U-Groove Weld Symbol
The U-groove weld symbol is a cup shape on a short stem that touches the reference line. It calls for a butt weld where both edges are machined with a radiused bottom, forming a U. Below the line means arrow side, above means other side, both sides is a double-U; sizes go left, root opening inside and groove angle beyond.
How to read the u-groove weld symbol
In a U-groove both edges are machined so the groove has a rounded bottom and fairly steep sides. Compared with a V, it needs less weld metal on thick plate because the sides do not open up as fast.
The cup below the line means prepare and weld the arrow side; above the line, the other side; on both sides, a double-U welded from both sides.
What each dimension position means
| Position | Meaning |
|---|---|
| Left (S) | Depth of groove preparation. |
| Left, in parentheses (E) | Groove weld size. |
| Inside (R) | Root opening. |
| Beyond (A) | Included groove angle of the U sides. |
| Groove radius and root face | Not shown on the symbol; given in a detail, a note or the tail reference. |
Example callout, read aloud
“On the arrow side, machine a U-groove with a 20-degree included angle, 5/8 inch deep, with a 1/16-inch root opening, and weld to a groove weld size of 5/8 inch; the tail note asks for a GTAW root pass.”
Example: reading the callout piece by piece
- U below the line: arrow side.
- 20° beyond: included angle of the groove sides.
- 1/16 inside: root opening.
- 5/8(5/8): preparation and weld size both 5/8 inch.
Result: On the arrow side, machine a U-groove with a 20-degree included angle, 5/8 inch deep, with a 1/16-inch root opening, and weld to a groove weld size of 5/8 inch; the tail note asks for a GTAW root pass.
When it is used
- Thick plate and heavy-wall pipe, where a U uses noticeably less filler than a V of the same depth.
- Pressure equipment and critical joints where the U shape gives good access to the root.
- Double-U on very thick sections welded from both sides.
Common mistakes
- Looking for the radius on the symbol. Groove radius and root face are in a detail or the tail reference.
- Treating the angle as per side. The angle is the included angle of the groove.
- Choosing a U for thin plate. The extra machining only pays off on thick sections.
- Confusing the U and J symbols. U is symmetric on a centre stem; J has a vertical leg on the left and prepares one member.
Related weld symbols
- J-groove weld: A J-groove is half a U: one member prepared.
- V-groove weld: A V is cheaper to prepare on thinner plate.
- Back and backing weld: A back weld often follows a single U.
- Bevel groove weld: A bevel is the straight-sided one-member groove.
- Square groove weld: No preparation on thin sheet.
Every weld symbol page: welding symbols chart
Calculators and further reading
Frequently asked questions
When is a U-groove better than a V-groove?
On thick sections, where the narrower U needs less weld metal and less heat than a V of the same depth.
Where is the groove radius shown?
In a joint detail, a note or the tail reference, not on the symbol itself.
What does a U on both sides of the line mean?
A double-U groove: both sides are prepared and welded.
What is the angle beyond the U symbol?
The included groove angle of the U sides.
Sources
- AWS A2.4 Standard Symbols for Welding, Brazing, and Nondestructive Examination, American Welding Society
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