Structural Engineered Composites

by John Kozel

12/17/2011

Engineered composites have become a solution for longer pump life.

With the market demanding cheaper prices, most pump manufactures have gone outside the U.S. for the casting of metallic parts. Unfortunately, the net effect for the pump owner or end user is a shorter pump life. Metallic parts cast overseas corrode faster and are more subject to cavitation damage. The net effect is that the life of some parts—such as impellers, rings, sleeves and casings have—been shortened.

A metallic impeller corroded and cavitated even through coating. A bad casting in Stainless Steel with pitting and pockets eroded out.

The structural composite downhole pump, which included composite diffusers, impellers, bushings, sleeves and the housing replaced type 316 stainless steel and outlasted the metallic pump by over three times.

Fortunately for the end user, there is a solution. Many customers are upgrading to structural engineered composites, which have been proven to outlast metallic parts by many years, because they resistant cavitation damage, and they are not subject to corrosion or electrolysis attack. The fibers in a structural engineered composite are not chopped, cut or macerated. Instead, they are interwoven in a bi-dimensional or tri-dimensional weave. Composites machined from solid blocks of structural engineered composite have a further benefit—they are mechanically better and much stronger. They do not have casting defects, and they are 100 percent balanced and stay balanced for the life of the product. Because of the flexibility of machining structural composites, any metallic part or pump can be upgraded to structural engineered composite.

A structural composite vertical turbine 4 stage pump will outlast and outperform the metallic pump by many times.

A structural composite vertical turbine 4 stage pump will outlast and outperform the metallic pump by many times.

Composite Materials

A composite is two or more dissimilar materials or elements combined together. For example, cement is a common composite. Today, composites for the pump industry are generally non-metallic composites. However, a composite can contain metallic fibers as well as non-metallic fibers. The fibers in a composite carry the bulk of the load, and the resin, or matrix, transfers the load between the fibers. The fibers are primarily responsible for setting the material properties of the composite. The material properties of the composite are set by the:

Type of fibers
Size of the fibers
Layout, or orientation of the fibers
Ratio of the resin to the fibers

The diagram above shows the interwoven fibers in a structural engineered composite as compared to a molded composite, which will always have air pockets and some porosity.

Composites can be molded by using different processes of low-pressure molding, such as: compression molding, resin transfer molding, bag molding or by hand lay-up molding. Composites can also be machined from solid blocks of composite using high-pressure processes such as laminating. Because pump parts involve pressure, it is best to use structural composites in which the fibers have not been cut or chopped for molding processes.
The highest material properties are achieved using tri-dimensional, interwoven fibers. For pump applications, machined, structural engineered composites produce the highest mechanical properties and the greatest reliability.

A molded non-structural composite impeller where the vanes were not suitable for the application. A machined structural engineered composite impeller, which lasted for years in service.

A metallic impeller corroded and cavitated even through coating.

A metallic impeller corroded and cavitated.

A bad casting in Stainless Steel with pitting and pockets eroded out.

A molded non-structural
composite impeller where the
vanes were not suitable for
the application.

A machined structural engineered
composite impeller, which lasted
for years in service.

Engineered Composite Advantages

Corrosion resistance. One of the most imperative advantages of composites when compared to metal is its ability to resist both corrosion and erosion in saltwater. Composites never corrode in saltwater.

These two impellers ran for three years in salt water–the composite impeller looks like new.

Most composites are also excellent in most chemical applications and are not subject to damage by gasoline, oil or refinery byproducts. Because of these outstanding characteristics, composites prove to be a worthwhile investment in the long run with the reduction of the costs of replacing these parts.

Cavitation resistance. Cavitation damage results when the liquid pressure of the liquid being pumped falls below the vapor pressure of the liquid resulting in the formation of vapor bubbles. These imploding bubbles cause severe damage to all parts resulting in holes in the impeller and casing volute.

The same impeller in structural engineered composite after over two (2) years of operation. It looks brand new. A metallic impeller, after only 3 months of operation is salt water. This impeller was subjected to corrosion and cavitation attack.

The same impeller in structural engineered composite is non-conductive and, therefore, will not be affected by the effects of electrolysis. A bronze impeller suffering from the effects of electrolysis after only 9 months of operation.

The same impeller in structural engineered composite after over two (2) years of operation. It looks brand new.

A metallic impeller, after only 3 months of operation is salt water. This impeller was subjected to corrosion and cavitation attack.

