Tank heads are the end caps on cylindrically-shaped pressure vessels. They generally comply with ASME standards or similar codes because of the high pressures they must withstand for use with gas storage tanks, driving cylinders, distillation towers, and reactors. Tank heads are important structural elements of pressure vessels, and may be used to contain materials that are highly volatile or hazardous. Both tank integrity and tank head integrity are maintained through proper design and construction. Often, tank heads are coated, heat treated, or made of stainless steel. Products that are designed for use with gases, propane, chemicals, air, water, or refrigerants may provide other features.
Tank heads vary by dimensions, materials of construction, compliance, and head shapes. Diameter, material thickness, radius (when applicable), and tolerances are important parameters to consider. Most tank heads are made of aluminum, carbon steel, stainless steel, or titanium. Cladded end caps are also available. Other materials of construction include A36, 44W, or SA516 Grade 70 steel. Common standards for compliance include ASME EG-32 and ASME UG-32 from the American Society of Mechanical Engineers (ASME). Choices for head shape include hemispherical, ellipsoidal, torispherical, flat, diffuser, and conical.
Hemispherical Tank Heads
Hemispherical tank heads are well-suited for high-pressure applications because the pressure in the vessel is divided equally across the surface of the head. With hemispheric end caps, the radius of the tank head equals the radius of the cylindrical part of the pressure vessel. Ellipsoidal tank heads are also available. They are sometimes called 2:1 elliptical heads or semi-elliptical tank heads because of their 2:1 ratio. Due to their shape, ellipsoidal heads are more economical than some other types of end caps. The height of the head is just 25% of the diameter, and the radius varies between the major and minor axes.
Torispherical Tank Heads
Torispherical tank heads feature a dish with a fixed radius. The knuckle, the transition between the cylinder and the disk, has a toroidal shape. There are two main types of torispherical tank heads: Klopper and Korbbogen. With Klopper heads or decimal heads, the radius of the dish is equal to the diameter of the cylinder. The radius of the knuckle is equal to 10% of the pressure cylinder’s diameter. Korbbogen tank heads are also torispherical, but have a dish radius that is 80% of the cylinder’s diameter.
Other Types of Tank Heads
Other types of tank heads are also available. Flat heads consist of a toroidal knuckle connected to a flat plate. Diffuser heads are inverted torispherical heads that resemble the end caps on some aerosol cans. Conical tank heads, as their name suggests, are cone-shaped.