Old compressor tank - hydro or not?

86turbodsl · Oct 22, 2017

I have an old compressor tank i'm looking to put into use, it has the following specs:

120 gallon horizontal

Ends - 0.195 in
Shell - 0.158 in

Build date: 1968

Some company in Milwaukee, WI.

It's been sitting indoors not used for about 15 years, as long as i've owned it. Before that, it probably sat outside for a while, i bought it from a guy in Chicago as a complete compressor, and have scrapped out the pump for a quincy 325. I want to use this tank if possible.

Those of you who are familiar with compressor tanks, and thicknesses, can you give me any level of assessment on how required a hydro test would be for this tank, and/or how the thickness of the steel in this tank compares to other tanks?

I did get a small amount of rust out of the tank by standing on end with my engine hoist. Probably a quart? (guess)

Right now, i have a large garage door that does not open, and it won't be able to for some time yet. I can get the tank out through my 36" Man-door with some difficulty. If i do remove it, i probably will have to put it back indoors to complete the compressor build and use for a while before i am ready to put into it's final place.

so i will have some wrestling to do if i decide to hydro the tank.

What would you do?

Strouty · Oct 22, 2017

True hydro test is cost prohibitive, some people do a stress test with pressure washer or grease gun, but on an old tank it could actually do damage to the metal. If those numbers are for what the tank was originally, the shell seems way too thin to start with.

JerryB · Oct 22, 2017

First, as a mechanical engineer, you must be somewhat knowledgeable as to the dangers of a catistrophic pneumatic tank rupture.

And, you probably also know that the most common (and fortunately infrequent) failure mode of pressure vessels is not a rupture of the shell material, but rather a rupture at a weld seam. This type of failure can be exacerbated by corrosion of the welds over time.

Second, you are asking a question that only effects the safety of you, your family members and friends. If your tank ruptures, it will most likely only hurt one of the above, not someone on this board who says, "No Problem, just use it."

Hydro-stating a pressure vessel is really simple, and will provide you with both a safe environment and peace of mind.

Just my opinion, but one of my early jobs was designing and constructing fairly large scale high pressure and high temperature pneumatic vessels. Never had a failure that damaged anything or anyone, but we always took the safe way home!!!

86turbodsl · Oct 22, 2017

JerryB said:
First, as a mechanical engineer, you must be somewhat knowledgeable as to the dangers of a catistrophic pneumatic tank rupture.

And, you probably also know that the most common (and fortunately infrequent) failure mode of pressure vessels is not a rupture of the shell material, but rather a rupture at a weld seam. This type of failure can be exacerbated by corrosion of the welds over time.

Second, you are asking a question that only effects the safety of you, your family members and friends. If your tank ruptures, it will most likely only hurt one of the above, not someone on this board who says, "No Problem, just use it."

Hydro-stating a pressure vessel is really simple, and will provide you with both a safe environment and peace of mind.

Just my opinion, but one of my early jobs was designing and constructing fairly large scale high pressure and high temperature pneumatic vessels. Never had a failure that damaged anything or anyone, but we always took the safe way home!!!

Of course i understand the danger of a failure. I also know that most failures are pinhole leaks rather than pure ruptures.

As with anything in life, there's risk involved. I am fully capable of doing the hydro test here, just wanted to gage the knowledge base out there as to how likely a failure is, and how my tank thicknesses scale with others that people have worked with. I don't really WANT to take the tank through the man door and go hydro it, especially if the general consensus is that this tank is quite thick. If it's NOT though, and maybe is thin, i would probably do the work involved.

I'm not generally a worrisome person, but at the same time, i don't design tanks for a living, and have no data point as to where mine sits. Hope that gives you some frame for where i sit on this.

sberry · Oct 22, 2017

I have never seen it happen, heard of a couple from this forum. One from a member and one where the same pic circulated for a decade every time this comes up. I would like to see some statistics on this. We know 50K plus die in cars, thousands injured, 2 hit deer on motorcycles I actually know, one down the road died and another broad riding shotgun on a trike is gonna do 12 weeks in the hospital.
I think the US has an electrocution about every day, lots from smoking and fast food. Wonder where the air tank ranks in this?

