Technical Measures to Prevent Shaft Bending in Steam Turbines
Source: Bearing Network | Date: April 8, 2013
To ensure the safe and efficient operation of steam turbines, it is crucial to implement specific technical measures that prevent shaft bending or tortuosity. These steps are essential during startup, operation, and shutdown to avoid mechanical damage and maintain optimal performance. 1. Before rushing the turbine, it is necessary to check for large-axis misalignment, which should be less than 0.076 mm. The runout of the main shaft should not exceed 0.02 mm from its original value. After an overhaul, use a dial gauge to measure the oil film clearance in each bearing. The spindle's runout on the ring should be less than 0.0254 mm. 2. If the temperature difference between the upper and lower cylinders exceeds 42°C—specifically in the high-pressure and intermediate pressure cylinder exhaust zones—the turbine must be stopped immediately. The main steam valve inlet temperature should have at least 56°C of superheat to prevent condensation. 3. Follow the "main steam parameters at start-up," "cold-state rotor heating regulation," and "hot-state recommended value" charts when performing cold or hot starts. This ensures proper thermal expansion and minimizes stress on components. 4. During any start-up, the first-stage steam temperature must not be more than 56°C below or 111°C above the top metal temperature. This helps avoid thermal shock and potential damage to the rotor. 5. When starting in a hot state, ensure that steam is supplied after the steam seals are engaged. Before sealing, make sure all moisture is removed from the system. Only proceed with steam seal injection once the pipeline is fully drained. 6. Maintain a superheat of at least 14°C for both main and low-pressure steam supply. The low-pressure steam temperature should be kept between 121°C and 177°C to prevent condensation. 7. Stop the steam seal supply before the unit is driven. This prevents unnecessary moisture accumulation in the system. 8. If the steam temperature for high- and medium-pressure steam seals drops below 150°C or the temperature difference between the steam seal and the high-pressure cylinder end wall is less than 85°C, close the steam seal water spray to prevent moisture ingress. 9. During the start-up process, follow the "recommended maintenance value of steam turbine speed," "cold rotor heating regulation," and "hot-state recommended value" curves for warming up. Begin warming up when the medium-pressure cylinder inlet steam temperature reaches 260°C. 10. A dedicated person should monitor the vibration of each bearing during start-up. The shaft vibration should remain below 0.125 mm. If the vibration exceeds 0.1 mm at critical speed or the relative shaft movement exceeds 0.254 mm, stop the turbine immediately. Never force the turbine through critical speed or reduce speed for warming. 11. While operating, the bearing vibration should not exceed 0.03 mm, and the relative shaft movement should not go beyond 0.08 mm. If these values increase significantly, investigate and resolve the issue promptly. If the bearing vibration increases by 0.05 mm suddenly, stop the turbine immediately. 12. According to the "Central Control Operation Regulations," if steam turbine water hammer is detected, stop the turbine immediately to prevent severe internal damage. 13. Ensure that all high, low, and deaerator water levels are monitored and tested regularly. If a heater leaks, stop it and close the exhaust check valve to prevent further damage. 14. After shutdown, perform timely turning gear operations. If the current is higher than normal or unusual noises occur, report to the relevant departments. If the steam seal issues are severe, position the rotor's high point at the top, drain the cylinder, monitor the temperature difference between the upper and lower cylinders, and supervise the rotor’s straightness. If the torsion is normal, use the manual turning gear (1800) to straighten the shaft. Do not use a crane to force the turning gear. If the turbine stops due to a problem, suspend the turning gear and continue monitoring the rotor’s torsion. 15. Throughout the start-up, operation, and shutdown processes, strictly follow the "Technical Measures to Prevent Cold Steam and Water from Entering the Steam Turbine." Be cautious when switching valves to prevent cold air, moisture, or condensate from entering the extraction or drainage pipes. 16. Each shift should verify the local water level gauges of the deaerator and heater against the CRT readings to ensure accurate monitoring. For more information on bearings and related technologies, visit China Bearing Network. This article is linked from http:// Please cite China Bearing Network as the source: http:// Previous: Common Issues When KOYO Bearings Are Excited Next: What Is Required for Crankshaft Overhaul?
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