Safety technology of the hottest oxygen pipeline a

2022-08-05
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Safety technology for oxygen pipes and accessories

1 selection of oxygen pipe materials and fittings

the materials of oxygen pipes shall be selected according to the pressure, temperature and flow rate of oxygen in the pipeline. In addition to meeting the strength conditions like other pipelines, oxygen pipelines also need to be corrosion-proof and rust proof to maintain the integrity of parts and components Fire protection requirements

1.1 selection of pipes

considering the temperature conditions, the oxygen pipes under normal temperature generally use steel pipes. However, in the oxygen plant, because the steel has cold brittleness below – 40 ℃, aluminum alloy, copper alloy or stainless steel must be used for pipes working at low temperature. These materials still have good strength and toughness at low temperature

from the perspective of pressure conditions, the oxygen pipeline with working pressure greater than 3 MPa shall adopt brass pipe or red copper pipe. Seamless steel pipes are generally used when the pressure is less than 3 MPa. In order to avoid the friction of high-pressure oxygen flow on the pipe wall when it flows at a high speed in the pipe and the possible pipe combustion caused by small combustibles, the oxygen flow rate of carbon steel pipes shall be limited

the selection of pipes shall comply with the provisions in Table 1

the range of 5 times the outer diameter behind the valve (not less than 1.5m); Within 5 times of the outer diameter (not less than 1.5m) at the front and rear of the pressure regulating valve group; Pressure vessel connecting pipe; Inside the oxygen pressure workshop; After the blow off valve; Wet oxygen transmission

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5 times beyond the back of the valve (not less than 1.5m); Within 5 times of the outer diameter (not less than 1.5m) at the front and rear of the pressure regulating valve group; Pressure vessel connecting pipe; Inside the oxygen pressure workshop; After the blow off valve; Wet oxygen transmission

general

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station

oxygen filling station and busbar room

note: 1, "√" is allowed“ ×” Not allowed

2. Carbon steel rolled steel pipe should be used when the working pressure is less than 0.1MPa and the pipe diameter exceeds that of the existing welded steel pipe, electric welded steel pipe and seamless steel pipe

3. Stainless steel plate coil welded pipe is allowed to be used in general places with pressure not higher than 5MPa under the condition that the inner wall weld is polished

1.2 selection of pipe fittings

the selection of elbows, bifurcation heads and reducer on oxygen pipes shall meet the following requirements:

it is strictly prohibited to use wrinkled elbows in oxygen pipes. When cold bending or hot bending is adopted for carbon steel elbow, the bending radius shall not be less than 5 times of the outer diameter of the pipe; When seamless or pressed welded carbon steel elbows are used, the bending radius shall not be less than 1.5 times of the outer diameter of the pipe; When stainless steel or copper base alloy seamless or pressed elbow is used, the bending radius shall not be less than the outer diameter of the pipe. For steel rolled welded pipes with working pressure not greater than 0.1MPa, welded elbows with bending radius not less than 1.5 times of the outer diameter of the pipe can be used. The inner wall of the elbow should be smooth without sharp edges, burrs and weld beading

seamless or pressed weldments should be used for the reducer of oxygen pipes. When welding, the length of the reducing part shall not be less than 3 times of the difference of each item outside the pipe at both ends; The inner wall shall be smooth without sharp edges, burrs and weld beading

the bifurcation head of the oxygen pipeline should be seamless or pressed weldment. When it cannot be obtained, it should be prefabricated in the factory or on site, but it should be processed to be free of acute angles, protruding parts and weld beading. It is not suitable to open holes or plug in on site

1.3 selection of pipe accessories

gaskets for flanges on oxygen pipes shall be selected according to relevant current national standards; Gaskets for pipe flanges shall be selected according to the following table:

gaskets for flanges on oxygen pipelines

annealed and softened copper strip

the connection of oxygen pipelines shall be welded, but the connection with equipment and valves can be connected by flanges or threads, and the wire mouth connection shall be connected by using lead oxide, water glass or polytetrafluoroethylene film as filler. It is strictly prohibited to use hemp or cotton thread coated with lead red or other materials containing grease

