How to clean the inside of ERW mild steel tubes for TIG?

  1. bigsid Member

    Messages:
    15
    Location:
    Derbyshire, UK
    Hi all,

    New to TIG and been practising on some mild steel rectangle ERW tubing 50x25x3mm for a project I'm hoping to do soon. Trying to stick offcuts of said tube to one another for some practice. Tacked it ok, but when I gave it the full beans the porosity was ridiculous and at one point the bead started to grow upwards. I tried going over the bead again, but the more I did the worse it got.

    The outside of the tube was clean. I'd hit it wish a silicon carbide wheel to get all the mill scale off and cleaned with acetone, but it was like the weld was reacting with moisture or chemicals. There were a lot of sparkles happening too.

    Argon flow was set at about 8L/m. I think that the problem is due to schmoo and impurities on the inside of the ERW tubing. So, my question is, what's the best way to clean the inside of tubes prior to TIG?

    Many Thanks!
    Sid
     
  2. Fazerruss

    Fazerruss Member

    Messages:
    2,597
    West Yorkshire
    Quite simply you don't because you can't. If you are "giving it some beans" then you are likely getting the metal far too hot and boiling it. Are you using triple deoxidised filler rod?
    When OxyAcet gas welding for example if you get the metal too hot it literally explodes. There is a limit to how much heat steel will accept.

    I'm no expert by the way but I've have discovered this over the years from my own mistakes. There will be someone along with a better explanation.
     
    Steveblade likes this.
  3. bigsid Member

    Messages:
    15
    Location:
    Derbyshire, UK
    Thanks for the advice. It's a bit weird though, because previously I'd practiced joining a couple of pieces of 3mm thick angle iron back to back using the same gas and amperage settings and the bead went down quite nicely. The only real difference is being angle iron I'd been able to properly clean all the surfaces whereas with the tube, I didn't bother trying to clean the inside.

    Here's some pictures for comparison...

    This is the 3mm angle iron which was cleaned on all surfaces.

    [​IMG]

    And here's the attempt at the rectangle tube...

    [​IMG]
     
  4. Shox Dr

    Shox Dr Chief Engineer to Carlos Fandango

    Messages:
    15,248
    Location:
    East Yorkshire
    Repeat until it sinks in;)

    I MUST sharpen the tungsten Every time I touch down, and Clean the area to be welded.

    what are your settings inc torch setup
     
    tom2207, slim_boy_fat and mtt.tr like this.
  5. bigsid Member

    Messages:
    15
    Location:
    Derbyshire, UK
    8L/m argon, 100amps DC. Lanthinated 2.4mm Tungsten and 2.4mm ER702-S filler rod. Err.. tungsten was sharp but might have been a tad dirty. However, work pieces were clean, at least on the outside.
     
  6. Munkul Member

    Messages:
    2,091
    Cumbria, UK
    Gas contamination? There's something majorly wrong there, and the one thing it isn't, is the internals of the hollow section. You aren't even hot enough for that, so it's coming from something else. Looks like gas to me.

    Unless the cut edges were full of oil, I wouldn;t expect it to be the material going by your photos.

    You ARE using pure argon?
     
  7. Shox Dr

    Shox Dr Chief Engineer to Carlos Fandango

    Messages:
    15,248
    Location:
    East Yorkshire
    Tungsten and rod too big. Go down to 1.6mm in both 85amp. No6cup 5-6mmmm stickout
     
  8. Munkul Member

    Messages:
    2,091
    Cumbria, UK
    Tungsten and rod size isn't going to do anything to change the above contamination....

    8lpm is on the low side for gas, should still be ok for a no.6 cup but I'd up it a bit to be sure... no good if you're using a monster cup though, you need loads of gas for those.

    I've welded loads of steel with a club for a tungsten by the end of the run and it still welds... just poorly...
     
