Hydro testing an air tank?

[StaggeringGoat]

I recently got a free 25 gallon crapsman compressor. The petcock on the bottom of the tank was jambed closed, so I removed it. I don't think it has ever been drained. The stuff that came out was NASTY!

Now I'm afraid to use the tank. Would it be a bad idea to try and hydro test it myself? I have another compressor that goes up to 300 PSI. I was thinking of filling the tank with water and then pressurizing it with the compressor. How much pressure should I put in? The tag on the tank says it's rated for 150 PSI.

 

[930dreamer]

For a certification, a shop would have to do it. I think the tank needs to be in water also?

 

[oldtractors]

Do not use air! It is compressable and will explode. Pressurize using water with a water pump. If the tank ruptures, it will only leak water. A small hand pump will do it. Some people will use a pressure washer and a relief valve, but if the relief valve fails, your tank will be turned to scrap iron in an instant.

 

[porschedude996TT]

Hello, I am an Aerospace Design Engineer and we hydrostat tubing and tanks quite often.

One and 1/2 the rated capacity is the normal amount of pressure to Hydrostat a tank (225 +/-10 psi). Fill with as much water as possible and hold the pressure for 5 minutes. If it ruptures the potential energy is only the small amount of air that is trapped. Worst case is you get wet.

The danger is when someone does a Pneumostat improperly. We also do pheumostats on certain things, but that is done in a vault made to contain an explosive failure.

The tank does not need to be immersed in water; there is very little energy in the tank since liquids are not compressible. The only energy storage is that small void of air space that you will try eliminate when you fill with water.

 

[Alchymist]

Fill the tank as completely as you can with H2O. Use a regulator on a nitrogen or helium cylinder, or even an argon cylinder. Run the regulator up to 50% over what your max operating pressure will be. Close the cylinder valve and let it set. After 10 minutes or so, bleed off the pressure, dump the water. With the tank full of water, even if it splits a seam or pops a rust hole, no explosion will occur, as the water won't compress. If no bulges or leaks appear, you are good to go.

 

[akdiesel]

You just got some great information to stay safe and get the correct job done.
Please follow their guides.

 

[930dreamer]

Make a video for us.

 

[rlitman]

Real hydrostatic testing requires volumetric measurement of the tank's plastic deformation during the test. Doing what was suggested above may confirm that the tank is in good shape, or may actually cause permanent damage that can bite you later. Only if you know whether or not the volume of the tank changed (and have calculations to back up what the acceptable limits are) is this a good idea.

 

[StaggeringGoat]

Use a regulator on a nitrogen or helium cylinder, or even an argon cylinder.

Any particular reason for those gasses instead of air? Like I said I have a compressor that goes up to over 300 PSI that I wanted to use. (converted A/C compressor)

Make a video for us.

I will...I definately want to catch that on tape if it pops. I'll probably do it in the field next to the shop with a long air hose.

Real hydrostatic testing requires volumetric measurement of the tank's plastic deformation during the test. Doing what was suggested above may confirm that the tank is in good shape, or may actually cause permanent damage that can bite you later. Only if you know whether or not the volume of the tank changed (and have calculations to back up what the acceptable limits are) is this a good idea.

Well, either I test it or I throw it away. If it was to ever "blow up", they usually just let the air out through a pin hole in the bottom, don't they? I'll probably put it up above my office where nobody ever goes just in case. It's got what looks like a 2" plug on the top of the tank, if I can get that out hopefully I can stick a flashlight in there and inspect the tank.

 

[akdiesel]

Any particular reason for those gasses instead of air? Like I said I have a compressor that goes up to over 300 PSI that I wanted to use. (converted A/C compressor)


I will...I definately want to catch that on tape if it pops. I'll probably do it in the field next to the shop with a long air hose.


Well, either I test it or I throw it away. If it was to ever "blow up", they usually just let the air out through a pin hole in the bottom, don't they? I'll probably put it up above my office where nobody ever goes just in case. It's got what looks like a 2" plug on the top of the tank, if I can get that out hopefully I can stick a flashlight in there and inspect the tank.

Chances are the corrosion would be at the bottom, but I have seen first hand what can happen when a gas product lets go under pressure. It is unpredictable, unless you have the means to UT or Xray the tank.

 

[Alchymist]

Any particular reason for those gasses instead of air? Like I said I have a compressor that goes up to over 300 PSI that I wanted to use. (converted A/C compressor)
Air is OK - just that most people would be more apt to have a gas cylinder and not a 300 psi capable compressor.

I will...I definately want to catch that on tape if it pops. I'll probably do it in the field next to the shop with a long air hose.


