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Up Topic Welding Industry / Technical Discussions / Thoughts and opinions..
- - By Kix (****) Date 03-25-2009 13:44
  http://i11.photobucket.com/albums/a189/vdubin474/Laddercrack1.jpg  http://i11.photobucket.com/albums/a189/vdubin474/laddercrack2.jpg  http://i11.photobucket.com/albums/a189/vdubin474/laddercrack3.jpg     You are looking at a crack along the toe of a weld.  This is a handrail support tube welded to a beam.  Handrail support is of a GLX-55 material and a thickness of .060" and the beam is of a A607 material and with a thickness of .075".  It is first MIG welded with a .035 ER802-D2 wire and if there are and defects, they get TIG dressed.  As you can see, the one in the picture has been TIG dressed probably because of some overlap in the first weld.

       So I'm looking for some thoughts and opinions on why this might of cracked where it did.  If you look at the TIG dressing, you can see that little or no filler was used around the toe of the weld.  If filler was used, it would be the same as the MIG wire (ER80S-D2).  I'm thinking that since no filler was used, the base material got way to hot and hot shorted, causing embrittlement right in the HAZ next to the toe.  So what else do you guys think it could be?

  Thanks, Kix
Parent - - By jwright650 (*****) Date 03-25-2009 13:47
HAZ too large? Material got too hot using the extra TIG heat to dress it up?
Parent - - By Kix (****) Date 03-25-2009 13:51
Thanks John!  Are your thoughts still the same even if I say that it was TIG dressed a week later?
Parent - - By Lawrence (*****) Date 03-25-2009 15:28
Hmm,

Not particularly familliar with the grade.

But overlap is most often caused by minimal heat at the toes and too much filler... This condition doesn't really suggest overheat conditions that would go way out into the HAZ does it?

If the GTAW (wash/cover) was very hot and slow--with no filler I could see an occurance of undercut.... Or no filler causing starvation of deoxidizers but those results are usually porosity rather than cracking.
Parent - By Kix (****) Date 03-25-2009 17:35
Lawrence,

"But overlap is most often caused by minimal heat at the toes and too much filler... This condition doesn't really suggest overheat conditions that would go way out into the HAZ does it?"  
    You are correct.  The overlap happened with the MIG weld.  Ladder gets inspected once complete, and defects such as overlap get dressed.  There is no undercut so we can't blame that.  You see this a lot in thin carbon steels when autogenous welding with oxy fuel.  It cracks right along the side of the puddle, not in the center like you would see with 6061-T6 or something.
Parent - - By jwright650 (*****) Date 03-25-2009 15:44
I was thinking along the lines of shrinkage due to the extra heat from the TIG passes and the material gave up in the HAZ.
Parent - - By Kix (****) Date 03-25-2009 17:17
That was my first thought, but the fact that the crack cracked later on in service is what threw me.  I guess shrinkage could of got it almost to the point of fracture and to where all it would take was just a bit of stress to crack it all the way.
Parent - By jwright650 (*****) Date 03-25-2009 17:34
It was purely a guess on my part. Maybe someone else will chime in that has experienced this before.
Parent - - By CHGuilford (****) Date 03-25-2009 21:31
You have a large heat sink there.  My guess is that the GTAW welds cooled too quickly - quenching and hardening on the weld toe.
Parent - By CWI555 (*****) Date 03-25-2009 22:45
I think that one's a winner
Parent - - By jwright650 (*****) Date 03-26-2009 12:33
hi Chet,
I missed the heat sink part...the materials are really thin(1/16"). Help me.....I don't see what you mean.
Parent - - By CHGuilford (****) Date 03-26-2009 13:10
Well...I guess I missed the part about 1/16" thickness.  From the photos, I thought that was the usual A500 tubing and the corner radius would indicate thicker than 1/16".  That's what happens when I speed read on my break.

However, if the GTAW was done at low heat input (low amps, fast travel)the weld would cool quickly which could quench the weld and HAZ. 
Is that likely to happen on 1/16" material? I'm not a TIGger so I don't know.
Parent - - By jwright650 (*****) Date 03-26-2009 14:17
LOL...I threw my guess at it...but don't know if will stick or not....LOL
Parent - - By Kix (****) Date 03-26-2009 17:30
Might depend on what you're throwing it at and how many volts and amps you're runnin. ;-)  I think we might have a combo of a couple things mentioned in here.
Parent - - By 803056 (*****) Date 03-27-2009 02:55
I'm not familiar with the GXL-55. What is the chemistry and mechanical properties?

My first guess would be along the lines of a hard HAZ due to rapid cooling and no preheat, but that would be dependent on the chemistry of the base metal that cracked.

Al
Parent - - By Kix (****) Date 03-27-2009 12:55
Al, your guess is as good as mine on that steel.  On the prints, in the bill of materials, all I get is a HRS or CRS for so many things.  This GLX-55 is what they had on the print so I posted it. lol  I was hoping one of you guys would know what it was.  It's a small, thin, square tube with no mill scale, I know that much. ;-)
Parent - - By 803056 (*****) Date 03-29-2009 20:00
I did a quick search. This is a website I found. I didn't have time to search further, but I thought it might help you.

http://www.weldreality.com/MisscellanousmetalEtoK.htm

Best regards - Al
Parent - By Kix (****) Date 03-30-2009 15:44
Thanks Al!  That's a really good link.
Up Topic Welding Industry / Technical Discussions / Thoughts and opinions..

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