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Why is it forbidden to use gate valve in oxygen pipeline?

In recent years, with the increase of oxygen consumption, oxygen pipelines are used by large oxygen users. Due to the long pipeline and wide distribution, and the quick opening or closing of valves, the combustion and explosion accidents of oxygen pipelines and valves occur frequently. Therefore, it is very important to comprehensively analyze the hidden dangers and dangers of oxygen pipelines and cold valves and take corresponding measures.

gate valve in oxygen pipeline

Analysis on the causes of combustion and explosion of several common oxygen pipelines and valves

1. The rust, dust and welding slag in the pipeline will burn in high temperature due to friction with the inner wall or valve port of the pipeline.
This situation is related to the type, particle size and air flow speed of impurities. Iron powder is easy to burn with oxygen, and the finer the particle size is, the lower the ignition point is; the faster the gas speed is, the more likely it is to burn.
2. There are grease, rubber and other substances with low ignition point in the pipeline or valve, which are ignited under local high temperature.

Ignition point of several combustibles in oxygen (at atmospheric pressure):

Name of combustible

Lubricating oil   

Steel paper pad

Rubber

Viton

Trichloroethyl

Polytetrafluoroethylene

Ignition point (℃)

273~305

304

130~170

474

392

507

3. The high temperature generated by adiabatic compression causes the combustibles to burn.
For example, 15MPa in front of the valve, 20 ℃ in temperature and 0.1MPa in atmospheric pressure behind the valve. If the valve is opened quickly, the oxygen temperature behind the valve can reach 553 ℃ according to the adiabatic compression formula, which has reached or exceeded the ignition point of some substances.
4. The ignition point reduction of combustibles in high pressure pure oxygen is the cause of combustion of oxygen pipeline valves.
Oxygen pipeline and valve are very dangerous in high-pressure pure oxygen. Experiments show that the ignition energy of ignition is inversely proportional to the square of pressure, which poses a great threat to oxygen pipeline and valve.

Preventive measures

1. The design shall comply with relevant regulations and standards.
The design shall be in accordance with the requirements of several regulations on oxygen pipe network of iron and steel enterprises issued by the Ministry of metallurgy in 1981, technical code for safety of oxygen and related gases (gb16912-1997), code for design of oxygen station (gb50030-91), etc.
(1) the maximum flow rate of oxygen in carbon steel pipe shall conform to the following table.
Maximum flow rate of oxygen in carbon steel pipe:

Working pressure (MPA)

≤0.1

0.1~0.6

0.6~1.6

1.6~3.0

Flow rate (M / s) 

20

13

10

8

(2) In order to prevent fire, after oxygen valve, a section of copper base alloy or stainless steel pipe with length not less than 5 times of pipe diameter and not less than 1.5m shall be connected.
(3) Elbows and bifurcations shall be set as less as possible for oxygen pipes. Elbows of oxygen pipes with working pressure higher than 0.1MPa shall be made by stamping into valve flange. The air flow direction of the bifurcation head shall be 45 ° to 60 ° with that of the main pipe.
(4) In the butt welding concave convex flange, the copper welding wire is used as the O-ring, which is a reliable fire-resistant sealing form for the oxygen flange.
(5) Oxygen pipeline shall have good conductive device, the grounding resistance shall be less than 10 Ω, and the resistance between flanges shall be less than 0.03 Ω.
(6) The end of the main oxygen pipeline in the workshop shall be provided with a vent pipe to facilitate the purging and replacement of the oxygen pipeline. Before the long oxygen pipeline enters the workshop control valve, a filter shall be provided.
2. Installation precautions
(1) All parts in contact with oxygen shall be degreased strictly, and the degreased parts shall be cleaned with dry air or nitrogen without oil.
(2) Argon arc welding or electric arc welding shall be adopted for welding.
3. Operation precautions
(1) The oxygen valve shall be opened and closed slowly. The operator shall stand on the side of the valve and open it once in place.
(2) It is forbidden to use oxygen to blow the pipeline or use oxygen to test the leakage and pressure.
(3) Implement the operation ticket system, and make a detailed description and regulation of the operation purpose, method and conditions in advance.
(4) For the manual oxygen valve with diameter greater than 70mm, it is allowed to operate when the pressure difference between the front and back of the valve is reduced to within 0.3MPa.
4. Precautions for maintenance
(1) Oxygen pipeline shall be inspected and maintained frequently, derusted and painted every 3-5 years.
(2) The safety valve and pressure gauge on the pipeline shall be regularly calibrated once a year.
(3) Improve the grounding device.
(4) Before hot work, replacement and purging shall be carried out, and it is qualified when the oxygen content in the blown gas is 18% – 23%.
(5) The selection of valves, flanges, gaskets, pipes and pipe fittings shall comply with the relevant provisions of technical code for safety of oxygen and related gases (gb16912-1997).
(6) Establish technical files, train operators, maintenance personnel.
5. Other safety measures
(1) Improve the attention of construction, maintenance and operation personnel to safety.
(2) Improve the vigilance of managers.
(3) Improve the level of science and technology.
(4) Constantly improve the oxygen delivery scheme.

