Why do Bearings fail?

 Following are the 16- top listed reasons for bearing failure or damages

1-Lubrication:

Following are the 7 major reasons for bearing failures related to lubrication

1-Lack of lubrication

2-Less lubrication

3-Over lubrication

4-Contaminants in lubricants

5-Wrong method of lubrication

6-Poor quality of lubricants

7-Selection of wrong lubrication

8-Lubricant failure

2-Bearing clearance:

Bearings may fail if the clearance between rolling elements & race is too less & too more. Lesser bearings clearance than desired creates friction & temperature rise.

More bearing clearance creates vibrations

3-Operating the bearings at higher vibrations for long time:

Bearings can operate satisfactory at the vibrations range up to 5 mm/sec, vibrations more than this reduces the bearing life & eventually failure.

Operation range: 0.5 to 3 mm/sec

Alarm Range: 3 to 5mm/sec

Trip range: > 5mm/sec

High vibrations in machine or bearings are due to;

1-Axial vibrations due to misalignment

2-Horizontal vibrations due to imbalance in machine

3-Vertical vibrations are due to looseness in foundation bolts

4-Shaft run out

4-Operating the bearing at excessive loads:

Excessive load on bearings leads to premature fatigue, over loading creates other side problems like bearing overheating, damage to rolling elements.

Brinelling occurs when loads exceed the elastic limit of the ring material. Brinell marks show as indentations in the raceways which increase bearing vibration (noise]. Severe brinell marks can cause premature fatigue failure.

 

5-Overheating

Overheating & damage of the bearings is due to;

1-Lack of lubrication

2-Over lubrication

3-Improper cooling of bearings

4-Excessive loads

6-Smaller clearance between rolling elements & race

Operating the boilers at higher temperature (>90 deg C for ball bearings & sump cooling) will lead to annealing the races & rolling elements that, eventually fails the bearings.

7-Miss alignment

Running the equipments at misaligned condition creates vibrations & excessive loads on bearings in axial, vertical & horizontal directions that causes bearing failures.

Misalignment also leads into failure of couplings & equipments parts like seals, impellers, pulley etc

8-Frequent start & stops of machine

Leads to jerk load on bearings & leading to reduction of its life

9-Not following of equipment/machine SOP:

If machine SOP (standard operating procedure) is being not followed, then it could cause not only bearing failure but also machine other elements.

For example if pump is not started with discharge valve closed or not stopped without closing discharge valves, it could cause jerk loads on bearings & impellers. After some cycle it will reflect it effect on misalignment, vibrations etc

10-Reverse rotation of machine or reverse loading of bearing element:

Some machines & bearings are not recommended for reverse rotation.

For example: Boiler feed pumps & screw compressors are meant to rotate in only one direction

Also Angular contact ball bearings are meant to take load only in one direction

11-Corrosion in Bearings:

Red brown areas on balls, raceways, cages, or bands of ball bearings are symptoms of corrosion. This condition results from exposing the bearings to corrosive fluids or a corrosive atmosphere. The usual result is increased vibration followed by wear, with subsequent increase in radial clearance or loss of preload. In extreme cases. Corrosion can initiate early fatigue failures.

12-Loose & tight fittings of bearings:

Fitting of bearings loose on shaft or loose in housing leads to rotation of bearings outer race in housing, this causes rubbing & bearing damage.

As like loose fitting, very tight fit can also cause excessive load on rolling elements which eventually creates overheating & vibrations

13-Entry of water in bearings grease

14-Material or manufacturing defects in bearings cause bearing failure as soon as it is been installed.

15-Leakage current in VFD motor bearings lead to bearing failure

16-Carrying out welding near bearings or Plummer blocks without proper earthing can lead to flow of currents through bearings, which ultimately causes bearing failure

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