DESIGN AND STRUCTURAL ANALYSIS OF LIQUIFIED CRYOGENIC TANK ...€¦ · allowable stress and to...

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International Journal of Mechanical Engineering and Technology (IJMET) Volume 7, Issue 6, November–December 2016, pp.345–366, Article ID: IJMET_07_06_034

Available online at

http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=7&IType=6

ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication

DESIGN AND STRUCTURAL ANALYSIS OF

LIQUIFIED CRYOGENIC TANK UNDER SEISMIC AND

OPERATING LOADING

K. Sunil Kumar

Assistant Professor, Mechanical Department, Vel Tech, Chennai, India

Dr. B. Nagalingeswara Raju

Professor, Mechanical Department, Vel Tech, Chennai, India

J. Arulmani


P. Amirthalingam


ABSTRACT

FEA analysis was performed to investigate the stresses in the structural attachments of

Cryogenics tank for argon liquid, based on EN-13458 .The areas in which the analysis was

performed is tested for operating load case, seismic loads and shipping load case. The areas of

interest in the model are inner shell and inner heads, outer shell and outer heads. Commercial FEA

software, ANSYS® Version 14 was used for the analysis. Elastic approach was adopted following

the Guidelines in EN-13458-2 Annex-A.

Key words: Liquified Cryogenic tank structural Analysis, Cryogenic tank seismic load Analysis,

Shipping load cases of Cryogenic tank, membrane stresses of cryogenic tank.

Cite this Article: K. Sunil Kumar, Dr. B. Nagalingeswara Raju, J. Arulmani and

P. Amirthalingam, Design and Structural Analysis of Liquified Cryogenic Tank under Seismic and

Operating Loading. International Journal of Mechanical Engineering and Technology, 7(6), 2016,

pp. 345–366.

http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=7&IType=6

1. INTRODUCTION

The cryogenic tank consists of an inner vessel containing cryogenic liquefied gases and an outer casing.

The liquid container is concentrically enclosed by the outer jacket. The space between the inner vessel and

the outer jacket is fully vacuumed for heat isolation. The whole tank is supported by a bottom skirt. [3] The

geometric parameters of the major components are shown in Table 1. Piping is not included in the model

since they are not the area of interest. However, the weight of the piping is taken into account for the

analysis in the model.

K. Sunil Kumar, Dr. B. Nagalingeswara Raju, J. Arulmani and P. Amirthalingam


2. OBJECTIVES

To determine the shell membrane stress at general locations and to determine the shell bending stress at

discontinuous and local area [2].By comparing the theoretical values obtained from the FEA results with

allowable stress and to calculate the stress linearization for seismic and operating loads and compare the

values obtained from seisimic and operating load cases with theoretical values [9].The areas of interest in

the model are inner shell and inner heads, outer shell and outer heads[12]. To determine the minimum

thickness for the inner top head, the outer head, necktube and trunion design to be adequate for the

investigated load cases [8].

3. GEOMETRIC MODEL

Figure 1 Geometry of the tank

Table 1 Specifications of the MB model

Component Dimensions

Outer shell

1300mm OD , 1900mm height ,5

mm thickness

Outer shell heads

DIN 28013,1300 OD ,

knuckle radius: 136mm; crown

radius: 1306 mm ,

SF 30mm, 6 mm thickness

Inner shell(liquid container shell)

1150mm OD ,1500 mm height ,8

mm thickness

Inner shell heads

2:1 elliptical,1150 mm OD, 8.2mm

thickness, SF 30mm

Design and Structural Analysis of Liquified Cryogenic Tank under Seismic and Operating Loading


4. BY ANALYTICAL APPROACH

Linear elastic approach is used for the stress analysis for different load conditions. The allowable stress

criteria are: At general locations, the shell membrane stress is classified as general primary (fm) membrane

stress [6]. At discontinuities and local area, the shell membrane stress is classified as local primary (fL)

membrane stress. The shell bending stress is a secondary (fg) stress at discontinuities. Local area is defined

as within 0.5 (Rt) ^0.5 from the discontinuity [15]. The allowable stresses criteria are: General primary

membrane stress in shell, fm ≤2K/3. Primary local membrane stress in shell, fL ≤ 1.1*2K/3. Primary

membrane plus bending stress, fL+ fb ≤ 1.5*K. Primary membrane plus secondary stress, fm +fb + fg ≤ 3K

and fL + fb+ fg ≤ 3K. The material for the entire tank is specified as 1.4301. K = 410MPa.

