In condition-based maintenance (CBM) for LNG plant compressors, what specific data obtained from vibration analysis indicates potential bearing failure?

In condition-based maintenance (CBM) for LNG plant compressors, specific data obtained from vibration analysis can indicate potential bearing failure. One key indicator is an increase in vibration amplitude at specific frequencies related to bearing defects. These frequencies are known as bearing defect frequencies and are calculated based on the bearing geometry (number of rolling elements, diameter, contact angle) and the compressor shaft speed. Common bearing defect frequencies include the Ball Pass Frequency Outer race (BPFO), Ball Pass Frequency Inner race (BPFI), Ball Spin Frequency (BSF), and Fundamental Train Frequency (FTF). An increase in vibration amplitude at or near these frequencies suggests damage to the corresponding bearing component. For example, if the vibration amplitude at the BPFO increases significantly, it indicates potential damage to the outer race of the bearing. Another indicator is the presence of harmonics of these defect frequencies. Harmonics are multiples of the fundamental defect frequencies. Their presence suggests more advanced stages of bearing damage. Overall elevated broadband vibration levels across a wide frequency range, without distinct peaks at specific defect frequencies, can also indicate bearing wear or looseness. Analyzing the vibration data in both the time domain and frequency domain provides a comprehensive assessment of bearing condition. Time-domain analysis can reveal impacts or impulses caused by bearing defects, while frequency-domain analysis (using techniques like Fast Fourier Transform) allows for the identification of specific defect frequencies. By monitoring these vibration parameters over time, trends can be established, and predictive maintenance actions can be taken to prevent catastrophic bearing failures.