Air tanks lined?

[3rdmdqm]

I used the search feature but found nothing related to this. I'm doing a complete frame off restoration on a '68 M35A2. Removed the air tanks to inspect, blast and paint. There are chunks of what I thought was rust inside the tank. Shook some out and it actually looks like some type of smooth maroon colored hard shiny wax like material, some of the chunks were fairly large and had to be broken up to get them out of the holes. Were these tanks lined with something originally? If so, what? The tanks hold air and don't appear to be in too bad condition, there is obvious rust inside from use and all these chunks coming out. If they were not lined, what could this stuff be? Would a clean out solution be to fill the tank with muriatic acid and let it sit overnight and flush out in a similar procedure to cleaning out old gas cans/tanks?

 

[cattlerepairman]

Good that you found that!! No, I am not aware that they were "lined" (although anything is possible). I recall them being painted with a reddish coloured primer. You definitely want that stuff out of there because random blockages of random air orifices are not fun. Probably disconnect the air hoses from the tanks at the other end and blow the lines through as well!

Muriatic acid eats rust (good) and metal (not so good) but it may or may not do anything with the chunks.

 

[3rdmdqm]

Good that you found that!! No, I am not aware that they were "lined" (although anything is possible). I recall them being painted with a reddish coloured primer. You definitely want that stuff out of there because random blockages of random air orifices are not fun. Probably disconnect the air hoses from the tanks at the other end and blow the lines through as well!

Muriatic acid eats rust (good) and metal (not so good) but it may or may not do anything with the chunks.

Thank you, that was my thought as well regarding blockages. I'm a bit leery of reusing these for fear of some more of that stuff breaking off and going somewhere throughout the system so not sure if I should invest in a NOS set or try the acid and see what happens. I've never seen anything like that before. I have read where people recommended using POR to line tanks but have always been afraid of cracking or loosening and the stuff getting forced into a line. Curious if anyone else has ever seen anything like this before. Appears to be in both of these tanks, although one is worse than the other. I'm guessing these are the original tanks, they both have "2 MIDLAND 68" and SAE CODE- J108 stamped on the ends.

 

[Mullaney]

Thank you, that was my thought as well regarding blockages. I'm a bit leery of reusing these for fear of some more of that stuff breaking off and going somewhere throughout the system so not sure if I should invest in a NOS set or try the acid and see what happens. I've never seen anything like that before. I have read where people recommended using POR to line tanks but have always been afraid of cracking or loosening and the stuff getting forced into a line. Curious if anyone else has ever seen anything like this before. Appears to be in both of these tanks, although one is worse than the other. I'm guessing these are the original tanks, they both have "2 MIDLAND 68" and SAE CODE- J108 stamped on the ends.

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It's an import, but you could get an endoscope attachment for your smart phone that has a light on it. It has a light on the end of it with a camera. App that I have is HD WiFi. I use it in my honeybee boxes when it is really cold outside... I can take a look without disturbing them.

Should work well using it to inspect the inside of your air tanks.

Similar to a bore scope you might use on a rifle.

 

[3rdmdqm]

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It's an import, but you could get an endoscope attachment for your smart phone that has a light on it. It has a light on the end of it with a camera. App that I have is HD WiFi. I use it in my honeybee boxes when it is really cold outside... I can take a look without disturbing them.

Should work well using it to inspect the inside of your air tanks.

Similar to a bore scope you might use on a rifle.

Great idea! I actually have one of those HD See scopes, thanks for reminding me, I'll check them tonight.

 

[Mullaney]

Great idea! I actually have one of those HD See scopes, thanks for reminding me, I'll check them tonight.

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Yeah! Great minds think alike.

 

[3rdmdqm]

So, I am perplexed. I did a scope camera inspection of the interior of the tank. Looks like your standard aging rust etc. It also looks like the interior of the tank was painted green at one time (didn't know they painted the inside). Have no idea where this waxy looking stuff has come from. If the tank was lined, maybe it's coming off, or maybe it was some kind of buildup of oils, rust and debris that formed. I don't know. But the insides don't really look all that bad. In the one photo you can see a large piece of rust/crud I haven't gotten out yet. Does the inside of this tank look pretty typical and usable? Should I look at replacement? Either this tank was lined in the bottom with something to slow the rusting process, or what was in the bottom is the years of sludge that has settled and solidified over time which is flaking out.

 

[Mullaney]

So, I am perplexed. I did a scope camera inspection of the interior of the tank. Looks like your standard aging rust etc. It also looks like the interior of the tank was painted green at one time (didn't know they painted the inside). Have no idea where this waxy looking stuff has come from. If the tank was lined, maybe it's coming off, or maybe it was some kind of buildup of oils, rust and debris that formed. I don't know. But the insides don't really look all that bad. In the one photo you can see a large piece of rust/crud I haven't gotten out yet. Does the inside of this tank look pretty typical and usable? Should I look at replacement? Either this tank was lined in the bottom with something to slow the rusting process, or what was in the bottom is the years of sludge that has settled and solidified over time which is flaking out.

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Wow. Me too... Almost looks like a coating of rust inside the tank - but the bits extracted earlier look like a coating rather than rust scale. Maybe we can get some other opinions. Maybe some fish tank gravel and shake the heck out of it and see what else comes out of at least one tank?

 

[87cr250r]

Looks like mill scale.

If you are going to do an acid wash you have to do a caustic wash first. Any oil residue from the compressor will prevent the acid from doing it's thing.

You may or may not care to manage the flash rusting as it dries.

Radiator and engine shops can hot tank items for a fee which will strip them bare.

You could also get it hot dip galvanized to slow future corrosion.

