Air tank corrosion, how thin can it go?

[3rdgendslmech]

I work in a corrosive environment ( deicing salt) and our operators arent the best at draining air tanks on trucks and equipment. Usually our tanks rot out from the outside if they cant be gotten to to get hosed off. Then there's the ones that don't get drained like they should.....Both instances result from anywhere from a pinhole air leak to cracks. Mind you these tanks are maybe 3 to 5 gallon tanks, so nowhere near your volume.

 

[workerbee]

Wow, thanks for all the replies. I never get email notifications on responses to my threads and just now happened to check back.
It's interesting the wide range of responses to the question. I'm baffled why some think a hydrostatic test can't be done by other than "professionals". Unless there's some Vodo involved I'm not aware of.

Next questions:
Who makes the best Pizza?
What car is better Chevy or Ford?

Many of the tests I have done would require you to evacuate your neighbors from their house unless they are a couple of hundred ft away. For an air tank at 300psi, I would make sure to use water and get all of the air out. Pressure it up from a safe distance (another room or behind something sturdy like a truck) and make sure to not overpressure it. Water is relatively incompressible and it will build pressure very fast. If there is no air in the system you could probably do it with a hand pump. A pressure washer would do it, but the pressure builds fast. Then you just monitor for 8 hours and write down temp and pressure every 15 minutes. I usually order a pizza for the guys doing the test especially if it is going to be overnight so we don't have to shut down the job to keep the testing area clear in order to limit the number of deaths and injuries if it goes bad.

 

[u2slow]

My 20 gal speedaire developed a slow leak in the weld next to the drain about 10 years ago. I don't mind it... Its very slow, and self-draining.

I'm trying an experiment with another 20gal horizontal pinholed tank... bit more than a pinhole though. Drilled it out to 3/8". Welded a large washer to a bolt; gooped it up, and fished it inside and secured by a nut from the outside. It seals. For safety, this tank is mounted up high on the shop wall, with the plugged side (bottom) facing the wall. I don't plan on more than 135psi.

I'm not going to say I recommend this, but I'm giving it a shot. See what happens.

 

[dkmc]

I should point out that I did the hydro test. I am not asking how to do the hydro test.

Many of the tests I have done would require you to evacuate your neighbors from their house unless they are a couple of hundred ft away. For an air tank at 300psi, I would make sure to use water and get all of the air out. Pressure it up from a safe distance (another room or behind something sturdy like a truck) and make sure to not overpressure it. Water is relatively incompressible and it will build pressure very fast. If there is no air in the system you could probably do it with a hand pump. A pressure washer would do it, but the pressure builds fast. Then you just monitor for 8 hours and write down temp and pressure every 15 minutes. I usually order a pizza for the guys doing the test especially if it is going to be overnight so we don't have to shut down the job to keep the testing area clear in order to limit the number of deaths and injuries if it goes bad.

 

[dkmc]

You tested it at the correct pressure: 1.5 times design pressure (Section VIII of the Boiler & Pressure Vessel code states minimum 1.3 X MAWP). If you have the dimension of the the tank, and the thickness readings, PM me & I can run the Fitness For Service Calculations.

As for the hammer test, that was commonly used before the ultrasonic meters became small enough to take in the field. A blunt pointed tip (think welding chipping hammer) was used. Typically used on refinery piping back when I started.

Mooky
NBIC, API 570 Inspector
AWS CWI
Retired

Hello Mooky, I sent you a PM with the tank specs a couple weeks ago. Please check your inbox?

 

[05snopro440]

The only definitive way to know for sure what it's rated for is to have it inspected and rated by someone qualified, not to guess based on your thickness measurements. Generally, since you've lost 30% of thickness you may be told to just replace it.

 

[dkmc]

The only definitive way to know for sure what it's rated for is to have it inspected and rated by someone qualified, not to guess based on your thickness measurements. Generally, since you've lost 30% of thickness you may be told to just replace it.

