Dished Heads
Dished heads, also known by various terms such as vessel head, dished ends, tank heads, ends, and caps, are categorized based on their application. There are several families of dished heads including dished heads, flat heads, conical heads, spherical caps, and hemispherical heads.
Key Characteristics of Dished Heads:

External or internal diameter
Crown radius (CR)
Knuckle radius (KR)
Nominal thickness of the plate or minimum thickness of the head
Right side (RS), which can feature different types of bevelling

Dished heads can be produced according to various standards. This article focuses on the French standard NFE81-100:

GRC Dished Heads (according to NFE 81-102): Known for a "large knuckle radius" (grand rayon de carre), this is the most commonly utilized dished head profile for manufacturing pressurized vessel heads.
PRC Dished Heads (according to NFE 81-101): Featuring a "small knuckle radius" (petit rayon de carre), this type is not recommended for pressurized vessels and is mainly used for non-pressurized storage tanks due to lower costs.
Elliptical Dished Heads (according to NFE 81-103): Deeper than GRC heads, this design is primarily chosen for pressurized vessels.
MRC Dished Heads (according to NFE 81-104): This type, known for a "medium knuckle radius" (moyen rayon de carre), is the least commonly used.

GRC Dished Heads NFE 81-102: Large Knuckle Radius Features:

The crown radius (CR) matches the head diameter.
The knuckle radius (KR) accounts for 10% of the head diameter.

PRC Dished Heads NFE 81-101: Small Knuckle Radius Features:

The crown radius (CR) exceeds the value of the head diameter.
The knuckle radius (KR) is dependent on the head diameter:

KR = 30 for diameters < 800mm
KR = 40 for diameters between 800mm and 1000mm
KR = 50 for diameters > 1000mm



In summary, a larger crown radius (CR) results in a shallower head, which is why the PRC head is less deep than the GRC dished head.
Elliptical Heads or Semi-Ellipsoidal Heads NFE 81-103 Features:

The crown radius (CR) is 0.8 times the head diameter.
The knuckle radius equals 0.154 times the head diameter.

With these specifications, the elliptical head is deeper than the GRC head.

Convex Discs or Spherical Caps:
Spherical caps are uniformly shaped discs defined by a specific radius across their surface. A spherical cap represents a segment of a sphere and is characterized by its diameter and crown radius (CR). Unlike other heads, convex discs or spherical caps do not feature a right side. The smaller the crown radius, the deeper the cap becomes, making it more challenging to manufacture. Spherical caps lack standardization.
Flat Heads:
A flat head is defined as a disc with a flanged edge characterized by a radius. These heads are commonly used in the agri-food industry for turning or distribution plates. The inner height of a flat head is determined by the sum of the knuckle radius and the right side. Similar to spherical caps, flat heads do not conform to any standards.
Conical Heads:
Conical heads are distinguished by a cone shape and a flanged edge on the larger diameter. The main components include:

The large diameter
The small diameter
The knuckle radius
The right side
Total height or the angle at the base, or half the angle at the top.