APPENDIX 7. Characteristics of explosive and harmful gases most often found in tanks and underground structures.

The following explosive and harmful gases are most often found in underground structures: methane, propane, butane, propylene, butylene, carbon monoxide, carbon dioxide, hydrogen sulfide and ammonia.

Methane CH 4 (swamp gas) is a colorless, odorless, flammable gas, lighter than air. Penetrates into underground structures from the soil. It is formed during the slow decomposition of plant substances without access to air: during the rotting of fiber under water (in swamps, stagnant waters, ponds) or the decomposition of plant residues in coal deposits. Methane is a component of industrial gas and, if the gas pipeline is faulty, can penetrate into underground structures. Not poisonous, but its presence reduces the amount of oxygen in air environment underground structures, which leads to disruption of normal breathing when working in these structures. When the methane content in the air is 5-15% by volume, an explosive mixture is formed.

Propane C3H8, butane C4H10, propylene C 3 H 6 and butylene C 4 H 8 - colorless flammable gases, heavier than air, odorless, difficult to mix with air. Inhaling propane and butane in small quantities does not cause poisoning; propylene and butylene have a narcotic effect.

Liquefied gases with air can form explosive mixtures at the following content, % by volume:

Propane………………… 2.3 – 9.5

Butane…………………. 1.6 - 8.5

Propylene………………. 2.2 - 9.7

Butylene……………….. 1.7 – 9.0

Protective equipment - hose gas masks PSh-1, PSh-2.

Carbon monoxide CO is a colorless, odorless, flammable and explosive gas, slightly lighter than air. Carbon monoxide is extremely poisonous. The physiological effects of carbon monoxide on humans depend on its concentration in the air and the duration of inhalation.

Inhaling air containing carbon monoxide above the maximum permissible concentration can lead to poisoning and even death. When the air contains 12.5-75% by volume of carbon monoxide, an explosive mixture is formed.

The means of protection is a CO filter gas mask.

Carbon dioxide CO 2 [carbon dioxide (dioxide)] is a colorless, odorless gas with a sour taste, heavier than air. Penetrates into underground structures from the soil. Formed as a result of the decomposition of organic substances. It is also formed in reservoirs (tanks, bunkers, etc.) in the presence of sulfonated coal or coal due to its slow oxidation.

Getting into an underground structure, carbon dioxide displaces the air, filling the space of the underground structure from the bottom. Carbon dioxide is not poisonous, but has a narcotic effect and can irritate mucous membranes. At high concentrations it causes suffocation due to a decrease in oxygen content in the air.

Protective equipment - hose gas masks PSh-1, PSh-2.

Hydrogen sulfide H 2 S is a colorless flammable gas, has the smell of rotten eggs, and is somewhat heavier than air. Poisonous, affects the nervous system, irritates the respiratory tract and the mucous membrane of the eyes.

When the hydrogen sulfide content in the air is 4.3 - 45.5% by volume, an explosive mixture is formed.

The means of protection is filtering gas masks of brands B, KD.

Ammonia NH 3 is a colorless flammable gas with a sharp characteristic odor, lighter than air, toxic, irritates the mucous membrane of the eyes and respiratory tract, causes suffocation. When the ammonia content in the air is 15-28% by volume, an explosive mixture is formed.

The means of protection is a filter gas mask of the KD brand.

Hydrogen H 2 is a colorless, odorless, tasteless flammable gas, much lighter than air. Hydrogen is a physiologically inert gas, but at high concentrations it causes asphyxiation due to a decrease in oxygen content. When acid-containing reagents come into contact with the metal walls of containers that do not have an anti-corrosion coating, hydrogen is formed. When the hydrogen content in the air is 4-75% by volume, an explosive mixture is formed.

Oxygen O 2 is a colorless gas, odorless and tasteless, heavier than air. Toxic properties does not, but with prolonged inhalation of pure oxygen (at atmospheric pressure), death occurs due to the development of pleural pulmonary edema.

Oxygen is not flammable, but is the main gas that supports combustion of substances. Highly active, combines with most elements. Oxygen forms explosive mixtures with flammable gases.

In many cities of our country, gas has become a widespread part of people's lives.

Oxygen plays a decisive role in its combustion. Close the air damper on the gas stove burner for a moment. The gas burner flame will become white, smoky and not hot enough. This is because the gas does not burn completely; it lacks the oxygen that it encounters in the air when leaving the burner.

