DESIGN OF PRESSURE VESSEL PROJECT REPORT Submitted by PDF

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DESIGN OF PRESSURE VESSEL PROJECT REPORT Submitted by\ MIJO JOSEPH VIPIN .M VISHNU VIJAY ABSTRACT This project work deals with a detailed study and design procedure of pressure vessel. A detailed study of various parts of pressure vessels like shell, closure, support, flanges, nozzles etc. Design is...

Description

DESIGN OF PRESSURE VESSEL

PROJECT REPORT

Submitted by\

MIJO JOSEPH

VIPIN .M VISHNU VIJAY ABSTRACT

This project work deals with a detailed study and design procedure of pressure vessel. A detailed study of various parts of pressure vessels like shell, closure, support, flanges, nozzles etc. Design is carried according to rules of ASME code section VIII, Division I.

The first chapter deals with detailed study of pressure vessel i.e. the various materials used in pressure construction and temperature are mentioned .It also deals with the study of various parts like flanges, support etc. Various methods of fabrication and testing are also included.

The second chapter includes design criteria .This is followed by procedure of design, which include design shell and its components, nozzles, reinforcements etc. LIST OF FIGURES

FIGURE

3.9.1

TYPES OF FLANGES

14

3.11.1

TYPES OF SKIRT

17

MODEL OF AMINE ABSORBER 5.1

TOP AND BOTTOM HEAD

29 32

5.2.1

TOP SECTION OF SHELL

35

5.2.2

BOTTOM SECTION OF SHELL

36

5.3

DESIGN OF NOZZLE

59

5.4

DESIGN OF REINFORCEMENT AREAS

72

LIST OF TABLES

DESIGN DATA 7

RESULT AND DISCUSSION

28 87

P :

design pressure, kg/cmA2

NOMENCLATURE

T :

design temperature, °C

C :

corrosion allowance, mm

Di :

inside diameter of the vessel, mm

Do : outside diameter of the vessel, mm

Ri :

inside radius of the vessel, mm

Ro :

outside radius of the vessel, mm

S :

maximum allowable stress, kg/cmA2

E :

Joint efficiency, %

T :

required the thickness, mm

tn :

trn :

fr :

Mt :

minimum thickness provided for the nozzle, mm

selected thickness for the nozzle, mm

strength reduction factor

moment at the skirt to head joint, kg-mm W :

weight of the vessel H :

height of center of gravity

Fe :

seismic coefficient

N:

Number of bolts

Ab :

area with in the bolt circles, mmA2

Cb :

circumference of bolt circle, mm

Ba :

required area of one bolt, mm

As :

area within the skirt, mmA2

Cs :

circumference on outer diameter of skirt, mm

P : Dso

design pressure, kg/cmA2 outer diameter of the skirt, mm

Dsi: inside diameter of the skirt, mm

Fb

: safe bearing load on the concrete, kg/cmA2

I :

width of the base plate, mm

The equations may be written in the following forms t = PRi/(SE-0.6P) = Pro / (SE-0.4P) Where, t t = minimum required thickness of the shell exclusively of Corrosion allowance

P=

design pressure, or maximum an allowable working Pressure welded -joint efficiency

S

maximum allowable stress

Ri

inside radius of the shell

Ro=

outside radius of the shell

If the thickness of the Shell exceeds 50% of the inside radius, or when the pressure exceeds 0.385SE, the lame equation should be used to calculate the vesselshell thickness. The following forms of the lame equation are given by the code.

With the pressure p known.

t = Ri(Vz-l) = Ro (Vz-1)/Vz

Where, z = S.E+P/(S.E-P) The equation for ellipsoidal head thickness is given by

t = PDi/ (2SE+0.2P) =PDo/ (2SE+1.8P) Where, t = minimum required thickness of the ellipsoidal head exclusive of corrosion allowance P = design pressure, or maximum allowable working pressure. E = welded - joint efficiency. S = Maximum allowable stress. Di = inside diameter of the shell Do=outside diameter of the shell

CHAPTER

.1

INTRODU

CTION

Chemical engineering involves the application of sciences to the process industries, which are primarily concerned, with the conversion of one material into another by ahemical or physical means. These processes require the handling or storing of large quantities of materials in containers of varied constructions, depending upon the existing state of the material, it's physical and chemical properties and the required operations, which are to be performed. For handling such liquids and gases, a container or vessel is used. It is called a pressure vessel, when they are containers for fluids subjected to pressure. They are leak proof containers. They may be of any shape ranging from types of processing equipment. Most process equipment units may be considered as vessels with various modifications necessary to enable the units to perform certain required functions, e.g. an autoclave may be considered as highpressure vessel equipped with agitation and heating sources.

