Bearing Failure

Brinelling – Bearing failure

Brinelling (true brinelling) refers to the permanent deformation of a bearing surface, commonly the rolling surface of the bearing raceways, caused by excessive load on the bearing.

Also referred to as:
True Brinelling, Overload, Loading Marks

What is brinelling?

Brinelling, also referred to as true brinelling, occurs when there is permanent deformation on a bearing surface—most often the rolling surfaces of the bearing raceways. This failure is due to excessive load that surpasses the material’s yield strength, leading to permanent indentations or depressions in the surface.

Brinelling is commonly observed when bearings experience static overload or shock loading. It creates elliptical or line-shaped marks depending on the type of rolling element involved. This form of bearing failure is often confused with false brinelling, which is a different mechanism caused by vibration-induced fretting corrosion, rather than overload. False brinelling damage results from surface wear, not plastic deformation.

Causes of brinelling

True brinelling is caused by an excessive load applied to a bearing, so that the contact stress exceeds the elastic limit of the ring or rolling element material. This excessive load can be either a static overload of the bearing or a shock load experienced during operation and can be caused either by a single overload event or a series of overloads.

A static overload can be experienced when the turbine rotor is locked during maintenance, or when the wind speed is not sufficient enough to rotate the rotor, and there is a high load applied to the bearing. These high loads could be caused during maintenance work, or could simply be from the rotor weight if the bearing has not been properly designed to withstand it. Excessive preloading or mishandling during transport or installation can also cause brinelling.

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Appearance of true brinelling marks

True brinell marks are a permanent deformation of the rolling surfaces of a bearing. The deformation marks are typically shaped either elliptic, round or rectangular depending on the shape of the Hertzian contact patch, which changes for different bearing types. Although identical in shape to a false brinell mark (see Fretting Corrosion), the original surface finish can still be seen in the depressions of a true brinell mark. Brinell marks in bearings are commonly seen in groups, as a single brinell mark will be created from each rolling element in the load zone where the contact stress exceeds the yield stress of the material. There may also be raised edges observed around the brinell mark as material around the edges are pushed upwards as the depression is created. Micropitting may be visible around the edges of the brinell marks.

Progression and damage

The plastic brinell depressions will create local stress concentration areas, and when overrun by other rolling elements during continued operation, cracks could initiate in the raceway surfaces. Potential sharp raised edges formed at the edge of the brinell marks can cause macropitting to occur when overrun during continued operation due to the increased cyclic stress at the edge of the brinell mark. This will typically occur downstream of the brinell mark, in the rolling direction. Also, a reduction in the oil film thickness may be seen due to the depressions allowing oil to fall into them. This can lead to increased wear particles in the oil due to more boundary contact between surface asperities, causing consequential damage to other components.

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Advanced sensing

Detection of brinelling

Method

Detection Efficiency

Notes

Borescope inspection

Easy

Provides clear visibility of true brinelling and can differentiate between true and false brinelling.

Visual inspection

Medium

Visible to the naked eye if accessible, but minor brinelling may require tools like a borescope.

Vibration analysis

Medium

Detects large brinelling marks through repeated impulses, indicating excessive stress or load.

SCADA data

Not applicable

SCADA systems do not provide helpful data for detecting brinelling.

Oil debris sensor

Not applicable

As no material is shed during brinelling, an oil debris sensor will not detect brinelling.

Oil sample analysis

Not applicable

As no material is shed during brinelling, an oil sample analysis will not detect brinelling.

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Preventing brinelling

To avoid brinelling, it’s important to take several precautions:

When mounting, apply the load to the race being mounted (inner ring for shaft mounting, outer ring for housing mounting) to prevent overloading.
Ensure that the bearing is properly designed for the static and dynamic load capacity required by the application.
During maintenance, avoid high static loads by ensuring that rotor weight and other forces are within the bearing’s load capacity.

Proper handling during transportation, installation, and maintenance is crucial for avoiding true brinelling and prolonging bearing life.

Conclusion

True brinelling can cause severe damage if not properly addressed. By understanding the causes, detection methods, and prevention strategies, operators can significantly extend the life of their bearings and avoid costly repairs. For advanced bearing failure prevention and detection systems, ONYX offers tailored solutions that minimise downtime and optimise operations.

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Severity rating

Rank 1 N/A

Detection:

N/A

Recommended action:

N/A

Rank 2 N/A

Detection:

N/A

Recommended action:

N/A

Rank 3 Permanent deformation depression in the shape of the Hertzian contact patch between the rolling elements and raceways (ellipse, round or rectangle). Material is pressed into the surface so the original surface finishing marks are visible. May see raised edges around the brinell mark.

Detection:

Borescope, vibration

Recommended action:

Run turbine. Increase inspection frequency to monitor for progression. Consider scheduling replacement.

Rank 4 Progresses to other failure modes

Detection:

N/A

Recommended action:

N/A