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Buzzer John
04-22-2009, 08:26 PM
My air compressor tank has developed a small rust hole and I am looking for the easiest fix that does not call for a new tank. I only use this thing for filling tires. I have thought of screwing in a sheet metal screw with a bit of a gasket. I might be able to weld it, but I would probably just burn a larger hole. Any other suggestions?
Thanks, John

pressurerelief
04-22-2009, 08:31 PM
Buzzer John, I would not repair but would replace. I know you said you did not want to do this but this is the only safe alternative. You probably have many other rust pockets waiting to break through. You have a potential failure of a pressure vessel on the horizon. Stay Safe.

P/R

Arcane
04-22-2009, 08:39 PM
If you don't want to buy a new tank, buy a used tank that is in good condition. That basically means it would pass a hydrostatic test. Rust holes are like rats, if you see one, there's many more that you don't see. Sometimes airtanks fail catastrophically like a bomb and sometimes they just leak and it's pretty well impossible to tell in advance which one it will be. There's been a few instances where a great deal of damage was done when one blew up and if you were right there when it went, you would stand a good chance of getting hurt very badly if not killed. That also applies to any innocent people nearby. It really isn't a good idea at all to try to fix a problem tank that probably has already paid for itself many times over.

Buzzer John
04-22-2009, 08:52 PM
Thanks for the comments about safety. Would an old propane tank be strong enough? I have see some made into a portable air tank, but I don't know how much pressure they hold. My unit cuts out around 100psi.
Again thanks, John

Roy Andrews
04-22-2009, 09:18 PM
i welded the tank on one of my compressors that developed a small pinhole leak from rust about 15 years ago. if your worried about your welding just clean it real well and braze it. rust holes or welding them closed will not cause any sort of catastrophic failure. rusting weld joints actually make a tank less likely to fail dramatically due to over pressurization as the weak seams open up fairly easily and relieve the pressure. i dont offer this as hearsay or old tales. i once worked for a company that made tanks and i was involved with the testing and failure analasys of a lot of tanks. we had fixtures that blew up tanks and we did it every day. it was incredible the damage a small 20 gal .125 wall tank would do.

Evan
04-22-2009, 09:21 PM
A 20 lb propane tank will work fine. They are rated to at least 300 psi. Take proper precations to avoid igniting residual propane. Washing with solvent and then hot soapy water followed by a rinse of boiling hot clean water will work.

Disclaimer: Some may say it is dangerous. It is but only because any vessel filled with compressed air is dangerous. Small propane tanks and small air tanks have the same steel and same construction as well as same burst pressure requirements. Actually, propane tanks are somewhat better regulated. YMMV.

Buzzer John
04-22-2009, 09:29 PM
Sounds like the propane tank is my best bet. I can probably pick one up at the local gas supplier. He used to have a pile of them with the old style valve.
John

websterz
04-22-2009, 09:29 PM
Thanks for the comments about safety. Would an old propane tank be strong enough? I have see some made into a portable air tank, but I don't know how much pressure they hold. My unit cuts out around 100psi.
Again thanks, John

Look at the collar that surrounds the valve. There SHOULD be a DOT rating stamped there, something like DOT-250. The number is the tanks safety rating in PSI. Give yourself a comfortable safety margin, say 75-100psi above what your compressor is capable of putting out and you should be fine.

wierdscience
04-22-2009, 09:58 PM
An old post on the subject.

http://bbs.homeshopmachinist.net/showthread.php?t=19099&highlight=COMPRESSOR+TANK

kendall
04-22-2009, 10:08 PM
I'm normally very willing to go with 'fixes' but for some reason I feel that the only real fix for an air tank is replacement.

I had a fantastic little compressor for work (carpenter, for nail guns etc) that I really loved because it was light, and extremely quiet ( a HUGE plus when you have to listen to it all day long!) I bought it used, and had it for over 15 years, and repaired several leaks towards the end of it's life with welds,braze, and even epoxy only to have a new leak show up a short while later. When I finally stripped it down, thee were 8 repairs along the bottom. (stupid, but when I find something I like, I try to keep it going as long as I can!)
I finally tossed the tank, because while prepping for another repair, I noticed several divots forming where I was sanding, and saw that I could easily press a needle through them.

You can't tell what the inside is like without a serious inspection, and if it was rusted enough to leak in one place, there are several others that are very close.

Find another tank, there are hundreds of tanks tossed all the time because the motor or compressor died, save the headache, replace the tank.

