A head is a component of a container, connected to the cylinder by welding. Depending on the geometric shape, it can be spherical, elliptical, dish-shaped, hemispherical, conical, and flat, among others. The spherical, elliptical, dish-shaped, and hemispherical heads are collectively referred to as convex heads. In terms of welding, they are divided into socket welding heads and plug welding heads. They are used in various types of equipment such as storage tanks, heat exchangers, towers, reactors, boilers, and separation equipment. Materials include carbon steel (A3, 20#, Q235, Q345B, 16Mn, etc.), stainless steel (304, 321, 304L, 316, 316L, etc.), alloy steel (15Mo3, 15CrMoV, 35CrMoV, 45CrMo), aluminum, titanium, copper, nickel, and nickel alloys.