Broad review of “White Etching Crack” failure in wind turbine gearbox bearings: Main factors and experimental investigations

•White Etching Crack is a premature failure in wind turbine rolling bearings.•Hydrogen, sliding contact and inclusions could act as main WEC drivers.•Electrical currents, temperature and high stresses act as accelerating WEC drivers.•DER, WEB and butterflies are microstructural changes different from and close to WEC. Subsurface crack networks surrounded by microstructural alterations, named as “White Etching Cracks” (WEC), lead to wind turbine gearbox bearing (WTGB) premature failures. This phenomenon has been studied for decades without yet reaching a sturdy and justified cause of its occurrence. This paper reviews the most recent literature regarding WEC discussing steel microstructural alterations, WEC initiation modes, main WEC drivers, experimental procedures, as well as the influence of coatings and heat treatments on the occurrence of this phenomenon. A broad insight of the effect of each driver in WEC formation is presented and an undisclosed hypothesis related to WEC initiation is suggested. From this work it may be concluded that in the majority of the tests where WEC has been generated, three drivers usually appear and act synergistically: non-metallic inclusions, sliding and hydrogen.