Stainless rust removal redux

Unfortunately, citric acid doesn't remove rust. It would be a great last step to repassivate everything after whatever else you do. Bead blasting with glass beads will definitely leave a matte finish. Never done it, but soda blasting may not hurt the finish and should remove the rust. You could try wiping in an out of sight area with BarKeepers Friend, which is supposed to remove rust, or maybe a dab of Naval Jelly or other phosphoric acid product, to see what the effect on the finish will be before doing the entire outside.

Hi,

I took note of the recent discussion concerning stainless steel and removing rust. Kept several good posts (thank you Ed, Carl...) for future reference.

A friend of mine kind of neglected his stainless revolver a bit too long and it has developed little rust spots here and there. Here are a few links to images that illustrate the problem:

A gunsmith friend thought bead-blasting it would be the best cure but the citric acid treatment sounded interesting to me. Neither of us care to try messing around with nitric acid. Mechanical means, buffing and such would probably be quite noticeable I think compared to the rest of the finish.

Any suggestions? Or would the best course be to just leave it alone, chalk it up as a lesson that stainless steel isn't necessarily carefree :)

I also wondered it electrolytic derusting works on stainless too. I remember people discussing the use of stainless for an electrode and toxic gas it would generate but not trying to derust the stainless piece itself. And how would that affect what was passivized? I've used electrolytic before on a few items with impressive results but nothing stainless. Messy as heck but it doesn't really generate any dangerous byproducts to dispose of.

Real Scotchbrite contains silicon cabide abrasive. It will leave the gun with a brushed look.

If it already has such a finish, no problem. If not, it will be noticeable, and he may not like the result.

THEN

Guess I was hoping it would. I remember wondering about that (removing rust) when I was reading your post. That's why I'm asking and thanks for the reply :)

Smith & Wesson, .45

Owner has already went over it pretty good with Hoppes... So it needs a bit more of something.

I've played the game before with stainless and anything abrasive. Either put up with the new pattern, go over the whole piece or maybe just leave it be (shrug). I was hoping for an idea/solution that didn't mess up the current brush job or texture...

Thanks for the input though!

Use oxalic acid. It'll remove the rust spots with minimal disturbance to the surface.

Bar Keepers Friend main ingredient is oxalic acid. Good source? or is there a better one?

Its most common use is as a wood bleach. If you check the deck cleaners for wooden decks it is pretty much Oxalic acid.

Savogran sells 1lb tubs of granular for $6 at hardware stores.

Paul K. Dickman

I am under the impression that citric acid does remove rust.

But one test is worth a thousand words. So I would recommend that you first try citric acid on some ordinary rusty steel and see if you think it removes rust. Then on some stainless with rust spots if you can find some.

You can find food grade citric acid at Tractor Supply. It is used to clean stainless tubing in milking systems.

Dan

We used to use that stuff on personal clothes in the mag cell. The little bit of chlorine that would leak out eventually ended up as hydrochloric acid on the metal frame of the building, so any condensation drips would stain your clothing. That's why I didn't go on the operating floor without putting on the mag suit (fire retardent cotton overalls and jumper, metatarsal guard boots, and hard hat with face shield). Oxalic would fix those stains.

Also used it once on a white cotton sweater my sister brought home from Egypt and made the mistake of washing in my folks' iron laden water. Nice even light rust shade.

Good luck.

Pete Keillor

I've tried rubbing with a citric acid paste (teaspoon of citric acid powder, drops of water to make thick paste), scrubbing with a paper towel and my 10% warm citric acid passivation solution, and soaking overnight with agitation in the 10% solution, and had zero luck removing orange red Fe2O3 rust spots or the blue to orange film from welding on 304SS. I would soak small pieces of 304SS in salt water until I got rust when testing the passivation procedure, then I tried to get rid of that rust and the welding scale from beads across my test pieces, with zero luck. If you make it work, please post how. Oxalic acid will, which is why I suggested BarKeepersFriend. Wasn't sure it had abrasive, which is why I suggested testing in a non-visible site. Under the handgrip would be good. Start by just dripping some on and let it soak, you may not have to rub at all in which case the abrasive won't matter. I guess I never tried citric acid on rusty mild steel, so can't say if that works or not but my strong expectation is not.

----- Regards, Carl Ijames

I am under the impression that citric acid does remove rust.

But one test is worth a thousand words. So I would recommend that you first try citric acid on some ordinary rusty steel and see if you think it removes rust. Then on some stainless with rust spots if you can find some.

You can find food grade citric acid at Tractor Supply. It is used to clean stainless tubing in milking systems.

Dan

I think the rust occurs BECAUSE iron particles have been exposed, else there wouldn't be any rust, right? Isn't the whole idea of a stainless steel that a chrome oxide of some sort forms over the surface and sorta covers up any carbon or iron particles? So, if rust forms, it means that something has removed the chrome oxide and uncovered the iron, yes? So I think you have to get the iron GONE and then allow the chrome to oxidize again to prevent further rust.

