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  1. #1
    Join Date
    Jun 2011
    Location
    New Milford ct
    Posts
    75

    Default Stainless 316 weld showing rust stains

    Welding SS 316L to SS 316L using 316L filler rod, this is a tight fit, basicaly a round plug into a tube welded from the outside using TIG with 2 passes. The tube is back filled with argon then welded. after welding and a hydrostatic test the inside shows some staining/rust. All tooling is clean and used only on stainless. the back side with the rust has no penetration as the weld is on the other side of the plug (thick) does not rquire full penetration. Any thoughts? I have a PDF of the layout but no luck putting in this post.

  2. #2
    Join Date
    Sep 2012
    Location
    seaford de
    Posts
    406

    Default

    you could have laid your filler in steel grinder dust, maybe someone used a grinder wheel on steel at some point or laid it in steel dust, unless you have a shop dedicated to non ferrous metals it is hard to not contaminate a piece of stainless

  3. #3
    Join Date
    Apr 2009
    Location
    Upstate SC
    Posts
    137

    Default

    Or if you go too slow or too hot, some of the Chromium will boil off and leave a less-stainless area.
    CG
    Old Miller Swinger 180 Buzzbox
    Miller Diversion 165
    Smithy Lathe/Mill

  4. #4
    Join Date
    Sep 2009
    Location
    Canada
    Posts
    169

    Default

    Tungsten contaminated?
    Clean filler rod?
    Wire brush contaminated?
    Did you remove the oxide layer from the stainless steel. If so, what did you use?
    Lincoln Idealarc 250 stick/tig
    Century Mig
    Thermal Dynamics Cutmaster 52
    Torchmate CNC table

    Owner/Operator Devlin Metal Works
    Custom CNC Plasma Cutting and Welding

  5. #5

    Default

    I've seen it where people thought they had "L" because that's what they ordered and/or that's what is even written on the stock but really didn't because of a problem with at mill. It's not the norm but it does happen on occasion. More so in the past and with older stock. Now-a-days however, even the 316 that is ordered is 316L (most of the time).

    A more common occurrance is as the others above have statedabove is contamination of some sort or dwelling to long.

  6. #6
    Join Date
    Dec 2012
    Location
    Simcoe Ontario
    Posts
    87

    Default Stainless 316 weld showing rust stains

    Most likely welded it too hot. It causes the chromium to collect at one area and leaves other areas with much less chromium. The chromium makes stainless not rust. Try not heating the area as much and quench with water to avoid that.

  7. #7
    Join Date
    Aug 2004
    Location
    Milan Michigan
    Posts
    1,633

    Default

    My guess is you over heated it ( Welded to slow with the tig )

    There is a process called pasivation, Its some form of acid that is used, There are a couple ways of doing it, Some are better than others.

    I'm told this will help the appearance.

    I have never had it done so I dont know anymore about it than what I have stated so I'd recommend you do a search on passivation.

  8. #8

    Default

    I worked at a factory making stainless food storage and processing tanks for a long time and know exactly what you mean and several causes. The metal in the weld pool suffers minor degradation from being welded and the company I worked for compensated by using 318 filler for 316 stainless for weld appearance. The main problem I see for you is that 316 is not a corrosion proof grade of stainless. If you put a piece outside in the rain it will quickly start shedding red stains. You need 340 or so before your stainless exposed to corrosion will survive. A good example is auto exhaust. Anything under 340 will quickly rust away in my northern climate even though it is called stainless steel.

  9. #9
    Join Date
    Apr 2009
    Location
    Upstate SC
    Posts
    137

    Default

    I beg to differ: 316 is a very high grade of stainless and will not rust. I've worked with it in chemical plants for 30 years.
    CG
    Old Miller Swinger 180 Buzzbox
    Miller Diversion 165
    Smithy Lathe/Mill

  10. #10

    Default

    All I can say is that all of the 5 thousand plus stainless steel tanks I tig welded and then hydro tested all showed the same signs of rust and staining that the original poster Makowicki is experiencing. Not just at the welds but over the whole sheet if the tank sat for days. It's easy enough to test, just wet a piece and leave it laying flat in the puddle over night. In the morning it will be brown and nasty.

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