Propane Tank

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I'd like to cut the end off a 500 gallon propane tank and weld a flat 3/8- 4'X4" plate on it. Stand it up and use it for hot water storage. I was told on a different forum that I shouldn't do it  that even 15psi. of water will generate thousands of pounds against the flat plat. I was told that tanks are domed for a reason.I don't quite understand this. Does anyone know this to be in fact-true?
Reply:I would just weld 4 very heavy duty legs on it and build some kind of base to stand it up on its end.Lincoln 300 Vantage 2008300 Commander 1999SA250 1999SA200 1968Miller Syncrowave 200XMT350MPA/S-52E/xr-15Xtreme 12vs Millermatic 251 w/30A  Millermatic 251 Dialarc 250 Hypertherm 1250 GEKA & Bantom Ironwokers
Reply:But will the pressure exerted against the bottom be real high because the top is domed and the sides are of course curved?This is what I don't understand. Seems to me pressure is pressure and a flat bottom shouldn't make any difference, but I'm no engineer
Reply:I have heard this too.   I have not seen it first hand, but have told the that air/water in a square tube will be come round. Makes sence you don't see psi tanks that are not round???   Many years ago I tied to make round cap for a 6" pipe. I welded a 1/4' plate on each end and then weld a bung to pressureize it to a 150 psi of air.   two weeks nothing.  then I heated up the end with a rosebud.  After a long time with the heat I got 3/8" bubble.  I scrap the project.  Daye
Reply:Well the weight is what it is and easy enough to calculate, no different than any barrel of water. As for PSI, water figures to around .45 to .47 PSI per foot of elevation.  That's decimal 45 to decimal 47 pounds per sqaure inch per foot of elevation. A tower 100 feet tall will have a water pressure of about but leass than 50 psi. Don't quote me on the .045, but it's so close there's little reason to piss around with the difference. Folks might be confusing static water pressure with air/gas pressurized systems.Last edited by Sandy; 08-02-2008 at 11:39 PM.
Reply:Water heaters are glass-lined to stop corrosion; propane tanks in either original or welded form will rust in a much shorter time, perhaps a few years. An anode will slow that down some.Will the tank be pressurized as a regular water heater would? If only the weight of the water will be on it, the flat plate should be fine. When a force is applied to the middle of a bar or a plate, it tends to bend it into a curved line or plate, just as a rope curves when suspended between two points. In other words, while the line is perfectly straight, no force exists to oppose a force which is perpendicular to the line. Once the line bends, there is a component in that direction which increases as the angle increases. So, if the tank bottom is made with a curved surface, it will better resist the forces stretching it (which would also break the glass surface in a water heater).
Reply:I would sudgest making legs, not welding flat plate, much better for pressure. Why can't you just use the tank horizontaly?All pressurized vessels I work on are rounded or coned, with the exception of a few that don't see anything above 15psi.Use can use a lining like belzona or equivalent to make sure it doesn't rust. You might want to call arround $$$$$, and the stuff is not fun to work with, pay someone to do this. Weight of water 8.34 lbs per gallon1 foot of water elavation = .433 psi
Reply:I've worked on 36 and 42 chilled water lines. All welded. Never had a problem. If you ever see tank farms in process piping chemical plants, many tanks are verticle with flat bottoms.I'm being told this:Area of a 30” dia circle is 706.5 sq inches(pi x radius squared=3.14x(15x15)=706.5)At 15 psi that comes to 10,597.5 pounds(706.5 x 15 psi).Thats why he said the flat bottom plate will be under such terrific pressure. I just don't see it. Wouldn't that be like the pressure against a gate or butterfly valve in pipe lines?
Reply:How in the world can they keep the bottoms of Oxygen tanks flat? Were talking 2500 psi. here.
Reply:DON'T do it! I used to work in the backflow industry and have seen what damage a hot water tank will do. If there was a problem it can/will explode! water expands 1700 times when it turns to steam. A 50 gallon water tank can level a house no problem! buy another water heater and install inline if you need more hot water.HobbyistLincoln 175 with gasLincoln 225 ac arcLongivity LC 416D Multi MachineHF mig 1004x6 bandsawSmithy AT 300 3n1 HF Compact Bender40x48 shopmajor tool habit!
Reply:I don't know your intended use of the hot water in this tank,but the smell alone would stop me if it was for anything other than a holding tank. Even water well holding tanks have a concave end on the bottom of the ones that stand verticle,there must be a reason. I've got a 4' butane sphere that still stinks after a month full of water outside-- any thoughts about how to clean out the smell? --next thing will be bleach,I hear that works. I'm also thinking about how to coat the inside with paint?rustoleum? fiberglass? any thoughts about that? How much paint would it take to coat the inside of such a sphere by just pouring it into the tank and rolling it around to coat it inside? I intend to use this tank for an extra air storage tank for a gas operated air compressor if that matters.
