MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER 1. INTRODUCTION Heat exchanger is a device, which is used for transfer of heat from fluid to another, usually separated by walls. Whenever a temperature gradient exists between two fluids, energy is transferred by heat transfer process. Classification: Based on the applications, heat exchangers are classified as boilers, condensers, heaters, coolers, recuperators etc. Depending on the configuration of fluid flow paths, heat exchangers are classified as parallel flow(co-flow) heat exchangers, counter current(counter flow) heat exchangers and single pass cross flow heat exchangers and multi pass cross flow heat exchangers. The most important difference between the four types lie on the relative amount of heat transfer surface area required to produce a given temperature rise for a given temperature difference between the two fluid streams where they benter the heat exchanger. Heat exchangers are employed in varied installations such as steam power plant, chemical processing plants, building heating, air-conditioning, refrigeration system etc to carry away the heat carried by the gases and it cools the gasses to a sufficiently low temperature, using a suitable fluid. Regenerative Heat Exchangers In Regenerative Heat exchangers the hot and cold fluid flow through the one and same passage and heated surface is alternately exposed to the hot and cold fluids. If the periods of heating and cooling are of equal duration, continuous heating requires two apparatus in
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Mechanical Design of shell and Tube Heat Exchanger
The heat exchanger selected for mechanical design is a fixed tube sheet type shell and tube heat exchanger. In this heat exchanger slop oil entering the tube side at 1450C is cooled to 500C using cooling water at 330C as cooling agent through the shell side. The design of this heat exchanger is done at FEDO (FACT Engineering & Design Organization) for KRL. This conforms to the ASME (American Society of Mechanical Engineers) Section VIII, Division 1 standards and TEMA (Tubular Exchanger Manufactures Association) standards. The mechanical design of shell and tube heat exchanger (Type BEM) is done manually with equations and analysed with B-JAC software.
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MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
1. INTRODUCTION
Heat exchanger is a device, which is used for transfer of heat from fluid to another, usually
separated by walls. Whenever a temperature gradient exists between two fluids, energy is
transferred by heat transfer process.
Classification:
Based on the applications, heat exchangers are classified as boilers, condensers, heaters,
coolers, recuperators etc. Depending on the configuration of fluid flow paths, heat
exchangers are classified as parallel flow(co-flow) heat exchangers, counter current(counter
flow) heat exchangers and single pass cross flow heat exchangers and multi pass cross flow
heat exchangers. The most important difference between the four types lie on the relative
amount of heat transfer surface area required to produce a given temperature rise for a
given temperature difference between the two fluid streams where they benter the heat
exchanger. Heat exchangers are employed in varied installations such as steam power plant,
chemical processing plants, building heating, air-conditioning, refrigeration system etc to
carry away the heat carried by the gases and it cools the gasses to a sufficiently low
temperature, using a suitable fluid.
Regenerative Heat Exchangers
In Regenerative Heat exchangers the hot and cold fluid flow through the one and same
passage and heated surface is alternately exposed to the hot and cold fluids. If the periods
of heating and cooling are of equal duration, continuous heating requires two apparatus in
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
which the hot fluid is cooled in one apparatus the cold fluid is heated in the other. After that
apparatus is switched over and heat transfer process is reversed. In Regenerative
exchangers the process of heat transfer is transient. The temperature varies as it cools or
heats variation in wall temperature is accompanied by change in fluid temperature with time
and along the heating surface as well.
Regenerators are mainly used in the branches of industry where there is waste gas at high
temperature and is required to heat air at a high temperature i.e. blast furnaces, open hearth
furnaces, coke and glass manufacturing. The performance of regenerators depends on
many factors as thickness of packing, its conductivity, accumulating capacity, duration of
periods and fluid temperature. While in operating conditions the heat transfer co-efficient
may vary due to the burning of gas in the regenerator.
Recuperative heat exchangers
The two fluids performing the exchange of heat in the exchangers can flow (a) with each
other in the same direction (parallel flow) or in opposite direction (counter flow) or (b) at
right angles to one another (cross flow) with both types of flow a single or multi pass
arrangement is possible. The element from which a recuperative matrix is built up is mainly
of two kinds, the fluid flows along the tubes on the inside and along across the tubes on the
outside. The fluid flows between consecutive plates arranged at a certain distance apart. To
reduce the equivalent diameter, the flow channels between the plates may be sub divided in
different ways by a folded or corrugated plate arranged between any two parallel plates
and thus forming a multiplicity of parallel flow channels, the shapes of which depend on the
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
kind and shape of corrugations. Heat transfer and flow resistance depend on size, shape
and arrangement of above elements. Any reduction in diameter leads to an increase in the
number of tubes for given mass flow and requires new methods for fixing in tubes in plates
of the headers. Further reduction in the equivalent diameter of flow channels about 6mm to
3mm leads to the use of plate type matrix
.
