Aluminum tank finishes

[dvrgaryc]

I work full-time in a dive store and I've been noticing something about the exterior of "shot-blasted" aluminum tanks that people bring in for visual inspections. Lately I've been seeing a lot of external corrosion on these tanks, especially under stickers and wraps. If one of these tanks have a nitrox wrap sticker or one of those Scuba Hides tank wraps and it's been anywhere near salt water, it looks like the tank is breaking out in hives. It may have something to do with the finish. Even if you rinse the exterior of the tank after each use, water still gets trapped under the stickers and the tiny pockmarks of the finish holds water. The finish of these tanks look pretty durable when you buy them new, but after a little bit of use you almost have to sand the exterior to get rid of the corrosion.

Has anyone else been noticing this?

 

[PerroneFord]

I remember reading about the same things years ago. That's why I went a different direction with my tanks.

 

[SparticleBrane]

I've noticed it as well. That's why I only use the "brushed no-coat" finish. Durable, decent looking, and lasts.

 

[muddiver]

Shot blast and aluminum are a bad combonation because the blasting using a round medium causes forged laps in the metal. Add a crossive environment and you get crevice corrosion which is a fast form of corrosion. Under any non-permiable covering and you will get really nice pit corrosion which leaves those pock marks you are talking about. The natural film of aluminum oxide that usually protects the aluminum only works on a smoth surface.

 

[Chris Brown Tech]

Yup, brush no coat is the best choice for saltwater. All my rental tanks that are shot blast are suffering the worst on the corrosion front.

I used to get charged more for brushed no coat, but these days they are all working out about the same price.

 

[oxyhacker]

Shot blasting seems to leave dimples deep enough to allow water to get in behind the stickers, with the result that either the stickers don't stay stuck, or corrosion occurs underneath them. Brushed and stripped tanks don't seem to have that problem, at least not to the same degree.

 

[dvrgaryc]

Thanks for the replies, y'all. At least I'm not the only one to notice this happening with these tanks.

The best finish DOES seem to be a non-coated brushed aluminum. With all the problems with the shot-blast finish, I kind of wonder why it's still on the market.

 

[daniel f aleman]

Shot blast tanks have been around a long time, well before the wide-spread use of stickers - and they're still the least expensive of aluminum tanks.

 

[SparticleBrane]

I am wondering why the brushed no-coat finish was originally more expensive.
In fact, I'm wondering why it isn't the cheapest option. It would make sense that not painting or shot-blasting the tanks would decrease cost, plus it would seem that most tanks get sanded anyway.
Do Luxfer and Catalina have to do anything extra to make the brushed no-coat finish?

 

[WD8CDH]

My favorite finish is just the natural color out of the heat treating. It's just a gray oxide. The neck and top of the brushed/clear coated tanks are that finish. The only other aluminum tanks that I have seen with that finish are the ones in the UDS-1 system.