In order to make fuller use of the calorific value of the gas, the burner is designed in such a way that when entering it, the gas sucks in air and, mixing with it, approaches the flame with an amount of oxygen that is sufficient for its complete combustion. The flame turns out bluish, short and very hot. By closing the gas burner tap, you reduce the flow of gas and thereby reduce air leaks.

The gas used in everyday life is most often extracted from the depths of the earth and is called natural gas.

Most natural gases are a mixture of organic compounds, mainly hydrocarbons, that is, compounds that include carbon and hydrogen. Both of these elements, when combined with oxygen, release enormous amounts of heat.

Currently, many large natural gas fields have been discovered. The Saratov region is especially rich in natural gases.

Through a special Saratov-Moscow gas pipeline, gas is supplied to the capital of our Motherland, where it is widely used in industry and for the domestic needs of the population.

The advantages of gaseous fuel over solid fuel are enormous. These primarily include ease of consumption, ease of supplying fuel to the firebox or gas burner, extreme ease of flame control and greater hygiene.

But the most important advantage of gaseous fuel is its high calorific value. The flame temperature of a burning gas is much higher than the temperature of a solid fuel flame and in some cases reaches 3000°.

How does the combustion process of solid and gaseous fuels take place?

When burning, solid fuel is first dried, and then so-called dry distillation occurs. Gaseous substances containing carbon are formed. The carbon of these combustible substances combines with oxygen in the air.

When carbon burns, it forms carbon dioxide (CO2). This generates heat. Part of this heat is spent on drying and distilling new parts of solid fuel; Part of the heat is taken by nitrogen, which enters the furnace along with oxygen.

When heated to a high temperature, nitrogen leaves the furnace, aimlessly carrying heat with it into the atmosphere. In addition, due to poor “mixing” of air with solid fuel, not all the oxygen entering the firebox participates in combustion; part of it, heating up along with nitrogen, also escapes into the atmosphere. A large amount of heat is wasted, and along with it many small particles of coal are carried away in the form of smoke.

When using gaseous fuel, some of these disadvantages are eliminated. The combustible gas mixes well with oxygen in the air even before approaching the flame. The air supply to the firebox can be adjusted so that it is sufficient for complete combustion of the gas and there is no unnecessary heat loss.

When heated gas and hot air are supplied to the furnace, heat loss is almost completely eliminated. The heat of gases coming out of the furnace is usually used to heat air and gas. Gaseous fuel is more economical and convenient than solid fuel.

Gaseous fuel can also be obtained artificially. For this purpose, so-called gas generator units are used.

Coal is loaded into a high column equipped with a grate at the bottom. Coal is loaded through the top loading hole. When the column is full, the hole is closed, leaving only a narrow outlet for gases. From the bottom of the column, air with a certain oxygen content is supplied under the grate and the coal is set on fire. The lower layers of coal, when burned in the presence of oxygen, form carbon dioxide and release heat. This heat rises up the column and heats the top layers of coal. Carbon dioxide produced by burning the lower layers passes through the upper layers of coal heated to 700°, gives them part of its oxygen and forms carbon monoxide. Carbon monoxide, together with air nitrogen, passes through the outlet and is collected in gas storage facilities.

The gas produced in generator sets is called generator gas.

If water vapor is introduced into the generator along with air, then hydrogen is formed simultaneously with carbon monoxide. The mixture of these gases is called water gas and is also used as gaseous fuel. When water gas burns, carbon monoxide combines with oxygen to form carbon dioxide. And hydrogen, when combined with oxygen, gives water.

Both generator gas and water gas contain carbon monoxide. Carbon monoxide is a colorless, odorless gas, slightly lighter than air. It is poisonous and causes fumes, which is where its other name comes from - carbon monoxide. In the dorms, we often think of “smoke” as the smell of unburned fuel. However, this smell does not belong to carbon monoxide, but to other combustion products that also contain carbon.

If you stay in a room for a long time (3-4 hours), where for every 100 thousand parts of air there is only one part of carbon monoxide, you can get burned. An admixture of one part of carbon monoxide to 800 parts of air is already extremely dangerous for human life and can cause death in half an hour.

The best remedy for the victim is clean air, and in case of severe poisoning - pure oxygen.

