Page 182 - CW E-Magazine (8-10-2024)

Special Report

also be applied as a protective layer about 7%, decreases frictional losses, lence, liquid pressure, liquid tempera-
over metal components. These are provides cost effective and long-term ture & range, pump duty type (inter-
usually applied as a powder and then corrosion prevention, and improves mittent or continuous), and end use
heated. During subsequent cooling, the MTBF. Adopting this technology some of water.
coating hardens. Some thermoplastic of the Indian industries have achieved
coatings can be reheated to correct and about 3.5% in energy savings and 5% Normally, CI is chosen for valve and
seal any flaws. of flow improvement. The internal pump bodies in normal applications.
parts (impeller and casing) of the pump For impellers, the material is selected
The coatings can be applied by: coated with Corrocoat are shown in on the basis of its suitability for cast-
Electrostatic spray: electrical charg- Figure-2. ing, machinability, strength, cavitative
ing is used to coat the powder on the wear resistance, abrasion resistance and
metal surface and the component is Corrosion prevention for water resistance to corrosion. CI impellers are
then heated, causing the powder to pumps occasionally used mainly on account of
melt and flow. Water pumps are critical for indus- their lower initial cost. They are inferior
Preheat spray application: the metal trial and agricultural business processes. for cavitation, corrosion and abrasion
part is preheated, and the coating Most of these pumps are subjected resistance. Brass is sometimes used for
sprayed onto it. It immediately melts to extreme environmental conditions steam and water, but not for seawater
and flows over the heated surface. such as variable temperatures and flow applications, as corrosion resistance is
Dip coating/fluidized bed: Preheated velocities. The water being pumped inadequate. Comparatively, bronze has
parts are immersed in a fluidized might contain corrosive contaminants, better machinability and casting pro-
thermoplastic powder coating, abrasive solid particles and vapour perties. Bronze impellers also have
which is attracted to and sub- bubbles. Hence, we must devise suit- moderate cavitation resistance. For a
sequently fuses to the heated surface. able corrosion prevention and protec- higher resistance to cavitation damage
tion strategies for reliable and economi- and corrosion damage (for freshwater
A special proprietary coating tech- cal operation of the water pumps. and seawater), phosphor bronze or
nique called ‘Corrocoating’ had been nickel aluminum bronze can be used.
developed in UK and the services are Materials for pumps and valves
provided by M/s Kirloskar Corrocoat The choice of water pump mate- Glass-reinforced plastic (GRP) can
for making centrifugal pumps corro- rials depends upon parameters such be used for pump impellers that pump
sion resistant. Additionally pump per- as water’s pH level, water impurities, seawater. SS can be chosen for severe
formance and efficiency improves by air & vapour entrapment, flow turbu- duty high-speed pumps on account of
their improved cavitation resistance.
Corrocoating of Pump casing and impeller This metal has moderate corrosion re-
Coating pump internals results in the following: sistance and abrasive wear resistance.
Pump performance and efficiency improve- From a cavitative corrosion resistance
ments. point of view, the life of a SS impel-
Protecting surfaces from chemicals. ler can be almost 200% higher than a
Decreases friction loss. comparable mild steel (MS) impellor.
Provide cost-effective and long term corrosion Ceramic coatings can further minimize
prevention. cavitation corrosion.
Improves MIBF.
Types of corrosion damage
Perfomance parameters achieved after corro- Water pumps are exposed to electro-
coating at DCM Shriram: chemical and mechanical degradation.
Energy savings – 3.5%. Cavitation corrosion, erosion corro-
Flow improvement – 5%. sion and fatigue are initially studied as
physical mechanisms, though electro-
chemical and chemical reactions are
necessarily occurring simultaneously.
Conversely, galvanic corrosion, uni-
Fig. 2: Corrocoating for prevention of erosion corrosion form corrosion, crevice corrosion and

182 Chemical Weekly October 8, 2024

Contents Index to Advertisers Index to Products Advertised