Project of Pressure Vessel

Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1

PRESSUR VESSEL DESIGN 1.1 INTRODUCTION Engineering plastic has been used for pressure vessel application for a long time. Pressure is closed containers designed to hold gases or liquids material under internal and external pressure. Pressure vessels are designed to operate safely at a specific pressure and temperature technically referred to as the design pressure and temperature. Pressure vessels may theoretically be almost any shapes made of section spheres and cones are usually employed. A common design is a cylindrical with hemispherical ends caps or heads. When the vessels walls is thin, the stresses distribution throughout its thickness will not vary significantly and so we will assume that it’s uniform or constant. The design rule in the codes and limited to vessels of cylindrical or spherical and ellipsoidal shapes under internal or external pressure and to head and nozzles attachment for such vessels rules for more complicated types of construction and for loading other than that due to pressure are beyond the scope of the codes to include such rule would turn the code in to design hand book and it would restrict the designer in working out his design in accordance with acceptable engineering principles. The code receives that the shell provided details of construction that will be as safe as those provided by the rules of the code. Some problem of designers of ellipsoidal pressure vessels that have their axis vertical and subjected to applied forces in addition to internal and external pressure the vertical forces considered are the weight of any attachments to vessels. Finally, pressure vessel are refers to those reservoirs and apparatus which work under internal and external pressure and operate under the pressure.

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1

1.2 Classification of pressure vessels Pressure vessels can be classified in different categories as follows:1.2.1. According to the dimension The pressure vessels according to their dimensions may be classified as thin shell or thick shell the ratio of equal thickness (t) of the shell to its diameters (D) deciding factor.

t D a) Thin shell: - if the ratio of

1 10 is less than

is called a thin shells.

t D

1 10

b) Thick shell:- if the ratio of is equal or greater than is called thick shell used in high pressure cylinders, gun, barrels and other equipments where as thin shell are used in boiler, tanks and pipes. 1.2.2. According to the end construction This can be classified in to two groups:a) Open end construction pressure vessels b) Closed end construction pressure vessels 1.2.3. According to the geometrical shapes a) Cylindrical geometrical shapes b) Conical and c) Spherical vessel with one or two cones. 1.2.4. According to the position arrangement a) Horizontal pressure vessel b) Vertical pressure vessel c) Spherical pressure vessel 1.2.5. According to the materials The pressure vessels are according the material classified as:a) Brittle material pressures vessels b) Ductile material pressure vessels 1.2.6. According to the direction of force acting on the wall of vessels.

 pi 

a) Subjected to internal pressure

 p

b) Subjected to external pressure

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1

1.3 component of pressure vessels There are four components of pressure vessels this are:A. B. C. D.

head shell nozzle and support

A. HEAD All pressure vessel shells must be closed at the ends by heads (or another shell section). Heads are typically curved rather than flat. 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. Head are usually categorized by their shapes. Ellipsoidal, hemispherical, torispherical, conical, toriconical and flat are the common types of heads. B. SHELL The shell is the primary component that contains the pressure. Pressure vessel shells are welded together to form a structure that has a common rotational axis. Most pressure vessel shells are cylindrical, spherical, or conical in shape. Horizontal drums have cylindrical shells and are fabricated in a wide range of diameters and lengths. C. NOZZLE A nozzle is a cylindrical component that penetrates the shell or heads of a pressure Vessel. The nozzle ends are usually flanged to allow for the necessary connections and to permit easy disassembly for maintenance or access. Nozzles are used for the following applications: Attach piping for flow into or out of the vessel.  Attach instrument connections, (e.g., level gauges, thermo wells, or pressure gauges).  Provide access to the vessel interior at man ways.  Provide for direct attachment of other equipment items, (e.g., a heat exchanger or mixer) D. SUPPORT The type of support that is used depends primarily on the size and orientation of the pressure vessel. In all cases, the pressure vessel support must be adequate for the applied weight, wind, and earthquake loads [3]. Calculated base loads are used to design of anchorage and foundation for the pressure vessels. Typical kinds of supports are as follow:i. 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). Skirts for spherical vessels are welded to the vessel near the mid-plane of the shell. The skirt is normally long enough to provide enough flexibility

