02 Joints, welds, and language · 14 min
Five joints, many welds
Butt, T, lap, corner, edge. Then the weld that actually joins them.
A joint is how the members meet. A weld is the metal that joins them. Inspectors who mix the two fail symbol questions. The five basic joints are butt, T, lap, corner, and edge.
| Joint | How the plates meet | Typical welds |
|---|---|---|
| Butt | Edges in the same plane | Groove (square, V, bevel, U, J), sometimes backing |
| T | One member at about 90° to the face of the other | Fillet, or groove into the stem |
| Lap | Overlapping faces | Fillet, plug, slot, spot |
| Corner | Edges form an L | Fillet or groove |
| Edge | Edges of parallel members | Edge weld / surfacing along the edge |
Groove geometry
Groove welds are named for the prepared shape: square, single or double V, bevel, U, J, flare-V (on round or bent members), flare-bevel. Depth of bevel is the prepared depth. Groove angle is the included angle. Root opening (gap) is the separation at the root. Root face (land) is the unbevelled portion at the root.
- CJP — complete joint penetration. Weld metal through the full thickness. Required when the drawing or WPS says so, often with backing, back gouging, or a qualified CJP procedure.
- PJP — partial joint penetration. Effective throat is less than the member thickness. Size is an effective throat dimension, not a wish.
- Fillet — triangular weld in a right-angle corner. Size is the leg length of the largest inscribed isosceles right triangle, unless an unequal-leg fillet is specified.
- Plug / slot — weld in a round or elongated hole, joining overlapping members.
- Spot / seam — resistance or arc spots; seam is a continuous series of spots.