1.3 selection of valves

an oxygen filter should be set at the inlet of the oxygen compressor. An oxygen filter should be set in front of the regulating valve. The shell should be made of stainless steel. The filter should be made of copper based alloy or pure copper. Its hole size should be 160-200 μ m。

the valve of the oxygen pipeline shall be a special oxygen valve, which shall meet the following requirements:

1.3.1 for the valve with working pressure greater than 0.1MPa, it is strictly prohibited to use gate valve

1.3.2 the oxygen valve with PN ≥ 0.1MPa and DN ≥ 150mm should be the valve with bypass

1.3.3 the materials of valves shall meet the requirements in Table 3

material selection requirements for oxygen valve

note: 1 The material of pressure or flow regulating valve with working pressure above 0.1MPa shall be stainless steel or copper base alloy or a combination of the above two

2. The sealing packing of the valve shall be graphite treated asbestos or polytetrafluoroethylene or expanded graphite

large diameter oxygen valves with PN ≥ 1.0MPa and DN ≥ 150mm that are frequently operated should adopt pneumatic remote control valves

2 selection of hose

2.1 the oxygen hose is composed of the inner and outer rubber layers of the hose and the middle cotton fiber layer. The entire hose needs special chemical treatment to prevent its high flammability. The following safety requirements shall be paid attention to in the manufacture, storage, transportation and use of rubber hoses:

2.1.1 rubber hoses shall have sufficient strength and flame retardant characteristics

2.1.2 pay attention to maintenance when storing, transporting and using the hose, and keep the hose clean and free from damage; For example, avoid exposure to sunlight, rain and snow, and contact with acids, alkalis, Oils and other organic solvents that affect the quality of the hose. The storage temperature shall be -15-401 ℃, and the distance from the heat source shall not be less than 1m. If the sulfur in the rubber hose is decomposed due to poor maintenance during storage and use, or the rubber hose is aging and brittle for a long time, it will often cause backfire and explosion accidents

2.1.3 before using a new hose, the talc powder on the inner wall of the hose must be blown away to prevent the passage of the welding torch from being blocked. During use, avoid external extrusion and mechanical damage, and do not contact with the above substances that affect the quality of the hose, and do not fold the hose

2.1.4 oxygen and acetylene hoses shall not be mixed or substituted, and oxygen shall not be used to blow away the blockage of acetylene hoses. At the same time, the defects such as gas leakage and blockage of the welding and cutting torch shall be checked and eliminated at any time to prevent the formation of oxygen and acetylene mixture in the rubber tube

2.1.5 if the oxygen hose is backfired and enters the oxygen hose, it cannot be used any more and must be replaced. Because tempering often burns out the rubber layer in the hose, and compressed pure oxygen is a strong oxidant, if it is used again, it will lose its original normal safety

2.2 color differentiation of oxygen tube: the inlet hose is black; Domestic hoses are red. The oxygen hose shall be arranged in a standard manner (when installing the oxygen hose on the welding base of the station, it shall be separated from the natural gas hose connector, and it shall be inspected after installation. It can be used only after it is qualified, but it is very cheap); The oxygen hose must be used for special purposes. The oxygen hose shall not be used as an oxygen delivery hose after being used for other purposes; The hose shall be protected from damage, thermal burn and chemical corrosion during use; Where the oxygen hose is easy to be worn on the station, protective treatment shall be done to avoid hose wear and leakage

3 degreasing of oxygen pipes

compressed oxygen will immediately burn violently and cause an explosion when it contacts a small amount of grease. Therefore, the phenomenon that the oxygen pipe hinders the relative movement on the contact surface. The pipes, fittings, padding and all materials in contact with oxygen must be degreased strictly before installation and use

