Scuba Tank

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Admission, I have absolutely no idea how to weld.  Realizing that, I thought I would come to those who do know to ask a question.  I've an art project in the works and I would like to cut open a circular section of an old scuba tank or possibly a fire extinguisher.  My question is, is that feasible?  Should I take this project to a local machine shop?  Is there a safe way to insure that all of the oxygen is out of the scuba tank (I've read some horror stories about dealing with oxygen tanks)?  General advice about how to proceed, anything y'all have would be greatly appreciated!  Thanks.Last edited by a.perseus; 07-23-2010 at 05:23 PM.
Reply:If the valve is open all the way and nothing is coming out of it you are good to go..During the July 4'Th weekend we needed a 7" launch tube for some rather large fireworks on a barge out in the middle of the lake..I took a old oxygen tank (OA Type Tank) and cut the top off with a bandsaw..Nothing to worry about.And the tube worked GREAT!...zap!Last edited by zapster; 07-23-2010 at 05:26 PM.I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Scuba cylinders contain air not oxygen. ( there are a few exceptions to this but usually it's rare overall.). Open up the valve and allow all the air to escape, then remove the valve. Most Scuba valves are o-ring sealed and will screw out by hand after a good blow with a mallet to loosen the valve. A few older steel ones (1970's and earlier) may be 1/2" pipe threaded. You will need a chain vise and a big wrench to open those. Be sure to stay well away from the direct line of the valve when removing them if you don't get any air out and the valve seams hard to turn. I've had a few bad valves over the years that wouldn't drain doing tank service on Scuba gear (very rare but it's happened). Usually as soon as the O ring seal is broken the gas will escape harmlessly, just wait and the continue. In a few rare cases with tapered threads, I've had the valves "pop" under pressure (500 psi or so)and fly across the shop. Just be sure not to be in front of it and that it's pointed in a safe direction.A good used alum 80cf Scuba cylinder will often sell from $50-125 depending if it's in hydro or not. You might keep this in mind before you just chop it up. You might find that it's worth trying to sell. I saw a local scrap hound had cut up 4 of them 3 weeks ago. Shame he could have made $200 plus easily on them by just selling them as is instead of a couple of cents a pound for the scrap plus the hassle of cutting them up so the scrap guy would take them.As far as fire extingushers, I can't really say. The CO2 ones should open easily once discharged. The dry chemical extingushers I have no idea.Any questions on what sort of cylinder you have and what it may be worth, PM me or post picts of the cylinder and markings and I'll let you know what it's probably worth..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:yeah if uve released the pressure its no biggie. on the oxygen u just get lots of sparklies if if a older cylinder. oxygen in the pores i geuss. we scrap em at work all the time jerk the valve and cut away on the oxygen ones.
Reply:I actually don't have a tank right now, I'm currently out of the country.  I wanted to see if my idea was feasible before I started hunting for one.  If there was the option of getting a steel or an aluminum one, which would y'all recommend on the basis of ease of working with?  I really appreciate the help.  Are there any other tanks that I should be on the lookout for?  As long as its an enclosed cylinder of roughly the same size/shape as a scuba tank it would be fine.
Reply:The old steel 72 cf cylinders can be had cheap if you can find them. Actually I think they make better dive cylinders than the aluminum ones. Newer steel scuba cylinders are worth 2 to 3 times that of the alum ones. Used they can go for $200-300 each easy.Your best bet would be to find a shop that services fire extingushers or a shop that hydro's cylinders and talk to them. I used to get cylinders free from the hydro shop we used for our hydro's. I just had to drill a hole in them before they left so the shop knew the cylinder wouldn't go back in service. We cut them and used them for displays. You might try a Scuba shop for a dead cylinder, but many are afraid people want them so they can put them back in service even though it's almost imposible to get them filled once they fail hydro. If you can find them, the old "E" series alum Scuba cylinders had major cracking issues due to alloy problems. Most places will fail them on hydro nowdays and won't fill them regardless of condition. You might be able to get one from a scuba shop or find some one who's stuck with what amounts to a worthless cylinder for $25 or so. At least they get more than the scrap value that way.As far as ease, the alum ones are close to 3/8" thick. the steels are thin like the one Zap showed. Steel is definatly easier to cut if you want anything other than a straight cut..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Awesome, sounds like a plan.  Again, thanks for the advice, I really appreciate it.  I'd like to cut out a circular section from the center of it on one side of the tank in order to install a clock.  I imagine my best bet would be to take it to a welding shop to get that done, right?
Reply:I'd go to a machine shop. If it's a plain circle, I'd cut it with a hole saw in my mill. You'd get the cleanest cut that way over cutting with a torch..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Thanks for the help.
