Non-Chemical Etching of Stainless Steel 1

[fogell21]

Hi guys,

Does anyone know of a non-chemical etchant for stainless steel that would delineate weld lines? I am trying to implement a weld analysis process into the workplace, but the visual is terrible without etching. I know that Sodium Hydroxide w/ a 9v battery works, but i was hoping to do without chemicals in order to limit safety hazards as well as limit costs (i.e. fume hood, other equipment). Anyone have some ideas?

Thanks

 

[moltenmetal]

What precisely IS a non-chemical etchant?

 

[fogell21]

Well thats what I am asking! Something that might be able to delineate the weld, but say without using caustic materials? Chemistry isn't my strong point, which is why I have posted this question.

 

[moltenmetal]

Etching by definition is a chemical process.

Anything which eats metal is going to be at least somewhat hazardous to handle.

You'll need the right PPE, safety shower/eyewash etc., but I'm not sure why you'd need a fumehood other than for convenience.

 

[fogell21]

Would it not be required for vapours?

 

[JoeyV87]

You'd need extra precautions for vapours, especially ones that could attack steel. Typically you would need respiratory protection in addition to extraction

 

[HgTX]

Some etchants (nital) are mild and you barely even need hand protection let alone a respirator. Some (ferric chloride) give off some nasty fumes.

My use of nital has been infrequent and limited enough at each go that often I haven't bothered with gloves. I just put the piece down in the sink, squirt, sit, rinse. I would recommend gloves, though, on principle. Or some of that nifty spray-on hand protectant which I now can't find online.

For the ferric chloride I had special nitrile gloves and a $30 teflon one-ounce dropper bottle (because it ate the rubber bulb of my other eyedropper) and I wished I had a fume hood but all I had was a window over the men's room sink(*). I can still smell it if I think about it. I strongly recommend the fume hood and maybe a respirator if you're going to do a lot of it.

But I was using both of those for carbon steel. I don't know what is best for stainless. Here's an article:

http://www.cartech.com/techarticles.aspx?id=1450

If nital will work for your purposes (and it shouldn't cost you much to get some and find out), that's probably the way to go as you won't need any special facilities.

Hg

(*) Gotta love grad school. I did it the especially non-fun way, mixing it up from hydrochloric acid (lesson learned: never use thermometer as stirrer, especially for exothermic reaction). In retrospect, perhaps I was being hazed, though my esteemed and illustrious advisor denies it.


Eng-Tips policies: faq731-376

 

[IRstuff]

And while you're on the subject of fume hoods, you need to check with your state EPA and other authorities to ensure that you don't also need to attach a scrubber to the fume hood's exhaust.

And, if you are intending to do this on a regular basis, the fume hood exhaust will need to be acid resistant. Otherwise, some years from now, some yucky gunk will start to come down from the ceiling where the condensed acid fumes ate through the metal ductwork that someone negligently installed.

TTFN

FAQ731-376

 

[IRstuff]

Oh, also, if you are doing a lot of this, your drains will need to be acid resistant, and the effluent will need to be treated before if gets to the sewer mains.

Reminds me of a previous company... The facilities guys come into our lab one day to inquire into what we're putting down our drains. "Why do you ask," says we. "Well," says they, "the drains appear to have been corroded away, and the effluent is now kind of leaking into the ground." "Oh," says we. And so began months of temporary aspiration of all of our etchants until a full-blown sewage treatment pad was installed. Apparently, no one had bothered to check what would happen if sulfuric, nitric, phosphoric, and hydrofluoric acids were dumped into the sewer system. Luckily, we never got to the level of birth defects and mutant frogs.

All and all, you'll need to evaluate the total potential costs and weigh that against just sending the stuff out to a lab that does this for a living.

TTFN

FAQ731-376

 

[moltenmetal]

For the OP's proposed etching process, "sodium hydroxide and a 9V battery", a fumehood would be a convenience at most. As to its effectiveness as an etching method, you'll need to refer to others.

Proper disposal of the waste from this process would depend on the jurisdiction. If it's periodic testing only, you will probably be OK with simply diluting with plenty of water and disposing down the sink, presuming the sewer drains are connected to a treatment works. Most treatment works tolerate (indeed encourage) somewhat alkaline discharges, with a tolerable pH range of 6 to 9 (6 being only modestly acidic, but 9 being quite alkaline). The treatment process itself generates acidity which requires base to neutralize it, and base costs money.

If the testing is more than occasional, you'll need to worry about the quantities of metals you're discharging with the waste etchant.

 

[EdStainless]

by using electrochemical you can use less aggressive chemicals. Oxalic or citric acid with 9V and you should get a nice etch. Even with only 5-10% acid.

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Plymouth Tube

 

[SMF1964]

Just a thought - If you wave a torch over the surface, would you get a different heat tint from the weld vs the base metal? of course, that could alter the heat treatment of the steel and create other issues, but the process is "non-chemical".