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How do you test an old compressor tank?

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Zira

12-20-2000 14:35:29




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I just acquired an older Kellogg compressor, mounted on a 30-gallon ASTME approved tank of un-known age. The tank looks okay, but I know it sat outdoors for a few weeks at least. How do I safely test the tank? Put a gage on the tank, put it out in the yard, hook up a long hose, go in to the house & turn on the compressor? I assume that if the tank doesn't leak or blow up @115 psi, it is still safe to use.

Thanks for any & all in puts.

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Greg

12-22-2000 22:55:50




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 Re: How do you test an old compressor tank? in reply to Zira, 12-20-2000 14:35:29  
Is cost the only factor why we never see stainless steel tanks on air compressors?



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T_Bone

12-23-2000 00:21:40




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 Re: Re: How do you test an old compressor tank? in reply to Greg, 12-22-2000 22:55:50  
Hi Greg, Yep as SS cost $1.35lb vs .44lb mild steel wholesale.

T_Bone



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T_Bone... Bomb?????

12-21-2000 10:15:22




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 Re: How do you test an old compressor tank? in reply to Zira, 12-20-2000 14:35:29  
Hi Zira, I like to test at twice what working pressure will be, 120psi=240psi test. A tank just doesn't explode like a bomb when it gets a hole in it or opens. Here in Arizona it gets pretty warm and I've had 30lb refrigeration can pop off on there rupture disc and all it does is make alot of noise. Rupture disc are set twice of high working pressure, so the last one blew at 500psi inside my van at 123 degree ouside ambient tempature, it had to be about 175 degrees inside the van and I was in it!!! Other than wasting $500 worth of refrigerent all is well.

A rupture disc is .625" in diameter by about 1/64" thick, sits in the top of the tank and when ruptured opens about 1/16" half way around the disc.

I do suggest however you stand a good ways away from testing any pressure vessel as too close and you could get hurt. Think about it guys if pressure would blow like a bomb, then when you took out a valve core from a tire or a nail the same would have too apply, and it doesn't!!! And some of those truck tires hold 85psi!!!

A tank would have to sit outside for several years before any strength would be lost.

T_Bone

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Nathan(GA)

12-22-2000 07:46:50




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 Re: Re: How do you test an old compressor tank? in reply to T_Bone... Bomb?????, 12-21-2000 10:15:22  
T_Bone, I am NOT an expert on this so I can't say. But, I would like to add that a guy near here was KILLED with a compressor. I don't know the details, but it blew up somehow and some body parts were cut off. So be careful.



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T_Bone

12-22-2000 17:31:37




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 Re: Re: Re: How do you test an old compressor tank? in reply to Nathan(GA), 12-22-2000 07:46:50  
Hi Nathan, I'm not stating that you don't have to respect pressure nor that you could not loose life with it but was reffering to how pressure releases. I've work for the past 30yrs on refrigeration equipment at normal presssures of 400psi continous, 500psi intermedient and have never seen a split or a chunk metal blow out. I have worked on 2000psi hydraulic systems and never seen a chunk blow-out. This is not to say that it can't happen but pressure is like a chain, it's stong to it's weakest link. Thats why I gave the reffence to a rupture disc as you can see the rupture disc is very thin comparred to the steel tank side wall. Under normal conditions pressure is safe and very abnormal conditions will hurt someone.

What the man was doing to cause such an explosion was not normal, a homemade under designed tank, using an old hot water heater tank, made a square tank? Who knows but whatever he did it wasn't normal or even close to normal and he paid dearly for that mistake.

T_Bone

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Larry Ks. Killer tanks...

12-24-2000 06:33:23




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 Re: Re: Re: Re: How do you test an old compressor tank? in reply to T_Bone, 12-22-2000 17:31:37  
I know of a guy that was killed by a tank to...In this case, they had welded a leak, and then turned it on--this guy was killed by shrapnel to. I would make one suggestion to all concerned--and I'm no expert either--normally I believe there is a pop off valve in the system to pop off when the pressure gets too high. I'd make damn sure there was a pop off valve, and never attempt to repair a leaking tank. As for the original question...I'd set the tank outside, turn the power on, and let it build up and see what happens. I personally woulnd't be overly concerned, maybe you could let it run for a little while, shut if off and listen for leaks, etc. and then go ahead and run it up to full pressure.

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Greg S

12-21-2000 08:36:30




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 Re: How do you test an old compressor tank? in reply to Zira, 12-20-2000 14:35:29  
How the tank looks on the outside is not a real indication of the structural integrity of the tank. As the air is compressed any moisture in the air will condense out inside the tank and eventually rust the tank from the inside. One of our neighbors when I was at home had a 20 gal tank split open on him, luckily it only opened up his calf to the bone from knee to ankle. Look inside the tank if at all possible. I can appreciate using older equipment (have done and still do) but sometimes it comes down to how much my safety is worth.

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JerryB

12-20-2000 17:10:55




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 Re: How do you test an old compressor tank? in reply to Zira, 12-20-2000 14:35:29  
ASME code for unfired pressure vessels (a fancy way of describing your air tank) require that the tank be tested at 1.5 times the maximum pressure. This means 180psi for a 120psi pressure tank. Note that the maximum pressure means what the safety valve will relieve at, not the compressor output or working pressure.

You can fairly safely test a tank by first removing all the safety valves or other relief devices and installing a pressure gauge that is known to be accurate. Fill the tank with water, working ALL the air bubbles out. This is critical. Now pressurize it with air. You must NOT allow any significant amount of air in the tank. Take the pressure to 1.5 times the safety valve rating. It is also important to either test or replace the safety valve(s).

