PRESSURE VESSELS
DESIGN PROCEDURES
Engr. Butch G. Bataller
ChE 192 Process Equipment Design
September 20, 2011
Pressure Vessels
 Closed vessel having an internal pressure
between 15 psig to 3000 psig
 ASME Boiler and Pressure Vessel Code contains
rules for the design, fabrication and inspection of
boilers and pressure vessels
 May include reflux drum, storage tanks, heat
exchangers, chemical reactors, distillation
columns, absorption tower, stripping columns,
etc.
PV Design: Shell Thickness
In general, the minimum wall thickness of
welded metal plates subject to pressure,
excluding corrosion allowances, should not
be less than 2.4 mm
a function of the ultimate tensile strength
of the metal at operating temperature,
operating pressure, vessel diameter and
welding joint efficiency
PV Design: Shell Thickness
For a cylinder based on Inside
diameter
PR
tp 
C
SE  0.6 P
where
tp = shell thickness required (inch) [m]
P = Internal design gauge pressure (psig) [kN/m2]
R = Inside Radius (inch) [m]
S = Allowable stress (psi) [kN/m2]
E = Joint efficiency factor (Table 6-2)
C = Corrosion allowance (inch) [m]
PV Design: Shell Thickness
For a cylinder based on Inside
diameter
PR
tp 
C
SE  0.6 P
Provided that
• tp less than or equal to
R
2
or
• Pressure is less than or equal to 0.385 SE (Jawad
and Farr, 1988)
PV Design: Shell Thickness
For a cylinder based on Outside
diameter
PR
tp 
C
SE  0.4 P
where
tp = shell thickness required (inch) [m]
P = Internal gauge pressure (psig) [kN/m2]
R = outside Radius (inch) [m]
S = Allowable stress (psi) [kN/m2]
E = Joint efficiency factor (Table 6-2)
C = Corrosion allowance (inch) [m]
PV Design: Shell Thickness
Allowance for Vertical PV
 For 10>( L/Di)2/ Pd>1.34:
tv = tp[0.75 + 0.22E( L/Di)2/Pd]
If (L/Di)2/Pd < 1.34, tv=tp
PV Design: Shell Thickness
Corrosion Allowance
 1/8 inch for noncorrosive conditions
 ¼ for corrosive environments.
ts = tV + tc
PV Design: Shell Thickness
For Vacuum Vessels
2
where
 Te 
2.6 
 Em
Do 

Pc 
0.5
 Te 
 Te 

  0.45 

 Do 
 Do 
Pc
Te
Do
Em
=
=
=
=
Collapsing pressure (psi)
Thickness to withstand external pressure (inch)
Outside diameter (inch)
Material’s modulus of elasticity [Table 6-4]
** Te must be high enough so that Pc is five times greater than the
difference between atmospheric pressure and design vacuum
pressure
PV Design: Shell Thickness
For Vacuum Vessels (alternate)
tE=1.3(PdL/EmDo)4
tEC=L(0.18Di-2.2 )x 10 -5- 0.19
tV = tE + tEC
where
Pd
Te
Do
Em
=
=
=
=
internal design gauge pressure (psi)
Thickness to withstand external pressure (inch)
Outside diameter (inch)
Material’s modulus of elasticity
PV Design: Shell Thickness
Spherical Vessels
P
where
SEt p
R  0.2t p
P
R
tp
E
S
=
=
=
=
=
 t  0.356ri

or P  0.665SEJ
internal design gauge pressure (psig)
Inside Radius (inch)
Minimum required thickness (inch)
Lowest joint efficiency
Max allowable stress (psi)
Design Temperature
design temperature may be equal to
operating temperatue plus 50oF
Design Pressure
Operating
Pressure ,Po
(psig)
0 -5
10 – 1,000
1,000 +
Design Pressure ,Pd (psig)
10
P= exp{0.60608 + 0.91615[ln Po]
+ 0.0015655 [ ln Po ]2 }
1.1Po
Material of Construction
Carbon Steel >>> Non-corrosive
environment, T= (-20 to 650 OF)
Low Alloy Steel >>> Non-corrosive
environment, T= (650 to 900 OF)
Stainless Steel 300 Series >>> can be
used up to 1,500 OF
Modulus of Elasticity Values
Temperature
