Galvanic protection...

[yyc_ranger_4x4]

So, I'm taking a Cathodic Protection course, and instead of doing homework...I'm out in the garage trying to unwind a bit. As I'm draining my compressor tank, it donned on me that having an anode in the bottom of the tank would actually be a good thing. It wouldn't cost much more manufacturing and it would keep corrosion to a bare minimum when there is water/**** in the bottom of the tank.

Going to pass the idea by the engineers I'm in class with and see what they say. What do you think?

 

[chaosracing]

It wont work like it does in a hot water tank or a ship. In order for the sacrificial anode to work, it must be submerged in water, something we are trying to prevent in a air compressor. The better and easier option would be to line the tanks with porcelain, glass, epoxy or something similar.

 

[southalabama]

Looks ingersoll rand thought it a good idea too. They have a anode as part of their system.

Cathodic protection system for air compressor tanks
Patent
US 6770177 B2

 

[yyc_ranger_4x4]

I am aware of the need of everything needed for a corrosion cell (anode, cathode, metallic path, electrolyte), and I'm not saying its a complete protection all the time, but when water is in our compressor tanks, it would help to mitigate corrosion. Obviously the anode would have to be mounted at the lowest part of the tank possible.

 

[ndm]

We use cathodic protection for towers at my company. Sacrificial anodes are buried near the guy wires but do require testing each year to be sure the system is working properly and to know when the anode is done for.

 

[6PTsocket]

I am aware of the need of everything needed for a corrosion cell (anode, cathode, metallic path, electrolyte), and I'm not saying its a complete protection all the time, but when water is in our compressor tanks, it would help to mitigate corrosion. Obviously the anode would have to be mounted at the lowest part of the tank possible.

I guess you could mount it to a plug on the bottom of the tank, if it does not interfere with draining the tank. I don't know how else you would get it in there. The anode needs good contact to the metal. Sounds good in theory and it can't hurt.

Sent from my SM-G900V using Tapatalk

 

[ndm]

I guess you could mount it to a plug on the bottom of the tank, if it does not interfere with draining the tank. I don't know how else you would get it in there. The anode needs good contact to the metal. Sounds good in theory and it can't hurt.

Sent from my SM-G900V using Tapatalk

Theoretically, the connection for the anode should be able to go anywhere on the tank, wouldnt it? Once connected with a good connection the whole tank should be bonded, right?

 

[6PTsocket]

Theoretically, the connection for the anode should be able to go anywhere on the tank, wouldnt it? Once connected with a good connection the whole tank should be bonded, right?

But it has to be inside the tank and in the water at the bottom, doesn't it? On a boat it is often in the form of a collar on the drivevshaft. You can't stick it on the outside of the tank. It is a sacrificial anode that erodes away instead of what it is protecting. It would not work at the top of the tank. You want it as close to the site of where rust could occur as possible.

Sent from my SM-G900V using Tapatalk

 

[yyc_ranger_4x4]

Theoretically, the connection for the anode should be able to go anywhere on the tank, wouldnt it? Once connected with a good connection the whole tank should be bonded, right?

For it to protect properly, the anode and cathode must be connected by a metallic path and both in contact with the electrolyte. So it would have to mounted in the bottom of the tank. Could be interesting to try out....

 

[matt_i]

If you could drill a blind hole in a solid pipe plug and then insert (pressfit or epoxy) a rod of the anode material (magnesium?) all the way thru the run of a small 1/4" or 1/8" pipe tee, screw this assembly into the bottom of the tank. Then, the water would have to be released from the side leg of the tee.

 

[6PTsocket]

If you could drill a blind hole in a solid pipe plug and then insert (pressfit or epoxy) a rod of the anode material (magnesium?) all the way thru the run of a small 1/4" or 1/8" pipe tee, screw this assembly into the bottom of the tank. Then, the water would have to be released from the side leg of the tee.

Zinc. They are a dime a dozen in any marine supply store..

Sent from my SM-G900V using Tapatalk

 

[wssix99]

It wouldn't cost much more manufacturing and it would keep corrosion to a bare minimum when there is water/**** in the bottom of the tank.

It won't do anything noticeable for you. The water in the tank is pure from the air and is a poor electrolyte, unlike water found in natural bodies. So, you shouldn't see noticeable galvanic corrosion.

You will see regular corrosion/oxidation, but a sacrificial anode won't stop that.

