Double-U butt weld
Applied to joint
Butt joint — plates aligned end to end
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Description
A butt weld with U-shaped preparations on both sides, forming a symmetrical or asymmetrical profile. Provides the greatest filler metal savings on very thick plate. Welded from both sides with backgouging.
In plain English
Both sides of the joint get the curved U-prep. Maximum filler savings on really thick plate -- 50 mm and above, this is often the most economical choice despite the machining cost. You weld one side, backgouge, then weld the other. The radiused root on each side gives excellent root fusion. Used on the heaviest pressure vessel and structural work where every kilo of weld metal saved matters.
Symbol position
Mirrored U symbols on both sides of the reference line.
Size notation
Root radius, groove angle, root face, and root gap for each side. Depths may be asymmetric.
Common uses
- Very thick plate joints (>40 mm)
- Pressure vessel and boiler drum longitudinal seams
- Nuclear containment vessel welds
- Heavy marine and offshore structural joints
