Anyone Ever Built an Air Tank?

[justinp61]

I'm in the process of getting everything together for a air compressor, already have a large Ingersoll Rand pump and have found a source for the motor. I can't find a decent tank near home. I do have some natural gas line pipe that is 30" od, 3/8" wall and a friend has a sheetmetal shop that can cut the ends (3/8") on his plasma cutter. Has anyone ever done this? I'm not worried about the welds, but is there anything else I need to look at?

Thanks, Justin

[KBar]

I never heard of anyone that has built their own air compressor but considering the pressure that is going to be in the tank, (30" WOW) you may want to reconsider. I did hear of the older tanks (50's style) blowing up on guys taking their leg off or worse.

[justinp61]

Make sure you dome those ends!;)

Can I buy domed ends?

[KEENAVV]

Buy a tank. You'll live longer!

[justinp61]

Buy a tank. You'll live longer!

You're probably right, I've been looking for a while. Shipping is outrageous on these things.:eek:

[kcstott]

Buy a tank. You'll live longer!

I second that. 30 inch end plate at 120 PSI is 84,823 total pounds of force or just over 42 tons. That's 900 pounds per linear inch of weld. No thanks I'd rather have that little tag on the side of the tank say it's been tested and certified. because if it does fail for any reason your insurance will not pay.
and that's the least of your worries

[aametalmaster]

I also would buy a tank. Without the ASME stamp on the tank you are asking for trouble someday...Bob

[KBar]

I’ll bet by the time you factor in the cost of the domes + the shipping, a replacement air compressor tank will be more appealing.

One cheap prosthetic alone is close to $10,000 let alone the pain & suffering. I among many others on this board would hate to see a fellow welder get hurt trying to save a couple dollars. :(

[Sberry]

I agree with most guys here, generally this is not a good idea, scares me to think of some of the stuff I did when I was a kid,, and then some.

[Broccoli1]

Buy a tank. You'll live longer!

I don't understand this line of thought as SOME ONE makes the tanks?

Why can't Iron head or any one else that is qualified to do so make their own tank?
:)

[KEENAVV]

I don't understand this line of thought as SOME ONE makes the tanks?

Why can't Iron head or any one else that is qualified to do so make their own tank?
:)

Check the requirements necessary for a high pres. welding cert.

[Broccoli1]

Check the requirements necessary for a high pres. welding cert.

As long as the person fabricating the Tank has the certs, what would be the problem?

[Laiky]

i think the problem is that the people who make the tanks, make hundreds and thousands of them. they have experience, empirical testing and certs. To make just one, you don't get any of that. I'd buy it so you can get the experience and quality of the above mentioned. Same reason some one who isn't an experienced welder shouldn't be doing critical work, and should pay a qualified person to do so, instead of suffering the learning curve for one job.

[enlpck]

As long as the person fabricating the Tank has the certs, what would be the problem?

It isn't just the weld job itself... It is the design process, material verification, NDE On the finished product, and about 50 other things. The risk is much greater than the (possibly nonexistant) cost saving. The risk may not show for several years.

For examlpe, a minor design issue led to some failures: http://www.cpsc.gov/cpscpub/prerel/prhtml02/02108.html

To get an idea of the energy involved,
http://www.railpictures.net/viewphoto.php?id=176187. The tanks on this locomotive arn't really that big. Well, weren't. Note the bent running board. The channel at the edge was maybe 4", maybe 6". The doors and engine compartment structure were also bent up (look at the roof... it is humped).

[kcstott]

Better yet, hydraulic cylinders, steam lines, on and on and on. ;)

Not saying you can't. Liability is one issue. And I'm not referring to damage to your own home how about the guy next door. If you house catches fire that tank if pressurized and no safety valve will end up a couple of zip codes away. Same goes for hydraulic cylinders. Are you willing to bet your life on your welds. Training, experience, those are the qualities of the guy i want welding my steam lines, hydro cylinders, and air receivers. But then when you take into consideration cost of materials and fab time. Along with learning how and why the tanks are designed the way the are. Add in the threaded bung fittings and safety valve it starts to add up. and to me it just ain't worth it. Oh did I mention I'm a cheep SOB too.:D and I still wouldn't make an air tank that big even at half the cost of new.

