Steel Stacks design guide

1. STEEL STACKS DESIGN GUIDE
This guide is prepared by myself Khaled Sayed on November 2015 due to lack of
information about this topic, this is as simple guidance line for steel stack design
based on best practice industrial design, the effort is dedicated this work to my
friend Jin from Sinoma-CDI China who passed on 13th
of November 2015
INTRODUCTION
This standard document covers terminology, loading, materials, structural design,
construction, inspection, maintenance and painting of both self-supporting and some
information about guyed stack form, the sequence are based on the Asme-Sts-1-2010 and
some information are extracted from the Indian standards, in my search this was found to
be a grey area between the mechanical engineer and the civil, very few books and
standers cover this topic.
STACKS
Due to the particular nature of stacks and their susceptibility to failures due to wind
and seismic-induced vibrations, along with corrosion and erosion, the design
process is a complex one. Additionally, recent regulations by the Environmental
Protection Agency concerning emissions have placed a strong emphasis on the
mechanical design of stack.
TYPES OF SUPPORTS
There are many types of stack
1. Free standing
2. Multi flue stacks
3. Base support and braced
4. Base support and guyed
There are also different types of supports vertical and lateral, or braced. Vertical
supports may be above ground. Examples of this kind of support would be a stack
supported on a steel frame within a structural tower or a stack supported on a floor
or on top of a building.
STACKS SUPPORTED BY OTHER STRUCTURES.
Stacks may be laterally supported by other structures such as towers and adjacent buildings. No
credit for shielding provided by the bracing building shall be considered when computing design
wind. The bracing assembly should allow vertical movement due to thermal expansion.

2. Stacks may also be vertically supported by
other structures. For proper analysis,
structural interaction between the stack and
its supporting structure should be
considered.
ADVANTAGES OF VERTICALLY
SUPPORTED AND BRACED STACKS.
Stacks supported above ground usually
have the option of receiving exhaust duct
attachment from below, as well as from the
sides. A braced stack will; require a
smaller foundation as compared to a free;
standing stack with the same height since
some of the wind load will be transferred
to the adjacent bracing: structure. Due to
the same load transfer, a braced stack 'also
has fewer shell stresses as compared to a
free-standing stack, therefore requiring
thinner shell or smaller diameter. For
multiplatform and tall stacks, sometimes
access to the platform can be provided by
catwalks from the adjacent building rather
than a ladder from ground level. In the case of the tower-supported stacks, the tower also has the
advantage of providing an easy and safe framework for staircase and test platforms.
DIMENSION OF STEEL STACK
Dimension of steel stack are cylindrical in shape the high depends on several factors such as gas
velocity, temperature. The chimney should be at least 5 meter taller than the surrounding area of
150 meter radius. The diameter of the stack can be calculated from the given formula however
the diameter shall be so chosen that the velocity will not exceed, under any cases 30m/sec. The
optimum range of velocity may be taken as 15 to 20 m/Sec. The height of chimney depends upon
the description requirement of the flue gases into the atmosphere

3. THERM
Different
include
(a) Betw
(b) At tes
(c) At roo
(d) At sta
(e) Betwe
(f) At we
MATE
Corrosion
1) Carbo
(2) High-
Specifica
(3) Stainl
(4) Stainl
clad steel
CORROS
GUY W
(a) Guy w
considera
(1) Alum
(2) Zinc-
Specifica
(3) Zinc-
(4) Stainl
AS1M A
MAL EXP
tial expansio
een external
st platform, c
of flashing a
ack tops and
een stack sh
eld joints bet
ERIAL CO
n allowance
n steels conf
-strength, low
ations.
less steels co
less chromiu
l conforming
SION ALLOW
WIRES, C
wires and ca
ation should
minum-coated
-coated (galv
ations
-coated (galv
less steel wi
A 368 Specifi
PANSION
on between c
l and interna
catwalk, and
and counter f
d truncated co
ells and exte
tween dissim
ONSIDER
s shall be co
forming to th
w steels con
onforming to
um-nickel ste
g to ASTM A
WANCE
CABLES
ables typicall
d be given to
d steel wire
vanized) stee
vanized) stee
re strand con
ication.
N
components
al shells of a
d ladder attac
flashing
one
ernal insulati
milar metals
RATION
onsidered (ty
he AS1M A
nforming to t
o the AS1M
eel clad plat
A 265 may b
, OR FIT
ly may be of
the initial st
strand confo
el wire strand
el wire rope
nforming to
of a stack sh
dual wall or
chment brac
ion
ypically to .)
36,A 283, o
the AS1M A
A 666 Spec
te conformin
be considere
TINGS
f one or more
tretch of the
orming to the
d conformin
conforming
the
hould be care
r multi-flue s
ckets
) for all type
or A 529 Spe
A 242, A 572
cification.
ng to AS1M
ed for use as
e of the follo
material:
e ASTM A 4
ng to the AS1
to the ASTM
efully studie
stack
es of steel. B
ecifications.
2 alloy, or A
A 264 and n
shell plate.
owing mater
474 Specific
1M A 475 an
M A 603 Spe
ed in areas to
Base plate sha
588
nickel-base a
rials, and
cation
nd A 586
ecification
o
all be
alloy

