National standard caps or end covers are divided into convex 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 heads are superior to other types of heads in terms of load-bearing, requiring less thickness for the same diameter and pressure, thereby saving materials and are often used in high-pressure containers. At the same time, the thickness difference between spherical heads and cylinder walls is significant in all types of head-to-cylinder connections, and the structure of their connection not only affects the manufacturing of the equipment but is also a critical factor for the container's operation.

National standard flanges are a component of containers (as shown in the figure above). 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 flanges are collectively referred to as convex flanges. In terms of welding, they are classified into socket weld flanges and insert weld flanges. They are used in various container equipment, such as storage tanks, heat exchangers, towers, reactors, boilers, and separation equipment, etc. Materials include carbon steel (A3, 20#, Q235), stainless steel, alloy steel, aluminum, titanium, copper, nickel, and nickel alloys.