Carbon monoxide is high in calories. When 1 gram of carbon monoxide (28 grams) is burned, 67,500 calories are released; This is 29,500 calories less than the heat generated by the combustion of 1 gram of carbon (12 grams):

(C + O 2 = CO 2 + 97,000 cal.)

(CO + V2O2 = CO 2 + 67,500 cal.)

It would seem that with such a ratio of thermal effects, it is inappropriate to convert coal into carbon monoxide, so that, ultimately, when burning it, less heat will be obtained. In reality this is not the case. If we calculate all the heat losses during the combustion of solid fuel, including losses due to ash, which amounts to 5-30 percent, then the use of generator gas will be beneficial.

It is even more expedient to obtain carbon monoxide at the coal site without extracting it to the surface. This method of producing gaseous fuel is called underground coal gasification.

The idea of ​​underground gasification of coal was first conceived by the great Russian chemist Mendeleev. In the 80s of the last century, he wrote: “Probably, over time, even an era will come when coal will not be removed from the ground, but there, in the ground, they will be able to turn it into flammable gases and distribute them through pipes over long distances.” .

This idea, bold for that time, was taken up by many scientists. The beginning of the implementation of the idea of ​​underground gasification was assessed by V.I. Lenin in the article “One of greatest victories in technology", published in Pravda in 1913. V.I. Lenin described underground gasification as a revolution in industry, tantamount to a gigantic technical revolution in perhaps the most important branch of production.

However, under the conditions of Tsarist Russia, it was not possible to develop underground gasification. This became possible only under Soviet rule.

In 1931, the Central Committee of the All-Union Communist Party made a decision to implement the problems of underground coal gasification. Since then, our country has been continuously working on the widespread introduction of this advanced method of extracting fuel from the bowels of the earth.

The benefits of this method are enormous.

Underground gasification significantly simplifies and reduces the cost of developing coal deposits and facilitates the work of miners. Transport is exempt from carrying large quantities of solid fuel.

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Oxygen

Oxygen is a gas without taste, odor and color, not flammable, but actively supports combustion, slightly heavier than air. At normal atmospheric pressure (760 mm Hg) at a temperature of 0 ° C, the mass of 1 cubic meter. oxygen is 1.43 kg, and at normal atmospheric pressure and temperature 20 ° C, the mass of 1 cubic meter. oxygen is 1.33 kg, the mass of 1 cubic meter of air is 1.29 kg.

In industry, oxygen is obtained from atmospheric air by deep cooling and rectification.

Technical oxygen for gas-flame work is obtained in special installations from atmospheric air in a liquid state. Liquid oxygen is a highly mobile, bluish liquid. The boiling point (beginning of evaporation) of liquid oxygen is minus 183° C.

Under normal conditions and a temperature of minus 183° C. it easily evaporates, turning into a gaseous state. As the temperature rises, the rate of evaporation increases. From 1 liter of liquid oxygen, about 860 liters of gaseous oxygen are formed.

Oxygen has great chemical activity. The reaction of its combination with oils, fats, coal dust, fabric fibers, etc., leads to instant oxidation, self-ignition and explosion at normal temperatures.

Oxygen mixed with flammable gases and vapors of flammable liquids forms explosive mixtures over a wide range.

“Technical gaseous oxygen” according to GOST 5583-78 is produced for welding and cutting in three grades: 1st - with a purity of at least 99.7%, 2nd - at least 99.5%, 3rd - at least 99.2 % by volume. The fewer gas impurities in oxygen, the higher the cutting speed, cleaner edges and lower oxygen consumption. It is supplied to the enterprise in a gaseous state, in blue steel oxygen cylinders with a capacity of 40 dm3. cube and pressure 150 kgf/cm2. Compressed oxygen is stored and transported in cylinders in accordance with GOST 949-73.

Propane- technical, colorless gas with a pungent odor, consisting of propane C3H8 or propane and propylene C3H6, the total content of which must be at least 93%. Propane is obtained by processing petroleum products. Propane-butane mixture is a mixture of gases, mainly technical propane and butane. These gases belong to the group of heavy hydrocarbons. The raw materials for their production are natural petroleum gases and waste gases from oil refineries. These gases are pure form or in the form of mixtures at normal temperature and at a large increase in pressure, they can be transferred from a gaseous state to a liquid state. The propane-butane mixture is stored and transported in a liquid state, and used in a gaseous state.

