Types of Pressure Vessel Heads
Cylindrical, horizontal, and vertical pressure vessels are the most common kinds of vessels and they all require specialized ASME caps on each end. These caps are called “heads” and there are three primary kinds.
Hemispherical Head
The depth of this head is half of its diameter and the standard head thickness is about half the thickness of the pressure vessel’s shell. Despite being the thinnest head, this design is often more expensive than the other head options, as it can’t be fabricated from a single flat sheet and requires welding assembly.
Ellipsoidal Head
This head has an elliptical shape and the most popular ratio is 2:1 (which means that the width of the ellipse is double the depth). When it comes to handling pressure stresses, this head is less efficient than a hemispherical head, so ASME specifications require increased thickness.
Flanged & Dished Heads
Flanged and dished heads (F&D) are common on pressure vessels where the height of the vessel is limited and where pressure is only moderate. The tight knuckle radius on F&D heads requires them to be thicker than the vessel’s shell.