duties not provided for in the instructions.

1. The main causes of boiler explosions are: violation of rules technical operation, their operating modes, as well as job descriptions, safety requirements due to non-compliance with labor and production discipline service personnel; defects and malfunctions of boiler design components. . Violations of these instructions and rules lead to the following main technical reasons for boiler explosions: a sharp decrease in the water level, excess operating pressure, unsatisfactory water conditions of the boiler, scale formation, and the presence of explosive flue gases. The largest number of accidents during the operation of steam boilers occurs due to a sharp decrease in the water level in the boiler. Due to a decrease in the water level below the line of contact of the boiler surface with hot gases in its combustion part, the boiler walls heat up higher critical temperature. In this case, the mechanical properties of the metal change, its strength decreases, and under steam pressure the walls are blown out, which can result in an explosion.

Common causes of boiler explosions due to defects and malfunctions of the main components are defects in structural elements, a decrease in their mechanical strength during operation, and malfunction of safety equipment and measuring instruments.

2. Explosions during compressor operation can occur due to excess pressure of compressed air, as well as due to an increase in its temperature during compression, the formation of explosive mixtures from air oxygen and light decomposition products of lubricating oils. Explosions caused by these reasons occur when safety requirements for the care, maintenance and operation of compressors are violated. They lead to the destruction of both the compressor itself and the building in which it is located, as well as to injuries with serious consequences. An increase in temperature sharply intensifies the process of decomposition of the lubricating oil, which increases the risk of explosion. The decomposition of lubricating oils occurs with the release of light explosive fractions (hydrogen, saturated and unsaturated gases, including acetylene), as well as heavy fractions (soot, tar, coke, asphaltenes and carboids). The latter are deposited on the walls of the compressor cylinder, valve devices and pipelines. This increases friction and leads to local overheating. A layer of soot from heavy fractions is capable of spontaneous combustion, which can cause an explosion of the compressor and pipelines.

At high temperature lubricating oils partially evaporate, and if there is excessive lubrication, they are sprayed in the form of fog, which can also form an explosive mixture with air if it contains 6-11% oil vapor. Such a mixture explodes at a temperature of 200 °C, which occurs when air is compressed to a pressure of about 0.4 MPa. To prevent explosions of compressors and refrigeration units, as well as the equipment (pressure vessels) and pipelines included in their system, and to ensure safety during their operation, the requirements of GOST 12.2.016--81 and GOST 12.2.003-- 74, as well as special requirements that can be divided into organizational ones, preventing excess pressure, overheating of installations, explosions of oil vapors, their decomposition products, as well as refrigerants. The placement of compressors must comply with the requirements of SNiP, fire safety standards for the construction design of industrial enterprises and sanitary standards for their design. Compressors should generally be located in free-standing, single-story buildings.

3. Enterprises use a variety of cylinders designed for storage, transportation and use of compressed (nitrogen, air, oxygen, hydrogen sulfide), liquefied (ammonia, sulfur dioxide, carbon dioxide, freon) and soluble (acetylene) gases under a pressure of 0.6- -15 MPa. In this regard, their explosions pose a danger regardless of whether the cylinders contain flammable or non-flammable gas.

The causes of explosions can be divided into common for all cylinders, as well as specific for individual ones. Common ones include: impacts or falls of the cylinder, especially at high or low temperatures, since in the first case the pressure in the cylinder increases sharply due to heating of the gas contained in it, and in the second case the material from which the cylinder is made becomes brittle; overfilling a cylinder with liquefied gas without leaving a free standardized volume of about 10% of the total volume of the cylinder; heating of the cylinder by sunlight or other sources, which leads to an increase in pressure in it above permissible values. Specific reasons inherent in oxygen cylinders: oil getting into the internal areas of the valve, the use of non-greased gaskets, as well as oiling the surface of the cylinder, since oxidation of the oil can cause it to ignite and explode; the presence of rust or scale in the cylinder, the movement of which can cause sparks and accumulate static electricity with subsequent neoplasm, which can cause an explosion of oxygen in the cylinder; rapid withdrawal of gas from the cylinder, which can cause sparking in the oxygen stream; inherent in acetylene cylinders: low quality or sediment of the porous mass (wood activated carbon); lack of acetone in the cylinder; the use of pressure reducing valves and pipelines) containing more than 70% copper, upon contact with which acetone reacts chemical reaction with a large release of heat; rapid withdrawal of gas from the cylinder, which can cause the removal of acetone, which, with an acetylene flow rate of 1.7 m3/h or more, should not exceed the permissible 20 g/m3 of gas.

