Machinery Lubrication magazine published by Noria Corporation
Issue link: http://www.e-digitaleditions.com/i/1504498
Reliable Plant Anniversary Edition | www . reliableplant.com 15 First, let's have a quick look at what Condition-Based Maintenance really is. WHAT IS CBM? Most failure modes are not age-related; however, they do provide some warning that they are about to occur. If we can find these signals, we can take preventive action to mini- mize the consequences of failure. As a strategy, CBM looks for physical evidence that a failure is happening or is about to happen. When thought of this way, CBM has broader applications outside its more common uses, like vibration monitoring. An important concept within CBM is the P-F curve shown in the figure 1 above is conceptual diagram shows that the functional performance of equipment deteri- orates over time to a point where a failure can now be detected (point "P"). If the failure isn't mitigated, the equipment will degrade until a functional failure occurs (point "F"). e time range between P and F, commonly called the P-F interval, is your window of opportunity to detect an imminent failure and address it. The length of the P-F interval varies depending on the specific failure mode and the condition monitoring technique used. You want to use a condition monitoring solution that gives you a reliable, repeat- able indication early enough for you to respond appropriately. WHY IMPLEMENT CBM? CBM lets you know a failure is about to happen, allowing you to plan for it and strategically choose the best time to address the impending failure. For example, let's say you have a scheduled outage next month, and according to your CBM, the drive-end bearing of your export pump will fail in roughly three months. Without CBM, that failure would have been unexpected, leaving you to deal with it as a breakdown, which is inefficient and expensive. But with CBM, you can prop- erly plan and schedule the fix during the scheduled outage, meaning the equipment is repaired safely, quickly, and at a lower cost, all of which reduces the impact on production. To be clear, the value of CBM is not in failure prevention; it's in identifying fail- ures before they occur. As a result, you can make a timely intervention that reduces the impact on production, decreases costs, and improves worker safety. But not all failure modes or equipment will benefit from Condition-Based Maintenance. TIME-BASED MAINTENANCE VS. CBM Failure modes that are clearly age-re- lated a re of ten best ma naged with a time-based repair or replacement task. If you know a component will wear out every 12 months, you simply replace it in time. You don't need a condition assessment every few months to determine if the component needs replacing. But research across different indus- tries (airline and military) has shown that between 70% and 90% of all failure modes are not age-re- lated, and for these failure mode s, t he li keli hood of failure doesn't (significantly) increase over time. This research is summa- rized in the six different failure patterns shown in figure 2 on page 16 is has major implications for our PM programs, which are filled with time-based mainte- nance tasks. It reveals that if most failure modes are not age-related, then we should be addressing them with some type of Condition-Based Maintenance. As a result, a significant part of your PM program should be CBM. In other words, CBM is essential to creating a reliable plant. You will not succeed without it. THE PROBLEM WITH CBM Effective condition monitoring generates "weak signals," or indicators of potential failure weeks, if not months, in advance. But what happens to those weak signals in a reactive maintenance environment? ey get ignored. People are too busy dealing with today's emergencies to worry about a pump bearing that might fail in six months' time. So, six months later, that exact same pump breaks down due to a bearing failure. Management asks why that bearing problem wasn't captured through the condi- tion monitoring program, only to be told that it was: the report with the vibration trends is there, and the CMMS work requests were raised, but nothing was done about it. is is the worst of both worlds. You're practicing run-to-failure — except it's more expensive because you're adding the cost of CBM to it. Sadly, this is a reality for facilities, and to be honest, I have personally experienced this myself. To resolve this, organizations need to ensure they have an effective planning and scheduling process in place so the work environment becomes more stable and can act on the "weak signals" that come from the CBM program. The P-F Curve Functional Performance Time smooth running further degration impending failure limited functionality F = functional failure P = change in condition or performance detected PF Interval = lead time to failure Figure 1.