Single-U butt weld
Applied to joint
Butt joint — plates aligned end to end
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Equipment for groove welds
MIG and TIG machines suited for groove weld preparations on plate.
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Description
A butt weld with a U-shaped groove preparation on both members. The curved profile requires machining or special gouging but significantly reduces the volume of weld metal compared to a V-prep, making it economical on thick plate (typically above 20 mm).
In plain English
Both plates get a curved (radiused) prep instead of a straight bevel, giving you a U-shaped channel. It takes more effort to machine than a V -- you typically need a J-prep cutter or carbon-arc gouge followed by grinding -- but you save a huge amount of filler metal on thick plate. On 40 mm plate, a U-prep might use half the filler of a V-prep. That also means less distortion, fewer passes, and less time welding. The break-even point where U beats V on cost is usually around 20-25 mm plate thickness.
Symbol position
U symbol on the reference line.
Size notation
Root radius, groove angle (of the flared sides above the radius), root face, and root gap all dimensioned.
Common uses
- Thick plate joints (>20 mm) where filler metal savings justify prep cost
- Pressure vessels and boiler drums
- Heavy structural steel connections
- Nuclear and high-integrity fabrication
