Stripping & painting AL Tanks

[nativenarcosis]

I am setting up a doubles rig using my AL80s. One was already aluminum finish but the other was painted. I of course being the aesthetic beast I am wanted them matching. I then stripped the paint off using paint stripper from Home Despot and finished it off with my DA sander and 400 grit sandpaper. Well, much to my dismay I took my newly finished tank in for a viz and the shop frowned on the process I used to stripped the paint off. Stated that it could have weakened the aluminum. Well.. me not being a metalurgist am coming to the higher power of the board to find out if this is indeed true.. or a farce.
I am thanking you in advance for the help I know I will receive from all you giants of knowledge!!

 

[Curt Bowen]

I am setting up a doubles rig using my AL80s. One was already aluminum finish but the other was painted. I of course being the aesthetic beast I am wanted them matching. I then stripped the paint off using paint stripper from Home Despot and finished it off with my DA sander and 400 grit sandpaper. Well, much to my dismay I took my newly finished tank in for a viz and the shop frowned on the process I used to stripped the paint off. Stated that it could have weakened the aluminum. Well.. me not being a metalurgist am coming to the higher power of the board to find out if this is indeed true.. or a farce.
I am thanking you in advance for the help I know I will receive from all you giants of knowledge!!

I have sand blasted a couple AL tanks in the past, seemed to work fine

 

[cyklon_300]

after stripping an Al80 with Aircraft Stripper and then HAND finishing with 600# wet/dry was this...

The shop threw a hissy, questioned me at length about the procedures I used, and demanded a hydro. No big deal, just do it and fill it.

To satisfy my curiousity, I called Luxfer directly and spoke to a technical specialist. He stated that as long as the paint was removed 'without power tools' and passed inspection, it was good to go. Mine passed and I've had it filled at least 125 times since.

Depending on how you used the sander and what kind of temperatures were generated in the process is the key to whether you made a garden gong or not.

 

[Drew Sailbum]

If you generate sufficient heat, you will change the metallurgy of the cylinder and it is no longer capable of holding up to the high pressures fo scuba service. I would tend to assume that a power sander would be capable of generating sufficient heat in localized spots to make a cylinder suspect.

Generally, if you used a power sander to strip a coating, I would not pass the cylinder on visual inspection.

 

[nativenarcosis]

If you generate sufficient heat, you will change the metallurgy of the cylinder and it is no longer capable of holding up to the high pressures fo scuba service. I would tend to assume that a power sander would be capable of generating sufficient heat in localized spots to make a cylinder suspect.

Generally, if you used a power sander to strip a coating, I would not pass the cylinder on visual inspection.

This is a pneumatic dual action sander that I use on the fiberglass on my Corvette. Heat is definately not a problem so I should be in the clear..

 

[Drew Sailbum]

This is a pneumatic dual action sander that I use on the fiberglass on my Corvette. Heat is definately not a problem so I should be in the clear..

As the visual inspector, I cannot tell what means were used to strip any coating. I can usually see tell-tale marks which come from a power sander.
You don't have to remove much metal to condemn a cylinder. In a typical 3AL cylinder, the removal of greater than .030 inches of metal in any one spot is enough to condemn the cylinder. If a cylinder was sanded and metal was removed, it may be difficult to determine where the original baseline was to measure pit depth.

 

[cra2]

I just got a couple of used aluminum 80's.
A) how do I clean 'em up - get all the stickers, scuffs off, etc?
B) can I paint them? If so, how?

Thanks,
cra2

 

[DA Aquamaster]

Old VIP stickers come off with a little heat. The key word here is "little. Use a hair dryer, not a heat gun, as a heat gun is too much heat and anything over 325-350 degrees is bad news for the heat treated alloys used in aluminum scuba tanks.

A razor blade can also be used to remove stickers with some 409 or WD40 to remove the remaining goo.

Painting is possible but surface prep is important. You do not want to use power tools to strip the old paint as it can generate excessive heat. You also want to use a stripper that is compatible with aluminum. Soda based strippers used for aircraft repainting are ideal.

Painting itself requires an appropriate self etching primer and preferably a two part paint such as imron or MTK that is fairly resistant to scrapes and dings. That type of paint will require the use of a suitable paint gun. There may be some paints out there in a spray can that hold up well, but I have yet to encounter one. A mild scuff sanding can help adhesion but mild is the key word as you do not want to introduce scatches that will reduce the strenght of the tank.

You also under no circumstances want to heat treat the paint as the temps involved can weaken the tank.

Be advised that newly painted Al tanks make dive shops nervous as more than one tank has exlpoded after the paint was baked in a paint boot. They will require a description of how you repainted the tank at a minimum and at worst may require a fresh hydro test in addiiton to a VIP. It's a good idea to talk to your LDS of choice about your plans first and maybe get their suggestions. You then will have a better chance of convicing them that you did not do something stupid with the tank once it is painted.

I have often considered just using a preparation like Zing on a tank to clean and brighten up an old aluminum tank. It works great on aluminum boat hulls but boat hulls contain very little pressure and I have never heard whether the acids in the Zing preparation could potentially weaken the walls of the tank.

 

[Former FLL Now MSP Diver]

Found a place nearby that will do them for me at about $25. http://www.hydrostat.com/hydrostat.htm

May just do that to save the effort!

Tom

Tom - did you ever get your tanks done there? How'd they turn out?

Marc

 

[nativenarcosis]

After doing my AL80s.. My recommendation is this:
Chemical strip (keeps the viz guys happy. They don't like seeing roughed up tanks.) And then hit them with some Mother's polishing compound. What I figure if it is good enough for my Corvette's wheels it will suffice for my AL80s. They now look MARVEE. Pardon the vainess of having nice and shiney tanks but I cannot help it.