Mixed type Heat Exchangers
The direct contact type heat exchanger is one in which the two fluids are not separated
from one another. If heat is to be transferred between gas and liquid, the gas is either
bubbled through the liquid or is sprayed in form of drops through the other. In this heat
transfer takes place with mass transfer. The heat is carried by the evaporation of cooled
water carried with air. Its performance not only depends upon the temperature difference
but also on relative humidity of air. Common examples of this type are feed heaters, cooling
towers and evaporative condensers. The influence of flow path arrangement on heat
transfer area is dependent on the temperature rise to be achieved for a given inlet
temperature difference the flow path arrangement does not affect heat transfer area. Parallel
flow arrangement should be restricted to this area. The counter flow arrangement requires
least area throughout range while cross flow arrangement requires slightly larger than
counter flow but is much better than parallel flow arrangement. Whenever temperature
changes in one or both fluid streams closely approach the temperature difference between
the entering fluid systems only counter flow arrangement has to be employed. The cross
flow arrangement is classified as single pass and multi pass cross flow. If both fluids
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
traverse the exchanger only once; the arrangement is called single pass heat exchanger. If
the fluids are made to shuttle back and forth across the heat transfer matrix more than once
that arrangement is called multi pass heat exchanger. If the fluid path on hot side is so
arranged as to make two passes and on the cold side 4-passes, then the heat exchanger is
called 2-4 heat exchanger.
2. LITERATURE SURVEY
Heat exchangers are practical devices used to transfer energy from one
fluid to another to get fluid streams to the right temperature for the next
process to condense vapours, to evaporate liquids, to recover heat to use
elsewhere and to drive a power cycle.
Shell and Tube Heat Exchangers:
Shell and tube heat exchangers come in a wide range of sizes and lengths to many needs.
This large unit features tantalum sheet and tubing to provide long life and corrosion
resistance in severe environments. They are widely used in process industries, especially
petro chemical and petroleum refineries, the use of shell and tube heat exchangers range
from chillers heat removers etc to reboilers, process steam coolers etc. Also there are no
moving parts. The shell and tube heat exchangers are grouped into three as “R” heat
exchangers, “C” heat exchangers and “B” heat exchangers, according to service standards
set by TEMA Class “R” heat exchangers are designed for severe service requirements
class “B”, for moderate service requirements and class “C” for chemical process
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
service.Although copper tubes and steel shells are the most common materials of
construction a wide range of metals are available for handling various fluids and gasses as
brass, aluminium, stainless steel, titanium and other alloys. Some application use glass or
plastic tubes to resist the attack of extremely corrosive substance or to avoid affecting the
flavour of food.The recent innovations in heat transfer technology had led to greater
efficiency of shell and tube type heat exchangers. Multiple pass, multiple module
constriction help to achieve a significant amount of heat transfer in a limited amount of
space. Even though sufficient space must be left for the cleaning of tubes and the removal of
tube bundles for repair, the units can be located just about anywhere. The shell and tube
heat exchanger is shown in figure 1.
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
Figure 1. Shell & Tube Heat Exchanger
Multiple pass, multiple module constriction help to achieve a significant amount of heat
transfer in a limited amount of space. Even though sufficient space must be left for the
cleaning of tubes and the removal of tube bundles for repair, the units can be located just
about anywhere.
The main components of shell and tube heat exchangers as mentioned above are the shell,
tube bundle, tube sheets, baffles, channels, flanges and nozzles.
Shell:
The shell consists of a cylinder made from seamless pipe rolled and welded with a bolting
flange at each end. It is often designed so as to withstand a pressure, one and half times its
rated pressure. Shells are often designated by letters E, F, G, H, J, K and X.