[kcstott]

It isn't just the weld job itself... It is the design process, material verification, NDE On the finished product, and about 50 other things. The risk is much greater than the (possibly nonexistant) cost saving. The risk may not show for several years.

For examlpe, a minor design issue led to some failures: http://www.cpsc.gov/cpscpub/prerel/prhtml02/02108.html

To get an idea of the energy involved,
http://www.railpictures.net/viewphoto.php?id=176187. The tanks on this locomotive arn't really that big. Well, weren't. Note the bent running board. The channel at the edge was maybe 4", maybe 6". The doors and engine compartment structure were also bent up (look at the roof... it is humped).

I did say 42 TONS of potential force

[Sberry]

I don't know how much 30 inch domes cost for that pipe but I would bet plenty, more than a tank. I bought a 12 inch for an oilfield job a while back and didn't look at the price, just passed it on but for it and a couple other parts it evidently was worth it to send someone on 2 hr road trip. The welding wouldn't worry me as much as some of the other design factors but the 3/8 wall pipe would certainly be adequate, not with flat ends though. I don't get too uptight about certifications for a lot of jobs but we usually know the design is overkill to some extent.
Same with trailer hitches, I look a lot at the customer, I have refused to do them when I didn't feel the person or truck was unsafe such as a broad with a 78 Ford pickup with one working brake wants to hook on a 4 place horse trailer to this piece of crap, no tail lights or working brakes, I am not working on that truck period.

[Sberry]

My Bud Cliff is another matter, would do any job he asked as he is fussy about his stuff, in good condition and takes every reasonable human effort to take care of it.

[willy]

I wouldnt do it - but I'm not a welder by trade either. I agree with the others that you definately dont want to use flat ends:eek:
Attached are some pics of a compressor my Dad built me about 10 years ago. He used weld caps on the ends, pop off valves etc....
Now before anyone jumps all over me, he was a pipe welder with all the certs and mostly welded high pressure steam lines for the local university and John Deere. He's retired now, but still the best welder I know of. I'd bet my life on that compressor never letting go, but on the same hand feel very very nervous filling a purchased portable air tank with 90psi, built by people who build them day in and day out (probably in China). I had a buddy on the receiving end of a purchased air tank that decided to let go. Wasnt a pretty site - the tank basically wrapped around his head. 10K later in plastic surgeory he still looks like Herman Munster (minus the bolts). Let me know if you would like any other pics of the tank. I'll get a picture of the tank that blew up on him when I get a chance - he kept it as a little reminder since the only thing he remembers is starting to fill it, then getting the hospital bill:)

[kcstott]

Yep
Here in California any pressure vessel larger then 10 gal has to be inspected every five years and be ultrasonically tested for signs of corrosion by Cal Osha. I don't remember off the top of my head but I think if the vessel lost 5% of it's wall thickness in any location the tank had to be retired. CalOsha has their own division just for pressure vessels.

As for the small home compressors having a service life it's most likely due to the lack of an automatic drain. Without one the tank will eventually fill with water.

First place I ever worked for had troubles with their air compressor. It wouldn't hold any real pressure or should I say it was cycling quite often like there was a high demand of air. Well no one listens to the new guy. And they proceeded to unbolt the compressor. and move it out and bought a replacement. turns out the compressor was half full of water. No drain on the tank no cycling air dryer nothing just a ball valve down stream of the tank in the air piping system

[lanceman73]

All tanks must be round on all sides. Pressure multiplies in corners!(square tanks)

[Craig in Denver]

I'd bet most air tanks are welded by computerized robotics.
I'm a home garage guy. A trick I learned years ago: Since my tank is going to leak down between uses anyway; when I bought my new compressor I set the drain to leak just a little. So, any moisture always gets pushed out. Since I couldn't hear a small leak, I used soapy water in a paper cup and just opened the drain til I got bubbles. Works fer me and YMMV. :)

[kcstott]

You are just full of information!:cool:
Leave it to California, but in this case I think that is a very good idea.;) Wonder if portable, (diesel driven) compressors fall under this same inspection?

