The Aftermarket: Applications
Repairs Made Stronger
Thomas Buckley, Henkel Corporation
How the proactive use of polymer composite materials on
pumps saves thousands of dollars and weeks of downtime.
M
ost industrial centrifugal pumps
carry a significant capital equipment
value. Maintaining them to run
close to their best efficiency point (BEP) saves
in downtime, repair costs, and overall power
consumption. Proactive maintenance extends
the useful life of a pump, reduces breakdowns,
increases longevity and reliability, and extends
the mean time between failure.
When a pump operates outside its BEP,
flow separation and turbulence occur. A
common result of turbulence is cavitation,
which can cause damage such as erosion and
vibration. Corrosion and chemical attack also
impact pump performance and longevity. All of
these factors can cause a pump to fail prematurely and depreciate at an accelerated rate.
While damaged pump components can
be replaced, the capital costs associated with
replacement and spare parts inventory can be
cost prohibitive. The most cost effective and
realistic solution is protecting and/or renewing damaged pump
surfaces.
Damage to pump surfaces is highly predictable, occurring
most often on specific parts such as casings and impellers. To
rebuild damaged equipment and provide ongoing protection,
maintenance professionals are turning to polymer composite
materials, a new category of aftermarket products that offer
durability rivaling that of metal coatings.
Three main categories of polymer composite materials for
equipment repair are 1) metal repair materials, 2) wear resistant coatings, and 3) chemically resistant coatings. Often used
together to correct operating problems related to wear, these
materials make repairing pumps significantly more cost effective than replacement.
Metal Repair Materials
Metal repair materials provide physical performance properties
similar to or better than those of the base metal undergoing
repair.
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April 2007
Figure 1. Severely pitted and gouged pump casing.
These polymer composites consist of an epoxy matrix
combined with steel, aluminum, or ferro-silicon powder fillers
that allow the material to mimic the physical properties of the
metal including color, strength, rate of thermal expansion, and
ability to be machined.
Metal repair materials are ideal for pump casings and
impellers that experience tremendous wear from corrosion, erosion, cavitation, sliding abrasion, and mechanical damage. For
example, during a recent scheduled pump teardown, maintenance personnel noticed voids in the pump’s casing that ranged
from 1/8-in pits to gouges from ½-in to 3-in deep. Figure 1
shows wear to the pump’s volute, which resulted in less efficient
performance and shortened the pump’s expected mean time
between repairs (MTBR).
Ordering a replacement casing would cost approximately
$11,000 and would require some period of downtime until the
part arrived. Traditional hard face welding repair techniques
involved a similar capital investment and required downtime
of five weeks. To solve the problem quickly and cost effectively,
the maintenance team chose to use polymer composite materi-
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Figure 2. After sand blasting to a near
white metal finish, metal repair materials are used to fill the voids.
Figure 3. Use of repair polymer composite returned the pump to its original
dimensions.
als that would repair the damage on-site, in a fraction of the
time and at a fraction of the cost of the other options.
The metal repair itself was quick and easy. Maintenance
staff prepped the interior of the casing by sand blasting it to a
near white metal finish (Figure 2). A high compressive strength,
non-rusting metal repair material was trowelled on and left to
cure for just 20 minutes.
Once the maintenance team applied the metal repair material, the pump was back to its original dimensions (Figure 3).
The job required no specially trained applicators. (More details
on this application example will come later.)
In general, metal repair materials have a putty-like consistency and are applied with a trowel. However, some flowable
liquid formulations can be molded and poured. Cure times for
these materials vary, ranging from a few minutes to 24 hours.
Length of cure is extremely dependant upon ambient temperature. Typically, a pump treated with metal repair materials can
return to service as soon as the material is fully cured.
Using metal repair materials reduces time to complete the
repair, minimizes downtime for the pump, and simplifies reinstallation. Cost savings come from the inexpensive nature of
these materials compared to the capital expenditures required
for replacement parts.
