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Up Topic Welding Industry / General Welding Discussion / high-low w/ M backing - closing the gap?
- - By hogan (****) Date 12-18-2007 16:08
i'm looking for any input for this situation. what we are doing is making a tapered tubes. the material we work with ranges in thickness from a36 3/8" to 3/4". tubes are all the same thickness (3/8 to 3/8, 3/4 to 3/4 ect...). we start with plate and have it formed into a tapered u shape. we then take two of the u shapes and weld them together, making a tube. the range of the taper is 30" down to 9", for a length of 20' to 40'. this makes it very difficult to work from the id.  these are welded per aws d1.1 B-U2a-GF. it is inherently difficult to fit these up with no high - low. currently we tack the b.u.b.'s to one side of the tube, fit the other side and weld. it is very difficult to do this without having a gap between the b.u.b. and the id of the tube on the side not tacked. our forming company is forming these in accordance to tolerances, and it would not be extremely difficult to make these at a perfect 90 degrees. any ideas as to how to reduce the gap? the gap currently does not exceed 1/8", typically smaller. thanks for any input
Parent - - By mountainman (***) Date 12-18-2007 17:02
hello Hogan, hopefully you don't see this as a stupid suggestion. we have in the past had situations similar to what you describe, our solution was to use a wider backup bar (we had the room) and run them through a drill press so that we could plug weld the bar to the surface rather than having the tacks all on one side which always pulls the dang thing up giving an unfavorable gap. hope it helps.

regards,
JJ
Parent - - By hogan (****) Date 12-18-2007 17:35
not at all. but, our our dot would not accept this. also, the welds are required to be ut tested to d1.1 tension. i think that this would cause issues. thanks for the suggestion though. if not for the ut and dot requirements i might try it.
Parent - - By Kix (****) Date 12-18-2007 19:31
What about welding some lugs all the way around the pipe and screw her down to get the high low out.  Ya might want to use some big bolts on the lugs for the 3/4". lol  These are good to get rid of some small situations or get you close within tolerance.
Parent - - By hogan (****) Date 12-18-2007 21:33
thanks kix. we tried something similar and dot threw a fit for welds out of weld areas. very picky on these, they are overhead (traffic)
Parent - By Kix (****) Date 12-19-2007 13:01
Yeah thats usually a big deal with lugs.  We had to have the areas PT'd after we did this.  Usually most of the pipes were good, but the big inch Duplex stainless was allways out of round and eventually you'd come across some foreign fittings that wern't the same as the pipe.
Parent - - By 803056 (*****) Date 12-18-2007 21:37 Edited 12-19-2007 03:43
Here's something you might try. Its a quick sketch to give you an idea of what I'm thinking of. The wife and two grandsons are waiting for me so we can go to dinner. Sorry for the rush and brush.

The toggle is welded to the backing bar (in black) on one side before fitting. The wedge (red) is driven in through the hole in the toggle to force the plate edges (in blue dashed lines) into alignment. Once the plates are tacked to the backing bar inside the groove, the toggle can be removed with a carbon arc gouger or what ever is handy. Tack the one side of the toggle that will be the driven side of the wedge.

You can also substitute a bar that is drilled and tapped on one end in place of the wedge. The bar is slid one quarter of the way through the toggle and the bolt is tightened against the plate on the high side to push the "high edge" down into position. You should grind the end of the bolt conical to keep it from walking sideways as you tighten it. If marks are objectionable, place a thin plate as a softener under the bolt point.

Another variation would be to tack weld the toggle to the groove face. The tack weld would to the "low edge" and it will be within the area welded and may be easier to remove in comparison to the toggle welded to the backing bar. However, the mechanical advantage is huge when the toggle is welded to the backing bar and a wedge is driven through.

Again, sorry for the bum's rush.

Best regards - Al
Parent - - By Kix (****) Date 12-19-2007 13:19
Thats good stuff Al I like it!! How do you get it out of the pipe on long runs though?  Or was this just thought up real quick for this particular situation where they can get it out. ;-)
Parent - By 803056 (*****) Date 12-20-2007 01:51
Hey Kix;

That would be a task, but luckily for us, this is a case where the backing is permanent.

Happy holidays you all!

Best regards - Al
Parent - By hogan (****) Date 12-19-2007 15:00
thanks 803056. we use something similar to that, it works good on the thinner stuff, up to 5/8". the tacks welds don't want to hold on anything over that. that is the only way we have found to do the rest of them. thanks again
Up Topic Welding Industry / General Welding Discussion / high-low w/ M backing - closing the gap?

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