External undercut on hotpass (stick pipe

Date 09-19-2005 02:30

I've been running hotpasses on a pipeline job. The hotpass is the second pass, and it's purpose is to clean slag out of the weld. I was welding hot and leaving the pass just a little below flush (.219 wall) Everything was clean and I was staying right behind the bead hands. The inspector on the job came up to me and said my hotpasses had too much undercut in them (external of course). There was some, but it was'nt any more than normal. I've never heard an inspector comment on external undercut on a hot pass. I always believed the filler and cap pass would easily take care of the undercut. I've never had a problem with x-ray with this problem. Can someone please explain this to me? I'm hot passing colder now, but I have to go slower. The pass is above flush in some places (especially tight fits). It's harder to see to cap when the preceding pass is above flush.

By JTMcC

Date 09-19-2005 15:06

Boy you've got a real winner of an inspector there.
When inspection comes up with stupid remarks like that I just ask to see their reference that backs up their claim.
You might point out that the bead hands are putting almost 100% external undercut on the weld. But of course it's imaterial if it no longer exists in the finished weld. Undercut in any pass, except internal on the bead or external on the cap, means nothing if it's properly filled (and thus no longer exists) by subsequent pass.
I don't know what code you're working to, but API 1104 specifically defines undercut as "a groove melted into the base metal adjacent to the toe or root of weld and left unfilled by weld metal.
My take.

JTMcC.

By thirdeye (***)

Date 09-19-2005 18:28

fishingrodburne,

That is unusual terminology used by the inspector to say the least since undercut is on the outside (or inside) face of the pipe, not in the bevel and on the bevel face where you are welding. In certain areas are you possibly washing away some of the bevel or maybe not tying in well to the sidewalls? Could one of the guys on the firing line be complaining? At any rate, have him point to the exact defect (as he sees it) and have him explain his reasoning.

~thirdeye~

By jon20013 (*****)

Date 09-19-2005 18:39

fishingrodburne; if I read your question correctly, it was not the inspector who termed the undercut as "external undercut" but yourself? My best guess is perhaps the inspector was concerned over the possibility of "wagon-tracks" showing up on RT film? This is pure speculation however...

By fishingrodburne (*)

Date 09-21-2005 01:57

Thanks for your response. All the welds had been clean before he even said anything. All the wagon tracks were being burned out. If it had been "internal undercut" that would have meant I had burned through the stringer bead and gouged the inside of the pipe. This would be a major repair and probably a cut out.

By Shane Feder (****)

Date 10-27-2005 00:38

Fishingrodburne,
JT would be the best one to explain this but I will give it a shot.
Some people do minimal grinding of the bead and put in a very hot pass, some people do more grinding and put in a colder hot pass. This is all personal preference.
The hot pass is put in using a flicking motion, as you flick forward you are gouging out the wagon tracks, as you step back you are pushing weld metal into the depression and hopefully washing the sidewalls. If you have any undercut on the hotpass from incorrect technique or too much heat you are going to create problems.
With all due respect I disagree with your statement that "fill and cap would take care of the problem".
All the pipelines I have worked on had the fill & cap put in with 4 or 5 mm 7010's. Even though cellulose rods have excellent penetration qualities they are not going to always burn out undercut, especially with 4 or 5 mm electrodes in the vertical down progression. Vertical up would be more likely to be able to burn it out.
Maybe the fill & cap crew asked the inspector to have a word with you, if there was a repair called after radiography and the repair area was identified as being between the hot pass and the fill who do you think would have been given the repair sheet.
Pipeline welders reputations are built on a combination of productivty and repair rates,if you are getting repairs due to what an earlier welder has done then you are going to be slightly p...ed!
Hope this helps,
Regards,
Shane

By fishingrodburne (*)

Date 10-31-2005 01:55

Thanks for the response Shane. You are the first person that's explained this to me well. I think I was burning too hot. We were not grinding the bead at all. It seems that going just a little slower and colder produces a clean hot pass with minimal undercut. Its easier to keep it narrow as well. I guess running downhill with a 7010 could indeed trap some undercutt causing a gas pocket I guess. Thanks again.