1.2 Pressure Vessels

A pressure vessel is defined as a container with a pressure differential between inside and outside (ambient). The vessel may carry, store, or receive fluids and may be of the form pipe, tank or any process vessel.

A shell is a curved plate-type structure such as cylindrical or spherical.

  • Vessels which have a wall thickness of less than about 5% of the inside diameter of a vessel are called as thin-walled vessels. Most of the process equipments meet this criteria.

  • Vessels larger in diameter than about 30 in (0.672 m) and above are fabricated from plates, which are formed into cylinders, called shells, and welded longitudinally. Shells smaller than 30 in may be extruded and thus will not contain a longitudinal weld. Shells may then be joined by welding circumferentially to form longer shells. After fabricating the shell, end caps, called heads, are welded to the shell to form the vessel.

    Because the weld may have imperfections, the joint-efficiency (\(J\)) has to be taken into consideration.