In recent years, with the increase in the amount of oxygen, oxygen is used to transport the large number of oxygen pipelines. Because the pipeline is long, widely distributed, coupled with the rapid opening or closing valves, oxygen pipelines and valve combustion explosion accidents occur, so, comprehensive analysis of oxygen pipelines and the hidden dangers of the unpopular, and take appropriate measures is essential.

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

1. The rust, dust, solder slag in the pipe and the inner wall of the pipe or the valve mouth friction produce high temperature combustion.

This situation is related to the types of impurities, particle size and airflow velocity, iron powder easily and oxygen burning, and the finer particle size, the lower the ignition point, the faster the gas speed, the more prone to combustion.

2. In the pipeline or valve in the presence of grease, rubber, such as low ignition of substances, in the local high-temperature ignition.

Ignition point of several combustible materials in oxygen (atmospheric pressure):

Combustible name Ignition Point (℃)

Lubricating Oil 273~305

Steel Paper Mat 304

Rubber 130~170

Fluorine Rubber 474

Tri-chloro Ethyl 392

PTFE 507

3. adiabatic compression produces the high temperature causes the combustiblematerial to burn

For example, the valve before 15MPa, temperature is 20 ℃, after the valve for atmospheric pressure 0.1MPa, if the valve is opened quickly, the oxygen temperature after the valve according to the adiabatic compression formula can be calculated up to 553 ℃, which has reached or exceeded the point of ignition of certain substances.

4. Reduction of ignition point of combustible material in high pressure pure oxygen is the inducement of oxygen pipe valve burning

Oxygen pipelines and valves in high pressure pure oxygen, the risk is very large, the test proved that the ignition of fire and the pressure is inversely proportional to the square, which poses a great threat to oxygen pipelines and valves.

Ii. Preventive measures

1. Design should comply with relevant regulations, standards and regulations

The design should be in accordance with the 1981 metallurgy issued by the "iron and steel enterprises oxygen Pipe Network," and "oxygen and related gas safety technical regulations" (gb16912-1997), "Oxygen Station design Code" (gb50030-91) and other regulatory standards.

(1) The maximum oxygen flow rate of the carbon steel pipe should conform to the table below.

Maximum flow rate of oxygen in carbon steel tubes:

Work 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 the oxygen valve, should be connected to a length of not less than 5 times times the diameter of the pipe, and not less than 1.5m copper base alloy or stainless steel pipe.

(3) Oxygen pipeline should be set as little as possible elbow and fork head, work pressure of more than 0.1MPa oxygen pipe elbow, should be taken into valve-type flange production. The flow direction of the bifurcation head shall be 45° to the 60° angle with the charge airflow direction.

(4) in the butt welding flange, the use of copper wire for O-ring, is the oxygen usage of blue fire-resistant reliable sealing form.

(5) The oxygen pipeline should be conductive good device, grounding resistance should be less than 10 Ω, the resistance between the flange should be less than 0.03 ω.

(6) The end of the main oxygen pipeline in the workshop shall be provided with a diffuse tube to facilitate the purge and replacement of the oxygen pipe, and the filter shall be set before the longer oxygen pipeline enters the workshop control valve.

2. Installation Considerations

(1) Where the contact with the oxygen to be strictly skimmed, skim after the use of oil-free dry air or nitrogen blown clean.

(2) welding should be using Argon arc welding or arc welding.

3. Operation Precautions

(1) Switch oxygen valve should be slow, operators should stand on the side of the valve, open to be in place once.

(2) It is strictly prohibited to use oxygen to blow the pipe or use oxygen to test the leak, test pressure.

(3) The operation of the ticket system, prior to the operation of the purpose, methods, conditions for a more detailed description and provisions.

(4) The diameter is larger than 70mm manual oxygen valve, when the valve is reduced before and after the pressure difference to 0.3MPa only to allow the operation.

4. Precautions for maintenance

(1) Oxygen pipeline to constantly check maintenance, derusting paint, every 3-5 years.

(2) The safety valve and pressure gauge on the road should be calibrated regularly, 1 years and 1 times.

(3) Perfect grounding device.

(4) Before the hot work, should be replaced, swept, blown out of the gas in the oxygen content in the 18%~23% for qualified.

(5) Valves, flanges, gaskets and pipes, fittings should be used in accordance with the "Oxygen and related gas safety technical regulations" (gb16912-1997) relevant provisions.

(6) Establish technical files, training operations, overhaul, maintenance personnel.

5. Other security measures

(1) To improve the construction, maintenance and operation of personnel to the safety of the degree of attention.

(2) Improve the vigilance of managers.

(3) Improve the level of science and technology.

(4) Continuously improve the oxygen delivery program.

Summary：

The real reason for disabling the gate valve is that the sealing surface of the gate valve in the relative motion (that is, valve switch) will cause abrasion damage caused by friction, once damaged, there is "iron powder" from the sealing surface off, so that small particles of iron powder is easy to fire burning, this is the real danger.

In fact, the oxygen pipeline to disable the gate valve, the other cut-off valve as there is an accident, the sealing surface of the valve will be damaged, as well as risk, many enterprises experience is the oxygen pipeline all use copper alloy valve, no carbon steel, stainless steel valves.

Copper base alloy valves with high mechanical strength, wear-resistant, safe (no static) and so on, so the real reason is because the gate valve sealing surface is very easy to wear the iron filings are the culprit, as to whether the sealing is not the key to decline.

In fact, many oxygen pipelines that do not use gate valves have exploded, generally appear in the valve on both sides of the larger pressure, the valve opened faster moments, many accidents also indicate that the source of fire and combustible material is the ultimate reason, the ban gate valve is only a means of control of combustible, and regularly remove rust, skim, The purpose of the prohibition of oil and other means is the same, as to control the flow rate, do a good job of electrostatic grounding is to eliminate the source of ignition. Personally think valve material is the first factor, in the hydrogen pipeline also appeared similar problems, the new norms have been "prohibited gate valve" word removed, is a proof that the key to find the reason, many enterprises in fact, regardless of operating pressure, are forced to use copper-based alloy valve, but the same explosion accident occurred, So control the source of fire and combustible materials, careful maintenance, tight security This string is the most critical.

In accordance with the "GB 16912-1997 oxygen and related gas safety technical regulations" on the valve material requirements:

When the pressure is greater than 0.1MPa, the use of gate valve is prohibited

0.1mpa<p≤0.6mpa, the disc is stainless steel,

0.6mpa<p≤10mpa, all stainless steel or all copper base alloy valves,

P>10mpa, all copper based alloys.