List the four joint types used in welding.
1. Butt joint: This is the most commonly used joint type in welding, where two pieces of metal are placed edge-to-edge and welded together along the joint.
2. Corner joint: This type of joint is formed when two pieces of metal are placed at a perpendicular angle and welded together at the corner.
3. Lap joint: In this joint, two pieces of metal overlap each other, and the welding is done along the overlapping portion.
4. T-joint: This joint is formed when two pieces of metal are arranged in a T-shape, with one piece placed perpendicular to the other. Welding is done along the intersection of the two pieces.