Acetylene bottle
An acetylene cylinder is a gas cylinder filled with the technical gas ethine (acetylene gas) with the empirical formula C 2 H 2 . The gas is used, among other things , in oxy-fuel welding , oxy-fuel cutting and brazing .
In conventional gas cylinders, gases such as nitrogen , oxygen or argon are typically pressed at 200 bar.
Since acetylene decomposes explosively at a pressure of over 2 bar when it is vibrated and exposed to heat, it is dissolved in acetone or dimethylformamide (DMA) for storage . Acetylene in dissolved form is also known as dissous gas ([ dɪˈsuˌɡaːs ], from French dissoudre , dissous : to dissolve).
The acetylene bottle is also filled with a porous solid that reduces the risk of explosion if the liquid acetone or DMA does not fill the entire cavity. Use calcium silicate hydrate (cement powder), diatomaceous earth or the specially developed fabric Agamassan .
Ethyne is stored in the solvent at a pressure of around 19 bar and a temperature of 20 ° C.
General
A filling pressure of 19 bar is often specified for acetylene cylinders. At 19 bar absolute pressure and at a standard temperature of 15 ° C, acetylene is in equilibrium with its solution with a concentration of 0.64 kg per kg of acetone. The equilibrium pressure of the gas phase increases with the temperature:
| concentration | ||
|---|---|---|
| kg ethyne / kg acetone | ||
| 0.64 | (1.00) | |
| temperature | pressure | |
| T / ° C | p A / bar | p A / bar |
| -10 | 9 | |
| 0 | 12 | |
| 10 | 15.5 | |
| 20th | 19th | (25) |
| 30th | 23 | |
| 40 | 29 | |
| 50 | about 38 | |
The bottle temperature must not exceed 50 ° C in order to prevent this internal pressure from becoming excessively high. The test pressure for acetylene gas cylinders is 60 bar, the pressure test is carried out with water every 10 years. The bursting pressure, which is only determined on individual copies during the production phase, must be at least 1.6 times the test pressure.
Acetylene could be liquefied purely physically by compressing it to around 50 bar at room temperature, but the acetylene molecules are particularly susceptible to exothermic decomposition into carbon and hydrogen H 2 when the packing is so tight . As a result of the solution in acetone, a larger amount of acetylene can be stored in the bottle than would otherwise be possible with the same pressure. In practice, at 15 or 20 ° C and 19 bar, 40 liter bottles are loaded with 8 kg of acetylene until they are saturated. The filling compound contains about 12.5 kg of acetone, i. H. the solution concentration is 0.64 kg of acetylene per kg of acetone.
8 kg of acetylene fill about 7 m 3 of volume at a pressure of 1 bar . That is 175 times the volume of the 40 liter steel bottle. To press an ideal gas to 1/175 volume, it would require 175 bar absolute pressure. Thanks to its solubility in acetone, 19 bar is sufficient. With decreasing concentration in the solution, i.e. with decreasing content, the equilibrium pressure of the acetylene in the bottle decreases somewhat less than linearly.
In contrast, other gases such as nitrogen , oxygen or noble gases such as argon are traded with 200 bar and 50 liter bottles. These gases remain gaseous even at 200 bar filling pressure and normal temperature.
The porous material such as cement powder inside the bottle prevents a possible explosive decomposition of the ethyne in the bottle through the valve or when exposed to external heat in the event of a flashback , as can occur when welding when the gas escaping from the bottle is too low. Until the 1990s, acetylene bottles were also filled with the heat-resistant mineral fiber asbestos . These asbestos-containing bottles are provided with an additional rectangular, black sticker that bears a white “a” for asbestos and indicates the danger of scrapping.
layout
According to DIN EN 1089–3, acetylene bottles have been colored chestnut brown (RAL 3009) since 1998, at least on the bottle shoulder. Until 2006 (transitional arrangement), acetylene bottles were yellow. There is a bracket connection (DIN 477-1, No. 3) at the top for gas extraction, in a bundle with the M28 x 1.5 counter-clockwise thread.
In Austria, the color code (on the shoulder or on the whole bottle) for acetylene was previously white. The bottle jacket can also be colored neutrally, i.e. burnished or painted black or white.
hazards
If an acetylene bottle is exposed to a high temperature, for example in the event of a fire, the bottle can burst several hours after the fire due to the relatively slow progression of acetylene decomposition in the porous filling material. The risk is reduced by long-term (> 24 h) cooling of the hot bottle, but this does not always succeed. The danger radius from flying bottle parts is 300 m. It is recommended to spray with coolant from a distance of 30 m and behind a cover that is stable against pieces of steel.
Alternatively, an attempt can be made to shoot through the pressure vessel from a distance of at least 50 m from cover by multiple radial firing with tracer ammunition . The pyrotechnic charge of the tracer ammunition is supposed to ignite the escaping ethyne when it penetrates, in order to safely burn the contents of the gas bottle. Under certain circumstances, escaping ethine can be ignited remotely with a stun grenade .
Hazard warnings
Since acetylene cylinders pose a considerable and unpredictable danger in the event of damage, it is advisable to observe the hazard warnings:
- The fittings should not come into contact with moisture and grease, as this can lead to uncontrolled reactions.
- Only technically flawless devices should be used to extract gas in order to avoid the flame flashing back into the cylinder.
- Inhalation of acetylene should be avoided as the gas is harmful. In the event of poisoning, a doctor should always be consulted and the person affected should be supplied with fresh air or ventilated as soon as possible.
- Valves or pipes made of alloys with copper, silver or mercury should not be used, otherwise explosive acetylides can form.
Web links
Individual evidence
- ↑ Commercial-Technical Advice Journal for Accident Prevention, Commercial Hygiene and Workers' Welfare…, September 1, 1903, What is aerogen gas ?, p. 87, column 1. Digitalisat, vdri.de, accessed August 23, 2017. - The association for industrial diligence in Berlin exposed a high price for an explanation of where certain acetylene explosions occurred that were demonstrably not caused by negligent inflammation.
- ↑ Acetylen ( Memento from April 30, 2016 in the Internet Archive ) bundesfeuerwehrverband.at, Information Acetylen, as of March 2014, accessed August 23, 2017.
- ↑ TRGS 407 - activities with gases, risk assessment asecos.com, technical rules for hazardous substances, status October 26, 2016, accessed August 23, 2017.