Stripping & painting AL Tanks

[WreckWriter]

I called them. They offer 2 finishes, just plain stripped "brushed" look, and the glossy look seen on their site. Turn-around time is 3-5 days. Cost is about $23 for the plain, about $29 for the glossy.

Tom

 

[wannabe]

Most painting (autobody) ovens don't get much above 140F because of concerns with CNG vehicles, fuel tank venting, and wrecking other stuff in the car that may not be high temperture friendly.

To start working with the temper of Al you will need to get to 300F+

With that said I would wait till a hydro was needed so if there was an issue from your dive shop about filling the tank the concerns would be squelched at that point.

 

[BlkPnthr]

I'm looking for links to sites that will provide information or information from members on in-expensive ways yet, effective ways to strip paint, prime and re-paint scuba tanks. The club I belong to is looking to "refresh" our rental tanks as the paint is peeling, have a few different colours and we'd like to standardize the colour. Anyone with information that they think could benifit us, we'd certainly appreciate it. We're dealing with both steel and Aluminum tanks.

Thank You

 

[Genesis]

is that both heat and mechanical removal (e.g. sandblasting) are prohibited.

This leaves chemical strippers.

As for repainting, aluminum is no fun. The trick is all in the primer, and good aluminum primers are VERY toxic. Be extremely careful not to get any INSIDE the tank!

I'd be looking at a two-part catalyzed topcoat paint if I was doing this. That stuff is not cheap, but its tough as nails. It also needs to be sprayed for good results, and most of these two-part paints contain isocyanates (BIGTIME toxic hazard - as in wear a pressure-fed moonsuit!) No single-part paint is going to hold up as well.

You might want to talk to someone who paints aluminum and steel boats (not bottom paint - topsides refinishing) - you might even be able to get them to spray your tanks with the "leftovers" from a boat job at a MAJOR cost savings.

 

[Dee]

They won't be pretty very long. Chemically strip the old paint off and to customize them, put a nice club sticker on them.

• You won't be looking at chipped paint again in a few months.
• With no paint, you can always tell the condition of your tank.
• The most you'll have to do to keep them looking nice is replace the club stickers.
• It's lots cheaper and less work!

 

[FredT]

"Bead blast" aluminum tanks with walnut shell media or ground corn cob. This will remove the paint, polish the exterior of the tank, and take little effort. If all else fails use a timed aircraft paint stripper, but this is expensive if doing a bunch of them. Walnut shell in a media recycling bead blasting booth is about the best bet $ and time wise. If using regular abrasive use a glass or silica free "slag" media of about 160 grit, and move fast. Black Beauty is a good media for blasting aluminum, but it cuts fairly fast if you dwell on a single spot AT ALL! 160 grit at about 90psi nozzle pressure and 8" nozzle separation will turn the surface to a nice satin finish fairly quickly. Blasting on a tumbler eliminates handling time and speeds up the process considerably. As Dee said, aluminums are best left bare and unbooted. When blasting use an OLD valve to protect the seal areas. It won't survive the process in useable condition.

For steel tanks the same methods will work, but finish topcoat with ZRC where ever the galvanizing is missing or damaged. I would avoid the Black Beauty and/or power brushing any tank that may have an intact galvanizing coating under the finish.


Dee is right with sticker idea. For semi-permanent ownership marking on either type use a laquer based coating and stencil. Permanent markings are best applied to the VALVE with metal stamps. (Misc stamps into the tank can annoy DOT/TC unless done in specific places and limited stamp depth.)

FT

 

[Genesis]

is it kosher to use a physical removal technique (e.g. sandblasting) on tanks? I know that heat is absolutely verboten, but I had heard that sandblasting was a "no go" as well as it would void the existing hydro (and require a retest after being complete.)

 

[FredT]

Genesis once bubbled...
is it kosher to use a physical removal technique (e.g. sandblasting) on tanks? I know that heat is absolutely verboten, but I had heard that sandblasting was a "no go" as well as it would void the existing hydro (and require a retest after being complete.)

Correct. Agressive sand blasting can erode material to a thickness less than minimum wall very quickly in a manner that can't be picked up on a visual. The media I suggested however are either softer than the metals being blasted, so they VERY non-agressive to the pressure vessel wall, or are so fine the cut rate is negligable. All will carry enough energy to remove paint, especially paint that is already experiencing adhesion failures. I've used the fine Black Beauty on VERY thin wall aluminum buoy hulls to prep the surface for re-application of a Mare Island Epoxy paint system. The trick there is to have a very fine abrasive particle and medium to low air pressure. 160 mesh will have a particle size smaller than .006" with most of it below 0.003". It looks like dust, and can clog a baghouse filter in a hurry. Media this size is effectively not reuseable, and it takes a lot to do a tank. Walnut shell will have a particle size about .06 to .1", with ground corn cob about twice that. Since both walnut and corn cob are re-useable the net abrasive material cost for doing a batch of tanks starts to get reasonable if doing more than about 6 tanks. The "polished" look either walnut or cob will give to the tank is a plus if doing the refinish for cosmetic reasons. Dry ice is another good paint removal blast medium that won't damage the base metal, but the investment necessary to do that one is $ignificant. Fine particle size Calcium Carbonate (limestone) media is also a realistic option.

My personal opinion is that the time to do tank exterior cleaning is when the bottle is due for hydro and a complete valve overhaul. It should also be done before the hydro. This allows for a good pre-hydro visual to be completed. That way you can cull a bad tank from the lot ealrly in the process. If there is external corrosion on a tank bad enough that it requires an immediate refinish an "extra" hydro may be a good idea anyway. If the tanks are just "ratty looking" on the outside with no visible exterior corrosion I'd probably let them ride to the next rebuild date.

FT

 

[Genesis]

for the clarification - that's what I thought...

 

[GP]

Fred, I have an OMS/Faber steel tank that has corrosion on the boot area of the tank. What's the best method to remove the corrosion? Should I hand sand it down and coat with ZRC and repaint? The tank is due for a vis and hydro next April. Just wondering if I can save this tank or not at this point.