Gaseous propane-butane mixture is a flammable gas without taste, odor and color, 2 times heavier than air, therefore, when gas leaks, it does not dissipate in the atmosphere, but falls down and fills the recesses of the floor or terrain.

The gaseous propane-butane mixture at atmospheric pressure does not have a toxic (poisonous) effect on the human body, since it dissolves little in the blood. But when it gets into the air, it mixes with it, displaces and reduces the oxygen content in the air. A person in such an atmosphere experiences oxygen starvation, and with significant concentrations of gas in the air can die from suffocation.

The maximum permissible concentration of propane-butane in the air of the working area should be no more than 300 mg/m 3 (in terms of carbon). If liquid propane-butane gets on the skin of the body, the normal temperature of which is 36.6 degrees. C, there is rapid evaporation and intense heat removal from the surface of the body, then frostbite occurs.

According to GOST 20448-80, the industry produces propane-butane mixture of 3 brands:

• technical propane, with a propane content of more than 93%, butane - less than 3 percent;
• technical butane, with butane content less than 93%, propane no more than 4 percent;
• propane-butane mixture, 2 types: winter and summer.

Propane-butane mixture is supplied to enterprises for gas-flame processing of metals in steel cylinders for winter and summer.

Winter propane-butane mixture contains 15% propane, 25% butane and other components.

Summer propane-butane mixture contains 60% butane, 40% propane and other components.

For combustion I cu. m of gaseous propane-butane mixture requires 25-27 cubic meters. m of air or 3.58 - 3.63 kg of oxygen.

Ignition temperature with air:

• propane - 510 degrees. WITH;
• butane - 540 degrees. WITH

Ignition temperature of propane-butane mixture:

• with air 490-510 degrees. WITH;
• with oxygen - 465-480 degrees. WITH.

The flame temperature of a propane-butane mixture with oxygen depends on its composition and is equal to 2200-2680 degrees. C. With an oxidizing flame (excess oxygen), the temperature rises.

The calorific value of the propane-butane mixture is 93,000 J/m3. (22000 kcal/m3).

Burning rate of propane-butane mixture:

• with normal combustion 0.8 - 1.5 m/sec.;
• with remote control (with explosion) 1.5 - 3.5 km/sec.

The explosion hazard limits of propane-butane at normal pressure are:

• mixed with air:

• lower – 1.5%;
• upper – 9.5%. lower – 2%;
  • mixed with oxygen:
• top – 46%.

Propane-butane mixtures in liquid form destroy rubber, so it is necessary to carefully monitor rubber products used in gas-flame equipment and, if necessary, replace them in a timely manner.

The greatest danger of rubber destruction exists in winter, due to the greater likelihood of the liquid phase of the propane-butane mixture getting into the hoses.

Acetylene is a flammable gas, colorless, tasteless, with a sharp, specific garlic odor, it is lighter than air. Its density relative to air is 0.9.

At normal atmospheric pressure (760 mm Hg) and temperature plus 20 degrees. From 1 cubic meter has a mass of 1.09 kg, air 1.20 kg.

At normal atmospheric pressure and temperature from - 82.4 degrees to - 84 degrees C, acetylene passes from a gaseous to a liquid state, and at a temperature of minus 85 degrees. C hardens.

Acetylene is the only gas widely used in industry, the combustion and explosion of which is possible in the absence of oxygen or other oxidizing agents.

In the gas-flame processing of metals, acetylene is used either in a gaseous state, obtained in mobile or stationary acetylene generators, or dissolved in acetylene cylinders. Dissolved acetylene according to GOST 5457-75 is a solution of gaseous acetylene in acetone, distributed in a porous filler under pressure up to 1.9 MPa (19 kgf/cm 2 ). Bulk fillers - birch activated carbon (BAC) and cast porous masses - are used as porous fillers.

The main raw material for the production of acetylene is calcium carbide. It is a dark gray or brownish solid. Acetylene is obtained as a result of the decomposition (hydrolysis) of pieces of calcium carbide with water. The yield of acetylene per 1 kg of calcium carbide is 250 dm3. To decompose 1 kg of calcium carbide, 5 to 20 dm3 is required. water. Calcium carbide is transported in hermetically sealed drums. The mass of carbide in one drum is from 50 to 130 kg.

At normal atmospheric pressure, acetylene with air and oxygen form explosive mixtures. Explosion limits of acetylene with air:

• lower – 2.2%;
• top – 81%.

