Rebuilding air compressor- tank question

[Josh the IH guy]

Hey, I'm rebuilding an old speedaire 80 gallon compressor. The tank is 30 years old, and I removed a bunch of rust from inside the tank. The tank is still solid. Should I spray something inside the tank to prevent or slow down additional rust? If so, what should I use?

 

[u2slow]

Maybe look for a coating used to line rusty fuel tanks?

 

[nadogail]

I would Hydro Test the tank before spending time and money coating the inside.

 

[Josh the IH guy]

I would Hydro Test the tank before spending time and money coating the inside.

I've checked it over, and I'm comfortable moving forward.

 

[Josh the IH guy]

Maybe look for a coating used to line rusty fuel tanks?

I'll do some googling. Thanks!

 

[mogandave]

I would not spray anything inside the tank. If I thought it was worth saving, I would wash the tank out with soapy water, let it dry and treat it with OSPHO. You can just pour it in, seal the tank and roll it around then drain it. Do not throw out what you drain as it is still good. This will stop the rust.

Better, if you have a place reasonably close to you that does hot-dip galvanizing you might see if they'll take it and get a price. They might charge by the before and after weight and can be cost effective.

 

[Josh the IH guy]

I would not spray anything inside the tank. If I thought it was worth saving, I would wash the tank out with soapy water, let it dry and treat it with OSPHO. You can just pour it in, seal the tank and roll it around then drain it. Do not throw out what you drain as it is still good. This will stop the rust.

Better, if you have a place reasonably close to you that does hot-dip galvanizing you might see if they'll take it and get a price. They might charge by the before and after weight and can be cost effective.

We do have a dipping place nearby. I didnt think of that. I'll give them a call. That would be ideal. I wouldn't have to even paint it! If that doesnt work out, I do have a few gallons of ospho.

 

[Walkers]

Leave it be. Anything you paint in there will end up in your air lines. Clean it up, drain the water regularly (or get an auto drain), and it will be fine.

 

[mogandave]

We do have a dipping place nearby. I didnt think of that. I'll give them a call. That would be ideal. I wouldn't have to even paint it! If that doesnt work out, I do have a few gallons of ospho.

Is OSPHO not the sh*t?

 

[mogandave]

Leave it be. Anything you paint in there will end up in your air lines. Clean it up, drain the water regularly (or get an auto drain), and it will be fine.

Once it's dry, OSPHO will absolutely not end up in the lines.

 

[djjsr]

I have used two different coatings in motorcycle tanks. Kreem and Red Kote. Good results with both. They hold up to gas and alcohol so I don't think air and moisture would be a problem. They require cleaning and etching prep.

 

[mogandave]

I have used two different coatings in motorcycle tanks. Kreem and Red Kote. Good results with both. They hold up to gas and alcohol so I don't think air and moisture would be a problem. They require cleaning and etching prep.

And they are a little easier to handle than an 80-gallon pressure vessel.

The problem with trying to paint the inside most tanks is getting them clean.

 

[rsanter]

I would clean the inside to bare metal and then pour in an epoxy based paint/coating and roll it around.
Then I would come Ford the bottom the the tank with an angle fitting to a pipe then a ball valve to make it easy to drain

 

[djjsr]

I wouldn't be to concerned about getting the entire tank coated. If you can just get the bottom few inches protected, the tank will probably outlast the pump.

 

[mogandave]

I would clean the inside to bare metal...

Therein lies the rub

 

[u2slow]

I would clean the inside to bare metal and then pour in an epoxy based paint/coating and roll it around.

Epoxy will crack and lift with age on steel that is repeatedly stressed. Usually big shards though.

 

[Josh the IH guy]

Is OSPHO not the sh*t?

Yes it is. I have old rusty internationals. I would be lost without it. Outstanding stuff.

 

[Josh the IH guy]

Leave it be. Anything you paint in there will end up in your air lines. Clean it up, drain the water regularly (or get an auto drain), and it will be fine.

I do have an auto drain that I will be installing. That is one of the "must haves".

 

[Josh the IH guy]

Therein lies the rub

Yeah, getting the inside of the tank back down to bare metal would be nearly impossible. And the hours spent doing something like that...I'd be better off finding a newer tank.. but even a newer tank will have rust....

 

[Josh the IH guy]

I have used two different coatings in motorcycle tanks. Kreem and Red Kote. Good results with both. They hold up to gas and alcohol so I don't think air and moisture would be a problem. They require cleaning and etching prep.

This is good information. I'll look onto this stuff. Thank you.

 

[Josh the IH guy]

I wouldn't be to concerned about getting the entire tank coated. If you can just get the bottom few inches protected, the tank will probably outlast the pump.