The same impeller in structural engineered composite is non-conductive and, therefore, will not be affected by the effects of electrolysis.

A bronze impeller suffering from the effects of electrolysis after only 9 months of operation.

Electrolysis and galvanic corrosion resistance. The graphite used in this structural engineered composite is non-conductive, which means that it will not support electrolysis or galvanic corrosion. It also means that the more composite used in the pump, the longer the pump will last. When applied in a corrosive environment, all metallic parts, or components will conduct electrolysis. However, composite materials do not. This enables the metallic pump to last significantly longer, because of the prevention of electrolysis and “pump wash out.”

Galvanic corrosion is corrosion that forms as a result of electrolysis, due to the difference in nobility between two dissimilar metals. Consequently, a reduction in electrolysis leads to an automatic reduction in galvanic corrosion.

Light weight. Composites are significantly lighter than metallic materials. Most composites weigh only 1/6 to 1/5 the weight of their metallic counterparts. The lighter mass means a substantial reduction in the start-up load, shaft movement and shaft deflection, resulting in longer life for the bearings, mechanical seals, casing and wear rings and sleeves. The light weight of the composite products proves to be an excellent investment.

Mechanical and hydraulic balance. Machined structural engineered composite impellers are perfectly balanced and maintain this perfect balance throughout the lifetime of the pump. This is due to precision machining from a solid block of the composite material. In regards to mechanical balance, the center of axis of rotation is in the center of the impeller, which creates perfect symmetry.

Composite impellers, rings and guide bearings will not corrode in saltwater and therefore will not reach an imbalance. In regards to hydraulic balance, all vanes are within 0.002 inches of each other, and all the exit ports are equally spaced with no casting imperfections. When tested alongside cast iron, bronze and stainless steel, composites were the only product that maintained both mechanical and hydraulic balance after six months of saltwater service.

Energy efficiency. With the increasing interest for companies to increase their “green” capabilities, machined composites offer unique possibilities. An existing pump can be made more efficient by redesigning the impeller to make the operating point in the plant, or system, the best efficiency point (BEP).

This bronze impeller from a cooling tower pump is completely cavitated after only one year in service. The same impeller in structural graphite composite after one year of service shows absolutely no wear or damage.

This bronze impeller from a cooling tower pump is completely cavitated after only one year in service.

The same impeller in structural graphite composite after one year of service shows absolutely no wear or damage.

Many composite pump companies offer dedicated engineering specialists who focus on improving and increasing efficiency and redesign of impellers to operate at the operating point in the system, which allows for the BEP to be the true operating point in each plant or ship system. The efficiency of the pump substantially improved, and the reliability of the pump is increased.

Life cycle. When the total operating years of composite pumps are examined, it becomes clear that composite materials are an excellent financial and operational solution. Most composite pumps and pump parts operate at least three to five times longer than their metallic counterparts. When the total cost of operation including down time, overhaul expenses, and reliability is reviewed, it becomes clear that composites will save the end user thousands of dollars in energy, operational, replacement and repair costs.

A main circulating impeller for a two stage intake pump at a power company in NYC after 18 years of service. A new structural engineered composite impeller for the same 2 stage main circulating pump.

A main circulating impeller for a two stage intake pump at a power company in NYC after 18 years of service.

A new structural engineered composite impeller for the same 2 stage main circulating pump.

A composite impeller from a main engine cooling pump after 17 years of service. This impeller replaced a bronze impeller which corroded in less than 18 months. A new composite impeller for the same salt water cooling pump aboard vessel.

A composite impeller from a main engine cooling pump after 17 years of service. This impeller replaced a bronze impeller which corroded in less than 18 months.

A new composite impeller for the same salt water cooling pump aboard vessel.

Improved efficiency. Because machined structural composites can be designed using state-of-the-art computerized fluid dynamics (CFD) techniques, structural composite pumps and pump parts (impellers) can be designed to maximize efficiency in a customer's system. For example, if a customer has a problem in which his motor is tripping the system, the impeller can be re-engineered and designed to operate at a higher efficiency without changing the entire pump and/or system.

Composite Impeller Surpasses Bronze Impeller Efficiency

Upon the request to redesign an impeller for a German based Pump Company, a structural engineered composite pump manufacturer took on the task to make modifications to improve the performance of the impeller. The composite impeller (left) exhibited an increase in efficiency of 87.8 percent compared to the bronze impeller's 83 percent.