Reply:Chuck172,Hard to believe, but the math in post #8 is correct.As to oxygen cylinders, the bottoms are not flat, but more of a conical shape.Probably not worth re-engineering the tank's shape.Good Luck
Reply:Chuck, those tanks only have head pressure (1psi, per 2.31 foot of elavated water) , but hot water heaters will have more then head pressure.  Mudbugone- the bleach might work, but it also might mask the smell. Try to put kitty littler in it or activated carbon, if it has a hole that you can get it in and out.
Reply:At 15 psi that comes to 10,597.5 pounds(706.5 x 15 psi).
Reply:I agree with you Sandy. The propane tank idea I have is to be used as a pressurized storage tank for my hot-water heating system. I have a Tarm Solo40 wood boiler. It's a gasification unit that works really well with plenty of storage. The pressure will not go over 30#, mostly in the 22-20psi. range. Cutting apart a propane tank will allow me to get in there with a pressure washer to wash out the mercaptan.I need to cut the dome off so it will fit in my basement vertically. Stratification is a real problem with horizontal tanks. Much better with vertical.I really can't see a 42" diameter propane tank 9' high, dome top, flat 3/8 or 1/2" 4X4' plate welded on the bottom, rounding off that bottom plate like a hotdog, with 30psi. can you?Last edited by chuck172; 08-03-2008 at 01:48 PM.Reason: second thought!
Reply:Check out this link: http://www.waterheaterblast.com/ or do a serch on google " hot water tank explodes"HobbyistLincoln 175 with gasLincoln 225 ac arcLongivity LC 416D Multi MachineHF mig 1004x6 bandsawSmithy AT 300 3n1 HF Compact Bender40x48 shopmajor tool habit!
Reply:I really can't see a 42" diameter propane tank 9' high, dome top, flat 3/8 or 1/2" 4X4' plate welded on the bottom, rounding off that bottom plate like a hotdog, with 30psi. can you?
Reply:Originally Posted by plepperCheck out this link: http://www.waterheaterblast.com/ or do a serch on google " hot water tank explodes"
Reply:I was gonna weld on two 4' pcs. of channel iron across the bottom as stiffeners anyway but I really don't think the bottom would bow out like a hot dog without them.thanks,
Reply:In no particular order:The pressure in the tank will be whatever it is, 15 psi or 60 psi or whatever.  Over a large area even a 'small' pressure can amount to a h-u-g-e amount of force.  (see post #8)But while the stress in a pressure vessel is related to the pressure, the geometry and construction of the pressure vessel influence what the stress caused by the pressure will be.  A curved shaped pressure vessel distributes the effect of the pressure to minimize stress concentration or geometry factors.  A sphere distributes pressure the 'best',  other shapes are usually a compromise (to varying degrees).  Worst are 'corners' or sharp transitions, hence real pressure vessels eliminate or minimize corners and try to make everything rounded/smooth.The plain steel propane tank will rust if used for water.A water heater or tank in hot water service should/must have a temperature and pressure relief valve.  The effect of a 'runaway' heater is DEVASTATING.  MythBusters did an episode where they bypassed the safeties (thermostat and T&P relief valve) of a medium sized 'household' electric water heater.  The tank exploded, released steam and hot water all over the place, went vertical like a rocket to the height in the triple-digits IIRC -after- punching through a 'typical' house roof (ceiling joists and roof rafters and plywood/OSB and fiberglass/asphalt roof shingles), and LEVELED the test building they made (stud walls, outside walls, etc).The residual mercaptan in the tank will render the tank unfit for pretty much any use other than as a propane tank.  The threshold of detection by the human nose is in the ppb range (0.002 ppm).  The listed exposure limit is only 0.5 ppm.  Btw, mercaptan is hazardous, can/will 'numb' the sense of smell with enough exposure (time and/or concentration).Mercaptan is not soluble in water.  You need to solvent wash it (strong alcohol like ethyl or methyl alcohol, ether, or acetone), or oxidize it (strong bleach or the 'skunk-off' mix of baking soda + 3% hydrogen peroxide + a little detergent/shampoo).  Search here for previous post(s) about mercaptan/propane.  Like http://weldingweb.com/vbb/showthread.php...ight=mercaptan  The best laid schemes ... Gang oft agley ...
Reply:My two cents. .The surface area of a 4' circle ( assuming a 4' dia. propane tank) contains 1809.5616 sq. in. (24" X 24" X 3.1416 + 1809.5616)Pressure that up to 15# per sq. in. and that becomes 27,142.424 pounds of pressure pushing on that flat plate. Increase that to the maxiumn 30 pounds mentioned in the post and you have 54,286.956 pounds of pressure pushing on the flat plate. That is without adding in the total weight of the water in the tank. The plate is going to deflect and the weld will probably fail. Make the plate thick enough to hold the pressure without flexing or recess the plate and put enough web braces underneth it and tied into the shell to prevent flex and it will probably work. If you can remove the ethyl mercaptan residue where the water is usuable you will still probably develop a leak in a few years. How quickly will be determined by the quality of your water and how hot it is. After all most water heaters with lined tanks are only guranteed for 6 years. Personally I would look at a commercially built tank if I were going to do this. Much safer and more long lived.
