1. What is design ?

The act of working out the form of some thing (as by marking a
sketch or out line or plan )

2. What is design interpretation?

Design interpretation means to interpret or under stand the
drawing.

3. Introduction to pressure vessel

Several types of equipment, which are used in the chemical,
petrochemical fertilizer industries are described bellow.

 Pressure vessel
 Storages vessel
 Distillation column i
 Heat exchanger
 Evaporator
 Reactor, etc.

In all this equipment pressure vessel is a basic and generally used in all
above types of industries.
Pressure vessel are usually spherical or cylindrical with domed ends. They
are provide with openings or nozzles with facilities for marking threaded
or flanged joints. Various methods are used for supporting the vessel.

4. Definition of vessel
A container or structural envelope in which material are processed, or
stored.

5. Definition of pressure vessel

A container or structural envelope in which material are processed,
treated, or stored which has been designed to operate at pressure above
15 Psi are knows as pressure vessel.
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6. Which codes used make design of pressure vessel?

Various code reference which is used for design and construction of
pressure vessel are as below.
 ASME sec viii div-1
 IS 2825
 BIS 5500

7. Why designing is required for pressure vessel?

The selection of the types of vessel based primarily upon the fictional
service of the vessel. The functional service requirements impose
certain operating conditions such as temperature, pressure, dimensional
limitation and various loads.
If the vessel is not designed properly the vessel may be fail in service.
The design of most structure is based on formulas. Formula may be used
form any relative code/standards so the value derived form that formula
is reliable.

8. Why necessary design of pressure vessel?

If vessel is not designed properly’ the vessel may be fail in service.
Failure may be occur in one or more manners such by the plastic
deformation resulting form excessive stress, or by elastic instability.

9. What parameter affect the failure of vessel?

Failure may also result form corrosion, wear or fatigue. Design of the
vessel to protect against such as failures involve the consideration of
these factors and the physical properties of the materials.
If the vessel is not properly designed then chances of failure is more
because we don’t know what is the maximum operating pressure and
temperature. We don’t know about maximum load, pressure or
temperature carrying capacities of the vessel.
10 . Stresses in pressure vessel
Pressure vessel are subjected to various loading which exert stresses
of different intensities in the vessel components.
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The various stresses, which are generating during working and service
time, are tabulated below.

11. Loading on pressure vessel

 Internal pressure
 External pressure
 Weight of vessel itself.
 Static reaction form piping other vessels, attached equipment,
support such as lugs, saddles, rings, legs, skirts and internals.
 Cyclic and dynamic reactions due to wind pressure, seismic
forces
 Impact reactions such as those due to fluid shock.
 Temperature gradients and differential thermal expansion

12. What is components of design pressure vessel?

The part which is common in any pressure vessel are described below
 Shell
 Head or cover
 Nozzle
 Reinforcement pad
 Support
The above parts are common parts of the pressure vessel. The all
above parts of the vessel requires designing before fabrication.
Some useful formula and calculation described in next topic.

13. Design of shell

Shell is a major components of vessel. Shells are made form sheet or
plate. Seamless or welded pipe may be also used.
There is two types of shell
1. Cylindrical shell
2. Spherical shell
Generally a cylindrical shell is mostly used for construction of pressure
vessel.
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14. Stresses in cylindrical shell

Uniform internal or external pressure includes in the longitudinal
seam a unit stress two times larger then in the circumferential seam because
of the geometry of the cylinder.

15. Design of shell under internal presser

Thickness of cylindrical shell in terms of inside dimension or
longitudinal joints
(code reference ASME sec. Viii div.1 UG 27 )
When thickness dose not exceed one half or the inside radius, p
dose not exceed 0.385 se the following formula shall apply.

Pr
T= +c.a.
Se-0.6p

16.design of various type of dish end.

Pressure vessel requires closer at ends. Which is attained by using
various dish ends. There are various aspects for selection of type head like
volume inside head & space available above vessel at site. The various types
of dished ends widely used are describe bellow.

