SECTOR FOCUS: TURBINE OILS
Lubricant Additives to Help Mitigate White Etching Cracks
Dr Aubrey Burrows, Senior Consultant, Nanol Technologies Oy
Introduction The growth of wind turbines as multi-megawatt power plants leads to ever higher pressures and forces, which have an adverse effect on the mechanical components. Bearing failure caused by white etching cracking (WEC) is commonly observed in wind turbine gearboxes.
The name WEC is derived from the white appearance of the fissures in the microstructure of steel, which can result in costly parts failure. The condition happens without warning because it occurs below the surface of a bearing and is not possible to detect.
Once WEC damage reaches the surface of a bearing it is too late. The resulting component failure can require extensive and costly maintenance to put right, particularly offshore.
WEC has been known about for several years, and there is no lack of theories to explain the phenomenon, but despite intensive lubricant research, it remains a mystery, and no effective lubricant solutions are available. Some studies have pointed to hydrogen embrittlement as playing a vital part in bearing failure, and that lubricants are the primary source of the hydrogen. This means that while lubricants should be protecting the metallurgy, they may actually be contributing to the WEC problem.
Figure 1: White etching cracks
Lubricant Challenges WEC has created a major challenge for the original equipment manufacturers (OEMs). The mechanical systems have had to be redesigned, by changing bearing surface finishes. OEMs have now become much more risk-averse and are reluctant to approve oils. The wind turbine industry is urgently seeking more effective lubricants, and has appealed to lubricant additive companies to find more creative technology. However, a breakthrough has been made with the discovery of a new lubricant additive solution for WEC, based on
16 LUBE MAGAZINE NO.161 FEBRUARY 2021
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