Bearings Tame Pump's High Vibration: A Case History
High vibration in an old horizontal pump was causing engineers at a major refinery to search for a bushing material to improve performance.
MODEL: Pacific Pump- Dresser, Model KHC-L-6 (circa 1966) (split case, single stage, double suction, between bearings)
SERVICE: Alky Charge Pump in Butane/Iso-Butane Service
OPERATING CONDITIONS: 40°F, 3550 RPM, 0.167 specific gravity
This process-critical pump was rushed to a repair shop for an emergency rebuild due to extremely high vibration readings.
The refinery has two of these pumps and if both pumps are out of service at the same time it could cost them $1.5 million/day in losses.
Repair Shop Findings: The Wrong Bushings
This pump had Nitronic 60 throat bushings running against a Nitronic 50 shaft. Once the pump was opened, the repair shop could see that the shaft was worn nearly in half by the throat bushings. The refinery engineer said, "I have never seen this kind of damage to a shaft from a throat bushing!"
This was an example of extreme galling – with material from the shaft being deposited onto the bushings. This is a risk when using metal wear parts in a pump. According to the engineer, “the material just transferred almost like fusion bonding to the bushing, the shaft was sacrificial.”
Both throat bushings had to be cut off to free the shaft and the shaft was extremely eroded under both these carriers. The erosion was so severe, they said “it was a miracle that the shaft did not split off into three pieces!”
The next issue the repair shop noticed was that the case wear ring, made of Vespel® CR-6100, had deteriorated and come apart. The surface of these rings had become extremely soft to the touch and would clearly not be an appropriate material for this pump anymore.
The Solution: The Graphalloy Upgrade – From Experience
The refinery’s new senior rotating equipment engineer, who had many years of experience using Graphalloy while previously working for Flowserve, told his team that they were going to install nickel-grade Graphalloy in place of the Nitronic bushings and the Vespel® case wear rings. The engineer knew from his experience that Graphalloy never galls, and can be designed with tighter clearances, which stabilizes the pump, reducing vibration and improving efficiency.
Years of Problem-Free Operation
It’s been over 5 years since this pump was upgraded to GRAPHALLOY and subsequently, the refinery upgraded the sister pump. The customer said that “for 30 years these pumps have been very hard to start and very hard to get up and running.” “Now they start up immediately.” The customer also said that the GRAPHALLOY fitted pumps “have great suction, make great head, the NPSH is perfect, and the vibration levels are constantly checked and performing better than ever before.”
GRAPHALLOY Solves Pump Problems Like These Every Day
GRAPHALLOY has a long history of pump upgrades to replace metals or plastic composite materials that are failing. Graphalloy is self-lubricating, non-galling, won’t swell and maintains clearances over a wide temperature range, from -400°F (-240°C) up to 1000°F (535°C) in air and higher in non-oxidizing temperatures.
Because Graphalloy can contact the shaft without causing damage, Graphalloy is often used where periods of dry-running or flashing are possible and is able to be designed with tighter running clearances than other materials.
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