 

[NY Tom]

I used black beauty blasting media and steel balls to clean mine out. Set them up in a lathe and Bridgeport to get them to tumble all around inside. Afterwards used the POR15 product to line them. No problems so far in the last 3 years.

Did come out with red looking primer dust and some small pieces similar to what you show after tumbling. i also did not know what it was.

 

[bprzyw]

Maybe steel shot in each and strap them to a tractor wheel or truck wheel and drive around a bit? Then coat with Ospho? Let it dry then prime? Just a though.

 

[3rdmdqm]

Update. I scoped the other tank. It's nasty inside but looks more caked/solid than broken pieces. The bottom around the drain orientation looks like chicken pox, and I have no idea what that giant piece of red bar is in two of the pictures, possibly solidified gunk of some sort. I think what's going on (and if anyone else has another thought please share) is this is years of rust, scale, oil, condensate and brake fluid that has lined the bottom and solidified as the tanks were, or maybe were not, drained over time. When pressurized, the air forced the gunk to the tank bottom floor solidifying it making it have a smooth texture appearance on top. In any event, these tanks were both stamped '68. I will play around with them, run gravel through and shake, hot tank and acid wash etc. to see how it goes, but at this point I'm not putting them back on the truck. I'm too worried about something breaking loose and fouling up the system. Airpack and master cylinder have been rebuilt and all air lines and brake lines have been completely disassembled and removed to be wire wheel brushed clean on the outside and cleaned out on the inside. I just took delivery of 2 NOS tanks that are stamped 00 (2000) and wow! they look brand new inside and out, so I'm happy with them and am going to use these for peace of mind on the truck.

 

[Mullaney]

Update. I scoped the other tank. It's nasty inside but looks more caked/solid than broken pieces. The bottom around the drain orientation looks like chicken pox, and I have no idea what that giant piece of red bar is in two of the pictures, possibly solidified gunk of some sort. I think what's going on (and if anyone else has another thought please share) is this is years of rust, scale, oil, condensate and brake fluid that has lined the bottom and solidified as the tanks were, or maybe were not, drained over time. When pressurized, the air forced the gunk to the tank bottom floor solidifying it making it have a smooth texture appearance on top. In any event, these tanks were both stamped '68. I will play around with them, run gravel through and shake, hot tank and acid wash etc. to see how it goes, but at this point I'm not putting them back on the truck. I'm too worried about something breaking loose and fouling up the system. Airpack and master cylinder have been rebuilt and all air lines and brake lines have been completely disassembled and removed to be wire wheel brushed clean on the outside and cleaned out on the inside. I just took delivery of 2 NOS tanks that are stamped 00 (2000) and wow! they look brand new inside and out, so I'm happy with them and am going to use these for peace of mind on the truck.

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I was rummaging through some old receipts and found where I had bought a pair of or new air tanks. They were aluminum, so it's a different kind of crud rather than rust when they collect "goop".

Daily draining really is important when you consider that the air in those tanks are a life and death sort of thing. There is always the potential for oil in the air made by your air pump.

You mentioned brake fluid. You won't have brake fluid in the air tanks. That is two completely separate (unconnected) systems. Yes, air over hydraulic brakes do use brake fluid but the "air part" of that system only provides air to the booster part of the system.

I am positive that you made a good decision to replace the air tanks.

 

[davidb56]

use a cigarette lighter and see if those chunks burn like oil or like some plastic type coating. the compressor always dumps oily crap in the tanks as the intake is at the engine or in some cases air filter.

 

[Captaincarrier]

use a cigarette lighter and see if those chunks burn like oil or like some plastic type coating. the compressor always dumps oily crap in the tanks as the intake is at the engine or in some cases air filter.

When we clean diesel fuel tanks we often find "PEANUT BRITTLE" like deposits. They will burn and turn to a white ash.

 

[rustystud]

That stuff looks like someone used "fuel tank sealer" to prevent rust. The only problem is it's not meant for air tanks.
I have a stainless steel air tank for my "main" or "wet" tank. Of course I also added two twenty gallon stainless steel tanks in the back for extra air to operated my air tools.

 

[HDN]

That stuff looks like someone used "fuel tank sealer" to prevent rust. The only problem is it's not meant for air tanks.
I have a stainless steel air tank for my "main" or "wet" tank. Of course I also added two twenty gallon stainless steel tanks in the back for extra air to operated my air tools.

I wondered about that. I think it's one thing cutting a fuel tank open to do a treatment coating and weld it back together. But an air tank that's at 120 psi? That sounds like a problem waiting to happen.

 

[Mullaney]

I wondered about that. I think it's one thing cutting a fuel tank open to do a treatment coating and weld it back together. But an air tank that's at 120 psi? That sounds like a problem waiting to happen.

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On an air tank - when you cut it open - then weld it back the coating gets burned off where the welding happens. And then too there is the quality of the weld. On pipelines, those welds are X-Rayed. Thinking out loud, are those little air tanks - the ones that are keeping the 80,000 pounds of truck from mashing the battery powered Prius - Are they X-Rayed?

I rummaged around the web. Never really found any solid answers. Specs for "reservoirs" require them to be pressure tested. But I have yet to find a requirement for Air Tank testing AFTER manufacturing.

(From the PDF below)
Reservoir Integrity: 49CFR571.121 S5.1.2.2 Each reservoir must withstand 5 times governor cut-out or 500 psi which ever is greater, for at least 10 minutes.

 

[87cr250r]

Air tanks do not get x-rayed. They are fabricated using a qualified welding procedure and then hydro tested. ASME Section XIII covers fabrication of pressure vessels.