Iintroduction to PV

8/11/2019 Iintroduction to PV

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INTRODUCTION TO

PRESSURE VESSELS


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PRESSURE VESSELS

Pressure vessels are the containers for fluids with apressure differential between inside and outside.

The fluid inside the vessel may undergo a change in

state (e.g. - steam boilers) or may combine with other

reagents (e.g. - chemical reactor) Pressure vessels often have a combination of high

pressures together with high temperatures, and in some

cases flammable fluids or highly radioactive materials.

The rupture of a pressure vessel has a potential to causeextensive physical injury and property damage

Hence these vessels have to be designed carefully .


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Pressure Vessels - Usage

They are used in a number of industries;

power generation industry - fossil /nuclear power

petrochemical industry - for storing and processingpetroleum crude in tank farms as well as storinggasoline in service stations

chemical reactors

food industries

pharmaceutical industries

- to name but a few


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Classification of vesselsAccording to pressure and its type

i. Internal Pressure Vessels - where the media pressure

inside the vessel is more than that outside.ii. External Pressure Vessels - where the media pressure

inside the vessel is less than that outside.

When the internal pressure < 0.1 MPa (abs),such vessels are called Vacuum Vessel.


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Low pressure vessel (L) : 0.1 P < 1.6 MPa

Med. pressure vessel (M) : 1.6 P < 10 MPa

High pressure vessel (H) : 10 P < 100 MPa

Ultra-high pressure vessel (U): P 100 MPa


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ii. According to temperature

Low temperature vessel : T < -20

Normal temperature vessel : -20< T 200

High temperature vessel - where the walltemperature is above the creep temperature.

Medium temperature vessel - between normal T& high T vessels


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High temperature vessel

Carbon steel & Low-alloy steel T> 420

Alloy steel (Cr-Mo steel) T> 450

Austenite stainless steel (Cr-Ni) T> 550


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iii. According to Grades

Grade (I)

Grade (II)

Grade (III)

Factor

P, P*V

media

importance

Degree of danger:

I < II < III


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Pressure Vessel - Shapes

The size and geometry of pressure vessels vary greatlyfrom the large vessels used for high-pressure gas storage

to the small size used as hydraulic units for aircraft.

Pressure vessels are usually spherical or cylindrical

(Vertical/horizontal), with domed ends. The cylindrical vessels are generally preferred, since they

present simpler manufacturing problems and make better

use of the available space.

However there are some special types of Vessels like

Regeneration Tower, Reactors but these names are given

according to their use only.


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Pressure Vessel - Shapes

Boiler drums, heat exchangers, chemical reactors etc

are generally cylindrical.

Spherical vessels require thinner walls for a given

pressure and diameter than the equivalent cylinder. Therefore they are used for large gas or liquid

containers, gas-cooled nuclear reactors, containment

buildings for nuclear plant, and so on


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HORIZONTAL PRESSURE VESSEL

Power plant

De-aerator


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VERTICAL PRESSURE VESSEL

The max. Shell length to diameter ratio for a small vertical

drum is about 5 : 1


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TALL VERTICAL TOWER

Constructed in a wider rangeof shell diameter and height.

They can be relatively small

in dia. and very large (e.g. 4 ftdia. And 200 ft talldistillation column.

They can be very large in dia.

and moderately tall (e.g. 3 ftdia. And 150 ft tall tower).

Internal trays are needed forflow distribution.


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FALLING FLIM

EVAPORATOR

FOUNDATION

FOUNDATION SKIRT

JUICE TANK

CALANDRIA

STEAM JACKET

DISH END20 Meter Fh


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VERTICAL REACTOR

Figure shows a typical reactorvessel with a cylindrical shell.

The process fluid undergoesa chemical reaction inside areactor.

This reaction is normallyfacilitated by the presence ofa catalyst which is held in oneor more catalyst beds.


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Pressurised Water Reactor


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SPHERICAL PRESSURIZED STORAGE

VESSEL


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MAIN COMPONENTS OF

PRESSURE VESSEL

Following are the main

components of pressure

Vessels in general

Shell

Head

Nozzle

Support

Shell

Head

Nozzle

Supports


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SHELL

It is the primary component that contains the

pressure.

plates are welded together to form a

structure that has a common rotational axis.

Shells are either cylindrical, spherical and

rarely conical in shape.


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SHELL

Horizontal drums have cylindrical shells and

are constructed in a wide range of diameter

and length.

The shell sections of a tall tower may be

constructed of different materials, thickness

and diameters due to process and phase

change of process fluid.

Shell of a spherical pressure vessel is

spherical as well.


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HE D

All the pressure vessels must be closed at

the ends by heads (or another shell section).

Heads are typically curved rather than flat. The reason is that 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 andare known as intermediate heads.

These intermediate heads are separate

sections of the pressure vessels to permit

different design conditions.


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NOZZLE

A nozzle is a cylindrical component that

penetrates into the shell or head of pressure

vessel.

They are used for -

Attach piping for flow into or out of the vessel.

Attach instrument connection (level gauges,

Thermowells, pressure gauges).

Provide access to the vessel interior atManway.

Provide for direct attachment of other equipment

items (e.g. heat exchangers).


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SUPPORT

Support is used to bear all the load of

pressure vessel, earthquake and wind loads.

There are different types of supports which

are used depending upon the size and

orientation of the pressure vessel.

It is considered to be the non-pressurized part

of the vessel.


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TYPES OF SUPPORTS

LEG SUPPORT:

Small vertical drums are typically supported on legsthat are welded to the lower portion of the shell.

The max. ratio of support leg length to drum diameteris typically 2 : 1

Reinforcing pads are welded to the shell first toprovide additional local reinforcement and loaddistribution.

The number of legs depends on the drum size andloads to be carried.

Support legs are also used for Spherical pressurizedstorage vessels.

Cross bracing between the legs is used to absorb windor earth quake loads.


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TYPES OF SUPPORTS

LUG SUPPORT:

Vertical pressure vessels mayalso be supported by lugs.

The use of lugs is typicallylimited to pressure vessels of

small and medium diameter (1to 10 ft)

Also moderate height todiameter ratios in the range of2:1 to 5:1

The lugs are typically bolted tohorizontal structural membersin order to provide stabilityagainst overturning loads.


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TYPES OF SUPPORTS

SADDLE SUPPORT:

Horizontal drums are typically supported at two locations by saddle

support.

It spreads over a large area of the shell to prevent an excessive local stress

in the shell at support point.

One saddle support is anchored whereas the other is free to permit

unstrained longitudinal thermal expansion of the drum.

SADDLE

SUPPORT


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TYPES OF SUPPORTS

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).

The skirt is normally long enough to provide enoughflexibility so that radial thermal expansion of the shell

does not cause high thermal stresses at its junction

with the skirt.


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PV Design - Basic Requirements

Enough strength - no breakage

Enough rigidity - set limits deformation

Enough stability - no collapse

Durability

guaranteed lifeTightness - no leakage

Materials Economy & minimal cost

Easy to manufacture, transport, install, operate andmaintain


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Steps:

i. Material Selectionii. Structure design

iii. Calculation of strength and thickness

iv. Seal design; select / design flangesv. Selection of support, Check for strength

vi. Design of reinforcements

vii. Selection of other parts and accessories

Iintroduction to PV

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