A propane, freon, or even another air tank is great. A few years ago I trashed an old water heater, and noticed a tag on the tank itself that stated 'not to exceed 300psi" Which is about what a lot of air tanks are rated for.

Ken.

airsmith282
04-22-2009, 10:21 PM
id defentaly get a new tank or complet new compressor, i dont take chances with my life or the lives of others , somethings are better left to goto the scrap pile

Evan
04-22-2009, 10:47 PM
300 psi seems to be a minimum standard for small portable pressure vessels. Spray paint cans, 1 lb propane canisters and a wide variety of small pressurized products all meet that standard.

saltmine
04-22-2009, 10:51 PM
The main reason you can't use an old propane tank for compressed air is COATING.

Even though propane tanks are rated for just as much (or more) pressure, they don't have any type of anti-rust coating inside....

I remember years ago, a company used to make adapters to convert discarded propane tanks into air tanks. I'm sure they sold a lot of them. My brother and I used to race off road, and we had several. But, they were pulled off the market because somebody had one blow up in his face...and sued the adapter manufacturer. The reason? Rust. Air tanks, used on compressors and as portable air supplies ALL have an epoxy coating inside to prevent weakening the shell of the tank through rust formation.
Usually, if you see rust patches or leaks forming on the outside of a compressed air tank, it's time to discard it, PRONTO. If the rust has progressed through the epoxy coating, the tank is shot.

A discarded propane tank will rust up imediately, inside. And will rust through in no time.

Even 30 lb Freon containers are not coated inside. (BT,DT.)

darryl
04-22-2009, 11:30 PM
Hmm. Interesting about the lack of a coating inside tanks. I suppose one could coat the inside by thoroughly swishing around an epoxy mixture, but for one you couldn't see the results so you wouldn't know if there were dry spots or not, and secondly you'd want to add a water drain which would probably mean drilling at least one hole in the tank. Hmm.

I've used propane tanks for air without problem except for smell, but I did NOT drill or modify the tanks. It occurs to me that some mod of the existing valve might be made anyway for air use, so one could instal a tube through that fitting which would reach very close to the bottom of the tank. The tube would have a separate valve on it which would open to drain water as long as there's some pressure in the tank. If you epoxy, there's bound to be a level spot inside at the bottom, so any water would have to spread out before it could build up enough depth to exit through the tube. That leaves a significant amount of water to remain in the tank even after it has been drained. I guess you could always just turn the tank upside down to drain the water through the air valve. I dunno, I have mixed feelings about re-using propane tanks after having done that a few times. I definitely wouldn't want to be using the air inside a small room, where it could and would smell up the place with mercaptan, the odorant in propane. The tanks themselves are rated to not blow until at least 1200 psi has been reached (from my previous research several years ago) so safety factor with air at 150 psi or less should be fine.

Something else that occurs to me is that the remaining odorant and propane infused into the metal might interfere with the epoxy coating. If one is willing to do the work, you could spring for a new, unfilled tank, plus about ten bucks worth of epoxy, and then maybe feel a little more secure about the integrity of the epoxy coating- again, I don't feel so great about going this general route for an air tank. I also would be surprised to find that any particular air tank one could buy would be coated- I have my doubts on that, especially these days.

Frank Ford
04-22-2009, 11:45 PM
Best fix? I could hardly guess.

Here's a NOT best fix:

I had this old hulk of an air compressor. It was a 60 gallon HEAVY tank with a REALLY heavy old (1939) compressor head and 1 HP motor in the standard horizontal configuration.

It had a small leak at the bottom and shed rust scales through the drain.

So I gave it to my old pal, Brian.

He said, "Hey thanks for the vacuum pump with the big reservoir." Then he slapped a simple epoxy patch on the outside, plumbed the pump in reverse and was ready to go.

D'oh. . . .

(not my first or my last, I'm sure)

Evan
04-22-2009, 11:47 PM
The main reason you can't use an old propane tank for compressed air is COATING.


I wonder why water pressure tanks aren't coated then? They are half full of air under pressure. That includes the ones with rubber bladders since the bladders always develop leaks. I made a compressor out of one that was retired for a smaller water tank. It lasted for only about 18 years. Tanks that rust through don't blow up. They develop pinhole leaks that gradually become larger. The most common cause of catastrophic air receiver failure is over pressure in really cold conditions, say -20 or lower. This makes the metal much more brittle and subject to cracking rather than tearing.

dhammer
04-23-2009, 12:02 AM
My air compressor tank has developed a small rust hole and I am looking for the easiest fix that does not call for a new tank. I only use this thing for filling tires. I have thought of screwing in a sheet metal screw with a bit of a gasket. I might be able to weld it, but I would probably just burn a larger hole. Any other suggestions?
Thanks, John
My advice is to replace the tank. Depending on what kind of compressor you have you might find it cheaper just to buy a new compressor. Another option is to purchase a new portable air tank and mount your pump, motor and controls on it..lots or work and maybe not worth the trouble.