Reply:Why not just cut the dome off and take out the length of the body of the tank that you don't have room for and weld the dome back on? Some short legs and you are good to go. Very professional looking to boot.SA200,Ranger8,Trailblazer251NT,MM250,Dayton225AC,T  D-XL75,SpoolMate3545SGA100C,HF-15-1  RFCS-14 When I stick it, it stays stuck!
Reply:O.K, I'll do it right, Take out a piece and weld the dome back in. I'll fabricate some type of legs for it. Thanks everyone for changing my mind.
Reply:HTML Code:As to pressurization of conventional house hold type tanks, it is minor in inconsequential to this scenario. Typical water systems coming into a home might have pressures in the 40 to 60 PSI range. So the tank in your house is already at 60 PSI , yet we sleep quite well, not even thinking about that. When was the last time a home hot water heater leveled a home? I sure don't know. Why are we not deathly afraid of this, because water does not have the stored energy that air and other gases have.Maybe not at 60 psi, but they can level a home - pop off valve stuck, thermostat stuck, Boom.http://reliefvalve.net/your_home1.html
Reply:Originally Posted by mooseyeWhy not just cut the dome off and take out the length of the body of the tank that you don't have room for and weld the dome back on? Some short legs and you are good to go. Very professional looking to boot.Why not just weld a stand for the tank and strap the tank to it?AWS certified welding inspectorAWS certified welder
Reply:I want a verticle tank Don. Takes up much less space and there is a stratification issue with horizontal tanks.The reason it must be cut is my basement cieling joists are 9'4'', the tank is 10' long.
Reply:Cut a piece out of the tank and weld the end back on and mount it in a stand...no extra material...use the removed ring for the base.
Reply:Originally Posted by Sandy. When was the last time a home hot water heater leveled a home? I sure don't know.  Why are we not deathly afraid of this, because water does not have the stored energy that air and other gases have. ?
Reply:Here's a much better one! 0-200kmh in 2.1 seconds.[ame]http://www.youtube.com/watch?v=lFxeHjHBOXU&feature=related[/ame]Miller EconotigCutmaster 38Yes ma'am, that IS a screwdriver in my pocket!
Reply:Believe it or not, I actually witnessed a house nearly leveled by a water heater. I was in 6th grade, so it was 1988. We were all on the playground during recess when out of the blue we here this god awful noise and look up to see the garage door from the house across the street land in the road. The entire garage side of the house was totalled. The brick outside walls of the garage were destroyed, and the inside wall landed in pieces in their kitchen. I would guess that he must have had a faulty safety valve, and his thermostat went bad. Water has WAAAAAAAAY more stored energy than gases, when it's hot enough to flash to steam upon release into the atmosphere. Ever seen a steam rocket?
Reply:Cut the cap off of the end and invert it.  Then weld it back in.  It will shorten the overall length of the tank without having to put a plate on the tank.I'm a Lover, Fighter, Wild horse Rider, and a pretty good welding man......
Reply:Personally I question the sanity of anyone who would even consider cutting into an old propane tank, but then again I have seen the end results of projects using oil and gas storage vessels when they didn't get lucky.You can't ever get completely rid of that smell. Mercaptan is considered hazardous and requires special handling and disposal. You can't just let it run out on the ground. Don't forget to check the radioactivity level of the tank as well.The difference between art and craft is the quality of the workmanship. I am an artist.
Reply:Originally Posted by chuck172I agree with you Sandy. The propane tank idea I have is to be used as a pressurized storage tank for my hot-water heating system. I have a Tarm Solo40 wood boiler. It's a gasification unit that works really well with plenty of storage. The pressure will not go over 30#, mostly in the 22-20psi. range. Cutting apart a propane tank will allow me to get in there with a pressure washer to wash out the mercaptan.I need to cut the dome off so it will fit in my basement vertically. Stratification is a real problem with horizontal tanks. Much better with vertical.I really can't see a 42" diameter propane tank 9' high, dome top, flat 3/8 or 1/2" 4X4' plate welded on the bottom, rounding off that bottom plate like a hotdog, with 30psi. can you?
Reply:Ok, I got the part about the heating system now. You don't see those around here. So I don't know too much about them. It appears you don't know too much about heated pressure vessels. I guarantee you there is a code that covers this system and this particular tank used in this manner (try API for heated pressure vessels as this is what this tank will be). Check with the local building inspector and the fire marshall before you get too tied up in this. It could save you a lot of headaches at the very least. When you add heat to pressure things change dramatically and can be very dangerous. I'm not even concerned about the end bulging out but much more concerned about the weld failing. There is a reason why the caps on pressure vessels are rounded and why the welds are made on the cylindrical portion of the tank before it gets to the dome. It has to do with physics and how stress is applied to the joint.Someone mentioned that oil is stored in flat bottom dome topped tanks and they don't bulge. They also have no pressure on them. It only takes ounces of pressure to make those things look like balloons. A couple of pounds will blow the ends out of them. I've seen them collapse under 15 inches of vacuum when the venting system failed.The difference between art and craft is the quality of the workmanship. I am an artist.