4. ANCHOR BOLTS, WASHERS, AND NUTS
Anchor bolts may be of threaded bolt and stud stock normally used as connectors, or of round
stock of structural material that may be threaded. They are typically one of the following
specifications:
(1) Carbon steel threaded fasteners conforming to the AS1M A 307 Specification
(2) Carbon steel bolts for general applications conforming to the AS1M A 449 Specification
(3) Alloy steel bolts, studs, and threaded fasteners conforming to the AS1M A 354 Specification
(4) Alloy steel bolts and studs with enhanced impact properties conforming to the AS1M A 687
Specification
(5) Carbon steel conforming to the ASTM A 36 Specification
BOLTS, WASHERS, AND NUTS
(a) Unless otherwise specified, carbon and high strength steel bolts conforming to the ASTM A
307, A 325, or A 449 Specifications will be utilized.
(b) High-strength alloy steel bolts may be required and these should conform to the ASTM A
354 or A 490 Specifications.
WELDING
LININGS
(a) Linings for the interior of steel stacks may be required to provide resistance to corrosive
gases, vapors, or condensates; to provide resistance to heat; and to maintain stack surface
temperatures for the prevent of condensate corrosion.
STRUCTURAL DESIGN
DEAD LOAD
The dead load shall consist of the weight of steel stack, coatings, internal liner, insulation, and
cladding, and all permanent accessories such as ladders, platforms, and gas sampling equipment.
The applied weight of the refractory material shall be used to calculate dead load stresses
LIVE LOAD
The minimum live load of shall be included for platforms and walkways, an estimate of
2.5kN/m2 is a good estimate. This load need not be considered for wind or earthquake
combinations. A horizontal load of 0.5 kN/m acting on the handrail capping piece to the outside or inside
must be assumed for measuring the handrails
WIND LOAD

5. THERMAL LOADS
According to the Indian standards Maximum permissible stresses as obtained shall be corrected
for the most adverse temperature conditions to which the member or part may reasonably be
expected to be exposed by multiplying with the appropriate temperature coefficient Kt given in
below the expected temperature of steel components shall not be allowed to exceed 400°C. For
temperatures exceeding 400°C the effects of temperature creep should be considered to avoid
creep rupture
Temperature,
°C
0-200 250 300 350 400
K t 1.0 0.75 0.67 0.6 0.5
NOTE — Intermediate values shall be linearly Interpolated.
.

6. THE F
To avoid
0.004whe
frequency
thickness
number o
FREQUEN
ovallity of the
ere t is the thic
y, first mode, f
, shall be calc
f convenient z
NCY CAL
e shell t/d mu
ckness and d
for a chimney
culated by div
zones as give
LCULATI
ust be greater
the diameter.
y of varying d
viding the chim
en in
ON
than
The natural
iameter or
mney into a

7. Large vortex-induced vibrations perpendicular to the wind direction may occur when the vortex
shedding frequency coincides with a natural frequency f of the chimney. This occurs at a mean
wind velocity “V” equal to the critical wind velocity “Vcr” determined by
V_Vcr_f · d / St
WIND EXCITED OSCILLATIONS
Chimneys are subject to oscillation due to wind action. This following explains the a very simple
procedures to include the effects of wind excited oscillations as enumerated and suggests
alternative procedures for making an appropriate increase in the design wind loading and
indicates when strengthening or the incorporation of devices for suppressing von Karman type of
oscillations is advisable has been found that chimneys of circular cross section oscillate strongly
across wind than along wind. It is, therefore, reasonable to continue with the current practice
which implies that along wind.