Pressure vessels are in accordance with ASME code. The code gives for thickness and stress of basic components, it is up to the designer to select appropriate analytical as procedure for determining stress due to other loadings. The designer must familiarize himself with the various types of stresses and loadings in order to

accurately apply the results of analysis. Designer must also consider some adequate stress or failure theory in order to confine stress and set allowable stress limits.

The methods of design are primarily based on elastic analysis. There are also other criteria such as stresses in plastic region, fatigue, creep, etc. which need consideration in certain cases. Elastic analysis is developed on the assumption that the material is isotropic and homogeneous and that it is loaded in the elastic region. This analysis is not applicable in the plastic range. Under cyclic variation of load causing plastic flow, the material to hardens and the behavior of material becomes purely elastic. This is a phenomenon called shakedown or cessation of plastic deformation under cyclic loading. Elastic analysis is therefore in most important method of designing pressure vessel shells and components beyond the elastic limit, the material yields and the plastic region (spreads with increased value of load. The load for which this occurs is called collapse load rusting pressure.

Limit analysis is concerned with calculating the load or pressure at which flow of jfitructure material occurs due to yielding. However, this method is not usually applied to Resign of pressure vessels. When vessels are subjected to cyclic loading, it is necessary to consider requirements for elastic cycling of the material and the effects of this on component behavior. In the case of a discontinuity of shape, load may give rise to plastic cycling. Under these conditions, shakedown with occur. Maximum shakedown load is twice the first yield load. Therefore, an elastic analysis is valid up to the range of load, under cyclic loading conditions. A factor of safety on the stress or

a factor of safety of twenty is applied on the numbers cycles. Design stress is accepted as the lower value.

CHAPTER.2 SCOPE

OF THE PROJECT

--In sophisticated pressure vessels encountered in engineering construction; high pressure, extremes of temperature and severity of functional performance requirements pose exciting design problems. The word "DESIGN" does not mean only the calculation of the detailed dimensions of a member, but rather is an allinclusive term, incorporating: 1. The reasoning that established the most likely mode of damage or failure; 2. The method of stress analysis employed and significance of results; ... 3. The selection of materials type and its environmental behaviour.

I The ever-increasing use of vessel has given special emphasis to analytical and experimental methods for determining their emphasis to analytical and experimental methods for determining their operating stresses. Of equal importance is the appraising the significance of these stresses. This appraisal entails the means of determining the values and extent of the stresses and strains, establishing the behaviour of the material involved, and evaluating the compatibility of these two factors in the media or environment to which they are subjected. Knowledge of

material behaviour is required not only to avoid failures, but also equally to permit maximum economy of material choice and amount used. CHAPTER.3

DESIGN CRITERIA

3.1 FACTORS INFLUENCING THE DESIGN

[Regardless of the nature of application of the vessels, a number of factors usually must be considered in designing the unit. The most important consideration often is the selection of the type of vessel that performs the required services in the most satisfactory manner. In developing the design, a number of other criteria must be considered such as the properties of material used, the induced stresses, the elastic stability, and the aesthetic appearance of the unit. The cost of fabricated vessel is also important in relation to its service and useful life.

3.2 DESIGN OF PRESSURE VESSELS TO CODE SPECIFICATION

American, Indian, British, Japanese, German and many other codes are available for design of pressure vessels. However the internationally accepted for design of pressure vessel code is American Society of Mechanical Engineering (ASME).

