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Old 07-30-2009, 10:21 AM
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Another compressor question

A friend of mine has a 5 year old pancake compressor he uses for his nail gun and other construction tools.
It developed a stress crack where one of the legs is welded to the tank on the bottom and has started to leak air. He asked me if I could use my mig and weld it up.
Is this something that can be done safely or should I tell him it's time to buy a new compressor?

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Old 07-30-2009, 10:38 AM
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I would not touch that job (for free or pay) w/a ten foot pole! And you won't either, if you own anything of value. In this litigation-crazed world, your liability is heavy, should an accident occur after you "fix" the tank.

Your best option is to recommend him to quit using the compressor IMMEDIATELY. Replace w/new or advise him to carry it to a licensed repair facility.
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Old 07-30-2009, 12:03 PM
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I have to agree. 5 years is plenty on one of these. Time for replacement.

A stress crack into the tank is a asking for a later rupture. Most people don't know how much energy is tored in an air tank. A chunk could blow out with more than enough force to stick deeply into you. If there is one crack there are probably several more just waiting to happen.

Replace it.
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Old 07-30-2009, 02:53 PM
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Buy a new compressor. Welding on a tank is not a good idea. Larger(very large) tanks MAY be repaired but have to be hydro tested afterward to make sure they are safe.
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Old 07-30-2009, 04:25 PM
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yes

Quote:
Originally Posted by roger1
A friend of mine has a 5 year old pancake compressor he uses for his nail gun and other construction tools.
It developed a stress crack where one of the legs is welded to the tank on the bottom and has started to leak air. He asked me if I could use my mig and weld it up.
Is this something that can be done safely or should I tell him it's time to buy a new compressor?
Yes it can be welded. I have had to repair air tanks on tractor trucks. First you have to stop drill the cracked area. Even if the crack has spidered you will use an 1/8 drill bit and drill at the very end of the affected area and also drill about a centimeter apart into the crack. When you are done drilling out the holes in the crack you will have to use a cutting wheel to remove some of the material in the crack. This is known as "V", out the crack. It works like it sounds. Do not worry if you cut to deep you will fill this in later with steel. Use a medium grade steel wire and argon or 50/50 argon and carbondioxide. You may want to warm up the cracked area with a torch. For a quick repair you braze it also but it will fail again later.
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Old 07-31-2009, 03:45 PM
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Quote:
Originally Posted by nobody
Yes it can be welded. I have had to repair air tanks on tractor trucks. First you have to stop drill the cracked area. Even if the crack has spidered you will use an 1/8 drill bit and drill at the very end of the affected area and also drill about a centimeter apart into the crack. When you are done drilling out the holes in the crack you will have to use a cutting wheel to remove some of the material in the crack. This is known as "V", out the crack. It works like it sounds. Do not worry if you cut to deep you will fill this in later with steel. Use a medium grade steel wire and argon or 50/50 argon and carbondioxide. You may want to warm up the cracked area with a torch. For a quick repair you braze it also but it will fail again later.


That is absolutely terrible advice! NEVER EVER weld an air compressor tank! What you are suggesting is a recipe for disaster and just because you may have done it and gotten away with it does not make it alright, the next time you do it could get you or someone else seriously hurt or killed, even one you may have already welded could be a time bomb. When a tank cracks it is a sure sign that the tank has reached the end of it's service life and the rest of the tank has weakened from fatigue just like the spot that cracked. When that spot has been repaired that allows the rest of the tank to continue to deteriorate and the next time, and there WILL be a next time, it may very well not just crack it can very well fail catastrophically leading to property or personal damage or even a fatality. If you have ever seen a real air tank explosion I seriously doubt you would suggest anyone ever attempt to weld a crack in one, this is serious business and make no mistake about it tanks can and do hurt and kill people!

