Post mortum on a holed compressor tank

[pkrankow]

I had purchased a 8 gallon Sears compressor used, and found it was holed. For $5 I was still ahead of the game if I recycled parts of it.

I repaired the tank with a bolt, nut and epoxy with good results. I started by using a center punch and working my way around the pinhole till I found solid metal. The hole was about 1/2 inch when I was done, and I put a 1/2 inch bolt with fender washers in the hole.

I then found a "NOS" 28 gallon upright compressor tank on Craigslist. After debating the idea I bought the tank for $40, and was happy. I cut the motor plate off the Sears unit and bolted it to the Campbell-Hausfeld motor plate so the belt driven pump could be used.

I decided to cut the Sears tank up so I could make a table top out of it that will eventually be a solid fuel forge. I cut the ends off inside the welds, and then cut the cylinder lengthwise through the rusted area, between the drain and the repaired hole. After flattening the tank some to open it up I measured the thickness along the edges.

At the top on the end cap edge I measured 0.100 to 0.105 inches. Along the bottom through the rusted area I measured .070 to .045 inches with typical measurements being between .060 and .050 inches.

Some pictures:




Draw your own conclusions about the safety of repairing a compressor tank.

Please remember to drain the water from your compressor tanks

Phil

[bigfootnampa]

Yes I think that once one has been holed it should be retired. Still as one who has used several through their lifespan I have noted that the catastrophic explosive failure is NOT common. Usually there will be a pinhole leak as a warning before any major failures. Just be sure that you pay attention!

[BIGGUNDOCTOR]

I worked for a company that part of our duties was to service auto shop air compressors. If it had a leak it was scrapped, no questions asked. The boss had a trade magazine article where a tank blew. It went through the cinder block wall, and killed the mechanic on the other side.

An air tank is not like a hydraulic tank. With hydraulics, you get an instant drop in pressure as soon as it opens up,due to liquids not being able to be compressed. An air compressor tank has a lot more stored energy in compressed air even after it opens up. There is more than say 20 gallons of air in a 20 gallon tank depending on the pressure. It doesn't take that many pounds per square inch to kill you. Figure out the square inches of that tank, then multiply it by say 120 psi. Then tell me if you want to repair a rusty tank.

[Dragons lair]

Figure out the sq inches then multiply bt 120? 120psi is 120lbs per sq inch last time I checked. Now I do agree partly about repairing rusty tanks. However have seen more than a few and plated a few. Usually happens on a Sat or Sun. Got a pinhole weld on a 6inch patch. If it don't burn thru ya finish the job. Look for a tank on Mon.(or wait for the next time) The only tank I ever saw go thru a wall was a full 180 o2 bottle 2600psi fell over and snapped the neck off. But thats 2600psi thru a 1inch hole.
Ken.

[Mainely,Bob]

I have to agree about the flying compressor myth.Most of the compressors that generate that kind of pressure are coupled to a remote mounted holding tank and those things are securely bolted down.

What causes most injuries is the surrounding loose material that gets tossed by the escaping air when one of these things fails.
It`s like being in a tornado.It ain`t the wind that kills you it`s the things that the wind has picked up and thrown.

[Tim McCoy]

Agreed ... replace leaking air compressor tanks. Making a repair for yourself IMHO is an experiment in terror ... it either works or it doesn't ... no inbetween :blink:

[HWHII]

While I recieved my training for my ASNT Level II visual inspector's certification for ASME IX pressure vessels we watched videos and saw photos of testing at the ASME labs and field failiers of presure vessels. It was ment to scare us and to take our jobs seriously when fabricating and inspecting pressure vessels and it work for me. Once you see a tank explode at 100 PSI it will get your attention.

I had a old neighbor where I use to live and he took a old water heater tank and made a spair air tank for his mechanics truck. He brazed the fittings on it and used closed nipple fittings to boot. Then mounted it under his truck. I guess you know whats coming next. You got it BOOOM! when he was driving down the road. A 1/2" nipple blew of and left a hole you could put your fist into. I tried to warn him but he though I was full of XXXX.

