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View Full Version : How do I prep and aluminum tank for paint?



Judge
11-02-2007, 11:48
Used to painting cars and motorcycles...and do not want to mess up the certifications etc of the tank. Should I just scuff the factory color and shoot it with primer and paint? Do I need to have it stripped and then prime and paint(if I stip it...what do I use?)

Ohmdiver
11-02-2007, 12:10
umm, I was under the impression that only a factory finish was acceptable. Warranties and lawyers and such....

I may be wrong but I would look into it if I were you....

RoadRacer1978
11-02-2007, 12:42
Although some people do repaint there own tanks I think it is kind of a NO No to do it. I know for sure that you are not supposed to use any paint that requires to be baked on for aluminum tanks.


Heres a link that may give you some ideas.

Luxfer: Technical Bulletins: August 9, 2006 (http://www.luxfercylinders.com/support/bulletins/20070116usa.htm)

woody
11-02-2007, 12:47
Here is a artical about heat and Cylinders. At the end of it it has some painting recomendataions.
Luxfer: Care & Maintenance (http://www.luxfercylinders.com/support/maintenance/cm5.shtml)

Here is some info about preping a Cylinder.
Luxfer: Care & Maintenance (http://www.luxfercylinders.com/support/maintenance/cm4.shtml)

WaScubaDude
11-02-2007, 13:18
Let us know how it goes!

awap
11-02-2007, 13:39
Scuff it up real good (without removing any metal) and then dive it for 10 or 15 years. Then repeat. If you really have your heart set on painting them, talk to your supporting LDS first si they will not give you a hard time come VIS and hydro time. Shops are often suspicious about newly painted tanks.

It really is unnecessary.

Judge
11-02-2007, 20:36
Here is a artical about heat and Cylinders. At the end of it it has some painting recomendataions.
Luxfer: Care & Maintenance (http://www.luxfercylinders.com/support/maintenance/cm5.shtml)

Here is some info about preping a Cylinder.
Luxfer: Care & Maintenance (http://www.luxfercylinders.com/support/maintenance/cm4.shtml)

My painter is going to call that number in their site.

mm2002
11-16-2007, 12:49
(because I didn't know any better) I painted one of our tanks. I paint cars, so I figured what the hey. I scuffed it, then base/cleared it. It passed visual and hydro just fine. Truth is, I'm not sure they even knew it was repainted!:smiley36:
Am I bad?

in_cavediver
11-16-2007, 16:43
As someone who inspects tanks, I'd recommend against painting. For AL tanks, its not needed and causes only to raise questions for people who fill it, hydro it or may later want to buy it. Why go to the expense to complicate the tanks life later, especially since the tank will get scuffed again! I don't see the logic.

Personally, I'd never pass a re-painted Al tank on VIP. Someone else can look at it and decide but its a major red flag to me. (no, I am not an LDS either, don't do commercial VIP or charge so no vested interest in pass/fail).

BSea
11-16-2007, 17:27
Personally, I'd never pass a re-painted Al tank on VIP. Someone else can look at it and decide but its a major red flag to me. (no, I am not an LDS either, don't do commercial VIP or charge so no vested interest in pass/fail).
I'm not trying to be argumentative, but why wouldn't you pass a re-painted AL tank? Especially if it had passed a hydro since repainting. Is their something about a re-painted tank that is dangerous, and can't be detected by a VIP?

Personally, I have to agree with awap. Why paint them at all? I recently bought an old steel 72. It had never been painted, and had obviously been owned by at least 1 diver that was more than a vacation diver. But it had a recent hydro, & I got it cheap. So, it may not be pretty, but it does the job.

mm2002
11-16-2007, 17:38
I had a good reason to repaint mine...it was pink! :smiley11:

in_cavediver
11-17-2007, 06:46
Personally, I'd never pass a re-painted Al tank on VIP. Someone else can look at it and decide but its a major red flag to me. (no, I am not an LDS either, don't do commercial VIP or charge so no vested interest in pass/fail).
I'm not trying to be argumentative, but why wouldn't you pass a re-painted AL tank? Especially if it had passed a hydro since repainting. Is their something about a re-painted tank that is dangerous, and can't be detected by a VIP?

Simply answer is yes, there can be many things not detected by VIP that make a tank dangerous. As for the Hydro, the problem isn't the first one that the VIP tech know/coordinates, its the next VIP or the question of when the hydro was done vs the paint job.

Case in point, if I see a tank that was re-painted, I have no idea when it was done in relation to a hydro test. You don't stamp 'paint dates'. Your only option is to trust the owner who has a vested interest in having the tank pass. (otherwise its scrap with a fancy paint job)

As to issues for why a tank may be suspect by repainting - Excess metal removed during tank prep, localized heat issues from mechanical heating during the tank prep and heat from paint curing (baked paints).

