In welding, due to the different thickness, structure and service conditions of weldments, their joint types and groove forms are also different.
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
The joint formed by two pieces of surface with an included angle of 135 ° or more and 180 ° or less is called butt joint.
It is the most widely used joint type in various welding structures.
The thickness of the steel plate is less than 6mm.
Except for important structures, there is generally no groove.
When the thickness difference (δ—δ 1) between the two plates butt welded by steel plates with different thicknesses does not exceed the provisions in Table 1-2, the basic form and size of the weld groove shall be selected according to the size data of the thicker plate;
Otherwise, the thick plate shall be thinned on one or both sides as shown in Fig. 1;
Its thinning length L ≥ 3（ δ—δ 1)。
Fig 1. Butt joint of plates with different thicknesses
(a) Single side thinning
(b) Double faced thinning
(2) Corner joint
A joint with an included angle of more than 30 ° and less than 135 ° between the end faces of two weldments is called a corner joint, as shown in Fig. 2.
This kind of joint is not in good stress condition and is often used in unimportant structures.
Fig. 2 Corner joint
(b) Single V-groove with blunt edge
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
(b) Plug welding in round hole;
(c) Long hole internal fillet welding
According to its structural form and strength requirements, the lap joint can be divided into three types: no groove, plug welding in round hole and fillet welding in long hole. See Fig. 4.
Lap joint of I-shaped groove is generally used for steel plate with thickness less than 12mm, and its overlap is ≥ 2（ δ 1+ δ 2) , double-sided welding.
This joint is used in unimportant structures.
When encountering a large area of overlap, the joint type of plug welding in round holes or fillet welding in long holes with different sizes and numbers can be adopted according to 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|