Reply:here's what a scuba tank looks like after it explodes in a house fire.  An extinguisher would be alot easier to cut (and cheaper) their wall thickness is often less than 1/8". Center punch and use a hole saw the correct size after it was emptied of course.  The powder in a regular dry chemical one is fairly non toxic although very messy and you wouldn't want to breath the fine powder for long and there WILL be residual powder.  Maybe make your pilot hole and run water in the help control the dust then drill your bigger hole and wash it out completely.  For what its woth "hydro" refers to pressure testing the cylinders and is required on a regular basis.  Travis Attached Images
Reply:That's impressive Travis. I'm surprised the burst disk didn't let go first. (had the burst disk let go on one just sitting in the house on Wed. night.) All the alum cylinders I've seen like that are usually from the hydro shop screwing up and testing the older 2015 psi cylinders as 3000 or 3500 psi cylinders. Mythbusters shot a full alum 80 with a .30-06 and all it did was punch a small hole in the cylinder. That one must have heated up pretty good to soften the alum to open up like that..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:It happened back in 01.  Let go with a big thunk and cuncussion pushed flames out the bedroom window good and made a big hole in the exterior wall that it was laying against but nothing more.  I think it had something to do with means of storage it was half full laying on it side.  There was one standing next to it which vented fine.  TB
Reply:OK that makes sense. The disks supposed to go at no more than 5K, so if the cyl was low that would give the metal a chance to soften before the rising pressure triped the burst disk..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:That tank is something else. City of L.A. Structural; Manual & Semi-Automatic;"Surely there is a mine for silver, and a place where gold is refined. Iron is taken from the earth, and copper is smelted from ore."Job 28:1,2Lincoln, Miller, Victor & ISV BibleDanny
Reply:Hi there! I was just googling where to take scrap aluminum scuba tanks and your post came up.  I have 2 of them if you're still interested.  They have failed hydro - valves are off and they are empty.  One is yellow and one is a navy blue.  I can post a pic if you're interested in picking them up in Chicago, paying shipping plus a minimal price for packaging.  I'd rather they go to some creative project than a scrap dealer.
Reply:Oh man. Welding, cutting and scuba all at once. I am a non-professional aspring welder and also a scuba instructor and cave diver. Too many passions in one thread to ignore.   The burst disks and valves will certainly let go in a fire, but the heat can cause the tank to rupture before the pressure has a chance to actually escape. Under the best circumstances it takes quite some time for that pressure to fully escape a tank. This is because the valve actually has a very small orifice that permits gas flow. If you have a gear failure underwater this is a big plus. Gives you more time to get back to the top.  If you are in a house fire, it means that a sudden temperature change can be disastrous.If any of you has drained a scuba tank (or any cylinder) fast, you notice it gets real cold. That expanding gas absorbs a crap ton of head from whatever is near it. Add in a strong heat source and you can have a wide range of temperatures across a very, very small amount of metal. Heat stress alone can cause issues.Bottom line, never gamble with heat and pressure. The less gradual the change in temperature, or the higher the temperature the less reliable burst disks can become. Also, as a cave diver I have to point out some realities. Some valves are NOT DOT approved. Not all countries require burst disks, and this does not prevent unknowing divers from dragging them home from travel or buying them on ebay. Additionally, some divers will bolt burst disk assemblies or use the wrong burst disks. Best practice in this case is to depressurize, then remove the valve completely. If you can't get it to work by the numbers that way due to faulty equipment really think hard about the next step, just to be safe.Most scuba cylinders have no surprises in their construction. Once empty they are no more difficult to cut than large pipe. Nothing in life is without caveats. There are some old ones out there that have liners and/or coatings inside of them. They are rare and a perfect example of a really great BAD idea. (Contrary to plan, pressure and water would get behind the linings causing plenty of issues. This sort of "weird" cylinder can easily show up when you find a "really good deal") I have no idea what sort of composition you might find, but they might be noxious if you heat them up enough. Just peek inside first, and exercise caution.If you are looking for a cylinder to cut up, and aluminum works, check a local dive shop. There are cylinders that can no longer pass hydro or be safely filled due to a the use of a specific alloy that the industry condemned due to the potential for failure. (T6351 to be precise.) These cylinders are fairly useless to divers because most fill stations won't fill them. If you can convince the dive shop you never intend to use it to hold pressure, they might let you have them for scrap weight. (or even free if you make a good impression! )If you slice an extinguisher, make sure you know what kind it is. Some of them have dry chemicals in them and therefore they can have residue you might need to clean out.
Reply:Stop by the local fire extinguisher shop.  The local guys here recover the fire retardant for reuse. They have stacks of drained, condemned tanks sitting outside that are waiting for the recycler.  They gave a ½ doz. for free.