Non-galvanized tank?

[engdiver]

I have two steel 72 tanks that I stripped the paint from. One has an obvious galvanized coating while the other stripped down to a dark brown coating that may be some form of rust. I can lightly sand this coating off the tank to reveal the metal. Is this a non-galvanized tank? The inside appears the same dark brown color. Is it worth the time and cost to keep? I am planning on using these as a doubles setup. Both are the same overall size. Original hydro dates are 2/67 and 11/68.

 

[Compressor]

Pictures would be helpful.

The inside appears rusted. It probably needs a tumble followed by a hydro and a VIP.
Conservative cost: $50/tank

The tanks are 72. In my opinion with the current bigger steel tanks, its not worth going this route. I would buy a new tanks.

 

[rcontrera]

We restored an old non-galvanized tank several years ago and it was an excercise in futility. We had the outside sandblasted down to the bare metal and then cold galvanized it. After that, we sealed it with a layer of epoxy paint to help stop rust. Total cost at that time was about $50 before we even added in the tumble and hydro. Was it worth it? Sure ... until we took it to salt water and sure enough it started to rust again. We turned it into a very expensive shop tool tank!

 

[engdiver]

I assume from the replys that this is most likely a non-galvanized tank. I wonder why USD would ever make tanks like this and galvanized ones at the same time. Anyway I will probably look for another tank of similiar dimensions and retire this one. Thanks for the input.

 

[PerroneFord]

I assume from the replys that this is most likely a non-galvanized tank. I wonder why USD would ever make tanks like this and galvanized ones at the same time. Anyway I will probably look for another tank of similiar dimensions and retire this one. Thanks for the input.

Faber still makes non-galvenized tanks, and people still buy them.

 

[rcontrera]

From the date on those tanks, this was in the infancy of the diving industry. Many tanks came from other uses (drink carbonation, fire extinguishers, welding, etc) and galvanizing was not needed.

We (the diving industry) experimented with forms of rust prevention on the inside in various forms but, primarily, epoxy. It was a great idea! Paint the inside of the tank to keep moisture from attacking the steel.

One thing that we forgot, though ... filling a tank will stretch it. The paint didn't stretch and would form tiny cracks that allowed the moisture to get at the steel anyway. What's worse is that the paint hid the damage being done by the rust until it was so bad that it formed a bubble. In the early days of visual inspection, it was normal to find the inspector banging the inside of cylinders with a metal rod to see if the paint chipped off. If it did, then the tank needed to be stripped. Not a hard job, just messy. Plus, I just didn't like putting paint stripper inside, hoping that it was neutralized after the tumble was done and the diver was breathing off of it.

Your brown inside the tank just may be an epoxy lining. They came in brown, a kind of mahogany red, light blue, white and gray. There may have been more colors but those are the only ones that we saw over they years.

 

[evil_xander]

Faber still makes non-galvenized tanks, and people still buy them.

You'd be suprised to come over to Europe, you can count non-Faber tanks using fingers on your one hand... almost. And over here we dive in the sea for the most part.

Yes, they require a bit of attention for a long life, but then again, what doesn't.

 

[crlavoie]

I have two steel 72 tanks that I stripped the paint from. One has an obvious galvanized coating while the other stripped down to a dark brown coating that may be some form of rust. I can lightly sand this coating off the tank to reveal the metal. Is this a non-galvanized tank? The inside appears the same dark brown color. Is it worth the time and cost to keep? I am planning on using these as a doubles setup. Both are the same overall size. Original hydro dates are 2/67 and 11/68.

What you are describing could very well be an iron phosphate coating which could be mistaken for flash rust residue. It is part of a 3 stage pretreatment for steel in industrial finishing applications. Normally, it's followed by a 2 component polyamide epoxy primer and either an isocyanate urethane or another epoxy finish coat. It's also a common pretreatment for modern powder coatings. Depending on the type and amount that was applied, it can withstand a moderate amount of moisture by it's self. Looking at the date, chances are it's a pretty good phosphate because it was done well before most of "the good stuff" was outlawed due to health and environmental concerns.

In short, don't remove it until you know what it is.

 

[captain]

For a while in the 60's USD sold both galvanized and vinyl coated tanks, some of the vinyl coated ones were galvanized under the vinyl. Also interior coating came in two flavors, white and brown. I stay away from the non-galvanized ones, too much upkeep.

 

[DA Aquamaster]

If the interior is a smooth surface with an even dark brown color and no apparent coating on it or texture to it, it could also be a patina finish similar to what occurs to some old and unrusted firearms. Like a rust blue process it is a stable and self limiting form of rust that will not normally progress to pitting. In my opinion, it is preferrable to a clean steel finish, which is much more suceptible to normal rust and pitting.

If the surface has any texture to it, bubbles in it, etc is probably a vinyl coating and generally speaking any vinyl coating still in use inside a tank should be removed as it can trap moisture underneath, hide rust, etc. We never used chemical stripper but instead tumbled them for a few days to a week as needed to completely remove the coating.

I second the concern with non-galvanized steel tanks. I have tried various two part epoxy paint processes MTK, Imron, etc) and have yet to find one that will hold up more than a year or two in service on scuba tanks. I don't know what Faber uses on theirs, but I have found nothing available commerically that will match it. You get chips and then you get rust and then you spend lots of time removing rust and touching up the paint. Cold galvanizing underneath helps reduce the rust removal but you still end up fixing paint chips.

USD offerred both galvanized and non galvanized tanks concurrently and on the vinyl coated tanks it's hard to tell which is which unless the vinyl finish has been gouged or chipped. In the old days, hydro testers did it right with heated stamps that did not chip or remove the vinyl. Lately, they just punch through/chip off the vinyl with the stamp leaving an area for rust to attack - which is a great way to tell whether it is galvanized or not.