MrK.

I recently used the oxalic acid (wood bleach) method to de-rust some chromed shelves that I have. It worked pretty good. I made a small pool out of 2x4s and plywood, lined it with plastic. I added about a cup and a half of oxalic acid powder and got the pH down to about 2.7. It took about 24 hours to remove the rust and it required rough scrubbing to get it done. I know there are some that worry about this method from an environmental standpoint but I'm not. This material is routinely used to clean decks and allowed to seep into the ground with no ill effects. In fact some plants love acid soil, I dumped about a gallon on each of my azaleas.
I'm a homebrewer. Have been for about 20 years. I use a sanitizer called Star San to sanitize my kegs, fermentation carboys and bottles. Star San is an acid based sanitizer that is described as "Odorless, flavorless, biodegradable,and environmentally friendly". I have dumped 100s of gallons of this sanitizer in my yard, on my plants and in the woods surrounding my house over the years. This is a "no rinse" foaming sanitizer which means that when you agitate a vessel (E.g. a bottle) you leave the residue in the vessel before you fill it with beer. There is no taste or harm as a result of this foamy residue. You can literally drink it. The active ingredients are Dodecylbenzenesulfonic Acid and Phosphoric Acid.
Enough of the brewing lesson and back to bikes. I was doing some beer stuff yesterday so mixed up 2.5 gallons of Star San. The mix ratio is 1oz to 5gal water. After I was done I started wondering how Star San would work as a rust remover. I checked the pH of the left over sanitizer and it was 2.3. I grabbed a piece of rusty strap metal and dropped it in the bucket.12 hours later I (glove less- mask-less) fished it out and lo and behold, rust free. This morning i dug around in my workshop and got a rusty chainring, a rusty pair of crappy brake arms and a rear dropout from an old Huffy that I hacked off to scavenge the tubing. I Dropped them in the bucket and let them go about 4 hours. When I fished them out I was very impressed. The package of oxalic acid I used was about $20 and I used about 1/3 of it. A 32oz btl of Star San costs about $14 and will make 5 gal of pH 2.3 acid for about 44 cents. Pics below

xiaoman1 

Impressive..I want to order some f this stuff for a project that I am working on, thanks.

Mr. Spadoni 

Not surprised by the results. I had some Star San in a bottle that I put on a shelf. The bottle leaked. Took all the varnish off the shelf. But I have never hesitated to dip my hands in the stuff multiple times on brew days and it never even ended up with chapped hands.
But with the results you got, I wanna try some B Brite on rusty parts. That stuff would probably strip chrome.

desconhecido 

Never heard of this stuff. Back in the 80s I brewed some pretty decent beer, but I always used either boiling or bleach for sanitizer. But, times have changed, so it seems, and so has home brewing practice.

Looked it up "STAR SAN is a blend of phosphoric acid and dodecylbenzenesulfonic acid. " I know what phosphoric acid is, the other, not so much. Typically, phosphoric acid will replace rust with some sort of iron phosphate which is dull and grey/black/yellowish in appearance. A phosphate coating on iron or steel will inhibit rust and also provides a good surface for painting, perhaps with some sanding, I don't know. Apparently, star san may harm chrome plating and it may remove zinc plating, so care should be exercised. Also, I don't know enough about the chemistry to say whether the reaction may or may not create free hydrogen, which can be detrimental to steel strength. If I were to consider this stuff as a normal tool for rust removal, I'd like to know what dodecylbenzenesulfonic acid is and how it interacts with the various metals that would be put into it and what the products of the reaction are.

Oxalic acid seems to be ok and I've not noticed any bad results other than that yellow crap and how to get the stuff/residue out of tubes and passages. Of the ones that I've used, a typical commercial phosphoric acid metal prep solution, probably mixed with a detergent, seems to give the expected result (rust/corrosion replaced with a gray/black iron phosphate, I think). Evaporust seems to be the least messy stuff though slower than oxalic acid. No unsightly residue and it seems to be decent with chrome. Cleans up easily and according to the seller is pretty harmless, though I don't think someone should drink it, apparently as some people do with Star San.

MrK.

I did a little Google snooping and found that dodecylbenzenesulfonic acid is an active ingredient in radiator flush used to remove rust and scale from clogged automotive radiators.

squirtdad

reminds me I have brew kits to i need to get going on thanks

dweenk

How does Star San work with alloy components? Like when you may drop alloy brake calipers into it in order to clean steel bolts and springs.

curbtender

It's acid, so don't use it for that. That Evaporust would be your best bet.

dweenk

That's what I thought. My son left some of sanitizers behind when he left home. He was a small brewer.