New replacement air tanks are hard to find, there are only two companies(that I know of) tht will sell you a bare tank..Graingers and aircompressor world.com. I bought a 60 gal bare tank from aircompressor world..$400.00 plus freight..Graingers was even more. I bought a bare pump from Eaton but they would not sell me a tank..liability and all.

Propane tanks will take the pressure. I believe the pressure relief valve on most DOT LP cylinders is set to go off at 240 psi. The problem with propane tanks is that there are not enough holes in the tank..for an air compressor you should have at least three "bungs"..inlet, outlet and drain. You could weld in more outlets but DOT regulations prohibit welding on tanks unless you are a certified tank repair shop.

Steve

kendall
04-23-2009, 12:13 AM
As far as the propane tanks, is there a reason you couldn't mount the tank upside down? use the fill as a combination fill/tap/drain?

Ken.

dhammer
04-23-2009, 12:20 AM
As far as the propane tanks, is there a reason you couldn't mount the tank upside down? use the fill as a combination fill/tap/drain?

Ken.
Air compressors have a check valve between the pump and tank, they also have a unloader valve so the motor..electric or gas doesn't have to start against head pressure. I don't think a tank with one hole would work.

J. Randall
04-23-2009, 12:26 AM
It is great to stay on the safe side of things, but there is a lot of misinformation in this thread. I have been around converted propane tanks used for shop air, and the mercaptan smell was never a problem, and they were not epoxy coated, and some of them are still going strong 30 yrs. later. If you are doing it for yourself, and use a little common sense you can weld all the bungs and drains on that you need. There are literally thousands of factory air tank still in service that are uncoated inside. Sure they will rust over time and some need to be replaced, but that is where the common sense comes in.
James

oldtiffie
04-23-2009, 12:40 AM
I wonder what your insurance company would have to say if you put in a claim and they found that you were using a pressure vessel other than for its rated and designed purpose and/or that was "Out of Test" (date) and/or over pressure and not either modified by a certified shop or certified by an Engineer?

My compressors are destroyed as soon as or before the 10-year test is required. A new compressor every 10 years is good going.

Same with all pressure vessels here - LPG included.

My oxy-acet and MIG bottles are rented and tested by the owner as required by Law. I just take them (LPG too) in and swap for new filled (and if required, re-tested and re-certified) as required. I have at least 4 oxy-acet and MIG bottle distributors/agents within 10 or so Km of here. I have a "Trade" account, so I just book it to the account.

There are at least two LPG re-fillers/bottle-swap in every town here.

I don't take chances with high-pressure gases or liquids.

Perhaps its (still?) more "Wild West" in the US than it is here.

Evan
04-23-2009, 04:11 AM
At least in Canada there is no requirement to test a compressor receiver every ten years or ever at all in a home shop setting with no employees. 20 lb propane tanks also do not require such testing. Only the valve must be replaced every ten years, not the tank, nor is the tank recertified or tested, just the valve body.

Tanks for industrial gasses such as CO2, acetylene, oxygen etc are a different matter as the pressures are much higher.


Drilling extra holes in a propane tank is just fine as long as the holes are in the end bell and not the less curved body. The more curved the section is the higher the hoop stress it can withstand. It is best to braze fittings in place than to weld but if welding is desired then the use of either mig or low hydrogen rod is appropriate.

As for air pressure vessels in general air receivers with a diameter of 4 inches or less are exempt from certification and testing in the first place in the US and Canada. That is why you see so many of the import compressors with double air tanks, each just 4 inches in diameter as well as some that use large diameter tubing as the frame and receiver as one.

The steel used in propane tanks is low carbon aluminum killed deoxidized fine grained steel made specifically for pressure vessels. This type of steel is much less likely to fail by brittle crack propagation than regular mild steels.

John Stevenson
04-23-2009, 04:36 AM
I have just cut a propane bottle open for the curved sections to make a trolley and can confirm they are not coated inside.
However think about this, Modern trucks have anything from 3 to 5 air tanks on them for their split braking systems, none of these are coated as I have cut many open, over an 8 or 10 year operating period these must cycle far more times than a normal compressor and the cycling is the factor with pressure vessels.