Conclusion:

The real reason why the gate valve is forbidden is that the sealing surface of the gate valve will be scratched and damaged due to friction in the relative movement (i.e. the switch of the valve). Once it is damaged, there will be “iron powder” falling off from the sealing surface, so that the small iron powder is easy to ignite and burn, which is the real danger.
As a matter of fact, gate valves are not allowed in oxygen pipelines. Other stop valves have accidents, and the sealing surface of stop valves will be damaged, which may cause danger. The experience of many enterprises is that all oxygen pipelines use copper based alloy valves instead of carbon steel and stainless steel valves.
The copper base alloy valve has the advantages of high mechanical strength, wear resistance, good safety (no static electricity), etc., so the real reason is that the iron chips produced due to the extremely easy wear of the sealing surface of the gate valve are the culprit, as for whether the sealing performance is reduced or not is not the key.
In fact, many oxygen pipelines without gate valve have the same explosion accidents, which usually occur at the moment when the pressure difference on both sides of the valve is large and the valve is opened quickly. Many accidents also show that the ignition source and combustibles are the final reason. Banning gate valve is just a means to control combustibles, and the purpose of regular removal of rust, degreasing, oil prohibition and other means is the same. As for the control of flow rate and electrostatic grounding, it is necessary to eliminate the ignition source.
I think the valve material is the first factor, and there are similar problems in the hydrogen pipeline. In the new specification, the word “forbidden gate valve” has been removed, which is a clear proof. The key is to find out the reason. In fact, many enterprises, regardless of the operating pressure, are forced to use copper based alloy valves, but there are also explosion accidents, so they control the fire source and combustibles and carefully maintain them. Safety is the key.
Source: Best china gate valve provider: www.pdxsteel.com

How can you tell if a gate valve is open or closed?

A clockwise rotation of the gate moves the stem back into the gate and closes thevalve. When the stem is no longer protruding beyond the handle, the gate valve isclosed. You can look at a gate valve and tell if it is open or closed by the position of the stem.

Can we choose a gate valve when the medium is oxygen?

According to the characteristics of the gate valve, the gate valve should not be used to adjust the flow and pressure. Otherwise, the sealing surface will wear quickly and the tightness will decrease.
Moreover, the gate valve cannot be pressure-regulated by slowly opening. Gate valves are not suitable for oxygen piping. The reason for disabling the gate valve in the peroxygen pipeline is that the sealing surface of the gate valve causes iron powder to be detached from the sealing surface due to friction during relative movement. Although this seems so trivial in our usual, in the high-pressure pure oxygen environment, these small particles of iron powder are very easy to burn after the ignition point, which will bury the safety hazard.
Here, there is one more point to note, that is, the safety hazards of the oxygen pipeline are not all blamed on the gate valve. An explosion can occur when the pressure difference between the two sides of the valve is large. From the lessons learned from the accident, the ban on gate valves is actually prohibiting the generation of combustibles. This is the same as the purpose of regularly removing rust, skim, and oil. To further control the flow rate, do a good job of electrostatic grounding, etc., to eliminate the fire source measures, this has a great relationship with the valve material. Although copper-based alloy gate valves have a significant effect on the elimination of combustibles than cast iron-cast gate valves, this does not mean that safety hazards do not exist. The reason is that there is no control of the fire source, and it is impossible for the source to control only whether the gate valve is safe or not. Attention to the operating pressure and careful maintenance of all stages of the pipeline must be tight and safe, not just the use of gate valves.

Why is it forbidden to use gate valve in oxygen medium pipeline? What is the reason for this rule?

In fact, this is mainly related to the movement mode of gate valve. The opening and closing mode of gate valve is the vertical movement of gate valve. Shutter and valve seat may produce strong friction and sparks. Since the contact between the valve plate and the valve seat is not continuous, static electricity may be generated. This makes the use of gate valves in flammable and explosive oxygen medium pipelines extremely dangerous. Next we will analyze this situation in detail.

Summary
Why is it forbidden to use gate valve in oxygen pipeline?
Article Name
Why is it forbidden to use gate valve in oxygen pipeline?
Description
The real reason why the gate valve is forbidden is that the sealing surface of the gate valve will be scratched and damaged due to friction in the relative movement (i.e. the switch of the valve).
Author
Publisher Name
www.pdxsteel.com
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