Analysis of Catalyst Support Ring in a pressure vessel based on ASME Section VIII Division 2 using ANSYS software

IJSRD - International Journal for Scientific Research & Development| Vol. 1, Issue 3, 2013 | ISSN (online): 2321-0613
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Analysis of Catalyst Support Ring in a pressure vessel based on ASME
Section VIII Division 2 using ANSYS software
Dhaivat S. Thakkar1
Bhargav Gadhvi2
1
M. E. student 2
Asst. Prof.
1, 2
Mechanical Engineering Department
1, 2
Indus Institute of Technology and Engineering, Rancharda, Ahmedabad, Gujarat, India
Abstract— In reactors, catalyst support rings and tray
support rings that support heavy catalyst beds and catalyst
support grids, are subjected to high pressure and temperature
and other dead loads, so their safe design is essential as they
are critical parts in a reactor and their finite element analysis
is carried out using ASME Sec VIII Div.2 in the industry.
Analysis of skirt support to bottom head junction is also
very important as this welded joint is subjected to wind
loads, seismic loads, dead loads, high thermal gradient etc.
The skirt support supports the whole reactor so the welded
joint must be strong enough to endure stresses due to
various reasons. This safety can be determined using FEA
software using ASME Sec VIII Div.2.
I. INTRODUCTION
Pressure vessel is a closed cylindrical vessel for storing
gaseous, liquids or solid products. The stored medium is at a
particular pressure and temperature. The cylindrical vessel is
closed at both ends by means of dished end, which may be
hemispherical, ellipsoidal and tori spherical. The pressure
vessels may be horizontal or vertical.
Loadings or forces are the “causes” of stresses in
pressure vessels. These forces and moments must be isolated
both to determine where they apply to the vessel and when
they apply to a vessel. Categories of loadings define where
these forces are applied. Loadings may be applied over a
large portion (general area) of the vessel or over a local area
of the vessel. These stresses are additive and define the
overall state of stress in the vessel or component. The
stresses applied more or less continuously and uniformly
across an entire section of the vessel are primary stresses.
The stresses due to pressure and wind are primary
membrane stresses. These stresses should be limited to the
code allowable. These stresses would cause the bursting or
collapse of the vessel if allowed to reach an unacceptably
high level. On the other hand, the stresses from the inward
radial load could be either a primary local stress or
secondary stress. It is a primary local stress if it is produced
from an unrelenting load or a secondary stress if produced
by a relenting load. Either stress may cause local
deformation but will not in and of itself cause the vessel to
fail. If it is a primary stress, the stress will be redistributed;
if it is a secondary stress, the load will relax once slight
deformation occurs.
The type and category of loading will determine
the type and category of stress. This will be expanded upon
later, but basically each combination of stresses (stress
categories) will have different allowables. i.e.:
 Primary stress: Pm < SE
 Primary membrane local (PL):
PL = Pm + PL < 1.5 SE
PL = Pm+ Qm < 1.5 SE
 Primary membrane + secondary (Q):
Pm + Q < 3 SE
ASME Code, Section VIII, Division 1 vs. Division 2
ASME Code, Section VIII, Division 1 does not
explicitly consider the effects of combined stress. Neither
does it give detailed methods on how stresses are combined.
ASME Code, Section VIII, Division 2, on the other hand,
provides specific guidelines for stresses, how they are
combined, and allowable stresses for categories of combined
stresses.
Division 2 is design by analysis whereas Division 1 is
design by rules
Unrelenting loads produce primary stresses.
Relenting loads (self-limiting) produce secondary stresses.
General loadings produce primary membrane and bending
stresses. Local loads produce local membrane and bending
stresses.
Primary stresses must be kept lower than secondary
stresses.
II. DESIGN DATA
Design Pressure : 8.36 MPa g (At top)
Design Temperature : 414°C
Operating pressure : 7.39 MPa g (At top)
Operating temperature : 389°C
Shell : SA 264
Poison’s ratio μ = 0.3
Density ρ = 7850 kg/m3
III. CHARACTERISTICS OF ELEMENTS FOR
ANALYSIS
For Thermal analysis:
For Mapped Mesh
Type of element : 3D Thermal solid SOLID 70
Number of nodes : 8
Degrees of Freedom: temperature at each node
For Structural analysis:
For Mapped Mesh
Type of element : 3D SOLID 185
Number of nodes : 8
Degrees of freedom: X, Y and Z direction translation at each
node
IV. MECHANICAL BOUNDARY CONDITIONS
For evaluating the thermal stresses and the stresses due to
structural loads, the bottom nodes of the vessel are fixed in