Well, either I test it or I throw it away. If it was to ever "blow up", they usually just let the air out through a pin hole in the bottom, don't they? I'll probably put it up above my office where nobody ever goes just in case. It's got what looks like a 2" plug on the top of the tank, if I can get that out hopefully I can stick a flashlight in there and inspect the tank.

Not necessarily - sometimes they go bang in a big way - people have been badly injured or killed by exploding air tanks.

 

[MoonRise]

Well, either I test it or I throw it away. If it was to ever "blow up", they usually just let the air out through a pin hole in the bottom, don't they? I'll probably put it up above my office where nobody ever goes just in case. It's got what looks like a 2" plug on the top of the tank, if I can get that out hopefully I can stick a flashlight in there and inspect the tank.

No, a catastrophic failure can occur with a pressure vessel like an air compressor tank.

They are not 'supposed' to fail catastrophically, but they can.

Want a thread with pictures and all, of an air compressor tank that 'burst'? No death in that case, but major injuries (broken femur and other broken bones, etc) and destruction.

http://weldingweb.com/showthread.php?t=48232

And yes, a real hydrostatic test of a high-pressure vessel involves not only determining if the vessel 'survives' the pressure test, but also about how much it expands during the pressure test and if it goes back to its original unpressurized volume. If it does not go back to its original unpressurized volume, even if it did not 'fail' while pressurized, means that the tank material has "yielded" and become permanently deformed (stretched out) from the pressure. Which means the tank has "failed". Those tests are done in a water bath, not only to contain/minimize tank shrapnel but also to measure the tank volume before, during, and after the test.

But most lower-pressure air compressor tanks are just tested to 1.5x the tank nameplate pressure.

How much is your life and health worth? Seriously, how much?

If there is any doubt about an old(er) air compressor tank, just scrap it (or turn it into a BBQ or smoker or whatever) and buy a brand new ASME-certified tank for $300-$600 or so.

Full-retail at Grainger, 30 gallon vertical 200-psi rated ASME-cetified tank, $629.50

http://www.grainger.com/Grainger/SPEEDAIRE-Air-Tank-1TZZ6?Pid=search

Full retail, 26 gallon 175 psi horizontal ASME-cetified tank, $530.00

http://www.grainger.com/Grainger/SPEEDAIRE-Air-Tank-1TZZ4?Pid=search

 

[BD1]

25 gallons ain't sh#t. Scrap it, not worth injury. Check this out from another site.
http://weldingweb.com/showthread.php?t=48232&highlight=air+compressor

 

[Professur]

Hydrotesting a tank costs peanuts .. get it done by a pro, or replace it outright. I'm all for doing things myself .. but something like this isn't one of them.

 

[DekeT]

25 gallons ain't sh#t. Scrap it, not worth injury. Check this out from another site.
http://weldingweb.com/showthread.php?t=48232&highlight=air+compressor

I read the link and I inferred that the most informed and experienced posters in that thread would not agree to scrap the tank without doing a hydro test. The people with actual experience in pressurized testing were clearly critical of the misconceptions perpetrated by the "internet" alarmists.

 

[wedge40]

25 gallons ain't sh#t. Scrap it, not worth injury. Check this out from another site.
http://weldingweb.com/showthread.php?t=48232&highlight=air+compressor

Holy **** on a cracker.

.

 

[StaggeringGoat]

Full-retail at Grainger, 30 gallon vertical 200-psi rated ASME-cetified tank, $629.50

http://www.grainger.com/Grainger/SPEEDAIRE-Air-Tank-1TZZ6?Pid=search

Full retail, 26 gallon 175 psi horizontal ASME-cetified tank, $530.00

http://www.grainger.com/Grainger/SPEEDAIRE-Air-Tank-1TZZ4?Pid=search

You gotta be kidding...I can get a tank with a compressor mounted on top for half that at Home Depot...

 

[Kevin C]

http://www.portlandcompressor.com/Store/p-140-ingersoll-rand-3hp-60-gallon-vertical-1-stage-compressor-103cfm-90psi.aspx

I Found that you can buy an Ingersoll Rand brand 60 gallon tank for about $599. They are in stock in Portland ( Not sure where in Oregon your located). The down side is it has some extra stuff bolted to it ( 3 HP motor and a pump).

Seriously, I have a 1980 Craftsman / Devilbiss compressor that I have owned since new. It still works great. At some point for my own peace of mind I need to get the tank checked.

So far my searches seem to indicate that low pressure compressor tanks are pressure (hydro)tested to 1.5 x the working pressure.

