Backing Bar Removal for Repair-All or Some??

Date 09-20-2007 18:10

Well, heres my opinion, and thats all it is. AWS D1.1-06 addresses the removal of backing in section 5.10, which covers both static and cyclic connections, so, alot depends on the joint designation. As for static connections, the removal of backing is at the disrection of the engineer. As for your comment about the complete removal of the entire backer for a repair makes little sense. Because once you remove the entire backing, then the complete length of the weld would have to be back gouged, re welded and UT'd. Then theres the issue of having just changed the type of groove which will require another WPS, and more expense to cover the time involved. If the repair is actually long enough to require the complete removal of the backer, then I guess thats what you need to do, but, if you've only got 3/4" of I.F. in a W14? WTF

By hogan

Date 09-20-2007 18:42

by the code i would ask the engineer. i would think that only removing part of the b-up bar would put two stress risers in the root of the weld.

By GRoberts (***)

Date 09-20-2007 19:10

One possible point of contention would be AWS D1.1 paragraph 5.10.2, which says that backing shall be made continuous for the full length of the weld. I think they are specifying that for before welding (which the commentary seems to support), but it doesn't explicitly say so.

By HgTX

Date 09-26-2007 15:58

Huh? "unwelded square butt joint in steel backing constitutes a severe notch that potentially leads to transverse cracks in the weld." Reference to notch means they're concerned about in-service stresses, not just condition at time of welding. Partial removal would not be as bad as the thin notch, but swnorris has it right--there would still be stress risers.

Hg

By jwright650 (*****)

Date 09-20-2007 19:19 Edited 09-20-2007 19:22

I have had welders trap a line of slag at the root and not even melt the backing strip(I have a piece of one laying right here, in fact) and when they go in to repair, we just took the thing out by backgouging and closed it back up. You end up with a full pen weld either way. I hate to see a portion of the bar left in place...just looks funny to me, like somebody did a halfway job repairing the joint.

edit: imagine trying to UT that joint after that repair...I dunno...I think you would see where the bar stops and starts

By swnorris (****)

Date 09-20-2007 21:55 Edited 09-20-2007 22:00

I'm not aware of D1.1 addressing backing removal with regards to repair. However, I don't think that backing removal should be at the discretion of your staff, but rather by the EOR. I would think that partial removal of the backing would create stress risers. With that being said, I agree that it should be referenced in your repair WPS as stating something similar to: "Partial removal of the backing in order to repair the root is prohibited unless approved by the EOR"