Elliptical heads, due to their ease of processing and superior strength, are widely used in low and medium pressure vessels across various industries including chemical, light industry, petroleum, and pharmaceuticals. The calculation of the elliptical head's unfolded area is based on this assumption; however, is the half-ellipsoid shell that constitutes the elliptical head truly an ellipsoid?

Elliptical Head Geometry

Basic Concepts of Rotational Shells:
A shell is an object bounded by two curved surfaces. The surface that equally divides the thickness of the shell at each point is called the middle surface of the shell. A shell whose middle surface is a surface of revolution is called a rotational shell. A surface of revolution is formed by rotating a plane curve about an axis in the same plane. This plane curve is called the generatrix of the surface of revolution. The geometry of rotational shells, especially thin rotational shells, is usually described by the generatrix of the middle surface.
   

Equation of the Middle Surface Generatrix:

An elliptical head with uniform thickness is undoubtedly a rotational shell, but whether formed by stamping or spinning, an elliptical head can only ensure that the inner surface (or outer surface) of its elliptical shell portion is an ellipsoid. The middle surface and the outer surface (or inner surface) are not ellipsoids; that is, its inner surface (or outer surface) generatrix is an ellipse, while the middle surface and outer surface (or inner surface) generatrices are not ellipses. The equation of the middle surface and outer surface (or inner surface) generatrix can be derived from the ellipse of the inner surface (or outer surface) generatrix using the following method.

Precautions for Head Usage:

Measure the outer perimeter of the head. Pre-process the cylinder. Divide the head's outer perimeter into four equal parts and mark the cylinder and the head. Perform positioning welding. Customers should choose positioning points according to the diameter and thickness. After positioning welding, perform welding.
Note: Protect the surface of the stainless steel head. After the head and cylinder are welded, promptly clean the weld seam, heat-affected zone, and surrounding spatter contaminants. Perform PT inspection and surface pickling to prevent scratches and bumps on the surface of the stainless steel head. Avoid direct contact with carbon steel to prevent iron ion contamination. Do not store outdoors to prevent rain. Prevent excessive restraint stress during forced assembly welding design. The water chloride ion content in the water pressure test should not exceed 25mg/L. Dry thoroughly after testing. For stainless steel pickling, do not use reducing acids such as hydrochloric acid.

English Marking for Elliptical Heads

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A draft for pressure vessel heads has been released, including flat heads and spherical heads. The head type codes have been slightly adjusted.
E is the first letter of elliptical, and H is the first letter of head. A—based on the inner diameter of the head; B—based on the outer diameter of the head.
EHA represents an elliptical head based on the inner diameter.
Dish heads are divided into DHA and DHB. However, the distinction is not based on inner and outer diameters, but on the transition fillet radius.
Conical heads are divided into CHA, CHB, and CHC, based on the half-apex angle and whether there is a transition section at the large end.
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