 

[pcmeiners]

I put anodes on my tanks, off a tee on the drain; marine supply has 1/2 threaded or larger anodes designed to fit in pipe.
Disagree the water from the tank is pure, it is far from pure, and conductive, containing absorbed CO2, NO, SO2 etc. from the air, as does acid rain, resulting in PH levels <6.

http://www.glaston.com/what-is-compressed-air-condensate-and-why-must-it-be-treated/

Threaded anode example....

http://www.boatzincs.com/engine-sizes.html?gclid=CPrh2LusztECFd1XDQodFEgPnw

 

[wssix99]

Disagree the water from the tank is pure, it is far from pure, and conductive, containing absorbed CO2, NO, SO2 etc. from the air, as does acid rain, resulting in PH levels <6.

That's fair. I would not want to take a drink of the water draining from my compressors. It would surprise me the water in a residential/light commercial compressor is as conductive as lake or salt water.

I'm not an expert in galvanic corrosion (maybe we need the OP to complete their homework!!!) but I recall that an electrical pathway is also needed.

If the water in a compressor tank were conductive, I would think that:
- The electrical pathway between the charged tank and the earthen ground would be disrupted by the rubber pads/feet.
- Without any rubber pads/feet, the electrical pathway for any electrical potential between the tank and earth would go from the tank to the feet to the ground and would not pass through the electrolyte, which would promote the galvanic reaction.

^ A boat is different because the electrolyte envelops the hull and is between the electrically charged structure and the earth.

 

[tcianci]

Hey, it just might be that compressor tanks last for several decades with moderate care and no anodes that may or may not be in contact with water that may or may not have the correct composition to be an electrolyte.

Although I, like many others here want to get the longest service life from my tools and equipment, there seems to be an underlying train of thought on this website that once we buy something, we are going to (with nothing but backyard engineering in most cases) "improve" on all the deficiencies that those idiot engineers didn't think of so that our new (insert your item here) will last forever.
It's a quest where you reach the point of diminishing returns (or worse) on short order.

Maybe GJ needs a whole forum section devoted to critical thinking.

 

[ChaseDE]

Well yes and no, planned and perceived obsolescence is a real thing, to what degree they factor into something like compressor design engineering we don't know, but usually there are ways to improve existing designs.

You are right though, sometimes the view is not worth the climb.

 

[Movover]

It wont work like it does in a hot water tank or a ship. In order for the sacrificial anode to work, it must be submerged in water, something we are trying to prevent in a air compressor. The better and easier option would be to line the tanks with porcelain, glass, epoxy or something similar.

Hmmmmm how hard would it be to do an epoxy coat on a new compressor? what about the stuff that is used to line gas tanks? Maybe this could add years to a compressor. Of course draining it like you are supposed to would also work

 

[Abeo]

Having an aftercooler with a water trap after would be better IMO than a passive cathodic protection system. You would greatly reduce the moisture going in the tank by dropping the dewpoint, while providing cleaner air to your tools. Eliminate the electrolyte = no corrosion. Also, with steel, you end up with lots of small cathode/anode cells just by the variance in the steel properties, so while the anode would help, there is no guarantee it will stop it. Never mind about MIC....

Also.... it doesn't really get all that humid in Calgary, even in the summer. I just drained my 60 gal for the first time in about 4 months, and got less than 200 ml out of it (this was after using the compressor to paint my truck).

 

[chaosracing]

Hmmmmm how hard would it be to do an epoxy coat on a new compressor? what about the stuff that is used to line gas tanks? Maybe this could add years to a compressor. Of course draining it like you are supposed to would also work

Its actually very simple (if you have proper tools) There is a guy on youtube that did one. It was actually scaled bad on the inside. He stripped everything off the tank, put some gravel inside. He used a lathe or something similar to spin the tank slowly and the scale was removed. He cleaned it. Water tested for pressure. Then after drying, dumped the epoxy inside, closed it again and to it for a spin.

There is no reason why the manufacturers do not do this now. Except to make something that needs to be replaced down the road.

 

[chaosracing]

Found it.

 

[pcmeiners]

"It would surprise me the water in a residential/light commercial compressor is as conductive as lake or salt water."
More conductive then lake water less then salt water.

"If the water in a compressor tank were conductive, I would think that:
- The electrical pathway between the charged tank and the earthen ground would be disrupted by the rubber pads/feet."
Catholic protection has nothing to do with an earthen ground path in this scenario.

"- Without any rubber pads/feet, the electrical pathway for any electrical potential between the tank and earth would go from the tank to the feet to the ground and would not pass through the electrolyte, which would promote the galvanic reaction."
Again a path to ground, or potential to ground, or rubber feet have nothing to do with providing cathodic protection in this case.

With an anode attached to the tank, the potential is between the oxidizing area (rust) and the anode.

