Unable to Remove Valve From Tank

[SDAnderson]

I may not be an expert but here's a couple more pennies for the fountain...

The momentary and direct heating of an aluminum (as the OP stated) scuba cylinder will not change the physical properties of aluminum unless the gun was allowed to spend a very long time in one spot. Aluminum conducts heat very well and the heat would dissipate quite quickly.

From the "Can't Have Your Cake and Eat It, Too" Department: If the heat gun is providing enough calories to alter the characteristics of the alloy, it’s providing enough heat to damage the alloy.

There's a very fine line here and crossing it can be deadly. The popularity of aluminium as a heat sink material has as much to do with its cost as its conductivity - and while EE's worry about heat sinks slagging they generally don't worry about them exploding. For what it's worth, steel transmits heat faster than aluminum does. I don't know what the thermal conductivity figure is for 3AL but it isn't as good as pure aluminum. At 340 Kelvin, the pure stuff conducts heat at 240 Watts per centimeter per degree Centigrade: fast but slow enough that damage can easily occur to the alloy. The tempering process that aluminum cylinders undergo increases their tensile strength by 20 times, a process that can easily be reversed by heat with truly disastrous consequences.

The standard is: any 3AL cylinder exposed to a heat source in excess of 350F shall be assumed to have been compromised and shall be removed from service. There is no time quotient to the standard.

OP: Remove the burst disk, put the thing in a big-ass chain vise and use a cheater bar. The thing is probably toast but at least you'll have the satisfaction of ripping it to shreds...a little bit of lube on a well-plated valve will help prevent the problem the next time.

 

[tc]

OP hasn't been online in a few days, starting to get concerned that he may have attempted one of the more violent methods suggested here.

 

[Davidstealey3]

havent seen anyone say anything about this yet, but i wonder if the last person put some christolube or dow corning 111 or the such on the vavle, and now the dissimalar metals have bonded.

if you are going to use lube on the valve the next time, make sure it is something like the two mentioned above.

if you do use some wd40 or pb blaster on it and do get it loose, make damn sure you get the tank cleaned. dont want to breath any of that stuff at depth.

opps should of read better, someone did say lube, just not what kind

 

[oxyhacker]

Actually, no. According the 49CFR 180.203 it's the heat of "any portion of the cylinder", not the source being used to heat it, that matters.

A quibble perhaps but probably worth mentioning, as just about all of the heat guns such as are often used to remove stickers have output temperatures above 350F, but their btu output is so small that it would be almost impossible to overheat the tank with one (though there are some heavy-duty industrial ones that could).

The standard is: any 3AL cylinder exposed to a heat source in excess of 350F shall be assumed to have been compromised and shall be removed from service. There is no time quotient to the standard.

 

[SDAnderson]

Actually, no. According the 49CFR 180.203 it's the heat of "any portion of the cylinder", not the source being used to heat it, that matters.

A quibble perhaps but probably worth mentioning, as just about all of the heat guns such as are often used to remove stickers have output temperatures above 350F, but their btu output is so small that it would be almost impossible to overheat the tank with one (though there are some heavy-duty industrial ones that could).

Fair point and, yes, I think it's a quibble.

There's a difference between heating a sticker enough to loosen the adhesive and heating the cylinder enough that the collar and neck expand to loosen the valve. That much heat and you're playing with fire. Literally.