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Trouble with 304 exhaust

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  • Trouble with 304 exhaust

    I have been making myself exhaust systems for a few years now. but on my last system I have noticed what looks like rust. Its only happening in the heat effected areas next to the welds. Is there something I am missing? I try to use as little heat as I can and back purge with argon.

    Here is a picture, its looks better in person but this gets the problem across. The parts looked great for the first few months.

    Name:  7c3daf3ac07538871bac268ed58ae2d4.jpg
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  • #2
    rust bloom ss welds

    If a steel-not SS brush is used before/after welding, this can occur.
    Any brush or abrasive used on SS, must not have been used on
    steel-prior, to avoid embedding particles of steel/iron into the SS.
    Do not allow SS to come in contact with steel dust and ideally-not
    contact steel during work. Multiple wet wiping, before/during/after
    processing helps a lot. Gloves just for SS. Clean cardboard, etc. over
    work area.

    Passivation after welding can remove the iron particles, but not
    allowing contamination in the first place is easier.

    The rust seen is reacting with the iron particles in the SS matrix.
    Trying to buff, sand, polish off the embedded iron particles removes
    some of them and pushes the rest of them deeper into the SS matrix.
    At the worst--this rust blooming will accelerate corrosion of the SS.

    Comment


    • #3
      Ive been using a chop saw with a metal blade to try and reduce contamination. What tools are best to clean up the cuts afterwards? Something hard like a grinding wheel or soft like a flap wheel?

      Comment


      • #4
        abrasives to use with SS?

        Originally posted by mrk1 View Post
        Ive been using a chop saw with a metal blade to try and reduce contamination. What tools are best to clean up the cuts afterwards? Something hard like a grinding wheel or soft like a flap wheel?
        Huh??? Did my previous answer confuse you?

        Whatever you use, it cannot have touched steel. If in doubt-use new. Segregate the finishing materials, ID them, keep them covered. Wrap SS with plastic wrap or wax paper, before holding in saw vise, etc. Clean grinder guards and grinders of any steel swarf.

        That pic you posted looks like the joints were brushed with a steel brush; or steel laden sanding disc--but you're not revealing what you used. For the education of everybody--not just yourself, what did you use on those joints?

        FWIW....I'm pretty religious about handling SS--as I briefly
        described.....and I don't get rust effects after the fact. On really fussy, primo-stuff,
        I may clean and passivate the new SS--before fabbing, then passivate-again; after fabbing.
        The extra care, cleaning, handling and attention SS needs is another reason 'why?' SS fab can cost 3-5X the same in steel fab.

        Comment


        • #5
          My process has been,

          -cut with SS metal bladed chop saw
          -grind off burs with bench grinding wheel (unsure of type, just what sears had)
          -brush with designated SS brush
          -wipe off with acetone
          -purge with argon, using purge caps when I can and blue tape otherwise
          -tig weld with 40-45 amps no pulse, #8 cup and gas lens, little to no filler of either 308L or 347 hard to say it was a long time ago. A 3/32nd tungsten was used.

          Even if I have a get a separate grinding wheel for SS can the wheel itself be a source of contamination? The chop saw can leave some decent sized burs especially if the blade is getting older.

          I have two of my exhausts in the shop both made by me and one looks like crap and the other looks great, I definitely need to track this contamination down. Also a side note, at the time I made these I was sharing my shop space so I cant say 100% that say the saw wasn't used for something else.

          I really only work in SS and Aluminum so my tools don't see much mild steel unless I build a jig or something. The chop saw has lead to a lot of issues for me and Im thinking of switching to a horizontal band saw but don't know how straight of cuts they can make.
          Last edited by mrk1; 09-11-2013, 06:16 AM.

          Comment


          • #6
            Originally posted by mrk1 View Post
            I have two of my exhausts in the shop both made by me and one looks like crap and the other looks great, I definitely need to track this contamination down. Also a side note, at the time I made these I was sharing my shop space so I cant say 100% that say the saw wasn't used for something else.

            I really only work in SS and Aluminum so my tools don't see much mild steel unless I build a jig or something. The chop saw has lead to a lot of issues for me and Im thinking of switching to a horizontal band saw but don't know how straight of cuts they can make.
            It is quite likely that some of the contamination occurs during manufacture shippment and handling long before you even see the tube...some may be due to poor QC in manufacture... do you know where the tube is made??

            as said before... Nitric acid passivation or even Phosphoric acid etch after the weld would help to reduce it...

            In my experience Electropolish would afford the best protection with the bonus of a bright shiny finish...

            Comment


            • #7
              Originally posted by H80N View Post
              It is quite likely that some of the contamination occurs during manufacture shippment and handling long before you even see the tube...some may be due to poor QC in manufacture... do you know where the tube is made??

              as said before... Nitric acid passivation or even Phosphoric acid etch after the weld would help to reduce it...

              In my experience Electropolish would afford the best protection with the bonus of a bright shiny finish...
              I get the tube from the same supplier and I would have to ask them as to where it comes from before that. Im thinking before my next project which we be in a week or to that I will use a brand new brush, saw blade, and grinding wheel. Only part that kinda sucks is I have to wait a while to see if its worked.

              Im not a huge fan of having big acid baths in my shop, sure the insurance company would have a field day with that one. I never knew that electro polish would have any anti corrosion property to it, I just am not a fan of chrome.

              The only other change that I can think of that happened before I made that bad part is that I switched supplier for my argon, from Air Gas to Arc Source.

              Comment


              • #8
                One thing that I did notice is that your beads look a little cold...

                could be that you don't have enough amps dialed in.. so you have to wait longer to get it to puddle... and in doing so cooking the HAZ

                You might raise your amps and increase your travel speed... better penetration and prettier, flatter beads... with narrower HAZ

                this would actually decrease the total heat input to the workpiece... I know it sounds counterintuitive but it is real

                see how that works out for you..
                Last edited by H80N; 09-11-2013, 09:31 AM.

                Comment


                • #9
                  poor quality stainless..

                  Seen it on exhaust tubing a lot. Simple poor quality. Mix the heating cycles of a running engine tubing corrodes.
                  Kevin

                  Comment


                  • #10
                    Originally posted by Tryagn5 View Post
                    Seen it on exhaust tubing a lot. Simple poor quality. Mix the heating cycles of a running engine tubing corrodes.
                    Kevin
                    Thats what I was thinking but what was pictured is the rear most section, the other two more forward sections show more evidence of heat as expected but they do not show the rust issue.

                    Joint closer to the front.

                    Last edited by mrk1; 09-11-2013, 05:35 PM.

                    Comment


                    • #11
                      You need to brush your welds AFTER you finished welding them also and the problem should go away.

                      Comment


                      • #12
                        Originally posted by fabricator View Post
                        You need to brush your welds AFTER you finished welding them also and the problem should go away.
                        I see what your getting at but I think brushing afterwards makes for an ugly final product, not that rust is any better.

                        Comment


                        • #13
                          make sure you are getting and using 304L (not just 304) tubing and that you are using the "L" version of whatever filler you are using. If you don't have the "L" version of the base material and filler you material will rust in the weld/HAZ.

                          The reasons other have stated could also be the problem.

                          Comment


                          • #14
                            Here is a close up of another part I made that was used for almost a year including one new england winter. This looks great and is from the same metal supplier.

                            Comment

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