I am not saying a tank can't be painted correctly, I am just saying a tank can be severely damaged during re-painting and a VIP can't detect the difference. I am personally not willing to sign off with my name for that. (I am sure someone else would though)

BSea
11-18-2007, 18:41
Personally, I'd never pass a re-painted Al tank on VIP. Someone else can look at it and decide but its a major red flag to me. (no, I am not an LDS either, don't do commercial VIP or charge so no vested interest in pass/fail).
I'm not trying to be argumentative, but why wouldn't you pass a re-painted AL tank? Especially if it had passed a hydro since repainting. Is their something about a re-painted tank that is dangerous, and can't be detected by a VIP?

Simply answer is yes, there can be many things not detected by VIP that make a tank dangerous. As for the Hydro, the problem isn't the first one that the VIP tech know/coordinates, its the next VIP or the question of when the hydro was done vs the paint jobCase in point, if I see a tank that was re-painted, I have no idea when it was done in relation to a hydro test. You don't stamp 'paint dates'. Your only option is to trust the owner who has a vested interest in having the tank pass. (otherwise its scrap with a fancy paint job)

As to issues for why a tank may be suspect by repainting - Excess metal removed during tank prep, localized heat issues from mechanical heating during the tank prep and heat from paint curing (baked paints).

I am not saying a tank can't be painted correctly, I am just saying a tank can be severely damaged during re-painting and a VIP can't detect the difference. I am personally not willing to sign off with my name for that. (I am sure someone else would though)

How would you be able to tell a factory job from a really good professional job? If you can't tell, then no painted tank should ever pass a VIP because there would be no sure way to tell.

Also, it seems that many painted tanks I've seen, you can easily tell the if the hydro was done after the painting because the stamp shows all the way to the metal. This wouldn't be the case for a tank painted after the hydro. That brings up the point of a new tank with a factory paint job. Aren't they all painted after the hydro?

I understand the problems associated with a heat cured tank, especially if it's been powder coated. But I've also seen many after market paint jobs on both AL & steel tanks. The owner of my LDS used to hydro tanks, and he has no problem filling painted tanks (AL or Steel). That's not to say he's right and you are wrong, but I'd hate to think anyone would scrap a good tank just because of the possibility of a problem when none existed.

I would say, that if in doubt, have the tank hydro'd.

mm2002
11-18-2007, 19:19
I don't know if this matters or not, but the tank I painted only had the original hydro stamp, and had never actually been used. It was basically NOS. By scuffing it with scotch brite, and refinishing it to a different color, I hardly think I compromised the integrity of the tank. The only thing I would consider an issue is that the tank was shipped to me with the valve off, so there could have been potential corrosion problems internally. Nobody knew how long the valve had been off, but I would certainly think that any issues would have been obvious with the visual.

Now, a 30 year old tank that was well used, had 5 or 6 hydro stamps, and repainted...yeah, that may throw up a red flag.

Puffer Fish
11-18-2007, 20:22
(because I didn't know any better) I painted one of our tanks. I paint cars, so I figured what the hey. I scuffed it, then base/cleared it. It passed visual and hydro just fine. Truth is, I'm not sure they even knew it was repainted!:smiley36:
Am I bad?
Well, yes you are, but it has nothing to do with painting a tank..:smilie39:

The chemical issue is a concern about hydrogen imbrittlement, the heat can change the hardness (and the brittleness) and obviously one can damage the tank with sand blasting, etc, etc. Don't do any of those things, and you are fine. A good urethane will not hurt the tank.

mm2002
11-18-2007, 20:50
Well, yes you are, but it has nothing to do with painting a tank..:smilie39:


Oh, now you sound like my wife! :smilie39:
Yes I agree, Urethane isn't a problem. Fortunately, most modern catalyzed finishes don't need to be baked. Sandblasting, of course, should be out of the question.

Soonerwink
11-18-2007, 21:12
I bought a 1992 AL80 tank off of ebay and sanded the paint off with a disc sander, then put 2 coats of paint on it. Took it to my LDS for hydro and VIP, passed with no questions. I did tell them what I did to it.

Flatliner
11-19-2007, 08:39
I just bought a well used steel 50 for my son. I am planning on painting it with a can of spray paint just to clean it up. Am I missing something. As long as I don't go down to bare metal when I prep it, what's the problem?

in_cavediver
11-19-2007, 11:05
Personally, I'd never pass a re-painted Al tank on VIP. Someone else can look at it and decide but its a major red flag to me. (no, I am not an LDS either, don't do commercial VIP or charge so no vested interest in pass/fail).
I'm not trying to be argumentative, but why wouldn't you pass a re-painted AL tank? Especially if it had passed a hydro since repainting. Is their something about a re-painted tank that is dangerous, and can't be detected by a VIP?