I have never seen one of these blow up or damaged other than the vehicle being involved in an accident and if there was a problem the Road Transport Board would have something to do about liaising with manufacturers about design.

.

derekm
04-23-2009, 07:10 AM
[QUOTE=Evan]

...

Drilling extra holes in a propane tank is just fine as long as the holes are in the end bell and not the less curved body. The more curved the section is the higher the hoop stress it can withstand. It is best to braze fittings in place than to weld but if welding is desired then the use of either mig or low hydrogen rod is appropriate.
...
[QUOTE]
I'm afraid I would be just plain lazy and use the tank upside down

airsmith282
04-23-2009, 08:06 AM
you know this is an idea , most are saying the tanks will rust form out side in and iam not going to say no to that what iam saying is whati f you repainted your compresser thank every year, this would prevent any rust up on the out side and should make the tank last like forever.. wooks for wood ,, i repaint my shop akak 8x12 shed every year and so far not one spec of rotten wood it still just like new , i also repaint my floor as well every year inside the shed as well to prevent swelling and rot from all the snow and water and crap that gets on the floor as well so far no problems, now iam not saying either to strip the paint off the tank but just respray it with a coat of paint every year and it shouldnt ever have a problem..

i have leaned now to leave my tanks full of air all the time and it is a blessing expecially to not have to hear the noise out of my 3 gallon tank every morring , i love my 8 gallon tank its so quiet ..

ya in know but i needed the 3 gallon one for its size and its job is to blow off the lathe and mill thats all its good for and it does the job..

propane tanks are cool to use as a portable sprayer, never heard of them used for use as a compressor , sounds like a cool idea, persoanly id just go out and get a new tank or a new compressor there getting so cheap now its crazy,, but if you get a new one then just paint it every year thats my idea ,, sorry for such a long post hear

Ron of Va
04-23-2009, 08:20 AM
I repaired a pin hole in a compressor tank with a large sheet metal screw. One installed with a 3/8 socket. I ran the screw in half way, then slathered the shaft of the screw with hot glue, and ran it in all the way while the glue was still hot. I was surprised to find the repair lasted for over 10 years, until I disposed of the entire unit.

pcarpenter
04-23-2009, 10:42 AM
That's sure lucky, Ron. Otherwise, you could have ended up with that screw imbedded in a body part.

The trouble with on-line forums is that you get information on what worked....but often those solutions depended on a lot of luck. This is a great example....that same screw could have become a projectile.

Pressure vessel failures can be pretty catastrophic. It's the very reason that they have to be hydro-tested from time to time in commercial environments. This is not an exercise that is done for the fun of it.

Want a new air compressor tank (small)? Go to www.surpluscenter.com (http://www.surpluscenter.com) and search on air tank. There are several small ones there with wheels, handles and mounting points for the motor and compressor.

Paul

Willy
04-23-2009, 10:45 AM
One thing I learned a loong time ago...you can't weld rust!

Evan
04-23-2009, 11:54 AM
Pressure vessel failures can be pretty catastrophic

That is particularly true of the large sizes and less so of the sizes used in the home shop. The type of strain the metal undergoes is directly dependent on the size of the tank. That has a direct influence on the failure modes.

Incidents involving catastrophic failure of small compressor receivers are very rare and incidents involving serious injury are nearly unheard of. The only real hazards involve operation in very cold conditions which should be avoided especially if a charged tank is left to cool to ambient and then moved. This applies to any size compressor or storage tank in cold climates. At a temperature of -40 the steel is close to a total transition to glassy metal behaviour and will shatter under fairly mild impact. If thinned by corrosion it may fail due to pressure alone.

The other cause for concern has nothing to do with the materials of the compressor or receiver but is caused by the use of improper compressor lubricant. If the wrong type or viscosity of oil is used it can cause a buildup of carbon in the compressor outlet and a buildup of oil in the tank. When air is compressed to 5 bar the partial pressure of oxygen is equivalent to a pure oxygen atmosphere. It takes only the sightest source of ignition from hot carbon particles to ignite excess oil in the compressor tank which will cause an immediate deflagration explosion and will violently rupture the tank regardless of what it is made from.

sidegrinder
04-23-2009, 11:59 AM
Like Ron, I filled a pinhole with a sheet metal screw and then brazed it in place. It's been 4 or 5yrs now with no problems. It was near the bottom of the tank, so if it ever would break loose there wouldn't be much in the line of fire anyway. YMMV, Sidegrinder.

ckelloug
04-23-2009, 12:54 PM
It's what you don't see in the tank when you patch it that way that will be your undoing.