 

[Rickss96]

“the anode and cathode must be connected by a metallic path..." and it must be an electrically
conductive path too. There are very small voltage potentials that cause this protection scheme to work, so I would expect you need a low resistance connection from the anode to the rest of the metal vessel. Hi resistance will reduce the current flow and hence the protection. This would be a good question for your instructor and class mates.
So if you need a low resistance connection between you added anode and rest of the vessel, using any old epoxy may not work well as it can be a poor conductor. I believe there are conductive epoxies around, someone here on GJ probably knows about this. There are conductive greases available for use in electrical assemblies/threaded connections too. Poke around an electrical supply shop for more info.

Best bet is to go with what the marine industry uses. They’ve been dealing with this problem for a long time. The threaded anode example, above, uses a brass pipe plug which is conductive.

 

[wssix99]

Of course draining it like you are supposed to would also work

Are you CRAZY??? That would involve reading the instructions.

 

[pcmeiners]

"Are you CRAZY??? That would involve reading the instructions."

Ease up, we all know real men don't need no f*king instructions. Instructions are only to be read in a hospital room after the accident (Man Card manual page 102, paragraph 3).

 

[Strouty]

Found it.

While that is neat, it is not the proper way to hydrotest anything. There is also the expansion factor of the material that comes into play based on the stress of the internal pressure. A true hydrotest allows for measuring the expansion so you know if the metal itself is an issue. I would however do the spinning with the gravel and then the epoxy, that is the neat part. I cleaned the **** out of my tank, then pressure washed it with hot water. I was going to try and paint it or put some sort of oil inside, but I decided that if I missed any spot at all, that area would rust faster than anywhere else and the tank would likely fail quicker. I did use an ultrasonic thickness gauge to see how close the steel was to the factory specs.

 

[yyc_ranger_4x4]

I've passed the idea over with the instructors, and I'm meeting with an engineer next week for work projects so I'll see what he says.

I have access to small diameter magnesium rod that could be used as an anode. Pressing it into a 1/8-1/4-3/8" npt steel plug for proper conductivity to the tank would not be an issue at all. My only issue is going to be getting another tapped hole in the bottom of the tank....(no, I'm not doing this myself)

Here's something for people to ponder. Steel will act as an anode to copper and brass. It's higher in the galvanic tables and hence will actually sacrifice to protect copper and brass. While the surface area of steel is much higher than that of any copper or brass within a compressor tank, especially those that are in contact with any electrolyte (water), this could be a determining factor in the premature deterioration of a steel tank. We have been discussing this regarding copper clad ground bars...if there is an scratch on the copper and the steel is exposed, the steel will sacrifice to protect the copper and you wind up with a ground rod that will fall apart.

Talking with one of our instructors who holds a few certifications with coatings, he likes the idea of the epoxy coating, but warns that any imperfection or holiday within the coating will make the corrosion more pronounced as it makes the surface area very small. Areas around bungs, drains, and any other fitting would be a suspect area. He definitely will be looking into this when he has time as he can't say there has been any work in this area as he knows.

 

[MikeF2316]

Hey, it just might be that compressor tanks last for several decades with moderate care and no anodes that may or may not be in contact with water that may or may not have the correct composition to be an electrolyte.

Although I, like many others here want to get the longest service life from my tools and equipment, there seems to be an underlying train of thought on this website that once we buy something, we are going to (with nothing but backyard engineering in most cases) "improve" on all the deficiencies that those idiot engineers didn't think of so that our new (insert your item here) will last forever.
It's a quest where you reach the point of diminishing returns (or worse) on short order.

Maybe GJ needs a whole forum section devoted to critical thinking.

Well, in some cases things are well engineered, and well built. In other cases, things are built to a price. These other cases are often where the "home engineer" can improve on them. I'd put cheap air compressors into this latter category.

Although I don't think gavanic protection is the way to go. I'd bet that a good cleaning with a suitable solvent followed by a pint of Tremclad sloshed around on the bottom when the tank is new would be the way to go.

 

[chaosracing]

Here is something else to consider. Sacrificial anode rods are a maintenance item. Meaning that someone would have to replace them. I have replaced water heaters and know of several others that have been replaced due to the anodes not being replaced.

In my opinion, the better solution would be to glass line the tanks and the manuf. should install an auto operating drain valve. But like I said before, if they were to do that, that would lead to less sales in the future for them.

 

[38Chevy454]

I am a metallurgical engr and have done some work with corrosion protection. Not for compressor tanks, but similar principles apply. I'll add my $.02 for the discussion.