Explosion limits of acetylene with oxygen:

• lower – 2.3%;
• top – 93%.

The most explosive concentrations of acetylene with air and oxygen are:

• lower – 7%;
• top – 13%.

For gas welding and cutting processes, various flammable gases can be used, when burned in a mixture with technical oxygen, the temperature of the gas flame exceeds 2000 °C. In terms of their chemical composition, with the exception of hydrogen, they are either hydrocarbon compounds or mixtures of various hydrocarbons.

For gas-flame processing, acetylene (C 2 H 2) is most widely used, during combustion, in the oxygen of which a flame is formed with a higher temperature than during the combustion of other flammable gases - acetylene substitutes.

Acetylene

Acetylene is an unsaturated hydrocarbon. Its chemical formula is C 2 H 2, structural formula H-C= S-N. At atmospheric pressure and normal temperature, acetylene is a colorless gas. Due to the presence of impurities in it, technical acetylene has a sharp, specific odor. At 20 °C and 0.1 MPa, the density of acetylene is p = 1.09 kg/m3. At atmospheric pressure, acetylene liquefies at a temperature of -82.4...-83.6 °C.

Complete combustion of acetylene occurs by the reaction

i.e., for complete combustion of 1 volume of acetylene, 2.5 volumes of oxygen are required. Higher heat of combustion of acetylene at 0 °C and 0.1 MPa (2 V = 58660 kJ/m 3. Heat of combustion of acetylene Q consists of the heat of the decomposition reaction of acetylene and the sum of the heat of the primary combustion reactions of carbon and hydrogen.

Acetylene decomposes according to the reaction

Heat of decomposition Qq = 225.8 kJ/mol or Qq = 8686 kJ/kg.

An important parameter of the welding flame, in addition to its temperature, is also the combustion intensity, which is understood as the product of the normal combustion rate and the heat of combustion of the mixture. Data on the combustion intensity of acetylene and some other combustibles are given in table. 2.1. Acetylene has the highest combustion intensity compared to other gases used in flame processing.

The auto-ignition temperature of acetylene lies in the range of 240-630 °C and depends on the pressure and the presence of various substances in acetylene. Increasing the pressure significantly reduces the auto-ignition temperature of acetylene. The presence of particles of other substances in acetylene increases the contact surface and thereby lowers the auto-ignition temperature.

When acetylene is compressed in a compressor to a pressure of 2.9 MPa, if the temperature at the end of compression does not exceed 275 °C, auto-ignition of acetylene does not occur. This allows you to fill cylinders with acetylene for long-term storage and transportation. With increasing pressure, the temperature limit for the beginning of the polymerization process decreases (Fig. 2.1).

In practice, when using acetylene, it is permissible to heat it to the following temperatures depending on the pressure: at a pressure of 0.1 MPa to 300 ° C, at a pressure of 0.25 MPa to 150-180 ° C, at higher pressures up to 100 ° C.

One of the important indicators of the explosiveness of flammable gases and vapors is ignition energy. The lower this value, the more explosive the substance is. The ignition energy of oxygen-gas mixtures is 100 times less than that of air-gas mixtures. Acetylene has the lowest ignition energy and is similar to hydrogen in terms of explosiveness.

Rice. 2.1.

Table 2.1

Gas combustion intensity

The presence of water vapor greatly reduces the ability of acetylene to spontaneously ignite from random heat sources and undergo explosive decomposition. In this regard, in acetylene generators, where acetylene is always saturated with water vapor, the maximum pressure by current standards is established: excess 0.15 MPa, absolute 0.25 MPa.

At atmospheric pressure, a mixture of acetylene with air is explosive if it contains 2.2% acetylene or more; mixture with oxygen - 2.8% acetylene or more. There is no upper explosive limit for mixtures of acetylene with air and oxygen, since pure acetylene can also explode with sufficient ignition energy.

The main method for producing acetylene is the processing of calcium carbide. This method is quite cumbersome, expensive and requires a large amount of electricity. Producing acetylene from natural gas is 30-40% cheaper than from calcium carbide. Pyrolysis acetylene, used for welding and cutting, is pumped into cylinders with a porous mass impregnated with acetone; its properties do not differ from acetylene obtained from calcium carbide.

In gas welding and cutting, the metal is heated by a high-temperature gas flame obtained by burning flammable gas or liquid vapor mixed with technically pure oxygen.

