Differences Between Elliptical Heads and Torispherical Heads

Differences Between Elliptical Heads and Torispherical Heads

Elliptical heads and torispherical heads are two distinct types of vessel heads, each with unique shapes and structural designs. These differences affect not only their applications but also their machining processes. Torispherical heads, for example, are comparatively easier to manufacture. Elliptical heads, when subjected to pressure, experience radial displacement at the joint. Conversely, torispherical heads are typically formed using a stamping process, making them simpler to produce.

One key distinction is in their bending radii. Elliptical heads have a continuous bending radius, preventing stress concentration and making them suitable for high-pressure vessels. Torispherical heads, however, have discontinuous joints where stress is present, making them more appropriate for low-pressure applications. While elliptical heads offer better stress distribution, torispherical heads require less material, making them more cost-effective.

Common Applications:

1. When a pipeline terminates without immediate extension, a head is welded onto the pipe, serving as an end cap.

2. Pressure vessels often feature heads on both the top and bottom, with a straight cylindrical section in the middle, forming a storage container for pressurized materials.

Elliptical heads typically have a long-to-short axis ratio of 2.0, often referred to as standard elliptical heads. Their mechanical properties rank between those of hemispherical and torispherical heads. Since the depth of an elliptical head falls between that of a hemispherical and a torispherical head, the equipment and mold requirements for manufacturing are also intermediate. The introduction of the spinning process has significantly improved the production of large-diameter elliptical heads, making them widely used in medium- and low-pressure vessels due to their balanced performance.

Recent advancements in manufacturing technology have further enhanced the production of elliptical heads, enabling the creation of larger sizes with ease. This has led to their increased adoption for medium- and low-pressure vessels, where they offer superior structural integrity and usability.

Key Differences Between Elliptical and Torispherical Heads:

1. Shape Variations:

• Elliptical heads, also called oval heads, consist of a half-ellipsoidal shape with a cylindrical straight edge. These heads offer the strength of hemispherical heads while maintaining a shallower depth compared to torispherical heads. The smooth curvature ensures even stress distribution.

• Torispherical heads, also known as dished heads, feature a spherical section, a cylindrical straight edge, and a transition section with a smaller radius than the main spherical surface.

2. Stress Distribution and Strength:

• Elliptical heads provide greater strength than torispherical heads. However, for the same diameter, an elliptical head is deeper than a torispherical head, making its manufacturing slightly more complex.

• Although elliptical heads require more material and are costlier, the difference in overall volume remains relatively small.

3. Structural and Standard Considerations:

• When selecting between elliptical and torispherical heads following JB4746 "Head for Steel Pressure Vessel" standards, elliptical heads are generally preferred. According to GB150 calculations, the wall thickness required for an elliptical head under the same pressure, temperature, and diameter is thinner compared to non-standard elliptical heads.

Comparative Table of Elliptical and Torispherical Heads

Elliptical heads and torispherical heads both have distinct advantages depending on the application. While elliptical heads are preferred for high-pressure environments due to their superior stress resistance, torispherical heads remain a practical and economical choice for low-pressure applications.