Splitter on Acetylene tank

> Hi,
>
> In my welding class we are learning safety precautions for Oxy-
> Acetylene processes. In this discussion we talked about how acetylene
> tanks are filled with a porous material and acetone to isolate the
> acetylene because it becomes unstable when stored together above
> 30psi. In this class we also discussed how we used splitters on the
> tanks to allow the use of two regulators on each tank. I noticed that
> the splitter, being located between the regulator and the tank
> contains raw acetylene at 400psi without anything to seperate the gas.
> How come the acetylene in the splitter does not become unstable, and
> what is the maximum space acetylene at 400 psi can occupy before it
> becomes unstable and may combust?

> Thanks,
>
> Ben

>> Hi,
>>
>> In my welding class we are learning safety precautions for Oxy-
>> Acetylene processes. In this discussion we talked about how acetylene
>> tanks are filled with a porous material and acetone to isolate the
>> acetylene because it becomes unstable when stored together above
>> 30psi. In this class we also discussed how we used splitters on the
>> tanks to allow the use of two regulators on each tank. I noticed that
>> the splitter, being located between the regulator and the tank
>> contains raw acetylene at 400psi without anything to seperate the gas.
>> How come the acetylene in the splitter does not become unstable, and
>> what is the maximum space acetylene at 400 psi can occupy before it
>> becomes unstable and may combust?

>
> We debated this same issue in class and no one knew the answer.
>
> It's not just the splitter, it's the entire top of the tank (above the
> acetone) and valve and the high pressure side of the regulator which is
> exposed to pure acetylene at pressure way over the 15 PSI safety limit in
> all tanks.
>
> We need someone that understands the chemistry that's related to the 15 psi
> safety limit to explain it. None of the books I've seen explained it other
> than to say it _can_ become unstable and explode (or burn??) at the higher
> pressures. They way I've seen it worded left me thinking it was a rare
> thing to begin with and would only happen under exactly the right (wrong!)
> conditions.
>
> The best I can come up with is the idea that for it to actually be a
> problem, there may need to be some O2 in the mix as might happen if air got
> mixed in it. In the hose, you always run the risk that it's filled with
> air when you first turn on the acetylene or might even have some pure O2
> which leaked back from the torch if there were no check valves. Maybe, the
> real danger is in those situations when you add acetylene to the hose under
> pressures over 15 PSI and it's mixed with some O2. As long as there's not
> (or very little) O2, it's not a safety issue??

>
> Then there's also the issue that you shouldn't use copper pipes in an
> acetylene manifold system because there's some sort of chemical reaction
> that takes place between copper and acetylene which can also create a
> safety issue.

> Curt Welch wrote:

>>> Hi,
>>>
>>> In my welding class we are learning safety precautions for Oxy-
>>> Acetylene processes. In this discussion we talked about how acetylene
>>> tanks are filled with a porous material and acetone to isolate the
>>> acetylene because it becomes unstable when stored together above
>>> 30psi. In this class we also discussed how we used splitters on the
>>> tanks to allow the use of two regulators on each tank. I noticed that
>>> the splitter, being located between the regulator and the tank
>>> contains raw acetylene at 400psi without anything to seperate the gas.
>>> How come the acetylene in the splitter does not become unstable, and
>>> what is the maximum space acetylene at 400 psi can occupy before it
>>> becomes unstable and may combust?

>>
>> We debated this same issue in class and no one knew the answer.
>>
>> It's not just the splitter, it's the entire top of the tank (above the
>> acetone) and valve and the high pressure side of the regulator which is
>> exposed to pure acetylene at pressure way over the 15 PSI safety limit in
>> all tanks.
>>
>> We need someone that understands the chemistry that's related to the
>> 15 psi
>> safety limit to explain it. None of the books I've seen explained it
>> other
>> than to say it _can_ become unstable and explode (or burn??) at the
>> higher
>> pressures. They way I've seen it worded left me thinking it was a rare
>> thing to begin with and would only happen under exactly the right
>> (wrong!)
>> conditions.
>>
>> The best I can come up with is the idea that for it to actually be a
>> problem, there may need to be some O2 in the mix as might happen if
>> air got
>> mixed in it. In the hose, you always run the risk that it's filled with
>> air when you first turn on the acetylene or might even have some pure O2
>> which leaked back from the torch if there were no check valves.
>> Maybe, the
>> real danger is in those situations when you add acetylene to the hose
>> under
>> pressures over 15 PSI and it's mixed with some O2. As long as there's
>> not
>> (or very little) O2, it's not a safety issue??

