Oxygen pipeline valves
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Why is it strictly prohibited to use gate valves when the pressure in the oxygen pipeline exceeds 0.1 MPa? I can’t figure it out; is it for explosion prevention?
It is recommended that the original poster refer to Article 9.0.3 of the \"Design Code for Oxygen Stations GB 50030-1991\" regarding the selection of valves for oxygen pipelines; such valves must meet the following requirements: 1. Gate valves shall not be used for valves operating under a pressure greater than 0.1 MPa； Oxygen users mainly use them to regulate and control flow, and gate valves are generally not used.
In recent years, as oxygen consumption has increased, major oxygen users have adopted oxygen pipelines for delivery. Due to the long lengths and wide distribution of the pipelines, coupled with valves that open or close rapidly, accidents involving combustion and explosion in oxygen pipelines and valves occur from time to time. Therefore, it is crucial to conduct a thorough analysis of the potential hazards associated with oxygen pipelines and valves, and to take appropriate measures. I. Analysis of the causes of combustion and explosion in several common oxygen pipelines and valves 1. Rust, dust, and slag inside the pipeline rub against the inner wall of the pipeline or the valve openings, generating high temperatures that lead to combustion. This phenomenon is related to the type and size of the impurities as well as the flow rate of air; iron powder readily burns in contact with oxygen, and the finer the particle size, the lower the ignition point ； The faster the gas flow rate, the more likely combustion will occur. Table 1: Ignition points of iron powder in oxygen at atmospheric pressure. Particle size (mesh): 10–20, 20–30, 30–50, 100, 200. Ignition points (°C): 421, 408, 392, 385, 315. 2. Substances with low ignition points such as grease and rubber present in the pipes or valves can catch fire due to local high temperatures. The ignition points of several combustibles in oxygen (at normal pressure) are shown in Table 2. Table 2 shows the ignition points of several combustible materials in oxygen (at normal pressure) as follows:
Com combustible material Name Lubricating oil Steel paper gasket Rubber Fluororubber Trichloroethane Polytetrafluoroethylene Ignition point (°C) 273–305 304 130–170 474 392 507
3. The high temperature generated by adiabatic compression causes the combustible materials to burn.
For example, if the pressure before the valve is 15 MPa and the temperature is 20°C, while the pressure after the valve is normal pressure of 0.1 MPa, opening the valve quickly can result in an oxygen temperature of 553°C according to the adiabatic compression formula – a value that reaches or exceeds the ignition point of certain substances. The relationship between temperature and pressure after adiabatic compression of air is shown in Table 3. Table 3: Relationship between temperature and pressure after adiabatic compression of air. V1/V2: 1, 2, 3, 4, 5, 10, 15, 20. Pressure (MPa): 0.1, 0.26, 0.47, 0.95, 2.5, 4.42, 6.6. Temperature (°C): 20, 112, 183, 284, 462, 592, 697. 4. The reduced ignition point of combustible materials in high-pressure pure oxygen is a cause of combustion in oxygen pipeline valves. Oxygen pipelines and valves are extremely dangerous when exposed to high-pressure pure oxygen; experiments have shown that the ignition energy is inversely proportional to the square of the pressure, which poses a serious threat to such pipelines and valves. II. Preventive Measures 1. The design shall comply with relevant laws and regulations and standards. The design must meet the requirements set out in the \"Several Provisions on Oxygen Pipeline