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International Journal of Advanced Engineering Research and Studies E-ISSN2249–8974

IJAERS/Vol. I/ Issue III/April-June, 2012/184-187

Research Paper

THERMAL ANALYSIS FOR SKIRT DISHED END JOINT OF

PRESSURE VESSEL USING FINITE ELEMENT ANALYSIS

APPROACH Kiran D. Parmar

1, Kiran A. Patel

2, Dinesh D Mevada

3

Address for Correspondence 1, 3

M. E. Student, 2Asst. Prof., Mechanical Engineering Department

L.D.R.P-institute of Technology and Research and Technology, Gandhinagar, India

ABSTRACT This paper presents the guideline in thermal analysis for skirt to dished end joint of pressure vessel. Pressure vessel in which

gases of high pressure and temperature are admitted through nozzle connections to shell to a dished end. So by these loading

(internal pressure and temperature) there is several cracks/failure are developed in skirt dished end joint. The examples of

crack/failure of skirt dished end joint are: cracking due to internal or external load, cracking due to lack of penetration,

cracking due to chemical attack. In order to minimize the engineering effort on these systems it is desirable to develop

standard “maximum” loads for skirt dished end joint configuration by Finite Element analysis approach. So for designing the

pressure vessel stresses should have to be reduced. By using a proper design method and analysis there may be stresses

developed parameters are find out. After analyzing by finite element method (FEM) the stress parameter are find out which

should be consider as a maximum parameter for these one and it can be reduced by optimization. After optimization reduce

the stresses of this joint due to change the weld size of skirt to dished end joint and also increase the life of pressure vessel.

KEYWORDS FEM; pressure vessel; Skirt dished end joint; Thermal

1 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 torispherical. The pressure vessels

may be horizontal or vertical. The skirt supporting

system of this vertical vessel plays an important role

in the performance of the equipment. Proper skirt

supporting system gives the safety and better

efficiency. The bottom skirt supports are critical

components since they are to be designed with much

care to avoid failure due to internal pressure with

temperature. Vessel is mostly used in storage or

pressure vessel in industry.

In pressure vessel whenever expansion or contraction

would occur normally as result of heating or cooling

an object is prevented, thermal stresses are

developed. The stress is always caused by some form

of mechanical restraint. There are many types of

stresses are developed in the element but they are

categorized into primary stresses and secondary

stresses. Primary stresses are generally due to internal

or external pressure or produced by sustained

external force and moments these are not self

limiting. Thermal stresses are secondary stresses

because they are self limiting. That is yielding or

deformation of the part relaxes the stress (except

thermal stress ratcheting).Thermal stresses will not

cause failure by rupture in ductile materials except by

fatigue over repeated applications. In pressure vessel

mostly cracks are developed in skirt dished end joint.

(5)

Metallic pressure vessel components such as dished

ends show different modes of failure depending upon

the geometrical and loading conditions. These are

mainly gross plastic deformation under static load,

loss of stability (buckling), fatigue crack initiation at

highly stressed locations under cyclic loading,

progressive plastic deformation (ratcheting) and

creep at high temperatures. Existing codes are mostly

used to determine necessary wall thickness (design

by rule) based on the static load-carrying capacity.

He was also present that all the failure modes

mentioned can be estimated by carrying out linear

and non-linear finite elements analyses.

A dished end in the Klopper shape with a central

nozzle submitted to internal Pressure and

supplementary axial forces (tensile and compressive)

will be used in the frame work. This kind of dished

end is widely used as a component in pressure vessels

of chemical plants (e.g. reactors at high temperature).

It is normally not possible to use design by rule for

all possible failure modes because codes do not and

cannot consider any special case. In this case, general

guidelines for design by analysis are normally

available. It is the responsibility of the design

engineer to choose the appropriate means of strength

analysis (analytical, experimental or numerical

methods).Nowadays, it should be common practice to

apply numerical instruments of analysis such as the

finite elements method (FEM) because of steadily

improving computer technology and sophisticated

software (detailed modelling, non-linear features).

Computer-aided simulation of the strength behaviour

of structures is much more precise than the

application of analytical methods and cheaper than

experimental verification.

Figure 1 Meshing of a torispherical end with a

centred nozzle

The structure to be considered is symmetrical with

respect to the main axis of rotation and with respect

to applied loads. It is possible to use plane elements

with an axisymmetric option in the Finite Element

model of the dished end with a central nozzle (Fig. 1)

which will considerably save the time for modeling

and computation. For the fatigue analysis in

particular, the model must be detailed enough to



include local stress concentration effects (e.g. weld

seams). The finite elements program package

ANSYS5.0 was used to carry out the different

analyses.

As per result we include other modes of failure (loss

of stability, progressive plastic deformation, creep,

fatigue) caused by special geometrical and/or loading

conditions. By and large, these supplementary failure

modes are normally not treated on a design by rule

basis in codes; Guidelines given for design by

analysis are more or less general.The finite elements

method provides a universal instrument of analysis.

