How to remove rust from inside HERMS Coil

[defrib]

A few months ago I bought a brew stand and kettles from a friend who had moved to Michigan too work for a brewery. When I went to pick up the equipment from storage I was surprised to find a large unopened box containing the HLT.

Here’s a picture of the interior and coil,

https://conical-fermenter.com/images/D/20g-liquor-tank-367-hl20tw-rhc-sg-el1-exp-800-12.jpg

Apparently, it was a custom order and didn’t arrive until after he’d moved so it was never used and not in the pictures of the equipment I thought I was buying. It turned about to be a really nice bonus except for one issue. When the HLT was built, it was assembled and the welds were tested for leaks and apparently the HERMS coil wasn’t drained before it shipped. It sat sealed in storage for over a year filled with water. When I took the coil out of the kettle and turned it upside down rusty water poured out and there were definite rust marks on both openings.
I would really like to remove the rust and restore interior finish to prevent and future corrosion. I know there are a few cleaners I can use (vinegar, Bar Keepers Friend…) but I don’t have any experience with them so I’d prefer to get some input first. I’ve also considered a mechanical solution but the coil diameter is about 6 inches so it’s difficult to snake anything inside. Another concern of mine is if I use the pump to circulate and cleaners I want to make sure they won’t damage the polysulfone pump head. If anyone has experience with this or similar problems please let me know how you handled it. And thanks to everyone who posts on Homebrew Talk, with the wealth of information here I’ve been able to answer every brewing question I’ve had while putting together my new system.

 

[Bobby_M]

Get a pound of Oxalic acid on Ebay. Make up a solution and recirculate it through the coil for a while.

 

[defrib]

Can you recommend a specific ratio for the solution and is there any danger in recirculating it for an extended period of time? I was thinking about running it while I get my strike water up to temp in my mash tun.

 

[wbarber69]

Clean your pots before attempting to start a brew

 

[Riot]

I'm not really sure how oxalic will effect polysulphone, though I imagine it will be fine. Even super concentrated BKF doesn't even irritate my skin so I doubt it will it the plastic but you never know. For as much of a score as that is its almost worth buying a $20 pump to do the cleaning with. Even if you wreck it I would say its money well spent considering what a coil that size would cost you retail

 

[orangehero]

@Bobby_M
Oxalic acid would work but the industry standard alternative to nitric acid is citric acid. Maybe it's cheaper or safer? Do you know the usage rate for oxalic acid on stainless steel?

From the ASTM guide to passivating stainless: For citric acid, make up a solution at 10% w/v concentration, heat it up to 160°F, and hold it for 30 mins to an hour. Personally I heat it up to near boiling and let it cool back to room temp overnight with good results. Repeat as necessary.

You can also use 50/50 citric acid and ascorbic acid at the same concentration, but it's a bit more expensive and the citric acid seems to work just fine alone.

https://www.homebrewtalk.com/showthread.php?t=447936

https://www.homebrewtalk.com/showthread.php?t=514240

https://www.homebrewtalk.com/showthread.php?p=6866769

 

[defrib]

Im going to give the oxalic acid a try because I tested it on some rusty stainless and it seemed to work quite well.

I found the following chart and it appears that the acid should not be a problem with polysulfone.

http://www.proplasticsinc.com/chemical_resistance_guide.pdf

There is enough visible rust in the open ends for me to determine its effectiveness. I'll post my results soon. Thanks for all the input.

 

[Bobby_M]

Actually I know very little about best acids and best concentrations. I just noticed how well BKF works and how much cheaper pure oxalic is. I think BKF is like 10% concentration so I wear gloves and glasses when I mess with 100% oxalic.

 

[Riot]

I'm in about the same boat as Bobby here. Not really sure what best practice is, just know that BKF just rips rust apart. I even got them stocking it in the kitchen where I work.

 

[orangehero]

How much is the oxalic acid? You can get a pound of citric acid for $9 shipped from ebay.

I don't know the relative effectiveness of oxalic acid either, but BKF is also mildly abrasive.

I like to use it first to knock off any rust with a good scrub and then do a hot soak in citric acid or Five Star Acid #5.

Also, if you have silicone or pvc tubing, oxalic acid is less compatible than citric acid. Depending on the concentration, temperature, and contact time the difference may not be noticable, though. Just something to keep in mind to make sure any plastics, hoses, or seals won't be degraded.

 

[defrib]

Thanks again for all the input. I've been to busy to try anything yet. I already have BKF and citric acid on hand from other projects. I plan to run the BKF through the coil until I don't see any visible rust in the coil openings. Once I'm confident the rust has been removed I'll run citric acid through at 160F or so to passivate the coil. Hopefully, the combo will clean off the rust and stem off future damage to the surface metal. I have some throwaway old tubing I can use to circulate to avoid damaging the silicone hoses I use for brewing.

 

[Tomn8r]

How did you go with this?
I have a similar issue and would love to know what works