Why can even the most reliable turbomachinery get tripped up? In some cases, it's all about bad vibrations--literally. This paper explores the challenges one site had with repeated centrifugal compressor trips causedby high vibration over a period of 25 days. It outlines the troubleshooting attempts made to remedy thisissue, it's root cause, and the resulting solution. This issue occurred at a site with a train configuration of gas turbine driven centrifugal compressors.After 48 hours of its first startup, the machine tripped due to high vibration at the compressor drive end.Initial attempts to fix the problem included checking the vibration probe gap voltage setting, as well asswapping vibrations probes. After these tasks were completed, the site again attempted to run the machine.48 hours later, it tripped again. During this time, the vibration gradually increased, staying above the alarmof 50 microns and tripping at 70 microns. The trip setting was increased to 75 microns, but after restarting,the unit continued to trip due to high vibrations. All components were removed and thoroughly examined. Clearances were measured per the standardchecklist. The condition of the couplings was found to be normal. The journal bearing pads had minorscratches. The thrust bearing pads were not affected by the failure. Alignment readings were found to benormal. However, residual unbalance was found on the rotor. This residual unbalance was found to be the root cause of the tripping issue. The journal bearingclearances were thus adjusted from 0.17 mm to 0.13 mm. It was also advised to perform high speed balancingchecks in the manufacturer's facility. The lube oil inlet pressure was adjusted to meet the requirements forthe new bearing clearance. Adjusting the bearing clearance, along with the adjustments in lube oil inlet pressure, resulted in improvedvibration readings. This case study provides the detailed analysis of the root cause of the frequent trips aswell as the process that was followed to fix the problem.
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