Research on Problems and treatment measures in equipment and pipeline design and installation of oxygen station
For the oxygen station, the equipment and pipeline are the key parts. Especially during the production, transportation and storage of the oxygen station, a little carelessness may lead to various emergencies, threatening the personal safety of the operators. If the accident involves a large area, it may even have a great impact on the whole oxygen station. Based on this, based on the installation of oxygen station equipment and pipeline, this paper focuses on the possible problems in the installation process, then puts forward the corresponding solutions according to the relevant problems, and puts forward the precautions in the installation process of equipment and pipeline.
Industrial gas is the blood of industry. In recent years, with the rapid rise of China’s manufacturing industry, the number of oxygen stations has increased rapidly. However, oxygen stations are different from other buildings. Oxygen has strong oxidizability and is a combustion supporting gas (some national standards are still in use)
Oxygen is classified as combustible gas for control), including design, installation, operation, maintenance, etc. The installation of oxygen station is the key factor to ensure the later operation, so it is easy to leave various hidden dangers in the process of equipment and pipeline installation. These hidden dangers may evolve into safety accidents when oxygen production and other operations are carried out in the later oxygen station. The installation of oxygen station equipment and pipeline is a work with great difficulty and high technical requirements, which needs to be installed by professional construction units with corresponding qualifications and experience. In the whole installation process, attention must be paid to the installation quality, key points, key points and difficulties, and corresponding measures shall be taken to deal with it in real time according to the installation status of equipment and pipeline, Fundamentally eliminate hidden dangers and ensure the safe and stable operation of oxygen station.
Relevant problems in equipment and pipeline installation of oxygen station
Material problems of oxygen system
The correct selection of oxygen system materials is the premise to ensure the safe operation of oxygen station. The oxygen system materials include pipe, valve, flange, flange sealing gasket, etc., and the main parameters of oxygen pipeline selection include material, pipe diameter, wall thickness, slotted or seamless pipe and surface roughness. The material of oxygen pipeline shall be compatible with the oxygen concentration used under the design conditions, such as liquid oxygen pipeline, low-pressure oxygen pipeline, medium pressure oxygen pipeline, high-pressure oxygen pipeline, etc. The material requirements of oxygen pipeline in special use places are different, and some parts can not be confused, and the design specifications of gas stations and other national standards. Professional construction units can find problems in time and propose engineering design changes to avoid engineering losses and safety accidents caused by wrong use of materials.
Degreasing of oxygen system
Grease has strong activity in high-purity oxygen. Oxygen can directly support combustion, especially organic grease, carbohydrates and oil. Under the condition of high-temperature oxygen combustion, it is likely to directly produce violent chemical reaction, resulting in explosion fire and metal explosion. Other impurities, such as debris particles of other metals, will also produce electrostatic friction under high-speed flow and under the strong driving and buffering force of gas, resulting in metal combustion and explosion. Under various low-temperature weather conditions, these metal impurities may also be adhered to other sports equipment parts, resulting in sports equipment failure. Therefore, when installing equipment and pipelines in the oxygen station, the cleanliness of the system must be guaranteed, and the stains therein shall be thoroughly removed, including carbohydrates, impurities, metal debris, welding material splash and paint, All impurities such as oxides and product packaging materials.
Solutions in equipment and pipeline installation of oxygen station
Quality assurance of oxygen system design and installation materials
The materials of oxygen system are divided into metal materials and non-metal materials. The metal materials suitable for oxygen system mainly include: carbon steel pipe, 304/304l stainless steel pipe, 316/316l stainless steel pipe, copper and copper alloy pipe, aluminum and aluminum alloy pipe, nickel and nickel alloy pipe; Non metallic materials suitable for oxygen system mainly include: mainly used for valve, thread and flange sealing gasket. Common fluorinated polymers are polytetrafluoroethylene (PTFE) and polytrifluoroethylene (PCTFE).
Correct selection of oxygen pipeline
The main parameters selected for oxygen pipeline include: material, pipe diameter, wall thickness, jointed or seamless pipe, surface roughness, etc. The selection of oxygen pipeline shall strictly consider oxygen pressure, oxygen medium (oxygen/liquid oxygen), oxygen flow, oxygen purity and place of use (general place/special place). During engineering design and installation, the selection requirements of materials under different use environments are as follows:
- (1) During the installation and selection of liquid oxygen pipeline, the liquid oxygen temperature shall be – 183 ℃, and the selected materials must be able to withstand the low temperature environment of – 183 ℃ for a long time. Considering the material performance and engineering cost, S304 stainless steel seamless steel pipe (06gr19ni10) is often used, and carbon steel is not allowed.
