A pressure vessel is a closed container designed to hold gases or liquids at a pressure substantially different from the ambient pressure.
Pressure Vessels are Design as per ASME Section VIII Div 1.
Pressure vessels can theoretically be almost any shape, but shapes made of sections of spheres, cylinders, and cones are usually employed. A common design is a cylinder with end caps called heads. Head shapes are frequently either hemispherical or dished (torispherical).