5. MATERIALS

The materials and material properties for inner vessel, outer tank, nozzle, trunion top and bottom, neck

tube and skirt are listed below in Table 2

Table 2 Material properties

6. MESHING

Figure 2 Mesh on the total assembly

Component Material

Specificati

on

Poison

s ratio

Density

(Kg/m3)

Elastic

modulus

(GPa)

Yield

Strength

(MPa)

Outer shell 1.4301 0.3 8000 200 250

Outer shell heads 1.4301 0.3 8000 200 250

Inner shell(liquid

container shell)

1.4301 0.3 8000 200 410

Inner shell heads 1.4301 0.3 8000 200 410

Trunion top 1.4301 0.3 8000 200 250

Trunion bottom 1.4301 0.3 8000 200 250

Neck tube 1.4301 0.3 8000 200 250

Nozzle 1.4301 0.3 8000 200 250



Shell model is created for the inner and outer shell. Quadrilateral elements are used for the tank with

shell geometry. Solid models were created for neck tube, nozzle, trunion top and trunion bottom. Mesh was

refined at critical areas. The total number of elements in the model was 101064 and total number of nodes

was 167180.

Figure 3 Mesh on the neck tube and nozzle assembly

Figure 4 SCL Lines

SCL1: primary stress in shell, fm, at mid plane. Primary plus secondary stress, f m +fb+ fg , at surface.

SCL2: primary stress in shell, fL , at mid plane. Primary + secondary stress, f m +fb+ fg , at surface.

SCL3: primary stress in necktube fL ,at mid plane. Primary + secondary stress, f m +fb+ fg , at surface.

SCL4: primary stress in necktube fm , at mid plane. Primary +secondary stress, f m +fb+ fg , at surface



Table 3 Allowable stress values for operating condition

fm

(MPa)

fL

(MPa)

fL+fb

(MPa)

fL+fb+fg

(MPa)

Inner casing 273 300.33 410 819

outer

casing/necktu

be

166.7 183.37 250 500

The allowable stresses criteria for the seismic load case we will consider 20% more than normal

allowable stresses

Table 4 Allowable stress values for seismic and shipping

fm

(MPa)

fL

(MPa)

fL+fb

(MPa)

fL+fb+fg

(MPa)

Inner casing 327.6 360.36 492 819

outer

casing/neckt

ube

200.04 220.044 300 500

7. LOADING AND BOUNDARY CONDITIONS

The basic design loads include:

V: Vacuum pressure on outer casing --- 0.1 MPa.

P: Operating pressure on the inner container --- 3.7 MPa

F: Load due to liquid, based on vessel maximum height and the density of Argon and for Maximum weight

(Hydrostatic pressure) --- 0.029412 MPa

D: Weight, including the vessel, piping, and attachment weight

E: Seismic load - E (Eh): Seismic Load, UBC-97 zone 3 only in horizontal direction.

7.1. Operating Load Case

Table 5 Load values for operating case

Load Condition Value Applied on

V 0.1 MPa Outer shell

P 3.8 MPa Inner vessel

F 0.029412 MPa Inner vessel

D1 1277 Kg Full model

R 27909 N Nozzle top flange

The above loads from table 5 were applied and then the bottom edge of the skirt was simply supported

as the constraint for the analysis. Static analysis was performed for the model to check the structural

integrity of the inner casing, outer casing, neck tube and trunion [19]



Figure 5 Load pattern for load case 1

7.2. Seismic Load Condition

Table 6 Load values for seismic load cases



P 3.8 MPa Inner vessel

F 0.029412 MPa Inner vessel

R 27909 N Nozzle top flange

Seismic load for argon Lateral Load

Inner tank 9796.127 N

Outer tank 1889.928 N

The seismic load case was applied for only the top half of the inner and outer shell as per APCI

specifications 4WEQ-1005[8]. Only lateral seismic load was applied, vertical seismic load was not applied.

The seismic load case data is shown in table 6.



Figure 6 Seismic load case

7.3. Shipping Condition

7.3.1. Case I: 2D transverse + 1D down + (Internal Pressure of 20 psig) + Vacuum

Table 7 Shipping load case I

Load condition Value Applied on

V 0.1 mpa Outer shell

P 0.23925 mpa Inner vessel

R 1040.137 n Nozzle top flange

Shipping 2g Lateral

1g Vertical



Figure 7 Shipping load case I

7.3.2. Case II: 2D longitudinal + (Internal Pressure of 20 psig) + Vacuum

Table 8 Shipping load values for case II



P 0.23925MPa Inner vessel

R 1040.137 N Nozzle top flange

Shipping 2g Vertical

Figure 8 Shipping load case II



8. RESULTS OBTAINED

8.1. Operating Load Case

In the below fig 9, the maximum membrane stress 373.48 MPa and membrane + bending stress 762.66

MPa are at the area connecting the neck tube and inner top head. We can ignore these stresses due to the

stress singularities in the model and stresses due to contacts. The areas of interest in the model are inner

shell and inner heads, outer shell and outer heads.