>
> Here's probably more than you want to know ...
>
> First. let me explain the difference between a deflagration and a
> detonation.
>
> A deflagration is when the reaction front moves slower [1] than the
> speed of sound in the material - if it moves above the speed of sound
> it's a detonation, that's the difference between a detonation and a
> deflagration. When a reaction front moves faster than the speed of sound
> some of the energy goes into making shock waves, which can be very
> damaging.
>
> [1] for acetylene slower can be anything from very slow to very fast
> indeed! The effects of fast deflagrations can be hard to tell from
> detonations, both are what is normally called an explosion. For
> instance, a gunpowder pipe bomb doesn't detonate, if deflagrates - but
> it still goes bang and fires shrapnel about.
>
>
>
> Next some acetylene chemistry. Acetylene can burn with air or oxygen,
> forming carbon dioxide and water:
>
> C2H2 + 3O2 -> 2CO2 + H2O (+ heat)
>
> The speed of the first reaction depends on the concentration of oxygen
> or air, as well as the temperature, pressure and volume (we'll get into
> the effects of volume later). The flammability limits for acetylene are
> very wide, and most concentrations will detonate if the volume is large
> enough.
>
> A typical example of this oxygen/acetylene detonation is a "pop" in the
> torch nozzle, but people also do stupid things like fill balloons with
> oxygen/acetylene mix - which can permanently damage your heating, or worse.
>
> At room temperatures oxygen/acetylene mixes can explode (either detonate
> or deflagrate) at well below atmospheric pressure. At similar pressures
> acetylene/air mixes, and especially acetylene/oxygen mixes, are far more
> dangerous the acetylene alone.
>
>
>
>
>
> Acetylene can also decompose exothermically (giving out a lot of heat)
> all by itself, with no oxygen present:
>
> C2H2 -> 2C + H2 (+ heat)
>
> (actually this reaction occurs in steps, and it can be reversible if it
> hasn't gone to completion - this is rare, but not unknown)
>
> The speed of this depends on the temperature, pressure and volume. At
> room temperatures and pressures below 15 psig acetylene alone can't
> detonate, and deflagrations are fairly slow. However at pressures above
> 15 psig acetylene can detonate - this is one of the worst outcomes, so
> it's the one most talked about.
>
> It's also the main reason why acetylene cylinders are filled with porous
> diatomaceous earth (in the UK, they use different materials elsewhere),
> and the acetylene is dissolved in acetone - the diatomaceous earth fills
> the cylinder completely, and the acetone comes about half way up. When
> the valve is opened the acetylene fizzes out of the acetone.
>
>
>
> But that's not all - acetylene decompositions can also occur slowly.
> This is what causes burning in the torch body when the oxygen is turned
> off, melts the hose, and if it gets into the cylinder it starts rocking,
> as the deflagration continues inside the cylinder, which can explode -
> this usually takes some time, maybe half an hour or more.
>
> Another example of a slow deflagration is in the regulator of an
> acetylene cylinder - this *always* happens to some extent when acetylene
> is used, caused by the expansion of the acetylene. Acetylene regulator
> passages are made small to limit the volume and thus lower the rate of
> reaction so that only a small proportion of the acetylene decomposes,
> and to ensure the deflagration does not become a detonation.
>
> So don't use anything except a proper regulator designed for acetylene
> with acetylene!
>
> Acetylene regulator manufacturers have another trick up their sleeves -
> remember I said the decomposition of acetylene can be reversible? The
> decomposition produces carbon in the form of soot, which is messy and
> can clog the hoses, flashback arrestors, etc, so they arrange things so
> that the partly-decomposed acetylene recombines. Clever chaps, those
> manufacturers!
>
>
> Now on to volume.
>
> Consider a sphere of reacting potentially-explosive material inside a
> volume of non-reacting potentially explosive material. The energy
> produced by the reacting material has to heat up let's say the next mm
> or so enough to make it react if the reaction is to continue. Now a
> sphere 1mm in diameter will have to heat up a sphere 3 mm in diameter,
> that's 9 times more than it's size - but a sphere 5 mm in diameter will
> have to heat up a sphere 7 mm in diameter, only 2.77 times as large.
>
> The smallest radius at which a reacting sphere can heat up the next bit
> enough that the reaction continues is known as the minimum detonation
> radius (for a detonation). Below this radius the detonation can't
> propagate.
>
> Now consider some explosive material in a tube, and detonate one end of
> it. The detonation wave will be slowed near the tube walls partly by
> cooling from the walls, and partly by other wall and edge effects which
> I won't go into. The effect of this is to curve the detonation wave so
> that it bulges out in the middle of the tube - and of the radius of that
> curve falls below the minimum detonation radius then the detonation
> can't propagate.
>
> The situation is similar for different shapes than tubes, but the math
> is more complex!
>
>
>
> Back to acetylene: detonations take a lot of energy being transferred to
> the unreacted material very quickly. Deflagrations on the other hand
> occur more slowly - this is why acetylene can decompose slowly at less
> than 15 psig eg in a hose or torch body, but can't detonate at 15 psig
> no matter how big the volume is.