Acetylene in ordinary cylinders (without porous mass) explodes at a pressure of more than 0.1 MPa. Therefore, to reduce its explosion hazard and increase the maximum filling pressure of cylinders, steel cylinders filled with a porous mass impregnated with acetylene are used. This allows 7.5 m3 of acetylene to be dissolved in acetone at a pressure of 2 MPa in a cylinder with a volume of 40 dm3.

Explosions of cylinders from impacts and falls are prevented by increasing their strength through the use of special materials and manufacturing methods, manufacturing quality control, supply of safety caps and support shoes, compliance with the rules of transportation and operation. For the manufacture of cylinders, seamless carbon steel pipes are used, for cylinders low pressure(up to 3 MPa) the use of welded cylinders is allowed. To prevent explosions due to improper filling or rapid gas withdrawal, the cylinders are equipped with a valve through which gas is filled and removed. To protect the valve from damage, it is closed with a metal cap. A pressure reducing valve is connected to the valve, providing gas selection at a lower pressure than in the cylinder. For each type of cylinder, pressure reducing valves specially designed for the gas it contains are used. They have 2 pressure gauges, one located on the high pressure side and the other on the low pressure side. The reduction chamber of the reducer is equipped with a pressure gauge and a safety valve adjusted to the maximum operating pressure provided for the container into which the gas is drawn.

To prevent the incorrect use of cylinders intended for different gases, the valves have different threads (for oxygen and inert gases - right, flammable - left, and for acetone - a clamp), which excludes the connection of pressure reducing valves to them.

To prevent overheating when storing cylinders on outdoors they must be protected from sunlight, as well as from exposure to precipitation. When used indoors, cylinders should not be located at a distance of less than 1.5 m from heating devices and gas stoves and less than 5 m from stoves and other sources of open fire.

Pipe ruptures heating surfaces are the main cause of emergency shutdowns and boiler failures. The most serious consequences with the mandatory shutdown of the boiler are observed when screen pipes rupture. When fistulas and cracks appear in economizers and superheaters, the boiler is sometimes allowed to operate for some time, but at the same time, control is strengthened, especially of defective areas, and, as soon as possible, the boiler is stopped to avoid more serious damage. Ruptures of screen pipes in drum boilers are accompanied by strong noise in the combustion chamber and gas ducts, a decrease in the water level in the drum (despite increased feeding), an increase in pressure in the furnace and the knocking out of gases from it, a decrease in pressure in the drum, etc. With ruptures in other heating surfaces Due to the smaller diameters of the pipes, these same symptoms manifest themselves to a lesser extent: rupture of superheater pipes does not affect changes in the water level.

The main causes of ruptures of pipe surfaces heating are: excess pressure; violation of temperature operating conditions; corrosion-erosion processes occurring on the outer and inner surfaces of pipes; unsatisfactory water regime of the boiler; fatigue failures and increased stresses (for example, when pipes are pinched); poor quality of pipe manufacturing and use of inappropriate material; poor-quality installation and repair (especially poor welding); insufficient technical supervision over the condition of pipes.

To avoid excessive pressure increases, safety valves are installed on the steam lines of fresh and secondary superheated steam, the serviceability of which is regularly monitored. Starting the boiler with faulty safety valves is prohibited. Violations of the temperature conditions of pipe operation are observed when the temperature rises above permissible limits or when its sharp fluctuations cause the appearance of fatigue cracks. The resistance of the metal to current loads decreases with increasing temperature, which can be caused by insufficient flow of steam or water through the pipe, an increase in gas temperature and heat flows, and the formation of significant internal deposits due to unstable circulation of the medium through the pipes.

