Reliability-Centered Maintenance Second Edition [John Moubray] on site. com. This book provides an authoritative and practical explanation of what RCM is and in the field who has helped users apply RCM and its more modern derivative, RCM2, Get your site here, or download a FREE site Reading App. Moubray, John. Edition. 2nd ed. Published. New York: Industrial Press, c to develop world-class maintenance strategies, RCM leads to rapid, sustained. John Moubray , All rights 11 Implementing RCM Recommendations Work which led to the development of RCM2 for industries other than.
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Book details Author: John Moubray Pages: pages Publisher: Industrial by the aviation industry, RCM is rapidly becoming fundamental to the Maintenance by John Moubray by John Moubray, Download is Easy. Written by an expert in the field who has helped users apply RCM and its more modern derivative, RCM2, at more than sites in 32 countries. The second. Our founder, John Moubray developed a profound and unique way to perform RCM One of the features of RCM2™ that distinguishes it from other interpretations of the RCM philosophy is the Download Aladon's RCM brochure here.
For events like these, more or better maintenance makes no difference. Instead the consequences of events like these should be mitigated through design.
And maintenance can do little about failures that are the result of poor design, lousy construction or bad procurement decisions. In other cases the impact of the failure is low so you simply accept a failure think general area lighting. So, good maintenance programs do not try to prevent all failures. Good maintenance plans and programs accept some level of failures and are prepared to deal with the failures they accept and deem credible.
Instead, for most failure modes the likelihood of occurrence is random. Later research by the United States Navy and others found very similar results. Apart from showing that most failure modes occur randomly. These failure patterns also highlight that infant mortality is common. And that it typically persists. That means that the probability of failure only becomes constant after a significant amount of time in service.
But many items degrade so slowly that wear out is not a practical concern. These items do not reach wear out zone in normal operating life. So what do these patterns tell us about our reliable maintenance programs? Historically maintenance was done in the belief that the likelihood of failure increased over time first generation maintenance thinking.
It was thought that well timed maintenance could reduce the likelihood of failure. It makes no sense to spend maintenance resources to service or replace an item whose reliability has not degraded.
Or whose reliability cannot be improved by that maintenance task. Yet most of our PM programs are full of time based replacements and overhauls. Principle 3: Some Failures Matter More Than Others When deciding on whether to do a maintenance task consider the consequence of not doing it. What would be the consequence of letting that specific failure mode occur?
Avoiding that consequence is the benefit of your maintenance.
The return on your investment. And that is exactly how maintenance should be seen: as an investment. You incur a maintenance cost in return for a benefit in sustained safety and reliability. And as with all good investments the benefit should outweigh the original investment.
So, understanding the consequences of failures is key to developing a good maintenance program. One with a good return on investment. Just as not all failures have the same probability, not all failures have the same consequence.
Even if it relates to the same type of equipment. Consider a leaking tank. The consequence of a leaking tank is severe if the tank contains a highly flammable liquid.
But if the tank is full of potable water the consequence might not be of great concern. Easy, right?
But what if the water is required for fire fighting? Same tank, same failure but now we might be more concerned. We would not want to end up in a scenario of not being able to fight a fire because we had an empty tank due to a leak.
Apart from the consequence of a failure you also need think about the likelihood of the failure actually occurring. Maintenance tasks should be developed for dominant failure modes only.
Those failures that occur frequently and those that have serious consequences but are less frequent to rare. Avoid assigning maintenance to non-credible failure modes. And avoid analyzing non-credible failure modes. It eats up your scarce resources for no return. A maintenance program should consider both the consequence and the likelihood of failures. Good maintenance programs use the concept of risk to assess where to use our scare resources to get the greatest benefit.
The biggest return on our investment. Each of these failures affects the organization in some way, but in each case, the effects are different. They may affect operations. They may also affect product quality, customer service, safety or the environment. They will all take time and cost money to repair.
