The head is a component of the container and is connected to the cylinder by welding. According to the differences in geometric shapes, they can be classified into several types such as spherical, elliptical, disc-shaped, spherical crown, conical shell and flat cover. Among them, spherical, elliptical, disc-shaped and spherical crown heads are collectively referred to as convex heads. In terms of welding, it is divided into butt welding heads and socket welding heads. It is used for various types of container equipment, such as storage tanks, heat exchangers, towers, reactors, boilers and separation equipment, etc. The 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, etc.

　　An alloy is a substance with metallic properties, which is formed by combining two or more metals with metals or non-metals through certain methods. It is generally obtained by melting into a uniform liquid and solidifying. According to the number of constituent elements, they can be classified into binary alloys, ternary alloys and multi-component alloys.