Networks in Steel Enterprises\" issued by the Ministry of Metallurgy in 1981, as well as other regulations and standards such as the \"Safety Technical Regulations for Oxygen and Related Gases\" (GB16912-1997) and the \"Design Code for Oxygen Stations\" (GB50030-91). (1) The maximum oxygen flow rate in carbon steel pipes shall comply with Table 4. Table 4 Maximum oxygen flow rate in carbon steel pipes. Operating pressure (MPa): ≤0.1, 0.1–0.6, 0.6–1.6, 1.6–3.0. Flow velocity (m/s): 20, 13, 10, 8. (2) To prevent ignition, a pipe made of copper-based alloy or stainless steel, with a length of at least 5 times the pipe diameter and at least 1.5 m in length, should be connected after the oxygen valve. (3) Oxygen pipelines should have as few elbows and branch connections as possible; for oxygen pipelines operating at a pressure higher than 0.1 MPa, the elbows should be manufactured using stamped valve-type flanges. The airflow direction at the branch point should form an angle of 45° to 60° with the airflow direction of the main pipe. (4) In butt-welded male and female flanges, using copper welding wire as the O-ring provides a reliable sealing method that ensures the flame resistance of flanges used for oxygen. (5) Oxygen pipelines shall be equipped with good conductive devices; the grounding resistance should be less than 10Ω, and the resistance between flanges should be less than 0.03Ω. (6) Bleed pipes should be installed at the ends of the main oxygen pipelines inside the workshop to facilitate purging and displacement of these pipelines. Filters should be placed before longer oxygen pipelines reach the control valves in the workshop. 2. Installation precautions (1) All areas in contact with oxygen must be thoroughly degreased; after degreasing, they should be cleaned using oil-free dry air or nitrogen. (2) Tungsten inert gas welding or arc welding should be used for welding. 3. Precautions for operation (1) The oxygen valve should be opened and closed slowly; the operator should stand to the side of the valve, and it should be opened completely in one motion. (2) It is strictly prohibited to use oxygen to clean pipes or to conduct leak tests or pressure tests with oxygen. (3) Implement an operation ticket system, providing detailed explanations and specifications in advance regarding the purpose, methods, and conditions of the operations. (4) For manual oxygen valves with a diameter greater than 70 mm, operation is permitted only when the pressure difference before and after the valve is reduced to within 0.3 MPa. 4. Precautions for maintenance (1) Oxygen pipelines should be regularly inspected and maintained, including rust removal and repainting, every 3 to 5 years. (2) The safety valves and pressure gauges on the pipelines must be calibrated regularly, once a year. (3) Improve the grounding system. (4) Before carrying out hot work, displacement and purging should be performed; the oxygen content in the blown-out gas is considered acceptable when it is between 18% and 23%. (5) The selection of valves, flanges, gaskets, as well as pipes and pipe fittings, shall comply with the relevant provisions of the \"Safety Technical Regulations for Oxygen and Related Gases\" (GB16912-1997). (6) Establish technical archives, and train operators, maintenance personnel, and repair staff. 5. Other safety measures (1) Raise the awareness of safety among construction, maintenance, and operating personnel. (2) Raise the vigilance of managers. (3) Improve the level of science and technology. (4) Continuously improve the oxygen delivery plan.
Com combustible material Name Lubricating oil Steel paper gasket Rubber Fluororubber Trichloroethane Polytetrafluoroethylene Ignition point (°C) 273–305 304 130–170 474 392 507