ASME has written lots of rules on pressure vessels found in http://www.asme.org/Codes/International_Boiler_Pressure.cfm The relevant section of the code to verify doing it right costs more than a manufactured new tank and a copy of the whole code is $13,000! These requirements are the legal basis for most pressure vessel safety regulations in the U.S. and Canada.

The ASME pressure vessel code was created to prevent the explosions of steam ship boilers at the beginning of the 20th century.

From an engineering perspective, you need to make pressure vessels that definitely won't fail under the usage circumstances: not one that might not fail if you are lucky. An HSM can make a one-off vessel to a lesser standard but he/she accepts all the risk but to do so would be disregarding a hundred years of engineering science and accepting the liability for the failure.

--Cameron
Registered Engineer In Training (E.I.T.) Alabama USA

Evan
04-23-2009, 01:59 PM
From an engineering perspective, you need to make pressure vessels that definitely won't fail under the usage circumstances:

That is something that engineers have never actually accomplished. In the effort to do so all obvious increases in risk are considered unacceptable even if the increase is too small to quantify. A typical engineer viewpoint. ;)

You should look up the subject of over pressure relief devices on large LPG transport containers. They are so useless in many circumstances that they are not permitted in some jurisdictions. Even on small containers their utility is in doubt.

Ron of Va
04-23-2009, 06:02 PM
I repaired a pin hole in a compressor tank with a large sheet metal screw. One installed with a 3/8 socket. I ran the screw in half way, then slathered the shaft of the screw with hot glue, and ran it in all the way while the glue was still hot. I was surprised to find the repair lasted for over 10 years, until I disposed of the entire unit.

I am the guy who used the sheet metal screw. My thoughts are:
There are millions of these homeowner air compressors in the country. If it is over a few years old, I am sure it has rust in the bottom. I have never heard of a catastrophic failure. Spring a leak; pop a safety valve, rust through on the bottom, yes it happens all the time.
More than likely there will just be another pinhole leak to repair.

Catastrophic failure, I am skeptical.

Maybe in a commercial environment with a 20 horsepower motor, maybe, I guess it has happened. But I have never heard of one of those either. But I guess unless someone was hurt, it wouldn’t make the news.

Bguns
04-23-2009, 06:17 PM
These Tanks CAN KILL, MAIM, DESTROY HOME OR SHOP..

Shall I send the next Widow your way with a Lawyer, because YOU said it was OK to fix something you ARE NOT QUALIFIED TO SPEAK ABOUT....

http://ncsp.tamu.edu/reports/WorkCover/Alerts.htm

http://www.civeng.carleton.ca/ECL/reports/ECL241/ecl241a.html

http://www.mass.gov/?pageID=eopsmodulechunk&L=4&L0=Home&L1=Consumer+Protection+%26+Business+Licensing&L2=License+Type+by+Business+Area&L3=Engineering+Division&sid=Eeops&b=terminalcontent&f=dps_inf_compressor_recall&csid=Eeops

Above link... 458,000 Compressors recalled... Kind of puts a dent in the Millions of safe Home Compressors theory.

Pressure Vessel Repairs Are matters of Life and Death.
And Regulations are written that detail exactly the Processes and Procedures required.

Unapproved/Tested Welding or any other Bandaid repair, Can/Will change ability to resist fracture due to constant pressure cycling...

Getting the required Repair Stamp certification alone, costs thousands...

At least most of the Steam Engine Modelers, Hydro test their Boilers yearly...

Boilers are built to higher standard than Air Receivers....

EDIT: That first link Tank was a Home Shop Size Unit...

Certified replacement Receivers are Fairly inexpensive, and available from many sources. Not as Cheap a piece of Coathanger wire and a torch, but I guess life is cheaper to some people..

Some odds we have to take... Others we can reduce to almost nothing for just a couple hundred dollars...

Ron of Va
04-23-2009, 06:23 PM
These Tanks CAN KILL, MAIM, DESTROY HOME OR SHOP..

Shall I send the next Widow your way with a Lawyer, because YOU said it was OK to fix something you ARE NOT QUALIFIED TO SPEAK ABOUT....

http://ncsp.tamu.edu/reports/WorkCover/Alerts.htm

Like I said, commercial environment. BTW, I only said I did it.:rolleyes:

I don’t doubt your sincerity, I am doubtful a homeowner has much to fear from a catastrophic failure.

