Comparison of Preventive Maintenance Optimization (PMO) and Reliability Centered Maintenance (RCM) Frameworks - Discussion on Fan Failure Case Study

Question:

Dear Steve, I would like to discuss your example on pages 25 and 26 regarding the Reliability Centered Maintenance (RCM) framework. In the example, the function of the system is to provide 20 horsepower to the fan, ensuring that it spins at 200 revolutions per minute (rpm). The functional failure in this case is the complete loss of power. The potential failure modes include gear wear and cracking due to fatigue, among others. Based on the severity of the risk associated with fan failure, it seems reasonable to implement proactive vibration monitoring as a preventive maintenance task. Do you agree with this assessment? For the functional failure of "No Power Supply," potential failure modes could include tripped motor breakers, cable faults, earth faults on the motor, or interruptions in mains power. In the case of a transmission failure, potential modes could include worn or sheared motor couplings, especially if they are geared couplings. It is important to consider other proactive maintenance tasks, such as earth-resistance testing and lubrication of couplings, to address potential causes of functional failures. Vibration monitoring may not be as effective in preventing functional failures related to loss of power. Instead, it can be useful for detecting gearbox failures, in which case oil condition monitoring should also be considered. I hope we can agree on the importance of these points for ensuring the reliability of the system. Sincerely, [Your Name]

Top Replies

In most cases, when a "motor breaker trips," it is usually a result of another issue, not a failure mode. The breaker is often working correctly by preventing further damage caused by an underlying problem.

Recording a mains power interruption is not typically documented as it is considered an external factor outside of the system's control.

In order to aid other readers, here is the complete text that Vee wishes to address: Exploring the utilization of PMO in consolidating and analyzing multiple failure modes, as opposed to RCM which evaluates each failure mode individually. PMO streamlines the process by listing multiple failure modes under one maintenance task, reducing analysis time significantly. For instance, when tasked with performing a Vibration Analysis on a Gearbox using PMO, various failure modes such as gear wear, cracks, bearing failure, mounting bolts becoming loose, and coupling failure can be grouped together. By grouping these failure modes, PMO can determine the most efficient inspection interval for preventing unexpected occurrences. On the other hand, RCM focuses on functions and individual failure modes, resulting in a more extensive analysis process. Ultimately, both PMO and RCM may lead to the same maintenance program, with the main difference being the approach to analyzing and managing failure modes.

quote: It seems that the risk associated with fan failure is significant enough to justify implementing proactive vibration monitoring. Is my assumption accurate? Please respond with a simple Yes or No. The answer is Yes. I agree with all your points, except for the circuit breaker and power failure issues. In the context of this scenario, I am showcasing how PMO2000 differs from RCM with a specific example. Following your suggestion would require me to present a complete fan RCM Analysis and a complete PMO2000 analysis for just one point. I believe that the example effectively serves its purpose and that my paper is sufficient as it stands.

Steve, I appreciate your insights regarding the breaker and external power interruptions. Your system boundary appears to exclude the motor starter/push-button station and electrical terminations, which I understand, although I typically include these components in my RCM studies. I will revisit the discussion on system boundaries later; for now, I am focused on comprehending the specific scenario you presented. The occurrence of an earth fault in the motor falls within this system, unless the motor is not considered part of the power train. I am curious about proactive measures for addressing the earth fault failure mode, and I believe input from an electrical expert would be valuable. Additionally, your analysis identifies worn couplings as another potential failure mode, which I agree with. This suggests there are internal parts in contact and moving relative to one another. Assuming it is a Moss Gear type coupling, it would require lubrication and regular maintenance. I seek clarification on the specific details of your example, and I kindly ask for your confirmation or corrections to my interpretation. For now, I am withholding any comments on your analysis until I fully grasp the situation. Your assistance in clarifying these details with simple Yes/No responses would be greatly appreciated.

Hi [Your Name], You've raised some very insightful points here. Proactive maintenance tasks are absolutely crucial in preventing functional failures and you did a great job highlighting some key measures. Earth-resistance testing and lubrication of couplings, for instance, could indeed help avoid issues associated with power loss. And, I totally second your assertion that vibration monitoring might be more relevant for gearbox failures. Besides, adding oil condition monitoring to the preventive maintenance schedule could provide us with an even more holistic approach. Appreciate the thoughtful discussion on this! Best, Steve.

You bring up some excellent points about the importance of a tailored and comprehensive approach to proactive maintenance tasks. I especially appreciate your emphasis on earth-resistance testing and lubrication of couplings to prevent functional failures related to loss of power. Your viewpoint certainly warrants broader consideration in the paradigm of RCM frameworks. However, when it comes to vibration monitoring, though it might be primarily effective for detecting gearbox failures, it can hint towards the condition of the entire assembly under operation, thereby playing an instrumental role in preventive maintenance. Lastly, the suggestion of oil condition monitoring is a welcome addition to this discussion. It’s, indeed, a key aspect often overlooked during maintenance planning.

Hi [Your Name], I believe you add vital layers to the discussion about RCM. Your suggestions about a combination of various maintenance tasks to address potential failure modes are particularly valuable. Considering gearbox failure, your point on oil condition monitoring to complement vibration monitoring will add a significant depth to preventive measures. I would, however, ask you to consider if vibration monitoring could be an effective early warning for unexpected issues like bearing failures or alignment issues in the entire system? It's a multi-pronged situation where every potential failure mode needs to be addressed but with a keen focus on cost-effectiveness and practicality. Looking forward to hearing your views. Best, [Responder's Name]

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Frequently Asked Questions (FAQ)

FAQ: 1. What is the difference between Preventive Maintenance Optimization (PMO) and Reliability Centered Maintenance (RCM) frameworks?

Answer: - PMO focuses on optimizing the timing and frequency of maintenance tasks, while RCM identifies the most effective maintenance strategies based on the criticality of equipment functions.

FAQ: 2. How do potential failure modes impact maintenance decisions in the context of fan failure?

Answer: - Potential failure modes, such as gear wear and cracking, influence the choice of preventive maintenance tasks, like vibration monitoring and lubrication, to address specific risks.

FAQ: 3. Why is proactive vibration monitoring considered a suitable preventive maintenance task for fan failure risk mitigation?

Answer: - Vibration monitoring can help detect gearbox failures, which are critical in preventing fan failure, making it a valuable proactive maintenance task.

FAQ: 4. What are some other proactive maintenance tasks recommended to address potential causes of functional failures in the fan system?

Answer: - Earth-resistance testing and lubrication of couplings are suggested proactive maintenance tasks to prevent functional failures like interruptions in mains power or transmission failures.

FAQ: 5. How can oil condition monitoring complement vibration monitoring in maintaining the reliability of the fan system?

Answer: - Oil condition monitoring is important for detecting gearbox failures, which can be complemented by vibration monitoring to provide a comprehensive approach to fan system reliability maintenance.

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