Insufficient flow cooling environment may occur due to operator inattention, loss of water from the drum, ruptures in pipes, instability or disruption of circulation, malfunction of instrumentation associated with the boiler power supply. The reason for the increase in gas temperature may be excessive fuel consumption, unsatisfactory combustion conditions, causing a general delay in combustion, or unevenness (“warps” of temperatures) of gases across the cross section of the furnace and flues (improper loading of burners).

Internal deposits appear due to unsatisfactory water conditions and chemical preparation, intensive corrosion processes, and insufficient steam purification. An increase in salt content in boilers is caused by moisture escaping from the drum when the water level rises above the permissible level. In addition to strict adherence to the operating mode and combustion process, as well as constant monitoring of instrument readings to reduce accidents due to pipe ruptures, plant personnel should regularly carry out water and acid flushes of the internal surfaces of pipes.

Corrosion processes leak both from the inside of the pipes and from the side of gas movement. Internal corrosion is determined by the presence of corrosive compounds (oxygen, hydrogen, carbon dioxide, nitrates, nitrites, etc.) in water or steam. Corrosion can occur both when the boiler is running and when the boiler is stopped (parking corrosion). During equipment operation, in most cases, internal corrosion occurs due to unsatisfactory deaeration of feed water and poor quality of intra-boiler water treatment.

Standstill corrosion caused by the penetration of atmospheric air into pipes during equipment shutdowns is eliminated during boiler conservation, which is carried out in accordance with the “Guidelines for the conservation of thermal power equipment.” External corrosion of pipes in high-temperature boilers is most pronounced when burning fuel oil and solid fuels with a high sulfur content (vanadium, sulfide corrosion) and in heating surfaces in the zone of low gas temperatures (low-temperature sulfur corrosion).

Boiler water mode largely determines corrosion processes and the formation of internal deposits. To reduce the accident rate in accordance with the requirements of the Technical Operation Rules, you should: maintain the total salt content of the feed water and the content of iron, copper, silicon, oxygen compounds not higher than permissible limits; correctly dose processing materials (hydrazine, ammonia, phosphate, etc.); maintain the required flow of continuous blowing water and perform periodic blowing in a timely manner; carry out pre-start flushing of boilers. Increased stresses and fatigue failures can be caused by improper equipment design, as well as jamming (pinching) of pipes and sudden temperature changes. When starting, stopping and operating equipment, they monitor the elongation of pipelines and the condition of the pipe surface, identify damaged areas and replace them in a timely manner.

Accidents and failures due to poor workmanship, installation and repair are caused by: metal defects; lack of entrance control; defective factory, installation or repair welded joints; use of inappropriate materials; violations of technology and scope of work.

Identifying the causes of pipe ruptures makes it possible to determine ways to eliminate them and emergency situations in which the boiler should be stopped immediately (even if damage has not occurred) in order to avoid serious consequences and its failure for a significant period.

In accordance with the “Technical Operation Rules”, the boiler is immediately stopped by protection or personnel when:

loss of water;

an unacceptable increase or decrease in its level in the drum, or failure of all water indicating devices;

a rapid decrease in water level, despite increased nutrition;

failure of all feedwater flow meters (in a once-through boiler) or interruption of power supply to any of its flows for more than 30 s;

stopping the operation of feed pumps;

unacceptable increase in pressure in the steam-water path; termination of operation of more than 50% of safety valves or their replacement devices.

When steam-water pipes rupture, the appearance of cracks, bulges, gaps in welded joints and connections of main elements (drum, manifold, bypass pipes, etc.), the boiler should be stopped immediately. In direct-flow boilers, with a sharp decrease in pressure in the duct up to the built-in valve, boiling of water can occur, which leads to uneven distribution of the steam-water mixture through individual pipes, causes pulsation of pressure and flow in them, and an increase in temperature. Therefore, if the pressure reaches the built-in valve, the boiler must be stopped if there is an unacceptable increase or decrease in pressure.

