White Etching Cracks
White etching cracks is a type of subsurface initiated pitting failure of hardened steels. These are commonly observed in wind turbine bearings. A subsurface crack is usually initiated on a metal inclusion, which then grows until it reaches the surface. They are characterised by early failure by pitting and can be viewed directly with subsurface analysis – viewing below the surface area using a sectioning, grinding and etching procedure. The WECs are cracks surround by a white etched area.
We generate WECs on small rollers and conduct subsurface analysis to confirm their presence.
The surface of a roller showing the presence of axial cracks and pits:
These axial cracks can then progress into a full subsurface pit. Examples are shown below from three repeat tests with a bad reference oil:
Sectioning the roller then reveals a network of cracks surrounded by white etching areas.
Any spalls found are associated with WEC networks: