AWS A2.4 weld symbol
U-Groove Weld Symbol
A U-groove weld symbol is a U on the reference line, calling for a curved preparation on both members that needs far less filler metal than a V on thick plate.
How to read the u-groove weld symbol
- Both members are machined or gouged to a curved profile.
- The groove angle, typically a narrow 15 to 20 degrees, is written outside the symbol.
- The root opening is written inside the symbol.
- Depth of bevel goes to the left, with the groove weld size in parentheses.
- A U above and below the reference line calls for a double-U joint.
Where the dimensions go
| Position | What it specifies |
|---|---|
| Inside the U | Root opening |
| Outside the U | Groove angle, typically 15–20° |
| Left of the symbol | Depth of bevel, with groove weld size in parentheses |
Joint types
- Butt joint
- Corner joint
Practical notes
- U-grooves are reserved for thick sections where the filler metal saved pays for the machining.
- The narrow included angle means much less weld metal, less shrinkage and less distortion than a V on the same thickness.
- Preparation requires machining or careful gouging, which is why the symbol is uncommon on light fabrication drawings.
U-Groove Weld symbol — common questions
When is a U-groove used instead of a V-groove?
On thick sections, typically above about 3/4 inch, where the volume of weld metal a V-groove would need becomes expensive. The U prep is narrower at the top, so it takes far less filler.
What is the difference between a U-groove and a J-groove?
A U-groove curves both members; a J-groove curves only one and leaves the other square. The J-groove symbol is half a U and carries a broken leader line.
What angle is a U-groove?
Typically 15 to 20 degrees included, far narrower than the 60 degrees of a standard V, because the curved root provides the access instead of the angle.
How is a U-groove prepared?
By machining or by air carbon-arc gouging followed by grinding. That extra preparation cost is why U-grooves appear only where the filler metal savings justify it.
Welding symbol anatomy
Every weld symbol attaches to the same framework. If any part of the diagram above is unfamiliar, the full guide to reading welding symbols walks through the whole system.
| Reference line | The horizontal backbone of every welding symbol. Everything else attaches to it, and it is always drawn horizontal on the drawing. |
|---|---|
| Arrow | The leader and arrowhead that connect the reference line to the joint. The side of the joint the arrow touches is the arrow side. |
| Weld symbol | The shape that says which kind of weld is required — triangle for a fillet, V for a V-groove, circle for a spot, and so on. |
| Arrow side (below the line) | A weld symbol drawn below the reference line calls for a weld on the side of the joint the arrow points to. This is the convention that catches people out most often. |
| Other side (above the line) | A weld symbol drawn above the reference line calls for a weld on the far side of the joint. |
| Both sides | Symbols drawn above and below the reference line call for welds on both sides of the joint. |
| Tail | An optional fork at the far end of the reference line, used to reference a specification, process or procedure such as GMAW or a WPS number. |
| Dimensions | Size is placed to the left of the weld symbol; length and pitch are placed to the right. |