3.1 degreaser

the properties and uses of common degreasers can be seen in the following table:

properties and uses of common degreasers

in the presence of water and metals, it can hydrolyze to produce trace hydrochloric acid, which can have a strong decomposition reaction with some hot light metals, and even explode

the degreasing ability is weak

3.1.1 dichloroethane, carbon tetrachloride and trichloroethylene can hydrolyze to produce trace hydrochloric acid under certain conditions, Therefore, the pipes and accessories that need to be degreased must be free of moisture, otherwise it will cause corrosion

3.1.2 dichloroethane, trichloroethylene and alcohol are inflammables, which can only be used for degreasing metal parts, not for non-metal parts, because when the non-metal is infiltrated into the solvent and not completely evaporated and dried, it will burn and explode in case of compressed oxygen. For these flammable and explosive dangerous chemicals, attention should be paid to safety during use. Although carbon tetrachloride does not burn, it will decompose and generate phosgene in case of burning objects, Therefore, smoking and all kindling are prohibited

3.1.3 the degreaser is volatile and should be stored in a sealed container in a cool and ventilated place without direct sunlight and away from the fire source

3.1.4 carbon tetrachloride, dichloroethane and trichloroethylene are toxic, so the operation should be carried out in the open air or in a ventilated shed

3.1.5 degreaser shall not contact with concentrated acid and alkali, nor with carbide and other chemical products; Different degreasers cannot be used together

3.1.6 the oil content of the organic solution used for degreasing shall not be greater than 50 mg/L. The solvent with large oil content can be used for crude degreasing, and then degrease again with clean solvent. The solvent with oil content greater than 500 mg/l shall not be used

3.2 degreasing method

before degreasing the pipeline, remove the rust, oil stain and organic matter on the pipeline surface, and then degrease with degreasing agent

3.2.1 degrease the inner surface of the pipe, inject solvent into the pipe, and seal the pipe end with wood plug or other methods. Plug the other end after filling with solvent, and keep it flat for 15-20 minutes; Flow the tube 3-4 times within this time; Then pour the degreaser into the container; The pipe can also be tilted on the rack, and then the lint binding rod can be passed through the pipe with iron wire, and then the degreaser can be poured into the pipe, and the iron wire can be pulled for several times

3.2.2 when the inside and outside of the pipe need to be degreased, pour the degreaser into a special tank, put the pipe into the solution for 15-20 minutes, rotate the pipe several times within this time, and clean it with a brush; The tank shall be provided with a sealing cover to prevent the volatilization of degreasing agent. Large diameter pipes can be wiped by wiping method

3.2.3 before degreasing, the valve shall be grinded and pressure tested to be qualified, then disassembled into parts, soaked in degreasing agent for 1-1.5 hours, and cleaned with gauze to be qualified without oil; The bolts and metal gaskets shall be degreased in the same way, and the valve shell that is inconvenient to be soaked can be wiped

3.2.4 for degreasing of non-metallic gaskets, carbon tetrachloride solvent shall be used. The gaskets shall be immersed in the solvent for 1.5-2 hours, and then they shall be taken out and hung in the air circulation place or ventilation device and blown dry one by one until there is no solvent odor

what stages should be carried out in the tensile test of the metal material tensile testing machine

3.2.5 the degreased parts should be promptly drained of their internal liquid degreaser after degreasing, and can be dried with clean, oil-free and dry air or nitrogen; For flammable solvents, dry them with nitrogen with purity greater than 95%; It is forbidden to remove residual liquid by evaporation drying

3.2.6 asbestos filler can be burned at 300 ℃ for 2-3 minutes (smoke flame is not allowed), and then impregnated with the specified coating. The red copper gasket can not be degreased after annealing

3.2.7 the place for degreasing shall be far away from personnel and well ventilated. The degreasing personnel shall wear grease free gloves, work clothes and masks, and the tools used and the cotton cloth used for scrubbing shall not be contaminated with oil

3.2.8 degreased pipes and valves shall be sealed with grease free film plastic or metal

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