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Cylinders or vessels are used in mechanics to contain a matter enclosed and pressurised. The cylinders are used for containing and compressing the fluids and gases to study and analyse their behaviour. And depending on their usage, the cylinders can be of different types. The cylinders can be classified as thick and thin based on their wall thickness. The wall thickness provides the cylinder’s ability to sustain a particular amount of pressure. Their use also varies due to their respective wall thickness; thin cylinders have more common use, while thick cylinders have broader utilisation in various industries.
A Thin Cylinder
A thin mechanical cylinder is described as a cylinder whose diameter is much larger with respect to its wall thickness; in other words, a thin mechanical cylinder or vessel is described as a cylinder with a wall thickness less than 1/20 of its internal diameter.
Consider a cylinder or a vessel with an internal diameter d and thickness t,
The wall thickness of this cylinder,
Wall thickness t < d/20,
t/d < 1/20, Or, d/t > 20.
The above expression gives a vessel, shell, or cylinder to be considered a thin cylinder. The radial stress is considered negligible in a mechanical calculation using a thin cylinder.
Usage of a Thin Cylinder
The thin cylinders are generally used in operations with lesser pressure force. These cylinders are designed for specific purposes. These cylinders are generally used in pipes, pressure shells and boilers. In calculating a mechanical operation done by a thin cylinder, the circumferential stresses are considered constant, and the radial stress is considered negligible.
A Thick Cylinder
A vessel, shell or cylinder can be used for mechanical operations with higher pressures; a thick cylinder is used in such operations. A thick cylinder is described as a cylinder with a bigger diameter; in other words, a thick cylinder or vessel is defined as a cylinder with a wall thickness of more than 1/20 of its inner diameter.
Consider a cylinder with an inner diameter d and a wall thickness d,
The wall thickness for a thick cylinder is given as,
The wall thickness t > d/20,
t/d > 1/20,
Or, d/t < 20.
The above expression gives the condition for a cylinder or a vessel to be classified as a thick cylinder.
Usage of a Thick Cylinder
Due to a greater wall thickness, a thick cylinder or vessel is generally used for heavy pressure operations. Thick cylinders are designed to bear a high-pressure environment; these cylinders are used to carry heavy materials, such as oil, petroleum, and dense gases. The thick cylinders are also used in nuclear power plants to carry fuels and radioactive materials.
Key Difference between Thin and Thick Cylinders
There are the following key differences between a thin and a thick cylinder,
- A thick cylinder has a smaller diameter with respect to its wall thickness, whereas a thin cylinder has a greater diameter with respect to its wall thickness
- A thin cylinder is used for operations with a lesser pressure value, whereas a thick cylinder is used for heavy pressure operations
- Unlike a thin cylinder, the circumferential stresses are not uniform in a thick cylinder; also, the radial stress is not negligible
- A thin cylinder is used for lab operations and small-scale usage, however, a thick cylinder has a much wider industrial use: it is used in pipelines and nuclear power plants
- A thin cylinder can only act on the internal pressure of the cylinder, while a thick cylinder can act on internal and external pressure
- The capacity of handling the stress of a thin cylinder is way less than that of a thick cylinder
Stresses in a Thick Cylinder
Lame equations are used to determine the values of the stresses in a thick cylinder; these equations give the value of the radial stress (σr) and Hoop’s stress (circumferential stress, σh).
The radial stress of a thick cylinder or a vessel is given by,
σr = A – (B/d2).
The Hoop’s Stress of a thick cylinder of a vessel is given by,
σh = A + (B/d2).
The above equations are called Lame’s equations here, the A and B are constants, and the boundary conditions of the cylinder determine their value.
Conclusion
Various kinds of cylinders are used for mechanical operations; these cylinders vary in shapes and sizes. These cylinders can be classified as thin and thick cylinders in broader classification.
A thin cylinder is defined as a relatively lesser thickness to its diameter, and a thick cylinder is one with a relatively larger thickness than its wall diameter. A thick cylinder has wider industrial usage than a thin cylinder; thick cylinders can deal with high internal and external pressures. The Hoop’s stress gives the value of circumferential stress in a thick cylinder. A thin cylinder is used for general functions like a boiler and a pressure pipe.
