Acetylene: Pressure v. Temperature.

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Sincere there was a claim here Acetylene Pressure in a full tank will drop to zero at -7°F.  So knowing different but not sure of the data and unable to find such date online quickly.  And the low temperature being -4°F here this morning.  I have collected some data.  The 28°F, data points were collected a few days ago.  Both low temp readings were taken ~6AM before dawn with my regulator, which has not been recently calibrated but was sufficient for this experiment.  My cylinders are stored outside on the Northeast corner of my shop.  Both cylinders are as filled by my LWS............. #4 Cylinder ......... #5 Cylinder60°F .......... 235 ................... 22528°F .......... 170 ................... 150-4°F .......... 135 ................... 110Just FYI for everyone.So even though the pressure and ability for the cylinder to supply a known CFH of acetylene has dropped, it is not zero and even at very cold temperatures you can still get ~1/2 of the performance of a warm tank.PS. Pressures are in psig.Last edited by Shade Tree Welder; 01-20-2008 at 04:49 PM.Ron ShopFloorTalk Millermatic 350P, M-25, M-40 gunsDynasty 300DX, Coolmate 3, Crafter CS-310 TorchTrailblazer 302, 12RC, WC-2430A spoolgunSpectrum 2050Thermal Arc Plasma Welder PS-3000/WC-100B
Reply:Kinda blows holes in that crackpot claim, doesn't it?
Reply:Lets hope he doesn't start up again, but don't hold your breath.  JohnSMAW,GMAW,FCAW,GTAW,SAW,PAC/PAW/OFCand Shielding Gases.  There all here. :
Reply:Interesting info, thanks.
Reply:I have been known to run the flame of the torch over a near empty tank to squeeze the last drop out to finish a job. I can see the pressure reading dropping but the fuel must still be in the tank at any temp. It can't magically disappear just because it is cold. Maybe if the tank were filled to a certain pressure at a high ambient temperature it could drop to 0 at a much colder temp. But it is my understanding that acetylene is sold by volume as in cu/ft not psi.SA200,Ranger8,Trailblazer251NT,MM250,Dayton225AC,T  D-XL75,SpoolMate3545SGA100C,HF-15-1  RFCS-14 When I stick it, it stays stuck!
Reply:Originally Posted by mooseyeI have been known to run the flame of the torch over a near empty tank to squeeze the last drop out to finish a job. I can see the pressure reading dropping but the fuel must still be in the tank at any temp. It can't magically disappear just because it is cold. Maybe if the tank were filled to a certain pressure at a high ambient temperature it could drop to 0 at a much colder temp. But it is my understanding that acetylene is sold by volume as in cu/ft not psi.
Reply:i freaked out once when i had just filled one of my tanks and came out the next day to see it was reading almost 1/2 empty  . i was ticked off, i been robbed, they gave me a 1/2 fill those *^$$^%*&&%%...  needless to say after i heated up the shop it was back up to PSI. good thing i heated the shop before calling them and making a real a$^ out of myself. that was my C-25 tank though. never checked my strait argon ?? any one know if argon is temp sensitive.they started filling tires with some thing, nitrogen i think. as it is not temp sensitive and keeps your tires at a steady temp for safer driving in the winter. so some gasses are not temp sensitive, or maybe just much less so.any one know about argon ?? summer is here, plant a tree for mother earth. if you dont have time or space, sponcer some one else to plant one for you.feel free to shoot me a PM or e-mail me at [email][email protected] i got lots of time.
Reply:Originally Posted by fun4now.i freaked out once when i had just filled one of my tanks and came out the next day to see it was reading almost 1/2 empty  . i was ticked off, i been robbed, they gave me a 1/2 fill those *^$$^%*&&%%...  needless to say after i heated up the shop it was back up to PSI. good thing i heated the shop before calling them and making a real a$^ out of myself. that was my C-25 tank though. never checked my strait argon ?? any one know if argon is temp sensitive.they started filling tires with some thing, nitrogen i think. as it is not temp sensitive and keeps your tires at a steady temp for safer driving in the winter. so some gasses are not temp sensitive, or maybe just much less so.any one know about argon ??
Reply:Originally Posted by Shade Tree WelderThe Ideal gas law applies to all gases, some are not so well behaved (not linear) but Argon is a well behaved gas.  So it applies very well.PV=nRT is the ideal gas law, whereP=pressureV=volumen=amount of gas in molesR=Ideal gas law constantT=TemperatureNow this can be simplified since we are assuming the tank is full and not leaking or being used.  And the tank is a constant volume.P1/P2 = T1/T2or  P1 = (P2*T1)/T2We know at ~70°F and cylinder of argon is 2250 psi.  And temperatures must be converted to Kelvin (or Rankine).So for approximation.°F ........ °K ....... Pressure70 ........ 294 ...... 225060 ........ 289 ...... 221250 ........ 283 ...... 216640 ........ 278 ...... 212830 ........ 272 ...... 208220 ........ 266 ...... 203610 ........ 261 ...... 19970 .......... 255 ..... 1952-10 ....... 250 ..... 1913-20 ....... 244 ..... 1867
Reply:CO2 and Acetylene are both measured by weight not pressure.     JohnSMAW,GMAW,FCAW,GTAW,SAW,PAC/PAW/OFCand Shielding Gases.  There all here. :
Reply:Originally Posted by Shade Tree WelderSo even though the pressure and ability for the cylinder to supply a known CFH of acetylene has dropped, it is not zero and even at very cold temperatures you can still get ~1/2 of the performance of a warm tank.
