Pressure Vessels

Pressure vessels are closed containers designed to hold gases or liquids at a pressure substantially different from the ambient pressure.

The pressure differential is potentially dangerous and many fatal accidents have occurred in the history of their development and operation. Consequently, their design, manufacture, and operation are regulated by engineering authorities backed up by laws. For these reasons, the definition of a pressure vessel varies from country to country, but involves parameters such as maximum safe operating pressure and temperature.

Shape of a pressure vessel

Pressure vessels may theoretically be almost any shape, but shapes made of sections of spheres, cylinders, and cones are usually employed. A common design is a cylinder with hemispherical end caps called heads. More complicated shapes have historically been much harder to analyze for safe operation and are usually far more difficult to construct.

Theoretically, a sphere would be the optimal shape of a pressure vessel. Unfortunately, a spherical shape is difficult to manufacture, therefore more expensive, so most pressure vessels are cylindrical with 2:1 semi-elliptical heads or end caps on each end. Smaller pressure vessels are assembled from a pipe and two covers. A disadvantage of these vessels is that larger diameters make them relatively more expensive, so that for example the most economic shape of a 1,000 litres (35 cu ft), 250 bars (3,600 psi) pressure vessel might be a diameter of 914.4 millimetres (36 in) and a length of 1,701.8 millimetres (67 in) including the 2:1 semi-elliptical domed end caps.