Run Like Clockwork
Brüel & Kjær Vibro has been actively involved with the LNG industry since 1998 for a number of LNG plants. During this time, we have been successfully monitoring hundreds of machines in all the major LNG production and delivery processes and have seen all kinds of machine faults. Two condition monitoring case studies are presented here because they required special attention. These are not about detecting wear and tear of components as they reach their lifetime, but about how important it is to detect incorrect assembly or component quality issues during commissioning or start-up after an overhaul. In both cases, the component fault development did not follow the typical failure mechanism. In the final analysis, specialized fault detection measurements and diagnostic expertise was needed to resolve the maintenance issues described in the case studies, but this extra functionality and service paid itself off quickly.
In case study 1, an instrument air compressor that was still under warranty showed early signs of a bearing fault with an unusual trend. Hence, we were asked to provide a diagnostic service to diagnose the fault and forecast repair. It turns out that it was a bearing fault that developed slowly at first – not long after commissioning – so the compressor was shut down. Upon disassembly, it was observed there was a manufacturing defect on the bearings, so these were replaced under warranty.
In case study 2, the constant percentage bandwidth (CPB) measurement detected a pronounced 1x vibration amplitude trend on the propane compressor gearbox. The alarm was not generated by exceeded alarm limits, but by a trend alarm function. Further analysis of the data from the 1x phase measurement revealed that the fault could have been detected 50% earlier than the CPB if it was monitored with the alarm trend function. When the gearbox was disassembled, the output shaft bull gear was found to be improperly mounted on its bearings.
Read more about these case studies here on Page 49.