While your idea has merit, the difficulty is as some suggested, it needs electrolyte (water) to be effective. Corrosion is nothing more than an electrical circuit, driven by the oxidation chemical reaction: Metal --> Metal (positive ion) plus electron. That electron has to go somewhere, and that is the role of the electrolyte, which for most all corrosion scenarios is water. Good thing is water is generally low conductance vs salt water or other liquids. Assuming you drain your compressor frequently enough, the sacrificial anode becomes negligible. You will still get a small amount of general corrosion of the tank since the steel itself sets up the small cells within the surface. Also the anode has protection that is sort of like a magnetic field, it gets weaker the farther away from the sacrificial material itself.

As your professor and some replies here stated, a coating is only as good as no break in the coating. This is the main reason why auto companies have gone to zinc coated steel for much of the vehicle body. The underlying zinc protects once the coating has a break through.

I think the compressor tank mfrs could put an anode, and it certainly can't hurt. But regular draining of the tank is going to benefit more. Plus tanks are made to a price level and not for ultimate life. They basically use thick enough steel there is substantial safety factor to account for some corrosion of the steel. For ultimate durability, the tank could be made from galvanized steel and then coated. Then put an anode at the low point, and have an auto drain to keep water build-up to minimum.

 

[borisdavenport]

what about an insulation coating inside the tank? I believe a think insulative coating (with good dielectric properties ) can prevent the reaction inside the tank.
Once solved a similar issue related to a boiler. www.automaticcoating.com these guys helped us. Another option for you is an epoxy coating, The coating thickness will count the dielectric strength.

 

[38Chevy454]

what about an insulation coating inside the tank? I believe a think insulative coating (with good dielectric properties ) can prevent the reaction inside the tank.
Once solved a similar issue related to a boiler. www.automaticcoating.com these guys help us. Another option for you is an epoxy coating, The coating thickness will count the dielectric strength.

Almost any coating (paint, epoxy, or similar organic type product) will be insulating. But again the coating is only as good as no breaks or holes in the coating. Multiple coats is better than a single thicker layer as the probability of a break/hole is reduced with multiple coats.

You would not want to use a coating with metallic particles, unless the coating specifically had an anodic metal that was intended to act like a sacrificial coating. Such as an aluminum-containing paint. But the problem is having a continuous conduction path from the metal particles through the coating matrix (the enamel, epoxy, polyurethane, latex, etc). So this is not as effective as it may appear. The chromate-containing paints are effective, but not because of the anodic/sacrifical aspects. They work because the chromates help lower the surface electropotential. Chromates are getting harder to buy since the most effective version are hexavalent chromate, and that is carcinogenic. Most used now is trivalent chromate.

 

[pcmeiners]

"My only issue is going to be getting another tapped hole in the bottom of the tank...."

No need for another tap. From your present drain plug, add street elbow, close ******, a tee (1/2"). On one end of remaining tee outlets, add a close ******, reducer, from 1/2" to 3/4" (female), add 3-4" 3/4"******, another reducer, them screw the threaded anode (linked in my previous post) into ****** assembly. You need the reducers to increase 3-4" ****** diameter to 3/4" to fit anode diameter . Other side of tee used for drain valve or auto drain. Even if tank is drained, a thin film of water remains to create a circuit; anode still sits in water if tank is drain due to 3/4" ****** assembly. Compressor water is always acid on the PH scale due to sulfuric/nitric oxides and other pollutants in the air, thus adding to conducting ability; granted, it would be better with the anode full submerged but that is the limitation of this scenario, unless your tank has a 3/4" drain tap, I doubt it.
Actually they make smaller diameter threaded anodes which would be easier to plumb, you might get one small enough to insert through average drain plug. They would need to be replaced more often. 3/8" would likely do it, requiring a close ******, one tee, the anode and a drain setup off the remaining tee port; anode would actually stick up into the tank.

http://www.starmarinedepot.com/b&s-...omplete.html?gclid=CLnTgOm84tECFYWKswoddU4ORA

Anode with built in drain....
https://jet.com/product/detail/9518...2&code=PLA15&gclid=CIfDrpa_4tECFZiIswodrucMsg

" Sacrificial anode rods are a maintenance item."
How much effort is it to wrench out a threaded anode every 5 years to check it, perhaps 60 seconds to remove it, same amount to replace or reinstall.

To add....anyone thinking about coating the inside of a tank, best you make sure there are no solvents vapors above explosive limits once your finished or your compressor might explosively change street addresses, along with you.

 

[toplessHO]

Zinc. They are a dime a dozen in any marine supply store..

Sent from my SM-G900V using Tapatalk

new pennies are actually 12 cents a dozen

 

[6PTsocket]

new pennies are actually 12 cents a dozen

Cute, but you have failed reading comprehension. What I said is that you can purchase 12 of an item for 10 cents. I said nothing about buying pennies. If you were older, you would know that "dime a dozen" was a common expression for something that was very cheap. To be funny what you say has to have some logic to it