Analysis of Catalyst Support Ring in a pressure vessel based on ASME Section VIII Division 2 using ANSYS software
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610
axial and tangential directions. Symmetry Boundary
conditions is applied on Symmetry face of vessel.
V. LOADING
Thermal Loads
The convective heat transfer coefficient is applied on
the model as thermal load. Thermal boundary conditions are
evaluated as given below.
 The equivalent convection coefficient
heq =
Where,
ti = Thickness of insulation = 115mm
hai = Film coefficient between air and insulation = 11.63 W/
m2
K
ki = Thermal conductivity of insulation = 0.09 W/mK
heq =
= 0.733 W/m3
K
= 0.733 x 10-6
W/ mm2
.K
Ta = temperature of inner fluid = 414˚C
Tb = temperature of outer fluid = 16 ˚C
r1 = radius of inner surface = 2.503 m
r2 = radius of intermediate surface = 2.599 m
r3 = radius of outer surface = 2.714 m
hb = Heat transfer coefficient.= 11.63
k1= Thermal conductivity of inner material = 35.4
k2= Thermal conductivity of outer material = 0.09
Uo = Overall Heat Transfer Coefficient
Uo =
( ) ( )
 Substituting the values
Uo= 0.8007 W/ m2
.K
VI. MECHANICAL LOADS
 Design pressure
Internal pressure applied on all inside surfaces
P= 8.36 Mpa
 Shell
Pressure thrust due to internal pressure = πpDi
2
/ 4A
Where,
Di = Inner Diameter of Shell = 5006 mm
A = annular area = π/4 (Do
2
– Di
2
)
Do =Outer shell diameter = 5198 mm
Di = Inner shell diameter = 5006mm
Therefore, Annular area = 1537946.88 mm2
So, Pressure thrust = 3.14 x 8.36 x 50062
/ 4 x 1537946.88
= 109.87 MPa
As the beam is supported at two ends, half of the
load is applied on the support ring at the contact area
between base block and support ring.
Beam Location
Effective load on
each beam (kg)
Beam Load considered
in the analysis (kg)
First beam –Near
Center
(550 mm from
centreline)
250394 250394/2 = 125197
Outer Beam ( 1000
mm from first beam)
200689 200689/2 = 100344.5
Table. 1: Beam Load for Catalyst Support Ring
Fig. 1: Effective load on beam-1 of catalyst support ring
Inside diameter of vessel, D =4997mm
Width of shaded region, X = 1000mm
Distance of Beam CL from vessel CL, Y=500mm
Inside radius, R = 2498.5 mm
Angle AOB, θ = 2 x cos-1(X / R)
= 2 x cos-1(1000/2498.5)
= 132.8°
Length AB = 2R x sin (θ/2)
= 2 x 2498.5 x sin (132.8/2) mm
= 4579.3 mm
Area of Sector OADB, A1 = x πR2
= 132.8/360 x π x
(2498.5)2
= 7234427.26 mm2
Area of triangle OAB, A2 = 2 x area of ∆ OAC
= 2 x ½ x OC x AC
= 2 x ½ x 1000 x
2289.65 mm2
= 2289651.12 mm2
Area of half circle, A3 = πR2 /2
= (3.141 x 2498.52) / 2
=9805699.60 mm2
Area of shaded region, AR= A3- A1 +A2
=4860922.34 mm2
Fig. 2: Effective load on beam-2 of catalyst support ring
Reactor Internal Diameter, D = 4997.00 mm
Width of shaded region, Y=100.00 mm
Distance of beam CL form vessel CL, Y1=1500mm