I should have never looked inside it. Lol! I'm certain that it would be just fine, if I left it alone. But i just cant bring myself to that, knowing that I coulda, shoulda, woulda...

 

[Metal-Marc]

Therein lies the rub

Get a new tank.

 

[Josh the IH guy]

Get a new tank.

Why? This tank is still solid. I'm not trying to repair it. I'm just trying to keep it from further decay....

 

[mikedodge]

The problem with coating it with anything is it's going over rust so it's going to continue rusting. Especially when you can't get in there to clean it or apply anything properly. Use it as is and drain it regularly. If it starts showing any signs of rusting through its time to replace it.

 

[mogandave]

The problem with coating it with anything is it's going over rust so it's going to continue rusting. Especially when you can't get in there to clean it or apply anything properly. Use it as is and drain it regularly. If it starts showing any signs of rusting through its time to replace it.

A good conversion coating will stop the rust.

 

[Big Bad Dad]

The OP stated he removed a bunch of rust from inside the tank, but it is still solid.. How did he remove that bunch of rust from inside a tank??
Check this out...

I cut open my air compressor tank. Take a look..

I watched a series of YouTube videos starting with this one: It got me to thinking about my old air compressor in my shop. I got it several years ago. It was well used, and I didn't know anything about it's history. It has served me well for my purposes which is mainly airing up tires...

www.garagejournal.com

 

[Norcal]

I put a solenoid valve on my tank with a push button on the combination starter* enclosure for the compressor, have thought about a time delay timer so it activates for a few seconds every time the compressor cycles.

*A combination starter is a factory assembled enclosure with a disconnect, which can be fusible, non-fusible switch, circuit breaker, motor circuit protector, or a molded case switch, and a magnetic starter, some may call them pump panels, as they are found all over as controls for AG pumps.

 

[mogandave]

I put a solenoid valve on my tank with a push button on the combination starter* enclosure for the compressor, have thought about a time delay timer so it activates for a few seconds every time the compressor cycles.

*A combination starter is a factory assembled enclosure with a disconnect, which can be fusible, non-fusible switch, circuit breaker, motor circuit protector, or a molded case switch, and a magnetic starter, some may call them pump panels, as they are found all over as controls for AG pumps.

With a cheap timer, you can also set them up to just “spit” fo a second or two every five minutes.

 

[kwb]

Auto drain and move on.

Tanks don't last forever but if this one has some life left to give safely - run it.

 

[rsanter]

Epoxy will crack and lift with age on steel that is repeatedly stressed. Usually big shards though.

Really? Interesting

So use some kind of flexible coating? Or?

 

[rsanter]

Therein lies the rub

I’m thinking a chemical that eats rust but not metal

 

[Josh the IH guy]

The OP stated he removed a bunch of rust from inside the tank, but it is still solid.. How did he remove that bunch of rust from inside a tank??
Check this out...

I cut open my air compressor tank. Take a look..

I watched a series of YouTube videos starting with this one: It got me to thinking about my old air compressor in my shop. I got it several years ago. It was well used, and I didn't know anything about it's history. It has served me well for my purposes which is mainly airing up tires...

www.garagejournal.com

I took out the outlet port, laid the tank down, and stuck a shop vac down in there. That link definitely gives food for thought tho. Even still, I think my tank is in better shape than that one. I have a 33 gal craftsman, and over the past 20 years I've owned it, I dont think I've ever drained it!

 

[Walkers]

Once it's dry, OSPHO will absolutely not end up in the lines.

Ospho also not paint. It is also an unknown quantity in a pressure vessel. You have no idea what it is going to do to the metal over time. Hydrogen induced cracking? Is the acid going to continue reacting with the metal over time? Who knows. I do know that tank manufacturers don’t use it.

 

[Big Bad Dad]

I took out the outlet port, laid the tank down, and stuck a shop vac down in there. That link definitely gives food for thought tho. Even still, I think my tank is in better shape than that one. I have a 33 gal craftsman, and over the past 20 years I've owned it, I dont think I've ever drained it!

I "think" my tank is in better shape than that one.
The tank I cut open, didn't seem too bad until I pecked on it a few times with a chipping hammer. The chunks that popped out from the very bottom were pretty thick. The best I could tell, the tank thickness was reduced by half in those areas, and what remained showed heavy rusting....
The 8 years or so I used that compressor, I drained it every time it shut down. But it was old and well used when I got it, so I have no idea how the previous owner took care of it.

 

[mogandave]

I’m thinking a chemical that eats rust but not metal

Like OSPHO?

 

[mikedodge]

A good conversion coating will stop the rust.

But you can't easily coat it everywhere or see where its had and where it can't seal it it can easily start rusting under it. Plus the converter is still supposed to be wiped down and painted over.

