Letter 25363

Steel and aluminum scuba tanks need refinishing   +++ I have one steel air scuba tank, and one aluminum air tank. I want to refinish them to make them look new again. The steel tank has 3 coats of paint on it. The aluminum has the original coat of paint on it. I will be getting a hydro test done prior to the paint, but I want to know how I can safely remove the existing finishes and prepare it, and paint it. I want to know what types of processes & products I can use. I also understand that there is a "shrink wrap" process and would appreciate any assistance that you can provide on this. Thank you for any assistance that you can provide. John Koster N/A - Bright's Grove, Ontario, Canada In general, you shouldn't try refinishing scuba tanks. The steel tank has a heavy galvanized (zinc) coating that is relatively impervious to scratches and nicks, but almost any non-engineered process to remove the paint will likely damage that coating, either chemically or mechanically. The aluminum tank was factory-finished, either powder-coated in a temperature-controlled or UV-cure process, or with a low-temperature air-cured coating. You'll play h3ll getting the coating off. You won't have a galvanized undercoating to damage, but the aluminum may be surface-passivated to limit surface corrosion, and you could damage that passivation. One issue specific to aluminum tanks -- ANY uncontrolled finishing process involving heat CAN create localized hot-spots on a tank that can significantly weaken the aluminum, and tank explosions have occurred with aluminum tanks that were powder-coated in a back-alley shop and cured improperly. In EITHER case, the recommendation in the dive industry is to never refinish tanks, because the processes involved in refinishing may not be controlled well enough to prevent damage to the tank. Most divers consider the "beauty marks" on their tanks to be signs of experience and honor, and while we do try not to bang our tanks around, we don't sweat the fact that when a tank has 300 dives on it, it won't ever look new again. If you want to change the tank's color, get a few cans of Krylon and prep the tanks with a water-based cleaner and some 400-grit wet-or-dry sandpaper, and spray away. It'll last about one dive before you get your first scratch. You may want to consider getting a tank wrap -- one style is 1/16" nylon-coated neoprene, and it's available in lots of colors. Or ... you can research DOT regulations on pressure vessels and see what they say about refinishing. Jim Strohm scuba instructor - Austin, Texas

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