Rusty painted LP72 tank: worth saving?

[tmassey]

tl;dr: look at the photos, particularly the tank bottom. Is this tank worth saving, and if so, how should I do it?

I had previously asked for some details about some tanks I bought (Question - Older steel 72 Pitt Depth) At the time, it seemed like they might have been galvanized, so I decided to move forward with them. I had put a light in them and knew they were a bit rusty inside, but no pits: they looked to be in solid shape. At a glance, the outside seemed OK: beat up, but basically sound. So I bought bands and valves for them, as well as some phosphoric acid, and assembled a quick roller board thingy to get ready to clean them up. I wanted to see if my roller board worked well enough, so I grabbed one of the tanks to give it a shot. Of course, I had to knock the boot off... and so my problems began.

As you can see from the photos, I learned a few things. One, these tanks are *not* galvanized, just painted. And two, the rubber-glove-style boots have done what they are well known for doing: they've rusted my tanks. Lesson learned: knock the boots off of tanks before you buy them... (Why didn't I think of that before?!?)

But I've got them now, and the question is: what to do with them? I have very little attachment or investment into them right now, and I'm not really looking for a 'labor of love' here. I only paid a few dollars for them, so besides the supplies I bought to clean them up and double them, I'm not yet out any real money.

So my questions revolve around this: are these tanks worth saving? (The other tank has some issues as well, but not nearly as bad.) By 'saving' these tanks, I mainly mean making them usable for a reasonably long time (at least a hydro or two), without having my dive buddies refuse to dive with me because they look like they might blow up... There's very little economic value in these tanks, and I'm not interested in pouring a large amount of either time or money into them. I have zero desire to make them works of art: just safe and functional.

Having said that, I'm willing to put *some* time and money into them -- I already put some money, time and effort into being able to move forward with cleaning up the inside. The idea of stripping them both completely and then coating them in ZRC -- at $60 a quart -- doesn't seem like it would make any kind of sense. But is there something short of that that might make sense to keep these tanks going?

At least the roller board seemed to work well: it should make agitating the tanks straightforward. My intention was to save the stickers: I'm not normally a vintage guy, but these tanks seemed like they needed to keep the stickers, so I didn't want to simply roll them around on the cement floor. Of course, it might not matter now... But who knows: maybe there's a way to address just the bottom of the tanks? I hope you tank experts out there can help!

And thank you for your time and attention. I appreciate it.

 

[rob.mwpropane]

Well I guess you'll never not pull the boots off again..so there's that. Bummer about the find. They look pretty bad, but I'm not at all a professional. I see enough 72's around it's probably not worth a lot of time and energy to refurbish them.

Hard to tell without sanding or maybe wire wheeling the bottom crud off?
Am honestly sorry about your luck, but pretty cool roller board... that's better than my concrete floor I use to play "fetch the tank" with myself.

 

[Gone for diving]

I personally would not worry to much,
just use a wire wheel on the 4.5" hand grinder, clean all the old paint and rust off the first few inches up the tank,
you could wash it with the phosphoric acid to prep it,
Lay a nice even layer of masking tape a few inches up all the way around, prime it with a rust primer, a few times to make it look pretty, the paint it with whatever color you want.

That's what I would do if it was my tank,
You can always send them to me for proper disposal

 

[Alaskan Scuba Dude]

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[Gone for diving]

Dude you are such a helpful
Dish soap and potatoes???
Do you get kick backs for posting links on this site?
Or have you actually used this stuff? If so
Please provide a picture of a tank you have used it on.

 

[tmassey]

tl;dr: After a brief clean (see photos), they're not as bad as I feared, and the standards for steel tanks allow a *lot* of damage. My thinking is to clean up the bottom of the tanks by hand with phosphoric acid, citrus paint remover and elbow grease, then hydro the tanks, then give them a final clean and coat them with Rustoleum Galvanizing Compound instead of primer and paint. Thoughts or suggestions are appreciated!

I see enough 72's around it's probably not worth a lot of time and energy to refurbish them.

You know, I *don't* see many around here. Even a decade ago they weren't that common, and now much less so. And when I do, they want something like most the cost of new AL80's... (Along with the rest of Grandpa's 1970's-era Dacor and neoprene, which they think is either vintage [who wants vintage life-support equipment?!?] or 'just as good as new' and is priced accordingly...) @Tracy lives near me and he's probably got a metric ton of them -- I've truly never seen another individual with more tanks --- but he isn't selling them for $25 each... (But they're not rusty, either. )

Hard to tell without sanding or maybe wire wheeling the bottom crud off?

Yeah, dumb of me: I should'a tackled that a bit before I bothered to post. So, now I have: see the attached photos.

I was tied up today and couldn't go to the store, so I was trying to figure out what I could do tonight with them with what I've got. I just got my food-grade 85% Phosphoric Acid today, but I really didn't want to waste it on this -- and then I remembered I had some industrial Phosphoric Acid from a previous project. So I poured some water in a bucket and put in something near the same amount of acid (so something like 10%-15% acid) and let it soak for about 25 minutes. I then scrubbed the bottom of the tank with a small stainless steel brush and a well-used drywall sanding sponge. The results are attached.