(ºF)
-20
200
400
650
700
800
900
Psi x 106
Carbon Steel Low-alloy
Steel
30.2
30.2
29.5
29.5
28.3
28.6
26.0
27.0
26.6
25.7
24.5
Recommended Stress Values
Joint efficiencies
For double-welded butt joints
If fully radiographed = 1.0
If spot-examined = 0.85
If not radiographed = 0.70
In general, for spot examined
If electric resistance weld = 0.85
If lap-welded = 0.80
If single-butt-welded = 0.60
Metal
Carbon steel
(SA-285, Gr. C)
Low-alloy steel
for resistance to
H2 and H2S
(SA-387, Gr. 12C1.1)
High-tensile steel
for heavy-wall
vessels
(SA-302, Gr.B)
Recommended stress values
Temp., ºC
-29 to 343
399
454
-29 to 427
510
565
649
-29 to 399
454
510
538
S, kPa
94,500
82,700
57,200
94,500
75,800
34,500
6,900
137,900
115,800
69,000
42,750
High-alloy steel
for cladding and
corrosion resistance
Stainless 304
(SA-240)
-29
343
427
538
128,900
77,200
72,400
66,900
Stainless 316
(SA-240)
-29
345
427
538
128,900
79,300
75,800
73,100
38
204
38
204
46,200
20,700
15,900
6,900
Nonferrous metals
Copper (SB-11)
Aluminum(SB-209, 1100-0)
Sample Problem
Determine the thickness of a 5 meter
inside diameter spherical tank for
handling a corrosive liquid at a design
pressure and temperature of 300KPa
and 27F, respectively. The material of
construction is made of carbon steel.
Sample Problem
If the height of the tank is 35m, what
is the thickness of the tank
incorporating earthquake and wind
load?
What if the given pressure is an
operating pressure?
Types of Welded Joints
Butt joint
Corner joint
Edge joint
Lap joint
T joint
Square Butt Joints
Used to butt weld light sheet metal
1/16 to 3/16 thick metal.
Beveled Butt Joints
Used to butt weld heavier pieces of metal
together
3/8 to ½ inch metal can welded using a
single V or U joint
½ Inch metal and up can be welded using
a double V or U joint
Beveled Cont.
Corner Joints
Used to join to pieces of metal that are
approximately right angles to each other
Closed corner joint is used on light sheet
metal were strength is not required at the
joint
Half open corner joint is used on heavier
metal when welding can only be done on
one side. Used when load is not severe.
Corner Cont.
Open corner joint is used on heavy
material. It is the strongest of the corner
joints
Corner joints on heavy material are
welded on both sides  The outside first
then reinforced on the inside
Corners Cont.
Edge Joints
Used to join two parallel or nearly parallel
pieces of metal (0.25 in thick or less). Not
very strong.
Used mainly to join edges of sheet metal,
reinforce flanges of I beams, and mufflers.
Lap Joints
Used to join two overlapping pieces of
metal
Single lap joint welded from one side
Single lap joint welded from two sides
develops full strength
Off set lap joint is used when two pieces
of metal need to be joined in the same
plain.
Lap Joints Cont.
A- single lap joint,
one weld.
B- single lap joint,
two welds.
C- offset lap joint.
Tee Joints
Used to join two pieces of metal that are
approximately 90 degrees to each other,
but the surface of one piece of metal is
not in the same plain as the other metal.
Tee Joints Cont.
A- plain tee
B- single beveled
C- double beveled
D- single J
E- double J
Types of Welds
Fillet weld- basic weld used. Used when
joining two pieces of metal without
preparing the surface of the metal first.
Groove weld- basic weld, used when
preparing the metal before welding it into
place.
