Rusty painted LP72 tank: worth saving?

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Tracy

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That will be fine. Bring them over this way for hydro. Quick sandblast and paint, it will look like new.
 

Endler's

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Before spending any more time/effort on tanks, you should probably speak with whomever does your VIP. I have heard of inspectors failing tanks, because they thought owner was trying to hide excessive corrosion under paint. 👁️
 
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tmassey

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Before spending any more time on tanks, you should probably speak with whomever does your VIP. I have heard of inspectors failing tanks, because they thought owner was trying to hide excessive corrosion under paint. 👁️

*I* do the VIP's -- except the federally-mandated one as part of the hydro. Which is also exactly why I won't paint them until after the hydro: I'm not trying to hide anything.

As for a scuba shop 'failing' a VIP: they have no legal right to condemn a tank, let alone do anything to the tank to remove it from service or such. The worst that they could do is to refuse to give it a sticker -- or to refuse to fill it, valid sticker or no. And I would support them in that: I personally would refuse to fill or VIP a tank that looked like mine did this afternoon. It's not worth the risk.

But fortunately I can do my own VIP's and fill my own tanks, so hopefully I can clean them up to the point where they are both provably safe (as demonstrated by the properly-executed federally-defined hydrostatic test with its own associated visual inspection) and visually reassuring -- and hopefully within a reasonable level of cost and effort.
 

rob.mwpropane

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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!



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. :) )



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'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!



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




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...
They cleaned up nice!!
 

Bob DBF

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My thinking was to go with Rustoleum Cold Galvanizing Compound instead of primer and paint.

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,

I've used that for old vintage tank bands, and it seems OK, but I'd probably go for the good stuff for a tank. For fresh water it may not make much of a difference.
 

captain

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None better.

 

AfterDark

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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.
I have 2 steel 50's looked the same way both keep passing VIP and hydro. I power wire brushed the rust and used cold galvanize paint
to cover and protect. My 50's have pitting also.
 

Eric Sedletzky

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I’ve restored old steel tanks way worse than that.
I have a lot of the proper equipment however to be able to do it correctly. I’ve been in the auto body industry, marine industry, refinishing industry of many different types, blah blah blah.

On something like that I would typically thoroughly inspect it inside and out. Pits can be deeper than you think and the tank can still have plenty of meat to be safe. I remove the valve and install a pipe thread plug that has a hole drilled sideways through the square knob on top so I can run a wire through it to hang it for refinishing.
I have a pressurized sand blaster that does a perfect job and removing all rust and scale down to what they can “white steel” which a term for super clean. After it’s blasted using something fine like 40-60 mesh sand, it either gets epoxy primed and top coated with a true polyurethane system (for shiny and a color), or you can use Galvite or other similar product which are 80% or higher pure zinc dust coatings. That is the simplest solution and they work excellent.
I always wire brush the insides down to clean brilliant steel too with my special cleaning tools that I designed and fabricated myself.
Then they go to hydro.
Hopefully they pass and all the work wasn’t in vain. On the positive side, I have never had one fail hydro that I’ve rescued. It’s worth the effort in my opinion.
Once they pass hydro they’re perfectly safe and ready to go just like any other tank.

Oh yeah, and the boot: I cut all mine down so the side lip or whatever you want to call it only goes up the tank about an inch or a little more. That way it’s easy to slip on and off for rinsing after use. The boot is only there for standing the tank up for filling or storage. I many times pull the boot off for diving and then carefully lay the tank down on it’s side on land, on the beach, grass, table, etc. however, if you’re using it on a boat and the rig is in a scuba tank station then you might want the boot on.

I never let a 72 or any other steel tank get away without first trying everything to save it.
 

rjgiddings

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I see tanks at every yard sale, so I can't imagine bothering w/ these tanks. You can find identical ones in about 4 minutes online : FB marketplace, Craigslist, OfferUp... Why spend the time/ $/ energy on these ? Seriously - tanks are everywhere.
 

Eric Sedletzky

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I see tanks at every yard sale, so I can't imagine bothering w/ these tanks. You can find identical ones in about 4 minutes online : FB marketplace, Craigslist, OfferUp... Why spend the time/ $/ energy on these ? Seriously - tanks are everywhere.
Tanks are everywhere, until they’re not.
 
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