INVESTIGATION INTO THE ALIGNMENT DISTURBANCE AND MECHANICAL SEAL FAILURE OF A HPCC PUMP

摘要

High pressure circulating water (HPCC) pumps are one of the critical equipments in a combined cycle power plant. Disturbances in the alignment between the pump and the motor shafts leading to mechanical seal failure, have been observed in one of the plants. Static and dynamic analysis are carried out for the complete piping system. Static analysis shows that the forces and moments exceed the permissible values given in API 610. It is also observed from the dynamic analysis that one of the natural frequencies in lateral direction (site observations confirmed this) is very near the pump rotational speed, contributing to the disturbance in the pump alignment. Various modifications are tried and finally a configuration is arrived at which satisfies the API code requirements and the mode shapes of the modified system are such that there are no displacements near the vicinity of the pump. This paper deals with details of the investigation.