Acetylene Regulators

[JDweld98]

In the past week I've been been using my Oxy/Acetylene torch more than I usually would and it got me thinking. As you probably know; Acetylene is unstable and can explode when pressurized anywhere from 15-32psi and will explode at 33psi, unless it is in an acetylene tank where it can be stabilized. But is is not stabilized in the hose which means an accident such as having the adjusting screw set to allow high pressure to flow to the torch when you open the cylinder, there could be an explosion. My question is why acetylene regulators do not have a mechanism which would automatically purge the line pressure if is exceeds 15psi. Obviously a mechanism can always fail so this would by no means be something that would replace following all safety precautions that should be carried out when working with acetylene, but it does seem like a bit of an insurance policy that could potentially reduce the chances of somebody messing up and possibly being killed. Especially in environments such as schools where people might not be familiar with operating these types of equipment I could see it being practical. Its possible that this is already exists but I've tried to find something like this and have not found anything. If anybody knows of a product like this that already exists, or if you have any thoughts of this and why it would be or why it might not be a good idea I would love to hear it. Thanks!

 

[bonneyman]

Don't have the answers you need - but I know a company who might.
I had these folks rebuild one of my regulators a couple of years ago. Great customer service, reasonable prices, fast repair and return ship. You might want to give them a call or send an email.

http://billswelderrepair.com/home.html

 

[G_P]

I dont think the acet will explode immediately if it goes over 15psi, and venting it into a grage or other building could lead to a massive explosion.
What baffles me is why the regulators are even capable of going so high. You would think they would be set up to limit you to around 15psi max.

 

[Superbec]

acetylene can explode if there's oxygen present, without oxygen there's no bumbum

 

[skruft]

I have noticed this and think the experts must see no great danger, or OSHA, etc. would have been all over it long ago and regulators would be limited. (Also note the number of very old regulators and hoses in use).

 

[pcmeiners]

Suppose you do have a mechanism to purge line, how many users would allow a great deal of gas to build up (in confined areas) before they re-adjust or turn off the gases? A good number, causing confined areas to explode massively, causing a great deal more damage then a hose explosion due to excess pressure. Seen a couple hose blow and flashing back into hoses.
A lot of the danger of excess pressure is somewhat mitigated by the materials transporting acetylene ( gas lines, hose, metal parts) absorbing heat of combustion. In regulators and flashback devices the sintered metal works in this manner as does the small diameter parts of regulators/valves.
Many years ago I worked cutting torch with no flashback or check valves in place, poor practices all around construction sites, many torches in operation, never had an "accident" on the sites which caused injury, lucky yes, but explosions due to excess pressure are not common. Best you can do is have arrestors at the torch and regulator, and know how to open tank valves and regulators.
You do NOT need oxygen for acetylene to explode under pressure.

Yo do not want to screw up with Acetylene, I have been in a couple natural gas explosions (windows blown out, wall gone, massive concussion). Natural gas compared to Acetylene is kindergarten to PHD studies, you do not ever want to see it go off in your garage.

 

[rlitman]

acetylene can explode if there's oxygen present, without oxygen there's no bumbum

This is incorrect!
Acetylene can polymerize at higher pressures. Quite exothermically.

 

[Zeke]

I dont think the acet will explode immediately if it goes over 15psi, and venting it into a grage or other building could lead to a massive explosion.
What baffles me is why the regulators are even capable of going so high. You would think they would be set up to limit you to around 15psi max.

This ^^^^. You don't want a relief valve on anywhere near your flame.

You can get any volume of acetylene you want by sizing your gauge, hose and tip appropriately. What some do is crank it up because the tip is starving and blows out with a large pop.

There are many, many articles on acetylene auto ignition. Some very scientific about how and what happens. You don't need to worry about how, just what.

If you want to be satiated with info, look up " Joule-Thompson coefficient" or "adiabatic compression or process." It's just the explanation of how.

In addition, while reading this stuff I ran across one cat that stated that no O2 need be present for an explosion. The acetylene molecule breaks down or decomposes and creates the unstable condition. I'm no expert but I think what he's saying is that acetylene has the potential to supply its own oxidant as it breaks down into hydrogen, etc. This is said to occur at 29> psi.

