Electrical Pitting Damage

• Results in damage to the bearing by intermittent arcing of electrical current as a result of voltage discharge across the oil film.

• The shaft and runner are usually effected as well.

Electrical Pitting Damage

• Electrical pits in a journal shell in the minimum film area.

Electrical Pitting Damage

• The shaft from the previous slide’s journal.

Electrical Pitting Damage

• “Frosting” due to stray currents on a shaft.

Electrical Pitting Damage

• Erosion of babbitt by electrical pitting.

• Note the angle of attack as the minimum film areas are affected first.

Electrical Pitting Damage

• More electrical pitting and similar angle of attack as previous slide.

Electrical Pitting Damage

• This shoe has both loss of babbitt due to electrical pitting and oil deposits.

• Note attack angle.

Electrical Pitting Damage

• Heavy pitting and scoring damage in a gearbox journal shell.

• The load pad on this 4-lobe bearing is effected.

Electrical Pitting Damage

• The shaft from the previous slide.

Electrical Pitting Damage

• Stray shaft currents on Kingsbury’s turbine driven test rig.

• Note the shoes were crowned.

Electrical Pitting Damage

• This damage was caused by welding. A large current was sent through the shoe and collar.

Abrasion

• Scratches caused by dirt and contaminants that enter the lube system.

• The particles must be small enough to enter the leading edge, by large enough to get caught before exiting the trailing edge.

Abrasion

• Scoring of thrust pad by dirt in oil.

• Note that the scratches follow the collars circular path.