Oxygen is the most common element on earth, found in the form of chemical compounds with various substances: in the earth - up to 50% by weight, in combination with hydrogen in water - about 86% by weight and in air - up to 21% by volume and 23% by weight.

Oxygen under normal conditions (temperature 20°C, pressure 0.1 MPa) is a colorless, non-flammable gas, slightly heavier than air, odorless, but actively supporting combustion. At normal atmospheric pressure and a temperature of 0°C, the mass of 1 m3 of oxygen is 1.43 kg, and at a temperature of 20°C and normal atmospheric pressure - 1.33 kg.

Oxygen has high chemical activity, forming compounds with all chemical elements except inert gases (argon, helium, xenon, krypton and neon). Reactions of the compound with oxygen occur with the release of a large amount of heat, i.e. they are exothermic in nature.

When compressed gaseous oxygen comes into contact with organic substances, oils, fats, coal dust, flammable plastics, they may spontaneously ignite as a result of the release of heat during rapid compression of oxygen, friction and impact of solid particles on metal, as well as an electrostatic spark discharge. Therefore, when using oxygen, care must be taken to ensure that it does not come into contact with flammable or combustible substances.

All oxygen equipment, oxygen lines and cylinders must be thoroughly degreased. Oxygen is capable of forming explosive mixtures with flammable gases or liquid flammable vapors over a wide range, which can also lead to explosions in the presence of an open flame or even a spark.

The noted features of oxygen should always be kept in mind when using it in gas-flame processing processes.

Atmospheric air is mainly a mechanical mixture of three gases with the following volume content: nitrogen - 78.08%, oxygen - 20.95%, argon - 0.94%, the rest - carbon dioxide, hydrogen, nitrous oxide, etc. Oxygen are obtained by dividing air into oxygen and nitrogen by the method of deep cooling (liquefaction), along with the separation of argon, the use of which in argon arc welding is continuously increasing. Nitrogen is used as a shielding gas when welding copper.

Oxygen can be obtained chemically or by electrolysis of water. Chemical methods inefficient and uneconomical. When water is electrolyzed with direct current, oxygen is produced as a by-product in the production of pure hydrogen.

In industry, oxygen is obtained from atmospheric air by deep cooling and rectification. In installations for obtaining oxygen and nitrogen from air, the latter is cleaned of harmful impurities, compressed in a compressor to the appropriate refrigeration cycle pressure of 0.6-20 MPa and cooled in heat exchangers to the liquefaction temperature, the difference in the liquefaction temperatures of oxygen and nitrogen is 13 ° C, which sufficient for their complete separation in the liquid phase.

Liquid pure oxygen accumulates in an air separation apparatus, evaporates and collects in a gas holder, from where it is pumped into cylinders by a compressor under a pressure of up to 20 MPa.

Technical oxygen is also transported via pipeline. The pressure of oxygen transported through the pipeline must be agreed upon between the manufacturer and the consumer. Oxygen is delivered to the welding site in oxygen cylinders, and in liquid form in special vessels with good thermal insulation.

To convert liquid oxygen into gas, gasifiers or pumps with liquid oxygen evaporators are used. At normal atmospheric pressure and temperature 20°C, 1 dm3 of liquid oxygen upon evaporation gives 860 dm3 of gaseous oxygen. Therefore, it is advisable to deliver oxygen to the welding site in a liquid state, since this reduces the weight of the container by 10 times, which saves metal for the manufacture of cylinders and reduces the cost of transporting and storing cylinders.

For welding and cutting in accordance with GOST 5583-78, technical oxygen is produced in three grades:

• 1st - purity of at least 99.7%
• 2nd - no less than 99.5%
• 3rd - no less than 99.2% by volume

Oxygen purity is of great importance for oxyfuel cutting. The less gas impurities it contains, the higher the cutting speed, the cleaner the edges and the lower the oxygen consumption.

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Technical gaseous oxygen

Oxygen is essential in gas welding additional material, which provides a high combustion temperature of the flame so that the metal of the required thickness can be melted. It is used as the main temperature force, while other gases have a protective function. Oxygen is technically colorless and odorless. It is not flammable by itself, but when interacting with other substances it significantly increases the combustion temperature. It is not explosive like many others in this area. This is an accessible and relatively inexpensive substance. There are several technical varieties that differ in the content of impurities, their volume and quantity. The main indicator of quality is the volume of clean gas.