I don't know how bad the rust is in this tank but I've seen compressors that had gallons of rusty water come out of them and years later they're still good.

 

[mogandave]

Ospho also not paint.

Point?

It is also an unknown quantity in a pressure vessel.

No, it is a known quantity in a pressure vessel.

You have no idea what it is going to do to the metal over time.

Yes, I do know what it's going to do over time.

Hydrogen induced cracking?

Yikes!

Is the acid going to continue reacting with the metal over time?

No

Who knows.

The Shadow?

I do know that tank manufacturers don’t use it.

How do you know that? Have you canvassed tank manufacturers around the world? As a fabricator, (not pressure vessels) I know I used a good bit of it over the years. In any event, are tank manufacturers building tanks, having them rust for ten years and then trying to sell them? Do you think it a tank manufacturer has ten tons of hot-roll sheet that gets rusty they just sh*t-can it? I think not.

You can treat structural steel with it, and where there is no rust it does nothing.

 

[Walkers]

Point?

I said a paint product, this is not a paint product.

No, it is a known quantity in a pressure vessel.

So you have used it in a pressure vessel? I would certainly be interested in seeing a product bulletin for that.

Yes, I do know what it's going to do over time.

really? How?

Yikes!

No

How do you know, there is no real procedure to neutralize it.

The Shadow?

That kind of my point.

How do you know that? Have you canvassed tank manufacturers around the world? As a fabricator, (not pressure vessels) I know I used a good bit of it over the years. In any event, are tank manufacturers building tanks, having them rust for ten years and then trying to sell them? Do you think it a tank manufacturer has ten tons of hot-roll sheet that gets rusty they just sh*t-can it? I think not.

I am also a fabricator, I own my own welding contracting company. While I do not currently work with pressure vessels I did for many years. I have never seen any sort of procedure or use of ospho in pressure vessel manufacturing, repair, or maintenance. Reason being is that they are pretty conservative people. If it doesn’t gain them anything, then they are not likely to go through all the testing to use it.

You can treat structural steel with it, and where there is no rust it does nothing.

To be clear, I think Ospho is a great product, and have used it a fair bit. I just don’t think putting phosphoric acid inside a pressure vessel is a great idea. I don’t think you will ever find anybody to put in writing that putting it inside your air compressor is a valid use of it.

 

[mogandave]

I said a paint product, this is not a paint product.

I understood what you said, I was asking what your point was.

So you have used it in a pressure vessel?

Yes, several

I would certainly be interested in seeing a product bulletin for that.

How much would it be worth to you? I might be persuaded to put something together...

really?

Really

How?

Because I have been using it successfully for almost forty years.

How do you know, there is no real procedure to neutralize it.

The manufacturer is clear that it is safe to paint over directly without even rinsing or even wiping it off, yes?

That kind of my point.

What, that without certification to a specific application a product is not safe to use?

I am also a fabricator, I own my own welding contracting company. While I do not currently work with pressure vessels I did for many years. I have never seen any sort of procedure or use of ospho in pressure vessel manufacturing, repair, or maintenance.

Well if you haven't seen it, that certainly proves it does not exist.

Reason being is that they are pretty conservative people. If it doesn’t gain them anything, then they are not likely to go through all the testing to use it.

You seem to be saying here that it is safe to use, but that it is not economically feasible for the manufacturer to certify it as such. Is that correct?

To be clear, I think Ospho is a great product, and have used it a fair bit. I just don’t think putting phosphoric acid inside a pressure vessel is a great idea.

I would probably not recommend it for use on the Space Shuttle, but to salvage an otherwise sound home compressor I absolutely recommend it.

I don’t think you will ever find anybody to put in writing that putting it inside your air compressor is a valid use of it.

I don't need anyone to put anything in writing, I already have it inside my air compressor, or at least I did until I moved and got a new SG compressor.

 

[Walkers]

I understood what you said, I was asking what your point was.

Yes, several

How much would it be worth to you? I might be persuaded to put something together...

Really

Because I have been using it successfully for almost forty years.

The manufacturer is clear that it is safe to paint over directly without even rinsing or even wiping it off, yes?

What, that without certification to a specific application a product is not safe to use?

Well if you haven't seen it, that certainly proves it does not exist.

You seem to be saying here that it is safe to use, but that it is not economically feasible for the manufacturer to certify it as such. Is that correct?

I would probably not recommend it for use on the Space Shuttle, but to salvage an otherwise sound home compressor I absolutely recommend it.

I don't need anyone to put anything in writing, I already have it inside my air compressor, or at least I did until I moved and got a new SG compressor.

Goody goody for you.