Tube bundle:
The tube bundle is made of tubes, tube sheet and cross baffles. Different types of tube
configurations are available. One common type is the U-tube configurations which is the
most economical. It has the fewest components one head assembly, one tube sheet and a
shell with flange opening to accept the tube bundle on one end. Even though the
arrangement features a removable, replaceable bundle, it is difficult to clean the tubes
mechanically. Efforts to overcome this disadvantage resulted in the introduction of straight
tube configuration. This configuration consists of a shell assembly with a flange on each end
and the tube is fixed at the both ends. The unit is durable, can handle higher pressures and
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
easy to maintain. The major disadvantages include the inability to tolerate large temperature
difference between the shell and tube side fluids, the failure or breaking of tubes from the
tube sheets due to the differential expansion and the nonreplicable bundle. Hybrid designs
are also available to overcome many temperature and pressure drawbacks. The complete
bundle can be removed in a hybrid heat exchanger. The most recent development in shell
and tube designs has the introduction of a double wall construction. The outer tube is rolled
into one header and the inside one extends past the outer tube and is rolled into a second
header. The failure of the tube can be detected by visual inspection or an electronic
monitoring device. The double wall construction offers significant protection and safety.
Tube Sheets:
Tube sheets are used to keep the tubes in position. The tubes can be either square pitched
or triangular pitched. Due care must be taken in the design of tube sheets as it is affected by
longitudinal stresses in shell and tube, tube compressive stress, tube to tube sheet joint
loads etc.
Baffles:
Baffles are used to induce turbulence outside the tubes as turbulence increases the heat
transfer coefficients. Baffles cause the liquid to flow through the shell at right angles to axes
of tubes. The centre to centre distance between baffles is called baffle pitch or baffle
spacing. There are several types of baffles like disks and doughnuts, orifice, strip and
segmental of which segmental baffles are most commonly used. Segmental baffles are
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
formed by cutting a segment from a disc. Segmental baffles are drilled plates with heights
which are generally 75% of the inside diameter of the shell and these are also called 25%
cut baffles. The cut portion of baffle is often called the window section. Baffle is efficient
and gives good heat transfer rates for pressure drop and power consumed
Flanges:
Flanges are used on the shell of a vessel to permit disassembly and removal or cleaning of
internal parts. They are also used for making connection for piping and nozzle attachments.
The standard types of flanges for different pressure ratings are welding neck type, slip on
type, screwed type, lap joint blind type etc.
Gaskets:
The functions of a gasket are to interpose a semi plastic material between the flange facings,
by which the material seals (through deformation under load) the minute surface
irregularities to prevent the leakage of the fluid. The amount of force required for this
purpose is known as yield or seating force. They are of different types; the most commonly
used are fabricated with a metal jacket and a soft filler (usually of asbestos). Such gaskets
can be used up to temperatures of about 8500 F and require comparatively less bolt load
to seat and keep tight.
Channel:
Channel is a tube side component. It has also got a cylindrical section. The tube side flows
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
through the channel. Partition plates are made use for multipass flow. The effective
thickness of the channel cover will be the thickness measured at the bottom of the pass
portion groove minus tubeside corrosion allowance.
Nozzles:
In the case of heat exchangers, nozzles are the pass ways for the in and out flow of the hot
and cold fluids. The strength of shell will be reduced due to the drilling of holes for the
insertion of nozzles. If the thickness of the shell is not sufficient to withstand the differential
stress thus developed additional metallic plate must be introduced in order to reinforce the
shell structure.
3. CODES & STANDARDS
Introduction:
The ASME boiler and pressure vessel code (BPVC) section VIII deals with the“Rules for
construction of pressure vessels” (unified). ASME BPVC section VIIIcomprises of the
following three divisions.
Section VIII : Rules for construction of pressure vessels
Division 1 : Rules for construction of pressure vessels
Division 2 : Alternate Rules
Division 3 : Alternate rules for construction of high pressure vessels
The ASME BPVC Section VIII, division is the most widely used code for the design and
construction of pressure vessels.
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
The ASME Code SECTION VIII, DIVISION 1:
The ASME BPVC Section VIII, division 1 adopts the design by formula (DBF) approach.
Division 1 uses approximate formulas, charts, and graphs in simple calculations, applies a
higher factor- of- safety (resulting in lower allowable stresses), is more tolerant to
fabrication techniques and fabrication defects as compared to other divisions of this section.
The design basis of division 1 is the “maximum principal stress theory”. The ASME BPVC
Section VIII, division 1is comprises of an introduction,3 subsections, 34 mandatory
appendices and 22 nonmandatory appendices.The sructure of division 1 is as follows.