There are other factors and this ain't no graduate course.

 

[laser3kw]

history - over a hundred years of it - have shown it is not a big enough issue to address in that manner.
If it did "self relieve" it would have a greater potential for fire or explosion.
Also, from wiki

acetylene, if initiated by intense heat or a shockwave, can decompose explosively if the absolute pressure of the gas exceeds about 200 kPa (29 psi). Most regulators and pressure gauges on equipment report gauge pressure and the safe limit for acetylene therefore is 101 kPagage or 15 psig.[37]

meaning acetylene becomes shock sensitive above 30 psi, not that it will automatically ignite at that pressure. I have heard of fork trucks running over the hose and causing a hose rupture via shock ignition.

 

[rlitman]

...meaning acetylene becomes shock sensitive above 30 psi, not that it will automatically ignite at that pressure...

Shock sensitivity is a very nebulous term. I suggest a good read of the book "Ignition!" is in order for you.

I for one am not playing around with anything "shock sensitive", regardless of how tame it may sound at first glance.

 

[Superbec]

This is incorrect!
Acetylene can polymerize at higher pressures. Quite exothermically.

Thanks, I understand you're right.

In addition, while reading this stuff I ran across one cat that stated that no O2 need be present for an explosion. The acetylene molecule breaks down or decomposes and creates the unstable condition. I'm no expert but I think what he's saying is that acetylene has the potential to supply its own oxidant as it breaks down into hydrogen, etc. This is said to occur at 29> psi.

There are other factors and this ain't no graduate course.

never knew acetylene is so dangerous ...


however ... acetylene's molecular formula is c2h2 , I think they talk about a mix of air and acetylene becoming explosive at 29bar.

I'm not a chemist though, but I watched all of Braking Bad episodes

 

[rlitman]

...however ... acetylene's molecular formula is c2h2 , I think they talk about a mix of air and acetylene becoming explosive at 29bar...

Nope. We're not talking about combustion, so oxygen is not involved.
And we're talking about PSI, not BAR. Though IIRC the reaction requires MORE than 30 PSI. The recommendation with acetylene is to stay under half that, for an additional safety margin.
Oxygen is a corner of the fire triangle, but is not necessary in oh so many types of explosives (in fact, with the exception of mixed fuel/oxidizing gases, most explosives either chemically provide their own oxygen in a single molecule which rearranges, or simply explode without it).

Acetylene is plenty dangerous without oxygen present.
Even worse than acetylene's reaction with itself at high pressures, is what it forms with certain metals, again, without oxygen present.
Copper acetylide is C2H2, and forms in crystaline form when acetyline is carried in copper plumbing. It is a highly shock sensitive high explosive. Oxygen is not involved in the slightest.
https://en.wikipedia.org/wiki/Copper(I)_acetylide

Hydrazine (N2H4) is yet another chemical off the top of my head that has no oxygen, that in the right conditions will detonate. It's normally used as a rocket fuel...

 

[JDweld98]

I dont think the acet will explode immediately if it goes over 15psi, and venting it into a grage or other building could lead to a massive explosion.
What baffles me is why the regulators are even capable of going so high. You would think they would be set up to limit you to around 15psi max.

It won't necessarily explode at 15psi but it is possible. Acetylene becomes unstable at 15-32psi which means it can spontaneously explode. It cannot be predicted if it will indeed explode at these pressures. At 33psi it's behavior becomes predictable again and it will explode. This is what I have been taught. I could always be wrong.

 

[sberry]

I agree not a problem. Someone worked on this way ahead of you, it has a long history of safe use on the supply side, most issues are on the user end in use.

 

[laser3kw]

Shock sensitivity is a very nebulous term.

quantified:

I have heard of fork trucks running over the hose and causing a hose rupture via shock ignition.

also dropping steel bars.
the thrust of the conversation is that at higher pressure acetylene can explode / ignite / detonate - whatever word scares you.
BUT it's not like at 14 psi no problems and at 15 psi nuclear detonation.
Know what you are working with and it's hazards.