Composite wear rings improve pump performance

Kulpsville, PA--By employing rotating impeller parts made from a composite, a south Texas refinery has reduced maintenance costs and improved the mean time between failure for its pumps.

The refinery, which was experiencing frequent catastrophic failures of its boiler feed water pumps, was paying out $15,000 per pump for repairs at six week intervals. To solve the problem, the refinery replaced stainless steel wear rings on the pumps with the composite.

The composite, made by Greene, Tweed & Co. and known as WR525, consists of carbon fiber and polyetheretherketone (PEEK) resin. It serves more effectively in the wear rings because its lubricity makes it non-seizing and non-galling. Those characteristics were critical for the refinery application, where occasional cavitation caused galling of the wear rings.

One of the key reasons for the material's performance in high temperature, high pressure applications is its thermal expansion coefficient, engineers say. Because it has a different thermal expansion coefficient than steel, it expands at a slower rate. As a result, when the heat of the application increases, the WR525 wear ring grows tighter around the shaft. This makes it almost impossible for the pump to seize. It also reduces pump vibration and improves pump efficiencies.

Greene, Tweed & Co. engineers say that the material's performance in such applications is important to a rapidly growing user community. "A few years ago, our customers were happy to get one year intervals between maintenance," notes Jonathon Pledger of Greene, Tweed & Co. "Today, they want five year intervals."

In the Texas refinery application, WR525 has increased the mean time between failure and reduced the average part repair cost from $15,000 to $3,000, Pledger says.