B.4.4 - STD Spec For Steel Stacks
B.4.4 - STD Spec For Steel Stacks
B.4.4 - STD Spec For Steel Stacks
TITLE:
DOCUMENT NO : 44LK-5100-00-V.02-0211-A4
Rev
No.
Issue Date
Pages
09.09.2008
Description
Prepared
By
Checked
By
Approved
By
SNK
CR
HSC
-1-
Jacobs
HPCL, MUMBAI
44LK-5100
STEEL STACKS
CONTENTS
1.0
GENERAL
2.0
3.0
TECHNICAL REQUIREMENTS
4.0
5.0
Page 2 of 6
Jacobs
HPCL, MUMBAI
Page 3 of 6
44LK-5100
STEEL STACKS
1.0
GENERAL
Steel Chimneys are required in process, power, refineries, furnaces, boilers, etc. to let
out flue gases into the atmosphere. The diameter and their heights are decided by
functional requirements and environmental considerations. These stacks could be
ground supported or installed at higher elevations like boiler mounted depending upon
how the flue gases are passed through them. Depending upon their usage, these
stacks could be unlined or lined with a suitable refractory system. The stacks are
structurally tall hence important aspects is the design of self-supporting stacks are wind
/seismic loading, wind excited oscillations, limitations of deflection. Very tall stack could
be designed supported by superimposed structure around the stack covering the entire
height like in flare stacks. Stack design using guy wire ropes are not to be considered.
Apart from following various codal requirements for design, certain statutory
requirements like provincial building by laws and the civil aviation requirements
pertaining to such structures are also to be taken care during design. Jacobs shall
review the design documents produced by the vendor.
2.0
IS 6533(Part 2)
IS 6
IS 8
IS 2042
IS 1363
IS 1364
IS 1893/site data
IS 2062:1999
BS 4076:1978
moderate
heat
duty fire
clay
Jacobs
HPCL, MUMBAI
44LK-5100
Page 4 of 6
STEEL STACKS
3.0
TECHNICAL REQUIREMENTS
3.1
General
The basic dimensions o the chimney (stack), namely clear diameter, height , etc. are
decided on consideration of temperature, composition of flue gases, Adjacent structures,
Pollution control, draft requirements However, certain recommended proportion should
be maintained for the strength and its stability.
Proportions of the basis dimensions of a self supporting chimney shall conform to the
following:
3.2
(i)
Minimum height of flare be equal to one third the height of the chimney.
(ii)
(iii)
Minimum outside diameter of flared chimney at base be equal to 1.6 times the
outside diameter of shell at top.
Minimum Thickness
The minimum thickness of stack shall be 6.0mm but shall not be less than calculated as
per following formula:
Wall Thickness = Dia. + 2.5 + Corrosion allowance
1000
3.3
Corrosion Allowance
The total allowance of corrosion shall be sum of the external and internal allowance and
shall be selected in line with IS 6533 recommendation unless specified otherwise.
3.4
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 a acting on the circular cross
section shall not be greater than h/200 where h is the unsupported height of the
chimney. Effect of cage ladder, platform and other pretensions shall be taken care
during calculation of wind deflection.
3.5
3.5.1
Allowable stresses is axial tension, sheer and bearing shall be as specified in IS 800. To
control buckling, the compressive stresses caused by the extreme fibre stresses due to
bending and direct load for the following load combinations shall be within safe limits
after considering temperature effects and allowance for large opening in shell:
Jacobs
HPCL, MUMBAI
44LK-5100
Page 5 of 6
STEEL STACKS
3.5.3
For design of chimney and its foundation, any of the following load combinations which
produce maximum forces and effects and consequently maximum stresses shall be
chosen.
I.
II.
III.
Dead load + load due to lining + imposed load on service platform + wind load or
IV.
In case of self supporting chimney, checking for resonance shall be carried out if the
critical velocity for as determined from Annexure A of IS 6533 Part 2.
0.5 to 0.8 times the design wind velocity for lined chimney
0.33 to 0.8 time the design wind velocity for unlined chimney.
For lined chimneys, checking for resonance shall be carried out for both the cases, that
is with or without lining. Chimney which have high diameter/thickness ratio may be
subjected to wind generated ovalling oscillating due to circumferentially varying and
fluctuating pressure. There shall be suitably taken care as per IS 6533 like providing
strake vanes, providing circumferential stiffeners for chimneys having high diameter to
thickness to avoid ovalling oscillations due to circumferentially varying and fluctuating
pressure etc. Design forces, bending moments and for first mode of oscillation
deflection shall be calculated as per IS 6533 Part 2.
3.6
Supporting
The chimney shall be structurally stable on its foundation. Allowable stress for
foundation bolts, its base plate, gussets, stool etc. shall be as per IS 800.
3.7
Chimney Top
The chimney top shall be provided with a rain hood at the top. This hood shall allow free
passage to the flue gases but save the top opening from rain water entering into it.
3.8
Jacobs
HPCL, MUMBAI
44LK-5100
Page 6 of 6
STEEL STACKS
4.0
5.0