Subsection Pertaining to
Introduction Defines the scope, establishment of design
requirements, responsibilities of
manufacturer and authorized inspector,
standards referenced by this code and units
of measurement
Subsection A General Requirements
Part UG General methods of all methods of
construction and all materials
Subsection B Requirements pertaining to methods of
fabrication of pressure vessels
Part UW Requirements of pressure vessels fabricated
by welding
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
Part UF Requirements of pressure vessels fabricated
by forging
Part UB Requirements of pressure vessels fabricated
by brazing
Subsection C Requirements pertaining to classes of
materials
Part UCS Requirements of pressure vessels
constructed of carbon and low alloy steel
Part UNF Requirements for pressure vessels
constructed of non ferrous materials
Part UHA Requirements for pressure vessels
constructed of high alloy steel
Part UCI Requirements for pressure vessels
constructed of cast iron
Part UCL Requirements for pressure vessels
constructed of materials with corrosion
resistant integral cladding
Part UCD Requirements for pressure vessels
constructed of cast ductile iron
Part UHT Requirements for pressure vessels
constructed of ferrite steels with tensile
properties enhanced by heat treatment
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
Part UHX Rules for shell- and- tube heat exchangers
Mandatory Appendices Mandatory Appendix 1 through 34 (34
nos.)
No mandatory Appendix No mandatory Appendix A, C, through H,
K, L, M, P, S, T, W, Y DD, EE, FF, GG,
HH and JJ (22 nos.)
Scope of ASME BPVC SECTION VIII, DIVISION 1:
The following pressure vessels are included in the scope of division 1. Vessels designed for
pressure above 15 psig (1.0546kg/cm2 = 1.0342 bar) and not exceeding 3000psig
(210.915 kg/cm2 = 206.84 bar). Vessels having inside diameter above 6 inches (150 to
40mm). Unfired steam boilers, evaporators, heat exchangers. The following pressure
vessels are excluded from the scope of division 1. Vessels covered by other sections.
Pressure containers, which are integral part of rotating machinery. Piping system and
components beyond battery limits. Vessels for human occupancy.
Organisation of the ASME boiler and pressure vessel codes:
The ASME BPVC is divided into many sections, divisions, parts, subparts. Some
of these sections relate to a specific kind of equipment and applications; others relate to a
specific materials and method of application and control of equipment; and others relate to
care and inspection of installed equipments.
Section Title
Section I Rules for construction of power boilers
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
Section II Materials
Part A Ferrous materials
Part B Nonferrous materials
Part C Specification for welding rods,
electrodes, and filler metals
Part D Properties
Section III Nuclear power plant components
This section is further divided into
subsection NCA, Division I, Division II and
Division III.Division I is divided into
subsections NB, NC, ND, NE, NF, NG
and NH
Section IV Recommended rules for care and operation
of heating boilers
Section VII Recommended guidelines for the care of
power boilers
Section VIII Rules for construction of Pressure vessels.
Division 1,Division 2 :Alternate Rules,
Division 3:Alternate Rules for construction
of high pressure vessels
Section IX Welding and Brazing Qualification
Section X Fibre reinforced plastic pressure vessels
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
Section XI Rules for in-service inspection of nuclear
power plant components
Section Rules for construction and continued service
of transport tanks
TEMA Standards
The most widely used consensus standard heat exchanger manufacture is the “Standards of
Tubular Manufacturer’s Association”. In short the TEMA standards first published in 1941,
this standard had evolved into something of an international document. Many countries have
accorded it he status of their international codes. TEMA standards specify three classes of
construction namely TEMA-R, TEMA-C, and TEMA-B. The formulas for determining
thickness are the same for all TEMA classes; however empirical guidelines for sizing no
pressure part items vary. TEMA-R, which specifies the most rugged construction, is widely
used in refinery service and nuclear power plant applications. TEMA-C and TEMA-B are
used in other industries. TEMA-B has been promulgated as an American National
Standard (ANSI B-78).
TEMA Nomenclature
As per TEMA, the STHE is divided into three parts, the front head (stationary head), the
shell and rear head (stationary or floating). Exchangers are described by alphabetic codes
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
for the three sections.