Various codes governing the procedures for the design, fabrication, inspection, testing and operation of pressure vessels have been developed; partly as safety measure. These procedures furnish standards by which, any state can be assured of the

safety of pressure vessels installed within its boundaries. The code used for unfired pressure vessels is Section VIII of the ASME boiler and pressure vessel code. It is usually necessary that the pressure vessel equipment be designed to a specific code in order to obtain insurance on the plant in which the vessel is to be used. Regardless of the method of design, pressure vessels with in the limits of the ASME code specification are usually checked against these specifications. 3.3 DEVELOPMENT AND SCOPE OF ASME CODE

In 1911, American Society of Mechanical Engineering established a committee to formulate standard specifications for the construction of steam boilers and other pressure vessels. This committee reviewed the existing Massachusetts and Ohio rules and eonducted an extensive survey among superintendents of inspection departments, Engineers, fabricators, and boiler operators. A number of preliminary reports were issued and revised. A final draft was prepared in 1914 and was approved as a code and copy righted in 1915.

The introduction to the code stated that public hearings on the code should be held every two years. In 1918, a revised edition of the ASME code was issued. In 1924, the code was revised with the addition of a new section VIII, which represented a new code for unfired pressure vessels.

3.4 THE API-ASME CODE

In 1931, a joint API-ASME committee on unfired pressure vessels was appointed to prepare a code for safe practice in the design, construction, inspection and repair of unfired pressure vessels.

3.5 SELECTION OF THE TYPE OF VESSEL

The first step in the design of any vessel is the selection of the type best suited for the particular service in question. The primary factors influencing this choice are,

. i.

ii. iii. iv.

The operating temperature and pressure.

Function and location of the vessel. Nature of fluid. Necessary volume for storage or capacity for processing.

It is possible to indicate some generalities in the existing uses of the common types of vessels. For storage of fluids at atmospheric pressure, cylindrical tanks with flat bottoms and conical roofs commonly used. Spheres or spheroids are employed for pressure storage where the volume required is large. For smaller volume under pressure, cylindrical tanks with formed heads are more economical.

3.6 TYPES OF PRESSURE VESSELS

3.6.1 OPEN VESSELS

Open vessels are commonly used as surge tanks between operations, as vats for batch operations where materials be mixed and blended as setting tanks, decarters, chemical reactors, reservoirs and so on. Obviously, this type of vessels is cheaper than covered or closed vessel of the same capacity and construction. The decision as to whether or not open vessels may be used depends up on the fluid to be handled and the operation.

3.6.2 CLOSED VESSELS

1

Combustible fluids, fluids emitting toxic or obnoxious fumes and gases must be

stored in closed vessels. Dangerous chemicals, such as acid or caustic, are less hazardous if stored in closed vessels. The combustible nature of petroleum and its products associates the use of closed vessels and tanks throughout the petroleum and petrochemical industries. Tanks used for the storage of crude oils and petroleum products and generally designed and constructed as per API specification for welded oil storage tanks. [3.6.3 CYLINDRICAL VESSELS WITH FLAT BOTTOMS AND CONICAL OR DOMED ROOFS.

The most economical design for a closed vessel operating at atmospheric pressure is the vertical cylindrical tank with a conical roof and a flat bottom resting directly on the bearing soil of a foundation composed of sand, gravel or crushed rock. In cases where it is desirable to use a gravity feed, the tank is raised above the ground, and columns and wooden joints or steel beams support the flat bottoms.

3.6.4 CYLINDRICAL VESSELS WITH FORMED ENDS

Closed cylindrical vessels with formed heads on both ends used where the vapour pressure of the stored liquid may dictate a stronger design, codes are developed through the efforts of the American petroleum Institute and the American Society of Mechanical Engineering to govern the design of such vessels. These vessels are usually less than 12 feet in diameter. If a large quantity of liquid is to be stored, a battery of vessels may be used.

3.6.5 SPHERICAL AND MODIFIED SPEHRICAL VESSELS

Storage containers for large volume under moderate pressure are usually fabricated in the shape of a sphere or spheroid. Capacities and pressures used in these types of yessels vary greatly for a given mass; the spherical type of tank is more economical for large volume, low-pressure storage operation.

