Pickling Stainless steel




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  1. #1
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    Default Pickling Stainless steel

    Hi there

    I've got a stainless part to weld up and I understand that one it's been heated by welding, the rust resistance of the stainless is compromised. So then you have to treat the welds with pickling gel, a combination of nitric and hydrofluoric acids which are super toxic.

    Any advise from those of you who have worked with it before? I have access to a fume hood which is probably a better option than just doing it outside in the shade. And what exactly is an acid resistant brush - natural fiber or synthetic?

    Thanks in advance
    Nic

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    Default Re: Pickling Stainless steel

    Just wear gloves, the fumes are not too bad. Only bad if you pickle when the part is still hot, which you should not do anyway.

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    Default Re: Pickling Stainless steel

    If you are stuck feel free to pop round to our w/shop in Plankenbrug.

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    Default Re: Pickling Stainless steel

    I believe it can be done with citric acid instead, this is obviously much safer etc.
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    Default Re: Pickling Stainless steel

    Quote Originally Posted by Serious? View Post
    If you are stuck feel free to pop round to our w/shop in Plankenbrug.
    StainlessTech? I think I bought the gel from you
    Last edited by niclemaitre; 2018/06/14 at 12:47 PM.

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    Default Re: Pickling Stainless steel

    I'd have the pickling and passivating done by the welding workshop: welding stainless is quite an art, beyond my welding skills
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    Default Re: Pickling Stainless steel

    [QUOTEStainlessTech? I think I bought the gel from you][/QUOTE]

    No, around the corner from them, but I am sure they assist as well.

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    Default Re: Pickling Stainless steel

    I believe it can be done with citric acid instead, this is obviously much safer etc.
    The gel is quite safe, will turn your skin yellow if in contact, and burn till you wash it off.

    Will be nasty if you get it into your eyes, but just don't be an idiot.

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    Default Re: Pickling Stainless steel

    Quote Originally Posted by jelo View Post
    I'd have the pickling and passivating done by the welding workshop: welding stainless is quite an art, beyond my welding skills
    Welding stainless (at least what I need to do - a simple butt weld) isn't too difficult if you can stick weld reasonably. Just have to get your rods/metal thickness/amps ratios correct. I've done a fair bit before, just never needed the welds to be really corrosion resistant, so I've never bothered with the pickling gel before.

    Quote Originally Posted by Serious? View Post
    The gel is quite safe, will turn your skin yellow if in contact, and burn till you wash it off.

    Will be nasty if you get it into your eyes, but just don't be an idiot.
    Ya nee, hydroflouric acid is not very nice stuff. 300 ppm/hour is enough to be fatal.

    I shall wear gloves and be nice and careful. If I get stuck I'll come by.

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    Default Re: Pickling Stainless steel

    I think the brush is horsehair. At least it looks like that. I just use an old toothbrush and turf it. First time I did this I had yellow fingers and even nails for weeks.
    If you scared of the stuff you can also polish the area of weld instead.Doing both is best.

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    Default Re: Pickling Stainless steel

    Never knew that welding stainless steel can cause it to rust.....I've been doing it for the last 35 years and have yet to see a dairy pipe "rust"
    We use pickling paste to clean the discoloration off the pipe....That's it.

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    Default Re: Pickling Stainless steel

    You can get the products from afrox...easypeasy ...just do what it says on the tin.

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    Default Re: Pickling Stainless steel

    I think it also comes down to which grade of stainless you are welding and wanting to pickle. Some are more prone to rust then others.
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    Default Re: Pickling Stainless steel

    I think the purpose of pickling is mainly for rust prevention and secondly just to make the welds easier to polish and be more presentable.Stainless can be funny stuff. I took a piece of 303 stainlesss and machined it and polished half of it. I left it out in the garden and six months later the polished section had no rust and the machined section had rusted.

    i notice 304 on the coast also rusts but is easy to bring back to a good state.

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    Default Re: Pickling Stainless steel

    All you need to do is get the discoloration off.
    Stainless has a passive layer, which is formed with oxygen/air. The discoloration will prevent restoration of the passive layer, and the material will "rust".
    Quote Originally Posted by GaryFrank View Post
    Never knew that welding stainless steel can cause it to rust.....I've been doing it for the last 35 years and have yet to see a dairy pipe "rust"
    We use pickling paste to clean the discoloration off the pipe....That's it.

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    Default Re: Pickling Stainless steel

    Quote Originally Posted by GaryFrank View Post
    Never knew that welding stainless steel can cause it to rust.....I've been doing it for the last 35 years and have yet to see a dairy pipe "rust"
    We use pickling paste to clean the discoloration off the pipe....That's it.
    Well, that is exactly what the pickling paste does, it re-passivates the stainless steel by forming a new surface layer of chromium oxide which is the main rust prevention mechanism for stainless steels. By removing the discoloration, you are letting the new passive surface layer form once again.
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    Default Re: Pickling Stainless steel

    The single most important thing to stainless finishing is iron in the area.
    If you have been working mild steel in the area and then change to SS you will pick up contamination from almost everything, from cutting discs to your work bench, and those iron bearing bits are what causes stainless to "rust".

    Avoiding 'iron' contamination

    Stainless steel supplied by reputable manufacturers, stockholders or fabricators will normally be clean and contamination free.
    These items should not show rust staining, unless contamination is introduced.

    The use of non-stainless steel processing and handling equipment is a frequent source of contamination. Work table bearers, lifting 'dogs' and chain marks have all been noted as causes. Non-metallic contact materials and vacuum lifting equipment should be used to avoid process contamination.
    Handling or fabricating stainless steel on equipment, using tools also used for non-stainless steels should be avoided. Working in 'mixed-metal' fabrication shops, without taking segregation and cleaning precautions can result in contamination.
    Cutting or grinding debris from non-stainless steels should not be allowed to settle on stainless steel items.

    As soon as any of this contamination becomes wet, rust staining will result.
    https://www.bssa.org.uk/topics.php?article=55
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  24. #18
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    Default Re: Pickling Stainless steel

    Interesting...

    I used the cutoff wheel on the grinder on this part, and that's definitely been used for mild steel. I'm going to be welding that cut line anyway, so I guess I just go ahead an pickle it as normal?

    I didn't know you are supposed to have separate tooling for SS and MS. Thanks for the info!

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    Default Re: Pickling Stainless steel

    I didn't know you are supposed to have separate tooling for SS and MS. Thanks for the info!
    Pickling will not sort this out unfortunately.

    Pferd and others make the stainless discs inner blue for this reason. The Stainless discs also have a higher working temp.

  26. #20
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    Default Re: Pickling Stainless steel

    I find the normal really thin (0.5mm?) cut off wheels on the grinder work perfectly for SS as well as MS, I just didn't know about the contamination issue. I'll get new ones and mark them to be used exclusively for SS.

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