Front (stationary) head type : A, B, C, N & D
Shell type : E, F, G, H, J, K & X
Rear head type : L, M, N, P, S, T, U &
The sequence of designating the shell and tube heat exchanger is: first the front (stationary)
end – then the shell – and finally the rear end. Various combinations like AES, AEP, CFU,
BEM, AKT, AJW, etc are possible. Each of these types has their relative merits and
demerits. The one most suitable for the specific service is selected by considering the pros
and cons of various constructional features
4. DESIGN FEATURES
In designing the heat exchanger, the following requirements were established. Eliminate or
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
at least eliminate fouling by not allowing the product to stick to the heated or cooled
surfaces, be opened easily and cleaned thoroughly, eliminate leaking gasket and withstand
high pressure.
The shell and tube heat exchanger meets the non fouling requirements by permitting the
product liquid flow to be set at velocity that can avoid or at least substantially minimise any
deposit even if it means large pressure drop. To prevent any potential deposits from lodging
the pockets, corners, crevices and zones, where the velocity cannot be strictly controlled
were eliminated. During the washing periods the washing liquids should penetrate
thoroughly.
The opening and closing operations were simplified so that even inexperienced workmen
could do them easily. The elements of unit were made sturdy material to avoid damage and
to satisfy all requirements and calculated pressure ratings, permanently. The flow channels
are completely smooth to avoid changes of cross-section. Change in the velocity of flow to
utilise the overall pressure drop to generate actual velocity and not be lost in return flow or
at sharp edges. In this way many irregularities in the flow patterns and changes of
cross-sections are avoided.
The pressure rating of each element must be calculated individually, independent of others.
The design is flexible enough to establish any velocity to be calculated. It is not desirable to
have more than one flow path in parallel. For this reason the parallel pipes used in shell and
tube heat exchanger avoided
Thermal Design:
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
The thermal design is very important in design of shell and tube heat exchanger.
The thermal design is accomplished using one of the simple methods as narrated by D Q
Kern. The heat transfer and coefficient pressure drop as predicted, particularly on the shell
side could vary considerably from the actual values obtained in operation. The search has
been instituted to develop more accurate predictive methods for thermal design. This is
particularly relevant for optimum use of more expensive materials of construction coupled
with the necessity for the increased reliability in operation.
The flow distribution, physical property variation, temperature correction, velocity
consideration and fouling factors are some of the criteria to be given due weightage to
accurately predict thermal performance.
Mechanical Design:
The mechanical designs of heat exchanger are based on reputed codes and standards. The
most common standard used in TEMA. The Tubular Exchanger Manufactures Association
(TEMA) was founded in the late 1930’s in an attempt establish standards for high quality
shell and tube heat exchanger. TEMA in turn refers to ASME section VIII wherever
necessary. ANSI and ASTM (American Standard for Testing Materials) are also referred.
The code provides only basic frame work at minimum acceptable practices with which
compliance is necessary to obtain a vessel that is structurally safe at the design temperature
and pressure. Additional requirements are left to the judgement of the user and designer.
Codes contain guidelines and recommendation covering design, material, fabrication,
inspection and testing. Simplified rules based on theory of elasticity and consolidated
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
experience are outlined for calculating thickness of pressure components along with the
permitted configurated and recommended shapes. Stress tables for various materials, weld
joints details and testing requirements are stipulated.
Heat Exchanger Design-An Over View:
Heat exchanger is the work home of the chemical industry and nuclear and thermal power
plants. As it is the most commonly used equipment, it is imperative that improvements are
continuously made in the design, for maximum cost effectiveness.
The total design involves the thermal design and mechanical design. In thermal design,
attempt is made to obtain a value, as realistic as possible, for the overall heat transfer
coefficient and pressure drops on the shell and tube sides. The heat transfer correlations for
the tube sides have a valid theoretical foundation, but those on the shell side are primarily
empirical in nature because of the difficulties encountered in mathematically analysing the
shell side flow.
After the thermal design comes the mechanical design. In small heat exchangers, there is no
need for stress analysis. However, with increasingly large chemical plants, nuclear and
thermal plants, such analysis also comes important. The mechanical design is covered by
ASME codes and TEMA standards
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
5. MECHANICAL DESIGN
Design Specifications:
The design specifications for TEMA class R 610-2438 BEM type heat exchanger is shown
below.
