1. Unbalance & Bend shaft:
is the uneven distribution of body mass in rotating machine.
unbalance & shat bend or bow lead to the bearing vibrations in radial
2. Miss alignment:
is non-coincidence of shaft centers of two rotating mating machines.
alignment lead to axial vibrations of bearings
3. Looseness in turbine base bolts or
leads to radial vibrations
4. More bearing clearance:
clearance in journal bearings leads to radial vibrations
5. Rotor rubbing:
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:
rubbing with rotating parts like rotor or blades to vibrations in horizontal
rubbing may due to improperly mounted seals or eccentricity of seals.
7. Distortions in foundations & casing:
& 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 &
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
This leads to the vibrations of journal
bearings in axial directions
11. Defects in
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
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
Lube oil containing burs & other foreign
materials can also lead to high bearing vibrations
14. Lube oil & Control oil pipe line
& non stress relieved pipe lines lead to bearing vibrations. Oil lines not
having expansion bellows may transfer vibrations from pump & lines to
15. Steam line forces & Aerodynamic forces:
steam line, improperly supported steam lines transfer vibrations to turbine
16. Changes in steam parameters:
quality of steam changes for an example, reduced steam temperature, wet steam
17. Overloading the Turbine:
turbine is loaded beyond the allowable capacity for long time without
consultation with OEM can certainly lead to bearings vibrations & subsequent
18. Other probable reasons for bearings
- Turbine resonance
- Operating the turbine in critical speed
- Wrong installation