A major oil refinery in the US was experiencing problems with a 4-stage vertical turbine pump, pumping Isopentane. This bronze fitted pump was shut down due to high vibration. The pump was sent to an OEM repair centre with a broken shaft. It had been taken out of service only three years earlier with a broken shaft in the same area. Pumps with this frequent need for repair become classified as "bad actors" and efforts are made to improve the reliability. The refinery strives for 10-year (120) month MTBR (mean time between repairs) for all its pumps.

Upon inspection, the bronze line shaft and pump shaft bearings had moderate to heavy rub damage and both had excessive clearances to the shaft. Further inspection of the bronze sleeve bushings showed corrosion damage on both the inside (ID) and outside (OD) diameters. Other parts within the pump also showed evidence of corrosion. The bearing damage provided a possible root cause for the broken shaft.

In addition to the Isopentane, there is an occasional inflow of caustic soda (sodium hydroxide or lye) into the pump and this material readily reacts with bronze as well as many other metals. A new bearing material needed to be selected that would work with both Isopentane and caustic soda.

• Service - Isopentane with occasional exposure to caustic 
• Pump - 14GH-4 stage vertical turbine
• Temperature - ambient.

A fluoropolymer composite material was considered, but found not to be compatible with the pumped liquid. One of the refinery engineers recommended Graphalloy (the graphite/metal alloy that serves as a unique self-lubricating bearing material). The Graphalloy material grade chosen was GM111.3, a nickel impregnated graphite that can operate in temperatures to 750?F (400?C) while offering self-lubricating and corrosion resistant properties. Graphalloy bushings were installed into the stuffing box, column, bowl and suction bell bearing fits.

The pump is now protected from future failures associated with the damaging effects of the corrosive product that caused the premature failure of the previous pump shaft material and bearings. This pump has not experienced any problems since it was put back in service after the Graphalloy upgrade.

AMT Enviraclean Technologies Pvt Ltd, 501, Sajona Chambers, Opposite IIPS Govandi Station Road, Deonar, Mumbai 400 088. Tel: 022-61545400, 67987870, 61545402/03/044. Fax: 91-22-66430345. Email: info@amtgroup.in