2. GOOD OPERATING PRACTICES
• Preparation for performing work on heat
exchangers involves two major elements
1. Choosing the proper tools and equipment
2. Observing the appropriate safety precautions
Choosing Tools and Equipment
The tools needed to perform maintenance on
heat exchangers are divided into 2 categories
1. Working Tools
2. Safety Equipment
• The first category includes hand tools and power tools
needed to do a maintenance job. The working tools
may include wrenches, impact tools , cleaning devices
such as high pressure water
guns, scrapers, brushes, squeegees
etc., shovels, towels, buckets and large containers.
• The equipment needed to seal or plug leaking tubes
may include plugs, screw drivers, wrenches, hammers
, welding equipment, and equipment to roll tube ends
into tube sheets.
• The second category includes the equipment required
to insure personal safety.
4. • For work on larger components , where work
must be done in a wet environment or in a
confined space, low voltage safety lighting is
needed. If high pressure water guns will be
used , or if a water box must be entered, rain
suits, boots, and goggles or safety glasses are
5. SAFETY PRECAUTIONS
• Work should be never done on a heat
exchanger until the system that includes the
heat exchanger is shut down and isolated, and
equipment such as valves , motors , pumps
, switchgear , and controls are tagged out so
that they will not be operated while
maintenance is going on.
• The heat exchanger should be drained and
vented before it is opened
6. • The nature of some heat exchangers necessitates
additional safety precautions .Work on large heat
exchangers, for example ,, often requires working in
confined work spaces. In such situations, air quality
checks are performed to make sure that there is
enough oxygen to breathe and that no dangerous gases
• The two man rule is always followed in confined areas
so that help is available if a worker encounters trouble
:One worker always stays outside of the confined
workspace and keeps steady contact with the worker
on the inside.
7. • Additional ventilation may be necessary in some areas
for two reasons
1. To remove dangerous gases and provide fresh air with
enough oxygen to breathe
2. To cool a confined space if work is being done on hot
equipment, such as a condenser being run under a
• The safety precautions associated with the rigging of
large , heavy parts, such as the heads of large heaters
as illustrated in figure-2 must be carefully observed
when large components are moved.
8. • The tools and equipment needed to perform
maintenance on heat exchangers can be
divided into two general categories.
• Important practices to be exercised by the
1. Always make sure that the heat exchanger
has been vented before start-up.Vapor is not
a good conductor of heat and will therefore
reduce its efficiency.
9. 2. Never increase the pressure or temperature
quickly when starting-up. This can cause
3. Report any mechanical rattling noises to your
supervisor. Baffles can come loose and wear
away the tubes. Moving baffles will rattle.
4. Check the inlet and outlet temperatures
regularly. They will indicate the efficiency of the
exchanger, its efficiency can be calculated by the
process engineer. However if temperatures
change check that:
10. • cooling fluid flow is correct and that the
temperature is at or below design
• The hot fluid flow is correct and that the inlet
temperature is at or below design
5. If these are not at fault the exchanger may be
fouled . This is a term used when a layer of solids
is deposited on the tubes. The solids reduce the
amount of heat transferred because they are
poor conductors of heat. If fouling is suspected
report this to the supervisor.
11. 6. Always use minimum number of air fans for air
duty. It is often possible in the winter to shut off
a fan yet still obtain the required amount of heat
exchange. This will reduce the energy costs.
7. Regularly check the fins on a finned fan
exchanger as they can become covered in dirt.
This reduces the amount of heat transferred and
should be reported if it occurs.
8. The cold fluid valve outlet may be opened slowly
until the cold fluid is passing through the
12. 9. Start opening the hot fluid inlet valve slowly
10. Both valves, the cold fluid outlet valve and
the hot fluid inlet valve should be opened
slowly until fully open.
13. THE START-UP AND SHUT-DOWN OF
• Heat exchangers must be warmed up slowly
and cooled off slowly. This is particularly
important when operating temperatures are
very high or very low.
• The sudden application of extreme
temperatures will cause great inequalities of
tube and or shell expansion. This may cause
leak or other damage
14. PROCEDURE TO TAKE HEAT
EXCHANGER OUT OF SERVICE
1. The hot fluid must be shut off before the cold fluid.
This should be done slowly to allow the exchanger to
cool down. The cold fluid must not be shut off first.
Otherwise, the heat from the hot side will cause the
cold fluid to increase in temperature and as there is
no place for the expansion , the pressure would build
up and cause exchanger ruptures.