Never seen a compressor with out a drain plug, seen lots of people who do not believe in draining the tanks! :eek:

All tanks do have drains. Manual drains. The Cal Osha requirement is for an automatic drain. A drain cycled by a solenoid or a float type drain either way it must be automatic and it must work. They will not certify the tank without it.
And yes portables are required as well as long as they are over ten gallons.

And I didn't go out of my way to learn this crap just because I have all this free time and no life:D I managed a maintenance shop for a large company.(100 employees and three shifts) I not only took care of all the facilities machinery and production machinery. I also had to take care of all the licenses, permits, and inspections too. Fire dept, Health dept, Cal Osha, CARB, Cal state water resources board. EPA. etc were all on my list of people that would pay me a visit every few months to at the very minimum once a year with follow up visits to prove compliance. Yeah it was FUN stuff with a capitol friggin F

[Vicegrip]

All tanks must be round on all sides. Pressure multiplies in corners!(square tanks)Might be better said that corners act as stress concentrators. The pressure is the same throughout a static pneumatic system.


Funny that folks are all nuts about a US welder making a tank to a way overbuilt spec but we think little of imported Chicom tanks that are made by who knows under what process control. Sure the first one was inspected and passed but how about the ones made when no one is looking which are most of them. They can't even keep lead out of paint or dog food and raw material for medicine clean, what makes anyone think that are using good methods, metal and filler to make pressure tanks?

[fjk]

Funny that folks are all nuts about a US welder making a tank to a way overbuilt spec but we think little of imported Chicom tanks that are made by who knows under what process control.

i think that the lesson to be learned here is that there's more to
making pressure tanks/etc/etc than just running a few quick beads
on some scrap that was laying around (i'm being a bit snarky just
to emphasize the point -- the original poster definitely was not
proposing such a bit of cruftsmanship).

reading the thread has reinforced my view that, as a weekend
weldor, there's no way in the netherworld that i'd want to take
on a job like this by myself. i'm fairly sure i'd blow myself up...

presumably, the original poster can use this information the same
way as i did, to decide what he'd overlooked, how to deal with it,
and so on.

some folks mentioned cost effectiveness. it may not be cost
effective to make your own tank -- but it might be a lot more fun
and give you a lot more satisfaction at the end of the day. as the
master card ad says, "priceless".

f

[shortarc]

I wouldnt do it - but I'm not a welder by trade either. I agree with the others that you definately dont want to use flat ends:eek:
Attached are some pics of a compressor my Dad built me about 10 years ago. He used weld caps on the ends, pop off valves etc....
Now before anyone jumps all over me, he was a pipe welder with all the certs and mostly welded high pressure steam lines for the local university and John Deere. He's retired now, but still the best welder I know of. I'd bet my life on that compressor never letting go, but on the same hand feel very very nervous filling a purchased portable air tank with 90psi, built by people who build them day in and day out (probably in China). I had a buddy on the receiving end of a purchased air tank that decided to let go. Wasnt a pretty site - the tank basically wrapped around his head. 10K later in plastic surgeory he still looks like Herman Munster (minus the bolts). Let me know if you would like any other pics of the tank. I'll get a picture of the tank that blew up on him when I get a chance - he kept it as a little reminder since the only thing he remembers is starting to fill it, then getting the hospital bill:)

Willy. That is a beautiful piece of work, I really like the rubber mounts on the compressor.

I'd be proud to have that one in my shop.

[aametalmaster]

Willy, Nice looking comp.
There are prob 100 guys on this forum that could weld up a tank, but with out the ASME stamp someone will be asking for trouble some day if something ever happened not saying it will. I have had 2nd thoughts about using mine that i scabbed together from a semi truck air tank that is prob 35 years old. I think its time to replace the tank with a store bought one and use my old one for an oil drum or something...Bob

[willy]

Willy. That is a beautiful piece of work, I really like the rubber mounts on the compressor.