 Torispherical head
As shown, this type of head consists of profile generated by two
different circles having crown radius & knuckle radius. Generally these
types of heads are used for low thick vessel.
The required thickness of a tori spherical head for the case in which the
knuckle radios is 6% of the inside crown radius, shall be determined by

0.885 pl
T= + c.a.
Se-0.1 p
T = minimum required thickness of head after forming, inch
P = internal design pressure Psi
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L= inside spherical or crown radius, inch

16. Ellipsoidal head

These types of head consists of 2:1 ellipse profile as shown in figure. These
types of heads are widely used in pressure vessel.

The thickness of the 2:1 ellipsoidal defined will be determined with the help
of given formula.
Pd
T= +c.a.
2se – 0.2p

D= inside diameter of the head / inside length of the major axis.

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17. Hemispherical head

As name implies the profile of this type head is half of sphere. These types of
head have throughout constant radius that allows maximum volume for
reaction gases. This is also a widely used head especially for high thick vessel
like reactors. Thickness of the hemispherical head shall be determined with
the help of following formula.

Pl
T= + c.a.
2se – 0.2 p
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19.conical head and sections (without transition knuckle

The required thickness of conical heads or conical shell sections shall be

determined with the help of given formula.

Pd
T= + c. A.
2cosa(se – 0.6 p)
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20. Toriconical heads

The required thickness of the Tori conical dished end shall be determined
by the following formula

A = one half of the included angle of the cone

Pdi
T= + c.a.
2cosa (se – 0.6 p)
Where di = 2cos a* at the center line of the head

21. Design of nozzle

Assembly of pipe or forging to flange is called nozzle.
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22. Types of nozzle

Radial nozzle: a nozzle, which is perpendicular to base of the shell or
dished end lies on the orientation line is called radial nozzle.
Offset nozzle : a nozzle, which is similar to radial nozzle but offset form
orientation line , is called as offset nozzle.
Tangential nozzle : a nozzle, which is on any tangential line of the shell,
is called tangential nozzle.
Angular nozzle : a nozzle, which is at an angle form the reference line, is
called as angular nozzle.

23.supports for vessel

Vessel have to be supported by different methods. Vertical vessel is
supported by bracket, column and saddle support horizontal vessels. The
choice of the type of supports depends on the
 Height and diameter of the vessel,
 Available floor space,
 Location of vessel
Types of supports which are commonly used
 Skirt supports
 Saddle supports
 Bracket or lug supports
 Leg supports

24. What is design of skirt supports ?

Tall vertical vessels are usually supported by cylindrical shell or skirts.
The skirts are welded to the bottom dished head, or outside of the shell.
A bearing plate is attached to the bottom of the skirts. This plate is made to
rest on concrete foundation and is securely anchored to the foundation by
means of anchor bolts in concrete prevent over turning form the moments
induced by wind or seismic loads.
The bearing plate is in the form of rolled angle or a single flat ring with or
without gussets.
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25. Design of saddle supports

Horizontal cylindrical vessel are supported on saddles. Theses are placed
as two positions.
For large thin wall vessel or vessels under vacuum, it is necessary to provides
ring supports.
The location of the saddle supports should be equal form the centerline of the
vessel or equal distance form the tan line of the both side of vessel

26. Design of bracket or lug type supports

These type can be easily fabricated form the plate and attach with the
vessel wall with minimum welding length. They are made to rest on short
columns or on beams of a structure depending on the elevation required. They
can be easily leveled.
Bracket supports are most suitable for vessel with thick walls.
The main loads on the brackets supports are the dead weight of the vessel with
its content and the wind load.

27. Design of leg supports

Structural sections such as angle, channels can be directly welded to the
pressure vessel shell to form vertical legs the legs is attached to the vessel by
fillet welds.
This type of support is use for small vessels. Several local stresses are
produced at the connection of the support to the vessel wall.
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39. What is types of drawing size ?

Size Length (mm) Width (mm)

A4 297 210
A3 420 297
A2 594 420
A1 840 594
A0 188 840

43. Describe minimum thickness of shell or head ?

The thick ness after forming and without for corrosion of any shell or head
subject to pressure shall not less than ¼ (6 mm) for carbon and low alloy
steel. Or 1/8 inch (3.2) for stainless steel and non-ferrous materials.

