In welding, the joint types and groove forms of weldments vary depending on their thickness, structure, and service conditions.
Related reading: Welding Basics You Should Know
The types of welding joints include butt joint, T-joint, corner joint and lap joint.
(1) Butt joint
A butt joint is formed when two surfaces meet at an angle of 135° or more, but no greater than 180°. It is the most commonly used joint in various welding structures, particularly when the steel plate thickness is less than 6mm. For non-critical structures, there is generally no need for a groove.
When butt welding two plates with different thicknesses and the thickness difference (δ-δ1) does not exceed the limits specified in Table 1-2, the weld groove’s size and basic form should be chosen based on the thicker plate’s size.
If the thickness difference exceeds the specified limit, the thicker plate needs to be thinned on one or both sides, as shown in Fig. 1. The thinning length L should be equal to or greater than 3 (δ-δ1).
Fig 1. Butt joint of plates with different thicknesses
(a) Single side thinning
(b) Double faced thinning
(2) Corner joint
A joint formed by welding the end faces of two weldments at an included angle of more than 30° but less than 135° is known as a corner joint, as shown in Fig. 2.
This type of joint does not provide optimal stress conditions and is typically utilized in less critical structures.
Fig. 2 Corner joint
(a) I-groove;
(b) Single V-groove with blunt edge
(3) T-joint
The end face of one piece and the surface of another piece form a right angle or approximate right angle joint, which is called T-joint. See Fig. 3.
Fig. 3 T-joint
(4) Lap joint
The joint formed by overlapping two parts is called lap joint, as shown in Fig. 4.
Fig. 4 Lap joint
(a) I-groove;
(b) Plug welding in round hole;
(c) Long hole internal fillet welding
The lap joint can be categorized into three types based on its structural form and strength requirements: no groove, plug welding in round holes, and fillet welding in long holes (see Fig. 4).
The lap joint with I-shaped groove is typically utilized for steel plates with a thickness of less than 12mm, and the overlap must be greater than or equal to 2(δ1 + δ2). Double-sided welding is also required. This joint is primarily employed in unimportant structures.
When dealing with a large overlapping area, the joint type of plug welding in round holes or fillet welding in long holes with varying sizes and numbers can be used based on the plate thickness and strength requirements.
| Thin plate thickness δ 1 | ≤2～5 | >5～9 | >9～12 | >12 |
| Allowable thickness difference（ δ—δ 1) | 1 | 2 | 3 | 4 |
