Reasons for large shaft displacement in centrifugal compressors

Inspect the drive side, coupling, and thrust bearing

It’s time for the cycle – check the outlet temperature and bearing temperature

⒈Thrust bearing wear, resulting in axial displacement； ⒉The thrust bearing has shifted.

The reasons for changes in turbine shaft displacement can serve as a reference; the principle is the same. What are the reasons for changes in the axial displacement indication of a running turbine? 1. Load variations. 2. Severe fouling of the blades. 3. Changes in steam temperature. 4. Variations in steam flow rate. 5. Significant leakage from the high-pressure shaft seal, leading to an increase in the temperature of the bearing housings. 6. Frequency changes. 7. Blade breakage during operation. 8. Water impact. 9. Wear or damage to the thrust bearings. 10. Disruption of the extraction steam supply, resulting in changes in axial thrust. 11. Movement of the generator rotor. 12. Changes in the pressure used for venting air from the high-pressure shaft seal. 13. Changes in vacuum level. 14. Electrical shaft displacement meters are affected by changes in frequency and voltage. 15. Hydraulic shaft displacement meters are influenced by changes in the oil pressure and temperature at the outlet of the main oil pump. The basic settlement of 16 can also affect changes in axial displacement; changes in axial displacement indicate that the relative position between the moving and stationary parts of the turbine has changed. If the value of the axial displacement approaches or exceeds the minimum axial clearance between the moving and stationary parts of the turbine, friction will occur, causing severe damage to the turbine. For example, during severe water impact, the axial thrust increases, leading to the melting of the bearing bush in the thrust bearings, and the axial displacement also increases. At this point, the vacuum should be broken to trigger an emergency shutdown; otherwise, the flowing components will collide with each other, leading to an escalation of the accident. If the unit is equipped with an axial displacement protection device, this device will automatically activate to trip and shut down the machine.

1 Caused by abnormal wear of the thrust bearing pads； 2 Changes in axial thrust due to load variations ； 3 Caused by excessive compressor load ；

What was written upstairs is already quite comprehensive; I’ll just add a few additional observations: it also has something to do with the structure of the shaft. When the shaft end is equipped with a speed measurement pin or other attachments, even minor changes in the manufacturing process can easily lead to the loosening of the fastening bolts.

The reasons are as follows: 1. Water impact (steam carrying water): Water droplets hitting the blades increase the axial thrust; at the same time, these droplets move slowly within the turbine, blocking the steam flow and creating a large pressure difference before and after the impeller. 2. Increased clearance in the shaft seal: Intense vibrations occur due to improper startup of the turbine, leading to increased air leakage. 3. Sudden drop in the temperature of the fresh steam: This causes the rotor’s temperature to drop, and its contraction is greater than that of the cylinder, increasing the load on the thrust bearings. When a flexible coupling is used in the turbine, it acts as a brake on the rotor’s movement, thereby increasing the thrust on the thrust bearings. With a gear-type coupling, problems become even more severe if the gears or claws are worn or stuck, making it easy for the thrust bearings to fail. 4. Drop in vacuum: A decrease in the vacuum level in the turbine’s condenser increases the reaction degree within the stages. 5. The turbine operating beyond its capacity. 6. Damage to the thrust bearings. 7. Sudden significant changes in the operating conditions of the heating extraction unit. 8. Defects in the lubrication system, such as too low pressure or too high oil temperature, can destroy the oil film, causing the thrust bearing surfaces to burn and the rotor to shift (reasons for oil film destruction: a) too low lubrication pressure, b) too high oil temperature, c) interruption in lubrication supply, d) poor quality of the oil, e) water in the oil, f) excessive gap between the bearing surfaces and the shaft, g) detachment of the bearing surfaces, h) electrical leakage from the generator or exciter). The hazards associated with axial displacement are well understood: overload of the thrust bearings, burning of the thrust bearing surfaces, friction between moving and stationary parts, breakage of the blades, bending of the main shaft, and fragmentation of the partitions and impellers – all of which are serious accidents

It’s not certain. We need to see if the temperature rises gradually. If it’s the thrust bearing that’s worn out, the temperature will definitely rise significantly; in worst cases, the bearing could burn out. I still suspect it’s an issue with the instruments, so a thorough analysis is needed

Reasons for increased shaft displacement: (if instrument issues are ruled out) 1. Increased load (changes in flow rate, molecular weight of the medium)； 2. Check whether there is a problem with the pressure in the balance tube ； 3. Wear of balance drum seal ； 4. Have the temperature and pressure of the lubricating oil changed?

Could it be that the stiffness of the support is insufficient? I just read it in a book