There are several categories of dished heads, including dished heads, flat heads, conical heads, spherical caps, and hemispherical heads.

Dished heads are characterized by the following features:

· External or internal diameter

· Crown radius (CR)

· Knuckle radius (KR)

· Nominal plate thickness or minimum thickness of the head

· The straight edge (RS): which may feature various types of beveling for completion.

These heads can be produced to comply with different standards. In this article, we focus on the French standard NFE81-100:

· GRC dished heads (as per NFE 81-102): These have a "large knuckle radius" (grand rayon de carre) and are the most widely used profile for manufacturing pressurized vessel heads.

· PRC dished heads (as per NFE 81-101): These have a "small knuckle radius" (petit rayon de carre). This type is not recommended for pressurized vessels but is primarily used for non-pressurized storage tanks due to its lower cost.

· Elliptical dished heads (as per NFE 81-103): These are deeper than GRC heads and are mainly chosen for pressurized vessels.

· MRC dished heads (as per NFE 81-104): These have a "medium knuckle radius" (moyen rayon de carre) but are less commonly used.

GRC Dished Heads (NFE 81-102): Large Knuckle Radius

Key characteristics of GRC dished heads as defined by NFE 81-102 include:

· The crown radius (CR) is equal to the diameter of the head.

· The knuckle radius (KR) measures 10% of the head's diameter.

PRC Dished Heads (NFE 81-101): Small Knuckle Radius

The defining characteristics of PRC dished heads, as specified by NFE 81-101, are:

· The crown radius (CR) is greater than the diameter of the head.

· The knuckle radius (KR), determined by the head diameter, follows these values:

o KR = 30 for diameters less than 800 mm

o KR = 40 for diameters between 800 mm and 1000 mm

o KR = 50 for diameters exceeding 1000 mm

It can be concluded that as the crown radius (CR) increases, the head becomes less deep. This explains why the PRC head is shallower than the GRC dished head.

Elliptical Head or Semi-Ellipsoidal Head (NFE 81-103)

The key specifications of elliptical dished heads according to NFE 81-103 are:

· The crown radius (CR) is 0.8 times the diameter of the head.

· The knuckle radius (KR) is 0.154 times the diameter of the head.

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

Convex Discs or Spherical Caps
Spherical caps are rounded discs formed to a specific radius across their entire surface. Essentially, a spherical cap is a segment of a sphere, defined by its diameter and crown radius (CR). Unlike other types of heads, a convex disc or spherical cap lacks a straight side.

The smaller the crown radius, the deeper the spherical cap, which makes its production more challenging.

Spherical caps are not standardized components.

Flat Heads
A flat head is a disc with a flanged edge shaped to a specific radius. These heads are commonly used in the agri-food sector for rotating or distribution plates.

The inner height of a flat head is determined by adding the knuckle radius to the straight edge. Similar to spherical caps, flat heads are not governed by any standards.

Conical Heads
A conical head consists of a cone with a flanged edge around its larger diameter.

The main features of a conical head include:

· The large diameter

· The small diameter

· The knuckle radius

· The straight edge

· The total height, base angle, or the half-angle at the top

To get more head products, please contact us.