Mcgyver
04-23-2009, 06:58 PM
These Tanks CAN KILL, MAIM, DESTROY HOME OR SHOP..

Shall I send the next Widow your way with a Lawyer, because YOU said it was OK to fix something you ARE NOT QUALIFIED TO SPEAK ABOUT....

http://ncsp.tamu.edu/reports/WorkCover/Alerts.htm

did you read that link? the tank exploded because of sparks and oil in the tank, the condition of the tank doesn't factor in.

I would replace the tank when a pin hole develops figuring its done, but so far as danger goes I'm more inclined to side with Ron. Inevitably when air tank discussions come up people think in terms of other pressure vessels. But what happens when an air tank leaks? Unlike a boiler, there's no mass liquid wanting to flash into steam with the pressure drop, unlike a gas cylinder, its not at 2000lb and wanting to launch itself all over the room, unlike propane there's no explosive gas released.

Then only way i can see it being dangerous is if a the entire perimeter of a section all of a sudden failed - like the entire weld around the end fails instantaneously and the end cap flies across the room. can't see that happening. if its going to rupture, a small seem or hole will open up, the noise might scare the crap out of you, and the pressure is quickly released.

there's just not a parallel to say a boiler where its the sudden drop in pressure that causes the explosion. The air tanks that explode seem to do so because of a volatile mixture of air, oil and spark - the spark can be static or just that the temps are so high through the restricted head to tank pipe (the diesel effect) - and the force is such that new or old the tank is ripped to shreds.

I'd like to hear what a qualified expert has to say - I can find lots of credible info on tanks exploding because of the diesel effect but none of an explosion because of leak and an explosion based on leaking just doesn't seem to make sense.

Rustybolt
04-23-2009, 07:08 PM
100 psi is 100 psi no matter what vessel it's in. OK. That being said, I think in a home compressor situation if you have a leak in the tank there is a greater danger of the motor running on and starting a fire than the tank bursting.
On commercial /industrial sized compressors I've seen the compressor siezed from lack of lubrication. I have seen tanks fill up with water. I have had flywheels come off the compressor-That's exciting, but never have I seen one burst.
The problem pin holes in a home compressor is it is usually only the first one.

Bguns
04-23-2009, 07:13 PM
Yes read link

Have you ever seen oil come out of a Tank drain?

Did you read third link?

Fuel based Explosion is not the only failure.. If a Seam Splits and there is an object close to it, say a Can of Paint guess what goes flying into something?? Possibly igniting with that nice blast of Air after it hits something creating a Spark....

Lots of other DEATHS caused by vibration loosening fittings to Receiver and sending Lines and piping flying... Look up Mine Safety. Usually larger stuff tho.

Just because it is a Home shop sized tank it is still deadly...

If Ron was right, Home tanks would not be ASME stamped Pressure Vessels.

They are, and thereby need to follow all Regulations for repair...

If an unauthorized repair fails, destroys restored car in Garage or blows hole in House, do you think Insurance Company will cover that... I don't...

Welding changes designed in safety factor of Standard Receiver .

They use carefully heat treated steel and approved welding techniques to maintain steel in proper Ductile range, so it will split instead of Blowing up like a bomb...

Even so, a big piece of steel unwrapping so suddenly is dangerous...

A Pin hole means its time to replace the Tank Not repair it....

oldtiffie
04-23-2009, 07:20 PM
I don't know how it is outside OZ, but the "loop-hole" for escaping because it is a non-commercial shop or that there are no employees or that there are under a specified number of employees vanishes as soon as you do anything for money or reward in that shop. That includes anything by way of value to or for another person - I presume outside your immediate family. So barter is included.

Further, it need not necessarily be a explosion relating to a "private" non-commercial job either as if the compressor or pressure vessels was/were in the shop when something was done for cash or reward is enough.

A lone operator working for cash or reward is classified as an employee.

Worksafe will be called in by the Police or the Courts if someone or property is injured or Coroner if someone is killed.

Next, your insurance company will look very closely at any claim submitted by you or another interested or injured party. You may not be pleased if you have inadequate insurance or have either not provided full and true information to your insurer - including working for reward or as a commercial shop and only declaring it to be a "home" or "hobby" shop. Your Public Liability will be on very shaky ground. The Courts take a pretty dim view of these suspect behaviours. Do you have the resources to stand those costs if awarded against you?

