The Gas injection compressors are critical for the oil production at offshore facilities. Any downtime of this compressor will bring down the oil production. This case study reflects on the Gas Injection Compression train of an offshore platform in the Middle East.

A steady increase in the vibration trends of the Low Pressure (LP) Compressor Non-Drive End radial bearing was observed over a period of time after the major compressor overhaul, that was carried out in 2014.  In particular, the vibration was high towards NDE bearing which reached 60 μm PP (Alarm 51 μm PP) at times in early November 2015 especially when the machine reaches to approximately 60 to 80% of the compressor load and at speeds of approx. 12300 RPM. The accurate vibration analysis using various plots revealed coupling pre-stretch issues and the adjustment of the same during a short shutdown successfully resolved the high vibration issue.

This case study is designed to outline how the gradual vibration increase was successfully diagnosed, the root cause for the high vibration, and finally how it was resolved. Lessons learned are also discussed on the discovery methodology using expert system available at site and the importance of monitoring key operating parameters.

Takeaways
1.  Maintaining coupling pre-stretch is an important aspect of the maintenance.
2. Importance of transient plots with phase information in diagnosing the issue.
3. Availability of historical information from online condition monitoring system enabled identification of the root cause.

A Senior Machinery Diagnostics Engineer working with Bently Nevada (BHGE) based out in Abu Dhabi, U.A.E. from past 5 years. He has more than 11 years of experience in the field of Vibration Analysis of Critical Rotating Plant Equipment’s, i.e. Steam/Gas Turbines, Compressors, Pumps etc. Involved in the resolution of plenty of High Vibration issues in rotating machines during his tenure in this field with the root cause analysis of the issues. Performed many single and multi-plane balancing of rotating equipment’s, i.e. steam/gas turbines, generators, motors, compressor & pumps successfully.