I guarantee any coating company is going to want to charge more for a coating they confirm will work for a food-safe hydrocarbon application than it would cost to just buy a stainless tank. Their coating might be acceptable but they’re not going to certify that for this use unfortunately
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Well I doubt that surface prepping that allows a polymer coating to stick takes anywhere near as much time as a proper food grade surface finish on stainless.
The cost of coating internal vessel per cubic ft is what I’d like to knoe.
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I looked into this earlier as well. Industrial Scale Processing - #265 by pangea
pdf warning from US Coatings: https://www.uscoatings.com/wp-content/uploads/pdf/GL-6700-HB-PDS.pdf
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Thats a bummer that they don’t have more comprehensive data. “Good” solvent resistance when immersed but no data on temperatures or solvents used. 
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I gotta say in this case @spdking is probably right.
In order for you to effectively coat the interior in a way that won’t leach PTFE or whatever you cost with, the surface has to be adequate in terms of roughness and cohesion to the coating. Otherwise you’ll leach it into your process fluid.
It’s gonna end up costing as much or more than a stainless vessel once you’re all in.
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Disinformation? You can’t fully clean tanks once they are corroded. You can’t get in there with polishing equipment to make it like new. Even a acid wash won’t do it any justice. It has nothing to do with stainless tanks. It has to do with having the right tools for every job. Air compressor tanks harvest water and the inside is like a cancer surface. It’s not suitable for coating. Even if some “coating company” wants to sell you services “coating”
We’re spec’ing out a clean air system for our packaging line and we’re getting a lined tank made for that, it’s standard for that application.
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Getting a 3A rating on a stainless vessel is actually pretty easy: usually mild grinding/polishing on the welds (or competent, thoroughly backpurged tig welding) and electropolish on 2B (the normal mill rolled finish for stainless, not the expensive no. 8 polished stuff) is sufficient for tanks
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How much did the lining cost you?
It’s an epoxy lined tank and it comes that way. It’s $1230 on my quote. 120gal
Hi @ScoobyDoobie ,
Sorry for the late reply, I’ve been on the road for the past few days.There are a few reasons why I would avoid that. Like a lot of the members mentioned here, used air tanks will most likely have rust or some corrosion in them if they are just plain carbon steel. This Is because the moisture in the air can condense in the tank due to the change in pressure.
On to coatings, like others mentioned… delamination from the surface will be an issue, especially with temperature changes and pressure fluctuations.
Most commonly air tanks are made from carbon steel, Cast would be too brittle for the application and would make basically a frag grenade if it ruptured.
Now technically speaking the steel tank would work, and does meet a safe psi rating with n-tane (although I would go for 350-400 psi for blends or pure propane). Where it carbon steel fails is the tank is not hygienic, a new tank would be a better choice than a used tank due to rust formation and known burst pressure/tank condition.
Basically your large air tank would be a larger version of this, which is a common use item.
@ScoobyDoobie ,did you have a spec/ budget on the tank you need? I could probably find you an option.
If you decide to use a carbon steel tank I would absolutely make sure your dryer is 100%, otherwise your going to get rust / ice formation.
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No Im not actually looking for this service, I don’t have a use for a tank that big I was just curious. It sounded like a better option compliance issues aside since there’s so many options for solvent resistant films available.
I like rogues idea of getting scrap stainless, I’ve seen big tanks and pressure vessels just sitting outside at scrap yards before but I’ve never had a reason to buy them.
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Yeah @Roguelab 's got it right. I was going to dm you a link for a used tank that met your specs. You can find surprisingly good deals on that kind of stuff. 
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