Pickling Stainless Steel

D

dbb-the-bruce

Dave
H-M Lifetime Diamond Member
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Well, just spent about an hour googling options for cleaning up SS after soldering or welding and oh boy....

From what I've found, the existing paste/gel/liquid pickle for SS (that's been in use for years) is pretty nasty stuff if you aren't careful. It contains really strong acids and has all sorts of safety and handling cautions. All in all not something I'd really want to mess with if I don't need to. Interestingly you can order it from McMaster and get it tomorrow without question? (I didn't proceed all the way to checkout to really find out).

I also found that there several other processes that are not as bio and eco dangerous, but these seem aimed at much bigger scale production cases.

Finally, there was one "eco safe" pickle in promoted in a video - but the product appears to unobtainim and it looked like the company was in Bopal (ha / yikes!).

So in short what are your experiences with using the dangerous traditional paste/gels and or do you know of and preferably use something a little less toxic?
 
dbb-the-bruce said:
Well, just spent about an hour googling options for cleaning up SS after soldering or welding and oh boy....

From what I've found, the existing paste/gel/liquid pickle for SS (that's been in use for years) is pretty nasty stuff if you aren't careful. It contains really strong acids and has all sorts of safety and handling cautions. All in all not something I'd really want to mess with if I don't need to. Interestingly you can order it from McMaster and get it tomorrow without question? (I didn't proceed all the way to checkout to really find out).

I also found that there several other processes that are not as bio and eco dangerous, but these seem aimed at much bigger scale production cases.

Finally, there was one "eco safe" pickle in promoted in a video - but the product appears to unobtainim and it looked like the company was in Bopal (ha / yikes!).

So in short what are your experiences with using the dangerous traditional paste/gels and or do you know of and preferably use something a little less toxic?
Click to expand...
Any kind of chemical procedure on stainless steel is not just about the acids. Sulphuric acid, for example, I consider to be eco-safe. It only has hydrogen, sulphur, and (lots of) oxygen. Very dangerous when concentrated, to be sure, and has to be added to the diluting water, rather than the other way around. Letting even a drop of water hit concentrated sulphuric acid is hot, instant splashing violence! For disposal, you can let it expend itself on a rock, or on the ground. It only makes stuff the whole land has in abundance. You only need diluted battery acid strength, but I am not sure why one would pickle stainless. You can get it definitively clean for any plating or suchlike stuff with more harmless cleaners.

Other acids, like chromic, nitric, or chlorine based acid hydrochloric, muriatic, swimming pool pH adjuster, whatever, are not so eco-friendly.

Phosphoric acid, as in Coca-Cola, is widely used as a rust stripper, and in rust conversion products. I have never been tempted by it.

The real danger is that stainless contains chromium, and in acid chemical cleaning, can expose you to hexavalent chromium in solution. The stuff is off the scale for extreme toxicity and carcinogenic effect. Do not do chemistry with stainless! It only needs to be ground clean for welding.
Google "hexavalent chrome", and you are bound to be put off by it all.
 
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I have done a lot of weld cleaning on stainless and did most all of it with a convolute deburring wheel and Scotchbrite wheels, also sometime bead blasting. Also, I seem to remember a product called Ospho.
 
The application of pickling SS appears to be quite common AFTER welding or fabricating. Specifically, if you don't the welds will not be as corrosion resistant. The tough oxide (chromium?) builds up quickly on SS that's exposed to oxygen (so even wear parts stay resistant). Learned a fair amount about it. The pickle contains floric acid(?) which is why there is so much caution about using it.

Check into it - I am by no means an expert but it appears to be a quite common process for cleaning up welded joints and for preparing "raw" SS from the mills.
 
My potential application is for small detail stuff that I will be torch soldering (think clock work / jewelry scale). Partly my torch soldering skills are mediocre to fair and I often end up with lots of scale and coloring that is really hard to remove abrasively. For instance the inside of a 1" square box.

I'd be happy to consider other ways to clean up. And clearly, being better at not producing a lot in the first place would also help.
 
Hex chrome is an issue if you inhale it or drink it. It is ok to handle. But don't snort, smoke, or inject it.

Most pickles are cheap HCL washes done warm and fairly dilute. Pickling stainless is an immersion process, but I don't see why wiping it on wouldn't work other than leaving an irregular finish. It's usually done to remove scale and prep for paint. It is also a mandatory prep for metallic plating and coating.

Typically we are more interested in pickling rust-prone steels. There are many acid combinations for different reasons, but it's meant as a wash and is meant to be cheap. Weak solutions of acid can be neutralized, diluted, and disposed of in the sink.
 
Oh jesus, don't even mention hydrofluoric acid. That is bad stuff for a reason.

Most strong acids are used when a flood of protons are needed, the anion can be selected for other reasons like subsequent processes or non-interaction. That's why most pickles use HCL, its' cheap and the chlorine doesn't matter as long as it gets rinsed off.
 
This is the stuff I was looking at
Having no experience with it I am quite concerned about using it safely and storing it - fully recognizing that using it correctly and safely happens all the time - I just want to know what that means and how do "be safe". Then I can decide if it's worth the trouble.

Here is the SDS

Kind of like when I worked around fluorine gas lasers - the instructions were "leave immediately, leave your buddy behind if the alarm goes off"
 
dbb-the-bruce said:
My potential application is for small detail stuff that I will be torch soldering (think clock work / jewelry scale). Partly my torch soldering skills are mediocre to fair and I often end up with lots of scale and coloring that is really hard to remove abrasively. For instance the inside of a 1" square box.

I'd be happy to consider other ways to clean up. And clearly, being better at not producing a lot in the first place would also help.
Click to expand...

What kind of flux are you using? For stainless, you need special flux, commonly the black stuff. Prep can be done mechanically, after degreasing. There is no need for pickling. Use tons of flux, and scoop any that runs off and pour it back on. If you do your brazing properly, the flux shouldn't burn. That's what makes cleanup so difficult.
 
More information than you asked for, but it does include a safe alternative. Also includes a good explanation of the process.
 
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