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1 so that radial thermal expansion of the shell does not cause high thermal stresses at its junction with the skirt ii. Leg support Small vertical drums are typically supported on legs that are welded to the lower portion of the shell. The maximum ratio of support leg length to drum diameter is typically 2:1. The number of legs needed depends on the drum size and the loads to be carried. Support legs are also typically used for spherical pressurized storage vessels. The support legs for small vertical drums and spherical pressurized Storage vessels may be made from structural steel columns or pipe sections, whichever provides a more efficient design. iii. Saddle support Horizontal drums are typically supported at two locations by saddle supports. A saddle Support spreads the weight load over a large area of the shell to prevent an excessive local stress in the shell at the support points. The width of the saddle, among other design details, is determined by the specific size and design conditions of the pressure vessel. One saddle support is normally fixed or anchored to its foundation. iv. Lug support Lugs that are welded to the pressure vessel shell, which are shown on, may also be used to support vertical pressure vessels. The use of lugs is typically limited to vessels of small to medium diameter (1 to 10 ft.) and moderate height-to-diameter ratios in the range of 2:1 to 5:1. Lug supports are often used for vessels of this size that are located above grade within structural steel. The lugs are typically bolted to horizontal structural members to provide stability against overturning loads; however, the bolt holes are often slotted to permit free radial thermal expansion of the drum.

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1

1.4. Objective of the design 1.4.1. Main objective The main objective of my project is to design a vertical pressure vessels position with ellipsoidal head by estimating the internal pressure and temperature on its effect and having a material of

15 low alloy steel and use medium of ammonia at the temperature of

45Mpa and pressure

.

1.4.2. Specific objective Specifically, I would like to design support, head, shell and nozzle and its has its own procedures to design each component and to design the hole assembled of pressure vessels.

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1

2. General Design procedures Design pressure A vessel must be designed to withstand the maximum pressure to which it is likely to be Subjected in operation. For vessels under internal pressure, the design pressure is normally taken as the pressure At which the relief device is set. This will normally be 5 to 10 per cent above the normal Working pressure, to avoid spurious operation during minor process upsets. When deciding The design pressure.

pD  po  po 

pD 45  45 

10 100

1 10



 49.5

2

N/mm

Design temperature The strength of metals decreases with increasing temperature so the maximum allowable design stress will depend on the material temperature. The design temperature at which the design stress is evaluated should be taken as the maximum working temperature of the material, with due allowance for any uncertainty involved in predicting vessel wall temperatures.

T 0  15O C Then From typical design stress table find the stress for low alloy steel:-

 D  240

Design stress: Tensile strength: -

2

N/mm

 t  550

2

N/mm

2.1. Design of shell

For cylindrical shell thickness required to resist internal pressure can be determined from the formula. Now assume outer diameter of the shell is our pressure is safe.

1M

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. Then check for which option that

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1



3

pD  0.385 SE.........................use t  Ro  

pD 0.385SE.........................use t 

z 1  ..........................(1) z 

pD R ..........................( 2) SE  0.4 pD

If Where S = allowable stress (Design stress) E = joint factor

49.5 N / mm2  0.385  240 N / mm2

 2

 49.5 N / mm2  92.4 N / mm2 Since

then, use equation

t

pD R SE  0.4 PD

49.5 N / mm2  500mm t 240 N / mm2  0.4 49.5 N / mm2 24750 t mm 259.8  t  95.26mm  95mm





2mm For carbon and low alloy steel corrosion allowance is

should be used

Therefore,

t  95mm  2mm  97mm 2). To calculate the length of the shell

L  K. for P  3.43MPa D where k  cons...... 4  K  6

K 4 But for economic purpose select

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1

L  4D  4  1000mm  L  4000mm Then,

L

Fig 2.1.1 cylindrical shell

3). To calculate the volume of the shell

V 



2

2



 Do  Di  L 4



but Di  Do  2t



 1000  2(97)  Di  806mm

  1000    806   4 4  V  1.10014m 3 V 

2

2

2.2. Design of Head All pressure vessel shell must be closed at the end by heads. The ends of cylindrical vessel are closed by head various shapes. This are: Flat plates head  Hemispherical head  Ellipsoidal head etc But my design head is ellipsoidal head.

2 :1 Most standard ellipsoidal are manufactured with a major and minor axis ratio of following equation can be calculated required thickness.

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the

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1 1) To calculate thickness

t

PD R SE  0.9 PD

49.5 N / mm2  500mm 240 N / mm2  0.9(49.5 N / mm2 )  t  86.97mm  87 mm t

h

h D

Do 4

Where

Fig 2.2.1. Ellipsoidal head 2) To calculate ellipsoidal head volume 2

 DO  h Vh  6  (1m) 2  0.25m  6 Vh  0.131m3 Calculate the stress on the shell using lame’s equation  Tangential stress: - is the maximum tensile stress and it is known as circumferential stress.  Radial stress: - is the maximum compressive stress and it is negative. The negative sign indicates that the radial stress is opposite to design stress equal. Since, if the stress is less than the maximum tensile strength of the material, then the design is safe. Now to calculate the value of stress. a) Tangential stress

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1

t 

PD Ri  R  1  O2 2 2  RO  Ri  Ri

  t

2



2

  

49.5 N / mm  (403mm) 2  (500mm) 2    1  (500mm) 2  (403mm) 2  (403mm) 2  2

 233.06 N / mm2 .........Tensile

b) Radial stress

r 

PD Ri  R  1  O2 2 2  RO  Ri  Ri



2



2

  

49.5 N / mm2  (403mm) 2  (500mm) 2    1  (500mm) 2  (403mm) 2  (403mm) 2 

 r

 49.5 N / mm2 .............compressiv e

c) Longitudinal stress 2

PD  L  2D i 2 DO  Di 

49.5 N / mm2  (806mm) 2 1000mm 2   806mm 2

  L  91.78 N / mm2

2.3. Design of Nozzle

The formula that I am going to calculate is the same as thickness formula to calculate for

At Di  300mm shell, the only difference is the diameter we use.

t

E 1

PD  Ri SE  0.4 PD

49.5 N / mm2  150mm 240 MPa  1  0.4 49.5 N / mm2   28.58mm



Length of nozzle

L  k where k  4  k  6  L  4  300mm D  L  1. 2 M

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1

D0  2t  Di  57.16mm  300mm  357.16mm Here no need of volume b/c its function is to as way of a fluid.

The stress developed on nozzle.

p  d 49.5 N / mm 2  300mm c    259.8 N / mm 2 2t 2  28.58mm

 c   t  259.8Mpa  550 MPa Then the design is safe.

2.4 .Design of support 2.4.1.

Total weight of the pressure vessel (dead weight)

The major sources of dead weight loads are: 1. The vessel shell. 2. The vessel fittings: man ways, nozzles. 3. Internal fittings: plates (plus the fluid on the plates); heating and cooling coils. 4. External fittings: ladders, platforms, piping. 5. Auxiliary equipment which is not self-supported; condensers, agitators. 6. Insulation. 7. The weight of liquid to fill the vessel. For preliminary calculations the approximate weight of a cylindrical vessel with domed ends, and uniform wall thickness, can be estimated from the following equation of steel vessels:

WS  240CV Dm  HV  0.8 Dm  t..............................................(2.3.1)

WS  Where

total weight of the shell, excluding internal fittings, such as plates, N,

CV 

A factor to account for the weight of nozzles, man ways, internal supports, Etc; which can be taken as

1.08

1.15 HV 

t

For vessels with only a few internal fittings, For distillation columns, or similar vessels, with several man ways,

Height, or length, between tangent lines (the length of the cylindrical section) Wali

l thickness, mm

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1

Dm  Mean diameter of vessel  Di  t  103 m





Dm  0.806m  0.097 m  0.903m WS  240  1.15  0.903m 4m  0.8  0.903m  0.097m Thus



WS  114.165 N

To find the weight of fluid which score the maximum weight?   604kg / m 3 The density of ammonia from the table we see WF  m f g

 vf  f g vf  Where

the volume of fluid in the vessel f  The maximum density of ammonia

WF    f  604kg / m

Weight of fluid

3

WF  1.23114m 3  604kg / m 3  9.81m / s 2  WF  7294.82 N

Thus, To find the total weight of the system will be

W  WS  W F  114.165 N  7294.82 N

W  7408.98 N I choose round bar as support that is skirt support is preferable to vertical position. The three

120o c skirt support is welded at

the cylindrical part of the shell.

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1

Wtotal 3 Therefore weight each support carries

Weach  P 

of load.

7408.98 N Wtotal P  2469.66 N 3 3

Let The material selection for skirt support is stainless. The length of weld part (x) is subject to pure shear and the bar weld at two part

p  2  0.707  S   allo  x

Where S  weld thickness

 allo  allowable shear stress p  weight of each load

 allo 

y 3n

n  factor of safty n  3.2

Where

 y  t Take

 t  540 Mpa in the standard table

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1

 allo 

y 3 n

540 Mpa 3  3 .2  97.43Mpa



S 10mm Take

p  2  0.707  S   allo  x x x

2469.66 N 2  0.707  10mm  97.43Mpa  17.93mm

Adding in 10.2mm starting and stopping welding

x  10.2mm  17.93mm  x  28mm

Then find the diameter of support The diameter of a support is determined by buckling consideration

 2 EI Pe  N2

Where pe  bulcking load  eulerian load  E  elastic mod ules of stainless steel N  length from the ground I  2 nd moment of inertia

Pe  n  p  3.2  2469.66 N  7902.91N Take N= 2m

I

pe  N 2  2 E

 D4 I 64 But

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1

Pe  N 2 64 D  2   E  4

Then diameter of support is.