[pkrankow]

Isn't house water typically under 60psi? My house water gauge reads 50 to 55 psi, and it is a new gauge last year.

Phil

[Mainely,Bob]

Bet that got his attention!
Isn`t it amazing how quickly you can go from retard to genius once someone you have warned has had an experience which caused them to change their shorts.

I don`t need to say anything except"Are you OK?".The smile kind of says it all after that.

[HWHII]

Figure out the sq inches then multiply bt 120? 120psi is 120lbs per sq inch last time I checked. Now I do agree partly about repairing rusty tanks. However have seen more than a few and plated a few. Usually happens on a Sat or Sun. Got a pinhole weld on a 6inch patch. If it don't burn thru ya finish the job. Look for a tank on Mon.(or wait for the next time) The only tank I ever saw go thru a wall was a full 180 o2 bottle 2600psi fell over and snapped the neck off. But thats 2600psi thru a 1inch hole.
Ken.

I have repaired boilers that had corrosion issues. ASME code gives you specs on how much area you need to ultra sound test and how thick the wall thickness is. Usually the area was then cut out and new plate installed, then Xrayed.

[thingmaker3]

Figure out the sq inches then multiply bt 120? 120psi is 120lbs per sq inch last time I checked.

Yes. Now multiply by each and every square inch for the total force. That's what the "per square inch" means. ;)

[BIGGUNDOCTOR]

Say it was only 1sq'. 12"x12"=144 sq" , now multiply that 144sq"x120(psi)= 17,280 pounds of total force pushing against that surface area. With enough corrosion it can open that plate like a zipper.

Sometimes looks can be deceiving. A friend had bought a Parker double barrel that had been reblued. He used it for dove hunting, and then later for cowboy action events. He came to one station where everyone was having a problem knocking the plate down. He had a couple of high brass loads with him, and popped them in. When he touched off the first round, one of the barrels let go. Luckily he avoided having his hand removed forcibly as the fore end splintered apart. Looking the barrel over it was discovered that a portion of the wall had been polished down to only .009" thickness. It held for quite some time, but when it went, it went big time. He still has that shotgun all blown apart as a reminder about safety at all times.

These were accidents, but are somewhat related as air was involved.

An auto mechanic at a dealership we serviced went to check the oil level in his lift. He puts his impact gun into the 1.5"-2" pipe plug and zips it out. The other mechanics told me that he flew backwards from the impact of that plug slamming him in the face. He had not bled the system down, and had a full 175 psi charge in the tank. It almost killed him, as it was he still needed full reconstructive surgery to put his face back together.

One of our guys went to pull a plug out of an air line in a shop, and got whacked in the forehead as the plug flew out. He had drained the system, but the main valve leaked some air back into the system. That is why we later locked the drain valves open, and didn't close them again until we were ready to test the system.

[pkrankow]

One of our guys went to pull a plug out of an air line in a shop, and got whacked in the forehead as the plug flew out. He had drained the system, but the main valve leaked some air back into the system. That is why we later locked the drain valves open, and didn't close them again until we were ready to test the system.

I'll remember that if I am working on an air system. I can't think of a different way to lock out pneumatics that cannot be disconnected.

Phil

[JNewman]

I have worked with core making machines in foundries where the air shutoff valve dumped all the air in the machine when the valve was turned off. So when off the cylinders were open to the atmosphere. This was in addition to the electric eye curtain that would lock everything up if you crossed it. Everyone working inside put a lock on the machine. These were about 14-18" cylinders so you would be pretty flat if caught inside.

[ptree]

A few things I will agree with and one or so I will disagree with in the above postings.

First, Hydraulic systems often trap siginifacant pressure, and a few drops will NOT release all the pressure. Look for an accumulator, they will store pressure. Second, I made my living working in a high pressure hydrostatic lab. I burst tested many of the items we work with. I have had hydrostatic failures in pipes that sounded like a dyamite explosion. Yes these were at 19,000 psi, but do illustrate. The bigger the volume, and the higher the pressure, the more elastic deformation in the steel and the more stored pressure. I have had larger items shoot out a jet of water and shoot across the test cell like a squid.

