I have some significant blackening in the bottom of my SS brew kettle. Most of it was cleaned up with bar keepers friend but there is stil some left.

Is muriatic a safe and effective solution to clean up what's left? Any other chemicals or something I could boil in the pot to revitalize the SS?

Chlorine and stainless don't mix.

I would let it soak for a couple days in PBW and then follow that up with the bar keepers friend. If you still have some scorched material leftover, you could try a warm soak in a vinegar solution or use one of the acid cleaners used for draft lines.

+1 to a PBW soak. It should help soften it up enough that another round of BKF should get it.

It's high chloride (not chlorine) concentration that is incompatible with ferrous metals including many grades of stainless steel. Muriatic acid (aka hydrochloric acid) should not be used on any steel. The preferred acid for cleaning steel is Nitric acid, but that is pretty hard to get.

A hot soak with PBW solution is a great alternative for removing carbonized films off of kettles. PBW says you can take it up to 160F for max effect.

NO NO NO~!!!


Muriatic acid will strip away the passive chrome oxide and rust your SST.

If you are bug fuck to use an acid get yourself some Citric acid They sell it Kosher on the Flea Bay for cheap.
Mix that with some water ratios are largely irrelevant. It will also provide the added benefit of doing a little passivisation while it's doing whatever else you are trying to accomplish - - assuming it removes the scale and crap - - I never tried it for that.

Muriatic acid will work, but you'll need to treat the SS to prevent rust which is not something easily done at home. Furthermore, HCl is not something I would go about casually using. I deal with it at work every day, as well as other much more toxic chemicals.

Citric acid is your best bet. I use it to clean stubbornly dirty cartridge brass for reloading. It's safe to go down your drain.

Is this blackening discoloration of the metal or is it baked on carbon from scorching? If the former I don't think there is much you can do about it. If the latter then elbow grease plus a scraper or a scrubbie (made of plastic) should eventually get it to let go. Also, if it is baked on carbon or organic material which has been oxidized nearly all the way to carbon, acid isn't going to touch it. You need an oxidizing agent. There are a couple of things I could suggest here but I won't both out of consideration for your health and the environment.

I've Used Metal Prep grade Phosporic Acid to clean the inside of my Keg Conversion....Mostly to remove the Bluing from welding though. I agree with with the guys saying Warm PBW.......Especially if it's organic material.