Removing Rust from Propane Tanks

[Thurmond1317]

Howdy everyone,
I recently bought two used 35 gallon propane tanks for my bus. They are the kind that get perma mounted to a location. (The guy said they are lifetime tanks but idk about that. He also mentioned he never had issues filling them or getting them filled with the rust but I'd like to be proactive regarding that.)
I'll probably only use one to start but since I'm aiming to have most of my appliances run with propane, it'll be good to have a spare. Only problem is they have rust. It seems to just be surface rust. The guy said they came off of his propane pickup truck so it was 1000% exposed to the copious amounts of road salt they use out here.
Anywho, they both appear to hold propane fine because there is some in them and has stayed in them, but how do I go about removing the rust at home? I don't have a sand blaster, I have a wire brush attachment for my drill but I've never worked with propane tanks, does that damage the tanks? I've heard of rust removing then protecting paint like POR15, is that safe on tanks? I do plan on getting them inspected before I use them but with half of the tank covered in surface rust, I don't want them to just deny it without actually looking at anything.
Thanks for any insight!

 

[ewo1]

wire brush off loose rust, lightly spray down with OSPHO. Let dry and paint.

 

[Cheezewhiz]

Corroseal is pretty amazing ****, and there's some cheaper knockoffs that do the same thing.

Its a chemical that converts red rust, the bad ****, to black rust, a protective layer. Encapsulated in a water based latex paint.

You hit the flaky spots with physical removal, and leave a layer of surface rust for it to bind to. Black (or purple for the off brand) magic!

 

[Thurmond1317]

Thank you both for your quick replies!
It looks like both products are relatively similar. Regarding application, after the whole thing is cleaned and flakey stuff removed, should I coat the whole tank in whatever rust remover I choose, or just the affected areas? It's only half of both tanks that are ugly.

 

[ewo1]

OSPHO- raw metal area. not required where you have a good bond of paint that is already protecting the surface.

 

[Cheezewhiz]

Corroseal, or the variants that are true to form ARE paint.

Covering rust, it'll come out blotchy, and purely cosmetic. Paint over the top as you like.

Ospho is an acid and you have to wash it off before you paint.

 

[Thurmond1317]

You guys are awesome, thanks so much!

 

[jbeech]

I'd argue for 100lb tanks (Northern Tool) at $200 a pop, instead.

Brand spankin' new so they're much lower risk than rusted tanks. Especially ones of unknown provenance.

In my opinion it's time to stop digging and walk away from the used tanks. Don't spend another penny on them.

Did you know 'throwing good money after bad' has a name? It's The Sunk Cost Fallacy. Google it. Anyway, my advice is eat the price of the used tanks and buy new ones. No brainer.

Silver lining, you can use them to make good burn barrels by cutting off the ends. Takes a drill for a hole to use a jigsaw with metal cutting blades. Considering the thickness of 55g drums means they last about a year, then propane tanks being several times thicker means the Cadillac of burn barrels!

Bottom line? Of the many expenditures to come for a bus, ponying up for $200 propane tanks don't move the scale. Not against the risk of catastrophic failure.

Regardless, not your decision. There's DOT regulation regarding mobile propane. Go to your state DOT and read the rules.

Remember, the ink for these kinds of things are written in blood.
--
My 2¢

 

[Ozbozz57]

jbeech, Northern Tool's 100 lb Worthington tanks are vertical, stationary tanks. Not for mobile use, nor can they be mounted horizontally.

 

[jbeech]

Great info, thanks!

 

[Thurmond1317]

I can see what you're saying jbeech.
I went the route I did because the new perma mounted tanks I was seeing were around the $500 mark for a smaller new one. That and I was planning on having it inspected regardless, I assumed they'd test for structural integrity. I'd imagine if the test is to prevent accidents that they would check for everything.
I do have safety as a top priority in this build. I'd like to be as safe as possible. But I also don't want to spend money for new things when I don't have to. It's my first time taking on a project like this so my meter will definitely be off in a lot of topics but I'm learning and growing with the help of you guys. It might take me a while to actually clean and get the tanks inspected but once I do, I'll try to update this thread with my results. I'll be sure to take before and after pictures and ask the inspector a boat load of questions to ensure I'm being safe about it. If they recommend a new tank, I'll take my loss. But if they say it's good, that'll be a satisfactory answer for me as well.

