Pressure Vessel Design Calculation
ASME BPVC Sec. VIII Div. 1
Pressure Vessel
 Pressure vessels are the containers for fluids under
high pressure.
 They are used in a variety of industries like
 Petroleum refining
 Chemical
 Power
 Food & beverage
 Pharmaceutica
Types of pressure vessels
There are three main types of pressure vessels
in general:
 Horizontal Pressure Vessels
 Vertical Pressure Vessels
 Spherical Pressure vessels
Horizontal Pressure Vessels
Vertical Pressure Vessels
 The max. Shell length to
diameter ratio for a small
vertical drum is about 5 : 1
Tall Vertical Tower




Constructed in a wider range of shell
diameter and height.
They can be relatively small in dia. and
very large (e.g. 4 ft dia. And 200 ft tall
distillation column.
They can be very large in dia. and
moderately tall (e.g. 3 ft dia. And 150 ft
tall tower).
Internal trays are needed for flow
distribution.
Vertical Reactor

Figure shows a typical reactor vessel
with a cylindrical shell.

The process fluid undergoes a
chemical reaction inside a reactor.

This reaction is normally facilitated by
the presence of a catalyst which is
held in one or more catalyst beds.
Spherical Pressurized storage
vessel
Pressure Vessel Component




Shell
Head
Nozzle
Support :
- Skirt
- Leg
- Saddle
- and Lug
Shell






It is the primary component that contains
the pressure.
Pressure vessel shells in the form of
different plates are welded together to
form a structure that has a common
rotational axis.
Shells are either cylindrical, spherical or
conical in shape.
Horizontal drums have cylindrical shells
and are constructed in a wide range of
diameter and length.
The shell sections of a tall tower may be
constructed of different materials,
thickness and diameters due to process
and phase change of process fluid.
Shell of a spherical pressure vessel is
spherical as well.
Shell
Head





All the pressure vessels must be
closed at the ends by heads (or
another shell section).
Heads are typically curved rather
than flat.
The reason is that curved
configurations are stronger and allow
the heads to be thinner, lighter and
less expensive than flat heads.
Heads can also be used inside a
vessel and are known as intermediate
heads.
These intermediate heads are
separate sections of the pressure
vessels to permit different design
conditions.
Nozzle


A nozzle is a cylindrical component
that penetrates into the shell or head
of pressure vessel.
They are used for the following
applications.




Attach piping for flow into or
out of the vessel.
Attach instrument connection
(level gauges, Thermowells,
pressure gauges).
Provide access to the vessel
interior at MANWAY.
Provide for direct attachment
of other equipment items
(e.g. heat exchangers).
Nozzle
Support

Support is used to bear all the load of
pressure vessel, earthquake and wind
loads.

There are different types of supports
which are used depending upon the
size and orientation of the pressure
vessel.

It is considered to be the nonpressurized part of the vessel.
Types of Supports
a. Saddle Support:

Horizontal drums are typically
supported at two locations by saddle
support.

It spreads over a large area of the
shell to prevent an excessive local
stress in the shell at support point.

One saddle support is anchored
whereas the other is free to permit
unstrained longitudinal thermal
expansion of the drum.
Types of Supports
b. Leg Support:

Small vertical drums are typically
supported on legs that are welded to
the lower portion of the shell.

The max. ratio of support leg length
to drum diameter is typically 2 : 1

Reinforcing pads are welded to the
shell first to provide additional local
reinforcement and load distribution.

The number of legs depends on the
drum size and loads to be carried.

Support legs are also used for
Spherical pressurized storage vessels.

Cross bracing between the legs is
used to absorb wind or earth quake
loads.
Types of Supports
c. Lug Support:

Vertical pressure vessels may also be
supported by lugs.

The use of lugs is typically limited to
pressure vessels of small and medium
diameter (1 to 10 ft)

Also moderate height to diameter
ratios in the range of 2:1 to 5:1

The lugs are typically bolted to
horizontal structural members in order
to provide stability against
overturning loads.
Types of Supports
c. Skirt Support:



Tall vertical cylindrical pressure
vessels are typically supported by
skirts.
A support skirt is a cylindrical
shell section that is welded either
to the lower portion of the vessel
shell or to the bottom head (for
cylindrical vessels).
The skirt is normally long enough
to provide enough flexibility so
that radial thermal expansion of
the shell does not cause high
thermal stresses at its junction
with the skirt.
Basic Design








Design pressure (Pd)
Design temperature (Td)
Diameter and length of vessel
Corrosion allowance (C)
Joint efficiency – (E) ASME Sec. VIII Div. 1 TABLE UW-12
Material Specification ASME Sec. II Part D TABLE 1A
Head Type
Vessel orientation, seismic zone, wind speed
Design Calculation
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
Static head (Ps)
Internal design pressure(P)
Shell thickness (ts), MAWPshell
Head thickness (th), MAWPhead
Nozzle thickness (tn), MAWPnozzle
Maximum Allowable Working Pressure (MAWP)
Hydrostatic test
Weight
Nozzle reinforcment
Wind load
Seismic load
a. Static head
Static head (Ps) is pressure effect by elevation of fluid in
vessel.
Ps   * H
H=Liquid Height
ρ=rho liquid
b. Internal design pressure(P)
P  Ps  Pd
Ps=Static Pressure
Pd=Design Pressure
c. Shell thickness
 Thickness of shell under internal pressure