All the failure modes mentioned can be modelled

after reasonable simplification of the materials laws.

Results for design against gross plastic deformation

and against fatigue failure can be depicted in the form

of factors based on parametric studies using the

programming environment of the FE program. These

results can be used directly for design by rule. In

cases where ratcheting is possible, special non-linear

finite elements analyses should be carried out, these

analyses are still rather time-consuming. The

hardening behaviour of the material should be

modelled as precisely as possible because of its

significant influence on progressing plastic strains.

Creep is a very dangerous failure mode for metallic

structures at high temperatures. It is possible to

implement creep laws within finite elements

programs. The time-dependent behavior of the

component can be estimated in this way. (1) 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 head, which may be hemispherical,

ellipsoidal. The pressure vessels may be horizontal or

vertical. The supporting system of this vertical vessel

plays an important role in the performance of the

equipment. Proper supporting system gives better

efficiency. The bottom supports are critical

components since they are to be designed with much

care to avoid failure due to internal pressure with

temperature. In this analysis, skirt support for vertical

vessel was analyzed as per the guidelines given in the

ASME (American Society of Mechanical

Engineering) section VIII division 2 and IBR (Indian

Boiler Regulations) standards. The stress analysis

was carried out for this support using a general

purpose FEM code, ANSYS macros. The coupled

field (Structural and Thermal) Analysis was carried

out for skirt support to find out the stresses in the

support. The analysis’s results were compared with

ASME code allowable stress values. The pressure

vessel design codes all use the “design by formula”

approach, which is essentially now used in section

VIII, Division1 of the ASME Code. The design by

formula method provides explicit rules for

calculating the vessel parts. The skirt support is

supporting the vessel which is subjected to the

internal pressure of 0.68 kg / mm2 and the design

temperature is 3400C. The material used is carbon

steel, SA 516 GR 70. The localized stress effects due

to combined loads acting on structural attachment

such as skirt support are being analyzed using FEM.

The skirt support is shown in Figure 2.

Figure 2 Skirt support

As per result we obtained maximum and minimum

stress values are obtained. The stresses induced in the

supports are within the allowable limit. ANSYS

analysis confirms the safety of the support. The

analysis may prove to be the most economical in the

long term. (2)

A simple method of estimating limit loads using a

sequence of elastic finite element analyses and the

lower bound theorem, termed elastic compensation,

is demonstrated on the problem of the estimation of

the limit behavior of torispherical pressure vessel

heads. Two possible techniques of elastic

compensation are discussed, one which has general

application and one possibly specific to heads. The

results are compared to a series of detailed elastic-

plastic finite element analyses and to classical

solutions.

Figure 3 Torispherical head geometry

The general pattern of behavior of torispherical ends

under internal pressure is thus well understood. As

pressure builds up, it tends to force the spherical cap

outwards along the axis and the meridional

membrane tensions pull the toroidal knuckle inwards

towards the axis.

Figure 4 Torispherical head deformation

mechanism

In order to determine the elasto-plastic behavior and

limit pressure in representative torispherical heads,

four geometries are employed. The models are

analysed independently here using the finite element

analysis system ANSYS. The elasto plastic analysis

undertaken here includes large deformation effects.

(3)



2 DESIGN SPECIFICATIONS

2.1 CYLINDRICAL SHELL:

Input Values: Internal Design Pressure P 41.801 bar

Shell Diameter D 4030 mm

Shell Material SA-516 70

Shell Allowable Stress at Temperature S 1406.14

kgf/cm²

Shell Allowable Stress At Ambient S 1406.14

kgf/cm²

Shell Thickness t 67 mm

Joint Efficiency of shell E 1

Corrosion Allowance C.A. 3 mm

2.1.1) Required Thickness due to Internal

Pressure [tr]:

= �P× R�

�S× E�.�× P� per UG-27 (c) (1)

= 63.98 mm

2.1.2) Max. Allowable Working Pressure at given

Thickness, corroded [MAWP]:

= �S× E× ��

�R .�× �� per UG-27 (c) (1) = 45.84 bar

2.1.3) Maximum Allowable Pressure, New and

Cold [MAPNC]:

= �S× E× ��

�R .�× �� per UG-27 (c) (1)

= 47.85 bar

2.1.4) Actual stress at given pressure and

thickness, corroded [Sact]:

= �P× �R .�× ��

�E× ��

= 1282.23 kgf/cm²

2.2 HEMISPHERICAL DISHED END:

Input values: Internal Design Pressure P 41.801 bar

Dished end Diameter D 4036 mm

Bottom head allowable Stress at

Temperature S

1406.14

kgf/cm²

Dished end Thickness t 33 mm

Bottom dished end Material SA 516Gr 70

2.2.1 Required Thickness due to Internal Pressure

[tr]:

