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Stainless 316 weld showing rust stains

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  • 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
    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

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    • #3
      Or if you go too slow or too hot, some of the Chromium will boil off and leave a less-stainless area.
      CG

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      • #4
        Tungsten contaminated?
        Clean filler rod?
        Wire brush contaminated?
        Did you remove the oxide layer from the stainless steel. If so, what did you use?

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        • #5
          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.

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          • #6
            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.

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            • #7
              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.

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              • #8
                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.

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                • #9
                  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

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                  • #10
                    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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                    • #11
                      316l is food grade and will show some staining if exposed to corrosive solutions but it depends on temperature as well. It may appear to have a brownish colour when exposed to a warm sea water environment. I would say there is some degredation caused by welding if you are seeing rust after only exposing it to water.
                      Last edited by jrscgsr; 05-05-2013, 05:16 AM.

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                      • #12
                        also keep in mind that 95% of suppliers store, move, clamp stainless with steel forks, racks and steel clamps... so there will be carbon transfer and were ever steel scratches or rests against stainless it will start to rust when exposed to water.. but from what you have said and is oxidizing in the weld zone i will agree that it was welded too slow and you burnt out the chrome in the weld zone (sugaring, or carbide participation). you can pickle the stainless after to help with the discoloration but it will still rust eventually as there is no chemical process that will add more chrome back to the weld zone to prevent this.

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