Xylem Heat Exchangers - Manual (Page 6)

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Clean exchangers subject to fouling
(scale, sludge deposits, etc.) periodi-
cally, depending on specific conditions.
A light sludge or scale coating on either
side of the tube greatly reduces its
effectiveness. A marked increase
in pressure drop and/or reduction in
performance usually indicates cleaning is
necessary. Since the difficulty of cleaning
increases rapidly as the scale thickens or
deposits increase, the intervals between
cleanings should not be excessive.
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Neglecting to keep tubes clean
may result in random tube plugging.
Con sequent over heating or cooling of
the plugged tubes, as compared to
surrounding tubes, will cause physical
damage and leaking tubes due to differ-
ential thermal expansion of the metals.
3
To clean or inspect the inside of the
tubes, remove only the necessary tube
side channel covers or bonnets, depend-
ing on type of exchanger construction.
4
If the heat exchanger is equipped with
sacrificial anodes or plates, replace these
as required.
5
To clean or inspect the outside of the
tubes, it may be necessary to remove the
tube bundle. (Fixed tubesheet exchanger
bundles are non-removable).
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When removing tube bundles from heat
exchangers for inspection or cleaning,
exercise care to see that they are not
damaged by improper handling.
• The weight of the tube bundle should
not be supported on individual
tubes but should be carried by the
tube sheets, support or baffle plates or
on blocks contoured to the periphery
of the tube bundles.
• Do not handle tube bundles with hooks
or other tools which might damage tubes.
Move tube bundles on cradles or skids.
• To withdraw tube bundles, pass rods
through two or more of the tubes and
take the load on the floating tubesheet.
• Rods should be threaded at both ends,
provided with nuts, and should pass
through a steel bearing plate at each
end of the bundle.
• Insert a soft wood filler board between
the bearing plate and tubesheet face to
prevent damage to the tube ends.
• Screw forged steel eyebolts into both
bearing plates for pulling and lifting.
• As an alternate to the rods, thread a
steel cable through one tube and return
through another tube.
• A hardwood spreader block must be
inserted between the cable and each
tubesheet to prevent damage to the
tube ends.
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If the heat exchanger has been in service
for a considerable length of time without
being removed, it may be necessary to use
a jack on the floating tubesheet to break
the bundle free.
• Use a good-sized steel bearing plate
with a filler board between the
tubesheet face and bearing plate to
protect the tube ends.
8
Lift tube bundles horizontally by means
of a cradle formed by bending a light-
gauge plate or plates into a U-shape.Make
attachments in the legs of the U for lifting.
9
Do not drag bundles, since baffles or
support plates may become easily bent.
Avoid any damage to baffles so that the
heat exchanger will function properly.
10
Some suggested methods of cleaning
either the shell side or tube side are listed
below:
• Circulating hot wash oil or light distil-
late through tube side or shell side will
usually effectively remove sludge or
similar soft deposits.
• Soft salt deposits may be washed out
by circulating hot fresh water.
• Some commercial cleaning compounds
such as “Oakite” or “Dowell” may be
effective in removing more stubborn
deposits. Use in accordance with the
manufacturer’s instructions.
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Some tubes have inserts or longitudinal
fins and can be damaged by cleaning
when mechanical means are employed.
Clean these types of tubes chemically or
consult the nearest ITT Heat Transfer rep-
resentative for the recommended method
of cleaning.
• If the scale is hard and the above meth-
ods are not effective, use a mechanical
means. Neither the inside nor the out-
side of the tube should be hammered
with a metallic tool. If it is necessary to
use scrapers, they should not be sharp
enough to cut the metal of the tubes.
Take extra care
when employing scra-
pers to prevent tube damage.
Do not attempt to clean tubes by
blowing steam through individual tubes.
This overheats the individual tube and
results in severe expansion strains and
leaking tube-to-tubesheet joints.
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Table 2 shows safe loads for steel rods
and eyebolts.
Maintenance
STEEL ROdS STEEL EyEBOLTS
Tube Rod Safe Load Size Safe Load
Size Size Per Rod
5/8” 3/8” 1,000 lbs. 3/4” 4,000 lbs.
3/4” 1/2” 2,000 lbs. 1” 6,000 lbs.
1” or 1-1/4” 10,000 lbs.
larger 5/8” 3,000 lbs. 1 -1/2” 15,000 lbs.
taBle 2
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