A much better way is to call the nearest compressor repair shop & have them do the above. They will have a low volume, high pressure water pump made for the purpose. I can absolutely guarantee that only your wallet will be injured by doing this, and it is usually pretty cheap (last one I had done was under $50).

Regards, JerryB

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Bart

12-20-2000 16:58:24




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 Re: How do you test an old compressor tank? in reply to Zira, 12-20-2000 14:35:29  
I read an article on this. The guy filled the tank with water. He put a grease zerk on the tank and used a grease gun to add water to desired preasure. He went above 200 lbs to be on the safe side.



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Bus Driver

12-21-2000 16:54:05




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 Re: Re: How do you test an old compressor tank? in reply to Bart, 12-20-2000 16:58:24  
The method Bart uses works well and costs essentially only your own labor. If the tank should rupture filled COMPLETELY with water, the stored kinetic energy is extremely small and only about a cup full of water would come out under pressure. With air, the tank would take out a side of your shop if it ruptured under pressure. Some compressor shops use the grease gun method too. My suggestion is do it your self with the grease gun or take it to a pro. Turn the fill fitting to the top and when it is full of water, then screw in the grease fitting. Caution, don't try for more than 2X the working pressure for a test. I kept pumping and the test fitting broke at 415 PSI. You might destroy your tank needlessly.

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Nathan(GA)

12-22-2000 07:48:47




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 Re: Re: Re: How do you test an old compressor tank? in reply to Bus Driver, 12-21-2000 16:54:05  
Could you explain exactly how to do this with the grease gun? Thanks!



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Bus Driver

12-22-2000 10:54:28




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 Re: Re: Re: Re: How do you test an old compressor tank? in reply to Nathan(GA), 12-22-2000 07:48:47  
In response to the question of Nathan, the test fitting setup would include a trusted pressure gauge of enough range to cover the contemplated test pressure. Perhaps a tee fastened to the tank with a nipple. I suggest 1/2" size. Use a bushing to fit the 1/2" tee and the grease fitting. Once the grease fitting is tightened in place, put the gun on it and start pumping while watching the gauge. Probably will take about half a tube of grease. I never worry about getting the grease out of the tank.
Since my last posting, I recalled when I was in the volunteer fire dept (drove the truck some), one of our trucks, a 1951 Ford, had a "booster pump". Our normal pressure was 100 PSI on a 2 1/2" line. This truck also had two 3/4" lines that could be pumped up to 700 PSI. I recall once we tested a tank with this pump. This amounts to the same procedure some of the other posts mentioned. Test your tank no more than 2X the working pressure. The grease gun might take it to 6000 PSI or more. Something would break. No need to destroy it.

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Nathan

12-22-2000 13:15:13




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 Re: Re: Re: Re: Re: How do you test an old compressor tank? in reply to Bus Driver, 12-22-2000 10:54:28  
Thanks Bus Driver!



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80 Grit

12-20-2000 16:31:51




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 Re: How do you test an old compressor tank? in reply to Zira, 12-20-2000 14:35:29  
Tanks are tested under a hydro test. They are filled with water and a small volume higher pressure pump is used to pump water into the tank. If it ruptures, the energy in the water is dissipated immediately with the leak as there is no stored energy from compression. Usually the burst pressure for the test is as much as 3.5 times the working pressure for safety reasons.



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Frank

12-20-2000 15:03:38




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 Re: How do you test an old compressor tank? in reply to Zira, 12-20-2000 14:35:29  
Trust me. You don't want to be anywhere near if it's going to blow up. I'm sure there is a way to test them but that's not it. If there's any doubt about the tank, I wouldn't use it. A 30 gallon tank is a mighty big bomb.



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Fred OH

12-21-2000 04:31:23




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 Re: Re: How do you test an old compressor tank? in reply to Frank, 12-20-2000 15:03:38  
I bought an older used compressor once and a fellow that inspected boilers and pressure vessels for a major insurance company was at the shop. He was concerned about the condition of the tank. (I call these kind of people friends). He had me take those big 2" pipe plugs out of the side of it and got out his flashlight and looked over the bottom of the tank real good. He told me that it looked real good inside and showed me where someone had marked on the inside of it with soapstone during manufacture. It looked like it was done yesterday and the tank date of mfg. was 1956. So, with this in mind, I would advise to look inside at the bottom of the tank with a flashlight. If it has major pitting or has any dents in the tank, it would be suspect for replacement. If it passes a visual inspection, I wouldn't be afraid of it. I'd cycle it through about three times from a distance and give it a clean bill of health. L8R----Fred OH

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jimmyzz

12-22-2000 21:14:01




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 Re: Re: Re: How do you test an old compressor tank? in reply to Fred OH, 12-21-2000 04:31:23  
We used to have to have all our tanks recertified at i think was 5 year intervals.Required by cal-osha and msha. They tested with a sonic device that they ran around tank (mostly bottom) that measured thickness. By the way all tank failures I have ever seen were at the welds where legs or mounts are attached.



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Frank

12-23-2000 09:33:01




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 Re: Re: Re: Re: How do you test an old compressor tank? in reply to jimmyzz, 12-22-2000 21:14:01  
About 20 years ago Sanborn had a recall on some of their portable compressors. The tanks would not drain properly and the bottom of the tank would rust. I worked at a place that sold some of the models that were recalled. Sanborn sent out new tanks with a petcock on them, to replace the recalled tanks. We would take the motors and pumps off the old unit and put it on the new tanks. One customer brought in a compressor with the tank turned wrong side out. The bottom of the tank had split from end to end and the sides of the tank were clear up around the motor and pump. This had happened sometime during the night. He found it like this when he walked in his shop one morning.
He was lucky no one was around it when it blew.

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