 

[sportyrick]

I've used that "change rust to primer", it works for a few years but eventually moisture gets into the rough texture left over by the "change" so I wouldn't recommend that for the terrible abuse it receives under a bus. I took all fittings out of my tank and had it sandblasted and powder coated, it turned out beautiful. Don't let it sit out unsealed long and definitely don't let water into it because you don't want any rust inside or it could give you trouble down the road like plugging orifices.

 

[jbeech]

No offense, but I wouldn't spend a nickle cleaning them. Take them to be pressure tested, first. Then if you want to clean them up, KYO. But until you know whether you bought a pig in a poke, why bother going to the effort?

 

[Thurmond1317]

Fair fair, don't know why I couldn't have thought of that. Having it tested prior to cleaned makes a lot more sense.

And I'm not too familiar with outlets or places that do sand blasting in my are but I'd imagine I could find someone somewhere. I do also like that idea a lot more than using rust curing paint.

Thanks guys!

 

[jbeech]

Again, and no offense, I'd avoid sand blasting.

If tanks pressure test OK, then I'd use chemical means to remove/convert the oxidation, instead. Why? It's because sand blasting means removing metal, which weakens the pressure vessel.

So let's pretend the tank was marginal, but passed before sandblasting. After sandblasting, it a) wouldn't pass again because removing metal weakened it, or b) it would pass again. Binary situation.

Problem is, like Schrödinger's cat (which may be considered both dead and alive in a sealed bow and you don't know which if you don't look), then after testing and sandblasting, absent testing again, you don't know if the tanks are still safe, or not!

So because your the goal isn't merely passing (which means they'll happily take your money and refill), but actually 'being' safe, then anything which weakens the tank after testing is to be avoided unless you're willing to test once again! Hence, advice to test, then chemically clean/convert, repaint.

Honestly? We're cruising blind trying to help, a few photos would have helped with guiding you because we may be talking surface rust, or may mean our recoiling in horror.

 

[Jolly Roger bus 223]

do not paint over the data plate on the tanks.
harbor freight has a cheap blaster and if you use walnut shells as the blast media it will not dig into the metal it will just remove the loose rust.

 

[Thurmond1317]

I'll try and grab some photos this weekend or next time I'm at the shop!

And no offense taken! I post here and ask questions specifically so you guys can smack me upside the head if I'm making dumb mistakes. My train of thought doesn't often move linearly so the additional input is super helpful and appreciated. And yes! I'll make 100% sure not to paint over the plates. Only clean them to the best of my ability, maybe clear coat over them so they don't pre-maturely rust.

Huh, didn't think of that either. I asked around a few places and most said no to sand blasting propane tanks. I doubt they'd change their answer for walnut blasting unfortunately.

 

[nikitis]

do not paint over the data plate on the tanks.
harbor freight has a cheap blaster and if you use walnut shells as the blast media it will not dig into the metal it will just remove the loose rust.

I will look into this. I've been wanting a rust remover like this.

 

[Thurmond1317]

Sorry that took so long, here are the pics of what I'm working with, It's about the same on both tanks, but only half of the tank looks like that, the other half if the flakey white that was painted on.
Hopefully the pictures all work decently.

 

[nikitis]

So a tank like that you'll never get a propane company to certify it and fill it up. Tanks have to be certfied for a company to fill it up.

Even If you removed all the rust, there would be pitting and if you painted over it, they'd see the pitting and not certify it.

You could maybe do bondo like they do with cars and smooth out the pitting and then paint it.

As long as there's no pin holes. You can pressure test it when you're done and watch the pressure to see if it drops, and if it doesn't and you've covered the pin holes, there's a small chance you can get it certified.

The reason after all that work I say there's a small chance is becuase they will look at the plate and see how old the tank is and may not certify it still but some companies will.