Abstract: During the sliding parameter shutdown of an 80 MW steam turbine unit in a steel cogeneration power plant, a sudden failure characterized by excessive vibration and severe shaft sticking occurred. A comprehensive retrospective analysis is presented covering the fault evolution process, realtime operational data, and the structural characteristics of the equipment system, thereby accurately identifying the triggering factors and thoroughly investigating the root causes of the failure. After comprehensive measures such as cylinder sealing, drainage, turning, and shaft calibration, the unit gradually recovered within about 6 hours, and the peak eccentricity of the shaft system decreased from 442.32 μm to 28.37 μm. Based on the actual site conditions, a targeted corrective scheme is formulated, which includes replacing the original check valve with a swingtype structure, optimizing the layout of the drainage pipeline, and adding interlock protection logic for the emergency drain electric valve of the shaft seal heater, along with several other technical modifications and operational improvements. The fault analysis methodology, troubleshooting procedure, and rectification experience presented in this paper can serve as a valuable reference for the sliding parameter shutdown control, equipment hazard management, and routine maintenance of similar cogeneration units.

Key words: steam turbine, sliding parameter shutdown, shaft seal water ingestion, shaft sticking, check valve failure