Fast forward 20 years and the thermally handicapped transformer is scheduled for new dielectric oil and all new gaskets. Additionally, all six transformer oil circulation pumps are to be rebuilt. (Sidebar: Power transformers use circulating transformer oil systems to serve both as an insulating dielectric and as a heat transfer cooling medium.)
The pumps were sent to the factory repair shop on an expedited basis for remanufacture and returned to the site. The customer performed a pre-installation check for proper rotation and noticed the pumps were rotating in the wrong direction. The customer demanded warranty compensation from the factory to fix the issue. The factory engineer stated that it was impossible for these pumps to be operating in the wrong direction unless the customer had reversed two of the three phases on their power leads at the site. The customer vowed that no lead changes had occurred. The factory engineer was on the next plane to the site.
Solution: The cool solution
The factory engineer was confident the transformer pump motors were correctly wired because of their in-house quality assurance/quality control (QA/QC) program. On arrival at the job site, and to his surprise, the engineer confirmed that the pumps were actually rotating in the wrong direction. In fact, the pumps had been rotating in the wrong direction for 20 years.
Note: a centrifugal pump operating in the wrong direction still produces flow in the correct direction and the customer’s rudimentary sight glass flow indicators could not differentiate between 600 gallons per minute (gpm) and 1,200 gpm. The correct rotation was established for all pumps, the power plant was started up and the transformer was energized. For the first time in 20 years, the transformer did not overheat at full load.
3. The reoccurring seized rotor—the definition of insanity.
At a steel mill in the Midwest, an eight-stage segmented casing pump is sent to a repair facility for a complete overhaul. The pump is returned and installed. During the setup, the millwrights discover that the pump rotor will not rotate by hand. The vendor is informed that the pump rotor is apparently seized.
The pump is sent back to the repair shop to be disassembled and inspected. The pump shop finds nothing wrong—they reassemble the pump and send it back to the customer. But again, the millwrights are not able to rotate the rotor due to an apparent rotor seizure. The pump is sent back to the shop, where again it is disassembled and inspected to find there is nothing wrong. The pump is returned to the customer a third time, but on this occasion the sales engineer decides to accompany the pump.
Solution: What is going on over at the plant?
The engineer accompanied the rebuilt pump to the mill and witnessed the work crew lift the pump off the truck using a small crane with two lifting straps—each attached to one end of the pump shaft. By improperly lifting the full pump weight on the shaft at both ends, the segmented casing rings were shifted out of alignment, consequently locking the pump rotor. Never lift a pump of this type by the shaft.
4. Seized rotor redux: watch out for dead ends.
Similar to the preceding example, this multistage boiler feed for a boiler feed pump at a factory somewhere in the middle of the country was rebuilt in a nearby repair shop and reinstalled. The pump operated for about 10 minutes and seized up. The pump was returned to the repair shop to be rebuilt and sent back, where the same scenario reoccurred. On the third attempt, a pump engineer and consultant were brought in by the customer for oversight purposes.
Solution: Seized rotor
The consultant examined the system and operation and maintenance procedures. It did not take long to determine the reason for the pump failures.
In any piping system when there is a section of pipe that has no flow (also known as a dead leg or trap), it becomes a place for the rust, scale, dirt and debris to accumulate and deposit. The suction line for the boiler feed pump was blocked when the pump was removed, but the system was still operating using the other parallel pumps. The dead leg was collecting the foreign debris in the system. When the pump was reinstalled and the suction line opened, the pump was flushed with the collected debris. The debris lodged in the wear ring fits, and the pump seized.
5. Going the wrong way on a one-way street; you can’t have it both ways.
Scene: the “oil patch” in the upper western U.S. where we have a single-stage group 3 ANSI pump on oil service in a middle stream process application. The local pump distributor contacted the factory with an issue: the pump would run for a day or two and then seize and fail. They pulled the pump, rebuilt and returned it to service. The pump would again operate well for a few days, and the issue would repeat.
The OEM engineer asked for photos of the damaged parts and more information on the operation. Based on those, it appeared as a clear and simple case of running the pump in the wrong direction. But, the distributor had their most experienced serviceman on the job who had personally checked for proper rotation three separate times. Time for some fresh eyes to visit the job site.