6768rogues · Oct 22, 2017

My father had a vertical tank upstairs in his shop. It failed when the weld at the base gave out (except for an inch) and the base hinged open. It blew a hole in the floor where it sat, ripped a door and sink off the wall below, lifted and broke a roof truss and cracked the concrete block exterior wall. Moments before it blew my father stepped out from beneath it, but he had a few shrapnel bruises on his legs. It was so loud the guy across the road came out to see what exploded.
I will never take a chance with an old tank. 100 psi is a hundred pounds of force for every square inch of surface. There is a lot of total potential energy in a tank.

Strouty · Oct 22, 2017

According to what I am seeing, the minimum thickness allowed for a pressure vessel is 3/16" or 0.219

Stuart in MN · Oct 22, 2017

I have no idea what it cost to do a hydro test, but it won't hurt making a few calls to local shops to find out.

The problem with corrosion inside an air tank (and all old tanks are going to have some) is that it's awful hard to tell if it's still safe or not by just looking at the thing from the outside. Youtuber Tubalcain made a pretty good video some time ago where he does an autopsy on a small air compressor that sprung a leak - it's worth watching.

86turbodsl · Oct 22, 2017

Here's the data tag.

Stuart in MN said:
I have no idea what it cost to do a hydro test, but it won't hurt making a few calls to local shops to find out.

The problem with corrosion inside an air tank (and all old tanks are going to have some) is that it's awful hard to tell if it's still safe or not by just looking at the thing from the outside. Youtuber Tubalcain made a pretty good video some time ago where he does an autopsy on a small air compressor that sprung a leak - it's worth watching.

Here's the data tag.

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dkmc · Oct 22, 2017

86turbodsl said:
I did get a small amount of rust out of the tank by standing on end with my engine hoist. Probably a quart? (guess)

A whole quart of rust scale-powder seems like a lot, maybe not??

6768rogues said:
My father had a vertical tank upstairs in his shop. It failed when the weld at the base gave out (except for an inch) and the base hinged open. It blew a hole in the floor where it sat, ripped a door and sink off the wall below, lifted and broke a roof truss and cracked the concrete block exterior wall. Moments before it blew my father stepped out from beneath it, but he had a few shrapnel bruises on his legs. It was so loud the guy across the road came out to see what exploded.
I will never take a chance with an old tank. 100 psi is a hundred pounds of force for every square inch of surface. There is a lot of total potential energy in a tank.

NOW.........yer scare'in me....
:eyecrazy:

Do you happen to have any pics of the damage you could share on here?

86turbodsl · Oct 22, 2017

dkmc said:
A whole quart of rust scale-powder seems like a lot, maybe not??

NOW.........yer scare'in me....

Here's the best I can do. Outside in the dark.

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86turbodsl · Oct 22, 2017

86turbodsl said:
Here's the best I can do. Outside in the dark.

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Diameter is about 23 or 24in. Best I can tell.

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sberry · Oct 22, 2017

I about blew my head off a couple times when I was a kid working on **** I had no business doing. I try to watch it today, I got enough simple **** to do that I can fuk up. I messed up and ran a paint job the other day, did it in the dark and half assed instead f taking 20 mins to get set up.
I used old stuff didn't help, its a job I am an expert on,,, yha. I built a sandblaster when I was a kid lucky didn't bomb the first time I fired it, when I realized what I did I condemned it.
I was genuinely interested in reports, thanks for posting some details of an event. Cope that posts on this forum had a bud die from one, ruptured a small tank, the guy may have been working on it.

