Gamesa G8X Wind Turbines Blade Bearing Inspections & Preventive Maintenance
ROLLIX non-geared double row 4-point contact ball bearing, 1900 cm raceway diameter
Location
Ayrshire, Scotland
Cost Analysis
+ £1.5 Million (potential revenue gain from existing components)
+ £6 Million (potential net revenue loss from catastrophic failures)
The
Scenario
One of our clients (a world leader in wind energy & one of the world’s largest integrated utility companies) had received some lubrication grease sample analysis reports of concern for 3 Gamesa G8X wind turbines blade bearings during routine servicing.
GEOX Engineering Ltd were asked to investigate and complete a comprehensive analysis & formal independent inspection to uncover a source for the abnormal lubrication sample analysis data of concern and provide current operational condition of the 9 blade bearings, where applicable RUL (remaining useful life).
Our
Analysis
During the bearing analysis & inspection, GEOX Engineering Ltd completed both dynamic and static data capture, this included bearing ultrasound during pitch motion, impedance, tilt clearance, acceleration (g) & relative angle run-out during pitch motion, visual audit – all subcomponents, independent re-evaluation of grease sample analysis reports, blade bearing intrusive borescope verification where applicable.
Turbine #1 had ultrasound data indicating some low-level friction and likely under-lubrication present, satisfactory tilt clearance, no acceleration impacts of concern, no angle run-out patterns of concern. Turbine #1 selected for further preventive maintenance by adequate purging/replenishment of grease to extend RUL (remaining useful life), no further borescope verification necessary.
Turbine #2 had ultrasound data indicating severe friction levels and highly likely deformity present, signature of concern (fatigue/wear/contamination), excessive tilt clearance present, some severe acceleration impacts of concern, relative angle run-out of concern. Borescope verification showed evidence of excessive cage, roller ball & raceway large debris, roller balls out of round, excessive cage clearance, destructive pitting and coalesced spalling.
Turbine #3 had ultrasound data indicating severe friction levels and highly likely deformity present, signature of concern (fatigue/wear/contamination), excessive tilt clearance present, some severe acceleration impacts of concern, relative angle run-out of concern. Borescope verification showed evidence of fractured cage, excessive roller ball & raceway large debris.
Evidence confirms, the bearings have significant under lubrication present. Continued operation with the blade bearings on Turbines #2 & #3 could highly likely result in catastrophic failure, this could have the potential to remove the turbines from operation for the remainder of their remaining useful life. A further 7 years remaining could result in > £6 Million net revenue loss for the client. Continued operation with the blade bearings on Turbine #1 would highly likely result in surface-initiated spalling/fatigue (or by definition failed, regardless of severity) within 2-3 years.
Our
Solution
Turbines #2 & #3 were advised inoperable by inspection team (to prevent further catastrophic failure), turbines to remain in stop pending blade bearing exchange at the earliest opportunity.
On Turbine #1 an extensive purge/flush of the current contaminated bearing lubrication grease was highly recommended during the inspections. All 3 blade bearings had been replenished with new grease lubrication as per specification and quantity as necessary by inspection team.
The specified OEM quantity of grease for replenishment each service and/or using an automated greasing unit is calculated as an estimated value only for a valid operating temperature, using good quality grease with a lithium thickener and mineral oil base, so when operating conditions differ, adjustments must be made to the lubrication intervals accordingly. On this occasion, due to extended periods between service lubrication and/or reduced quantity during service, an increase in suitable quantity for adequate bearing replenishment should be taking place with careful consideration to operating/run hours.
Due to GEOX Engineering Ltd.’s effective purging/flushing of the contaminated grease and replenishment of new grease fill in each blade bearing on Turbine #1, using industry adjustment factors for calculating bearing rating life we should extend RUL (remaining useful life) up to 100%. All 3 blade bearings had an estimated RUL (or when it would reach incipient spalling category 3 damage for failure whatever the severity) of 2-3 years, by correcting the contaminated grease we should extend RUL to 5-6 years minimum (propagation of spalling inception), provided there is no further issues with service lubrication, water ingress or hydraulic oil leakage penetration of inner blade bearing seals.
A total of 21 years life extension is predicted across 3 blade bearings on Turbine #1. Cost analysis shows this equates into a predicted > £1.5 Million net revenue gain from existing components for the client.
A total of 14 years life extension is predicted across Turbines #2 & #3 by GEOX Engineering Ltd advising immediate stop on both turbines pending bearing exchange due to advanced bearing failure and margin for safety conditions met. Cost analysis shows this equates into a predicted > £6 Million from potential net revenue loss from catastrophic failure.
NB: Adding too much or too little grease is one of the most common reasons for bearing failure. Too much grease builds up and eventually causes increased friction and pressure, and that causes excess heat. Too little of grease has the same life-shortening effect on bearings too.
