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AMAZON multi-meters discounts AMAZON oscilloscope discounts 6. Other Maintenance Strategies Maintenance Tasks to Prevent Failures An asset has a predefined life expectancy based upon how it has been designed. The design life of most assets requires periodic maintenance. For example, belts and chains require adjustment; alignment of shafts such as pump-motor shafts need to be properly maintained; filters need to be changed at regular intervals; proper lubrication on rotating machinery is required; and so on. In some cases, certain components need replacement after a specified number of hours of operations, e.g., a pump bearing on a hydraulic system to ensure that the system lasts through its design life. Anytime we fail to perform maintenance activities, we may be shortening the operating life of the asset. Over the past 40 years, many cost effective approaches have been developed to insure an asset reaches or exceeds its design life. Instead of waiting for assets to fail and then fixing them, maintenance actions are performed to keep assets in good working condition to provide continuous service. When an asset breaks down, it fails to perform its intended function and disrupts scheduled operation. This functional loss - partial or total - may result in defective parts, speed reduction, reduced output, and unsafe conditions. For example, a wear or slight damage on a pump impeller, which reduces output, is a function reduction failure. Function disruption or reduction failures that are not given due attention will soon develop into asset stoppage if not acted on. Many abnormalities such as cracks, deformations, slacks, leaks, corrosion, erosion, scratches, excessive heat, noise, and vibration, are indicators of imminent troubles. Sometimes these abnormalities are neglected because of the insignificance or the perception that such abnormalities won’t contribute to any major breakdowns. The tendency to overlook such minor abnormalities may contribute to serious catastrophic failures. It’s not uncommon to receive queries from production staff in response to a "high temperature or vibration condition" about how long they can continue running. It has been observed that a high percentage of failures occur during startups and shutdowns. However, asset failure could also be due to poor maintenance. Causes that go unnoticed are termed as "hidden abnormalities." The key to achieving zero failures is to uncover and remedy these hidden abnormalities before failure actually occurs. This is the fundamental concept of maintenance, specifically Preventive and Condition/ Predictive Maintenance. Preventive Maintenance (PM) Preventive maintenance refers to a series of actions that are performed on an asset on schedule. That schedule may be either based on time or based upon machine runtime or the number of machine cycles. These actions are designed to detect, preclude, or mitigate degradation of a system and its components. The goal of a preventive maintenance approach is to minimize system and component degradation and thus sustain or extend the useful life of the asset. Preventive maintenance is the planned maintenance of assets designed to improve asset life and avoid unscheduled maintenance activity. PM includes cleaning, adjusting, and lubricating, as well as minor component replacement, to extend the life of assets and facilities. Its purpose is to minimize failures. Neither assets nor facilities should be allowed to go to the breaking point unless we have selected a run-to-failure strategy for that specific asset. In its simplest form, preventive maintenance can be compared to the service schedule for an automobile. The amount of preventive maintenance needed at a facility varies greatly. It can range from walkthrough inspections of assets and facilities to measuring bearing clearances, checking pump and motor alignment, etc., while noting other deficiencies for later corrections. The objective of preventive maintenance can be summarized as follows: • Maintain assets and facilities in satisfactory operating condition by providing for systematic inspection, detection, and correction of incipient failures either before they occur or before they develop into a major failure. • Perform maintenance, including tests, measurements, adjustments, and parts replacement, specifically to prevent failure from occurring. • Record asset health condition for analysis, which leads to the development of corrective tasks. Preventive maintenance is typically performed based upon calendar time. Maintenance personnel schedule periodic visits to an asset based on fixed time intervals , for example, every three or six months. Although better than no PM at all, time-based PMs are not the optimal way to run PM programs. They may result in too much time being spent on an asset. Numerous visits to assets with "no data - abnormalities found" can be regarded as wasted maintenance dollars. If this happens, the PM periodicity should be reevaluated and adjusted. Nevertheless, time-based PMs are a good approach for assets having fixed operating schedule such as 24/7 or 80 hours/week operation. Typically, the next step up from time-based PMs is performing PMs based upon asset cycles or runtime (operations-based