Technical oxygen in cylinders

Even with impurities, the gas retains high chemical activity. It forms a lot of chemical compounds that are found on Earth. Inert gases do not interact with it to form compounds. Gold, silver, platinum and other noble metals also survive its effects without a trace. Oxygen is most often stored in liquid form, as it is more compact, convenient and economical. Often its transformation into a gaseous state begins at the point of use.

Scope of application in welding

Technical gaseous oxygen is very widely used in welding in shielding gases. Regardless of the main shielding gas, the second substance supplied to the torch is almost always oxygen. It can be found in construction, where metal structures and frames for future buildings are created. It is also mandatory in every welding workshop. Gas is used in the repair of pipes, thin metal products, in repair shops, in production in assembly shops, and so on.

Oxygen is most actively used when cutting metal. Here the substance is fed into the burner under high pressure, which gives a long and powerful jet. This allows you to cut through metal products to a greater thickness. With this burning, the edges turn out to be quite smooth.

Types of technical oxygen

Technical gaseous oxygen is produced in accordance with GOST 5583-65. According to this standard, there are two main grades that are used in industry. Naturally, there are other, more contaminated options that can be used in the private sphere, but they are not relevant to the standards of serious production work, where high responsibility is placed on the connections. There are first and second grades of gas with different technical characteristics.

Characteristics of brands of oxygen gas

Despite the fact that both grades are used in almost the same field and in many cases are interchangeable, sometimes only the first grade is required for welding. The differences in their characteristics are also not fundamentally significant, just like the differences in composition. Here are the basic details for each option:

Characteristics of brands of liquid technical oxygen

Liquid oxygen is pale blue in color. Thanks to this, oxygen is supplied in blue cylinders. The liquid is a powerful paramagnetic. The specific density of this material is 1.141 g/cm3. The liquid has moderately cryogenic properties. Its freezing point is -222.65 degrees Celsius. It begins to boil already at a temperature of -182.96 degrees Celsius. This substance is produced in an industrial environment by fractional distillation of air.

Technical designation

The main standard by which technical oxygen is produced is GOST 5583-78. This standard applies to both medical and technical oxygen. Gas is obtained from atmospheric air, for which low-temperature rectification is used, or by electrolysis of water. The composition, permissible presence and ratio of impurities for each grade are indicated here. There are also operating instructions and other important data. For use in official enterprises, this GOST is the main one.

Instructions for the use of technical oxygen in welding

Before starting welding, you need to check the cylinder. There should be no oil or other contaminants on it, as this may cause fire and accident. The cylinder must be in a vertical position and be well secured so that it does not fall when the welder moves.

The distance from the cylinder to the flame source should not be less than 5 meters.”

Before starting welding, shielding gas is first introduced. Having figured out what oxygen is needed for, it is worth understanding that it significantly increases the combustion temperature and to check the functionality of the burner, as well as to warm up the parts, its use may be unnecessary. When the actual welding begins. Then it is worth releasing gas according to the welding parameters for a particular case, depending on the workpiece.

Security measures

To avoid an accident during use, you should follow certain rules that can reduce all dangers to a minimum. The main security measures include the following:

• Do not allow the gas concentration in the room to exceed 23%, as this may lead to an increased risk of fire;
• Despite the fact that oxygen is a non-flammable substance, it has a strong effect on other elements, so when working with it you need to use only a certain range of approved materials;
• If contact occurs with oily substances, they oxidize almost instantly, which can cause an explosion or fire;
• It is strictly forbidden to use cylinders that previously contained oxygen for other flammable substances;
• During transportation, it is necessary to exclude the possibility of shocks, falls and other factors of damage.

Conclusion

Physical and chemical properties oxygen make it a unique gas for the welding field. If protective gases have analogues and can be replaced, if necessary, then there is nothing to replace this one with. The use has its own safety features, but it is not as scary as when using acetylene and other gases.

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To produce a high-temperature welding flame, gas or vapor of a flammable liquid is burned in pure oxygen. If the combustion of fuel occurs not in oxygen, but in air, where oxygen makes up 7% by volume, then the flame temperature will be much lower.

Oxygen at atmospheric pressure and ordinary temperature is a colorless, odorless gas. It is heavier than air. At atmospheric pressure and temperature 0°C, 1 m3 of oxygen weighs 1.43 kg.