7902.91N   2m  64  2 2  3.14  210000 N / mm 3.14  D  42.65mm 2



2.5. Design of bolts Use the following formula important to find the size and number of bolt. Let D = internal diameter of cylinder P = pressure in the cylinder dc = core diameter of the bolt

 tb  Permissible tensile stress of the bolt n = number of bolt Here we know that the upward face acting on the cylinder cover is:

F

 D   .........................................1 4

This force is resisted by n number of bolt and the resisting force offered by n number of bolts is

FR 

 2 dc   tb  n.................................. 2  4

From equation (1) the upward force acting on cylinder cover is

F

  806 2  49.5  F  25243230.87 N 4

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1

From equation (2) the resisting force by the bolt

FR 

  dc 2   tb  n 4

 tb  550 N / mm2 Here select the material for the bolt low alloy steel. So,

and the core

M 60 diameter is from the table by taking standard Designation

pitch mm

size.

nominal

pitch

core diameter

Diameter nut $

diameter bolt

nut

depth of stress bolt mm area

mm2 Bolt (d=D) mm

M 60

5 .5

60

mm

56.428

mm

mm

53.177 54.046

3.374

2360

dc  53.177 mm From the table

  53.177 2  550  n 4 FR  1220899.77  n Since F  FR FR 

n 

F 25243230.87   20.67  21 bolts 1220899.77 1220899.77 2.6. Design of nut

If the bolt and nut are made up of similar material then the effective height of the nut made equal to the nominal diameter of the bolt. Since the bolt diameter is 60mm. so the effective height of the nut is also 60mm.

2.7. Flange design Standard flanges will be specified for most applications. Special designs would be used only if no suitable standard flange were available; or for large flanges, such as the body flanges of vessels, where it may be cheaper to size a flange specifically for the duty required rather than to accept the nearest standard flange, which of necessity would be over-sized.

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1

Standard flanges are available in a range of types, sizes and materials; and are used extensively for pipes, nozzles and other attachments to pressure vessels.

Nom. size

100

pipe o.d. d1

Flange D

b

114.3

210

16

Raised face

Drilling

Boss

h

d4

f

d2

k

d3

40

148

3

18

170

130

Figure 2.5.1. Typical standard flange design (All dimensions mm).

2.8. Design of Gaskets Gaskets are used to make a leak-tight joint between two surfaces. It is impractical to machine flanges to the degree of surface finish that would be required to make a satisfactory seal under pressure without a gasket. Gaskets are made from “semi-plastic” materials; which will deform and flow under load to fill the surface irregularities between the flange faces, The following factors must be considered when selecting a gasket material: 1. The process conditions: pressure, temperature, corrosive nature of the process fluid. 2. Whether repeated assembly and disassembly of the joint is required. 3. The types of flange and flange face.

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1

Based all the above mentioned factors considering the operating temperature and corrosiveness of the process fluid will be the controlling factor in gasket selection. Vegetable 100 o c. fibre and synthetic rubber gaskets can be used at temperatures of up to

Summary This course provided an overview of pressure vessel mechanical design requirements. It summarized the main components of pressure vessels. Materials of construction, design requirements and considerations, fabrication, inspection and testing. Participants now have a good overall understanding of pressure vessel mechanical design requirements, are prepared to use this knowledge in their jobs, and have sufficient prerequisite information to take more detailed pressure vessel courses.

Acknowledgements First of all I would like to thanks for my Advisor Ato Abdul hakim Shukutea for that he has given me all the information and the procedure, all the data and for he has given the reference books. Secondly I would like to thanks my dormitory for giving me the chance to talk with 5th them about my design and I would thanks for year Mechanical engineering student wondem to give the information. And, finally thanks for all being with me.

REFERENCE BOOKS  R.K. Sinnot, Coulson & Richardson’s, Chemical Engineering, volume 6, Third Edition.

 Paul Buthod and Tulsa, Oklahoma, pressure vessel handbook, Tenth Edition.  Dennis R. Moss, Pressure Vessel Design Manual, Third Edition.

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1

 Mr. G. Ghanbari, Mr. Mohammad Raza Lazadi and M. Serai. Pressure Vessel Design Guides & Procedures.

Table content CHAPTER- I 1.1 1.2 1.3 1.4

Introduction of pressure vessel………………………………(1) Classification of pressure vessel……………………………….(2) Component of pressure vessel…………………………………..(3) Objective of the design……………………………………………….(5)

CHAPTER-II DESIGN PROCEDURE

2.1

Design of cylindrical shell

.......................................... 6 

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1

2.2

Design of ellipsoidal head

2.3

Design of nozzle

2.4

Design of support

2.5

Design of bolt

2.6

Design of nut

2.7

Design of flange

2.8

Design of gasket

2.9

Summery

.............................................. 8

......................................................................10  ..................................................................11

.........................................................................13

........................................................................15 ......................................................................15 ......................................................................16 

....................................................................................16 

ACKNOWLEDGEMENTS REFERENCE

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1

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Dep’t of Mechanical and Marine Engineering, B/ Dar University, Machine Design project. 1

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