Last edited by oldred; 08-02-2009 at 10:58 AM.
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Old 07-31-2009, 05:53 PM
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No one is going to re-heat treat your little tank for you after welding and re-certify it. Its a pressure vessel and its broken, replace it.
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Old 07-31-2009, 06:23 PM
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Quote:
Originally Posted by oldred
That is absolutely terrible advice! NEVER EVER weld an air compressor tank! What you are suggesting is is a recipe for disaster and just because you may have done it and gotten away with it does not make it alright, the next time you do it could get you or someone else seriously hurt or killed, even one you may have already welded could be a time bomb. When a tank cracks it is a sure sign that the tank has reached the end of it's service life and the rest of the tank has weakened from fatigue just like the spot that cracked. When that spot has been repaired that allows the rest of the tank to continue to deteriorate and the next time, and there WILL be a next time, it may very well not just crack it can very well fail catastrophically leading to property or personal damage or even a fatality. If you have ever seen a real air tank explosion I seriously doubt you would suggest anyone ever attempt to weld a crack in one, this is serious business and make no mistake about it tanks can and do hurt and kill people!
Thanks Oldred. I figured you would chime in on this.
You gave the answer that I kind of expected.
I told my friend no and and why and he went out and bought a new one. Then he took the old one to a pawn shop and they gave him $75 for it. (Don't know what he told them.)
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Old 07-31-2009, 08:57 PM
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It is rare for a tank to do much more than crack when it first begins to fail (otherwise they would simply be impractical) but unfortunately catastrophic failures can and do occur. Of those that fail violently the vast majority of them do so because of attempts to repair a worn out (cracked) one or sometimes they have been damaged by accident, by far the "repaired" ones are the most common that are involved in accidents. If one small area of a tank is cracking due to metal fatigue from vibration or expansion/contraction then common sense would dictate that other areas of the tank are weakened also. When a tank cracks it should be thought of as a warning that the tank has reached the end of it's service life and the user should consider himself lucky that a crack is all that happened, attempt to repair the crack and they, or someone else, very well may not be so lucky the next time!
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Old 08-03-2009, 09:22 AM
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????

