WN Flange weld shrinkage rotates my SS flange 3

[ProjectEng99]

What is BEST PRACTICE for welding a 60" Dia SS WN flange to keep the weld from shrinking & rotating the flange face 1/8" at OD. The flange lays back at OD when weld shrinks.
Thank you
Dee Anderson

 

[metengr]

What is the welding process and fixturing (if any) you are using to join the weld neck flange? Are you joining to a pipe, nozzle or vessel wall ? What is the wall thickness of the part that you are joining to the flange.

 

[ProjectEng99]

Welding to 3/8" wall ss pipe.
ID bevels on Flange & Pipe with 1/6" lands.
1. Tig root ID
2. Flux core ID 1 pass
3. Sub Arc ID
4. BAck gouge OD & Sub ARc 1 pass

The flange face was flat until step 4 where it pulled 1/8" towards the weld the flange OD.
We had 1/8" lands at first and it pulled worse.
We tried 200F preheat but it was no help.
Thank you,
Dee Anderson

 

[metengr]

One option to consider is to use a modified double-vee weld prep versus a single-vee with back gouging and welding from the OD. If you go this route, I would use all FCAW versus GTAW and SAW. With the double-vee weld prep for this application, you might be able to balance the residual stresses from weld shrinkage using both sides of the weld joint on this large a diameter to maintain the position of the flange face.

 

[stanweld]

Since the problem occured during step 4, another method would be to change step 4 to lightly grind the weld from the OD side to uniform sound metal and then back weld with the FCAW process in approximately 12" long increments using a backstep technique and alternating 180 degrees from pass to pass about the circumference; i.e, start first segment at 12:00, second segment at 6:00, third segment to tie-in to the first segment and so on.

The primary cause of the problem is the high volume of deposited weld metal in the last pass coupled with high heat input using the SAW process in a single continuous pass. Accomodation for growth about the circumference was not provided as well as the effects of the volumetric weld shrinkage. The 1/8" land was worse because, after backgouging, a greater volume of weld metal was deposited with the single pass. It would also be interesting to know what the depth of penetration and profile (narrow or wide)of the final bead.