611
Distance of shaded region from vessel CL,
X= 100 mm
Distance of beam tray OD, d= 20 mm
Inside radius R= 2498.5 mm
Area of half circle, Ac= 9805700 mm2
Length AB = 4579.3 mm
Angle AOB, θ = 2 x cos-1
(X / R)
= 132.814˚
Area of sector OADB, A1= πR2
=7235169.02 mm2
Area of triangle OAB, A2 =2289651.12 mm2
Angle SOD, θ’= 2 x cos-1
(y1 / R)
= 73.648˚
Length SH, SH = 2R x sin (θ’/2)
= 2995.0mm
Area of sector OSDH, A3 =4012057.45 mm2
Area of triangle OSH, A4 = 2994997.33 mm2
Area of SDHS, A5 = A3 - A4
=1017060.12 mm2
Area of shaded region ADB, A6 = A1 – A2 – A5
A6 = 3928457.78 mm2
Calculation for effective load on each beam
 For beam 1(500mm from centerline)
Wdg = Approx. grid weight = 3824.9 kg
AT = total grid area = πD2
/4
= 19611399.21 mm2
Pg= Grid weight per unit area = Wg / AT
= 3824.9 / 19611399.21 kg/mm2
= 0.0002 kg/mm2
PD = Pressure drop= 0.050 kg/mm2
P = PD + Pg
= 0.050 + 0.0002
=0.0502 kg/mm2
Effective Load, W = P*AE + Ps
Where,
AE=Effective load area for beam = 4860922.34 mm2
Ps = Beam self-weight as per drawing = 6400kg
W1 = 0.0502*4860922.34 + 6400 kg
W1 = 250394 kg= 1.228e6 N
 For beam 2 (1000 from first beam)
Wg = Approx. grid weight = 3824.9 kg
AT = total grid area = πD2
/4
= 19611399.21 mm2
Pg= Grid weight per unit area = Wg / AT
= 3824.9 / 19611399.21 kg/mm2
= 0.0002 kg/mm2
PD = Pressure drop= 0.050 kg/mm2
P = PD + Pg
= 0.050 + 0.0002
= 0.0502 kg/mm2
Effective Load, W = P*AE + Ps
Where, AE=Effective load area for beam = 3928457.78 mm2
Ps = Beam self-weight as per drawing = 3500kg
W2= (0.0502*3928457.78) + 3500
W2 = 200689 kg
= 98.43 e3 N
VII. FINITE ELEMENT ANALYSIS
Fig. 3: 3D axisymmetric model of catalyst support ring
welded to shell
Fig. 4: Meshing for structural analysis, 4 elements in
thickness direction, each element size 50 mm
Fig. 5: Internal pressure, 4 elements in thickness direction,
50 mm element size

612
Fig. 6: Thermal stress, 4 elements in thickness direction, 50
mm element size
Fig. 7: Temperature distribution 4 elements in direction 50
mm element size
Fig. 8: Beam stress, 4 elements in thickness direction 100
mm size of element
Fig. 9: Combination of mechanical and thermal loads
50mm size of element
50mm size of element
VIII. VALIDATION OF NUMERICAL ANALYSIS
General Primary membrane stress for shell
= + 0.5P
= 222.15 N/mm2
Primary + secondary stress intensity at inside surface
=
Where,
Y= outer radius / inner radius
= 2599/2503
=1.038
Substituting the value of Y
=
=
=232.89 N/mm2
4 elements in
thickness
direction,
50mm element
size
4 elements in
thickness
direction,
100mm
element size
3 elements in
thickness
direction,
50mm element
size
3 elements in
thickness
direction,
100mm
element size
227.693 MPa 227.645 MPa 227.558 MPa 227.499 MPa
Actual value = 232.89 N/mm2
Table. 2: Primary + secondary at inside surface

613
Thermal stress:
σ =
( )
=
( )
( )
=
=1.79 MPa
Thermal stress by numerical Analysis = 1.89 MPa
IX. CONCLUSION
The finite element analysis of catalyst support ring to shell
junction and head to skirt junction was carried out using
ASME Sec 8 div.2. The analytical results were compared to
numerical results obtained on Ansys. It was found that both
results were almost equal. Meshing was made finer to attain
convergence and results for different mesh densities were
compared to each other. Stress linearization was carried out
on analysis to check whether the stress values exceeded
equivalent allowable stress values depicted in ASME Sec
VIII div.2 at discontinuities as well as regions away from
discontinuities and at local places. The stress categories
were tabulated along with induced stress under different
load combinations and eventually design of both junctions
got passed. So the thesis depicts the usage of ASME Sec.
VIII div. 2 which is for design by analysis for critical
junctions in pressure vessels and in which detailed stress
classification under various loadings is carried out unlike
div.1 which only considers primary membrane stresses and
uses higher factor of safety. While div. 2 because of detailed
stress classification discovers lower factor of safety thus
avoiding sage of excess material as compared to div. 1 and
allows more stresses at local regions and discontinuities.
REFERENCES
[1]. Process equipment design manual by Henry Bednar
[2]. Pressure vessel design manual by Denniss R Moss
[3]. Process equipment design by Joshi
[4]. ASME codes/standards for pressure vessels and boilers

Analysis of Catalyst Support Ring in a pressure vessel based on ASME Section VIII Division 2 using ANSYS software

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