1. Unbalance & Bend shaft:
Unbalance is the uneven distribution of body mass in rotating machine.
Machine unbalance & shat bend or bow lead to the bearing vibrations in radial direction
2. Miss alignment:
Miss alignment is non-coincidence of shaft centers of two rotating mating machines.
Miss alignment lead to axial vibrations of bearings
3. Looseness in turbine base bolts or foundation bolts leads to radial vibrations
4. More bearing clearance:
More clearance in journal bearings leads to radial vibrations
5. Rotor rubbing:
If Turbine rotor rubbing with any other stationary parts leads to more radial & axial vibrations. If it is rubbing radially then radial vibrations increase & if it is rubbing in axial direction then there will be more axial vibrations.
6. Seal rubbing:
Seal rubbing with rotating parts like rotor or blades to vibrations in horizontal directions.
This rubbing may due to improperly mounted seals or eccentricity of seals.
7. Distortions in foundations & casing:
Distortion & deflection of foundation include base frame and structure on which turbine is rested. In such cases bearing vibrations are most likely in radial direction & in axial direction. Also vibrations on base frame & on foundations show more.
Similarly bearings vibrations increase in radial direction due to casing distortion. Also casing vibrations show more.
8. Defective bearings:
Bearings vibrations are high in radial direction if bearing is defective in respect to pitting, wear, cracks & more clearance.
9. Inadequate Rigidity in bearing Pedestals:
Bearings start to vibrate in horizontal, vertical & axial directions if pedestal rigidity is less in horizontal, vertical & axial directions respectively.
10. Damage of thrust bearings
This leads to the vibrations of journal bearings in axial directions
11. Defects in coupling:
Coupling defects like more run out, looseness or crack also lead to turbine bearings vibrations
Defective couplings lead to bearings vibrations in both axial & radial directions.
12. High lube oil temperature:
High lube oil temperature causes decrease in viscosity of oil, which in turn reduces the oil film between journal & bearings leading to high vibrations in radial directions.
13. Contaminants in oil:
Lube oil containing burs & other foreign materials can also lead to high bearing vibrations
14. Lube oil & Control oil pipe line forces:
Improperly aligned & non stress relieved pipe lines lead to bearing vibrations. Oil lines not having expansion bellows may transfer vibrations from pump & lines to turbine bearings
15. Steam line forces & Aerodynamic forces:
Stresses in steam line, improperly supported steam lines transfer vibrations to turbine
16. Changes in steam parameters:
If the quality of steam changes for an example, reduced steam temperature, wet steam etc
17. Overloading the Turbine:
If the turbine is loaded beyond the allowable capacity for long time without consultation with OEM can certainly lead to bearings vibrations & subsequent failure.
18. Other probable reasons for bearings vibrations are
- Turbine resonance
- Operating the turbine in critical speed
- Wrong installation