Reply:Originally Posted by GeorgeGOK, here's a question for somebody,  If I have psi?  What accounts for the difference in pressure for the same amount of gas?  Ia tank of O2 and a tank of Avcetylene, and they are both the same size, say 75-80 cuft of gas at 70F,  why is the O2 at 2200 psi and the acetylene at 220 s the physical size of the tanks doesn't seem to be that different.
Reply:Originally Posted by Shade Tree Welder...And temperatures must be converted to Kelvin ...°F ........ °K ....... Pressure70 ........ 294 ...... 225030 ........ 272 ...... 2082
Reply:Originally Posted by gnm109Gases such as oxygen, helum, nitrogen and argon are quite stable when stored under pressure. When I worked on a Rocket Engine Test stand years ago, the "stand high" pressures plumbed for those gases when used on the test stand were usually around 3,000 psi. They used dry nitrogen (GN2) for operating the large 8-10" Anin Valves to control water flow. On the other hand, acetylene is unstable when compressed at high pressures. Apparently around 200-250 psi is the most that is considered safe when acetylene is stored in a cylinder. As you probably know, acetylene is calcium carbide gas dissolved in acetone and held in a porous stone inside the cylinder. The instability can be seen if you attempt to run your acetylene regulator much over 10-12 psi. You will get a rapid burn which if you persist could turn into an explosion. When I weld with oxygen-acetylene, I set the oxygen to about 8 psi and the acetylene to 5 psi. For cutting I keep the acetylene about the same and set the oxygen to around 30 psi and then regulate with the cutting torch.  From Wikipedia Key Word "Acetylene". CompressionDue to the carbon-to-carbon triple bond, acetylene gas is fundamentally unstable, and will decompose in an exothermic reaction if compressed to any great extent. Acetylene can explode with extreme violence if the pressure of the gas exceeds about 100 kPa (≈14.5 psi) as a gas or when in liquid or solid form, so it is shipped and stored dissolved in acetone or dimethylformamide (DMF), contained in a metal cylinder with porous filling (Agamassan), which renders it safe to transport and use.
Reply:GeorgeG - It has to do with the vapor pressure of the contents, some cylinder contents are stored in a gaseous state, and others as a liquid.A cylinder storing liquid, -which boils to gas as drawn- offers denser storage; thus more contents when measured as CF of gas; compared to a cylinder storing gas only, at an equal pressure.Wish I had a simpler way to say that!Last edited by denrep; 05-16-2008 at 10:13 AM.
Reply:Originally Posted by GeorgeGMaybe I'm missing the point here, if so please excuse me, but, I'm not wondering why acetylene is limited to 220 psi. I know that's a function of acetone solubility or whatever.   I'm wondering why, for the same apparent volume ( 80 cuft in my example) O2 and acetylene have different pressures.
Reply:Originally Posted by gnm109 ...So, to repeat: It'a unstable at high pressure. It's unstable at... And, if you simply cannot accept this...
Reply:Originally Posted by denrepGnm109, I think you're being a little rough on GeorgeG. You may have misread, and missed his point.Carefully read his questions again:The difference is storage in liquid vs gas state.
Reply:Well, it's actually dissolved IN a liquid (for the above-mentioned safety reasons) and comes out of solution as it is drawn off.  There are likely better ways to say that, but that's the difference.Because it is in a solution, there are limits as to how fast it can come out of that solution and be used.  The 1/7 rule means you never use a tip with a flow rate that is higher than 1/7 the capacity of the cylinder.CO2 is also stored as a liquid, but all by itself, and has no limits on its draw.
Reply:Originally Posted by denrepGnm109, I think you're being a little rough on GeorgeG. You may have misread, and missed his point.Carefully read his questions again:The difference is storage in liquid vs gas state.
Reply:Originally Posted by fun4now.they started filling tires with some thing, nitrogen i think. as it is not temp sensitive and keeps your tires at a steady temp for safer driving in the winter. so some gasses are not temp sensitive, or maybe just much less so.
Reply:Originally Posted by GeorgeGThanks for the answer to my question.  I can see what you're saying and it makes sense.Too bad I wasn't asking the question Gnm109 wanted to answer.
Reply:Originally Posted by gnm109Your question was answered by myself and others. Time for some exercise now.
Reply:Originally Posted by GeorgeGYou, gm109, did not answer my question at all.  Apparently sir, you find it hard to say you're wrong.  You strike me as a bully with anger issues.