>>
>> Then there's also the issue that you shouldn't use copper pipes in an
>> acetylene manifold system because there's some sort of chemical reaction
>> that takes place between copper and acetylene which can also create a
>> safety issue.

>
> Acetylene reacts with copper to form copper acetylide (and also to a
> lesser extent with silver, forming silver acetylide), which is a highly
> sensitive high explosive.
>
>
> -- Peter Fairbrother

> Peter Fairbrother wrote:

>> Curt Welch wrote:

>>>> Hi,
>>>>
>>>> In my welding class we are learning safety precautions for Oxy-
>>>> Acetylene processes. In this discussion we talked about how acetylene
>>>> tanks are filled with a porous material and acetone to isolate the
>>>> acetylene because it becomes unstable when stored together above
>>>> 30psi. In this class we also discussed how we used splitters on the
>>>> tanks to allow the use of two regulators on each tank. I noticed that
>>>> the splitter, being located between the regulator and the tank
>>>> contains raw acetylene at 400psi without anything to seperate the gas.
>>>> How come the acetylene in the splitter does not become unstable, and
>>>> what is the maximum space acetylene at 400 psi can occupy before it
>>>> becomes unstable and may combust?
>>>
>>> We debated this same issue in class and no one knew the answer.
>>>
>>> It's not just the splitter, it's the entire top of the tank (above the
>>> acetone) and valve and the high pressure side of the regulator which is
>>> exposed to pure acetylene at pressure way over the 15 PSI safety
>>> limit in
>>> all tanks.
>>>
>>> We need someone that understands the chemistry that's related to the
>>> 15 psi
>>> safety limit to explain it. None of the books I've seen explained it
>>> other
>>> than to say it _can_ become unstable and explode (or burn??) at the
>>> higher
>>> pressures. They way I've seen it worded left me thinking it was a rare
>>> thing to begin with and would only happen under exactly the right
>>> (wrong!)
>>> conditions.
>>>
>>> The best I can come up with is the idea that for it to actually be a
>>> problem, there may need to be some O2 in the mix as might happen if
>>> air got
>>> mixed in it. In the hose, you always run the risk that it's filled with
>>> air when you first turn on the acetylene or might even have some pure O2
>>> which leaked back from the torch if there were no check valves.
>>> Maybe, the
>>> real danger is in those situations when you add acetylene to the hose
>>> under
>>> pressures over 15 PSI and it's mixed with some O2. As long as
>>> there's not
>>> (or very little) O2, it's not a safety issue??

