Muriatic acid and galvanization?

[Nick]

Spent some quality time with the search function, but didn't turn up anything.

I've got a project in mind for an early style barrel padlock, and I want to use some pipe for the barrel. The only problem is the only pipe of the right size readily avaliable to me is galvanized.

I know all about the health risks of galvy, I knew about that long before I even thought about picking up the hammer. But though I've used galvanized wire a lot in the past for making chainmaille, I've never had cause to remove the galvanization before.

I've got some Muriatic acid, and I thought that might do the trick, but I wanted some input first. Will it remove the galvanization, and should I dillute it or use it straight up?

Nick

[trying-it]

Nick, I myself have used muriatic acid (diluted some with water) on numerous occasions for etching and/or for removing galvanized. [Follow acid & water mixing and all other related safeguards]

I was taught the trick in a university level artist blacksmithing class. There are numerous pieces of rusty scrap to be had that have a dangerous zinc/galvaized coating lurking just under the rusty coat. I now automatically give a muriatic test bath to all rusty parts too. When placed in diluted muriatic zinc/galvanized will almost instantly begin to react & fizz, even if it is hidden under a rusty layer. Continue bath until ALL fizzing stops, then rinse in baking soda & water to neutralize. Before using this safety process I had zinc sneak up & bite me a few times will sickening results.

Be safe, not sorry! I would much rather talk to you than about you!

Hope this info helps.

[Nick]

Thank you, it does. I'd be out getting the pipe right now, except it seems my uncle has made off with my car's battery. Long story, don't know exactly what he did, hope he's back soon.

What kind of fumes are released during this process? I'll be ventilating, but it'd be nice to know what I'm ventilating for, which might change the whitertos and the whyfors.

[trying-it]

Nick it works great for zinc removal and/or as a pattern weld etchant! For either use I combine the muriatic acid with a little water too. Follow all safety rules related to acid use, mixing, storage, disposal, etc.

I was taught this method in university level artist blacksmithing courses. Many are unaware that zinc/galvanized can actually remain hidden under a rusty coating too. I automatically test all rusty materials now too as I have had zinc sneak up & bite me on more than one occasion with sickening consequences.

Place item in solution and if even a small amount of zinc is present (seen or unseen) a reaction and fizzing will begin almost immediately. Allow acid bath to continue until ALL fizzing stops, then rinse item in baking soda & water to neutralize.

BE SAFE, NOT SORRY!

I would much rather talk to you than about you!

Hope this info helps!

[trying-it]

If at all possible do process completely outside so fumes are of less concern. It also saves an even bigger mess from happening if solution(spills) or fizzing foam gets on shop floor. In that event a lot of baking soda & some water will neutralize that mess too.

[Don A]

Nick,

Home Depot, Lowes, or most any hardware usually carries black-iron pipe in any length, from 1" nipples to 10' pipes.

1/2" up to 1.5" ID is common.

A short length of black-iron pipe is probably going to be cheaper the the muratic acid, not to mention a lot less trouble.

As with any sort of material from such stores, the longer the piece you buy, the less your cost per inch.

Don

[evfreek]

Hi Nick. This works just fine. It is cheap, easy, and you don't have to breathe the zinc fumes. Dilute the acid, and let it sit a long time. The less it froths, the less collateral rust damage you will have caused by aerosolized HCl.

How much to use? Here is a quick calculation:

A 1/2" schedule 40 galvanized pipe will have about 1.8 oz/sq ft of zinc. For 1 ft of pipe with id 5/8" and od 7/8", this is

7/8/12*3.1416*1.8 + 5/8/12*3.1416*1.8 = .7061 oz/ft

assuming the inner layer is intact. For most cheap blacksmiths, however, the inner layer will be almost missing due to corrosion, else why was the pipe free in the first place.

Pool hydrochloric acid is about 30% by weight HCl. The density is 1.149. HCl has a molar weight of 36.14, so one gram of pool acid has:

.3/36.14 = 0.0083 moles of H+, two of which are required to dissolve one mole of divalent zinc with a molar weight of 63.4.

(.3/36.14)*63.4/2 = .2631 grams of zinc dissolved by one gram of pool acid,
or the same number of ounces of zinc dissolved by one (weight) ounce of acid. This must be debited to convert to fluid ounces, since pool acid is slightly denser than water:

.7061/.2631/1.149 = 2.3356 fluid ounces of acid per foot of 1/2" sch 40 pipe.

Use more to make sure its all gone in a reasonable time, or use less if the pipe is heavily corroded. I have noticed that even if a lot more is used, not all the zinc is dissolved. It can flare up when you hit the hot metal with a hammer dislodging a piece of rust (remember, cheap pipe has lumps of rust inside) which protected some zinc. Do not inhale.

I hope the numbers are correct.

Disposing of the acid? Evaporate to make cheap killed acid soldering flux, or neutralize with baking soda, or pour on concrete, and it will slowly neutralize by itself. Does zinc disposed of in this manner create more water pollution than it would create air pollution from burning it off? I don't know.

[ThomasPowers]

Gas created is hydrogen. Using muratic/HCl in your shop will often result in your tools rusting due to acid fumes. Outside or forced air fume hood suggested!

Thomas