High temperature in the turbine thrust bearing

It might be due to imbalance in the impeller or shaft, causing vibration.

Just two months after the replacement of the front bearing in the Siemens turbine, the temperature rose to 120°C again; this is a typical recurring fault. This indicates that the root cause of the problem lies not in the bearing itself, but in deeper systemic issues or installation defects. Simply replacing the bearing only addresses the “symptom,” not the “cause.” The following is a systematic analysis of the possible causes along with suggested steps for resolution: I. Analysis of main causes (ordered by likelihood) 1. Issues with the maintenance and installation process (highest likelihood) This is the primary suspect when faults recur after replacing new components. Improper bearing installation: The contact angle and contact area between the bearing and the shaft journal do not meet the requirements. Too small a contact area results in an excessive load per unit area, while too large a contact area hinders the formation of an oil film; both situations can lead to abnormal heating. Gap adjustment error: Radial gap (bearing clearance/overhead clearance) and axial gap (thrust clearance) are the key parameters. The gap is too small, resulting in an insufficient oil film thickness and direct friction ； An excessive gap can cause unstable oil flow and rotor vibration, which in turn generates heat. It is necessary to strictly follow the manufacturer’s standards provided by Siemens. Poor alignment: Excessive misalignment between the turbine rotor and the generator rotor is one of the most common causes of uneven bearing loads and increased temperatures. After two months of operation, factors such as foundation settlement, pipe stress, and thermal expansion may degrade the initial alignment. Preload issue: Uneven or insufficient preload on the fastening bolts of the bearing cover can cause the bearing housing to deform or vibrate during operation, thereby disrupting the stability of the oil film. 2. Lubricating oil system issues: The cooling and lubrication of bearings depend entirely on the lubricating oil system. Oil quality issues: The new oil may have quality problems, or there may be old oil, moisture, and impurities remaining in the system. After two months of operation, oil emulsification, oxidation, or contamination may occur, leading to a decline in lubrication performance and a reduced cooling effect. Insufficient oil volume/pressure: The throttle orifice plate supplying the bearing is clogged or of incorrect size, resulting in an insufficient actual flow rate. A decrease in the oil pump’s output, clogged filters, and pipeline leaks can also cause insufficient system oil pressure. Excessively high oil inlet temperature: Reduced efficiency of the oil cooler (scaling, blockages), high temperature of the cooling water or insufficient flow rate, all of which lead to an oil inlet temperature that exceeds the specified limit in the entire lubricating oil system. Nozzle/oil sac blockage: Residual materials from installation (such as weld slag, sealant) or impurities generated during operation block the oil inlet of the bearing or the oil sac (oil wedge area), disrupting the formation of the oil film. 3. Problems with the bearings and the bearing holes themselves: Deformation or damage to the bearing holes: Previous overheating issues may have caused the bearing holes to become out of round, tapered, or abraded. When a new bearing is installed in a deformed seat hole, it is not possible to achieve the correct geometric fit, which inevitably leads to abnormal operation. Incorrect bearing model or parameters: Although it is a new bearing, it is necessary to verify that its model, dimensions, and alloy material are exactly consistent with Siemens’ original design. The parameters of the replacement parts may vary slightly. Rotor journal damage: If the journal has been worn, abraded, or out of round due to previous high-temperature operation, installing new bearings will not result in a good fitting surface, and the component will wear out quickly and generate heat. 4. Operation and monitoring issues: Load or operating condition changes: During these two months, have the load rate, steam parameters, and extraction conditions of the unit differed from those in the past? Certain special operating conditions may cause changes in the axial thrust or the forces acting on the rotor, thereby increasing the load on the front bearings. Instrument indication error: There may be a fault with the temperature sensing element (thermal resistor/thermocouple) or its wiring, as well as with the display instrument, resulting in the displayed temperature being higher than the actual temperature. It is recommended to immediately use a portable infrared thermometer or spot thermometer to conduct comparative measurements at locations near the outer surface of the bearing housing for preliminary verification. 