304 Stainless signs.....rusting!
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  1. #1
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    304 Stainless signs.....rusting!

    While I am usually offering advice on this forum (plasma cutting)....our building's and grounds people asked me why the large 304 stainless steel signs in front of about 10 of Hypertherm's manufacturing facilities in NH are rusting. These signs are 304 stainless, 1/4" thick with Hypertherm cut with plasma (of course!). After cutting they were shot blasted with a media that contains no iron or material that will rust. Any ideas on this...and how to prevent it?

    Jim Colt
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    Last edited by jimcolt; 06-10-2013 at 01:20 PM.

  2. #2
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    Re: 304 Stainless signs.....rusting!

    how are they connected to the cement wall?
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  3. #3
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    Re: 304 Stainless signs.....rusting!

    it looks like the rust is bleeding from the back of the letters...but its called stainless not (stainnever)..with the right chemical content everything will corrode over time..
    Of all the things I lost I miss my mind the most...
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  4. #4
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    Re: 304 Stainless signs.....rusting!

    The picture is rotated 90 degrees. They are bolted to concrete sidewalks with galvanized brackets.

    Jim



    Quote Originally Posted by roadkillbobb View Post
    how are they connected to the cement wall?

  5. #5
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    Re: 304 Stainless signs.....rusting!

    try muriatic acid diluted on a few spots and see if that cleans the concrete of the rust, try not to get it on the stainless, put in a spray bottle and spot treat, let stand a few minutes and hose off with lots of water, once cleaned , nutrealize the acid with baking soda dissolved in water.
    Of all the things I lost I miss my mind the most...
    I know just enough about everything to be dangerous......
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  6. #6
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    Re: 304 Stainless signs.....rusting!

    it almost has to be contamination. the St. Louis arch is 304 and does not show any signs of corrosion.

    try getting someone to passivate it for you, I would think that would "cure" the issue.
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  7. #7
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    Re: 304 Stainless signs.....rusting!

    Quote Originally Posted by jimcolt View Post
    The picture is rotated 90 degrees. They are bolted to concrete sidewalks with galvanized brackets.

    Jim
    AH, now its clearer, at first it loked like the letters where on a backing, now I see its a large piece of stainles with the letters cut out....did it start after the winter,were the sidewalks salted or some other chemical put down?
    Of all the things I lost I miss my mind the most...
    I know just enough about everything to be dangerous......
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  8. #8
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    Re: 304 Stainless signs.....rusting!

    We are not concerned with the concrete, rather we want to do what is necessary to stop the stainless from rusting!

    Jim


    Quote Originally Posted by roadkillbobb View Post
    try muriatic acid diluted on a few spots and see if that cleans the concrete of the rust, try not to get it on the stainless, put in a spray bottle and spot treat, let stand a few minutes and hose off with lots of water, once cleaned , nutrealize the acid with baking soda dissolved in water.

  9. #9
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    Re: 304 Stainless signs.....rusting!

    What is the process to "passivate" the stainless?



    Quote Originally Posted by sjames View Post
    it almost has to be contamination. the St. Louis arch is 304 and does not show any signs of corrosion.

    try getting someone to passivate it for you, I would think that would "cure" the issue.

  10. #10
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    Re: 304 Stainless signs.....rusting!

    Would a cheap can of clear coat help prevent this?
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  11. #11
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    Re: 304 Stainless signs.....rusting!

    Stainless is only a common name for any of a variety of low-corrosion rate steel alloys. None of the so-called "stainless steel" alloys are 100% guaranteed against corrosion. Ask any mariner about stainless. Even 316 will rust, especially in an ocean water environment, it just takes longer than plain steel.

    I presume these signs are in or around Hanover, NH. The environment in New England is high in acidic rain as all the chemicals tossed into the air by our industrialized society all the way across North America contaminate the air and rain clouds that come our way.

    Without replacing the signs entirely I can only suggest periodic cleaning and polishing and adding some sort of clear coating to limit the exposure to the acid rain and other air-borne corrosive chemicals.

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  12. #12
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    Re: 304 Stainless signs.....rusting!

    Quote Originally Posted by jimcolt View Post
    We are not concerned with the concrete, rather we want to do what is necessary to stop the stainless from rusting!

    Jim
    originally thought letters where mounted on concrete, just the way it looked in first pic..
    Of all the things I lost I miss my mind the most...
    I know just enough about everything to be dangerous......
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  13. #13
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    Re: 304 Stainless signs.....rusting!

    Stainless will rust in an oxygen poor environment. The chromium in the alloy reacts with oxygen and forms a thin layer of Chrome oxide on the surface of the material that prevents the iron reacting and forming ferrous oxide (aka rust). Shut off the oxygen and ferrous oxide forms and thus prevents the chromium oxide layer from forming a contiguous film.

    My guess is that somehow the texture of the blasted surface and the atmospheric conditions are combining to prevent the oxide layer from forming. Is the lawn surrounding the sign kept mowed? Any harsh chemicals or fertilizer being applied to the lawn? Dunno, just WAG'ing here but some fertilizers will corrode anything.

    I think you might end up resorting to having the signs passivated to clean them and reform the oxide layer, possibly have them re-polished like they do to refurb stainless counter tops. An electro/chemical process sort of akin to reverse plating.

    Might contact a plating shop in your area and see if they have a ready solution.
    Last edited by Rog02; 06-10-2013 at 01:51 PM.
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  14. #14
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    Re: 304 Stainless signs.....rusting!

    Was your blasting grit put into a machine that prior had other media in it?

    If yes:
    Two things, machine not cleaned out well enough.
    Or, since the blasting media eats into the hose that carries it to the tip, there is grit stuck in the walls of the hose - further blasting eats farther into the hose and also breaks those loose into the blasting stream.

