Pre-placement of root pass before completing joint.

By Scamperator Date 02-10-2011 13:06 Edited 02-14-2011 13:10

(GMAW process .045" Metalcore wire)(AWS D1.1)
Welding in a 1G position, in a T configuration (turn the T on its side and that is the joint in question), the Vertical parent metal extends approx. 8" above the joint to be welded and the other parent metal extends horizontaly several feet from the joint. The vertical member is 4" thick and the horizontal is 1/2" thick. Because of lack of access to the "other" side, there is a 1/4" backing bar placed first to the vertical member with 1/4" extending from the tip of the 45 degree bevel that is placed on the vertical member for a single bevel full pin joint config. Now the question is, if we pre-weld a root pass joining the backing bar to the parent metal (at the edge of the bevel), and THEN place the Horizontal member against the backing bar and tack into place, then weld a second root pass joinint the backing bar to the vertical member, and then finish out the bevel with the necessary hot passes, IS the first root pass we place considered part of the horizontal member now and we then need another 3/16" root opening beyond the toe of that, OR is the first root pass just considered pre-welding a portion of the joint before it is assembled?

The reason for doing the pre-pass is because of the gun angle not being sufficient enough with the restriction from the vertical member extending above the joint.

SHORT VERSION........Without writing some strange confusing weld procedure, can a part of a weld be added to the joint prior to the joint design being completed? I imagine this can be addressed in a weld symbol, but by doing this would it be violating a Pre-Qualified weld procedure.

Attachment: Pre-weldedrootpass.jpg (70k)

By Hoo

Date 02-23-2011 03:58 Edited 02-23-2011 04:00

Im curious to hear the answer too, but my take is that it would be seen as having a 3/8" root gap (assuming the leg of the first weld on the backer is 3/16", and the subsequent opening when fit together is 3/16") If that is that case, then it would violate the prequalified joint that you are working to.

What position is that 1st bead going to be welded in? If it is to be made with the vertical member in position then you might have bigger issues trying to make the metal core bead stay on the backer, Its not meant to be run horizontal.

By Scamperator Date 02-23-2011 15:52

Everything is welded in the 1G position. I attached a drawing if you would like to view it. I think I may have been too confusing trying to put it in writing!

By welderbrent (*****)

Date 02-23-2011 16:18

If welding to D1.1, your WPS should call out the pre-approved joint design which should match one of the section 3 Figures and have a chart on fit up tolerances.

Without having all the numbers that would apply to your exact joint I would hazard a guess (probably shouldn't, but I will) that you would be allowed a root gap of 3/8" with the tolerances for the specified joint.

That would make it easier to get that next weld in without having to worry about the penetration.

You can't hold the first pass down a little smaller?

BTW, even though you start out in the groove, being a fillet weld with a backing plate, horizontal plate and a vertical plate makes that a 2F position according to Clause 4, Figure 4.5. At least that's my take on it based upon your pic. Unless you want to roll it so it is in a vee trough.

Have a Great Day, Brent

By Scamperator Date 02-23-2011 18:39

Thanks,
Yes it allows a 3/8" root opening as fit.
Your last sentence is actually the meat and potatoes of this question because if we fit up the joint, no pre-weld, that joint is a Groove weld and that FIRST root pass could go into the same place as show in the diagram if we make the root pass of this groove weld in TWO passes. So if we make that FIRST pass before we place that other plate, are we still welding a Single Bevel Groove Joint? The weld procedure covers the position for fillet or groove so there is no question there. Just the concept of pre-welding a root pass before building the joint was in question on a customer concern.