I'd be proud to have that one in my shop.

Thanks - It's kind of one of the show pieces of my shop. There are so many neat little things on it that the pictures dont show - Dad is definately good...I'm trying to learn:)

He built one for himself, myself, my brother, my brother-in-law, and one of his close friends. I've got to take it all apart to clean it again one of these days - I'll get some photos and post them - with a disclaimer of course "Don't try this at Home":eek:

[willy]

Willy, Nice looking comp.
There are prob 100 guys on this forum that could weld up a tank, but with out the ASME stamp someone will be asking for trouble some day if something ever happened not saying it will. I have had 2nd thoughts about using mine that i scabbed together from a semi truck air tank that is prob 35 years old. I think its time to replace the tank with a store bought one and use my old one for an oil drum or something...Bob

Thanks - I agree with you 100%
If I didnt know the source that it came from I'd be leary as well;)

[aametalmaster]

I'll get some photos and post them - with a disclaimer of course "Don't try this at Home":eek:

I think we all have some of them too...Bob

[justinp61]

I've found a 80 gallon tank locally. All I have to do now is fab up the mount for the compressor and motor and plumb it all up. The new motor should be here Monday, so hopefully I'll have it running next week. I know full well the dangers of air tanks, a neighbor of mine lost one of his legs from the knee down from a failure. Unfortunately he just happend to be walking by when it failed, yes it was a factory made tank. I'd never seen anyone build their own tank, that's why I asked here. The ends were something I was not sure of, hence the original post. There are people on here with far more experience than I have, or will ever have. There was no intention on my part to cobble something out of scrap. I am very capable of building it and doing a good job at it. I have a street/strip 69 Dart that runs low 7.20s at 95 mph in the 1/8 mile that I did all of the fab work on, so I trust my work. If I was not confident in my skills i would never even consider tackling such a job. Thanks to all of you that offered useful information :).

[kcstott]

Justin
Well said. And I'm not here to tell anyone what they should do either. Just pass along my experience and hope I help someone out.
If I had a nickel for every time someone told me I can't do something or I should leave it to a "professional" I'd have enough money to pay someone else to do it.
Things that I've done that most would not attempt or should not attempt.
(Keep in mind I'm talking about the general public, not people that post here)
rebuilt my first truck engine at 18 rebuilt my motorcycle engine at 20, i was already reloading ammo for a few guns at the time too. Rebuilt the diff in my jeep at 25, Learned how and did anodizing in my garage for four years for real paying customers, Rebuilt a few rifles i.e. stocks and barrels including setting the head space. And just in general fixed what was broke improved what needed improving Fabed, welded, and machined anything i needed all with little help from anyone.
I'm not boasting what I'm saying is if you are skilled and fully understand all the intricacies involved with a project then by all means have at it.
But do the research first and find out if there is something you're missing.
you'll be a better person for it and keep all your fingers too.
Kerry

[lanceman73]

Listen, I've made my own 30 gal. tanks out of 3 11 gal. tanks. I agree that the chinese products are inferrior. To buy a tank though, is almost unaffordable. I was quoted $1500.00 per tank for what I made for about $300.
Thanks,
Lance

[Anti-GMAW]

As far as I'm concerned the ASME cert. tags on most compreors are for liability purposes. I'd trust some of the farmer welds my dad makes before some of those chinese tanks.:p At work some pressure vesseles don't even require ultra sound or X-ray testing and they hold as much as 2,500psi. However, They are engineared with about as much overkill as a WW2 Tiger tank.:D I think the highest any of ou'r vessels get to is usualy around 4,500psi.


Here's a small one:


http://i162.photobucket.com/albums/t280/deathbot3000/Picture063.jpg

[justinp61]

anti-GMAW, I think the tank in you're photo would hold enough air for me:D. It would wear my compressor out filling it though:).

[Synchroman]

Buy a tank. You'll live longer!

