1) Pressure vessels are containers that store fluids under pressure. They are designed to withstand internal pressure loads. 2) Key components of pressure vessel design include the shell, end closures, nozzles, flanged joints, and vessel supports. The shell must be designed to withstand internal pressure as well as combined loading. 3) End closures can be flat heads or formed heads like hemispherical, torispherical, or elliptical heads. Vertical vessels are supported by brackets or skirts and horizontal vessels use saddles.

1. GANDHINAGAR INSTITUTE OF
TECHNOLOGY

2. Introduction
 Pressure vessels are the containers or pipelines used for storing,
receiving or carrying the fluids under the pressure.
 The fluid being stored may remain as it is, as in case of storage
vessels or may undergo a change of state while inside the pressure
vessels, as in case of steam boilers or it may combine with other
reagents, as in case of chemical processing vessels.

3. Design of unfired pressure vessels
1. Pressure vessel shell
2. End closures
3. Nozzles and openings
4. Flanged joints
5. Vessel supports

4. Design of pressure vessel shell
 The design of pressure vessel shell in discussed under two different
conditions :
1. Pressure vessel shell subjected to Internal Pressure
2. Pressure vessel shell under combined loading

5. 1. Pressure vessel shell subjected to Internal
Pressure

7. 2. Pressure vessel shell under combined loading

11.  Bending stress due to total weight of vessel and its contents in case of
horizontal pressure vessels or due to wind load and seismic load in
case of vertical pressure vessels :

13. 2. Bending moment acting on vertical pressure vessel shell :

17. END CLOSURES IN UNFIRED PRESSURE
VESSELS
 The cylindrical pressure vessels are closed at ends by either
1. Flat Heads
2. Formed Heads
 The heads are either welded or bolted with the main vessel shell.

18. 1. Flat Heads

19. 2. Formed Heads
 The formed heads, which are commonly used in pressure vessels, are
normally fabricated from a single circular flat plate by fowling.
 The different types of formed heads used in pressure vessels are
discussed below :
1. Plain Formed Head
2. Tori spherical Dished Head
3. Semi-Elliptical Dished Head
4. Hemispherical Head
5. Conical Head

20.  Plain Formed Head

21.  Torispherical Dished Head

23.  Semi-Elliptical Dished Head

24.  Hemispherical Head

25.  Conical Head

26. Attachment of Head to Shell :
 The heads are attached to the pressure vessel shell by a welded or bolted joints.
 The different varieties of welded connections used for attachment are shown in Fig.

27. Support for pressure vessels
 The vertical pressure vessels are supported by the bracket or skirt,
while the horizontal pressure are supported by saddles.
 Support for vertical pressure vessels :
 Two types of supports, used for vertical pressure vessels, are discussed below :
1. Bracket or Lug support
2. Skirt support

28.  Bracket or Lug support
Each bracket is made of two horizontal and two vertical plates welded to
vessel shell. The brackets are made to rest on short columns.
Due to the eccentricity of this type of supports and the resulting bending
moment ; tensile, compressive and shear stresses are induced in the vessel
shell.
Bracket supports are ideal for thick walled vessels, as these supports are
capable of absorbing bending stresses due to eccentricity of loads.
 In thin walled vessels, the areas where the brackets are to be attached,
are reinforced by welding the pads. The brackets are then welded on the
pads.
Bracket supports are normally used for vessels of smaller height.
The loads on the bracket support are the dead weight of the vessel with its contents and the
wind load.
The wind load tends to overturn the vessel, particularly when the vessel is empty. The
weight of the vessel when filled with liquid tends to stabilize it.
The maximum compressive stresses in the supports occur on the leeward side when the
vessel is full, because dead weight and wind load have supporting effect.

29.  The maximum tensile stresses in the supports occur on the windward side when the
vessel is empty because, dead weight and wind load have opposing effects.
 Therefore, the stresses on the leeward side are determining factor for design of the
supports.

30.  Skirt support
 The tall vertical pressure vessels are usually supported by skirts. The skirt may be
straight skirt or angular skirt.
 The skirt has high section modulus, and hence gives better resistance to bending.
Therefore, the skirt support is an economical design for a tall vertical pressure
vessels.
 A bearing plate is attached to the bottom of the skirt. This plate is fixed to the
concrete foundation by means of anchor bolts to prevent the overturning of the
vessel due to wind or seismic loads.
 The skirt is subjected to a direct compressive stress due to a dead weight of the
vessel and its contents and a bending stresses due to wind and seismic loads.

32.  Supports for Horizontal Pressure Vessels :
 The horizontal pressure vessels are supported on saddles. Sometimes, if necessary, the
shell of the vessel is strengthened by stiffeners located on the shell area surrounding the
saddle.
 There are two types of saddle supports
1. Plate Type
2. Ring Type
1. Plate Type Saddle Support :
 For a small vessels, a plate type supports may be used.
2. Ring Type Saddle Support :
 For a large thin walled vessels, which require supports at more than two
positions and which are liable to be weakened by heavy loads, ring
type supports are preferred.