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FAILURE: ROOT CAUSE ANALYSIS


Fatigue damage originating from the raceway edge of a blade bearing


BLADE BEARING – PROBLEM A wind turbine blade bearing was taken out of service due to pitch angle asymmetry. Upon disassembly, the failure was identified as macropitting at the edge of the bearing raceway. Macropitting is a progressive failure mode driven by fatigue of the steel material.


BLADE BEARING – CAUSE The damage was caused by excessive contact stress at the edge of the raceway where the contact area of the rolling elements had shifted beyond the raceway edge, referred to as ‘ellipse truncation’. The increased stress this causes to the components reduces fatigue life, leading to early failure.


BLADE BEARING – SOLUTION Design improvements were made to improve the raceway contact, thus minimising the edge contact stresses during ellipse truncation. This was achieved by stiffening the rings, adjusting pre-load and optimising the micro-geometry of the raceway profile. The failure costs of the installed base can be alleviated by periodic grease sample analysis. Early detection of failures allows forecasting for bearing replacement, thus minimising downtime and crane fees.


RCA BENEFIT


Without knowledge of the failure cause the turbine owner would have replaced failures with new bearings destined to fail. The RCA has enabled the owner to source aftermarket bearings with the necessary design improvements.


Romax Technology Click to view more info


FE analysis shows the high contact stresses at the edge of the raceway


ED’S NOTE


Abridged version please read full article online – link here


Click to view more info


www.windenergynetwork.co.uk


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