An Overview of Various Pressure Vessel Head Types

An Overview of Various Pressure Vessel Head Types

Pressure vessel heads are essential components that contribute to the safety and efficiency of pressure vessels. These sealed enclosures are specifically engineered to contain either toxic or non-toxic gases and liquids under pressure levels that differ significantly from the external environment.

The primary function of pressure vessel heads is to evenly distribute internal pressure across the vessel while effectively sealing the ends to prevent leakage of stored gases or fluids. If a pressure vessel head fails to withstand the applied pressure, it can result in leaks or severe damage, posing risks to both people and property nearby.

The design and fabrication of pressure vessels and their corresponding heads must adhere to strict regulations outlined by the ASME (American Society of Mechanical Engineers) Boiler and Pressure Vessel Code (BPVC). In the U.S. and Canada, compliance with Code Section III is mandatory for these structures.

Beyond regulatory requirements, selecting an appropriate pressure vessel head is crucial as it influences the vessel’s overall design, performance, and suitability for specific applications. Therefore, understanding the various types of pressure vessel heads and their respective benefits is essential.

Semi-Elliptical (SE) Heads

SE heads rank among the most commonly utilized head designs in pressure vessels. Their shape resembles half of an ellipse, with a depth-to-width ratio of 2:1, meaning the depth of the head is four times its width.

This design offers several key benefits:

• Superior Pressure Resistance: The 2:1 ratio enhances pressure resistance, making SE heads ideal for high-pressure applications.

• Cost Efficiency: These heads are constructed using thinner materials, such as flat plates, which help reduce manufacturing costs.

• ASME Compliance: The ASME code provides two approximations for SE heads to ensure they effectively withstand pressure. One approximation involves a sphere with a radius equal to 90% of the head’s diameter (0.90D), while the other includes a knuckle radius measuring 17% of the head’s diameter (0.17D).

ASME Flanged and Dished (ASME F&D) Heads

As indicated by their name, these heads are well-suited for vessels operating under moderate pressures. The design features a flanged rim that extends outward, along with a dished contour that curves inward. These structural elements enhance the strength and integrity of the vessel.

Advantages of ASME F&D heads include:

• Space-Saving Design: Their relatively low-profile shape makes them suitable for pressure vessels with height limitations.

• Enhanced Strength: These heads are generally thicker than semi-Elliptical Heads, providing added durability for moderate-pressure applications.

• Offset Seam: The head-to-shell circumferential seam is typically configured with a 3:1 offset ratio, which helps reduce stress concentration and ensures structural stability.

• Versatility: Their flatter design makes them ideal for applications such as mixing tanks, where a lower-mounted mixer is required.

Flat Heads

Flat heads feature a completely level surface, making them well-suited for applications that require an interior flat surface. These heads are primarily used in non-pressure environments, such as storage or holding tanks, where stress concentration is not a primary concern. However, when employed in pressure applications, flat heads can be more expensive than other head types.

Additionally, flat heads are preferred when a pressure vessel’s design necessitates a head with a low-profile or reduced height.

Hemispherical Heads

Hemispherical heads are shaped like a half-sphere, with a depth equal to half of their diameter. This design incorporates two pressure heads positioned back-to-back, forming a storage sphere that efficiently contains materials under high pressure.

Key features of hemispherical heads include:

• Thinner Construction: Compared to cylindrical shells, hemispherical heads have a thinner profile.

• ASME Standard Compliance: These heads adhere to a 3:1 taper transition standard.

• Higher Costs: While they are the most expensive option, they offer superior pressure resistance.

• Ideal for Large-Scale Use: Their strength and durability make them well-suited for large-diameter vessels and high-pressure applications.

Discover ASME Pressure Vessel Heads with Haipei Industry

Pressure vessel heads are available in multiple shapes and configurations to accommodate varying pressure needs, structural demands, and operational requirements. If you need assistance in selecting the most appropriate head type for your specific application, consulting a reputable manufacturer like Haipei Industry can be beneficial.

With decades of experience, Haipei Industry specializes in fabricating pressure vessels with different head designs, including high-pressure tanks and ASME-compliant or non-code vessels with SE and F&D heads. Contact us today to find the ideal pressure vessel solution for your needs.