I certainly agree. Furthermore, when you do buy your tank, make sure that it is marked with an "ASME" tag. I have an 80 gallon vertical air compressor with an ASME tank and I wouldn't want to be anywhere near it if it ever blows. An ASME certification is worth more than mere talk. It signifies that the tank was built and tested to a known specificaton and that it is safe for the use intended.

My tank is abut 15 years old and it was made in USA.

Assuming an operating pressure of 150 psi, that's going to amount to a lot of pressure on each square foot.

It's more than merely being able to fabricate and weld the tank. It's the material you would use and the necessary hydrostatic testing after it's "done".

Uh-uh. That's not a job I'd tackle. There are certified tanks available from places like MCS and Grainger. That would be my course of action.

Gutless in Sacramento. :D

[grnxrymnky]

check out ebay item number 130220533358 :eek:

now that's an air tank :)

[kcstott]

check out ebay item number 130220533358 :eek:

now that's an air tank :)

I installed a tank like that at my old day job. But the guy selling is a wee bit off on his math. It's about 500 gallons not 900.

[superredd]

Has anyone used propane cylinders as a cheap alternative to buying airtanks? for example you could get a 100lb propane cylinder and rig it for an extra air resevoir on your trailer or in your shop or something?? i've always thought of this and was told there was a safety factor of 3 or something built into the tanks.. not quite sure but a full cylinder yeilds 100 psi abouts last time i checked. What do you guys think?:rolleyes:

[platypus20]

An 80 gallon air tank holds 80 gallon at zero psig , at 150 psi that 80 gallon tank in really holding the equivent of 896 gallons of air at atomospheric pressure, because of the density of the compressed air. If you use the formula to figure density, this explains why a 220 cuft gas cylinder, is small enough to carry, as a cubic foot of air is the air volume in 3' x 3' x 3' box at atomospheric pressure. As the pressure goes up the stored air is actually engergy, trying to uncompress itself.

cylinder or tank pressure + 14.7 / 14.7 = density factor

using the 80 gal tank at 150psi

150psi +14.7 = 164.7 / 14.7 = 11.2 density factor
80 gal x 11.2 = 896 gallons




example a 220 cuft oxygen cylinder at 2200 psi

2200 + 14.7 = 2214.7 / 14.7 = 150.6 density factor

220 cuft / 150.6 = 1.4 cuft the actual capacity of the cylinder at atomospheric pressure.

Jack

[lanceman73]

I wouldn't do it! Propane tanks are made of about 16 gauge steel and never see moisture.

[DSW]

as a cubic foot of air is the air volume in 3' x 3' x 3' box at atomospheric pressure.

:confused: How is a cubic foot = to 3 feet X 3 feet X 3 feet? My math works to a cubic Yard or 27 CF. Your other calcs make sense to me, sort of. I know 14.7 psi is equal to air at sea level and you need to add that to anything if you are calulating absolute presures.

I usually work from a known volume say 104 cf @ 2640 psi and then calculate CF basied on presure so at 1320psi you have 52 cf. The math gives you 1 cf @ 25.38 psi. That same tank would hold a bit over 165 cf if you could push the psi to say 4200psi.


Wonder if portable, (diesel driven) compressors fall under this same inspection?


I'm trying to remebmber most of the portable diesel comps I worked with when I worked at the comp shop. I know they are mostly rotery screw machines and I doubt that they have a "tank" if so its a small one. I would guess that they run air straight from the compressor as those screw machines generate very large volumes of gas so storage would not be required.

[platypus20]

:confused: How is a cubic foot = to 3 feet X 3 feet X 3 feet? My math works to a cubic Yard or 27 CF. Your other calcs make sense to me, sort of. I know 14.7 psi is equal to air at sea level and you need to add that to anything if you are calulating absolute presures.

