Which type of weld is characterized by a concave or flat profile?

A fillet weld is characterized by its concave or flat profile, which is formed when two pieces of metal are joined together along the edges. This type of weld is commonly used in structural applications where the weld is made at an angle between two surfaces, such as in the corner of a joint. The concave or flat shape provides a strong bond between the two joined pieces, as it equally distributes stress over the weld.

In contrast, butt welds typically have a flush profile where the surfaces of the joined pieces are aligned and welded together without any gap, making them less visible than fillet welds. Plug welds involve welding a section of the material together in a hole that has been drilled or punched into one piece, so they won't exhibit the same profile characteristics. Corner welds are a type of fillet weld that specifically joins two surfaces at a right angle but may not always feature a concave profile as they might have a different visual appearance when applied based on the welding technique used.

By understanding the characteristics of fillet welds, including their profiles, one can better identify and apply the correct welding methods based on the structural requirements.