2. After the hot fluid has been shut off, both on the inlet
and outlet of the exchanger and the temperature has
cooled to that of the cold fluid, then the cold fluid can
be shut off on both inlet and outlet valves.
15. 3. Both shell and tube side should now be
pumped out to slop or drain down.
4. Both inlet and outlet lines should be blanked
off for safety.
5. If the exchanger is in sour oil service or any
iron sulfide scale is expected, the exchanger
should be washed before opening to the
16. PROCEDURE TO PLACE A HEAT
EXCHANGER IN SERVICE
1. Check the exchanger carefully to ensure that all
plugs have been replaced and that all pipe work
is ready for the exchanger to be placed in
2. All valves should be in shut position.
3. Open hot and cold fluid vent valves.
4. Crack open cold fluid inlet valve- vent all air
when liquid is full. Close cold fluid vent valve.
5. Crack open hot fluid inlet valve and vent all the
air, then close hot fluid vent valve. At this
stage, the exchange is liquid full of both hot and
cold flowing fluids-open cold fluid inlet valve
and hot fluid outlet valves fully.
17. PREVENTIVE MAINTENANCE OF HEAT
• Whenever the plant’s systems are shut
down, or whenever a system’s load is
reduced, it is possible to schedule inspection
and maintenance routines to ensure the
proper operation of the major components in
the system. In many systems, two heat
exchangers are installed in parallel with each
• Inspection and cleaning allow early detection
of developing problems before they
contribute to problems throughout the
18. • Preventive maintenance cannot catch every
failure before it occurs.
• Troubleshooting is a responsibility shared in three
1. By operators who monitor the plant’s operation
2. By lab people who keep checks on the
environmental and plant chemistry and
3. By maintenance personnel who are responsible
for keeping individual components of plant
system in proper order.
19. • Operating Personnel- can tell if a system, or some part
of a system, is not functioning properly by checking
gauges and recorders and observing alarms that warn
of malfunctions. For example , an operator might
notice a change in the temperature and flow of cooling
water through a condenser.
• If the flow of cooling water must be increased to keep
the flow and temperature of the condensate within the
normal operating ranges, this is an indication of
probable blockage in the condensers water side from
contamination that has bypassed filter screens.
20. • Lab Personnel- check samples of system fluids for signs
of contamination . Oil in the feed water , for instance
may lead the lab to suspect a leak in a fuel oil heater.
• Personnel responsible for maintenance- perform
simple checks during the daily routine of other duties.
Bearing temperature is easily checked on components
that require cooling of lubricating fluids. Any rise
beyond the normal temperatures may indicate failure
of a cooler to fulfill its job. Such impurities can cause
failure in critical machine components.
21. • Reporting any problems that are found to a
supervisor ensures that proper steps are taken
to prevent potential problems from affecting
the system as a whole.
• These two checks – temperature and sight
glass readings are examples of early warnings
that can indicate potential problems before
22. CATEGORIES OF HEAT EXCHANGER
• Maintenance problems associated with heat
exchangers can be grouped into two basic
1. Blockage and
• The causes of specific maintenance problems
also depend on the fluids involved and the
temperatures and pressures at which the two
• Blockage is caused by impurities in the fluids
passing through the unit.
• It is a gradual build up of impurities on heat
exchanger tube walls.
• Any blockage causes a loss in the efficiency of the
• Impurities range from chemical impurities that
can cause corrosion deposits to build up, to silt
and mud and marine life that may accumulate in
• Mud and marine life such as plants, fish and eels
may build up so heavily that the flow through the
tube is lessened or stopped
24. • Blockage can also cause problems in direct
contact heat exchangers. Gases trapped in the
water can be corrosive, and chemicals can
cause a build up of deposits in the inlet and
25. METHODS OF REMOVING BLOCKAGE
FROM HEAT EXCHANGER
1. CLEANING OUT BLOCKAGE
2. PLUGGING LEAKS
• The two basic categories of heat exchanger
maintenance problems are blockage and leakage.
• Blockage is accumulation of foreign
material, impurities or buildup from chemical
action within a heat exchanger that interferes with
• Leakage is generally internal leakage- one fluid
leaking into the other, external leakage- leakage of
liquid out of the heat exchanger(rare problem)
26. • Blockage can interfere with heat exchanger
operation in two ways :
1. As an accumulation on a heat exchanger’s heat
transfer surfaces, blockage can prevent efficient
heat transfer and
2. As an accumulation that blocks the flow paths of
the fluids in heat exchanger, causing reduced
• Blockage is a common problem with both
surface heat exchangers and direct contact heat
• Leakage problems are generally associated only
with surface heat exchangers- condensers and
shell and tube heat exchangers.
