Vibration analysis

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1. Failure analysis of hood fouling and scale shedding in a certain catalytic cracking unit 1 Equipment situation overview This set of main fans is driven by a motor and an exhaust turbine. The overall appearance of the unit is shown in Figure 1. The unit is monitored through the monitoring fault diagnosis center data. Since September, the vibration channels of exhaust gas turbine hoods have shown a synchronous upward trend (Figure 2), and an early warning has been issued to users. The reason for the increased vibration trend is rotor fouling. It is recommended to clean the rotor when there is an opportunity for maintenance. At 17:20 on October 18, the vibration channel of the cigarette machine suddenly mutated, with the highest vibration value reaching 100 μm. The Shengu Remote Monitoring Fault Diagnosis Center quickly gave the user diagnostic conclusions and suggestions. The cause of the sudden vibration was the detachment of the rotor scale layer. It was recommended that the user stop for maintenance, clean the rotor or replace the spare rotor. 2 Analysis of equipment anomalies 1. Recently, the vibration trend of the exhaust side of the main fan has a slow upward trend (Figure 3), mainly composed of 1X components, and the phase changes synchronously (Figure 5). No anti-precession is found in the axis trajectory diagram. On August 5, 2017, there was a sudden change in the vibration trend, but the magnitude was small. The rising vibration trend of the hood was caused by an imbalance problem. The hood runs for a long time, and the overall trend changes slowly, with occasional small-magnitude mutations. 2. At 17:20 on October 18, the vibration channel of the cigarette machine suddenly mutated suddenly (Figure 4), with the maximum rising to 100 μm. It was mainly dominated by the 1X component, with synchronous changes in phase. The trends of the 2X and 0.5X components were stable (Figures 6 and 7). In the waveform spectrum diagram, the 1X amplitude increased significantly (Figure 8). 3. The axis trajectory on the exhaust side has obvious edges and corners, and the axis trajectory screening shows anti-precession (Figures 9 and 10). 3 Diagnostic Conclusions and Suggestions Based on the above analysis, the conclusions of the diagnosis and analysis of the rising trend and sudden change of cigarette machine vibration are as follows:: (1) The vibration value of the hood has been on an upward trend since September. The reason is that the rotor is fouled. It is recommended that users clean the rotor when they have the opportunity for maintenance. ； (2) On October 18, the vibration of the cigarette machine suddenly changed. The reason was that the scale layer fell off. It is recommended that the user stop the machine for maintenance, clean the rotor or replace the spare rotor. 4 Conclusion The verification site shut down the machine for disassembly and inspection on October 19, 2017. It was found that the rotor of the hood was severely scaled. After replacing the spare rotor, it started running smoothly again. Figure 11 Photos of on-site rotor scaling