Hydraulic is safe since liquids are not compressable. WRONG! Liquids are compressable, the folks that wrote that law just did not have the instruments and equipment to measure it. Water IS compressable, and at pressure of say 10,000 psi you can see 1/2% per thousand PSI. Small amount of compression, HUGE amount of energy. Second a pin hole at 3000 psi will inject under the skin and cut like a razor. The clothes you are wearing as you sit there reading this were probably just cut by a waterjet at something like 5000 to 10,000 psi.

Next, I have seen a photo of a boiler that failed at a measly 25 psi. Flipped a 60,000# weight traction engine on its back.

I have seen far too many failure photos to share all, just please please consider the possible consequences of a shoddy repair.

And for reference, ASME code stamped pressure vessels for non-fired use, like compressed air are tested at the maker for 1.5 times the rated design working pressure. So if you read that name plate and see the ASME in a sheid, and the working pressure is 250PSI, it was tested to 375 psi at the factory. Usually the actual burst test pressure will be at least 6 times higher when new, to account for corrosin etc over the life of the device.
Ptree who worked for an ASME code shop making valves, fittings, boilers, and refrigeration equipment for 21 years, and designed the test equipment to do the hydros for most of that time.

[Dragons lair]

Yes. Now multiply by each and every square inch for the total force. That's what the "per square inch" means.

So the tires on my truck are not at 32psi but have several thousand pounds of pressure. Perhaps I was mistaught 50 yrs ago. Teacher said PSI is pounds per square inch. This is the first I have ever heard of X area. How is it that my air tools won't run if my 100 gal tank gets down to 40 psi? This old phart is going to sleep on this one.
Ken.

[Dragons lair]

A few things I will agree with and one or so I will disagree with in the above postings.

First, Hydraulic systems often trap siginifacant pressure, and a few drops will NOT release all the pressure. Look for an accumulator, they will store pressure. Second, I made my living working in a high pressure hydrostatic lab. I burst tested many of the items we work with. I have had hydrostatic failures in pipes that sounded like a dyamite explosion. Yes these were at 19,000 psi, but do illustrate. The bigger the volume, and the higher the pressure, the more elastic deformation in the steel and the more stored pressure. I have had larger items shoot out a jet of water and shoot across the test cell like a squid.

Hydraulic is safe since liquids are not compressable. WRONG! Liquids are compressable, the folks that wrote that law just did not have the instruments and equipment to measure it. Water IS compressable, and at pressure of say 10,000 psi you can see 1/2% per thousand PSI. Small amount of compression, HUGE amount of energy. Second a pin hole at 3000 psi will inject under the skin and cut like a razor. The clothes you are wearing as you sit there reading this were probably just cut by a waterjet at something like 5000 to 10,000 psi.

Next, I have seen a photo of a boiler that failed at a measly 25 psi. Flipped a 60,000# weight traction engine on its back.

I have seen far too many failure photos to share all, just please please consider the possible consequences of a shoddy repair.

And for reference, ASME code stamped pressure vessels for non-fired use, like compressed air are tested at the maker for 1.5 times the rated design working pressure. So if you read that name plate and see the ASME in a sheid, and the working pressure is 250PSI, it was tested to 375 psi at the factory. Usually the actual burst test pressure will be at least 6 times higher when new, to account for corrosin etc over the life of the device.
Ptree who worked for an ASME code shop making valves, fittings, boilers, and refrigeration equipment for 21 years, and designed the test equipment to do the hydros for most of that time.

Guys pay attention to the hydro info. A pin hole in a skidloader or fork lift line can kill ya. think tornado a straw thru a steel shovel. Say 3500 lbs psi now at .010 hole. It will hurt ya. injected hyd fluid can kill or at least blind ya.
Ken.