PM, not the same as operator-based PM). Intuitively, this approach makes sense. An asset does not have to be checked repeatedly if it has not been used. Generally speaking, it’s the actual operation of the asset that wears it down, so it makes sense to check the asset after it has been working for a specified amount of time to cause some wear. It may be necessary either to adjust or replace the component. PM Myths and Practices If we were to conduct a survey among the maintenance professionals to ascertain how their PM came about or the basis of their program, the responses would probably fail to provide definitive and meaningful information. Most existing PM programs cannot be traced to their origins. For those that can, most are unlikely to make sense. The following reasons are usually the ones given for a PM program: • OEM Recommendations. The vendor / equipment supplier says "do this." The problem with this argument is that the vendor's recommendations are mainly based on their judgment. But the vendor frequently does not know how this equipment will be used. The equipment may be designed for steady-state operations, but the real application could be highly cyclical. Moreover, vendors want us to check everything because it doesn't cost them anything. • Experience. This is the most common answer given to justify current PM tasks. "It has been done this way for years, so it must be good." • Failure Prevention. The belief that all failures can be prevented suggests that an overhaul task can help reduce the failures - without understanding the mechanism of failure. But the overextended use of overhauls can be counterproductive. It can create failures that were not present before the overhaul. Some items wear out with age, but many items don't. In the absence of wear out or aging mechanisms, correcting a problem that does not exist is a waste of money. • Brute Force. "More is always better." Thus, if it’s physically possible to do something on equipment that appears to have PM characteristics, then it must be a good thing to do. This belief leads to over-lubrication, or cleaning when equipment shouldn't even be touched, part replacement when the installed part is fine, etc. • Regulations. Many products and services come under the governance of some sort of regulatory agency such as EPA, FDA, OSHA, NRC, or a Public Utilities Commission. In their well meaning ways, these regulations can mandate PM actions that are potentially counterproductive to their objectives. Rather than using the preceding reasons, a good PM program should be based on a FMEA / RCM analysis. In addition, there is a risk of poor workmanship in performing PM tasks. Typically, risk may include: • Damage to the asset receiving the PM - damage during inspection, repair, adjustment, or installation of a replacement part or material that is defective • Incorrect reassembly or wrong-installation of parts • Infant mortality of replaced parts or material • Damage to adjacent equipment/machinery during a PM task Traditional thinking has been that the goal of preventive maintenance (PM) is to preserve assets. On the surface, it makes sense, but the problem is in that mindset. In fact, that thinking has been proven to be flawed at its core. The blind quest to preserve assets has produced many problems, such as being overly conservative with any maintenance actions that could cause damage due to intrusive actions, thereby increasing the chances of human error. Other flaws include both thinking that all failures are equal and performing maintenance simply because there is an opportunity to do so. The 10 Percent Rule of PM A PM plan must be executed per schedule. The best practice is to use the 10 percent rule of PM - a time-based PM must be accomplished within 10 percent of the time frequency to remain within compliance. Many organizations use a "PM compliance" metric as a measurement of their maintenance department's performance. If an asset is on a 30-day PM schedule, it should be executed within +/- 3 days of its due date; otherwise it’s out of compliance. This rule should apply to all PMs, but we must ensure that, at a minimum, critical assets are being maintained properly at the right time, within 10 percent of time frequency. Organizations that have implemented the 10 percent rule have been found to have increased reliability of the assets due to a consistent and disciplined approach. If we are performing Preventive Maintenance on an asset that continues to fail, we are in a reactive maintenance mode. The PM plan should be reviewed and adjusted. Run-to-Failure (RTF) RTF is a maintenance strategy where the organization decides to allow specific assets/systems to fail without any PM or CBM performed against them. This strategy is not the same as reactive maintenance. (In reactive maintenance, an organization does not have a structured maintenance program, which would include elements of PM, CBM, and RTF spread throughout the facility, with each asset/system having its own specific maintenance strategy.) For assets where the cost and impact of failure is less than the cost of preventive (PM and CBM) actions, RTF may be an appropriate maintenance strategy. It’s a deliberate decision based on economical effectiveness. Many times, we do consider and accept