- (2) The oxygen service pressure is ≥ 3.0MPa. The available pipes are: stainless steel seamless steel pipe, copper and copper alloy pipe (excluding aluminum copper alloy), nickel and nickel alloy pipe, stainless steel plate coil welded pipe (under the condition of inner wall weld polishing, it is allowed to be used in general places with service pressure less than 5MPa). When the oxygen service pressure is greater than 10MPa and the place of use is oxygen filling system and busbar system, stainless steel seamless steel pipe is not allowed.
- (3) When the oxygen service pressure is 0.6 – 3.0MPa, the available pipes include: stainless steel welded steel pipe, seamless steel pipe, stainless steel plate coil welded pipe, stainless steel seamless steel pipe, copper and copper alloy pipe, nickel and nickel alloy pipe; However, seamless steel pipes are not allowed to be used in the following situations: within the range of 5 times of the outer diameter behind the valve (not less than 1.5m) and 5 times of the outer diameter before and after the pressure regulating valve group (not less than 1.5m each), because the air flow in the upstream and downstream pipelines of the pressure regulating valve group changes sharply, and the impact phenomenon is easy to occur when the particles collide with the system wall caused by high-speed air flow and large eddy current.
- (4) When the oxygen service pressure is ≤ 0.6MPa, a wide range of pipes can be used, including welded steel pipe, stainless steel welded steel pipe, seamless steel pipe, stainless steel plate welded pipe, stainless steel seamless steel pipe, copper and copper alloy pipe, nickel and nickel alloy pipe; However, welded steel pipes and seamless steel pipes are not allowed to be used after the frequent operation area of valves on the distribution main pipe and after the blow off valve.
The selection of pipe diameter is mainly based on the flow rate. The flow rate refers to the average axial speed in the pipeline under the minimum pressure, temperature and maximum flow of design operation, which shall be considered from the flow rate of the minimum cross section of the pipeline or valve. Oxygen purity is also a factor affecting pipeline selection. For the bulk purification system of electronic gas, EP pipes are required for oxygen pipelines with oxygen purity ≥ 99.999% and dew point < – 70 ℃, and the valves shall also adopt diaphragm valves or bellows valves of low-carbon stainless steel of the same grade.
Quality assurance of on-site incoming materials
Pairing test shall be carried out for the purchased materials, and the correct specification, grade and accuracy of all accessories shall be confirmed. For example, for valves with flanges, whether the flanges, valves, pipe elbows and joints with confirmed pressure grades and specifications are the same as the pipe diameter and wall thickness. The material supplier shall provide the material certificate, which shall include the material composition, wall thickness, manufacturing standard, heat number, brand and inspection date of the material; Upon arrival of materials on site, unpacking inspection shall be carried out immediately to compare and recheck with the material certification documents. The wall thickness, heat number and appearance inspection shall be carried out on site. If damaged materials are found, the material supplier shall be contacted in time for replacement and delivery. It is strictly prohibited to use damaged materials. The arrival of materials and accessories shall be registered and classified, and the material registration system shall be established and improved. At the same time, it shall be noted that stainless steel pipes shall not be stored in contact with any carbon steel materials to avoid intergranular corrosion of stainless steel.
Before degreasing, the pipes shall be cleaned and dedusted, and the pipe fittings and valves shall also be dedusted. Trichloroethylene is recommended as degreasing agent, and carbon tetrachloride is prohibited. Containers, tools, gloves, etc. for degreasing must be degreased in advance, and pipes, gaskets, flanges, valves and other accessories installed in the oxygen system must be degreased. During degreasing of oxygen equipment pipeline, attention shall be paid to:
(1) After the degreasing agent is discharged, dry it with clean compressed air or dry nitrogen without oil and water.
(2) When degreasing the valve and flange, immerse the disassembled valve in a sealed container containing solvent for 1 – 1.5h, and then take it out for drying.