[ptree]

Not only will high pressure fluid through a pin hole cut, It will inject you with a automatic infection. Think about what is in regular hydraulic fluid and you will almost always find bacteria. High pressure airless paint sprayers will also inject, that is the reason for that little guard at the nozzle.
One thing, when you have high pressure from a pin hole, it usually loses energy pretty quick as it moves away from the nozzle. So a 5000 psi jet that will cut you to the bone if you drag your hand across the hole will burn you from friction at a couple of inches and just make you wet at a foot or so.

NEVER look for a small leak by rubbing the suspected leak. Avoid ever handling hydraulic hoses that are under pressure.

[pkrankow]

So the tires on my truck are not at 32psi but have several thousand pounds of pressure. Perhaps I was mistaught 50 yrs ago. Teacher said PSI is pounds per square inch. This is the first I have ever heard of X area. How is it that my air tools won't run if my 100 gal tank gets down to 40 psi? This old phart is going to sleep on this one.
Ken.

Um, yes and no. The pressure is 32 psi, but the weight of the vehicle is 4000 pounds (light truck right?) Now if you measure your tire footprint and multiply by the pressure in the tire you get the weight of the vehicle. This is a middle school pressure assignment for science class, but not actually done at most schools.

Now working backwards 4000lbs divided by 4 tires = 1000 lb load per tire.
1000 pounds divided 32 psi makes 31.25 square inches of tire contact area.

Or as the middle school assignment goes, take 2 straight edges and a ruler and measure the surface contact of the tires on your parents car, then measure the tire pressure to each tire and record all the information. Now figure the contact area of each tire and multiply by the pressure in each tire and you get the weight of the vehicle!

Phil

[Mainely,Bob]

Not only will high pressure fluid through a pin hole cut, It will inject you with a automatic infection. Think about what is in regular hydraulic fluid and you will almost always find bacteria. High pressure airless paint sprayers will also inject, that is the reason for that little guard at the nozzle.
One thing, when you have high pressure from a pin hole, it usually loses energy pretty quick as it moves away from the nozzle. So a 5000 psi jet that will cut you to the bone if you drag your hand across the hole will burn you from friction at a couple of inches and just make you wet at a foot or so.

NEVER look for a small leak by rubbing the suspected leak. Avoid ever handling hydraulic hoses that are under pressure.

I`d like to add to Ptree`s post by adding a caution about the MIG welders we are all so fond of.Be very careful about how you handle the nozzle on these torches.
I have seen the results of more than one accident where the operator had a gloved or bare hand over the tip and the trigger was hit.The wire punctured the skin thru the glove and the leather acted as a seal between the nozzle and the skin.Once the wire punctured the skin the shield gas was injected through that puncture into the tissue of that hand.Very bad stuff followed quickly,like within less than an hour.

[Dragons lair]

Um, yes and no. The pressure is 32 psi, but the weight of the vehicle is 4000 pounds (light truck right?) Now if you measure your tire footprint and multiply by the pressure in the tire you get the weight of the vehicle. This is a middle school pressure assignment for science class, but not actually done at most schools.

Now working backwards 4000lbs divided by 4 tires = 1000 lb load per tire.
1000 pounds divided 32 psi makes 31.25 square inches of tire contact area.

Or as the middle school assignment goes, take 2 straight edges and a ruler and measure the surface contact of the tires on your parents car, then measure the tire pressure to each tire and record all the information. Now figure the contact area of each tire and multiply by the pressure in each tire and you get the weight of the vehicle!

Phil

Phil, The original statement was "take the psi and multiply X # of sq inchs to get total pressure thsts what PSI is" Lets look at this another way. Compressor
tank 24" dia 60" tall. Thats 75" around X 60" tall X psi or 75X60X135=607,500=
total pressure. And it still shuts off at 135lb. Using that formula.75X60X10=
45,000total pressure( thats what psi is)Air tools woun't run on 10 psi. As to your car problem. It would not matter if the tires were air filled or solid the weight psi would be the same.
Smaller the tire size more the psi. On a givin auto a 950 15 snow tire will get ya stuck. A 560 15 will get ya there. More psi on the road. Learned that one the hard way.