Hydrocarbon Processing - January 2021 - 59

Valves, Pumps and Turbomachinery
to be used in rotor balancing. This observation supported the
hypothesis that the balancing procedure was not done properly. As a result, a residual imbalance remained in the rotor,
which was displayed when ramped up to full speed. From this
analysis, it was clear that the imbalance effect at full speed was
dominated by the bowed shaft and, therefore, would not contribute much to the overall vibration.
Solution. A conclusion was made that the high vibration of
the pump was mainly due to shaft sag and rotor/coupling imbalance. A decision was made to conduct field balancing on
the pump's coupling and to raise the bearing housing at both
sides by 2 mm. The pump was then left to run long enough
to straighten up under the influence of the centrifugal forces.
Recommendations. Based on this previous analysis, the following recommendations were provided:
1. If the overall vibration plots indicate that the rotor is
behaving as if it is not well-positioned in the pump
casing, then personnel should check whether the
bearing clearance is about 6 mm pk-pk. This action
might be challenging, considering that it is a
multi-lobe bearing.
2. Do a lift and drop test of the rotor in the bearing,
with an emphasis on the I/B side.
3. Depending on the results of Step 1, lift the bearing
housing so that the shaft rises 2 mm pk-pk to
3 mm pk-pk in the stuffing box in a vertical upward
direction (compared to the actual position).
4. After completing the lift, check whether the rotor
is still capable of freely rotating.
5. If the lift and drop test show an anomaly, or if it is
impossible to adjust the rotor so that it is freely
rotating, the pump might need to be reopened.
6. After completing all of these steps, restart the pump
and measure the vibration.
After implementing these recommendations, the pump was
retested. The vibration level dropped from 4.5 mm pk-pk to
1.8 mm pk-pk at full speed. This proved that the sag shaft was
causing a rub at full speed-and, consequently, a vibration of
4.5 mm pk-pk.

Results. The I/B vibration level reached a maximum of
1.7 mm pk-pk in the subsequent run (i.e., after the recommendations were implemented). This indicated a clear reduction
in vibration level. However, there is still room for improvement, especially for trim balancing.
ACKNOWLEDGMENTS
Special thanks to the support of Saudi Aramco for permission to publish this
article and to the specific individuals who contributed: Khaleel Al Hussain, Rehan
Farooqi, Abdulkarim Rinawi and Salman Al Salman.
WESAM A. ALHARBI has been working as a Vibration Engineer at Saudi
Aramco's Consulting Services Department since 2015. He provides technical
consultations to resolve complex rotating machinery and static equipment
vibration issues. His scope covers all Saudi Aramco oil and gas facilities in
Saudi Arabia. Mr. Alharbi holds several international certifications in the field
of condition monitoring and reliability and has a wide experience in technology
evaluation and deployment of pilot programs.
AHMED GHAZAL is the Technical Lead for Saudi Aramco's additive
manufacturing strategy and responsible for deployment and value creation.
He has more than 6 yr of experience in the oil and gas industry. He began
his career as a dynamic analysis engineer, providing technical consultations
to Saudi Aramco facilities and resolving issues related to machinery and
structural vibrations.
DR. DORU C. TURCAN is a vibration engineer. At present, his role includes
vibration analysis, conducting vibration analysis trainings, standards
and procedures development and conducting a company-wide vibration
monitoring benchmarking program. He has more than 20 yr of rotating
equipment troubleshooting experience.

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FIG. 5. Motion amplification shows high displacement at coupling I/B.
Hydrocarbon Processing | JANUARY 2021 59

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