National standard heads or end caps are divided into convex heads, conical heads (only used for certain special purpose containers), and flat heads (except for cover plates used for manholes and handholes in pressure vessels).
The national standard head is a component of a container (as shown in the figure above), which can be divided into several types according to its geometric shape, such as spherical, elliptical, disc-shaped, spherical crown shaped, conical shell, and flat cover. Among them, spherical, elliptical, disc-shaped, and spherical crown shaped heads are also collectively referred to as convex heads. In welding, it is divided into butt welding heads and socket welding heads. Used for various container equipment, such as storage tanks, heat exchangers, towers, reactors, boilers, and separation equipment. The materials include carbon steel (A3, 20 #, Q235), stainless steel, alloy steel, aluminum, titanium, copper, nickel, and nickel alloys.