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19th July 2012, 07:22 PM #1Philomath in training
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Alternatives to stainless acid pickles
Seven or so years back I worked in a place that made stainless water heaters. Once the tanks were welded, they would be pickled with a Hydrofluoric/ Nitric acid mix. After hearing what it would do if splashed on skin I promised myself that I wouldn't go anywhere near something like that for the shed (there was the small children factor for a start).
On the rare occasions I weld stainless (at home) I usually finish up with a wire brush or abrasive to take off the oxide. Does anyone know if anything been developed that can replace the HF/HNO3 mix that is relatively safe if spilt?
Michael
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19th July 2012 07:22 PM # ADSGoogle Adsense Advertisement
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20th July 2012, 07:15 PM #2Senior Member
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I doubt if there is anything as effective but would like to hear if there is. I use it at home and hate the stuff but I am just careful, brush on very gentally, wear gloves and usually got my overalls and goggles, boots etc on anyway while welding. Yeah keep the billy lids and pets away for sure.
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20th July 2012, 08:56 PM #3
The latest method as far as I am aware involves using an electronic machine with a wand of some kind and a liquid. I have seen it used at work by maintenance and contractors. It is safer than the old mix which is the stuff of nightmares but I cannot be more specific. I have my doubts whether it is viable for hobby use but that is not based on actual knowledge so don't think it is. If anyone is really interested I could ask some questions.
Dean
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20th July 2012, 09:03 PM #4
Here's the wand kind of pickle...
It's a form of electrolytic cleaning - phosphoric and citric acid + current.
[ame=http://www.youtube.com/watch?v=NoKa4TBxmRE]Pickling Stainless Steel: Stainless steel fabricators in a pickle no longer - YouTube[/ame]
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20th July 2012, 09:50 PM #5Member
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Aussie developed and Aussie made.
Metal Science Technologies | mepBLITz
Cheers
Pete
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20th July 2012, 11:00 PM #6
Well there you go. Next question is how much?
Dean
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21st July 2012, 08:10 AM #7vapourforge.com
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21st July 2012, 08:29 AM #8Philomath in training
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Interesting stuff guys - I picked up a price on the 'net of $8 to $9k for the big brother unit to the one shown in the video. I have an email in to see what the smaller version (the one shown in the video) will set a buyer back.
The added bit - Still not cheap. Even the baby Surfox unit is still $1800 ish. Looking at these though I'm now wondering how sophisticated they are. The lunchbox size inverters are getting common and cheaper too (a several hundred dollars). The rest of the set up doesn't look very complicated. While not as good as a purpose designed unit, would that work for an occasional user? Thoughts?
MichaelLast edited by Michael G; 21st July 2012 at 08:38 AM. Reason: looked at Russell's links
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21st July 2012, 09:34 AM #9
I did a bit of googling and came up with
TIG Welder for Stainless Weld Discoloration Removal
I happen to have both phosphoric and citric acid already. May be I will try with my little battery charger. One day. Am very interested in anybody else posting their results. I am trying to clean up my shed not make more mess LOL.
Dean
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22nd July 2012, 06:55 PM #10
I must be missing something here why not simply polish it there a many different methods that can be used to polish stainless upto a mirror finish...............and best of all no fiendish chemicals!!!!
Regards LouJust Do The Best You Can With What You HAve At The Time
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22nd July 2012, 07:35 PM #11
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22nd July 2012, 07:53 PM #12Engineers are qualified to make claims
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I believe that contaminants stop chromium oxide molecules forming as the protective barrier. SS needs oxygen to get to the surface in order to form the chromium oxide. Contaminated surfaces after welding prevent oxygen getting to the chromium which can then allow it to rust. You can often see on dirty stainless steel there is a brown rust formation known as tea staining, this is because oxygen is not able to get to the chromium in those areas to form the protective barrier.
Regards
John
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24th July 2012, 07:38 PM #13GOLD MEMBER
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I am glad to see the healthy respect that is being shown for pickling paste - it truly is fiendish stuff.
The electrolytic methods work really well, but at a high set up cost.
Tecnically, to gain the utmost corrosion resistance you are supposed to pickle and neutralise, which is a two step process. Most skip the neutralising step in my experience.
To be honest, unless the environment is really nasty, I have never seen too much go awry after a good wire brush (stainlless brush of course) or a rub with a scotchbrite pad. As far a polishing stainless goes, it's a mongrel job! Plus once polished you must maintain it or it gets daggy looking and show marks etc. A brushed finish is probably a little more user friendly and much faster to achieve while hiding effectively any small blemishes etc. A full on polish will show every surface blemish and ripple.
If pickling is a must, then use good chemical gloves and a full face mask - safety glasses just don't cut it, (you can also get a neutralising solution for use in a first aid scenario but it is very expensive and has a limited life I believe) and make sure that you use plenty of water to dilute any residue, (hot water seems to work best when washing the solution off by the way).
The need to pickle can be minimised by correct amperage settings - don't get the weld too hot or you get really thick black oxides, the rainbow hues are what you want to see and consider purge welding components to provide a gas cover on the root side of the weld.
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24th July 2012, 07:55 PM #14Philomath in training
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Got an email back on the Aussie made electrolysis units. The TIG champ retails for around $3k and the megaBlitz is around $5k.
Not cheap. Perhaps it's the wire brush after all.
Michael
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27th July 2012, 08:18 PM #15SENIOR MEMBER
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I looked up stainless passivation earlier this year and found an article that said to use 30% nitric acid in water. It made the steel shot blasted 316 that had gone tea brown after a day in the rain, go silver white in appearance and it's been fine for the last 5 months or so. I did several coats and rinsed off in between with the hose so the it didn't dry out with acid on it. Nitric is an oxidising acid apparently.
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