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Up Topic Welding Industry / General Welding Discussion / cracked tack welds in backing bars
- - By keithhanson Date 10-19-2001 03:43
I have seen cracks in the tacks holding the backing bar in place on finished cp welds in group 4+5 moment columns on the job that i'm on.
the contractor refuses to remove and/or repair them without a code reference. i remember seeing one, but i can't find it anywhere- can anyone pinpoint the publication or code section in question?
Parent - By Kamaruzaman (*) Date 10-19-2001 13:33
finished cp welds ?
Parent - By - Date 10-19-2001 21:50
Surely the aceptance criteria for surface defects (as found for example with MPI) would rule out any crack-like defect? Look under this section in the code.

Regards
Niekie
Parent - By CHGuilford (****) Date 10-22-2001 17:12
From what you are describing I'm guessing the small tacks used to fit backing bars have broken clean through as a result of distortion caused by the groove weld. That isn't unusual to find and normally the broken weld can't propagate into the base metal. So I see 2 views here.

From a practical point of view, the cracks likely won't cause any difficulties other than they don't look good, and not many people will see them. If you have them removed, the contractor will probably cut them with a cold chisel (if they are small) in which case you have the same as before except with a wider gap. Or someone will attack the tacks with a grinder and you could end up with notches and cuts that are worse than the original problem. Often the owner will side with the contractor in leaving the tacks as is.

From a code point of view, D1.1 has provisions (5.18.2.3) that tack welds not incorporated into the final welds shall be removed, except in statically loaded structures they can remain unless removal is required by the engineer. Also, 5.18.2 subjects tack welds to the same quality requirements as the final welds (ie: no cracks).

If you are the engineer, you can require tack removal, cracked or not.
If you are the inspector, the quality isn't there. But I would make sure I consulted with the Owner/Engineer for their view before I told the Contractor to do address them. Hopefully, you can get it in writing.
Have a happy
CHGuilford
Parent - - By boilermaker (**) Date 11-21-2001 02:50
Why don't they just do an open butt groove weld with backgouging to ensure full pen?
Parent - - By DGXL (***) Date 11-21-2001 16:43
Moment frame connections are typically T joints with a single bevel groove weld (girder to column). Trying to back gouge the web area is somewhat difficult. That is why backing is used. This has been an industry standard for many years. Welds without backing for this joint configuration are not practical.

It was discovered after the Northridge earthquake that welds deemed insignificant to the contractor (tack welds) were one of the sources of the failure at the weld joint area. These "non-structural" tack welds propogated into the base metal. When using group 4/5, I would be even more concerned about this problem. The code sections referenced by CHG are applicable.

A crack is a crack, is a crack. I've never seen a crack get smaller.
Parent - By bmaas1 (***) Date 12-13-2001 15:21
The statement by DGXL is right on. I've worked in the St. Louis area where they do a lot of moment connections for seismic conditions. I usually see the tack welds on the weld side where they become part of the final weld, just for ease of placement. These connections usually get ut inspected anyway.
Parent - By thomas_1999 Date 12-12-2001 12:38
Were the tacks holding the backing in place from the weld side or the back of the joint? When did you note the cracks, after the final weld or before? Did the tacks crack down the center or tear out of the base metal?

If these were after the completed weld and have created defects in the base metal then you'll have to have them repaired. If this is a continuous problem, specify where you want the tacks so they HAVE to be incorporated into the weld.

If you need to quote the code book look under D1.1 - Fabrication sect. 5.10 Backing which refers to lengths required, thicknesses and lengths of welds required for cyclically and statically loaded structures. Otherwise depend on the acceptance criteria for discontinuities and defects.

TAB
Up Topic Welding Industry / General Welding Discussion / cracked tack welds in backing bars

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