Background: In this case study, we examine an incident of rotor rubbing in a high-speed Motor-Gearbox-Pump. rubbing, a common yet critical issue, can cause severe damage to both the rotor and stator components, leading to significant operational disruptions and costly repairs.
Incident Description: A power plant reported unusual vibrations and noise emanating from one of its gas turbines. The turbine, a key component in the plant’s energy generation process, had been operating under normal conditions until these anomalies were detected. The maintenance team observed the following symptoms:
- Increased vibration levels, particularly in the axial direction.
- Abnormal noise, described as a grinding or scraping sound.
- Elevated temperatures in the bearing housing.
Diagnostic Approach: Upon receiving the report, our team conducted a thorough diagnostic analysis, employing both online and offline monitoring techniques. The following steps were undertaken:
- Vibration Analysis: Utilizing high-frequency vibration sensors, we measured and analyzed the vibration spectrum. The data indicated high-amplitude peaks at frequencies corresponding to the rotor’s rotational speed, suggesting rotor-stator interaction.
- Thermal Imaging: Infrared cameras were used to detect hotspots around the bearing housing and rotor assembly, confirming elevated temperatures consistent with friction-induced heating.
- Borescope Inspection: A borescope inspection revealed physical evidence of rubbing marks on the rotor and stator surfaces, corroborating our initial findings.
Root Cause Analysis: The root cause analysis identified several contributing factors:
- Misalignment: Minor misalignment between the rotor and stator components was detected, likely exacerbated by thermal expansion.
- Lubrication Issues: Inadequate lubrication in the bearing housing resulted in increased friction and wear.
- Operational Overload: The system had been operating under higher-than-normal loads, which increased the likelihood of rotor displacement and subsequent rubbing.
Corrective Actions: To mitigate the issue and prevent recurrence, the following corrective actions were implemented:
- Realignment: Precision alignment of the rotor and stator was performed using laser alignment tools to ensure optimal positioning.
- Lubrication System Upgrade: The lubrication system was upgraded to provide consistent and adequate lubrication, reducing friction and wear.
- Operational Controls: Operational parameters were reviewed and adjusted to avoid excessive loading conditions.
Outcome: Post-implementation, the turbine was monitored closely to assess the effectiveness of the corrective measures. The results were positive, with significant reductions in vibration levels and noise. The turbine returned to normal operational status without further incidents of rotor rubbing.
Conclusion: This case study highlights the importance of early detection and comprehensive diagnostic analysis in addressing rotor rubbing issues in turbomachinery. By identifying and rectifying the root causes, we were able to restore the turbine to optimal performance, ensuring continued reliability and efficiency in power generation operations
Author : Özgün Yakar, Resonance Institute
