Fatigue in which cracks grow under repeated contact stress and break out small pieces of metal, leaving craters usually half a millimetre across or larger. Initial pitting on new gears can stop once the high spots wear in; progressive pitting keeps spreading into spalling, noise and eventually tooth fracture. Oil analysis catches it as a rising PQ and fatigue particles on the ferrogram, and vibration picks up the gear mesh sidebands.
Progressive pitting across the pitch line on two teeth, trend it monthly on vibration until the shutdown.
Also heard as
- macropitting
- fatigue pitting
Related terms
Micropitting
Fatigue damage made of tiny pits, about 10 to 20 microns deep, that turns gear and bearing surfaces dull gray.
Spalling
Flaking of large chunks from a bearing race or gear tooth after fatigue cracks below the surface link up.
Analytical ferrography
Microscope study of wear particles pulled from oil by a magnet, used to identify how a machine is wearing.
PQ index
Magnetic measure of total ferrous debris in an oil sample, including large particles that spectrometers miss.