Causes of explosions in oxygen pipelines and valves and preventive measures

Thread Content

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 situation is related to the type and particle size of the impurities as well as the airflow velocity; iron powder tends to burn in reaction with oxygen, and the finer the particle size, the lower the ignition point ； The faster the gas flow rate, the easier it is for combustion to occur. 2. Substances with a low ignition point such as grease or rubber are present inside the pipes or valves, and they catch fire under local high temperatures. Ignition points of several combustibles in oxygen (at normal pressure): 3. The high temperature generated by adiabatic compression causes the combustibles 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 0.1 MPa at normal pressure, 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 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 energy required to initiate a fire 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. It should 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 the table below. Maximum flow rate of oxygen in carbon steel pipes: (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 long 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) The oxygen pipeline 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 installed 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, and 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 all the way at once. (2) It is strictly prohibited to use oxygen to clean pipes or to perform leak testing or pressure testing 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, purging and blowing should be performed; the oxygen content in the blown 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 operational personnel. (2) Raise the awareness of managers. (3) Improve the level of science and technology. (4) Continuously improve the oxygen delivery plan.