RTF for specific non-critical assets or components. However, we usually fail to document this fact in our CMMS. It’s imperative that we document that RTF was chosen on purpose and what the criteria or basis was for this decision. Additionally, we must have a plan to repair the failure, if and when it happens. An example is a spare parts program for the specifically-selected RTF assets/components that allow for minimal downtime for these. Documentation minimizes the excitement when RTF failure occurs. We need to understand that it was a deliberate economical decision not to have a PM program for that asset. This maintenance strategy can be a valid stand-alone maintenance strategy, especially in today's budget constrained environment. However, the RTF strategy needs more discussion throughout the maintenance com munity regarding how to establish it more formally as an effective piece of your overall maintenance strategy. Such a discussion will allow this strategy to stretch beyond its near-reactive tendencies by some organizations. Final Thoughts on Maintenance Optimization Finally, it’s suggested that all assets or, at a minimum, critical assets should have an asset management strategy established and documented. An asset management strategy should have the following: • Maintenance strategies selected and why (basis) • List by subassembly or components • Asset hierarchy structure identified • Suggested spare parts needed - when and how many (basis) • List of PM and CBM actions/tasks/routes • Major repair plans • Operating guidelines or procedures • List of key troubleshooting procedures • Any specific qualification/certification needs for maintenance personnel 7 Summary Reliability-Centered Maintenance, often known as RCM, is a maintenance improvement approach focused on identifying and establishing the operational, maintenance, and design improvement strategies that will manage the risks of asset failure most effectively. The technical standard SAE JA1011 has established evaluation criteria for RCM, which specifies that RCM address, at a minimum, the following seven questions: 1. What is the asset or component supposed to do? (functions) 2. In what ways can it fail to provide the required functions? (functional failures) 3. What are the events that cause each failure? (failure modes) 4. What happens when each failure occurs? (failure effect) 5. Why does the failure matter? (failure consequences) 6. What task can be performed proactively to prevent, or to diminish to a satisfactory degree, the consequences of the failure? 7. What must be done if a suitable preventive task cannot be found? Thus, RCM is a process that determines what must be done to ensure that assets continue to do what their users need them for in a certain operating context. RCM analysis provides a structured framework for analyzing the functions and potential failures of assets. RCM is a maintenance / PM plan optimizing strategy. However, RCM analysis provides the maximum benefits during the asset's life. Condition-Based Maintenance (CBM) is a process that determines what must be done to ensure that assets continue to function cost-effectively in the desired manner based on actual operating environment. CBM is based on using real-time data to assess the condition of the assets utilizing predictive maintenance technologies. The data and its analysis help us to make better decisions to optimize maintenance resources. CBM will determine the equipment's health, and act only when maintenance is actually necessary. Condition-Based Maintenance endeavors to predict impending failure based on actual operating data instead of relying on traditional Preventive Maintenance, generally eliminating unnecessary maintenance performed. Thus, CBM is another maintenance optimizing strategy. In fact, when it’s used with RCM in establishing maintenance tasks, it produces a much better return on investment. Preventive Maintenance (PM) is the basic asset (maintenance) strategy that many organizations use to begin their formal maintenance pro gram. PM is probably the first program that most maintenance experts use to establish a maintenance program in any organization. Most PM pro grams are either calendar time-based or operations runtime-based. Run-to-failure (RTF) is another economically valid strategy for specifically identified assets/systems. This strategy must be deliberately selected for non-critical assets only. It should be documented and planned with the right level of support, such as spare parts. 8 QUIZ __1 What is RCM? How did it get its start? Tell a little about RCM's history. __2 Which Standards Development Organization (SDO) developed RCM Standard JA1011? __3 Describe the 4 principles of RCM. What is the key objective of RCM analysis? __4 During what phases of asset development do we get the maxi mum benefit of a RCM analysis? Why? __5 Describe the 9-step RCM analysis process. __6 Which type of failure mode is not evident to asset operator? __7 What are the benefits of RCM? __8 What is meant by CBM and PdM? What methods are used to perform these? __9 What is the difference between diagnostic and prognostic analysis? __10 What is velocity analysis? With which CBM technology is it associated? What does a peak at twice rotational speed indicate? +++++ |