What are the different types of tank heads?

What are the different types of tank heads?

The end tank head cap is a crucial component used to seal the end of a container, ensuring isolation between the internal and external mediums. Also known as the end cap, this element is typically a rotational shell in cylindrical containers. Based on the surface shape, end caps can be categorized into convex, conical, flat, and composite types. A convex end cap, for instance, has a raised surface and includes variations such as hemispherical, elliptical, dish-shaped, and spherical end caps without folding edges.

In practical applications, certain gas cylinders incorporate a composite bottom end cap with the convex side facing inward. This design not only meets structural strength requirements but also enhances safety. End caps are widely utilized in various container-based equipment, including storage tanks, heat exchangers, towers, reactors, boilers, and separation equipment. Materials used for manufacturing these components range from carbon steel (A3, 20#, Q235, Q345B, 16Mn, etc.) and stainless steel (304, 321, 304L, 316, 316L, etc.) to alloy steel (15Mo3, 15CrMoV, 35CrMoV, 45CrMo), as well as aluminum, titanium, copper, nickel, and nickel alloys.

Given their extensive applications, end caps have become indispensable in pressure vessel systems across industries such as petrochemicals, nuclear energy, and food and pharmaceuticals. As a critical sealing component, the end cap serves as a primary pressure-bearing element in pressure vessels, playing a significant role in ensuring operational integrity.

How are these end caps applied? Typically, they are used in two key ways: as the top and bottom closures of tank-shaped pressure vessels and as pipe seals when a pipeline reaches its endpoint with no further extension.

It is important to note that other products serve similar functions, such as blind plates and pipe caps. However, while those components can be removed when necessary, an end cap—once welded—becomes a permanent fixture. Compatible fittings for these components include pressure vessels, pipelines, flanges, elbows, tees, crosses, and other associated products. The quality of an end cap directly impacts the long-term safety and reliability of pressure vessels.

End caps can be classified into various types based on their shape, including hemispherical, non-folded, elliptical, butterfly, and conical heads. Each type has distinct characteristics and is suited for different applications. Below is a closer look at some of the common types:

Hemispherical HeadAlso known as a spherical head, this design offers an ideal force distribution and considerable depth. However, due to the complexity of its manufacturing process, hemispherical heads are primarily used in high-pressure and large-diameter pressure vessels rather than everyday applications.

Flat Bottom HeadWith a flat base and upward-curved sides, this type of end cap has a simple structure and is easier to manufacture. However, its force-bearing capability is weaker compared to other designs, necessitating a greater thickness under equivalent pressure conditions. Despite this drawback, flat-bottom heads are cost-effective and commonly used in low-pressure, small-diameter containers.

Elliptical HeadThis type consists of half an elliptical surface and a cylindrical straight edge segment. It merges the strengths of a hemispherical head’s excellent stress distribution with the shallower depth of a dished head. Its smooth and continuous curvature results in uniform stress distribution and overall strong performance. Elliptical Heads are among the most commonly used end caps and are frequently applied in low-pressure vessels such as storage tanks, reactors, and heat exchangers.

Butterfly HeadAlso referred to as a spherical head with a folded edge, this design features a spherical surface, a cylindrical straight edge, and a transition section. Its curvature radius is smaller than that of a typical spherical surface. This head has a shallow depth, consumes less material, and is easier and more cost-effective to manufacture. When elliptical heads are challenging to produce, butterfly heads are often used as an alternative.

Conical HeadComprising a conical shell, a transition arc, and a cylindrical straight edge segment, this type of end cap facilitates smooth flow transitions, particularly for viscous liquids and solid-particle materials. However, conical heads exhibit lower mechanical properties, and manufacturing them becomes increasingly complex as wall thickness increases. Therefore, they are used only when required by specific industrial processes.

Key Considerations for End Cap Usage

As primary pressure-bearing components of boilers and pressure vessels, end caps must be carefully designed and fabricated to ensure structural integrity and safe operation. Their correct selection and installation are crucial for maintaining the efficiency and reliability of pressure equipment across various industries.