Feed pipeline ruptures and main steam pipelines are observed much less frequently than ruptures of heating surface pipes. However, in terms of their destructive consequences, these injuries are much more dangerous. Among the reasons for ruptures, it should be noted:

excess pressure of the working medium; corrosion (internal) processes;

erosive (internal) wear in places where control valves are installed;

development of fatigue cracks; the appearance of increased stresses due to pinched pipelines or sudden changes in temperature;

low quality metal, welded joints or structures;

mismatch of pipe material.

To prevent these ruptures, the condition of the pipelines is regularly checked in accordance with the “Instructions for monitoring and control of metal of pipelines and boilers.” During inspections, damaged sections of pipelines are promptly discarded and subsequently replaced. Particularly carefully inspect pipes that have worked for a time close to the maximum permissible. In the event of a rupture of a section of a pipeline (or steam line), the steam boiler is immediately stopped, turning off all inlets to the emergency area and outlets from it. Signs of a pipeline rupture are strong noise and steam in the workshop premises, a sharp drop in pressure in the main line, a decrease in the flow of steam and water (behind the rupture area, in the supply main pipelines).

Damage to fittings are caused by excess pressure, the development of fatigue and corrosion cracks, a violation of the tightness of stuffing box and flange connections, as well as wear and destruction of sealing surfaces (rings, valves and spindles). If a rupture or cracks are detected in the fittings of large diameter pipelines (more than 50 mm), the boiler should be stopped immediately. If small leaks and steam are detected, the boiler also requires shutdown, but with the permission of the chief engineer it can continue to operate for some time.

Pops and explosions in furnaces and flue ducts occur due to the accumulation of significant amounts of unreacted fuel during unregulated combustion conditions, torch breakage and re-ignition without ventilation, and especially when coal dust is supplied to an unheated furnace. Pops and explosions can also occur when large blocks of slag collapse into the water bath of the slag chest. When burning gaseous fuel, explosions (often with serious consequences) are observed during the lighting of a boiler with an unventilated firebox when gas leaks into it, as well as the ignition of a torch (after a break) without prior ventilation of the firebox and flues. Fires and explosions when burning liquid fuel occur due to poor atomization and an unregulated combustion process. In the event of an explosion in the firebox or flues, especially in the event of destruction of the lining, frame or other elements, the boiler should be stopped immediately. The boiler must also be shut down in situations that could cause an explosion with serious consequences. Such emergency situations are the extinguishing of the torch and an unacceptable decrease in pressure behind the gas or fuel oil control valves. Accidents with pops and explosions mostly occur due to the fault of operating personnel who violate startup and operating instructions, in particular instructions on ventilating the boiler before startup.

Fires in gas ducts arise as a result of unsatisfactory management of the combustion process, when the products of incomplete combustion (unburned fuel, soot, tarry substances) settle and accumulate on the heating surfaces of economizers and air heaters. Ignition of these deposits causes serious damage to heating surfaces and flue ducts. Signs of fires are an increase in gas temperature that is unusual for this zone, deterioration of draft, knocking out of flames, and heating of the casing. Having discovered a fire, immediately stop the fuel supply, localize the combustion (by turning off the blower fans and smoke exhausters and tightly closing the gas and air dampers) and

include local fire extinguishing.

In addition to fires in gas ducts, fires can occur in boiler rooms or other workshops. Depending on the location and size of the fire, appropriate measures are taken and it is eliminated by all available means. In the event of a fire that threatens personnel or equipment, or the system remote control and shut-off protection valves, the boiler is stopped immediately.

Slagging of furnaces and heating surfaces also reduces the reliability of operation and creates emergency situations. In addition to uneven heating of pipes and disruption of circulation, slagging causes deformation and damage to individual screen pipes and their suspension system, destruction of the cold funnel, slag shafts, slag removal devices and lining (when slag blocks fall), increases the temperature in the furnace and increases heat flows to unslagged sections of pipes . Slagging of screens and heating surfaces significantly limits the boiler power and increases draft costs. In case of severe slagging of the furnace, when the slag overlaps its lower part and the cessation of its output with accumulation in the furnace is observed, an emergency shutdown of the boiler is performed.