(3) Close the nozzle of the degreased pipe and inject dry nitrogen to prevent it from being polluted again. When degreasing the inner wall of the pipe, the reference data of solvent consumption are shown in the table:
Table. 1 reference for amount of degreasing solvent for inner wall of pipe
|Pipe inner diameter/mm||15||25||40||50||80||100|
(4) After degreasing, conduct appearance inspection first. There is no degreasing agent residue, corrosion, scaling, particulate matter, welding slag, electric welding or brazing flux, chips, sand or on-site garbage. After the degreasing inspection method is irradiated with ultraviolet lamp, there is no purple blue fluorescence and a little discoloration is acceptable. During pipeline inspection, the degreasing gauze can be inserted from one end and pulled out from the other end. The degreasing gauze can be illuminated by ultraviolet lamp to check whether there is purple blue fluorescence.
Precautions for equipment and pipeline design and installation of oxygen station
As the oxygen is transported through the pipeline with strong combustion supporting property, if a large amount of oxygen leakage occurs in the oxygen pipeline, it is very easy to cause fire and explosion accidents. Therefore, there should be some special safety requirements for the safety layout design of the oxygen pipeline to ensure the normal operation and safety of the oxygen pipeline.
- (1) The oxygen pipeline should be laid overhead, and the setting depth must meet the requirements. In short, the direct buried depth of the oxygen supply pipeline should be determined according to the load on the ground, and the pipe top should be ≥ 0.7m from the ground; When the pipeline passes through railways and roads, it is necessary to set casing, and its crossing angle shall be ≥ 45 °. Anti corrosion measures. At the same time, buried oxygen pipelines shall not be equipped with valves or flanges. When valves must be installed, independent valve wells shall be set.
- (2) When laying pipes in the workshop, they shall not directly pass through the indoor personal daily living room and office; In addition, the equipment pipeline of the oxygen station shall not pass through the area with high temperature. If it is necessary to arrange and operate in this area, thermal insulation protection measures shall be added in the special oxygen pipe section. The thermal insulation protection temperature in the pipe wall shall not be too high, usually not more than 70 ℃.
Welding process matters
In order to ensure the internal cleanliness of the oxygen pipeline, the internal welding forming surface must be smooth and free of welding slag and overlap, so as to ensure the smoothness of the welding surface of the oxygen pipeline. During welding, carbon steel pipes shall be primed with argon arc welding, and stainless steel pipes shall be pickled with full argon arc welding GTAW to remove the surface oxide layer. In order to ensure weld quality, 99.999% argon shall be used as protective gas in the pipeline during welding.
Non destructive radiographic testing shall be adopted for the weld quality of oxygen pipeline. The detection proportion of liquid oxygen pipeline and oxygen pipeline with design pressure > 4.0Mpa shall be 100%, and the quality grade shall be ≥ class II; The design pressure of oxygen pipeline is 1.0 – 4.0Mpa. Sampling inspection is adopted. The inspection proportion is generally 40% for fixed welded junction and 15% for rotating welded junction. The quality grade is ≥ class II; The design pressure of oxygen pipeline is less than 1.0MPa, the detection proportion is ≥ 5%, and the quality grade is ≥ grade III.
The gasket of the oxygen system shall be made of materials compatible with oxygen. During installation, the gasket size must be checked in detail to match the inner diameter of the pipe, so as to eliminate accumulated particles. At the same time, gasket sealant shall be avoided to prevent the sealant from entering the oxygen pipe due to extrusion. All parts of the oxygen system shall be designed and installed without lubricant. However, if lubrication is necessary for assembly, operation or operation of some parts, select a lubricant compatible with oxygen. Halogenated chlorotrifluoroethylene (CTFE) is generally used. The lubricant shall be on the lubricating surface and the amount shall be kept to a minimum.
For the ultra-high purity oxygen system used in electronic gas project, in addition to weld detection, the “five detection” pressure test, trace oxygen detection, trace water detection, particle detection and helium leak detection must also be carried out.
To sum up, with the rapid development of China’s industrial field, the use of oxygen by relevant enterprises continues to rise. If the stable and safe operation of the oxygen station cannot be guaranteed, it may threaten personal and equipment safety, and may also cause relevant enterprises to bear certain losses. Therefore, when designing and installing oxygen station equipment and pipelines, it is best to pay attention to relevant problems in the installation process, and take measures to ensure material quality and degrease, so as to effectively deal with relevant problems in the installation. In addition, in order to ensure the actual safety of the installation process, relevant personnel need to pay attention to matters related to layout, welding, etc.
Author: Xiao Peng
Source: China Oxygen Pipeline Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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