1. Component: Shell Cylinder
[As per ASME SECTION VIII, DIVISION II]
Material selected: SA 516 GR 60
P= Shell side design pressure = 0.735 Mpa
IR=inside radius of shell = 304.8 mm
S=Maximum allowable stress =118MPa [From ASME SECTION II, Part D]
E=Joint efficiency =0.85
Corrosion allowance =3
Required wall thickness of the cylinder, greater of:
Circumferential stress
t = (P*IR / (S*E-0.6*P)) +CAI+CAO+tol = 5.27 mm [UG-27(c)(1)]
Longitudinal stress
t = (P*IR / (2*S*E+0.4*P)) +CAI+CAO+tol = 4.13 mm [UG-27(c)(2)]
Actual wall thickness of cylinder: tnom = 12 mm
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
2. Component: Front and Rear Head Cylinder
[As per ASME SECTION VIII, DIVISION II]
Material selected: SA 516 GR 60
P =1.4715 Mpa
S=Maximum allowable stress= 118MPa [From ASME SECTION II, Part D]
E= 1
Required wall thickness of the cylinder, greater of:
Circumferential stress
t = (P*IR / (S*E-0.6*P)) +CAI+CAO+tol = 6.87 mm [UG-27(c)(1)]
Longitudinal stress
t = (P*IR / (2*S*E+0.4*P)) +CAI+CAO+tol = 4.92 mm [UG-27(c) (2)]
Actual wall thickness of cylinder: tnom = 12 mm
3. Component: Front and Rear Head Cover
ASME Section VIII-1 2004 A06 UG-32 Formed Heads, and Sections,
Pressure on Concave Side
Ellipsoidal Cover Internal Pressure with t/L >= 0.002
Material: SA 516 GR 60
Design pressure P = 0.15 kg/mm2
Design temperature T = 170 C
Radiography = Full Joint efficiency E = 1
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
Design stress S = 12.022 kg/mm2
TEMA min. thickness tm = 9.5 mm
Inside corrosion allowance CAI = 3 mm
Major/minor rat. D/2h = 2.0
Forming tolerance Tol = 0 mm
Corroded min. thk t = 3.85 mm
Equiv.dish radius L = 554 mm
Ratio t/L = 0.01263
Outside diameter OD = 629.6 mm
Corroded diameter ID = 615.6 mm
Proportion factor K = 0.1667*(2+ (D/2h) ^2) = 1.0002
Required wall thickness of the cover:
4. Component: Tubes
[As per ASME SECTION VIII, DIVISION II]
Material selected: SA179
P=1.471 Mpa
OR=25 mm
S = 92.4 Mpa
E= 1
Corrosion allowance=3
Required wall thickness of the cylinder, greater of:
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
Circumferential stress
t = (P*OR / (S*E+0.4*P)) +CAI+CAO+tol = 0.2 mm [APP.1-1(A)]
Longitudinal stress
t = (P*IR / (2*S*E+0.4*P)) +cai+cao+tol = - [UG-27(c) (2)]
Actual wall thickness of cylinder: tnom = 1.25 mm
ASME Section VIII-1 2004 A06 UG-28 Thickness of Shells under External Pressure
Material: SA-179
Design pressure P = 0.075 kg/mm2
Design temperature T = 170 C
Inside corr. allow. CAI = 0 mm
Corrosion allowance CAO = 0 mm
Radiography = Full Material tol.
Tol = 0 mm
Cylinder outside diameter Do = 25 mm
Cylinder length EP L = 2438 mm
Nominal thickness tnom = 1.25 mm (tnom-CAI-CAO-Tol) t = 1.25 mm
L/Do ratio Ldo = 97.52
Do/t Dot = 20.08
(2*S) or (0.9*yield) SE = - Modules of elasticity ME = 19649 kg/mm2
A factor, A = 0.002734 [From ASME SECTION II, Part D, figure G]
B factor CS-1, B = 8.52 [From ASME SECTION II, Part D, figure CS-1]
Max allowed external pressure:
MECHANICAL DESIGN OF SHELL & TUBE HEAT EXCHANGER
Pa = 4*B / (3*Dot) = 0.5653 kg/mm2
Actual external design pressure:
P = 0.075 kg/mm2
t = (P*ID*K / (2*S*E-0.2*P)) +CAI+CAO+tol = 6.85 mm [App. 1-4(c)]
Actual wall thickness of cover: tnom = 10 mm
5. Tube-to-Tubesheet Welds
ASME Section VIII Div.1 2004 A06 UW-20 Tube-To-Tubesheet Welds