sberry · Oct 22, 2017

That's a pretty sturdy tank but its big. You mentioned moving it to hydro, could do it in place. If I was really doing hydro might even go so far as to rig up a pressure relief valve or possibly a pressure washer with an unloader, rig up a bypass valve and a gage. You could make up a receiver for grease too so it didn't make a mess in the tank.
If a guy has another source of air could hook a garden hose to the tank drain and pump the water off

Strouty · Oct 22, 2017

I had about a 5 gallon bucket of rust from my 200 gallon tank. After cleaning it out, I used an ultrasonic tester to measure the thickness. I only found one spot that was even close to being an issue, but I also found my tank was built to better standards than most tanks. I used it, after doing a lot of research it did not make me as nervous.

lakeroadster · Oct 22, 2017

86turbodsl said:
Diameter is about 23 or 24in. Best I can tell.

Wrap a tape around the outside of the tank and get a circumference... then divide by 3.14

dkmc · Oct 22, 2017

Strouty said:
I had about a 5 gallon bucket of rust from my 200 gallon tank. After cleaning it out, I used an ultrasonic tester to measure the thickness. I only found one spot that was even close to being an issue, but I also found my tank was built to better standards than most tanks. I used it, after doing a lot of research it did not make me as nervous.

How much thinner was that one spot compared to the new steel thickness?

It would be cool if old tanks could be xrayed for flaws and rust thinned areas.
Probably cost as much as a new tank tho.....

davejo · Oct 23, 2017

this thread has some good links in the posts. the national board website has some good leads but i could never access the actual official inspection and testing info. you have to be a member. i never found a minimum thickness chart for these small tanks but the larger diameter, the thicker they need to be. i never found an official testing facility within my general vicinity

https://www.garagejournal.com/forum/showthread.php?t=314828

the 80 gallon vertical tank under discussion was about 18-20 in diameter

shell .199 head .162

Strouty · Oct 23, 2017

What most people consider a “hydro test “ is wrong. After doing my research, the only true way to do it is to fill the tank with water, but also submerge the tank in water. When doing the test they also take into consideration the amount the tank expands. When you do it with a pressure washer or grease gun, you have no idea what is going on. So if you do that as a test, think of it as a Proof Test, by that, I mean look at what you will use for air, say you want 125 PSI, then tear it to 150 and make sure it holds the pressure. Don’t test it to 300 PSI or something like that. Make sure you have decent pressure relief valves, I have them on the, tank and in the first leg of my pipe.

Strouty · Oct 23, 2017

dkmc said:
How much thinner was that one spot compared to the new steel thickness?

It would be cool if old tanks could be xrayed for flaws and rust thinned areas.
Probably cost as much as a new tank tho.....

The manufacturer spec was 0.228 and the thinnest spot I found was 0.198. When I started looking at new tanks, most had a thickness less than that, I rolled with it. I have another tank that I am going to do an inspection on if it is better, I will use it and get rid of the other one. A brand new one with the setup for duplex pumps was just shy of $1,500. Once I get two good pumps and motors, I may buy a new tank, then I really know what I have.

86turbodsl · Oct 23, 2017

Strouty said:
The manufacturer spec was 0.228 and the thinnest spot I found was 0.198. When I started looking at new tanks, most had a thickness less than that, I rolled with it. I have another tank that I am going to do an inspection on if it is better, I will use it and get rid of the other one. A brand new one with the setup for duplex pumps was just shy of $1,500. Once I get two good pumps and motors, I may buy a new tank, then I really know what I have.

At least yours started out that thick. Looks like mine was a good bit thinner to start out. Probably the el-cheapo version of the tank from 1968.

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lakeroadster · Oct 23, 2017

The end user of a "U" stamped ASME Section VIII Div. 1 pressure vessel should never pressurize the vessel above its rated MAWP... never.

Manufacturer's and Repair organizations go through strict audits in order to be qualified to build, repair and alter pressure vessels. They have mandatory 3rd party inspection to ensure compliance. They are authorized, under certain rules and regulations, to test a vessel above it's rated capacity. This is typically done during the vessels hydrostatic test before the ASME "U" Stamp is applied, or during a vessel alteration.