>>
>> Here's probably more than you want to know ...
>>
>> First. let me explain the difference between a deflagration and a
>> detonation.
>>
>> A deflagration is when the reaction front moves slower [1] than the
>> speed of sound in the material - if it moves above the speed of sound
>> it's a detonation, that's the difference between a detonation and a
>> deflagration. When a reaction front moves faster than the speed of
>> sound some of the energy goes into making shock waves, which can be
>> very damaging.
>>
>> [1] for acetylene slower can be anything from very slow to very fast
>> indeed! The effects of fast deflagrations can be hard to tell from
>> detonations, both are what is normally called an explosion. For
>> instance, a gunpowder pipe bomb doesn't detonate, if deflagrates - but
>> it still goes bang and fires shrapnel about.
>>
>>
>>
>> Next some acetylene chemistry. Acetylene can burn with air or oxygen,
>> forming carbon dioxide and water:
>>
>> C2H2 + 3O2 -> 2CO2 + H2O (+ heat)
>>
>> The speed of the first reaction depends on the concentration of oxygen
>> or air, as well as the temperature, pressure and volume (we'll get
>> into the effects of volume later). The flammability limits for
>> acetylene are very wide, and most concentrations will detonate if the
>> volume is large enough.
>>
>> A typical example of this oxygen/acetylene detonation is a "pop" in
>> the torch nozzle, but people also do stupid things like fill balloons
>> with oxygen/acetylene mix - which can permanently damage your heating,
>> or worse.
>>
>> At room temperatures oxygen/acetylene mixes can explode (either
>> detonate or deflagrate) at well below atmospheric pressure. At similar
>> pressures acetylene/air mixes, and especially acetylene/oxygen mixes,
>> are far more dangerous the acetylene alone.
>>
>>
>>
>>
>>
>> Acetylene can also decompose exothermically (giving out a lot of heat)
>> all by itself, with no oxygen present:
>>
>> C2H2 -> 2C + H2 (+ heat)
>>
>> (actually this reaction occurs in steps, and it can be reversible if
>> it hasn't gone to completion - this is rare, but not unknown)
>>
>> The speed of this depends on the temperature, pressure and volume. At
>> room temperatures and pressures below 15 psig acetylene alone can't
>> detonate, and deflagrations are fairly slow. However at pressures
>> above 15 psig acetylene can detonate - this is one of the worst
>> outcomes, so it's the one most talked about.
>>
>> It's also the main reason why acetylene cylinders are filled with
>> porous diatomaceous earth (in the UK, they use different materials
>> elsewhere), and the acetylene is dissolved in acetone - the
>> diatomaceous earth fills the cylinder completely, and the acetone
>> comes about half way up. When the valve is opened the acetylene fizzes
>> out of the acetone.
>>
>>
>>
>> But that's not all - acetylene decompositions can also occur slowly.
>> This is what causes burning in the torch body when the oxygen is
>> turned off, melts the hose, and if it gets into the cylinder it starts
>> rocking, as the deflagration continues inside the cylinder, which can
>> explode - this usually takes some time, maybe half an hour or more.
>>
>> Another example of a slow deflagration is in the regulator of an
>> acetylene cylinder - this *always* happens to some extent when
>> acetylene is used, caused by the expansion of the acetylene. Acetylene
>> regulator passages are made small to limit the volume and thus lower
>> the rate of reaction so that only a small proportion of the acetylene
>> decomposes, and to ensure the deflagration does not become a detonation.
>>
>> So don't use anything except a proper regulator designed for acetylene
>> with acetylene!
>>
>> Acetylene regulator manufacturers have another trick up their sleeves
>> - remember I said the decomposition of acetylene can be reversible?
>> The decomposition produces carbon in the form of soot, which is messy
>> and can clog the hoses, flashback arrestors, etc, so they arrange
>> things so that the partly-decomposed acetylene recombines. Clever
>> chaps, those manufacturers!
>>
>>
>> Now on to volume.
>>
>> Consider a sphere of reacting potentially-explosive material inside a
>> volume of non-reacting potentially explosive material. The energy
>> produced by the reacting material has to heat up let's say the next mm
>> or so enough to make it react if the reaction is to continue. Now a
>> sphere 1mm in diameter will have to heat up a sphere 3 mm in diameter,
>> that's 9 times more than it's size - but a sphere 5 mm in diameter
>> will have to heat up a sphere 7 mm in diameter, only 2.77 times as large.
>>
>> The smallest radius at which a reacting sphere can heat up the next
>> bit enough that the reaction continues is known as the minimum
>> detonation radius (for a detonation). Below this radius the detonation
>> can't propagate.
>>
>> Now consider some explosive material in a tube, and detonate one end
>> of it. The detonation wave will be slowed near the tube walls partly
>> by cooling from the walls, and partly by other wall and edge effects
>> which I won't go into. The effect of this is to curve the detonation
>> wave so that it bulges out in the middle of the tube - and of the
>> radius of that curve falls below the minimum detonation radius then
>> the detonation can't propagate.
>>
>> The situation is similar for different shapes than tubes, but the math
>> is more complex!
>>
>>
>>
>> Back to acetylene: detonations take a lot of energy being transferred
>> to the unreacted material very quickly. Deflagrations on the other
>> hand occur more slowly - this is why acetylene can decompose slowly at
>> less than 15 psig eg in a hose or torch body, but can't detonate at 15
>> psig no matter how big the volume is.

>
> I forgot to mention minimum ignition energy: for acetylene/air and
> acetylene/oxygen mixes the minimum amount of energy required to set off
> a detonation is extremely small - the acetylene/oxygen reaction gives
> out a lot of heat, so the minimum radius is small (the ignition energy
> is approximately the energy required to heat up a sphere of the minimum
> radius).
>
> For acetylene alone the minimum energy is quite a lot higher, as the
> sphere to be heated up is bigger, and the required temperature is higher
> - which is why acetylene detonations are as rare as they are, even in
> higher pressures - but don't take the risk of relying on that!
>
> Makers of acetylene compressors and the like do rely on the higher
> minimum energy, but they are experts and acetylene compressors are
> operated remotely, and even then they are in explosion-proof bunkers (or
> underwater).

>
>
>

>>>
>>> Then there's also the issue that you shouldn't use copper pipes in an
>>> acetylene manifold system because there's some sort of chemical reaction
>>> that takes place between copper and acetylene which can also create a
>>> safety issue.

>>
>> Acetylene reacts with copper to form copper acetylide (and also to a
>> lesser extent with silver, forming silver acetylide), which is a
>> highly sensitive high explosive.
>>
>>
>> -- Peter Fairbrother

>
> -- Peter Fairbrother