Several Reasons and Preventive Measures for Flame and Explosion of Oxygen Valve, Pipeline Valve
With the increase of oxygen consumption, oxygen pipelines are used for transport large oxygen. Owing to the long pipeline and wide distribution, combined with the quick opening or quick closing of valves, accidents of combustion and explosion of oxygen pipelines and valves occur from time to time. Therefore, it is essential to comprehensively analyze the hidden dangers and dangers of oxygen pipelines and cold valves and take corresponding measures.
I. Causes of Combustion and Explosion of Several Common Oxygen Pipelines and Valves
1.1 The rust, dust, welding slag in the pipeline rubs against the inner wall of the pipeline or the valve orifice to produce high temperature combustion.
This situation is related to the type of impurities, particle size and gas velocity. Iron powder is easy to burn with oxygen, and the finer the particle size, the lower the ignition point; the faster the gas velocity, the easier the combustion occurs.
1.2. Low ignition point substances such as grease and rubber exist in pipes or valves and ignite at local high temperature.
The ignition point of several combustibles in oxygen (atmospheric pressure);
Name of combustibles: ignition point ()
Steel Paper Cushion 304
Ethyl trichloride 392
1.3 The high temperature produced by adiabatic compression causes combustibles to burn.
For example, the front of the valve is 15 MPa, the temperature is 20 C, and the back of the valve is 0.1 MPa. If the valve is opened quickly, the oxygen temperature behind the valve can be calculated as 553 C according to adiabatic compression formula, which has reached or exceeded the ignition point of some substances.
1.4 Reduction of ignition point of combustibles in high pressure pure oxygen is the cause of combustion of oxygen pipeline valves.
Oxygen pipelines and valves are very dangerous in high-pressure pure oxygen. Experiments show that the ignition energy is inversely proportional to the square of pressure, which poses a great threat to oxygen pipelines and valves.
2, Preventive Measures
2.1 Design shall comply with relevant regulations and standards.
The design shall meet the requirements of the Regulations on Oxygen Gas Network in Iron and Steel Enterprises issued by the Ministry of Metallurgy in 1981, and the Regulations on Oxygen and Related Gas Safety (GB16912-1997), and the Design Code for Oxygen Stations (GB50030-91).
(1) The maximum flow rate of oxygen in carbon steel pipe should conform to the following table.
Maximum flow rate of oxygen in carbon steel pipe:
Working pressure (MPa) = 0.10.1-0.60.6-1.61.6-3.0
Flow velocity (m/s) 20 13 108
(2) In order to prevent fire, after the oxygen valve, a section of pipe with a length not less than 5 times the diameter and no less than 1.5 m should be connected.
(3) Oxygen pipeline should have as few elbows and bifurcations as possible. Oxygen pipeline elbows with working pressure higher than 0.1 MPa should be stamped into valve flanges. The direction of the air flow at the bifurcation head should be 45 to 60 degrees from the direction of the main air flow.
(4) In butt-welding concave-convex flange, copper wire is used as O-ring sealing ring, which is a reliable sealing form for flame resistance of oxygen flange.
(5) Oxygen pipeline should have good conductive device, grounding resistance should be less than 10_, and resistance between flanges should be less than 0.03_.
(6) The end of the main oxygen pipeline in the workshop should be equipped with a release pipe to clean and replace the oxygen pipeline, and a filter should be installed before the longer oxygen pipeline enters the workshop control valve.
2.2 installation notes
(1) All parts in contact with oxygen should be degreased strictly and cleaned with dry oil-free air or nitrogen after degreasing.
(2) Argon arc welding or arc welding should be adopted.
2.3 matters needing attention in operation
(1) Switching oxygen valves should be carried out slowly. Operators should stand on the side of the valves and open them once in place.
(2) It is strictly forbidden to use oxygen to blow pipes or to test leakage or pressure with oxygen.
(3) Implementing the operation order system, and specifying in detail the purpose, method and conditions of operation in advance.
(4) Manual oxygen valves larger than 70 mm in diameter are allowed to operate when the pressure difference between front and back of the valves is reduced to less than 0.3 MPa.
2.4 Matters needing attention in maintenance
(1) Oxygen gas pipeline should be inspected and maintained regularly, rust removal and paint every 3-5 years.
(2) Safety valves and pressure gauges on pipelines shall be checked regularly once a year.
(3) Improve the grounding device.
(4) Before ignition, replacement and purging should be carried out. When the oxygen content in the blown gas is between 18% and 23%, it is qualified.
(5) Valves, flanges, gaskets, pipes and fittings shall be selected in accordance with the relevant provisions of the Technical Regulations for Oxygen and Related Gas Safety (GB16912-1997).
(6) Establishing technical files, training operation, overhaul and maintenance personnel.
2.5 other safety measures
(1) Improving the attention paid to safety by construction, maintenance and operators.
(2) Enhance the vigilance of managers.
(3) Improve the level of science and technology.
(4) Continuously improve the oxygen delivery scheme.
The real reason for banning the gate valve is that the sealing surface of the gate valve will be damaged by friction in relative motion (that is, the switch of the valve). Once damaged, the self-sealing surface of the “iron powder” will fall off, so that the fine iron powder can easily ignite and burn, which is the real danger.
In fact, gate valves are forbidden in oxygen pipelines. Accidents occur in other globe valves. The sealing surface of globe valves will be damaged as well as dangerous. The experience of many enterprises is that all oxygen pipelines adopt copper-based alloy valves instead of carbon steel and stainless steel valves.
Copper-based alloy valves have the advantages of high mechanical strength, wear resistance and safety (no static electricity), so the real reason is the sealing of gate valves.