Sure or just buy an new compressor and/or tank for $5k and be done with it. And not bother with asking questions and learning about procedures because it's a waste of time as well. But you do what you want, and I will too. I'm not putting the tank in service based on any guesses that's a given if you've misinterpreted it that way.

 

[05snopro440]

Sure or just buy an new compressor and/or tank for $5k and be done with it. And not bother with asking questions and learning about procedures because it's a waste of time as well. But you do what you want, and I will too. I'm not putting the tank in service based on any guesses that's a given if you've misinterpreted it that way.

You're pretty defensive for someone who said he was asking for advice.

I didn't say you shouldn't ask questions or for advice. I said that the only definitive way to determine an accurate pressure rating was to have someone qualified look at it. As an engineer who deals with corrosion and many other aspects of metals and design, no, none of us can say that 125 psi is its new rating is reasonable as we don't know. We don't know if there are cracks in the corroded area, making it susceptible to fracture in the near future when those cracks progress. Sure, it might just give you a pinhole, but it may not. 150 gallons of air at 100+ psi is a lot of air to escape when something goes wrong. Are you comfortable with that gamble from a safety perspective?

Using a thickness tester is not giving you the whole story. You're assuming it lost thickness smoothly, which it most certainly hasn't. The inside is likely pitted which will derate the pressure rating significantly and corrosion pits are great places for cracks to initiate as I mentioned.

You're free to do what you like, sure. I'm giving an educated opinion from experience, as I investigate failed equipment daily.

 

[dkmc]

The testing I'm doing is in conjunction with using the tank at reduced pressure. I've seen tanks put into service that I wouldn't pressurize to 5 psi and the operator has no fear and no clue. I'm taking a cautious approach and haven't finished with the investigation or made a decision on the tanks usability. Not defensive, just exploring used equipment options instead of new.

 

[FredWanaker]

on a hydro test sometimes the tank is cleaned of rust with an abrasive in it by tumbling it, since rust provides its own oxygen to continue rusting where it started. It is filled with water that has no air in it and placed in a large sealed safety tank. It is then pressurized to a specific pressure and the displacement from the tank swelling is measured. If it swells too much or leaks then it fails. If it doesn't leak or swell too much it is passed and a new date stamp put on it. There are also other type tests that can be done looking for magnetic and electric anomalies on the tank. The cost varies but it used to be $50 - $90. I should probably get mine done.

 

[dkmc]

There are also other type tests that can be done looking for magnetic and electric anomalies on the tank. The cost varies but it used to be $50 - $90. I should probably get mine done.

If that price is accurate for a 150 gallon tank, I'd gladly pay it. I wonder if there are such test facilities anywhere in my region.

 

[FredWanaker]

If that price is accurate for a 150 gallon tank, I'd gladly pay it. I wonder if there are such test facilities anywhere in my region.

I'd get the dimensions and make a couple calls. The PITA is taking everything off and taking it to them. It is done on their site. The reason water is used is that if the tank fails it doesn't become a bomb - water can't be compressed so if the water blows out there is a little **** instead of a big one. I did a quick search. See if any are near you. https://www.thomasnet.com/upstate-new-york/hydrostatic-testing-services-96152996-1.html

 

[dkmc]

I'd get the dimensions and make a couple calls. The PITA is taking everything off and taking it to them. It is done on their site. The reason water is used is that if the tank fails it doesn't become a bomb - water can't be compressed so if the water blows out there is a little **** instead of a big one. I did a quick search. See if any are near you. https://www.thomasnet.com/upstate-new-york/hydrostatic-testing-services-96152996-1.html

It's a bare tank right now so no problem with that. I'm familiar why water is used, I used it as well. The closest facility on the list is 200 miles and 3 hours away.

 

[FredWanaker]

It's a bare tank right now so no problem with that. I'm familiar why water is used, I used it as well. The closest facility on the list is 200 miles and 3 hours away.

might ask the local fire dept who does their air tanks. They may know someone closer.