3. The high temperature generated by adiabatic compression causes the combustible materials to burn.
For example, if the pressure before the valve is 15 MPa and the temperature is 20°C, while the pressure after the valve is normal pressure of 0.1 MPa, opening the valve quickly can result in an oxygen temperature of 553°C according to the adiabatic compression formula – a value that reaches or exceeds the ignition point of certain substances. The relationship between temperature and pressure after adiabatic compression of air is shown in Table 3. Table 3: Relationship between temperature and pressure after adiabatic compression of air. V1/V2: 1, 2, 3, 4, 5, 10, 15, 20. Pressure (MPa): 0.1, 0.26, 0.47, 0.95, 2.5, 4.42, 6.6. Temperature (°C): 20, 112, 183, 284, 462, 592, 697. 4. The reduced ignition point of combustible materials in high-pressure pure oxygen is a cause of combustion in oxygen pipeline valves. Oxygen pipelines and valves are extremely dangerous when exposed to high-pressure pure oxygen; experiments have shown that the ignition energy is inversely proportional to the square of the pressure, which poses a serious threat to such pipelines and valves. II. Preventive Measures 1. The design shall comply with relevant laws and regulations and standards. The design must meet the requirements set out in the \"Several Provisions on Oxygen Pipeline Networks in Steel Enterprises\" issued by the Ministry of Metallurgy in 1981, as well as other regulations and standards such as the \"Safety Technical Regulations for Oxygen and Related Gases\" (GB16912-1997) and the \"Design Code for Oxygen Stations\" (GB50030-91). (1) The maximum oxygen flow rate in carbon steel pipes shall comply with Table 4. Table 4 Maximum oxygen flow rate in carbon steel pipes. Operating pressure (MPa): ≤0.1, 0.1–0.6, 0.6–1.6, 1.6–3.0. Flow velocity (m/s): 20, 13, 10, 8. (2) To prevent ignition, a pipe made of copper-based alloy or stainless steel, with a length of at least 5 times the pipe diameter and at least 1.5 m in length, should be connected after the oxygen valve. (3) Oxygen pipelines should have as few elbows and branch connections as possible; for oxygen pipelines operating at a pressure higher than 0.1 MPa, the elbows should be manufactured using stamped valve-type flanges. The airflow direction at the branch point should form an angle of 45° to 60° with the airflow direction of the main pipe. (4) In butt-welded male and female flanges, using copper welding wire as the O-ring provides a reliable sealing method that ensures the flame resistance of flanges used for oxygen. (5) Oxygen pipelines shall be equipped with good conductive devices; the grounding resistance should be less than 10Ω, and the resistance between flanges should be less than 0.03Ω. (6) Bleed pipes should be installed at the ends of the main oxygen pipelines inside the workshop to facilitate purging and displacement of these pipelines. Filters should be placed before longer oxygen pipelines reach the control valves in the workshop. 2. Installation precautions (1) All areas in contact with oxygen must be thoroughly degreased; after degreasing, they should be cleaned using oil-free dry air or nitrogen. (2) Tungsten inert gas welding or arc welding should be used for welding. 3. Precautions for operation (1) The oxygen valve should be opened and closed slowly; the operator should stand to the side of the valve, and it should be opened completely in one motion. (2) It is strictly prohibited to use oxygen to clean pipes or to conduct leak tests or pressure tests with oxygen. (3) Implement an operation ticket system, providing detailed explanations and specifications in advance regarding the purpose, methods, and conditions of the operations. (4) For manual oxygen valves with a diameter greater than 70 mm, operation is permitted only when the pressure difference before and after the valve is reduced to within 0.3 MPa. 4. Precautions for maintenance (1) Oxygen pipelines should be regularly inspected and maintained, including rust removal and repainting, every 3 to 5 years. (2) The safety valves and pressure gauges on the pipelines must be calibrated regularly, once a year. (3) Improve the grounding system. (4) Before carrying out hot work, displacement and purging should be performed; the oxygen content in the blown-out gas is considered acceptable when it is between 18% and 23%. (5) The selection of valves, flanges, gaskets, as well as pipes and pipe fittings, shall comply with the relevant provisions of the \"Safety Technical Regulations for Oxygen and Related Gases\" (GB16912-1997). (6) Establish technical archives, and train operators, maintenance personnel, and repair staff. 5. Other safety measures (1) Raise the awareness of safety among construction, maintenance, and operating personnel. (2) Raise the vigilance of managers. (3) Improve the level of science and technology. (4) Continuously improve the oxygen delivery plan.
When the gate and seat of a gate valve move, sparks may be generated or iron shavings may fall off, which is very dangerous; therefore, gate valves are prohibited from use.
During the opening and closing process of a gate valve, friction occurs between the valve disc and the valve seat, and debris tends to accumulate inside the valve seat.
For oxygen pipelines, the valves required are not of the quick-open/quick-close type; gate valves do not meet the requirements.
Oil-free treatment should also be applied, and it is better to choose copper or stainless steel valves.