Welding Joint Types & Design

Welding joint types explained: butt, lap, tee, corner, and edge joints. Groove preparation, included angles, root opening, root face dimensions, and joint selection by application.

Joint design determines weld strength, accessibility, and cost before you ever strike an arc. The five basic joints (butt, lap, tee, corner, edge) combine with different groove preparations to handle every structural and fabrication situation. Picking the right joint saves filler metal, reduces distortion, and produces stronger connections.

Butt joints bring two pieces edge-to-edge. On material under 3/16 inch, a square butt with 1/16 inch root opening gets full penetration. Thicker plate needs groove preparation: single-V (beveled from one side), double-V (beveled from both sides to reduce filler volume), single-bevel, or J-groove. The standard single-V uses a 60-degree included angle, 1/16 inch root face, and 1/16 to 1/8 inch root opening. These dimensions give the arc access to the root while leaving enough metal to prevent burn-through.

Tee joints create a perpendicular connection and make up roughly 80% of structural welds. Most tee joints use fillet welds, sized by leg length (3/16, 1/4, 5/16 inch, etc.). The fillet weld throat (the shortest distance from root to face) determines load capacity. For full-strength connections on thick tees, a complete joint penetration groove weld replaces the fillet.

Lap joints overlap two pieces and work well on sheet metal and thin plate. The overlap should be at least 3 times the thinner plate’s thickness. Fillet welds on one or both sides complete the joint. Single-sided lap joints create an eccentric load path that can peel under bending, so double-sided laps are preferred for structural work.

Corner joints form an angle (usually 90 degrees) and appear in box sections, frames, and enclosures. Open corners expose the root and can be welded from outside, inside, or both. Closed corners hide the root and rely on fusion from the outside.

Edge joints join two parallel pieces along their edges. They’re the weakest joint type and primarily used for non-structural sheet metal work, flanging, and cosmetic connections.

The guides below cover groove dimensions, joint selection criteria, and fit-up tolerances for each joint type.

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