What is a Dished Head?

What is a Dished Head?

Dished heads, also referred to as dish ends or tank heads, are essential components used in multiple industries, including pressure vessels, storage tanks, and boilers. These curved structures function as end closures, enhancing strength, structural integrity, and sealing capabilities for the vessels to which they are attached.

Alternative Names for Dished Heads

Dished heads are known by various names depending on their application, such as vessel heads, dished ends, tank heads, caps, and ends.

Types of Dished Heads

Dished heads can be categorized into different families based on their shape and usage, including:

• Dished heads

• Flat heads

• Conical heads

• Spherical caps

• Hemispherical heads

Defining Characteristics of Dished Heads

The key parameters that define dished heads include:

• External or internal diameter

• Crown radius (CR)

• Knuckle radius (KR)

• Nominal plate thickness or minimum head thickness

• The right side (RS), which can be finished with various types of beveling

Manufacturing Standards for Dished Heads

Dished heads are produced according to various industry standards. In this article, we focus on the French standard NFE81-100, which includes:

• GRC Dished Heads (NFE 81-102): These have a "large knuckle radius" ("grand rayon de carre") and are the most widely used profile for manufacturing pressure vessel heads.

• PRC Dished Heads (NFE 81-101): Featuring a "small knuckle radius" ("petit rayon de carre"), this type is not recommended for pressure vessels but is preferred for non-pressurized storage tanks due to its lower cost.

• Elliptical Dished Heads (NFE 81-103): Deeper than the GRC type, these heads are primarily selected for pressurized vessels.

• MRC Dished Heads (NFE 81-104): With a "medium knuckle radius" ("moyen rayon de carre"), this type is less frequently used.

Features of GRC Dished Heads (NFE 81-102)

The GRC dished heads, following the NFE 81-102 standard, possess the following characteristics:

• The crown radius (CR) matches the head's diameter.

• The knuckle radius (KR) is 10% of the head's diameter.

These dished heads are crucial in various industrial applications, ensuring durability and reliability in pressure containment systems.