Here's how to strip aluminum tanks...

[halocline]

The paint stripper does attack old galvanizing, I know that for a fact, but it's much slower and less damaging to the galvanizing than to the paint. When I stripped my 72s, all the paint came off and a tiny bit of the galvanized surface in spots. I roughed it up with some fine sandpaper and sprayed a couple of coats of ZRC galvilite cold galvanizing compound. Worked great.

 

[Eric Sedletzky]

You could take it one step further and polish those aluminum tanks out.
See my avatar pic of the polished aluminum tank.





<--------

 

[Culcuhain]

That is a pretty tank.... how long did it take you to polish it out?

 

[davetowz]

I would be afraid to dive a tank I spent that much time on! Pretty though!

 

[Eric Sedletzky]

That is a pretty tank.... how long did it take you to polish it out?

It's about a three hour process start to finish.
It's very similar to polishing out aluminum wheels or fuel tanks on big rigs.

 

[spectrum]

It's about a three hour process start to finish.
It's very similar to polishing out aluminum wheels or fuel tanks on big rigs.

Eric,

Did you do the polish job with one that had been corroded under the paint like #1 from the original poster? I have 2 like that that I striped the same way a few years ago. The depth of the etch where salt was trapped below loose paint would require a risky amount of metal removal to clear and blend.

I see the OP used plastic scrapers. When I did mine I found that the plastic blade soon wore to the radius of the cylinder OD and then it really worked well.

If a paint finish isn't a perfect encasement you are better off without it.

Pete

 

[Eric Sedletzky]

Eric,

Did you do the polish job with one that had been corroded under the paint like #1 from the original poster? I have 2 like that that I striped the same way a few years ago. The depth of the etch where salt was trapped below loose paint would require a risky amount of metal removal to clear and blend.

I see the OP used plastic scrapers. When I did mine I found that the plastic blade soon wore to the radius of the cylinder OD and then it really worked well.

If a paint finish isn't a perfect encasement you are better off without it.

Pete

Yes I have sanded and polished aluminum tanks that where that bad or worse. That's what started the whole tank polishing thing. It was either that or repaint them.

In my opinion you are better off with a bare aluminum tank then one that is painted. White rust can develop under paint and creep underneath causing a blister, but what's worse is that blister containing zinc oxide will hold salt water and then you will get deep pits before you even know how bad they are. At least with bare aluminum you can rinse it and see what's going on.
If you think about it, the tank is only as strong as it's thinnest spot so if you sand down around the area of a pit then the tank is still fine, just don't go past the depth of the pit.
When I used to have aluminum tanks the first thing I did when I got them home was sand off all the paint with an orbital sander first with 80 grit to quickly rip off the paint, then follow that up with 240 grit, then go over it with 400 grit then polish.
When I was done you could still see some of the factory texture lines in the surface of the tank so I knew I was nowhere near compromising the integrity of the tank. You'd be surprised how thick those tanks are and how much you actually have to work with.
If there's ever a question then sand and polish a tank that's trashed and up for hydro. After it's all pimped out send it in and if it passes you'll know there's nothing to worry about.

Polished tanks hold up better than any other surface because water just beads off and salt has nowhere to bite in.
Chlorine on the other hand trashes them and they come out dull after a soak in a clorinated pool. I used to have to go over them with hand polish (Zephyr Pro 40) to bring them back up after doing DM stuff in a public pool.

Here's link to the system I use for all my metal polishing:
https://www.zephyrpro40.com/s2/Scripts/default.asp

 

[Codiak]

Anyone tried to get a tanks exterior anodized?

 

[Gilldiver]

Anyone tried to get a tanks exterior anodized?

,
There have been a few. The only anodize I would recommend for tanks is MIL-S-8625 Type IIB, thin film sulfuric. But that is because I would on aircraft and have to worry about high cycle fatigue debits cause by the anodize coating.

In the real world, aluminum 6061 is very corrosion resistant and as long as you rinse and let dry fully, that means no web straps from a BC to hold water on the metal, it will go to a medium grey and eventually seal itself. If you feel that you need to paint a tank, then forget the paints used by the tank manufacturers, I have never seen a factory paint job that will last more then a few years. Also, NEVER use a powder coat that needs to be baked above 225F, the bake will destroy the heat treat condition of the tank and could make it into a bomb.

Instead use a catalyzed epoxy primer for aluminum and a catalyzed polyurethane top coat. The standard US NAVY system for aluminum aircraft is Primer: MIL-PRF-23377 or MIL-PRF-85582 with a topcoat of polyurethane MIL-PRF-85285.

These paints hold up well but can be very hard to strip at a later date, especially the primers. Compared to helicopters sitting on a flight deck of a Marine amphibious ship, where they get bathed in salt spray and acidic stack gasses, the life of an aluminum SCUBA tank is very pampered.

 

[Eric Sedletzky]

,
There have been a few. The only anodize I would recommend for tanks is MIL-S-8625 Type IIB, thin film sulfuric. But that is because I would on aircraft and have to worry about high cycle fatigue debits cause by the anodize coating.

In the real world, aluminum 6061 is very corrosion resistant and as long as you rinse and let dry fully, that means no web straps from a BC to hold water on the metal, it will go to a medium grey and eventually seal itself. If you feel that you need to paint a tank, then forget the paints used by the tank manufacturers, I have never seen a factory paint job that will last more then a few years. Also, NEVER use a powder coat that needs to be baked above 225F, the bake will destroy the heat treat condition of the tank and could make it into a bomb.

Instead use a catalyzed epoxy primer for aluminum and a catalyzed polyurethane top coat. The standard US NAVY system for aluminum aircraft is Primer: MIL-PRF-23377 or MIL-PRF-85582 with a topcoat of polyurethane MIL-PRF-85285.

These paints hold up well but can be very hard to strip at a later date, especially the primers. Compared to helicopters sitting on a flight deck of a Marine amphibious ship, where they get bathed in salt spray and acidic stack gasses, the life of an aluminum SCUBA tank is very pampered.

The way I understand it is that 6061 is harder than say 5052 because of a higher silicon content but not necessarily more corrosion resistant.
Aluminum is a horrible metal to try and protect from corrosion.
I have gone to using an epoxy primer/topcoat made by DuPont called Corlar 25P. It's basically like sprayable JB weld.
It's a two part 1:1 part A/ part B material available in limited colors or grey, white, or black. It can be used as a primer or singular as a final coat. However like all epoxy materials it is not UV proof and will chalk out quickly when exposed to UV.
It is designed for immersion service meaning it can be submerged in water indefinitely and will not be subject to water penetration via osmosis.
I use it on white clean sand blasted steel with excellent results but will not use it on Aluminum because it would be like powder coat, one tiny nick and water will creep under and cause a white rust blister. At least with steel you can see the red start up and can do something about it before it becomes problem.