Objective The rotor speed of operating centrifugal compressor units needs to be regulated according to working conditions and output requirements. Within the operational speed range, the rotors typically experience fluctuating vibrations in response to speed variations, which generally do not require special attention. However, in certain cases, rotor vibration can lead to abnormal equipment vibration. Therefore, analyzing the causes of complex vibrations occurring in rotating equipment due to speed regulation and implementing targeted maintenance operations are essential to ensure the safe and stable operation of centrifugal compressor units.

Methods The complex behaviors of vibration in centrifugal compressor units due to varying speeds were systematically analyzed and classified. Based on the fundamental principles of rotor dynamics, an in-depth examination was conducted on three key factors that may affect vibration following speed changes: critical speed, unbalance, and anisotropic stiffness. As a result, four essential parameters were identified: 1× frequency amplitude, 1× frequency phase, shaft center trajectory, and shaft center position. By employing tools such as trend charts, shaft center trajectory plots, and shaft center position diagrams, the real-world operation of in-service centrifugal compressor units operated by the China Oil and Gas Pipeline Network Corporation (PipeChina) was analyzed to verify the effectiveness and accuracy of the proposed analytical approach. This investigation into abnormal vibration caused by speed regulation revealed the root causes of such vibrations, supporting the targeted solutions subsequently proposed.

Results Excessive vibration resulting from approaching critical speed can be addressed through speed regulation, dynamic balancing, or optimization of the rotor system. Abnormal vibration caused by changes in unbalance can be mitigated by dynamic balancing or by optimizing the cooling system’s functionality. In cases where abnormal vibration occurs due to changes in anisotropic stiffness, solutions include adjusting the bearing installation position and modifying the bearing shell clearance.

Conclusion The research results can assist on-site technicians in identifying vibration behaviors and deepen their understanding of the various causes of vibration in centrifugal compressor units following rotor speed changes. The findings are valuable for analyzing the causes of abnormal vibration resulting from speed regulation, enabling the timely and accurate identification of the locations and causes of consequential faults, and helping formulate targeted maintenance plans. Ultimately, this analysis provides insights into ensuring the stable and safe operation of centrifugal compressor units in long-distance natural gas transmission pipelines.