  9. Shox Dr

    Shox Dr Chief Engineer to Carlos Fandango

    Messages:
    15,248
    Location:
    East Yorkshire
    All true, I’ve done the same. I was going to take a picture of my tungsten, then saw the state of it:laughing:. But that comes with experience. Far easier to start fresh everytime when you are learning.

    (Piccy for S&G:ashamed:)
    image.jpg
     
    Munkul likes this.
  10. bigsid Member

    Messages:
    15
    Location:
    Derbyshire, UK
    Yes, pure argon. No. 8 cup. I just cleaned some offcuts in acetone (dunked them in, scrubbed the insiders with a toothbrush), tried some beads just on the flat outside surfaces of the tube. Not as bad, but similar porosity issues.

    [​IMG]

    I don't know what's going on. I've tried various amps from 65 -100 and no discernible difference in the appearance of the weld. I know there's a bit of mill scale on this piece, but I did the same on a polished up piece and the results were similar.
     
  11. mtt.tr

    mtt.tr Member

    Messages:
    2,935
    Essex England
    thats gas coverage, show us a pic of your tungsten

    What angle is your torch at, and it is set up with the proper insulators?
     
  12. Shox Dr

    Shox Dr Chief Engineer to Carlos Fandango

    Messages:
    15,248
    Location:
    East Yorkshire
    You also need to remove the millscale
     
    Arclikeharrypotter likes this.
  13. Shox Dr

    Shox Dr Chief Engineer to Carlos Fandango

    Messages:
    15,248
    Location:
    East Yorkshire
    lack of consistency doesnt help you
     
    8ob likes this.
  14. bigsid Member

    Messages:
    15
    Location:
    Derbyshire, UK
    TIG is so hard I think because there are so many variables and I'm being impatient which also doesn't help. However, I went back to a ceriated 1.6mm tungsten, no7 cup, 1.6mm filler wire, checked all the gas line connections (they were fine) and upped the gas flow rate and got a much better result with no porosity. I try to keep my torch angle maximum about 20-30 degs off vertical. Tungsten is protruding about 5-7mm from end of cup. Seems ok now. I guess this all just comes with lots of experience and all the hints and tips from the knowledgable folk on here :)
     
    ScoobyMick, Shox Dr and slim_boy_fat like this.
  15. BelgiqueB Member

    Messages:
    99
    Location:
    Belgium
    Is the torch on the negative?
     
  16. Munkul Member

    Messages:
    2,091
    Cumbria, UK
    What he said... looks like its just polished on top. It will always contaminate to a degree, and spit back, also can be worse than it first looks.
     
  17. Fazerruss

    Fazerruss Member

    Messages:
    2,597
    West Yorkshire
    I've tigged all sorts of sh17e covered in milscale, rust, paint, oil, poo but never had porosity that bad. To me that looks like a gas issue or a draft blowing during welding.
     
    bigsid likes this.
  18. anto44

    anto44 Member

    Messages:
    1,353
    Location:
    ireland
    First thing I'd do is carry out a gas test. I read about it on here but can't remember who posted it (I think it might have been @Welderpaul ) . Get a piece of clean metal, something like 6mm so you don't penetrate through it, fit a freshly ground tungsten. Set the amps to about 90 and set post flow to about 6 seconds, and hold the torch with the tungsten square to the metal and a nice tight arc gap, light up just long enough to create a nice puddle and let off, hold the torch in position until the post flow stops. You should have little to no discoloration in the weld pool and in the area around it covered by the torch.
     
  19. Brad93

    Brad93 M J B Engineering

    Messages:
    8,476
    Location:
    Essex
    That’s either covered in grease and oil or more likely you’ve got a gas issue.
     
  20. Brad93

    Brad93 M J B Engineering

    Messages:
    8,476
    Location:
    Essex
    Take a picture of your gas lens, the mesh/gauze bit.

    Is the o-ring on the Backcap in good condition?

    8LPM is fine with that size gas lens, I’d run 6-7lpm on steel with that setup no problem.

    You could have a pinhole in your gas line.

    get some soapy water or even better leak detector and check all connections and hoses.
     
Advertisements