Yes you are right, my mistake that a cubic yark, not a cubic foot, which is 1' x 1' x 1'. sorry

Jack

[weekend welder]

Look into a large horizontal propane tank. The two most popular sizes are 500 and 1000 gal. They are built to an ASME standard. They have a ASME tag. IS there a difference between the standards of an air tank compared to a propane tank?? I had a 1000 gal size i bought from a propane supplier, the ASME tag had been knoked off of the tank and they were no longer allowed to use it. After i bought it i filled it with water and then did a hydro test to 300 psi, double the 150 psi that a portable screw compressor made. I used it as a resivor to blow steam whistles.

Weekend Welder

[lanceman73]

So, you fill a air tank with 15 psi. Then you fill another tank with thicker walls, it's still the same. I've worked with hydraulics for a long time. 150 PSI is nothing. If that tank explodes, it'll just crack a seem and leek out. There will be no explosions at all. Look at gas cylinders, 2500 PSI, stored on service trucks. There is no problems with that. Still, no propane tanks in my opinion, should be used for compressed air. They are too fat in diameter. I'm not an engineer, but happy with my homemade setup.

Thanks,
Lance

[aametalmaster]

150 PSI is nothing. If that tank explodes, it'll just crack a seem and leek out.

Thanks,
Lance

I saw a portable air tank explode on my dads leg. He was in the hospital for a week. The tank had a crack about 12 long in the welded area and opened right up against his leg...Bob

[enlpck]

So, you fill a air tank with 15 psi. Then you fill another tank with thicker walls, it's still the same. I've worked with hydraulics for a long time. 150 PSI is nothing. If that tank explodes, it'll just crack a seem and leek out. There will be no explosions at all. Look at gas cylinders, 2500 PSI, stored on service trucks. There is no problems with that. Still, no propane tanks in my opinion, should be used for compressed air. They are too fat in diameter. I'm not an engineer, but happy with my homemade setup.

Thanks,
Lance

You are most certainly correct: you are not an engineer

Air, or other compressible fluid (gas) is NOT hydraulic fluid. Compressed gasses store much, much more energy than liquids. The stored energy is available to do a great deal of damage in the case of a failure. Rough rule: 40gal of air compressed to 100PSIG is equivalent to one stick of straight dynamite (if you ar about to respond 'no one here knows what a stick of dynamite is', you are missing the point: even if you have never used it, you wouldn't hold a tin can with a stick in it while it was detonated, nor would you want it in your home.)

[flukecej]

Actually my dad had me make a replacement tank for our 1.5 HP 2 cylinder WW Grainger compressor. The twin hotdog tanks rusted out and they were very thin metal wise. My dad had purchased 8" weld on cap ends from a pipe supplier. These were rated as Sch. 40 for pressure application on underground lines. He had me cut a section of 8" Sch. 40 steel pipe to make the body of the tank from. Anyway, my dad said that this compressor will never be sold to anybody cause it doesn't have the ASME / ASTM tags to go on it, because it was home built basically. I welded in couplings and transferred all connections and safety devices from the old tanks to the one I built. Max air pressure is 125 PSI. I cut the compressor mounts and handle from the old tanks and welded them to the new tank I built.

Also, as part of our storage system, we are using a 40 gallon Butane Tank from an Oliver tractor. My dad had come up with two tanks from scrapping out two tractors. One of the tanks was bad, big hole in it from being run into by something. Anyway, the tank wall thickness was pretty thick, 3/8". So my dad put 125 PSI of air from our shop compressor on the other tank and soaped all the fitting and joints and let the tank set. It held air and didn't appear to have any leaks around the fittings. That tank is still used to this day for our air storage.

When I was at Texas Tech studying Mechanical Engineering, my faculty advisor and Thermodynamics professor related a story from Oak Ridge National Labs. After WW2, the lab was using surplus torpedo tanks for air storage. They were compressing air to 4200 PSI. One day, someone asked what would happen if one failed. My professor described the tanks from the torpedoes to be about 24" in diameter and about 20 ft. long. The tanks had been nested in racks about 3 tanks high and 5 tanks across. Well, to answer the question about what would happen if one failed, they took one out to a large open field and purposely caused it to fail with the 4200 PSI air charge on board. The destruction from the blast and flying shrapnel was described as a tiny nuke. After seeing what happened, the storage pressure was reduced to 2400 PSI and the nesting was changed. The tanks were stacked 2 high, and had steel plate between each stack of 2 tanks. Also, the tanks were housed in a hardened blast house in such a way that in case of another failure the shrapnel and carnage would be directed away from people and buildings and out into a "blast zone". That is the story he told us in class one day while we were studying about high pressure steam turbines.