•
Cylindrical Shells
Circumferential Stress (Longitudinal Joints).
Thickness:
MAWP:
PRs
ts 
SE  0.6 P
P
SEt s
Rs  0.6t s
When the thickness exceeds one-half of the inside radius, or P exceed 0.385SE,
the formula given in ASME Sec. VIII Div.1 Appendix 1-2 shall be applied.
•
Longitudinal Stress (Circumferential Joints).
Thickness:
MAWP:
s
s
t 
PR
2 SE  0.4 P
2SEt s
P
Rs  0.4t s
When the thickness exceeds one-half of the inside radius, or P exceeds 1.25SE,
the formula given in ASME Sec. VIII Div.1 Appendix 1-2 shall be applied.
c. Shell thickness (Cont.)
 Thickness of shell under internal pressure

Spherical Shells. When the thickness of the shell of a wholly spherical vessel
does not exceed 0.356R, or P does not exceed 0.665SE, the following formulas
shall apply:
Thickness:
MAWP:
PRs
ts 
2 SE  0.2 P
P
2 SEt s
Rs  0.2t s
d. Head thickness
Formulas for the design of formed heads under internal pressure:
a)
Ellipsoidal Heads
Thickness:
PDh
th 
2SE  0.2 P
MAWP:
2SEt h
P
Dh  0.2t h
For ellipsoidal heads, where the ratio of major and minor axis is other than 2:1,
ASME Sec. VIII Div.1 Appendix 1-4 shall be applied.
d. Head thickness (Cont.)
b) Torispherical Heads
When L/r = 16^2/3
Thickness:
0.885 PL
th 
SE  0.1P
When L/r less than 16^2/3
Thickness:
PLM
th 
2SE  0.2 P
MAWP:
SEt h
P
0.885L  0.1t h
MAWP:
2SEth
P
LM  0.2t h
d. Head thickness (Cont.)
c) Hemispherical Heads
Thickness:
PL
th 
2SE  0.2 P
MAWP:
2SEt h
P
L  0.2t h
When the thickness of a hemispherical head exceeds
0.356L, or P exceeds 0.665SE. the formula given in
ASME Sec. VIII Div.1 Appendix 1-3 shall be applied.
d. Head thickness (Cont.)
d) Conical Heads and Sections
Thickness:
MAWP:
PD
th 
2 cos  ( SE  0.6 P)
2SEth cos 
P
D  1.2t h cos 
When a is greather than 30O, Special analysis is
required. ASME Sec. VIII Div.1 Appendix 1-5(e)
shall be applied.
e. Nozzle thickness

Wall Thicknesses Required
tn 
PRn
SE  0.6 P

Minimum Nozzle Wall Thickness by UG-45

UG-45 b(1) for Internal Pressure :
Thickness:
MAWP:
PRs
tn 
SE  0.6 P
SEtn
`
P
Rs  0.6t n
P=Internal pressure
Rs=Radius of shell

UG-45 b(2) for External Pressure
Thickness:
MAWP:
PRs
tn 
SE  0.6 P
SEtn `
P
Rs  0.6t n
P=External pressure
R=Radius of shell
e. Nozzle thickness (Cont.)

UG-16(b) Minimum Thickness of Pressure Retaining Components.
t n  Min.Thk .(1.5mm)  CA

UG-45 b(4)
t n  Table UG  45  CA

UG-45 a for Internal Pressure
PRn
tn 
SE  0.6 P
P=Internal Pressure
R=Radius of nozzle
Result :
Step 1= Max ( UG 45b(1) , UG 16b)
Step 2= Max ( UG 45b(2) , UG 16b)
Step 3= Max ( Step1 , Step 2)
Step 4= Min ( Step3 , UG-45 b(4))
Step 5= Max ( Step4 , UG-45 (a))
f. Maximum Allowable Working
Pressure (MAWP)
MAWP is the least of the values found for maximum
allowable working pressure for any of the essential parts
of the vessel
MAWP  Min ( MAWPshell , MAWPhead , MAWPnozzle )
g. Hydrostatic test
Hydrostatic test accordance UG99(b)
HTP  1.3 * MAWP * Stress Ratio
St
Stress Ratio 
Sd
Where
=.
St  allowable
stress material at test temperature
S d  allowablestress material at Desain temperature
h. Weight

Fabricated weight: Total weight as fabricated in the shop.
• Weight of shell
• Weight of head
• Weight of nozlle
• Weight of internal and external attachment
• Weight of weld process
• Weight of platform and ladder

Shipping weight: Fabrication wight plus any weight added for shipping
purposes, such as shipping saddles.

Erection weight: Fabrication weight plus any weight installed for the erection
equipment, such as any insulation,fireproofing,piping,ladders,platform.
of the

Empty weight: The overall weight of the vessel sitting on the foundation, fully
waiting for operating liquid.
dressed


Operating weight: Empty weight plus any operating liquid weight.
Test weight: This weight can be either shop or field test weight. That is the
of water.
vessel
i. Nozzle reinforcment
 Area required reinforcement
Areqd  ( d )(t s )
An=Smaller of:
 1

2  2 Ts Tn  t n 
 2

An  Areqd
 1
or
2 2


2
Tn Tn  t n 
= Acceptable configuration

j. Wind load
Application of wind forces:
k. Seismic load
THANK YOU