What is Reliability-Centered Maintenance?
“A reliability-centered maintenance program includes only those tasks which satisfy the criteria for both applicability and effectiveness. The applicability of a task is determined by the characteristics of the item, and its effectiveness is defined in terms of the consequences the task is designed to prevent.” (Source: Nowlan and Heap, 1978)
In wind farm operations, Reliability-centered Maintenance (RCM) is an advanced strategy used to optimize reliability, production, and asset life for wind farm owners. RCM emphasizes the use of Predictive Testing and Inspection (PT&I) techniques in combination with traditional reactive, preventive, and proactive measures to determine the optimum tasks based on the consequences, costs, and safety risk.
A study of reliability-centered asset management in power distribution systems points out that “almost one third of all the maintenance costs are wasted as the result of unnecessary or improper maintenance activities which blindly and also indiscriminately involve almost all types of components with no or little consideration to the equipment’s lifetime, outage statistics, and economical value.” (Source: Dehghanian, Fotuhi-Firuzabad, Bagheri-Shouraki, Kazemi, 2012)
History of RCM for managing physical assets
RCM programs have existed since the 1960s and were originally developed and proven in the aviation industry and the principles were later adopted by the nuclear energy industry. Although there are many similarities between aviation, nuclear energy, and wind energy in terms of maintenance practices, wind seems to have been a late adopter of the cost effective strategies of RCM.
The SAE Standard for RCM (SAE JA1011) was created to help evaluate the RCM process across all industries where companies are looking to manage their physical assets responsibly. Companies must comply with the minimum RCM requirements in order to be in compliance with the SAE JA1011. SAE also developed the JA1012, “A Guide to the Reliability-Centered Maintenance (RCM) Standard”, to help guide organizations implement an RCM process.
In wind, larger turbines and a massive increase in the installed worldwide capacity has led to an emphasis on reducing operations & maintenance (“O&M”) expenses. To accomplish this goal more advanced maintenance strategies must be implemented. RCM is a process that lengthens the lifetime of the assets, optimizes the spare parts and components usage, and helps reduce OpEx. The strategy incorporates four different maintenance practices and a new implementation structure:
Components of an RCM Program
In a NASA study of RCM, four different types of maintenance programs were examined and combined in order to determine what the components of an RCM program looks like.
Value of an RCM Program
Optimizing maintenance with a systematic RCM approach can greatly reduce the OpEx of a wind farm. The graph below examines the long term cost benefits of transitioning from reactive-based practices to an RCM based approach. The net effect is a reduction of both repair and total maintenance costs. After a brief increase in implementation costs, the wind farm operator will realize a dramatic decrease in overall OpEx.
Effect on Maintenance and Repair Costs
(Source: NASA RCM Guide, 2008)
An RCM program must be clearly defined in order to be efficiently implemented. To do so, the technical standard SAE JA1011 defines the minimum criteria for the evaluation of RCM processes which begins with the below seven questions in consecutive order:
- Function – What is the item supposed to do? What are its associated performance standards?
- Failure modes – In what ways can it fail to provide the required functions?
- Failure causes – What are the events that cause each failure?
- Failure results – What happens when each failure occurs?
- Importance – In what way does each failure matter?
- Preventatives – What systematic task can be performed proactively to prevent, or to diminish to a satisfactory degree, the consequences of the failure?
- Alternatives – What must be done if a suitable preventive task cannot be found?
Example Applications of RCM on Wind Farms
The implementation of an RCM program on a wind farm can be analyzed by individual WTG subsystems. A 2011 IEEE research paper focused on the major components that comprise two turbine models’ distribution of downtime. The two technologies were similar in that the generator, electrical systems, drive train, and gearbox were the subsystems responsible for approximately 50% of the downtime. Preventative maintenance measures can be implemented on these subsystems, theoretically reducing 50% of the total downtime and driving down OpEx related to the maintenance and repair of these specific systems.
(Source: Fischer, Besnard, Bertling, IEEE 2011)
Wind Turbine Gearbox Example
The maintenance strategies for the gearbox, generator, electrical systems, and hydraulic systems can all be optimized with an RCM program. For Example, the gearbox’s components such as the bearings, gears, and lubrication components can be monitored and have data analyzed to predict failures and schedule optimal maintenance tasks. Replacing a failing bearing based on vibration data can prevent a catastrophic gearbox failure, saving a wind farm operator the expense of a new gearbox and lost production due to unplanned downtime.
“Prioritizing components for maintenance activities due to the scarce resources in distribution power system utilities is indispensable and RCM is the ﬁrst step toward a systematic maintenance trend.” (Source: Dehghanian, Fotuhi-Firuzabad, Bagheri-Shouraki, Kazemi, 2012)
Incorporating the four existing maintenance techniques (reactive, preventive, PT&I, and proactive) and making informed decisions based on consequences of the task, cost, and safety risk will ultimately drive down OpEx. Predictive maintenance alone is not enough; O&M providers need to adopt the RCM principles into their everyday processes and decision making to responsibly manage their assets.
John Ugland is the Manager of Performance Engineering for UpWind Solutions. John obtained a B.S. in Mechanical Engineering from the University of Colorado at Boulder, and spent several years in the medical device industry and commercial aviation before entering the wind industry over four years ago. John quite literally started from the ground up, and spent two years as a wind turbine technician and site lead.