Oh, and another thing.

Here, the State and Federal Tax and Regulators are aware or made aware of these cases when they come to Court.

Do you seriously think that you will be any less injured (or dead?? or incapacitated??) if your shop is "personal" or "non-commercial"?

If you are injured or disabled to the extent that you can't do your day job, just what do you think your employer will do or say? And just what may any future potential employers think - or do - or not do?

I run my shop as it if were a commercial shop (there are "holes" in that) as I don't fancy taking those risks with myself nor do I fancy landing my wife with the consequences of an "accident" that may well have been preventable.

A serious enough "event" may well render your shop unusable so far as you are concerned - and what will or can you do about that?

I will never eliminate all risk nor will (or was I) ever "bullet-proof".

My compressor is "blown down" at least every three months and the condensate examined while I am at it. I do leave it charged over-night. I "unload" the line regulator to zero and disconnect the hose (line) from the regulator as soon as I have finished with the compressor or at the end of the day - even if only blowing down a job or pumping up the tyres on the car. The power supply is turned off at the wall outlet - every day after work has finished. I keep a good eye on the tank/receiver pressure guage at all times to see if it is falling or not. If falling, I go chasing the cause of the loss/leak - and fix it - or get it fixed - or replace the entire compressor if needs be.

It seems a lot but it isn't - just a few minutes a day.

KenL
04-23-2009, 07:31 PM
I'd like to hear what a qualified expert has to say - I can find lots of credible info on tanks exploding because of the diesel effect but none of an explosion because of leak and an explosion based on leaking just doesn't seem to make sense.[/QUOTE]

Hello alll. I'm new to the forum but not at all new (55 real soon) and have been in the engineering business for 38 of those years.

I suppose that "qualified expert" depends on what you mean, but I am a professional engineer who has designed many large (250,00lb naptha towers large) and small pressure vessels (5000psi aircraft accumulators) over my career, so I suppose that I can claim some expertise in the field and would offer the following:

It is generally the case as somone noted that a single rust pit (hole) does not exist in isolation, so if you have one leak, you likely are on the verge of more. Note likely, not certainly; engineering is based on statistics you know.

A minor leak will generally get bigger since rust has essentially no strength unless it is repaired. Repairing a leak is not a very good idea unless the rest of the tank can be inspected to ascertain that there is no other damage. For a small home shop tank, there is a significant risk that the thing could come unzippered from cumulative damage and the consequences are not worth the minor savings of a replacement.

My dad didn't accept that this was the case and repaired his compressor tank, a sort of pot shaped affair similar to a propane tank, against my advice to the contrary. When the seam unzipped at 125psi, if the broken gauge was to be believed, it drove the compressor, motor and all, all the way to the ceiling of the old one-room school house he used for a shop, over 20 feet!! It did not hit anyone on the way up or the way down but there was serious potential for death here.

New tanks are available at most automotive supply places including what I call an air pig (a small portable tank for inflating tires) for cheap. I am not trying to tell folks what to do, I'm just saying....

Ken in Ottawa

Evan
04-23-2009, 08:02 PM
These Tanks CAN KILL, MAIM, DESTROY HOME OR SHOP..



Theoretically that is true based on the amount of energy that could conceivably be released if a catastrophic failure ocurred. An internal explosion of combustible products is not a failure of the receiver design.

The interesting thing is that it is nearly impossible to find any documented case of a small air receiver failing in such a manner and in my searching in times past when this was discussed I could not find a single incident where a death was caused by a low pressure air receiver failure due to bursting under pressure with one exception being a burst that ocurred in extreme cold.

The size of tanks used at the home shop level simply are not in the class that industrial tanks are. They will not and cannot fail in the same manner because the behaviour of materials does not scale linearly with size.

radkins
04-23-2009, 08:56 PM
NEVER EVER weld a rust hole in an air tank! Even if you manage to get it plugged without weakening the tank further the fact that it already has a hole rusted through is PROOF POSITIVE that the tank is rusted out and has reached the end of it's service life and to patch one in that condition is creating a bomb! Trying to weld a rust hole in an air tank is just plain stupid! I hate to be so blunt but doing that can easily get someone killed! I have seen several safety bulletins over the years that involved air tank explosions and almost all of them involved modifications and/or rusting in an old tank.


www.cprlaw.com/Grovatt-v.-Midwest-Products,-Inc.--3-4102-221.html


Here is one that ruptured due to rust.