An in-service hydrostatic test is performed by filling a vessel with water and pressurizing it to or below the vessels MAWP. You don't do the test under water. You are checking the vessel for leaks. I have seen vessels where pin hole leaks didn't become apparent for hours... as was evident by water on the outside of the vessel. Extreme care should be exercised to ensure air is not trapped in the vessel during this test. This can end in catastrophic results and is why untrained individuals performing these tests can be very dangerous.

Sometimes a manufacturer will perform a proof test. A proof test is when the vessel is pressurized until it fails. This is done under controlled conditions by professionals, according to written approved procedure. Proof tests are used when a design is beyond the scope of the ASME code... something where there are no calculations applicable to the new design.

86turbodsl said:
At least yours started out that thick. Looks like mine was a good bit thinner to start out. Probably the el-cheapo version of the tank from 1968.

The thickness stamped on the nameplate is the minimum required thickness.... not the thickness of the tank when it was new. Newer nameplates do not show this data.

86turbodsl · Oct 23, 2017

lakeroadster said:
The end user of a "U" stamped ASME Section VIII Div. 1 pressure vessel should never pressurize the vessel above its rated MAWP... never.

Manufacturer's and Repair organizations go through strict audits in order to be qualified to build, repair and alter pressure vessels. They have mandatory 3rd party inspection to ensure compliance. They are authorized, under certain rules and regulations, to test a vessel above it's rated capacity. This is typically done during the vessels hydrostatic test before the ASME "U" Stamp is applied, or during a vessel alteration.

An in-service hydrostatic test is performed by filling a vessel with water and pressurizing it to or below the vessels MAWP. You don't do the test under water. You are checking the vessel for leaks. I have seen vessels where pin hole leaks didn't become apparent for hours... as was evident by water on the outside of the vessel.

Sometimes a manufacturer will perform a proof test. A proof test is when the vessel is pressurized until it fails. This is done under controlled conditions by professionals, according to written approved procedure. Proof tests are used when a design is beyond the scope of the ASME code... something where there are no calculations applicable to the new design.

Lakeroadster,

Any comment on the stamped thicknesses of the tank in question to your experience with 200psi MAWP tanks?

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pancho400cid · Oct 23, 2017

Your tank is thin to be 120 Gal. It's got an ASME "U" stamp so that says it met the boiler and pressure vessel code rules and satisfied an inspector when it was made.

Per the interweb:

"The U Code Symbol on a vessel is used to confirm that the stamped item is in conformance to the latest edition of the Code and that the pressure vessel has been designed and manufactured in accordance with ASME."

I looked into hydro-testing tanks quite a bit for the same reasons you are. There are places that do hydro tests on all kinds of stuff as you might imagine.

What all the youtube grease-gun testers miss is checking for yield.

The "real" places submerge the tank in a larger tank and both fill it with water and submerge it in water. They pressurize the tank under test AND very accurately measure the displaced water in the outer tank. When the test tank gets pressurized, it swells. The testers make sure that it returns to the pre-test non-pressurized volume. If there is any displaced volume once the tank under test is de-pressurized, the assumption is the tank yielded and failed the test.

Strouty · Oct 23, 2017

pancho400cid said:
What all the youtube grease-gun testers miss is checking for yield.

The "real" places submerge the tank in a larger tank and both fill it with water and submerge it in water. They pressurize the tank under test AND very accurately measure the displaced water in the outer tank. When the test tank gets pressurized, it swells. The testers make sure that it returns to the pre-test non-pressurized volume. If there is any displaced volume once the tank under test is de-pressurized, the assumption is the tank yielded and failed the test.