Most larger low pressure testing ( 150 PSI air compressors) seems to be just a pressure test, not a pressure displacement test. The pressure displacment test seems to be reserved for higher pressure containers like fire extinguishers. Still looking for good info, might need to make a few calls.

 

[PT Doc]

Cut it up and turn it into a forge.

 

[fflintstone]

Fill it with water, put a tee on it. A pressure gauge in one and a zerk fitting in another. Pump it up to 1.5 x your max pressure with your grease gun.
Do not use compressed air, nitrogen or any other gas!

 

[porschedude996TT]

Fill it with water, put a tee on it. A pressure gauge in one and a zerk fitting in another. Pump it up to 1.5 x your max pressure with your grease gun.
Do not use compressed air, nitrogen or any other gas!

Why not, what do you think could happen. Using a zerk fitting and a grease gun could take a while.

 

[Dale B]

If the tank is full to the max with water , you will only need about 3-6 pumps to compress the little air bubble in the fitting . It a good test , and perfectly safe .

 

[DekeT]

I would think a way to de-pressurize the tank easily such as a ball valve is a good idea too. You do not want to have to unscrew anything to reduce pressure.

 

[Jarhead0408]

.......just scrap it (or turn it into a BBQ or smoker or whatever.....


Thanks for the idea man! I've got an old Keystone 60 gallon Air compressor.
The pump and motor are in great shape, But I stuck my scope down in there and saw quarter size chunks of rust splitting off from the bottom. So the tank is without a doubt bad.

I couldn't stand the idea of scrapping it though. My wife wanted to cut the tank in half and use it for a flower bed/tub. But now that I saw your post I think a BBQ cooker mounted on a small trailer frame is the way to go! Thanks!

 

[The Maxx]

I used to test water tanks with air for leaks in a factory. When a tank with 120 psi of air failed it was a VIOLENT situation. Even in a thick steel enclosure it sometimes blew out the lights overhead from the shock. Had your ears ringing for hours even though you had ear plugs in. The whole plant heard it, sounded like a bomb going off. It would peel the tank apart. You would swear to look at it that explosives had gone off inside it. ( Just no burn marks ) Lucky for us welders very very few failed.

So NEVER EVER TEST WITH AIR.

On the flip side, once a month we would take one model of every tank we made that had already passed production tests and pressurize it with water until failure. At 300 plus psi when the tank failed it leaked a bit of water and that was it. This was after the tank was so deformed it was almost completely round and the metal was stretched.

This time of year we used to take those rounded tanks and cut a face in them with a plasma cutter, paint them orange and put a light inside. Made a hell of a pumpkin!

 

[DekeT]

Why not, what do you think could happen. Using a zerk fitting and a grease gun could take a while.

Are you asking if after filling the tank completely with water using a small amount of gas to pressurize it to 150% is ok?

 

[Alchymist]

Do not use compressed air, nitrogen or any other gas!

And why would you be advocating that?

 

[NUTTSGT]

When an abundant amount of nasty rusty water comes out the bottom of a compressor of unknown heritage, I'd throw it in the scrap pile. That's exactly what I did with the compressor that came with my garage.

 

[danski0224]

Well, either I test it or I throw it away. If it was to ever "blow up", they usually just let the air out through a pin hole in the bottom, don't they?

Then you just weld it up....

 

[f575gtc]

Sorry for the thread revival.

Will a normal air gauge work or do you need something setup for a fluid?

Also when you test the tanks, if the tank doesn't fail past 200PSI is it safe to repeatedly pressurize the tank to 175psi after wards?

 

[Alchymist]

Sorry for the thread revival.

Will a normal air gauge work or do you need something setup for a fluid?

Also when you test the tanks, if the tank doesn't fail past 200PSI is it safe to repeatedly pressurize the tank to 175psi after wards?

Air gauge works OK. Test pressure should b 150% of working pressure. In your case, about 260 PSI.

 

[f575gtc]

I just recently upgraded my single stage air compressor to a 2 stage and the tank I am running has a MAX W.P of 150psi stamped on it. I want to run the pump at 150-155psi cut off, so I want to hydro test the tank before I do this.

Found a nice video on youtube that showed me how to do a test with a grease gun so I will be testing my tank this week.

Thanks for your answers.

 

[vonhef]

You should not run the compressor over max w.p. of the tank. You will want a safety pressure relief valve set BELOW the tanks rated pressure.


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[f575gtc]

You should not run the compressor over max w.p. of the tank. You will want a safety pressure relief valve set BELOW the tanks rated pressure.


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Aren't these air tanks tested to a pressure much higher than the stated working pressure?

The tank is in excellent shape with no rust, but I still want to hydro test it to be sure.