Fillet Welds
Groove Welds
Weld/Joint Efficiency
Welding
– heats the metal surrounding the welding area
- results in warping, shrinking of the welded area
Stress Relieving
- required to release locked up
localized stress
- annealing or hammering
Radiographing
- locate weld defects and other
structural trouble
- welded joints are exposed to x-ray to detect
excessive porosity, defective fusion and other
defects in the welding process
Weld/Joint Efficiency
For carbon steels (t ≤ 1.25 in)
 requires only 10% x-ray check
 E = 85%
For thicker walls
 requires 100% x-ray check
 E = 100%
Weld/Joint Efficiency
Longitudinal joints should be butt- welded
Vessels in lethal application should be
butt-welded and fully radiographed
All vessels fabricated on carbon or alloy
steel requires post-heat treatment
All welded joints of cryogenic tanks must
be butt welded, postweld heat treated and
X- ray examined
 For double butt joint, the following
are the corresponding efficiencies
Full radiography
Spot radiography
No radiography
100%
85%
70 %
** when welded joint efficiency is not known, assume a no
spot radiography
Welded Joints Categories
Category A – Longitudinal welded joints within
main parts (shells, heads, cones, flat plates,
nozzles, and the attachment weld of a hemispherical
head to a shell)
Welded Joints Categories
Catefory B – Circumferential welded joints within
the main parts (shell, cone, nozzles and the
attachment joint between formed heads (elliptical
and torispherical) and shell).
Category C – welded joints connecting flanges, tubesheets, flat heads to main shell, to formed heads, to transition in d
Welded Joints Categories
Category C – welded joints connecting flanges,
tubesheets, flat heads to main shell, formed heads,
transition in diameter, nozzles, or any welded joint
connecting one side plate to another side plate of a
flat-sided vessel
Category C – welded joints connecting flanges, tubesheets, flat heads to main shell, to formed heads, to transition in d
Welded Joints Categories
Category D – welded joints connecting nozzles to
main shells, spheres, formed heads, flat heads, flatsided vessels.
Maximum Allowable Joint Efficiencies
for Arc and Gas Welded Joints
Type
No.
Joint Description
Limitations
Joint
Category
Degree of Radiographic
Examination
a
b
c
Full
Butt joints as attained by double(1) welding or by other means which
will obtain the same quality of
deposited weld metal on the inside
and outside weld surfaces to agree
with the requirements of UW-35;
welds using metal backing strips
which remain in place are excluded.
(2)
Single welded butt joint with
backing strip other than those
included in (1)
None
A, B, C
&D
Spot
None
1.0 0.85 0.70
(a) None except as A, B, C 0,90 0.80 0.65
shown in (b) below
&D
(b)
Circumferential A, B & 0.90 0.80 0.65
butt joints with one
C
plate offset, see UW13(c) and Fig. UW13.1 (k).
Type
No.
Joint Description
Limitations
Joint
Category
Degree of
Radiographic
Examination
a
b
c
Full
Spot
None
Circumferential
butt A, B & NA
C
(3) Single-welded butt joint without joints only. Not over
use of backing strip
5/8in. thick and not over
24in outside diameter
(4)
Double full fillet lap joint
Double full fillet lap joint
longitudinal joints not
over 3/8in. thick
A
circumferential
joints B & C
not over 5/8in. thick
NA 0.60
NA
NA 0.55
NA
NA 0.55
Type
No.
(5)
(6)
Joint Description
Single full fillet lap joints with plug
welds confirming to UW-17
Single full fillet lap joints with plug
welds confirming to UW-17
Single full fillet lap joints without
plug welds
Limitations
(a) Circumferential joints2 for
attachment of heads not over 24in.
outside diameter to shells not over
1/2in. thick.
(b) Circumferential joint for the
attachment to shells of jackets not
over 5/8in.
in nominal thickness
where the distance from the center of
the plug weld to the edge of the plate
is not less than 1-1/2 times the
diameter of the hole for the plug.
(a) For the attachment of heads
convex to pressure to shells not over
5/8in. required thickness. only with
use of fillet weld on
inside of shells, or
(b) For attachment of heads having
pressure on either side. To shells not
over 24in. inside diameter and not
over 1/4in. required thickness with
fillet weld on outside of head flange
only.
Joint
Category
Degree of Radiographic
Examination
a
b
c
Full
Spot
None
B
NA
NA 0.50
C
NA
NA 0.50
A&B
NA
NA 0.50