    If no: ignore above.

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  15. #15
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    Re: 304 Stainless signs.....rusting!

    Look around here. You will probably find exactly what you need to do this job.


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  16. #16
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    Re: 304 Stainless signs.....rusting!

    Quote Originally Posted by jimcolt View Post
    What is the process to "passivate" the stainless?
    im no expert on the process, but it involves a heated bath in a nitric acid solution.

    one source lists 20% nitric acid at 140F for 30 minutes.
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  17. #17
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    Re: 304 Stainless signs.....rusting!

    Were the signs cut on a water table that had been used to cut regular steel? I guessing here.
    It is strange that 10 signs in 10 locations are doing the same thing. could the material have been a faulty lot of 304?

  18. #18
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    Re: 304 Stainless signs.....rusting!

    They were produced at different times....at least 3 batches.

    Jim


    Quote Originally Posted by Scott Young View Post
    Were the signs cut on a water table that had been used to cut regular steel? I guessing here.
    It is strange that 10 signs in 10 locations are doing the same thing. could the material have been a faulty lot of 304?

  19. #19
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    Re: 304 Stainless signs.....rusting!

    Quote Originally Posted by jimcolt View Post
    While I am usually offering advice on this forum (plasma cutting)....our building's and grounds people asked me why the large 304 stainless steel signs in front of about 10 of Hypertherm's manufacturing facilities in NH are rusting. These signs are 304 stainless, 1/4" thick with Hypertherm cut with plasma (of course!). After cutting they were shot blasted with a media that contains no iron or material that will rust. Any ideas on this...and how to prevent it?

    Jim Colt
    Several items.

    First, as mentioned, it is 'stainless' steel, not 'this-steel-will-never-corrode-no-matter-what' steel.

    Next, shot blasted with exactly what media? Was it brand-new media, never used for any other job? Or was it some media that was previously used and then recycled and re-used for this job on the stainless plates? If the media was re-used from previous use on other steel jobs, then it was contaminated with ferrous dust/grit/particles which were then driven into/onto the stainless surface. Which then rusted.

    Next item. A smooth polished surface will corrode 'less' and 'slower' than a rougher surface. So the rather rough grit-blasted surface of your stainless plates will be more prone to corrode than a smoother finish on the plates would.

    Also, the plasma jet itself will lead to localized metallurgical changes as it melts and oxidizes the base metal. Note the slightly 'darker' (more prevalent) corrosion right at the surface of the cut edges.

    And as mentioned, passivation is often called out for stainless, in order to minimized corrosion effects.

    Over the 'net, from a few pictures, I'd guess that the media blasting 'messed up' the surface (at least a little bit), combined with the now rougher surface and not being passivated all contributed to your rusty stainless plates.

    http://www.azom.com/article.aspx?ArticleID=1142


    Possible fix? Media blast (with 'clean' virgin media!!!!) or use brand-new Scoth-Brite type abrasives to remove the existing rust, then clean (to remove grease, oil, fingerprints, etc) and passivate the plates.

    Prevention? If my over-the-net-from-a-few-pictures guess is correct, make sure the media blasting is done with 'clean' virgin media and passivate the plates.
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  20. #20
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    Re: 304 Stainless signs.....rusting!

    Reblast and clear coat with Perma-lac. The media blasting left it non passive, allowing the iron in it to rust.

  21. #21
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    Re: 304 Stainless signs.....rusting!

    The most likely culprit is the CaCl2 used in the manufacturing of the concrete is leading to Chloride pitting.

    http://products.asminternational.org...ighlight=false

  22. #22
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    Re: 304 Stainless signs.....rusting!

    We use citric acid (made for passivation) on anything we make out of 304 or 316. The air is super salty in maui so things rust quick. We built some 316 shrouds for motor controls for the water department. They are constantly getting overspray from the neighboring golf course sprinklers. 3 years and now rust.
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  23. #23
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    Re: 304 Stainless signs.....rusting!

    Jim,

    If you're looking for a process your staff can do in-house, try the following:

    1 - Remove existing corrosion with paint stripper discs in a 4.5" angle grinder. These will also tend to smooth out the surface of the stainless steel. You will also need to do some hand cleanup with scotchbrite pads on the edges inside the plasma cut letters. Be very thorough, as any residual corrosion will return.

    2 - follow the procedures in the link below for citric acid cleanup. See figures 4 and 5 in the link shown below. Citric acid is much safer to work around, and doesn't create the hazardous waste cleanup problems that nitric acid does.

    http://www.cartech.com/techarticles.aspx?id=1566

    You can mail order citric acid from amazon or lots of other companies.

    [ame]http://www.amazon.com/Citric-Acid-Organic-Non-GMO-Granu/dp/B0039CZIOY[/ame]

    [ame]http://www.amazon.com/Wagner-Power-Products-513041-Replacement/dp/B000FFVBO4/ref=pd_sim_hi_5[/ame]

    All you need is a plastic container big enough to hold the signs and enough solution to cover.

    Once the signs are clean and dry, coat with a clear enamel or clear powdercoat to protect the passive surface from environmental contamination.
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  24. #24
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    Re: 304 Stainless signs.....rusting!

    Stainless seems to be a term of art these days

    I got stainless (yeah right!!) dinnerware that's rusting to beat the band

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  25. #25
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    Re: 304 Stainless signs.....rusting!

    Yep, it stain-less not stain-proof.
    I have seen alot of stainless have very light signs of rust on the lower areas where moisture would tend to migrate to.
    But this is Oregon and EVERYTHING rusts in this state.....so it seems.
    got rain?
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