Simply answer is yes, there can be many things not detected by VIP that make a tank dangerous. As for the Hydro, the problem isn't the first one that the VIP tech know/coordinates, its the next VIP or the question of when the hydro was done vs the paint jobCase in point, if I see a tank that was re-painted, I have no idea when it was done in relation to a hydro test. You don't stamp 'paint dates'. Your only option is to trust the owner who has a vested interest in having the tank pass. (otherwise its scrap with a fancy paint job)

As to issues for why a tank may be suspect by repainting - Excess metal removed during tank prep, localized heat issues from mechanical heating during the tank prep and heat from paint curing (baked paints).

I am not saying a tank can't be painted correctly, I am just saying a tank can be severely damaged during re-painting and a VIP can't detect the difference. I am personally not willing to sign off with my name for that. (I am sure someone else would though)

How would you be able to tell a factory job from a really good professional job? If you can't tell, then no painted tank should ever pass a VIP because there would be no sure way to tell.

Also, it seems that many painted tanks I've seen, you can easily tell the if the hydro was done after the painting because the stamp shows all the way to the metal. This wouldn't be the case for a tank painted after the hydro. That brings up the point of a new tank with a factory paint job. Aren't they all painted after the hydro?

I understand the problems associated with a heat cured tank, especially if it's been powder coated. But I've also seen many after market paint jobs on both AL & steel tanks. The owner of my LDS used to hydro tanks, and he has no problem filling painted tanks (AL or Steel). That's not to say he's right and you are wrong, but I'd hate to think anyone would scrap a good tank just because of the possibility of a problem when none existed.

I would say, that if in doubt, have the tank hydro'd.

You are quite correct. A really good paint job would be hard pressed to tell from a factory paint job. As for the paint in the hydro marks, some hydro shops and some divers touch up the marks anyway. My point is for an obviously repainted tank, there are just so many ways in the re-painting process the heat treatment/metalurgy can be messed up that its not worth the risk to me sign off on it.

As I said, I won't touch them but I don't do it commercially, just for close diving friends and my own tank collection. For me, the risk/reward equation is just not worth it to deal with any tank that is in any way questionable. There are lots of others who would be happy to handle them.

CompuDude
11-19-2007, 12:04
Sand Blasting of Aluminum Cylinders - ScubaBoard (http://www.scubaboard.com/forums/tanks-valves-bands/203284-sand-blasting-aluminum-cylinders.html)

mm2002
11-21-2007, 10:32
I never thought about plastic or even walnut shell media. I know that would be safe.

PsychDiver
11-22-2007, 11:11
I have two al 80s that I was thinking about cleaning up with blasting to get all the old label glue off of them and for looks. Glad I read this forum. I do have a crushed walnut product that I use to tumble my 357 mag cartridges with to shine them up. I could use that to blast them with since it is much softer than al and wouldn't remove any metal. But I am pretty conservative so I may wait until I get more info. They still work even very ugly!

mcc2318
11-26-2007, 20:54
i thought that was a no no

rje634
11-26-2007, 21:10
Personally, I'd never pass a re-painted Al tank on VIP. Someone else can look at it and decide but its a major red flag to me. (no, I am not an LDS either, don't do commercial VIP or charge so no vested interest in pass/fail).
I'm not trying to be argumentative, but why wouldn't you pass a re-painted AL tank? Especially if it had passed a hydro since repainting. Is their something about a re-painted tank that is dangerous, and can't be detected by a VIP?

Personally, I have to agree with awap. Why paint them at all? I recently bought an old steel 72. It had never been painted, and had obviously been owned by at least 1 diver that was more than a vacation diver. But it had a recent hydro, & I got it cheap. So, it may not be pretty, but it does the job.
Because the LDS will have no idea wheter or not the painted finish was "baked on", which weakens the metal of the tank at a molecular level making the metal (aluminium or steel) brittle....

Judge
11-28-2007, 09:14
I had a good reason to repaint mine...it was pink! :smiley11:


The tank I picked up is too. As long as no heat is used and you do not shot peen it...there is no worries. If you are worried about removing aluminum: how much thinner do you thnk the area where they stamp it upon certification becomes? Look at your tank and see how deep they stamp it. The tank is being prepped.....pearl white with candy green flames comming from the valve down.

Puffer Fish
11-28-2007, 09:29
Personally, I'd never pass a re-painted Al tank on VIP. Someone else can look at it and decide but its a major red flag to me. (no, I am not an LDS either, don't do commercial VIP or charge so no vested interest in pass/fail).
I'm not trying to be argumentative, but why wouldn't you pass a re-painted AL tank? Especially if it had passed a hydro since repainting. Is their something about a re-painted tank that is dangerous, and can't be detected by a VIP?

