Exploring the Four Primary Head Types for Pressure Vessels

Numerous industries rely on pressure vessels, and their design and construction involve various critical components. The vessel head is one such component, which serves as the end closure of the vessel. In this article, we will explore the four most common types of heads used for pressure vessels, their characteristics, and their applications.

Elliptical Heads (or 2:1 Elliptical Heads):

A. Characteristics:

 Shape:

Elliptical heads are characterized by their elliptical or football-like shape, with the major axis being twice the length of the minor axis, resulting in a 2:1 aspect ratio.

 Stress Distribution:

The elliptical shape offers a smooth transition from the cylindrical body of the vessel, which reduces stress concentrations, making them suitable for high-pressure applications.

Strength:

A. They provide good structural integrity, making them a reliable choice for pressure vessels.

B. Elliptical heads are among the most commonly used head shapes in pressure vessels.

C. They have a distinctive elliptical or football-like shape, with a major axis twice the length of the minor axis, hence the name “2:1 elliptical.”

D. These heads offer a smooth transition from the cylindrical body of the vessel, reducing stress concentrations.

E. Moreover, Elliptical heads provide good structural integrity and are well-suited for high-pressure applications.

B. Applications:

A. Elliptical heads find widespread use in various industries, including petrochemical, oil and gas, and power generation.

B. They are suitable for pressure vessels such as boilers, storage tanks, and heat exchangers.

Hemispherical Heads:

A. Characteristics:

Shape:

Hemispherical heads have a semi-spherical shape, resembling half of a complete sphere. This shape provides a uniform curvature.

Stress Distribution:

The uniform curvature results in excellent stress distribution, making hemispherical heads ideal for containing high-pressure gases or liquids.

Strength:

They offer the highest possible strength among head shapes.

A. Hemispherical heads have a semi-spherical shape and provide excellent stress distribution due to their uniform curvature.

B. They offer a large volume-to-surface area ratio, making them efficient for containing high-pressure gases or liquids.

C. Additionally, Hemispherical heads provide the highest possible strength among head shapes.

B. Applications:

These heads are commonly used in applications where maximum pressure containment is required, such as high-pressure gas storage vessels, industrial autoclaves, and some types of nuclear reactors.

Torispherical Heads (or ASME F&D Heads):

A. Characteristics:

Shape:

Torispherical heads combine a spherical crown with a conical knuckle, resulting in a head shape that resembles a squashed sphere.

Stress Distribution:

This design offers good stress distribution, making them suitable for a wide range of pressure vessel applications.

Flexibility:

A. The knuckle radius can be adjusted to meet specific design requirements.

B. Torispherical heads combine a spherical crown with a conical knuckle, resulting in a head shape resembling a squashed sphere.

C. They offer good strength and stress distribution, making them suitable for a wide range of pressure vessel applications.

D. Furthermore, the knuckle radius can be adjusted to meet specific design requirements.

B. Applications:

A. Torispherical heads are versatile and used in various industries, including chemical processing, food and beverage, and pharmaceuticals.

B. They are often chosen for medium to high-pressure vessels like storage tanks, distillation columns, and reactors.

Flat Heads (or Dished Heads):

A. Characteristics:

Shape:

Flat heads are essentially flat plates used as the heads of pressure vessels.

Simplicity:

They are the simplest and most economical head shape in terms of manufacturing and installation.

Pressure Limitation:

A. Flat heads are typically used for low-pressure or atmospheric vessels due to their limited pressure containment capability.

B. Flat heads are essentially flat plates used as heads in pressure vessels.

C. They are the simplest and most economical head shape.

D. Moreover, flat heads can be easily manufactured and installed, making them suitable for low-pressure or atmospheric vessels.

B. Applications:

Flat heads are commonly found in applications where pressure containment is not a primary concern, such as atmospheric storage tanks, some types of silos, and vessels for bulk material handling.

The selection of a head type for a pressure vessel is a critical engineering decision that takes into account factors like the vessel’s intended purpose, operating conditions, and design specifications. Each of these common head types offers unique advantages in terms of stress distribution, pressure containment, and cost-effectiveness, making them suitable for various applications across different industries. Properly chosen and designed heads ensure the safety, efficiency, and reliability of pressure vessels in diverse industrial settings.