5. Structural or fundamental issues: Pipe stress: The main steam, extraction steam, and exhaust steam pipes connected to the cylinder generate significant stress on the cylinder when it is under heat; this stress can be transmitted to the cylinder and affect the alignment of the bearing housings. Deformation of the foundation frame: Uneven settlement of the unit’s foundation or insufficient rigidity of the frame can cause deformation during operation. Heat conduction/radiation: Is the front bearing too close to the high-temperature cylinder block? Has the insulation come loose, causing the bearing’s ambient temperature to become too high? II. Recommendations for systematic solution steps Principle: Start from the easy tasks to the more difficult ones, and proceed from the outside in, conducting a systematic investigation. Phase 1: Rapid inspection and handling without shutting down the system. Verify the accuracy of temperatures: Use a portable thermometer to measure the temperature at multiple points on the bearing housing and nearby oil pipes, and compare these values with those displayed by the DCS/TSI. Inspect the lubricating oil system: Check the oil level and color in the main tank, and take samples for laboratory analysis of oil quality (viscosity, moisture, particle count). Check the oil temperature and water temperature before and after the cold oil cooler to evaluate its efficiency. Check the filter on the bearing lubrication pipeline, as well as the pressure difference before and after the throttle orifice plate. Check whether the pressure throughout the lubrication system is stable. Check the operation records: Retrieve the trend curves for the past two months to analyze whether the temperature increase occurred suddenly or gradually, and whether it is associated with changes in load, speed, and vibration levels. External inspection: Check whether the insulation of the bearing housing and adjacent pipes is in good condition, listen for any abnormal noises during the operation of the bearings, and check for oil leaks. Phase 2: Planned shutdown for maintenance and thorough inspection. If the problem cannot be resolved without a shutdown, it is necessary to arrange a shutdown for maintenance, during which the following items should be checked carefully: Inspection of bearings: Record in detail any signs of wear on the new bearings; use red lead or blue ink to examine the contact points in order to determine whether the contact is satisfactory. Precision measurement: Use the lead pressure method or specialized tools to measure the radial clearance ； Measure the axial thrust clearance using a dial indicator. Comparison with Siemens maintenance manual standards. Check the journal and bearing alloy surfaces for scratches, wear, flaking, or corrosion. Inspect the bearing housing hole: Use an inner diameter micrometer to measure the roundness and cylindricity of the housing hole at multiple sections, to ensure there is no deformation. Recheck alignment data: At low temperature, conduct the shaft alignment check again strictly in accordance with the standards. Special attention should be paid to the thermal expansion value during unit operation, and \"cold-state alignment pre-compensation\" data should be used for verification. Thoroughly clean the lubrication circuit: Blow out or chemically clean all pipelines from the oil tank to the bearing supply ports in sections to ensure there are no blockages. Inspect the rotor: Carefully examine the shaft journals and polish them if necessary to ensure their smoothness and roundness. Phase 3: Advanced diagnosis If the above steps do not resolve the issue, it is necessary to consider hiring original Siemens technicians or experienced experts for on-site diagnosis. Perform hot alignment or online vibration spectrum analysis to identify hidden force misalignment or structural resonance issues. Consider conducting specialized simulation calculations of the bearing’s operating conditions to assess the compatibility between the design conditions and actual operating conditions. Summary and recommendations: The most likely combination of causes is improper bearing installation clearance/poor contact + minor issues in the lubricating oil system (such as slight deterioration of the oil quality or slight blockage of the orifice plates). Action roadmap: Immediate: Verify the temperature, check the oil system, oil quality, and operation records. As soon as possible: Schedule a shutdown to thoroughly check the installation clearance and contact points, and clean the oil supply lines of this bearing completely. At the same time: Check the geometric dimensions of the bearing housing hole and the condition of the shaft journal. If it recurs: a thorough and detailed recheck of the shaft alignment is necessary, along with seeking higher-level technical support. Be sure to keep all the inspection data, measurement records, and photos from this maintenance session; comparing them with the data from the previous maintenance is key to identifying any differences and issues. I hope these analyses can help you systematically identify and resolve issues.

The instructions that come with it randomly should be used to check the installation in accordance with the bearing installation requirements provided by the manufacturer; this will generally resolve any issues.