8. NUMBER OF STRESS CHANGES
The number of stress changes must be determined for the respective critical wind speed in
order to verify the fatigue limit. For example, if several critical wind speeds arise in the case
of offset stacks, the respective critical loads with the accompanying number of stress changes
can be combined into a single group. The number of stress changes is proportional to the
service life. The number N of stress changes can be determined according to equation (A.30)
for a service life of 50 years, assuming a wind frequency distribution according to Weibull.
EXISTING SUPPRESSION MECHANISMS
The dynamic control of stacks is a complex problem. Many methods already exist to suppress
vibrations, including helical strakes, shrouds, and variation of structural parameters such as wall
thickness and diameter. Figure 1-1 shows various suppression devices which are designed to
alter the flow field around the cylinder to prevent periodic vortex shedding.
HELICAL STRAKES.
A three-start set of curved-plate helical strakes 120 deg apart on the stack circumference may
be attached to the outer surface of the stack with the strake plate approximately perpendicular to
the stack surface at all points. The pitch of the helix should be five times the aerodynamic
diameter and the strake should project ~o diam. from the aerodynamic diameter. Strakes
of adequate structural thickness should be provided on the top ~ of the stack height. Each strake
is to be aerodynamically continuous except at specific locations where cuts may be necessary to
clear ring stiffeners or other attachments. The maximum gap allowed between the stack shell and
helical strake shall be equal to 0.1 x strake width. The presence of strakes significantly increases
the drag forces and a drag force coefficient of 1.4 used in conjunction with the outside diameter
(including insulation and lagging) of the stack is recommended. Segments of flat vertical strakes
at helical locations are not acceptable methods for disrupting vortices.

9. ALLOWABLE STRESSES
An increase in allowable shell stresses due to wind or seismic loads shall not be allowed, the
following equation must be satisfied this means the shell must be thin.
ALLOWABLE DEFLECTION
The maximum deflection at the top of the steel chimney produced by the wind load without
taking into account the dynamic factors, calculated as acting on the circular cross section shall
not be greater than h/200. Where ‘h’ is the unsupported height of the chimney, while for the EN
1993-3-2 it provides h/50 which seems too large displacement.
CASE 1 LONGITUDINAL COMPRESSION.
The longitudinal compressive stress in cylindrical stacks and liners (P / A) shall not exceed the
allowable limit, Sci
CASE 2 LONGITUDINAL COMPRESSION AND BENDING
The combined longitudinal compressive and bending stress in cylindrical stacks and liners shall
not exceed the allowable stress, Sbl' the details are as shown in the example below

10. The follo
used a qu
CIRCUM
.The size
(a) T
d
CONSTR
Consider
wind and
CIRCUM
The circu
spaced at
MINIMU
owing table i
uick guidanc
MFERENTIAL
e of stiffener
The stiffener
etermined b
RUCTION LO
ration shall b
d seismic loa
MFERENTIAL
umferential
t distance, ls
UM PLATE T
is a guidance
ce
L COMPRES
s shall satisf
and plate se
by the follow
OADS.
be given in th
ads that may
STRESS.
stress in th
s, shall be de
THICKNESS
e for the stre
SSION IN ST
fy the follow
ection shall h
wing equation
he design fo
reasonably
he shell due t
etermined us
ess according
TIFFENERS
wing three req
have a mome
n:
r applied con
be expected
to external w
ing
g to the IS65
quirements
ent of inertia
nstruction lo
d to occur du
wind pressur
533 for fy 25
a equal to or
oads in comb
uring constru
e pz between
50Mpa can b
greater than
bination with
uction
n stiffeners
be
n that
h