44. Describe the selection of material thickness ?

The selected thickness of material shell be such that the forming, heat
treatment, and other fabrication processes will not reduce the thickness of
the material at any point below the minimum value required by the rules.

45.describe the corrosion allowance in design formula ?

The dimensional symbols used in all design formulas thought out the
division represent dimensions in the corroded condition.

46.describe the lodes ?

Internal and external pressure including static head. Weight of vessel and
normal contents under operating or test conditions. Superimposed loads,
such as other vessel operating equipment, insulation, corrosion resistance
or erosion resistant lining and piping. Wind loads, snow loads and
earthquake loads.

47.why corrosion allowance is required in shell plates.

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Vessel and part there of subject to loss of metal by corrosion , erosion ,

mechanical abrasions or other environmental effect shall have provisions
made for such loss during the design or specified life of the vessel by a
suitable increase in or addition tool a thickness of the base metal over that
determined by the design formula or stress analysis.

48.why corrosion allowance is required in shell plate ?

Material added an included for these losses need not be of the same
thickness for all parts of the vessel. If different rates of attack are excepted
for the various parts. No additional thickness need be provided when
previous experience in like service as soon that corrosion does not occur or
is of only a superficial nature .

49. Why required lining in the shell ?

Corrosion resistance or abrasion resistance lining are these not integrally
attach to the vessel wall. They are intermittently attach or not attach at all .
In either case, such lining shell not be given any credit when calculating the
thickness of the vessel wall.

50.defination of the design pressure.

Design pressure is the pressure at the top of the vessel and which together
with the applicable co incident( metal.) Temperature is stamped on the
name plate. The pressure at the top of the vessel is also the basis for the
pressure setting of the pressure relief device protecting the vessel.

51.defination of the design temperature?

The temperature used in the design shall be based on the actual metal
temperature expected under operating condition for the part considered at
the designated coincident pressure.

52.definition of the operating pressure?

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The operating pressure is the pressure at the top of the vessel at which it
normally operators. The operating pressure shall not exceed the design
pressure and is usually kept at a suitable level bellow it to prevent the
frequent opening of the pressure relieving devices.

53.defination of the test pressure ?

The test pressure is the pressure to be applied at the top of the vessel during
the test . This pressure +any pressure due to static head at any point under
consideration is used in the applicable formula to check the vessel under
test condition.

68.what is the ASME code followed for design of piping systems in

process piping ?
B 31.3
69. While welding of pipe trunion to pipe/reinforcement pad you have to
put a hole or leave some portion of welding why ?
For venting of hot gas which may get generated due to welding
70.what should be the radius of long radius elbow?
1.5 d
71. Normally where do we use the following ?
Eccentric reducers & concentric reducers
1.eccentric reducer = pump suction to avoid cavitations, to maintain
elevation in rack
2.concentric reducers = pump discharge, vertical pipe line et
72. What do you mean by NPSH ?
Net positive suction head.
80. What is the ansi/ASME dimensional standard for steel flange &
fitting?
B 16.5
81.how can flanges be classified based on facing ?
Flat face, raised face, tongue and groove, ring type joint
83.which are the different types of gaskets ?
Full face, spiral wound, octagonal ring type, metal jacketed and inside bolt
circle.
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87. What is the ASME code followed for design of piping systems in
Process
Pipings (Refineries & Chemical Industries)?
Ans. B31.3
90. What is the difference between stub in and stub on branches?
Describe with
Sketch. Which one is preferred?
For branching of one size lesser of run pipe, Stub On is preferred. For other
branching
Less than one size of run pipe stub in is preferred. The Design is based on
ANSI B 31.3
91. What is the difference between Pipe and Tube?
Ans: Pipe is identified by NB and thickness is defined by Schedule whereas
Tube is
Identified by OD.
92. From which size onwards NB of pipe is equal to OD of Pipe?
Ans: From the size 14” and onwards NB = OD of pipe.
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