Figure 9 Stresses on the tank in operating condition

Below in figure 10, the probed membrane stress values in the inner top head and outer top head are

shown.

Figure 10 Probed membrane stress in the tank

Below in fig 11, the probed membrane + bending stress values in the inner top head and outer top head

are shown. The reason for the membrane and membrane +bending stress stresses in the inner shell are

covered in the code calculations.



Figure 11 Probed membrane+bending stress

Below in the figure 12, the stresses on the trunion top and trunion bottom are shown. The maximum

stresses are near the area connecting the inner bottom head to trunion top, some probed stresses are shown

below the stresses which are below the allowable stresses for the general membrane stress, 250MPa. No

stress linearization is required.

Figure 12 Stresses on the trunion top and trunion bottom

Below in the fig 13, the stresses on the necktube are shown. The maximum stress is 304.27 MPa which

is near the area connecting the inner top head to necktube. The maximum stress is ignored as it includes

stress from singularity and contacts. So the stress linearization line, SCL 3 taken is one element above the

element in contact.



Figure 13 Stress in the necktube

Below in fig 14, the stress results has been shown on the necktube, the maximum membrane stress is

171.26 MPa , which is lower than the allowable stress 250 MPa. The maximum membrane +bending stress

are 253.25 MPa, which is lower than the allowable stress of 500 MPa.

Figure 14 Linearized stress in the necktube

The distance of 0.5 *(RT) ^.5 is above where the tapered area starts (SCL 4). From the probed stress

values shown in the figure 15, above the transition area, the stress on the both inside and outside are

around 125 MPa and 86 MPa respectively which is lower than allowable for general primary membrane

stress, 167 MPa. So no is performed.



Figure 15 Stress on the SCL 4

In fig 16, the stresses on the SCL lines on outer top head are shown under operating condition. The

comparisons with the allowable stresses are shown in table 10.

Figure 16 Stresses near SCL lines on the outer top head

Table 9 Stress comparison on outer casing top head

scl lines membrane stress

(mpa)/allowable stress

membrane + bending

(mpa)/ allowable

stress

1 50.858/183.37 64.865/250

2 58.815/250 189.83/500

In fig 17, the stresses on the SCL lines on inner top head are shown under operating condition. The




Figure 17 Stresses on the SCL lines

Table 10 Stress comparison with allowable stress values

SCL lines Membrane Stress

(MPa)/Allowable Stress

Membrane + bending

(MPa)/ Allowable Stress

1 317.93/300.33 387.33/410

2 364.68/410 641.24 /819

From the above table 10, we can notice that the stresses on the SCL lines are lower than the allowable

stresses. From table 9, the outer head thickness of 6mm is sufficient. The inner shell head thickness of 8.2

mm is not sufficient for operating load condition, so the inner head thickness was changed to 8.7 mm and

the analysis results are shown in 3.1.4.

8.2. Seismic Load Case

In the below figure 18, the maximum membrane stress 380.78 MPa and membrane + bending stress 805.35



shell and inner heads, outer shell and outer heads.



Figure 18 Stresses on the tank in seismic condition

In figure 19 and 20, probed membrane stress and probed membrane +bending stress are shown below:

Figure 19 Probed membrane + bending stress under seismic loads

Figure 20 Probed membrane stress under seismic loads

Below in the figure 21, the stresses on the trunion top and trunion bottom are shown. The maximum

stresses are near the area connecting the inner bottom head to trunion top, some probed stresses are shown

below the stresses which are below the allowable stresses for the general membrane stress, 250MPa. No

stress linearization is required.



Figure 21 Probed stresses on trunion top and trunion bottom for seismic load case

Below in the fig 22, the stresses on the necktube are shown. The maximum stresses are near the area

connecting the inner top head to necktube, some probed stresses are shown, the stresses are below the

allowable stresses

Figure 22 Stress on the necktube under seismic load case

Below in fig 23, the stress results has been shown on the necktube, the maximum membrane stress is

178.42 MPa , which is lower than the allowable stress 300 MPa. The maximum membrane +bending stress

are 263.24 MPa, which is lower than the allowable stress of 500 MPa.