Wear Resistant Coatings
Wear resistant coatings are polymer composite materials that act
as sacrificial and renewable working surfaces and protect the
structural integrity of pump components.
Highly filled with ceramic beads, powder, or fibers, these
materials provide unparalleled resistance to sliding abrasion and
cavitation that far exceeds the resistance of uncoated metals.
Pumps & Systems
Figure 4. Ceramic wear resistant coating
provided a smooth, low friction surface
that will resist sliding abrasion and cavitation, extending the life of the pump.
One type of wear resistant coating provides a low friction finish
that enables a pump to operate at its BEP while consuming less
energy, thus lowering associated energy costs.
These coatings are often applied in several different colored layers to help monitor wear during preventative maintenance checks. As colors begin to show through the top layer of
the protective coating, maintenance staff can determine the rate
of wear and the necessary proactive maintenance steps.
Continuing the repair application example begun earlier,
pits and gouges to the metal casing had been repaired in less
than one hour using metal repair materials. The casing surface
was now smooth and unpitted. In a proactive effort to combat
future wear to the pump surfaces, the maintenance team went
one step further. They applied two coats of a white brushable
ceramic wear resistant coating to the inside of the casing, then
two more coats of the same coating in gray. These smooth, lowfriction coatings help resist future sliding abrasion and cavitation, and provide a visual wear indicator for upcoming scheduled maintenance. Figure 4 shows the application of the wear
resistant coating along the interior of the pump casing.
The entire repair cost the plant just $500 and took a total
of five hours. When the pump returned to service, its glasssmooth, low friction surface resulting from this repair reduced
the internal casing friction so the pump could operate at its
BEP and consume less energy.
Chemically Resistant Coatings
Chemically resistant coatings are composite reinforced epoxies formulated to resist some of the toughest chemicals in the
industrial marketplace.
Certain chemicals can cause corrosion on either the
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April 2007
49
The Aftermarket: Applications
interior or exterior of industrial equipment, resulting in aesthetic and performance problems. Exterior corrosion can also
make it difficult to disassemble equipment for preventative
maintenance checks.
While all epoxies offer some degree of chemical resistance,
chemically resistant coatings protect in severe environments
– such as applications where acids are the materials being
pumped through the system. These products are especially
useful for pumps in secondary containment areas where there is
a risk of chemical spill.
Chemically resistant materials leave a smooth surface and
are ideal for preventing corrosion on and around the footings
of a pump or at its base, where compromised alignment can
lead to potentially disastrous problems like vibration and bearing failure. On pumps used to transport caustic acids, coated
interior components will prevent acids from eroding the pump
from the inside out.
Chemically resistant coatings are typically brush or roller
applied and have a much thinner consistency than wear resistant coatings. These polymer composites are basically thick,
chemically resistant epoxy paints that do not use special fillers to achieve their performance properties. They can be used
to coat virtually any device, including pumps, gearboxes, and
motors, and will protect metal surfaces from moisture and
chemical attack.
Chemically resistant coatings typically cure in 24 hours,
depending upon ambient temperature. When applied to the
outside of the pump, heat generated by the pump helps the
coating to cure faster, allowing the pump to return to service
very quickly. These coatings make routine maintenance easier
and faster by eliminating corrosion, extending the useful life of
the pump and increasing the time interval between repairs.
Repair or Replace?
Repair. Repair. Repair. By using all three categories of polymer
composite materials during routine pump maintenance, facilities can greatly extend the operating life of their pumps and
reduce capital and maintenance costs.
With all new equipment, maintenance teams should seriously consider applying wear resistant and chemically resistant
polymer composite materials to appropriate interior and exterior pump surfaces. This simple proactive effort can minimize
surface wear, premature failure, and rapid depreciation.
P&S
Thomas Buckley is an application engineer and a certified maintenance and reliability professional with Henkel
Corporation, 1001 Trout Brook Crossing, Rocky Hill, CT
06067, 860-257-6250, www.henkel.us.
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