Personally, I have to agree with awap. Why paint them at all? I recently bought an old steel 72. It had never been painted, and had obviously been owned by at least 1 diver that was more than a vacation diver. But it had a recent hydro, & I got it cheap. So, it may not be pretty, but it does the job.
Because the LDS will have no idea wheter or not the painted finish was "baked on", which weakens the metal of the tank at a molecular level making the metal (aluminium or steel) brittle....
How would any LDS know if a tank was repainted? Obviously, if the paint is still wet, or is in perfect condition on a 10 year old tank, but what if the finish was applied after the last hydro/inspection, and has at least a years worth of wear? Faber tanks, by the way, come with a high bake, powder coating on them... which cures around the 400 degree level...

CompuDude
11-28-2007, 13:12
How would any LDS know if a tank was repainted? Obviously, if the paint is still wet, or is in perfect condition on a 10 year old tank, but what if the finish was applied after the last hydro/inspection, and has at least a years worth of wear? Faber tanks, by the way, come with a high bake, powder coating on them... which cures around the 400 degree level...

That bake is done at a specific point in the manuf. process, however... I certainly would hope no one tries to duplicate a factory finish by baking their tanks!

Puffer Fish
11-28-2007, 13:27
How would any LDS know if a tank was repainted? Obviously, if the paint is still wet, or is in perfect condition on a 10 year old tank, but what if the finish was applied after the last hydro/inspection, and has at least a years worth of wear? Faber tanks, by the way, come with a high bake, powder coating on them... which cures around the 400 degree level...

That bake is done at a specific point in the manuf. process, however... I certainly would hope no one tries to duplicate a factory finish by baking their tanks!
How many would you like???

And it is done on Faber after the hydro...

Actually, that is a major issue with Aluminum, but not so much with steel. I have not looked at Chrome Moly precipation hardening rules, but I'm betting it would be safe to do, if done correctly. But steel tanks are made from a lot of other alloy's.

I would worry more about doing chemical stripping on either tanks, and the potential for hydrogen embrittlement issues.

I have powder coated a few million cylinders (no Dive ones) and it is technically possible to cure high temperature powder without heating up the object (oil filters are coated, for example, after assembly, and the high heat would damage the paper.

Us mfg engineers can be quite crafty.

mm2002
11-29-2007, 10:10
it is technically possible to cure high temperature powder without heating up the object (oil filters are coated, for example, after assembly, and the high heat would damage the paper.

Us mfg engineers can be quite crafty.


Care to go into a little more detail about that process? Interesting.

Judge
11-29-2007, 10:20
it is technically possible to cure high temperature powder without heating up the object (oil filters are coated, for example, after assembly, and the high heat would damage the paper.

Us mfg engineers can be quite crafty.


Care to go into a little more detail about that process? Interesting.


IR lighting is one...the powder gets baked...the stuff under it hardley gets warm

mm2002
11-29-2007, 10:32
I can't imagine getting the powder to 400 without heating the substrate. I use IR for spot curing automotive finishes, and the metal gets very hot. They must use a very intense heat with a very short duration, no?

Puffer Fish
11-29-2007, 11:03
it is technically possible to cure high temperature powder without heating up the object (oil filters are coated, for example, after assembly, and the high heat would damage the paper.

Us mfg engineers can be quite crafty.


Care to go into a little more detail about that process? Interesting.


IR lighting is one...the powder gets baked...the stuff under it hardley gets warm

You obviously know... have done engine blocks for Ford trucks that way... as heating up an engine block would take a ton of energy, and not cool for days.

UV cured powder is also available now (not in retail stores), and while the curing is UV, the lights make as much heat as any IR system would.. but the product cures in seconds... again, no heating of the product.

The fastest I have ever seen done is the oil filters for IR, with an exposure time of under 10 seconds...

Puffer Fish
11-29-2007, 11:06
I can't imagine getting the powder to 400 without heating the substrate. I use IR for spot curing automotive finishes, and the metal gets very hot. They must use a very intense heat with a very short duration, no?

The typical installation for high speed IR uses the ceramic tiles like used on the space shuttle, with holes thru it, and air blowing on the IR tubes (most of the tubes, by the way, are made outside of atlanta we use here). Their surface temperature is well over 2,000 degrees, and without the cooling, would melt the high temperature borosilicated glass.

mm2002
11-29-2007, 14:36
Interesting indeed!

mpd525
11-29-2007, 17:49
wow, now i feel stupid.

Puffer Fish
11-29-2007, 18:00
wow, now i feel stupid.
Why would you say that??? Knowing Avogadro's number, for example, does not make one person smarter or another person stupider...just people involved in different things.

Judge
11-29-2007, 23:56
wow, now i feel stupid.


Don't, I work in the auto industry so I deal with this stuff all the time. Also TIG, MIG and stick welding too.....so knowing metal properties is part of the job.