How to Select the most Economical Vessel Head?

Selecting the most Economical Vessel Head

The cost of any pressure vessel head is based on a combination of metal costs and manufacturing costs. Manufacturing cost is based on a combination of shape, thickness, and method of forming. As the metal becomes more expensive, it becomes necessary to use thinner and small blank diameter for forming the head. Thinner materials require more severe configurations that increase the cost of fabrication. The designer should select a head thickness that can be formed as economically as possible.

• Hemispherical, tori spherical and elliptical heads are commonly used for process equipment.

• The hemispherical head is used only for special purposes because of its very high fabrication cost.

• The elliptical head is used for pressures above 15 kg/cm2 and requires higher wall thickness and is very difficult and costly to fabricate.
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• Torispherical and shallow flanged dished head have been very common for low-pressure operations. Heads can be formed by hot forming or cold forming. The cold-forming technique is preferred.

• Torispherical head with 100-6 design is common. It means the crown radius equal to the diameter of the vessel and knuckle radius 6% of the diameter. For economic reasons 80-10 head i.e. a dish radius equal to 80% of the head diameter and a knuckle radius equal to 10% of the head diameter can be used. It requires less thickness as compared to the standard tori spherical head.

• The thickness of the tori spherical head depends upon the ratio of the crown radius to the knuckle radius also. Torispherical heads are classified as 100 -10; 100 6; 80-10 and so on.

• 100-10 tori spherical head means the crown radius of the head is equal to the diameter of the vessel and the knuckle radius is 10% of the diameter of the vessel. Similarly, other types are designated.
• The thickness required for 80 10 tori spherical head is less than of 100-6 tori spherical head used for the same diameter vessel and the same operating conditions.

• The thickness required for the elliptical head for the same diameter vessel and the same operating conditions is still less than that of any type of tori spherical head, but the cost of fabrication of the elliptical head is more than that of tori spherical head.