Technical oxygen is obtained from air at oxygen plants and delivered to the welding site, usually in compressed form in steel cylinders under a pressure of 150 atm.

Oxygen can also be supplied to the welding site through a pipeline from an oxygen station at a pressure of 5 to 30 atm.

At a temperature of minus 183 ° C and atmospheric pressure, oxygen turns into a bluish, easily evaporating liquid. 1 liter of liquid oxygen upon evaporation gives 790 liters, or 0.79 m\ of gaseous oxygen at atmospheric pressure and temperature 0°C.

Liquid oxygen is stored and transported in special vessels (tanks), well insulated from heat environment.

When using liquid oxygen for welding and cutting, it is first converted into gas by evaporating in special devices called gasifiers.

Combustible gases and flammable liquids form explosive mixtures when combined with oxygen. Fat and oil may spontaneously ignite when in contact with compressed oxygen. In order to protect against possible accidents, all oxygen equipment is thoroughly degreased. During operation, it is necessary to strictly ensure that oil and grease cannot get on the parts of the oxygen equipment.

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Gas for welding - what provides such a powerful flame?

There are many types of welding. The division is based on the method of producing a high-temperature weld pool (type of energy). For example, welding with electric arc, ultrasound, gas flame and others. This torch can cut and weld any metal. The edges of the metal parts being welded literally melt and, when joined, form a new single structure at the place of the alloy, called the weld.

Welding gases include, first of all, acetylene for welding, released as a result of the reaction of calcium carbide with water. Mixing with oxygen, it allows you to obtain a flame temperature of over three thousand degrees.

Propanes, butanes, liquefied MAFs (new gases that replaced acetylene), benzenes, kerosenes and others are also considered welding. An important feature of the use of welding gases is the mandatory presence of oxygen as a combustion catalyst. Moreover, the developed temperature also depends on the quality (purity) of oxygen supplied to the burner.

The gas mixture for welding using technically pure oxygen provides very intense and complete combustion of the mixture itself or vapors of combustible substances, since it provides very high combustion temperatures. The amount of oxygen in the flame will determine its oxidizing or reducing properties.

On the other hand, the use of technical (pure) oxygen requires special cylinders for its storage and supply. When mixed with such oxygen, some gases or compounds may be explosive (due to the extremely high rate of their combustion in such a catalyst).

Often they themselves can be dangerous due to their toxicity. For example, acetylenes, cyanines, etc.

The use of oxygen contained in atmospheric air makes welding gas mixtures less effective. Their combustion slows down, which sharply reduces the flame temperature. The reason is that in the air oxygen makes up no more than a fifth of it; other gases are present to a greater extent, the same nitrogen, for example.

In addition to the above, welding under conditions of using atmospheric oxygen often does not produce the required geometry of the connecting seam and changes the properties of the metal in this zone, which ultimately affects the quality of the connection.

Technical gases are used not only in welding. Shielding gases are also widely used for electric arc welding, etc. The use of various inert (helium, argon) or active (nitrogen, CO2, hydrogen, oxygen) gases as a protective medium for the welding molten pool significantly improves the quality of the result, increases the speed of work, allows you to obtain the required seam parameters, etc.

The principle of gas shielded welding is simple. The required composition is supplied to the arc zone through the nozzle of a special burner under pressure, creating this very protective environment. Popular semi-automatic welding systems are based on this principle.

Such welding is available not only in factory conditions, it is widely used in workshops and even in private garages. Most often, the gas for semi-automatic welding is a mixture of inert and carbon dioxide (in various proportions). Of the inert ones, helium and argon are more applicable. In practice, it is common to use argon, which is why CO2 and argon are present in the composition.

In general, inert gas for welding is needed to protect the molten pool from external exposure to air, as well as if it is necessary to carry out high-quality welding work on stainless steels, titanium and its alloys, non-ferrous metals (nickel, copper, aluminum and alloys), etc. When In this case, the electrode can be anything: a classic melting one, which does not change its shape and structure (serving to create an arc), etc.

The choice of gas needed for welding is influenced by what metal is used in the work. The same mixture of CO2 and argon when welding steel elements contains more carbon dioxide component (about 18%). And when welding stainless steels, argon predominates (98%), CO2 makes up only two percent.

Thus, what gas is used for welding is determined by the metal, its grade, the necessary properties of the seam, the types of welding equipment, requirements for the chemical composition and even the shape of the seams, work conditions, etc.