POWER November 2011 - 45

CONDENSER LIFE CYCLE
6. Cross section of a tube plug. Source: Conco Systems Inc.
Positive gripping cleats
tural integrity is not threatened. The epoxy coating
is engineered to withstand physical abuse,
impact, and other physical/chemical stresses
associated with the operation of a cooling water
system. Figure 8 shows this thick cladding on a
tubesheet after 15 years in service.
Tube-end ID Coating. Copper-based tube
alloys can be subject to selective erosion within
the first several tube diameters of the inlet tube
end. Other tube materials can deteriorate because
of galvanic or microbiological issues.
Inlet-end erosion is due to turbulence presTorque
as recommended
Durable DuPont chloroprene cylinder
7. Galvanic attack at point of
thin-film coating failure. Courtesy:
Plastocor Inc.
8. Thick epoxy tubesheet cladding
after 15 years service. Courtesy: Plastocor
Inc.
ent at the initial section of tube before laminar
flow is established. The degree of erosion depends
on the nature and amount of entrained
solids in the cooling water, the type of tube alloy
and its susceptibility to corrosion, water velocities,
micro/macrofouling of tube surfaces,
and other design/operating factors. Outlet-end
erosion may also occur due to outlet flow-induced
turbulences or cavitation.
The tube-end IDs can be selectively coated
to protect this specific area of the tube. In this
case, three coats of alternating colors are applied
to provide complete protection. The epoxy
coating can be installed to any depth and
is applied in conjunction with the tubesheet
coating. Each coat is approximately 2 to 3
mils thick and is applied just past the previous
coat. This three-stage method creates a
feathered termination, eliminating the chance
of step-erosion at the end of the coating.
This method of application also can bridge
9. Tube-end ID coating with tubesheet epoxy coating. Source: Plastocor Inc.
Note: Plastocor
tube-end coating
can seal small
holes
Plastocor cladding
Deteriorated tube
First coat (white)
Second coat (grey)
Third coat (red)
Tubesheet
small perforations of the tube wall, thereby
repairing the tube and speeding up its return
to service. The joining of the tubesheet coating
with the inlet coating creates a uniform
and smooth transition from waterbox chamber
to tube interior. This reduces fouling and
turbulence, which raises flow efficiencies.
The tube ID is not significantly reduced,
which permits the unrestricted use of ECT
and most tube-cleaning methods.
Figure 9 shows a cross-section scheThree
coats are feathered for
a turbulent-free termination
Tubesheet
bronze tubesheet with titanium tubes in salt
water where a thin tubesheet coating had spot
failures. Galvanic corrosion caused a rapid
loss of tube joint integrity at that spot.
The tubesheet and tubes are completely encapsulated
and locked in by a thick, flat, layer
of 180 ±40 mil epoxy. This process fashions a
radial-flared, high-gloss inlet and outlet tube
opening, serving to dramatically reduce flow
resistance and fouling. The flat and smooth
November 2011 | POWER
surface allows for easier leak detection and
reduces sponge ball wear if an online tubecleaning
system is used. The substantial nature
of the system adds strength and integrity
to the tube-to-tubesheet joint. Tube push-out
strength is increased by 2,000 pounds by the
adhesive value of the coating system.
Tubesheet coating can be applied to any
tube-to-tubesheet configuration experiencing
any level of deterioration, provided that strucwww.powermag.com
matic
of the tube-end ID coating along with
the tubesheet coating. If the tube ends are
thinned to the point where structural integrity
is threatened, then a metallic insert can be incorporated
into the system. Here, the insert is
precisely sized and glued in place.
Waterboxes, Piping, and Tunnels. Condenser
waterboxes and circulating water piping/tunnels
are also routinely coated. In these
applications, the coating system usually consists
of an epoxy liner installed from 40 to 125
mils in thickness. The thicker applications are
used when corroded surfaces are coated or
where a " bullet proof " lining is required.
Exterior Flange Sealing. Air in-leakage
into the steam side of condensers has farreaching
consequences for plant efficiency
and equipment life. High levels of dissolved
O2
45
elevate corrosion in the feedwater heater
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POWER November 2011

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