Strouty · Oct 23, 2017

Proof testing is the only way to go, when you do the water, you may want to add some colorant to it, that way you can be certain that the water is coming from the inside and not sweating or something spilled. Another cool thing that I found was that using a hot water pressure washer to clean the tank it got hot enough that after draining all the water it dries the inside of the tank from the heat. I was stupid, I did my proof test 60 feet away with no water in the tank, but the only reason I did it was after using the ultrasonic tester to see how thick my tank was over a very large area. I know for a fact that the thin areas are going to become thinner rapidly, that is why I still want to replace my tank in the long term.

The Tool Tyrant · Oct 23, 2017

Take a look here...https://hansontank.com/airreceivers.html

Click on any particular receiver or storage tank and you will see the related drawing with specs.

You'll see that shell and head thickness changes for varying diameters and applications.
You can see a large difference between a 'storage' tank versus a platform mount receiver, which makes sense as the induced stresses caused by the vibration of the pump and motor.

My 120 gal. receiver with platform has a .227 shell & .186 heads, whereas my 240 gal. storage tank has .166 heads & shell.

Strouty · Oct 23, 2017

I have considered removing the pumps and putting the air tank elsewhere. Could be a good secondary safety. Will have to think about that.

lakeroadster · Oct 23, 2017

86turbodsl said:
Lakeroadster,
Any comment on the stamped thicknesses of the tank in question to your experience with 200psi MAWP tanks?

Depends on the materials of construction and the weld joint design.

Assuming a 24" o.d. vessel:

If the shell has an allowable stress of 17,500 psi (SA-516-70)
If the longitudinal seam efficiency is 0.70
Then the min. shell thickness is 0.194"

If the 2:1 elliptical heads have an allowable stress of 15,000 psi (SA-516-60)
If the circumferential seam efficiency is 0.65
Then the min. head thickness is 0.152"

Again, this is the minimum thicknesses and is useless since it is based on the above assumptions. But it matches the stamped nameplate pretty darn close.

The nameplate stated values are good... no reason to question them.

86turbodsl · Oct 23, 2017

lakeroadster said:
Depends on the materials of construction and the weld joint design.

Assuming a 24" o.d. vessel:

If the shell has an allowable stress of 17,500 psi (SA-516-70)
If the longitudinal seam efficiency is 0.70
Then the min. shell thickness is 0.194"

If the 2:1 elliptical heads have an allowable stress of 15,000 psi (SA-516-60)
If the circumferential seam efficiency is 0.65
Then the min. head thickness is 0.152"

Again, this is the minimum thicknesses and is useless since it is based on the above assumptions. But it matches the stamped nameplate pretty darn close.

The nameplate stated values are good... no reason to question them.

I'm sure i'm out in left field here, but i spent some time this morning data mining used tanks on epay many of which are listed with data plates that can be read. i graphed the thicknesses of all the 200 psi mawp tanks WRT to shell and head thickness. I also graphed with respect to time. Oldest tank was 1952. Newest was 2017.

My tank was more towards the thicker end of the distribution. I also added trendlines for the graphed data and found a downward slope, shells were 0.2" at the older end, and 0.17 at the newer end, and heads were 0.18 at the old end, and 0.14 at the newer end. Dataset based on 10 samples, both 120 gallon and 80 gallon, horizontal and vertical.

That was all the used tank data i was able to gather.

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lakeroadster · Oct 23, 2017

Capacity of the tank has little to do with the wall thickness, on these smaller air receivers.

On a large liquid storage tank... sure, there can be an impact on shell thickness. But on an air receiver, usually not the case.

Have you checked any local rental places to see if they have ultrasonic thickness testers?

Cutting through all the "scroogled by googling" here on this thread... that's really what you need to verify wall thickness of your tank. And a bore scope would be useful too if the tank doesn't have inspection ports.

86turbodsl · Oct 23, 2017

Well, where would one rent an ultrasonic thickness checker? Every time i've tried to rent something esoteric (read beyond the local rent-all) the prices are starting at $500+ a day. IR camera for mapping my in-floor heat tubing being a prime example.

For the $500 it would cost, i would just apply to a new tank.