3.6.6 VERTICAL AND HORIZONTAL VESSELS

In general, functional requirements determine whether the vessel shall be vertical or jjiorizontal. Eg. Distilling columns, a packed tower, which utilizes gravity, require vertical installation.

Heat exchanges and storage vessels are either horizontal or vertical. If the vessel to be installed outdoor, wind loads etc, are to be calculated to prevent overturning, thus jhorizontal is more economical. However, floor space, ground area and maintenance requirements should be considered.

3.6.7 VESSELS OPERATING AT LOW TEMPERATURE RANGES

Pressure vessels constructed in such a manner that, a sudden change of section producing a notch effect is present, are usually not recommended for low temperature range operations. The reason is that, they may create a state of stress such that the material will be incapable of relaxing high-localized stresses by plastic deformation, therefore, the materials used for low temperature operations are tested for notch ductility.

Carbon steels can be used down to 60 degree C. Notch ductility is controlled in such as materials through proper composition steel making practice, fabrication practice and heat treatment. They have an increased manganese carbon ratio. Aluminium is usually added to promote fine grain size and improve notch ductility.

Ductility of certain materials including carbon and low alloy steels is considerably diminished when the operating temperature is reduced below certain critical value is usually described as the transition temperature, depends upon the material, method of manufacture, previous treatment and stress system present. Below transition temperature, fracture may take place in a brittle manner with little or no deformation. Whereas, at temperatures above the transition temperature, fracture occurs only after considerable plastic strain or deformation. 3.6.8 VESSELS OPERATING AT ELEVATED TEMPERATURE.

Embrittlement of carbon and alloy steel may occur due to service at elevated temperature. In most instances, brittleness is manifest only when the material is cooled to

jK>om

temperature. This inhibited by addition of molybdenum and also improve tensile and creep properties. Two main criteria in selecting the steel elevated temperature are metallurgical strength and stability. Carbon steels are reduced in their strength properties due to rise in temperature and are liable to creep. Therefore, the use of carbon steel is generally limited to 500dege C.

The SA-283 steels cannot be used in applications with temperatures over 340degreC. The SA-285 steels cannot be used for services with temperature over 482degreC. However, both SA-285 and SA-285 SA-212 steels have very low allowable stress, at higher temperature.

3.7 MATERIAL SPECIFICATION

Plain carbon and low alloy steels plates are usually and where service condition permit because of the lesser cost and greater availability of these steels. Such steels may me fabricated by fusion welding and oxygen cutting if the carbon content does not exceed 0.35%.vessels may be fabricated.

Vessel may be fabricated of plate steels meeting the specification of SA-7, SA-113, Grade A, B, C&D, provided that, 1. operating temperature is between -28degreeC&360degreeC 2. The plate thickness does not exceed 1.5cm 3. The vessels does not contain lethal liquids and gases 4. The steel is manufactured by the electric furnace or open hearth process 5. The material is not used for unfired steam boilers

One of the most widely used steel for general purpose in the construction of ressure vessel is SA-283, Grade C. This steel has good ductility and forms welds and machines easily. It is also one of the most economical steel suitable for pressure vessels. [However, its use is limited to vessels with plate thickness not exceeding 1.5cm.

For vessels having shells of grater thickness. SA-285 Grade C is most widely used Hi moderate pressure applications. In case of high pressure or large diameter vessels, high strength steel may be used to advantage to reduce the wall thickness. SA-212, GradeB is well suit for such application and requires a shell thickness of only 79% of that required by SA-285, Grade C. This steel also is fabricated but is more expensive than other steels.

Now, many new series of materials like low alloy, high alloy steels, high temperature and low temperature materials are available which can be selected to suit the requirement of every individual need of process industry.

The important materials generally accepted for construction of pressure vessels are indicated here. Metals used are generally divided into three groups as.

1. Low cost

Cast iron, Cast carbon and low alloy steel, wrought carbon and

low alloy steel. 2. Medium cost - High alloy steel (12%chromium and above), Aluminum, Nickel, Copper and their alloys, Lead. 3. High cost

...