From personal experience, I have seen what 60 PSI and 200 gallons of water can do on a galvanized pressure tank that the bottom weld gave way on. The tank in question was a 300 standard air pressure tank. About 3-1/2 ft. in diameter and around 7 ft. tall. The bottom of the tank was still on the floor of the well house when we arrived to replace it. There was a big gaping hole in the roof of the metal frame and sheet metal well house. All of the plumbing and control wiring was gone, it flew with the tank and was strewn out from the well house to were the tank landed some 300 ft. away.

That's all I have to share on this.

Charlie

[shenandoah]

Happened to be watching some "Mega Marvel Something-Or-Other" TV program about building tires and high-end mountain bikes. The statement was made that a 70/70 mountain bike tire, filled to 120psi had enough energy to blow a 200# man to an altitude of 10,000 feet!

Now, I don't know if that is true or not, but they said it right there on TV, so it must be.

[Sberry]

You think that makes sense?

[kcstott]

They get crap wrong all the time. I've been a machinist for a long time and every time there is something machine related I can point out a few mistakes.
The probably got the decimal in the wrong spot

[lanceman73]

Me no genius, you must be smarter.
You are most certainly correct: you are not an engineer

Air, or other compressible fluid (gas) is NOT hydraulic fluid. Compressed gasses store much, much more energy than liquids. The stored energy is available to do a great deal of damage in the case of a failure. Rough rule: 40gal of air compressed to 100PSIG is equivalent to one stick of straight dynamite (if you ar about to respond 'no one here knows what a stick of dynamite is', you are missing the point: even if you have never used it, you wouldn't hold a tin can with a stick in it while it was detonated, nor would you want it in your home.)

[griff01]

So, you fill a air tank with 15 psi. Then you fill another tank with thicker walls, it's still the same. I've worked with hydraulics for a long time. 150 PSI is nothing. If that tank explodes, it'll just crack a seem and leek out. There will be no explosions at all. Look at gas cylinders, 2500 PSI, stored on service trucks. There is no problems with that. Still, no propane tanks in my opinion, should be used for compressed air. They are too fat in diameter. I'm not an engineer, but happy with my homemade setup.

Thanks,
Lance

Obviously, YOU have never seen an air tank blow. I have.
Air (volume) is compressed. Hydraulic fluid is not.
Getting by with something for a long time does not validate that procedure.

Griff

[Wacko Welder]

How about this . . . .if you just need volume at a low price, buy a NEW unused propane home supply tank. $300.00 will get you a 30" diameter tank 5 feet long . . . and it is safe to 150 psi . . .

Another thought, you build a tank & it carries no certs, it blows, someone is injured, your insurer is going to say . . . . "TOUGH LUCK" buddy . . .

[Sberry]

Lots of opinions about what an insurance company will or wont pay for. One of the main reasons to carry it is in case you do something dumb.

[Stillwelding]

I'm in the process of getting everything together for a air compressor, already have a large Ingersoll Rand pump and have found a source for the motor. I can't find a decent tank near home. I do have some natural gas line pipe that is 30" od, 3/8" wall and a friend has a sheetmetal shop that can cut the ends (3/8") on his plasma cutter. Has anyone ever done this? I'm not worried about the welds, but is there anything else I need to look at?

Thanks, Justin

is there anything else I need to look at?

You may want to look at some Life Insurance. :D

[lanceman73]

Why not? The prices I was given for two 30 gallon tanks was $1500.00 each. I've got money, but not that kind of money. I guess that it depends on your needs. My home made tanks are incased in the body and secure from "explosions".