= �P× R�

��× S× E�.�× P� per UG-27 (d)

= 33.08 mm

2.2.2 Max. Allowable Working Pressure at given

Thickness, corroded [MAWP]:

= ��× S× E× ��

�R .�× �� per UG-27 (d)

= 45.84 bar

2.2.3) Maximum Allowable Pressure, New and

Cold [MAPNC]:

= ��× S× E× ��

�R .�× �� per UG-27 (d)

= 50.07 bar

2.2.4) Actual stress at given pressure and

thickness, corroded [Sact]:

= �P× �R .�× ��

��× E× ��

= 1282.28 kgf/cm²

2.3 SKIRT SUPPORT:

Input values Skirt Outside Diameter at Base O.D. 4088 mm

Skirt Thickness t 22 mm

Skirt Internal Corrosion Allowance CA 0 mm

Skirt External Corrosion Allowance CA 1 mm

Skirt Material SA-285 C

3. GEOMETRY AND FEM MODEL

Figure 5 Assembly of Skirt Dished end joint

4. BOUNDARY CONDITION

4.1 3-D Model in ANSYS

Figure 6 Model in ANSYS Workbench

4.2 Define Temperature

The temperature considering for steady state thermal

analysis is 250 °C.

Figure 7 Temperature inside the surface of model

4.3 Apply convective heat transfer co-efficient at

the inner side

Figure 8 Apply Convective Heat Transfer Co-

efficient

5 THERMAL ANALYSIS

The ANSYS Workbench environment is a Finite

Element Analysis tool that is used in conjunction

with CAD systems and/or Design Modeler. ANSYS

Workbench is a software environment for performing

structural, thermal and electromagnetic analysis. The

focuses on attaching existing geometry, setting up the

Finite Element model, solving and reviewing results.

� Define Type of Analysis : Thermo

Structural Analysis

� Method : Steady State Thermal Analysis

• When the flow of heat does not vary

with time, heat transfer is referred to as

steady-state condition.



• Since the flow of heat does not vary

with time, the temperature of the system

and the thermal loads on the system also

do not vary with time

• From the First Law of

Thermodynamics, the steady-state heat

balance can be expressed simply as:

Energy in - Energy out = 0

For steady-state heat transfer, the differential

equation expressing thermal equilibrium is:

The corresponding finite element equation expressing

equilibrium is

6 RESULT AND DISCUSSION

6.1 Run the Analysis

6.1.1 Temperature Results

Figure 9 Temperature Contour

6.1.2 Heat flux Results

Figure 10 Total Heat Flux

6.2 Structural Analysis

Above Analysis Data is transfer to Static Structural

Module for Structural Analysis.

Apply internal Pressure 0.1 Mpa inside the model.

6.2.1 Run the Structural Analysis

� Equivalent Von Misses Stresses and shear

stresses :

Figure 11 Equivalent Von Misses Stresses

Figure 12 Shear Stresses

6.2.2 Results Table Weld size Von Misses

stresses

Maximum Shear

stresses

45 121.04 66.909

7 CONCLUSION

The study shows that in pressure vessel different

types of cracks/failure are developed. After

investigating different methods it should be

concluded that skirt to dished end joint is part of

pressure vessel in which maximum cracks are

developed. The analyzing by different finite element

methods gives different parameters. After analyzing

the ‘maximum’ parameters are find out which gives

maximum strength for skirt to dished end joint.

The analysis for skirt to dished end joint of pressure

vessel by finite element method which can reduce the

stresses and crack/failure of skirt dished end joint.

After analysis the optimum parameters should be

considered which can minimize the stresses in these

joint. This can increase the life of pressure vessel and

reduce the cost of pressure vessel which is benefit for

applicant.

It should be concluded that stress and other

parameters are also decreased by changing the weld

size of the skirt to dished end joint.

ACKNOWLEDGEMENT

Authors are grateful to Hindustan Dorr-Oliver limited

(HDO), Ahmedabad for allowing them to carry out

the project work during the course of study.

REFERENCES [1] A.Lietzmann, J. Rudoiph, E. Weib , “Failure modes of

pressure vessel components and their consideration in analyses” , Chemical Engineering and Processing 35

(1996) 287-293.

[2] K.Tamil Mannan, Rakesh Saxena,R. Murugavel an P.L.Sah, “Stress Analysis of Conical Shell Skirt

Support For High Pressure Vessel Using Finite

Element Method”, Multidiscipline Modeling in Mat. and Str.5(2009)355-362

[3] Jinhua Shi,D.Mackenzie & J.T.Boyle, A Method of

Estimating Limit Loads by Iterative Elastic Analysis. Torisphericai Heads Under Internal Pressure , Int. J.

Pres. Ves. & Piping 53 (1993) 121-142.

[4] ASME Code, Section VIII, Division 1,2007 A-08. [5] Moss D.R.Pressure Vessel design manual Third edition.

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