27. Removing Blockage
• The procedure that is used to clean a particular
heat exchanger depends on three factors:
1. The type of heat exchanger
2. The physical size of heat exchanger
3. The types of fluids flowing through the heat
• The main cause of blockage in a direct contact
heat exchanger is scale formation.
• Corrosion problems in a direct contact heat
exchangers come from some of the non-
condensable gases that are released during heat
28. • The method used for cleaning surface heat exchanger
depends on the physical size of the heat exchanger and
the type of fluids that flow through it.
• If river water is used for cooling, blockage may be
caused by accumulation of mud, water plants and
• The method of cleaning a particular surface heat
exchanger also depends on whether the tube side, the
shell side or both sides must be cleaned. Water boxes
and tube sheets are generally cleaned by brushing or
picking and scraping.
• For deposits that are harder to remove, rubber
squeegees, wire brushes, or metal scrapers can be shot
through the tubes of straight –tube heat exchangers.
• Leakage in a heat exchanger is generally internal
leakage, external leakage is rarely a problem.
• For example any impurities in the feed water
going to a boiler can quickly lead to failure of
boiler tubes. In a lubricating or hydraulic
system, cooling water in oil can cause failure of
• Leakage is usually caused by failure of the metals
due to 1. erosion from the flow of fluids passing
by or 2. cracking caused by corrosion and
30. Leakage caused by erosion is affected by several factors:
2. Temperature and pressure
3. Type of fluid involved
• Erosion is wearing away of a material caused by the
physical(not chemical) action of another substance.
• By design, the flow of fluids in a surface heat exchanger is
directed in some way to minimize erosion of tubes and tube
• Temperature and pressure affect the rate at which metal
• The type of fluid passing through the heat exchanger also
affects the rate of erosion of metal parts, because different
fluids have different physical properties.
31. • The second cause of leakage in a heat
exchanger is corrosion. Corrosion is a chemical
‘eating away ‘ of the materials used in a heat
exchanger caused by impurities in the fluids.
Using sacrificial Anodes:
• Heat exchangers that use non-purified water
for cooling are particularly subjected to
• The zinc plates used in this way are called
sacrificial anodes or sacrificial zincs, because
they are gradually eaten away by the corrosive
action of chemicals.
32. Stopping leaks
• Internal leakage in a surface heat exchanger either a
condenser or a shell and tube heat exchanger –
generally occurs in one of two places:
1. Leaks develop in the tubes or
2. Leakage occurs through the joints where the tubes
pass through the tube sheets.
3. Leakage within tubes is usually stopped by plugging
both ends of leaking tubes so that there is no flow
4. Leakage where the tubes pass through the tube
sheets can be stopped by welding the affected tubes
to the tube sheet.
33. • Tubes are typically set into tube sheets in one of the
two ways: 1. Rolling 2. Welding
• Rolling tubes is a method of expanding the tubes
into corrugated holes in the tube sheets.
• Welding is one when
temperature, pressure, vibration, or a combination
of these factors make rolling the tubes insufficient
Sacrificial Anodes – are large pieces of zinc that are
used in some heat exchangers to minimize
corrosion of the metals that make up the heat
exchanger. The zinc plates are more susceptible to
corrosion than heat exchanger metals are called
sacrificial anodes as they are gradually eaten away
34. LOCATING AND SEALING LEAKS IN
LARGE HEAT EXCHANGERS
1. VACUUM TEST
2. DYE TEST
• Vacuum test is a common check on condensers
and other heat exchangers that run under a
vacuum. With the component’s water boxes
open to the atmosphere, a vacuum is drawn on
the shell side. Pumps are used to evacuate the
air in the shell, however if a condenser is being
run at reduced load with one half open, a
vacuum already exists on the steam(shell) side.
35. • To make the test, material such as kitchen plastic wrap
is placed over both tube sheets so that it covers the
openings of the tubes at both ends. The tube sheets
are wetted first so that the plastic wrap clings to the
surfaces. Sheets of the wrap are overlapped and
pressed tightly to make sure that the sheets adhere to
• Soap suds and foam can also be used for this type of
leak testing. Suds or light foam is brushed over the
• The dye test is used on condensers as well as on other
types of surface heat exchangers. The shell side of the
component is flooded with water that contains a
fluorescent dye. Leaks in the tubes or where the tubes
pass through the tube sheets will become evident
when exposed to black light from a ultraviolet lamp
36. Sealing leaks in heat exchangers
• The two methods used are 1. Plugging and 2.
