Analysis & Engineering Upgrades Solve Ring Section Pump Failure

A major power plant in the United States experienced high vibration and recirculation issues with several ring section (BB4) boiler feed pumps, resulting in multiple catastrophic failures and unplanned outages. This case study details one of the pumps that was shipped to an aftermarket pump service center for a full analysis, troubleshooting, repair plan, rebuild and performance testing.

In combined-cycle plants, the demand for robust, yet expensive, barrel pumps diminished as the industry moved toward less expensive segmental rings pumps. Due to the recent shifts in the power industry, operators often face a shorter mean time between repair (MTBR), internal wear and high vibration issues on newly installed units.

After experiencing numerous boiler feed pump performance and reliability issues at their power plant, the plant owner opted to pursue a comprehensive root cause analysis and repair plan with an aftermarket pump service center in Los Angeles, California. The investigation ultimately revealed a series of underlying issues linked to the performance problems and unexpected pump failures.



The Hidden Dangers of Shaft Stiffness

The pump shaft is the central component of the rotating element and is responsible for transmitting energy to the rotating components. The shaft carries the impellers, sleeves and couplings for the rotating element assembly. The stiffness of the combined assembly is responsible for ensuring that the pump stationary components do not come into contact with the rotating components.

Unfortunately, this is not always achieved and many pump rotors cannot be described as classically stiff. This can have dire consequences for machine reliability, particularly if, during the rotor build process, the technicians are not aware of the subtleties of the machine design.