11. ACCORDING TO THE ASME
WHILE IN THE INDIAN STANDARDS
Thickness of the structural chimney shell in single or multiple shell constructions, shall be the
calculated thickness obtained from stress and deflection considerations plus the corrosion
allowance, but shall not be less than 6.0 mm nor less than 1/500 of the outside diameter of the
chimney at the considered height in my opinion these values seems more practical also consider
that to avoid ovality it should be 1/250.
FATIGUE
Aerodynamic methods disturb the formation of vortices on the sides of the stack and limit the
source of vibration Helical Strakes. A three-start set of curved-plate helical strakes 120 deg apart
on the stack circumference may be attached to the outer surface of the stack with the
strake plate approximately perpendicular to the stack surface at all points. The pitch of the helix
should be five times the aerodynamic diameter and the strake should project ~o diam. from the
aerodynamic diameter. Strakes of adequate structural thickness should be provided on
the top ~ of the stack height. Each strake is to be aerodynamically
continuous except at specific locations where cuts may be necessary to clear ring stiffeners or
other attachments. The maximum gap allowed between the stack shell and helical strake shall be
equal to 0.1 x strake
width.
OPENINGS
Openings have to be strengthened to prevent local reduction of Strength
Resistance against fatigue and instability The strength of the cross-section with openings is the
same as the strength of an undisturbed section if the section modulus is the same. This equality
of section moduli is sufficient to fulfill the first condition of strength Across section with an
opening is sensitive to the effects of buckling.
This is due to the stiffness of the weakened cross-section being reduced by the possibility of the
shell bending in or out at the edges of the opening. To prevent this the reinforcement stiffeners

12. have to be placed normal to the shell {see Figures C5.2 & C5.3) and concentrated along the edge
of the opening However, sudden ending of of the reinforcement above and below the opening
can cause stress concentrations. These can treble stresses locally and lead to fatigue damage such
as local cracks. To avoid this, in the case of openings with width greater than 40% of the
chimney diameter locally, the vertical stiffeners should connect at each end with a horizontal
stiffener extending around the full circumference (see fig. C5.2).When the width of opening is
less than 40% of the chimney’s diameter locally, it is not necessary to provide a horizontal
stiffener extending around the full circumference and a more local arrangement may be used (see
fig.. C5.3). Vertical reinforcement should be continued above and below the opening to a point
where the added stress is unimportant. The code deems that continuing the reinforcement beyond
horizontal stiffeners above and below the opening a distance at least 0.5 times the width of the
opening will suffice. If the vertical height of the opening is more than twice its horizontal width,
a stability check is needed. Guidance on such checks is given in the chapter on bending of plates
under lateral loads in “Plates and shells”, by Timoshenko. When the duty of the chimney
requires flue gas inlets whose width exceeds two-thirds of the structural shell’s diameter, a
possible solution would be to provide a large number of small circular openings, giving a total
area equivalent to that required. Reinforcement could then be threaded between the small holes
and around the whole group, as require
COMMON PROBLEMS
a) Atmospheric corrosion and weathering on exterior surface
(b) Corrosion due to acid condensation in flue gases on internal surfaces
(c) Fly ash or particulate collection at the base, false bottom, or roof cap of the stack
(d) Moisture condensate at the base of the stack
(e) Acid/moisture infiltration of insulation
(f) Deformation due to thermal or other loading
(g) Corrosion of anchor bolts
(h) Fatigue cracks
(i) Loss or deterioration of insulation, coating, or linings
(j) Loosening of anchor bolts.

13. INSPECTION
For early detection of the commonly occurring problems,
it is recommended that the stack be inspected
periodically to enable the user of the stack to take appropriate
measures to counteract such problems.
FOUNDATION DESIGN
The foundation for stacks shall be
designed for all cases of loading, any
foundation movement or rotation will
cause partial or total collapse so
foundation must be carefully designed,
the foundation must be of size and shape
that the load on the soil below will not
exceed the maximum load which it will
fully support also no allowance for
tension by any means below foundation
since earth have no strength whatever in
tension. The connection of the shell to
the concrete foundation or to the
supporting structure should
resist the overturning moment, normal
force and shear force developed at the shell base and transmitted to
the foundation
BASE PLATE DESIGN
Either a full raft or an annular raft
can be provided. The latter .has the
, advantage that because of a higher
uniform soil pressure under dead
loads, it minimizes possible gradual
tilting of a foundation laid on
cohesive soil when the structure is
subjected to lateral loads from a
predominant wind direction

14. REFERENCES
 ASME STS COMMITTEE “Steel Stacks - Asme-Sts-1-2006”
 “Foundation design hand book” Hydrocarbon processing. Gulf publishing company 1968
 “German standards DIN4133”
 “BSI (2011) BS EN 13084-1:2007” - Free-standing industrial chimneys - Part 1: General
requirements.