National standard flanges or end caps are divided into hemispherical caps, conical caps (used only for certain special-purpose containers), and flat caps (used as manhole and handhole covers in pressure vessels).

In pressure vessels, spherical end caps have better stress distribution compared to other types of end caps. They require less thickness for the same diameter and pressure, saving materials, and are thus commonly used in containers with higher pressures. At the same time, the thickness difference between spherical end caps and cylindrical shells is significant in all forms of connections, which not only affects equipment manufacturing but is also a crucial factor for the container's operation.

National standard flanged heads are a component of containers (as shown in the diagram). They can be divided into several types according to different geometric shapes, such as spherical, elliptical, dish-shaped, hemispherical, conical shell, and flat cover, among which spherical, elliptical, dish-shaped, and hemispherical heads are collectively referred to as convex flanged heads. In terms of welding, they are classified into butt-welded flanged heads and socket-welded flanged heads. They are used in various container equipment such as storage tanks, heat exchangers, towers, reactors, boilers, and separation equipment, etc. The materials include carbon steel (A3, 20#, Q235), stainless steel, alloy steel, aluminum, titanium, copper, nickel, and nickel alloys.