 

[dkmc]

Well here's an interesting observation. Two tags from tanks at one of the box stores. Blue one is a Quincy, black one is some lesser known brand, I didn't pay attention to the name. I think both tanks are 80 gallon, both 200psi rated. So the blue one is .135 Head thickness and .135 Shell thickness. Black one is: Head .116 and Shell .096! Quite a bit thinner than the current thickness readings I got on my used and somewhat rusty tank which was orig. .149 head, and the bottom showed readings as thin as .124. For sure that black tank leaves no room for corrosion issues. I'm a bit more confident using mine at 115psi max at this point.

 

[andyvh1959]

I bought my 60 gal vertical 8hp Sanborn air compressor brand new from Menards back in 1998 I think. Just realized this week its got a pin hole leak on the bottom dome, bit off center. It pumps up to 100 psi no sweat, and then the limit switch cuts it off. I'll be moving the air compressor from the attached garage to my shop garage soon, so now I know I have another project to repair the base of the tank.

Since the inside of the tank is raw material anyway, meaning no anti-rust coating, is it reasonable for a home-shop application to have a qualified welder (not myself, I'm a better grinder than a welder) cut out a section on the bottom of the tank and weld in a thicker material patch? TIG weld instead of MIG?

I await the onslaught of replies........

 

[dkmc]

Since the inside of the tank is raw material anyway, meaning no anti-rust coating, is it reasonable for a home-shop application to have a qualified welder (not myself, I'm a better grinder than a welder) cut out a section on the bottom of the tank and weld in a thicker material patch? TIG weld instead of MIG?

I await the onslaught of replies........

Absolutely not. It's time to replace the tank or the entire unit.

 

[58Yeoman]

I bought my Sanborn 60 gallon a/c at Farm and Fleet around '74. It lasted until just a few years ago, when it developed pinholes in the bottom. I went to Menard's and bought another Sanborn 60 gallon a/c for less than $400 and sold the motor and pump off the old one. I am much more vigilant about draining the water now.

 

[PoorUB]

Since the inside of the tank is raw material anyway, meaning no anti-rust coating, is it reasonable for a home-shop application to have a qualified welder (not myself, I'm a better grinder than a welder) cut out a section on the bottom of the tank and weld in a thicker material patch? TIG weld instead of MIG?

I await the onslaught of replies........

Use the pin hole as an indicator to replace the tank or the whole unit!

I seriously doubt you will find a welder that will repair it.

 

[Citation]

andyvh1959, scrap the tank. The compressor has politely told you that the bottom of the tank has rusted to the point where it can't hold air. Don't second guess it. If you fix it the tank might not be as polite next time. If the pump and motor are good move them to another tank or sell them.

 

[andyvh1959]

Got it. Thanks.

 

[The Cobbler]

You have your answer & you acknowledged , I'm glad you heeded the advice !
It would cost more to have a properly ticketed welder repair a pressure tank than to but a new one .
time to repurpose the old tank , maybe a smoker?

 

[pcmeiners]

*I have had FANTASTIC pizza outside of New York, so it isn't the water or some special loyalty to the area that I espouse, but it sure can be hard to find good pizza elsewhere. OTOH, so long as you stay out of a chain store, most pizza here will be at least acceptable, whereas outside of New York, most pizza is, well, ****.

True words of wisdom.

 

[rancherbill]

I have a 150 gallon vertical air receiver,

That's huge, I am having trouble imagining a tank that is bigger than 3 oil drums. hahaha

Do you have an automatic drain on the unit? If so, and you have tested it at 300 ponds then I would not have a problem using it.

 

[cvairwerks]

That's huge, I am having trouble imagining a tank that is bigger than 3 oil drums. hahaha

You would have freaked if you saw our receivers at work a number of years back. There were 8 or 10 vertical tanks about the size of a chemical rail car in the air system room. Besides all the screw compressors that were replacing the piston units, it was crazy in there. We still had two huge single piston CP compressors out where I work, until just a few years ago. Our main air line was an 18" trunk, about 4 miles long.