The biggest takeaway is that it looked much worse than it was. Much of the corrosion was residue on *top* of the paint; there's still chunks of corrosion, but it's not nearly as extensive as it seemed. And the cool thing is that I can see bare metal peeking through now. It's far from clean, but it lets me know there's not *that* much damage.

So I pulled my TDI VIP manual off the shelf and checked the standards. According to it, the CGA Pamphlet 6 defines General Corrosion as 'somewhat uniform loss of metal in a relatively large area', and that general corrosion should not exceed 20% of the surface area. I'm nowhere near that. While I'm at it: isolated pits (which I don't seem to have here) should not exceed 33% of minimum wall thickness. Once again, I'm much less than that here. I also reviewed the TDI class slides. There was one that made me feel noticeably better, summarizing the rupture pressure of new cylinders vs corroded cylinders: there was almost no difference between the cylinders tested. So, I feel better about this whole process now.

I've said it before, and I'll say it again: if divers understood how loose the requirements for things like VIP's actually are (not what some dive store owner tells you!), and truly how much margin is built into these tanks, they would not worry nearly as much. The number of people I've seen telling someone they're going to die because of a 25% overfill or because a tank is 15 years old... But I digress.

I personally would not worry to much,
just use a wire wheel on the 4.5" hand grinder, clean all the old paint and rust off the first few inches up the tank,
you could wash it with the phosphoric acid to prep it,
Lay a nice even layer of masking tape a few inches up all the way around, prime it with a rust primer, a few times to make it look pretty, the paint it with whatever color you want.

That's what I would do if it was my tank,

I'm worrying a bit less now, thank you. I'm not ready to attack the tank with power tools just yet: I'm lazy, but I'm also a coward, so I'll substitute a bit of elbow grease for additional safety margin. (But I reserve the right to change my mind depending on how hard it its... ). My research led me to create a similar plan: see what you (and others!) think:

I'll soak it a bit more in the phosphoric acid, mainly because I've already started. It's not much of a paint remover, but it should help to remove the rust. I might step up to a citrus paint and varnish remover, though I understand that Motsenbocker's is better, but harder to get. Like you describe, I'm planning on only taking off the bottom 3 inches or so. I also have some synthetic steel wool (3M green and red) which I might bring to the task as well. I really want to avoid the angle-grinder...

Anyway, the goal will be to get the bottom of the tank clean. Not necessarily bright and shiny, but clean, with the phosphoric acid to passivate and hopefully minimize the surface rust. Then the idea is to hydro the tanks *before* I paint them. I'm not trying to hide anything: I want safe tanks, so let the tester see the warts.

Assuming they come back OK, then I would 'paint' them. Yes, I'll likely have to go at them again with more phosphoric acid when they come back, but I'll have to do that with the insides anyway, so not that big a deal. My thinking was to go with Rustoleum Cold Galvanizing Compound instead of primer and paint. I assume it's not as good as ZRC, though the specs seem quite similar and it's a *lot* cheaper, so even if I have to reapply in a year or two I'm still way ahead.

Any thoughts or criticisms? It's a lot easier to change the plan now, so let me know!

You can always send them to me for proper disposal

Was that joke ever funny? (The answer is: sure, it's made me chuckle before -- when I'm not the target. )

Am honestly sorry about your luck, but pretty cool roller board... that's better than my concrete floor I use to play "fetch the tank" with myself.

Not much of a loss, here: I still have two (6351) Al80's, and I only paid $50 total. If the only thing that happened was I learned a little bit about steel tank cleanup and treatment and an object lesson to always remove the tank boots, the knowledge is still cheap at the price.

And yeah, I'm reasonably pleased with my roller board. Even if you ignore the fact that I wanted to try to save the tank labels, it'll be a lot easier on my back then bending over pushing around a tank for 20 minutes...

 

[Curious_George]

Dude you are such a helpful
Dish soap and potatoes???
Do you get kick backs for posting links on this site?
Or have you actually used this stuff? If so
Please provide a picture of a tank you have used it on.

Nothing personal Roy - I’ve enjoyed chatting with you more than once, but I’ve got a real question.

If he weren’t a real person, would he actually care about your reply? It does seem like you are trying to engage in a conversation. Maybe DM him and let us know how it goes.

 

[Gone for diving]

Rustoleum Cold Galvanizing Compound

Never used this brand of cold galvanizing,
I am usually not impress with most cold galvanized, I have one brand, ( I think it comes from Holland used in green houses) that seems quite good,
I do like most rustoleum stuff,,, keep us posted,

 

[Cthippo]

I recently picked up a pair of these, along with some sort of poly bottle, for $30 on Craigslist. Even with needing VIP, hydro and new valves, I think they will be a good investments for "I just need to jump in the lake for a few minutes" kinds of dives.

Still trying to figure out what the poly bottle is, though...

 

[Gone for diving]

Nothing personal Roy - I’ve enjoyed chatting with you more than once, but I’ve got a real question.

If he weren’t a real person, would he actually care about your reply? It does seem like you are trying to engage in a conversation. Maybe DM him and let us know how it goes.

I would like to see some of his handy work, a few pictures of his own be nice,, not just links, hardly ever doing I see any answer back, quite interesting...
hardly ever does it defend its self, and then when it does, its gets even more strange...