Advanced Reinforced Composite Coating Systems Improve Pump Performance and Energy Efficiency

The water industry’s interest in pump energy efficiency has grown in recent years.

Th Chesterton Picture 2

The water industry’s interest in pump energy efficiency has grown in recent years. Studies conducted by the US Department of Energy determined that pumps consume approximately 20% of all electrical energy produced for industry each day. Further, it has been found that 20% to 50% of this energy is wasted.

There are several reasons for this waste including oversized pumps, oversized motors and operation away from the pumps’ best efficiency point (B.E.P). However, all pumps constructed from metallic components suffer from erosion/corrosion, abrasive wear and build-up. These conditions will significantly impact both energy efficiency and overall pump performance.

Th Chesterton Picture 2
Reinforced composite coatings can reduce or eliminate performance losses by interrupting the erosion/corrosion process.
Click here to enlarge image

Advanced reinforced composite coating technologies have been used for many years to rebuild worn surfaces and restore pumps to “better than new” condition. Work conducted in Europe, as part of the European Union’s Motor Challenge Program, has also confirmed the benefits of coating a pump’s wet-end to optimize energy efficiency and improve performance.

The use of coatings to improve centrifugal pump performance and energy efficiency has been well known by pump designers and coatings manufacturers for many years. In 1948, A. J. Stepanoff discussed in his book “Centrifugal and Axial Flow Pumps” the use and benefits derived from porcelain enameling a pump’s wet-end.

Performance Degradation

Most centrifugal pumps use cast iron, steel or some other metallic alloy for the construction of their wet-end components which include the impeller(s), wear rings and casing. As soon as these pumps are placed into operation, their performance begins to degrade and their subsequent net energy consumption begins to increase, resulting in lower efficiency and higher life cycle costs.

Th Chesterton Picture 3
Coatings can restore pump performance to “better than new.”
Click here to enlarge image

This occurs as a result of erosion/corrosion and abrasion of the metallic components. Based on studies conducted in Europe, a typical water pump will lose between 10 to 15 points of efficiency over a 10 year period. The amount of wear, corrosion and subsequent degradation of the pump’s performance will be further accelerated if the pump is handling a fluid with solids/slurries, higher fluid temperatures or that is more corrosive than water.

The erosion/corrosion process is experienced by all metal components, including stainless steel because all metals form an oxide layer that is weakly bonded to the surface of the bulk metal. In the continual flow experienced in a pump, this oxide layer is constantly washed and worn away.

Just like human skin, the oxide layer regenerates so the process continues until bulk material is lost resulting in a change of dimensional tolerances as well as an increase in surface roughness. Therefore, replacing worn components with new metallic components will only provide short term improvement as the new metallic components will experience the same erosion/corrosion process.

The effects of erosion/corrosion is more pronounced in lower specific speed pumps where the developed head is higher and there are abrupt changes in flow direction through the wet-end.

As this process continues, the pump’s performance will begin to be effected. The amount of head and flow produced will decrease along with a corresponding loss in efficiency resulting in greater energy consumption per unit volume of flow.

Studies conducted as part of the European Union’s Motor Challenge program have shown that a majority of this performance degradation occurs in the first five to 10 years of pump operation. If unchecked, the degradation will continue until significant loss in performance results in total failure of the pump.

Pump Coatings

Reinforced composite coatings can reduce or eliminate this loss in performance by interrupting the erosion/corrosion process. This occurs because the polymer does not form an oxide layer like metal. As well, depending on the amount and type(s) of reinforcements used within the coating system, abrasive wear can be significantly reduced extending the overall wear life of the pump.

Th Chesterton Photo 1
Corrosion and erosion begins as soon as pumps are placed into service.
Click here to enlarge image

The composite coating replaces the lost metal and does not reform the weak oxide layer which therefore can not be “washed away” under normal fluid flow conditions.

Composite coatings will improve a centrifugal pump’s performance and subsequent energy efficiency four ways. These include:

  • Significantly reducing the surface roughness over the base metal component.
  • Decreasing the surface energy resulting in less “wetting” of the pump’s internal surfaces and subsequently reducing overall friction.
  • Eliminating the erosion/corrosion process resulting in smoother flow passages and less friction.
  • Increased resistance to the effects of abrasion in applications with solids or slurries resulting in less wear and loss of tolerances.

Conclusion

The benefits derived from the use of coatings varies based on several factors including the coating technology chosen for the application, the pump’s hydraulic design, whether the pump is new or has been in service for a period of time and the application quality of the coating.

When applied properly, a reinforced composite coating can give the pump’s wet-end components a “glass like” finish which significantly improves performance. Additionally, the reinforcement system used in the composite system will increase the surface hardness resulting in reductions in the amount of wear generated by abrasives in the pumped fluid.

Academic knowledge and experience have shown that through the use of coatings, the amount of wear, corrosion and subsequent degradation of the pump’s performance can be reduced resulting in significant improvements in the pump’s overall reliability, maintaining efficiency levels over a longer period of time and significantly reducing the life cycle costs of the pumping application.

About the Author:

Alan Evans is a mechanical engineer with over 25 years of pump and system experience. He is currently the Global Business Development Manager for the Commercial Water Industry for the A.W. Chesterton Company. He maybe contacted at evansa@chesterton.com

More in Energy Management