U-Groove Weld Symbol
How to read a U-groove weld symbol — U-shape on the reference line, root radius in cross-section detail only. Symmetric preparation, prequalified CJP joint details per D1.1:2025.
U-Groove Symbol Dimensions
The U-groove symbol looks like a U sitting on the reference line — a curved bottom with two vertical sides. Unlike bevel and J-groove welds, the U-groove prepares both members symmetrically, so no broken arrow is needed.
What Goes on the Symbol
Root opening (R) — INSIDE the U symbol.
Groove angle (α) — above or below the weld symbol as appropriate per A2.4 §7.3.2.
Groove depth (D) — to the LEFT for PJP (partial joint penetration) welds.
Weld size (S) — in parentheses to the LEFT for PJP. Omitting D and S specifies CJP.
What Does NOT Go on the Symbol
Root radius (r) and root face (f) — per A2.4 §7.3.3, these MUST appear in a cross-section detail or other data with reference in the tail. Not on the symbol line. This is unique to U-groove and J-groove welds and is a common drafting error.
Arrow Side vs. Other Side
When the U-groove symbol sits below the reference line, the preparation is on the arrow side of the joint. Above the line means other side. Both above and below (double-U) means both members are prepared from both sides.
Prequalified U-Groove CJP Joints
D1.1:2025 Figure 5.1 Type 6 (single-U) specifies prequalified CJP butt joint details. All prequalified U-groove CJP joints require backgouge from the second side before depositing the back weld.
| Parameter | SMAW | GMAW / FCAW |
|---|---|---|
| Joint designation | B-U6 | B-U6-GF |
| Groove angle (α) | 45° (pos. A) · 20° (pos. F, OH) | 20° (pos. A) |
| Root face (f) | 1/8" (3 mm) | 1/8" (3 mm) |
| Root radius (r) | 1/4" (6 mm) | 1/4" (6 mm) |
| Root opening (R) | 0–1/8" (0–3 mm) | 0–1/8" (0–3 mm) |
| Backgouge | Required | Required |