Bell & Gossett HT 320B SM Models “OE” Straight Tube, Fixed Tubesheet Heat Exchangers - Manual (Page 3)

d. If none of the above described methods are effective for
the removal of hard scale or coke a mechanical means
may be used. The interior of the tubes may be rodded.
e. The exterior or shell side of the tubes of a fixed tube sheet
heat exchanger can only be cleaned chemically by using a
chemical dissolved in water solution. We suggest that the
user contact the manufacturer of the cleaning chemical for
instructions.
WARNING: Care must be exercised when handling
certain fluids. Follow manufacturers instructions. Use
eye and skin protection. Wear a respirator when required.
4. To clean or inspect inside of tubes, remove channel cover and
rear head. On exchangers having bonnet type heads (without
channel cover), piping must be disconnected and both heads
removed.
5. Do not attempt to clean tubes by blowing steam through indi-
vidual tubes. This overheats the tube and results in tube
expansion strains and sometimes leaking tubes.
6. When replacing heads, use a torque wrench.* Tighten 1 /
2
"
diameter bolts to 40 ft. lbs. and 5 /
8
" diameter bolts to 80 ft. lbs.
If the gasket joint still leaks, tighten in 5 ft. lbs. increments until
leak stops.
* The above torque values apply to well lubricated nut bearing
surfaces.
7. All bolted joints should be tightened uniformly and in a dia-
metrically staggered pattern as illustrated below:
8. Frequently and at regular intervals, observe interior and exte-
rior condition of all tubes and keep them clean. Frequency of
cleaning should be according to scale build-up.
CAUTION: Neglect in keeping all tubes clean may
result in complete stoppage of flow through some
tubes with consequent overheating of these tubes, resulting
in severe expansion strains, leaking tube joints, and damage
to the heat exchanger.
9. Exchangers subject to fouling or scaling should be cleaned
periodically. A light sludge or scale coating on the tube greatly
reduces its effectiveness. Therefore, low-fouling fluids should
be used in the shell side of all heat exchangers with non-
removable tube bundles. A marked increase in pressure drop
and/or reduction in performance usually indicates cleaning is
necessary, especially if the unit has been checked for air or
vapor binding and this has been found not to be the cause.
Since the difficulty of cleaning increases rapidly as the scale
thickens or deposits increase, the interval between cleanings
should not be excessive.
OPERATION
1. When placing a unit in operation, open the vent connections
and start to circulate the cold medium only. Be sure that the
passages in the exchanger are entirely filled with the cold fluid
before closing the vents. The hot medium should then be
introduced gradually until all passages are filled with liquid,
close vents and slowly bring the unit up to temperature.
2. Start operation gradually. Do not admit hot fluid to the unit
suddenly when empty or cold. Do not shock unit with cold fluid
when unit is hot.
CAUTION: Fluids must be gradually introduced to the
unit. Failure to do so can cause damage to the heat
exchanger.
3. In shutting down, flow of hot medium should be shut off first.
If it is necessary to stop circulation of cooling medium the cir-
culation of hot medium should also be stopped by by-passing
or otherwise.
4. Do not operate equipment under conditions in excess of those
specified on nameplate.
WARNING: Failure to operate the heat exchanger
within the design pressure and temperature on the
nameplate may result in damage to the heat exchanger and
potential injury to adjacent personnel.
5. Drain all fluids when shutting down to eliminate possibility of
freezing and corrosion. To guard against water hammer, con-
densate should be drained from steam heaters and similar
apparatus both when starting up and when shutting down.
6. In all installations there should be no pulsation of fluids since
this causes vibration and strain with resulting leaks.
7. All gasketed joints should be checked after starting for leaks
and tightened if necessary.
MAINTENANCE
1. Do not open heads until all pressure is off equipment and the
unit is drained.
2. Do not blow out heat exchangers with air when operating fluids
are of a flammable or otherwise hazardous nature.
WARNING: Proper precautions must be taken (special
clothing, equipment, etc.) to protect personnel from
injury due to escaping fluids.
3. Provide convenient means for frequently cleaning heat
exchangers as suggested below:
a. Circulating hot wash oil or light distillate through tubes or
shell at good velocity will effectually remove sludge or other
similar soft deposits.
b. Soft salt deposits may be washed out by circulating hot
fresh water.
c. Some cleaning compounds on the market, such as
“Oakite” may be used to advantage for removing sludge or
coke, provided hot wash oil or water, as described above,
does not give satisfactory results.
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