I don't know what you are talking about. Now the question was Can it be done. the answer is yes. Tank repair is done all the time. Compressor tanks are welded together like torque converters. It would only be dangerous if you are not good at welding, don't know what your doing, or don't have the right equipment. And as far as exploding. That is a movie gimick. When a tank Bursts from structure fatigue it blows out from the side due to overpressurizing the tank.
The crack on this one is by the leg on the bottom of the tank. It cracked on the leg because of vibration from setting the compressor down on a concrete surface and the compressor motor running. This type of damage occurs on due to a process called natural sound resonation. It is where a specific frequency of vibration causes damage to the material. Just like a music note breaking glass.
Now, what will turn any compressor into a time bomb is over pressurization. Now the 80 gallon 5.7hp compressor in my shop has been repaired 2 times and it holds 180 psi in the tank and it cracked in around the bottom near the leg. The compressor is more then 10 years old and it can not be repaired again because of its age. Our repair guy will likely sell us a new Tank. Now if you have the money to spend for a new compressor then yes feel free.
Now as far a tank being a timebomb.....New does not mean good. I get new parts all the time that are faulty. It happens. But there is nothing wrong with welding a tank if it cracks. Take to a specialist if you lack the ability to operate the correct equipment, or can not decide for yourself what the proper coarse of action would be. The only exception to welding a tank is when you fracture the side of the tank. Then you just cut the cylinder out reuse the end caps and weld a new cylinder to the old caps. This is also common practice today
And now last, but not least, yes I have seen tanks burst they are not explosive like you say they are and anyone who watches Discovery channel knows this. I believe this was busted on myth busters about a month ago.
So there you have it. Can the tank be welded? Yes. Is it safe? Yes, if the welder knows what he is doing, and it depends on the age of the tank, and where it cracks. You can not weld the cylinder but you can weld the end caps. A pancake compressor is a single stamped steel item so same rules apply weld only top or bottom parts. If the crack at the leg stretches more than 3 inches into the cylinder don't weld it. replace the tank. If money is not in abundance then grab hand tools.
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Old 08-03-2009, 09:38 AM
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For the type of compressor it is, just best to replace it. These are cheap units and the tanks are not certifyied. On larger units the tanks have a tag showing that the tank was tested at certain pressure's and is good for XXpsi working pressure.
The portable stuff is not worth repairing as the pump will soon fail after any tank repairs are done.
The big IF, is a repaired tank used in construction environment is not treated to the best of care. Should there be a tank rupture no one knows where the bits of tank will fly.
Many times it is best to replace, in the long run it's not worth it!
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Old 08-03-2009, 09:59 AM
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With all due respect you are absolutely wrong! Mythbusters? Are you kidding we are talking about something that can kill someone and the cases of this happening are FACT not myth! Tanks can and do explode and they can and do seriously injure people and sometimes even kill people! In the 30 or so years in the business I have seen many, FAR to many, accident bulletins concerning air vessel failure and a great many of these (most) were from attempts at repair, OSHA and MSHA do not spread "myths". There is no comparison to the factory assembly welding and "repair" welding on a fatigued tank and as far as "it is done all the time" that is true for only those who don't know any better or are just plain reckless. Tanks only explode in the movies? That statement is 100% USDA certified BS and just underlines how little you know about the subject! I personally have seen the results of tank explosions, one 40 gallon tank took the top of a DM 800 Mack truck cab off! It peeled that thing open like the proverbial Sardine can and one person was seriously injured. Another one took out the side of a block garage and left a hole big enough to drive a pickup truck through. This is only a couple of what I have seen or heard/read about, not at all suprising since I dealt with the darn things for nearly thirty years. Vibration does indeed cause cracking, usually around the welds however so does metal fatigue from expansion and contraction which will affect the entire tank but that does not matter anyway since once it is cracked from fatigue, regardless of the cause, it has reached the end of it's service life and has to be replaced-NEVER EVER "repaired". This is not just a disagreement on some method or procedure it is very serious business and people do get hurt and killed from doing it whether you believe it or not so do as you wish and you may get lucky, or you may not but make no mistake tanks DO explode in the real world! You do as you wish but if you refuse to listen at least don't recommend to others doing something this dangerous, welding on a fatigued and cracked air tank is just plain stupid and most people know that!



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Ok, these are just a few and there are many, many more examples of tank ruptures causing injuries and fatalities but it is almost always the same story. Certainly one can argue that these tanks were probably old and/or in bad shape but that is exactly the point, they were in bad shape just like ANY tank that has cracked from fatigue. They don't have to be old for them to be dangerous and if they have failed to the point that a crack has developed they ARE in bad shape and they are dangerous!

Mythbusters,

Last edited by oldred; 08-03-2009 at 08:44 PM.
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Old 08-03-2009, 05:09 PM
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Hey I was just at the local Meijerstore (food, clothes, hardware, ect., ect.) in the home improvement section they had pabcake and twin tank compressors for $120.00. At that price it's not fooling with. Any way buying a new compressor is a tax write-off, tools. $120 is darn cheap compared to winding up in court being suied for dammages because a tank failed and hurt someone.
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Old 08-03-2009, 08:41 PM
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Even those small tanks can do a lot of damage, they have about the same or maybe a bit less volume than a truck tire but a bit more pressure and look what an exploding truck tire can do.
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Old 08-03-2009, 10:17 PM
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Thanks oldred! Added info on this to our wiki safety article. I found the applicable OSHA standard too, and this NIOSH report with explosion pics. It's all in the "air compressors" section of the safety article.

nobody -- if you can document your position on safe repair of air compressor tanks, please do so, and we can alter the safety article accordingly, to present an opposing viewpoint. I'd like to take a look at the Mythbusters coverage on this too, but couldn't find it in Google.

If anyone else has any additional information on air compressor safety, please add it to the the wiki article.
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