• Plugs for leaking tubes are available in several types.
The type most commonly used is a tapered plug, which
is shaped like a cork or rubber stopper for a bottle or
jar and is used in a similar fashion.
• Some metal plugs are threaded so that they can be
screwed into the ends of leaking tubes.
• There are also two general styles of expandable plugs.
One is a rubber doughnut sandwiched between two
large washers with a bolt through the middle. When
the bolt is tightened, the rubber expands to make a
tight seal in the tube end.
37. • The second kind is an expandable metal plug-
a tapered plug of soft metal with a hard metal
pin in the center.
• A fourth type is an explosive plug, which is
used in heat exchangers run under extremes
of temperature and pressure, such as steam
generators in nuclear power plants. This type
of plug contains an explosive charge that is
detonated to expand the plug into the tube
38. TUBE REPLACEMENT
• When heat exchanger tubes are replaced, the
old tubes must be cut away carefully to avoid
damage to the tube sheet. After the tube has
been cut loose, it is carefully withdrawn and a
new tube is inserted to replace it. Tubes may
be cut away using several tools such as
1. Safety ripping chisel
2. Round nose gouge or
3. General purpose cutter
39. CLEANING LARGE HEAT EXCHANGERS
• Accumulation of mud, water plants, and marine
life in the water boxes and tube sof heat
exchangers that use river water as a source of
• Tube side cleaning- the method used to clean the
tube side of a large heat exchanger depend on
several factors including the following:
1. The amount of work space available- cleaning
must often be done in confined areas
2. The tube configuration- U tubes in a shell- and –
tube heat exchanger may limit the choice of
40. 3. The kind and amount of deposits – different
approaches are required for cleaning heavy
accumulations of mud and debris than removing
light scale buildup.
• Cleaning out the tube side of a component such
as a condenser typically includes the following
1. Ranking, scraping, or picking accumulated
blockage off the tube sheets.
2. Shoveling or troweling accumulations out of
3. Shooting the tubes with a high pressure water
gun to clear them of built up slime, silt and
crushed deposits, rakes, scrapers and picks are
typically used to remove heavy accumulations
from the tube sheets
41. • After the blockage is removed from the tube
sheets , the next step is usually shoveling or
troweling any heavy accumulation out of water
• A variety of implements can be forced through
the tubes by the water from the water from the
gun; the choice of implements depends on what
has to be removed. These implements are often
referred to as “bullets”, they may be hard rubber
squeegees that just fit the insides of the
tubes, wire brushes with rubber squeegees that
just fit insides of the tubes, wire brushes with
rubber squeegees on each end , or meatl-
42. Shell side cleaning
• Shell side cleaning is done only on shell and tube heat
• Rigging for tube bundle removal involves separating
the large flanged connection between the shell and the
• Solvents may be used to remove oil from the tube
• Automatic cleaning methods
• Automatic cleaning systems operate while heat
exchangers are in service to reduce the accumulation
of deposits. These systems can be divided into two
1. Mechanical systems and
2. Chemical systems
43. • In one mechanical system sponge balls with
rough surfaces are circulated through the tubes in
a condenser. These balls remove deposits from
inside the tubes. The balls are caught by a screen
trap and pumped back to the inlet for
• Automatic chlorination is one type of chemical
cleaning system chlorine is periodically
introduced into the incoming water to kill algae
and thus prevent the buildup of algae growth on
44. MAINTENANCE OF SMALLER HEAT
• Five major steps are involved in servicing small
heat exchangers in the shop
1. Testing for leaks
3. Cleaning , inspection and repair
4. Reassembly and
5. Final testing
45. MAINTENANCE PROCEDURES
• Testing of leaks is usually done prior to
disassembly, because it is helpful to identify
what needs to be done to the component and
what parts will be necessary for the job.
• Leak testing is accomplished by pressurizing
the shell in one of two ways. One method
illustrated in fig 10 is to plug the outlet and
feed compressed air at moderate pressure
into the inlet.
46. • Another means of testing for leaks is to fill the
tube side with water and plug the outlet. The
application of pressure from the inlet water
source makes it possible to look for leakage into
the shell. Any water found in the shell side is an
indication of leakage. Care must be taken to avoid
exceeding the maximum rated pressure of the
component being tested.
• Rodding – a method of cleaning tubes in a
smaller heat exchanger is as shown in figure.
47. • When the heat exchanger has been
successfully tested, it can be returned to
service or put into stock for future use. If the
component fails to pass this final test, it will
be necessary to look further for the source of
leakage, this inspection should include the
tubes, the tube bundle, and gasket