Figure 23 Linearised stress on the necktube under seismic load case



The distance of 0.5 *(RT) ^.5 is above where the tapered area starts (SCL 4). From the probed stress

values shown in the figure 24, above the transition area, the stress on the both inside and outside are

around 116 MPa and 70 MPa respectively which is lower than allowable for general primary membrane

stress, 200.4 MPa. So no is performed

Figure 24 Stress on SCL 4

In fig 25, the stresses on the SCL lines on outer top head are shown under seismic condition. The


Figure 25 Stresses on the SCL lines on outer top head for seismic load case

Table 11 Stress comparison under seismic load Case

Line Membrane

stress/allowable

( mpa)

Membrane+ bending

stress/ allowable (

mpa)

1 43.522/220.044 76.315/300

2 70.669/300 220.48/500

In fig 26, the stresses on the SCL lines on inner top head are shown under seismic condition. The




Figure 26 Stresses on the SCL on inner top headlines for seismic load case

Table 12 Maximum stress summary in the outer tank under the seismic load cases

Line Membrane

stress/allowable

( mpa)

Membrane+

bending stress/

allowable ( mpa)

1 313.85/360.36 387.97/492

2 370.4/492 670.67/819

From table 11 and 12, the membrane stress and membrane + bending stress are lower than the

allowable stress values, So the inner head thickness of 8.2 mm and outer head thickness of 6 mm is

sufficient for seismic load case.

8.3. Shipping Condition Case

8.3.1 Case I: 2D transverse + 1D down + (Internal Pressure of 20 psig) + Vacuum:


MPa are at the area connecting the neck tube and inner top head. These values are lower than the allowable

stress values.

Figure 27 Stresses on the tank in shipping condition case I

Below in fig 28, stresses on the trunion top and trunion bottom are shown. The maximum stress 108.7

MPa is on the edge of the trunion top .these stress is lower than the allowable general membrane stress of

300 MPa. No stress is evaluated.



Figure 28 Stresses on the SCL lines on outer top head for shipping load case I

Table 13 Stress comparison for shipping condition case I

SCL Line Membrane

stress/Allowable

(MPa)

Membrane+

Bending stress/

Allowable (MPa)

1 7.292/220.044 39.197/300

2 36.182/300 76.772/500

In fig 29, the stresses on the SCL lines on inner top head are shown under shipping condition. The


Figure 29 Stresses on the SCL lines on outer top head for shipping load case I

Table 14 Stress comparison on SCL lines with allowable

SCL Line Membrane

stress/Allowable(MPa)

Membrane+

Bending stress/

Allowable (MPa)

1 16 /360.36 45.806/492

2 40.557/492 85.298/819

8.3.2:Case II: 2g longitudinal + 1D down + (Internal Pressure of 20 psig) + Vacuum:



In the below fig 30, the maximum membrane stress 44.049 MPa and membrane + bending stress

102.36 MPa are at the area connecting the neck tube and inner top head. These values are lower than the

allowable stress values

Figure 30 Stresses on the tank in shipping condition case II

Figure 31 Probed membrane + bending stress on the tank under shipping condition case II

Table 15 Stress comparison on outer casing top head

Scl line Membrane

stress/allowable

( mpa)

Membrane+ bending

stress/ allowable (

mpa)

1 24.014/220.044 34.736300

2 26.123/300 82.618/500



Figure 32 Stresses on the SCL on inner top headlines for shipping load case II

In fig 32, the stresses on the SCL lines on inner top head are shown under shipping condition. The


Table 16 Maximum stress summary in the outer tank under the shipping load cases

Scl line Membrane

stress/allowable

( mpa)

Membrane+

bending stress/

allowable ( mpa)

1 26.9/360.36 34.689/492

2 31.011/492 80.348/819

From table 13, 14, 15 and 16, the membrane stress and membrane + bending stress are lower than the

allowable stress values for shipping load case I and II. So the inner head thickness of 8.2 mm is sufficient

for shipping load case.

8.4. Operating Load Case for 8.7 mm Thick




shell and inner heads, outer shell and outer heads

Figure 33 Stresses on the inner tank for operating condition with 8.7 head thick



Figure 34 Probed stresses on SCL lines

In fig 34, the stresses on the SCL lines on inner top head are shown under operating condition. The


Table 17 Stress comparison on SCL lines

Scl lines Membrane stress

(mpa)/allowable stress

Membrane +

bending (mpa)/

allowable stress

1 298.18/300.33 363.19/410

2 345.21/410 590.42/819

From the above table 17, all the stresses are lower than the allowable stress values. Therefore the

minimum thickness of 8.7 mm is recommended for the inner head.

9. CONCLUSION

Based on the FEA results, the original inner top head design thickness of 8.2 mm is not adequate for the

operating condition. Minimum thickness of 8.7 mm is recommended for the inner top head, the outer head,

necktube and trunion design are adequate for the investigated load case. From table 13, 14, 15 and 16, the

membrane stress and membrane + bending stress are lower than the allowable stress values for shipping

load case I and II. So the inner head thickness of 8.2 mm is sufficient for shipping load case.

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