I can do the hydro "check" for pretty cheap. If it passes, i'll probably work on scouring the internal surfaces and coating with paint to slow down further corrosion and put into service. I'm not made of money, and the wife disapproves of large expenditures that she sees no benefit of.

Strouty · Oct 23, 2017

I vote not on coating the inside. If you do that and miss a spot, that spot will get attacked exponentially more due to the coating every where else.

86turbodsl · Oct 23, 2017

Strouty said:
I vote not on coating the inside. If you do that and miss a spot, that spot will get attacked exponentially more due to the coating every where else.

I ran across a video on youtube of a company reconditioning tanks the process was pretty thorough. Since it's also probably just going to be a reciever and not mount the hardware once i get to final location, it can also be reoriented to put new metal down in the puddle too. They painted the tank innards.

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Strouty · Oct 23, 2017

I don't think anything will stop the rust anyways. Just remember not to tell anyone if you decide to weld to the tank, that is pretty close to using PVC for the air lines.

86turbodsl · Oct 23, 2017

Strouty said:
I don't think anything will stop the rust anyways. Just remember not to tell anyone if you decide to weld to the tank, that is pretty close to using PVC for the air lines.

I wouldn't do that anyways. Not on something that thin. I did weld to a propane once. The shell was 0.5in though. I felt pretty safe.

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86turbodsl · Oct 23, 2017

86turbodsl said:
I wouldn't do that anyways. Not on something that thin. I did weld to a propane once. The shell was 0.5in though. I felt pretty safe.

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Rental better be pretty cheap, i just found a dwyer UST gage online for $224. For purchase!!!

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lakeroadster · Oct 23, 2017

86turbodsl said:
Well, where would one rent an ultrasonic thickness checker? Every time i've tried to rent something esoteric (read beyond the local rent-all) the prices are starting at $500+ a day. IR camera for mapping my in-floor heat tubing being a prime example.

For the $500 it would cost, i would just apply to a new tank.

I can do the hydro "check" for pretty cheap. If it passes, i'll probably work on scouring the internal surfaces and coating with paint to slow down further corrosion and put into service. I'm not made of money, and the wife disapproves of large expenditures that she sees no benefit of.

You are starting to understand why a lot of people just buy a new tank. So you have to weigh you and your families safety -v-s the price of inspecting it correctly -vs- the price of a new tank.

Call around, look for places that calibrate, inspect and sell pressure gauges and instrumentation in your area. They can likely hook you up with a company that can provide you with a UTT meter.

davejo · Oct 23, 2017

Since you have an lc4, you can borrow my ultrasonic tester if you promise not to break it. But I don't know how you can find pinhole rust spots on a large tank, lots of acreage to scan.

It seems like the dimensions for a given volume tank would be pretty standard so the nameplates would all read the same thicknesses if that was wear limit stamped on the plate. Lakeroadster's explanation of the plate data puts strouty's tank way out of tolerance.

Other issues i have yet to be satisfied about are claims that asme tanks don't usually rupture when they fail from corrosion, they just spring leaks due to "superior ductility" etc etc.

mike93lx · Oct 23, 2017

6768rogues said:
My father had a vertical tank upstairs in his shop. It failed when the weld at the base gave out (except for an inch) and the base hinged open. It blew a hole in the floor where it sat, ripped a door and sink off the wall below, lifted and broke a roof truss and cracked the concrete block exterior wall. Moments before it blew my father stepped out from beneath it, but he had a few shrapnel bruises on his legs. It was so loud the guy across the road came out to see what exploded.
I will never take a chance with an old tank. 100 psi is a hundred pounds of force for every square inch of surface. There is a lot of total potential energy in a tank.

it's **** like this that made my sell by 60 gal compressor and buy an aluminum tank 5 gal portable. being able to run a impact wrench, sander or die grinder wasn't worth the constant worry about what could happen if it popped, regardless of how unlikely.

Old compressor tank - hydro or not?

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