When electrical potential discharges through a bearing, small arcs can locally melt the lining and mating surface. Repeated events produce pitting, frosting or tracks that degrade the surface and can generate further debris.
What the Damage Looks Like
- Fine pitting or a frosted, matt surface over the loaded area
- Isolated craters with locally melted edges
- Branching, dotted or circumferential spark tracks
- Corresponding marks on the shaft or thrust collar
Likely Contributing Factors
- Stray shaft current or residual shaft magnetism
- Ineffective, damaged or contaminated grounding arrangements
- Insulation unintentionally bridged by services or instrumentation
- Electrical machine faults or unsuitable earthing design
- Welding current passing through the shaft and bearing path
Diagnosis and Response
Move From Damage to Root Cause
What to Inspect
- Examine both bearing and mating surface under magnification
- Measure shaft magnetism and investigate shaft-voltage history
- Check grounding brushes, straps, insulation and monitoring devices
- Look for services or instrumentation that bridge insulated components
- Review welding and maintenance practices around the machine
Corrective Actions to Consider
- Correct the source and intended path of shaft current
- Restore effective grounding or insulation for the machine design
- Degauss components where residual magnetism is confirmed
- Prevent welding return current from crossing bearings
- Inspect and clean the oil system if discharge has released debris
Repair or Replace?
Electrical pitting cannot be solved by replacing the bearing alone. After the electrical path is corrected, assess crater depth, lining integrity and the shaft or collar surface to determine whether re-lining, machining or component replacement is required.
Diagnosis Note
Fine pitting can resemble erosion, corrosion or debris damage. Surface morphology, matching marks, electrical measurements and the machine configuration should be considered together before electrical discharge is assigned as the cause.
Need an Engineering Assessment?
Send photographs, operating data and failure history for an initial review by Oiltech Bearings.