www.doli.state.mn.us/airtank.html

jb-mck
04-23-2009, 09:15 PM
Fix the tank and you may be a candidate for the Darwin awards!

randyjaco
04-23-2009, 09:31 PM
This discussion is just like the compressed air piping in PVC debate. Everybody knows that neither is safe, but there are a few that are going to do it anyway just because they are cheap and they don't believe that bad things are going to happen to them. Most will get away with the risk. A few will suffer catastrophic consequences. Just remember each day you walk into the shop with that risk present; you ought ask yourself "Do you feel lucky today?" :eek:

Evan
04-23-2009, 09:56 PM
The first link is loaded with BS in the description of the claims in court. Most of what was claimed doesn't even apply to the type of air tank in question. The ASME standards don't apply nor does any sort of inspection to air receivers under 5 cubic feet and less than 250 psig working pressure. Some jurisdictions use 15 cubic feet as the threshold and it is up to the local state codes. Note also the the claims state "recommended by the ASME" not "Required".

The second link shows the result of a defect in manufacturing, the use of too thin material and probably the wrong type judging by the way it failed. That's where a propane vessel is safer than an unregulated air receiver design in that propane tanks are regulated in all sizes.

Evan
04-23-2009, 09:58 PM
A few will suffer catastrophic consequences

Not likely. Try to find a single instance of injury from using a small propane tank as an air receiver.

bborr01
04-23-2009, 11:27 PM
All this talk about leaking tanks is giving me.........Ok, I feel better now. Glad I am in the shop alone tonight. My 2 cents worth. I have several compressors, from a 2 gallon oilless to a 80 gallon sullair 2 stage. I also use a 30# propane tank as a portable air tank. I've been using the propane tank for about 10 years or so with no problems. There has been a lot of talk on this subject about hydro-testing tanks. An oxygen or similar tank with 2500 psi gets a lot more of my respect than a plumbers torch acetylene tank with 150 or 200 psi. (considering the pressure only and not the contents) When I traded out my plumbers torch acetylene tank recently, I asked that it be replaced with a tank that would be current on hydro-testing for several years as I don't use it often. Welding guy informed me that these tanks do not get routing testing due to their small size. A one gallon tank at 150 psi is likely not nearly as dangerous as an 80 gal. tank at 100 psi. Use common sense.
I hate to throw a good compressor away. But I was given a small compressor recently with a pin hole in the bottom. (no drain, no wonder) I have already salvaged the regulator. I plan to salvage the pressure switch. If I can find someone that needs a motor and pump, that will become donor material. I will scrap the tank. I have no doubt that I can cut out the damaged area and weld in new, but for the price of a new or good used compressor I can't make a case for the repair. If you come away from all of this with one thing, at least learn to drain your tank regurlarly.

J. Randall
04-23-2009, 11:53 PM
Ken, if you are going to tell us that kind of story , tell us what he did to cause that kind of failure, so someone won't repeat his mistake. I doubt it was a metal screw in the bottom in a rust pit.
James
Edit to add: Forgot to say Welcome to the forum.

KenL
04-24-2009, 06:53 AM
Ken, if you are going to tell us that kind of story , tell us what he did to cause that kind of failure, so someone won't repeat his mistake. I doubt it was a metal screw in the bottom in a rust pit.
James
Edit to add: Forgot to say Welcome to the forum.


Thanks for the welcome.

I should have described Dad's "fix". He found a small rust hole near the base, drilled it out as I recall about 3/16" or so, pretty small, then plug welded the hole. He then put her back to work painting a truck. The failure mode had nothing to do with the repair but had everything to do with the ring of rust all the way around the base at the same level that he could not see through the small hole he drilled. It finally fatigued off, a couple of months, later and blew. The tank bottom came unzipped just like you cut it off with a can-opener. So, like many failure investigations that I have been involved in, it was not so much the result of his specific action, but rather the consequence of what he didn't do. He could have cut the whole bottom off, removed the rusty section, rewelded it (he was a qualified welder), pressure tested it to proof, put her back to work (maybe) and been safe.

By the by, this incident scared my rather fearless father and me too! He went out and bought a new compressor and no more fooling with repairs.

This happened in 1979, Balmoral, Nova Scotia.

Ken in Ottawa

J. Randall
04-24-2009, 06:21 PM
Ken, thanks for explaining, must have been a very uniform ring of rust from a a quantity of water sitting in it for a long time. I am really surprised it just did not pinhole again. I bet it was scary.
James