There is a single stage vertical pump installed in a petrochemical plant. The unit is vertical feed pump driven by induction motor through a flexible shim pack coupling. High vibration levels were observed on the motor, pump and structure for a long time with 1X dominant vibration (1Xmotor). Assuming that the issue is of complete structural issue even though this motor was running well in the past, there were some structural modifications have been carried out at site.  The modifications included welding a total mass of 100 Kg on the structure in addition to the installation of braces to the structure which did not yield any positive results. A systematic structural measurement along with the Operating Deflection Shape carried out at site with the help of experts did not reveal a significant issue with the structure itself except for the structural natural frequency slightly closer to the running frequency of the motor. The timely right decision by the experts to carry out an onsite balancing on the motor which was intended to remove the excitation force yielded good results.
This case study is designed to outline how the high vibration issue was successfully diagnosed using various tests at site including the operating deflection shape, the root cause for the high vibration and finally how it was mitigated.

Takeaways
1. Operating Deflection Shape Analysis.
2. Impact test to identify the structural natural frequency.
3. How to differential a structural issue Vs the rotor issue.

Machinery Diagnostics Technical Leader for GE Bently Nevada Machinery Diagnostics Services, MENAT region. Bachelor Mechanical Engineering (1993) from Bharathidasan University, India.
Over 20 years experience in vibration field and 10 years with GE Bently Nevada, including rotating equipment balancing, vibration analysis, diagnostics and root cause analysis.
Published case studies in various international conferences.