I'd vote for a try with the Barkeeper's friend, using the oxalic acid to eat the iron. As said previously, try in on an out of sight area.

I have tried citric acid on stainless steel that I have hot forged. when hot forging stainless steel, two problems occur since we are seriously disturbing the chrome oxide coating:

-iron particles come become exposed (and they rust later)

-carbon particle become exposed (and they stay black forever) While the citric acid may have some effect on both issues, it is miserably slow in my limited experience. The oxalic acid that I use for cleaning erector set girders works slowly too, but a lot faster than does citric acid.

Pete Stanaitis

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"has already went [sic] over it..." Illiterate.

When you are hot forging, are you using stainless steel hammers and a SS anvil? If not, you are embedding iron from your tooling in the surface of the SS, which then leads to rust pits later if it isn't removed, or it can get transferred to the interior if you fold the metal, and then come back to the surface by later machining. Same problem if you use a carbon steel wire brush, or a SS wire brush that has been used on mild steel, or mill and/or lathe tooling that was used on mild steel first. Citric acid will remove free iron from the surface but won't take off rust that has already formed. I think you need a stronger acid pickle after hot forging, then do citric acid passivation. Oxalic acid might be enough, but a quick hydrochloric acid (or nitric if you can get it) wash might be needed. Another technique that hasn't been mentioned is electropolishing. It will clean and passivate and polish the surface all at one time but is generally limited to the outside surface, it does not penetrate down holes. It will remove up to a few 0.001" from a flat surface and can take lots more off of a sharp edge if you go too long. It works well on small pieces but it is hard to get a uniform surface finish on large irregular surfaces.

I think the rust occurs BECAUSE iron particles have been exposed, else there wouldn't be any rust, right? Isn't the whole idea of a stainless steel that a chrome oxide of some sort forms over the surface and sorta covers up any carbon or iron particles? So, if rust forms, it means that something has removed the chrome oxide and uncovered the iron, yes? So I think you have to get the iron GONE and then allow the chrome to oxidize again to prevent further rust.

I'd vote for a try with the Barkeeper's friend, using the oxalic acid to eat the iron. As said previously, try in on an out of sight area.

I have tried citric acid on stainless steel that I have hot forged. when hot forging stainless steel, two problems occur since we are seriously disturbing the chrome oxide coating:

-iron particles come become exposed (and they rust later)

-carbon particle become exposed (and they stay black forever) While the citric acid may have some effect on both issues, it is miserably slow in my limited experience. The oxalic acid that I use for cleaning erector set girders works slowly too, but a lot faster than does citric acid.

Pete Stanaitis

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Glass-bead-blasting can be quite gentle; I've used it on corroded brass and plastic, and brittle corrosion products got removed without any harm to the rest. A piece of charred fiberglass, for instance, turned into a clean piece of fiberglass with a depression with a beard of intact glass fibers.

A Dremel tool, with the felt buffer, and some white rouge, would be my second choice. Appearance may change, but it already has changed, that's what the rust spots did to you.

had zero luck removing orange red Fe2O3 rust spots

. If you make it work, please

I have not tried fluxes to protect stainless when welding, but have read ab out them. One is Solar Flux and another is Superior Flux 9. Not especiall y cheap, but there are some sellers on Ebay that sell small amounts. Erni e says using flux to protect stainless when welding is not as good as argon purge, but it is worth using.

Citric acid does work to remove rust from ordinary steel. I have used it o n a bunch of files that got wet.

I have not tried oxalic acid on ordinary steel. I will do that.

Dan

Various people have mentioned weak acids for this de-rusting and Ernie has mentioned a number of times a Citric acid based weld discolouration removal chemical AFAIK Citrisurf? but what hasn't been mentioned is that it is used in conjunction with an electric power supply and wand to assist the scale removal. A local fabricator near me in the UK uses a similar system but it is phosphoric acid based and again uses electrical assist. I know phosphoric acid is used for rust removal on steel but don't know of its effects on stainless, I suppose it should work as it is removing rust. I do have some phosphoric acid based alloy wheel cleaning solution so intend to try that for removing the discolouration of SS welds at some point.

Thanks for the sources. This gives us a few more possibilities...

And thanks to everyone else for their comments and input. I'll pass the info along and save for my own personal use :)

Regarding the poster who asked if I was using all stainless steel tooling while forging stainless steel:

You are right on! No, I wasn't, and I even knew better. It is very hard to make a "stainless steel forge shop" for just occasional use. That's one reason why I tend to avoid working with stainless steel forgings.

Pete Stanaitis

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I did not do a proper test, but Barkeeper Friend does not seem to remove rust from some rusty nails. I am now trying vinegar.

Dan