It is these consequences which most strongly influence the extent to which we try to prevent each failure. In other words, if a failure has serious consequences, we are likely to go to great lengths to try to avoid it. On the other hand, if it has little or no effect, then we may decide to do no routine maintenance beyond basic cleaning and lubrication. A great strength of RCM is that it recognizes that the consequences of failures are far more important than their technical characteristics.
In fact, it recognizes that the only reason for doing any kind of proactive maintenance is not to avoid failures per se, but to avoid or at least to reduce the consequences of failure.
The RCM process classifies these consequences into four groups, as follows: Hidden failure consequences: Hidden failures have no direct impact, but they expose the organization to multiple failures with serious, often catastrophic, consequences. Most of these failures are associated with protective devices which are not fail-safe.
Safety and environmental consequences: A failure has safety consequences if it could hurt or kill someone. It has environmental consequences if it could lead to a breach of any corporate, regional, national or international environmental standard.
Operational consequences: A failure has operational consequences if it affects production output, product quality, customer service or operating costs in addition to the direct cost of repair Non-operational consequences: Evident failures which fall into this category affect neither safety nor production, so they involve only the direct cost of repair.
We will see later how the RCM process uses these categories as the basis of a strategic framework for maintenance decision-making. By forcing a structured review of the consequences of each failure mode in terms of the above categories, it integrates the operational, environmental and safety objectives of the maintenance function. This helps to bring safety and the environment into the mainstream of maintenance management.
The consequence evaluation process also shifts emphasis away from the idea that all failures are bad and must be prevented. In so doing, it focuses attention on the maintenance activities which have most effect on the performance of the organization, and diverts energy away from those which have little or no effect.
It also encourages us to think more broadly about different ways of managing failure, rather than to concentrate only on failure prevention. Failure management techniques are divided into two categories: proactive tasks: these are tasks undertaken before a failure occurs, in order to prevent the item from getting into a failed state.
They embrace what is traditionally known as 'predictive' and 'preventive' maintenance, although we will see later that RCM uses the terms scheduled restoration scheduled discard and on-condition maintenance default actions: these deal with the failed state, and are chosen when it is not possible to identify an effective proactive task. Default actions include failure-finding, redesign and run-to-failure.
The consequence evaluation process is discussed again briefly later this chapter, and in much more detail in Chapter 5 of the book. The next section of this chapter looks at proactive tasks in more detail. Proactive Tasks Many people still believe that the best way to optimize plant availability is to do some kind of proactive maintenance on a routine basis.
Second Generation wisdom suggested that this should consist of overhauls of component replacements at fixed intervals. Classical thinking suggests that extensive records about failure will enable us to determine this life and so make plans to take preventive action shortly before the item is due to fail in future.
This model is true for certain types of simple equipment, and for some complex items with dominant failure modes. In particular, wear-out char-acteristics are often found where equipment comes into direct contact with the product.
Age-related failures are also often associated with fatigue, corrosion, abrasion and evaporation. However, equipment in general is far more complex than it was twenty years ago. This has led to startling changes in the patterns of failure, as shown in Figure 1. The graphs show conditional probability of failure against operating age for a variety of electrical and mechanical items.
Pattern A is the well-known bathtub curve. It begins with a high incidence of failure known as infant mortality followed by a constant or gradually increasing conditional probability of failure, then by a wear-out zone. Pattern B shows constant or slowly increasing conditional prob-ability of failure, ending in a wear-out zone the same as Figure 1.
RCM II (John Moubray)
Pattern C shows slowly increasing conditional probability of failure, but there is no identifiable wear-out age. Pattern D shows low conditional probability of failure when the item is new or just out of the shop, then a rapid increase to a constant level, while pattern E shows a constant conditional probability of failure at all ages random failure. Pattern F starts with high infant mortality, which drops eventually to a constant or very slowly increasing conditional probability of failure.
The number of times these patterns occur in aircraft is not necessarily the same as in industry. But there is no doubt that as assets become more complex, we see more and more of patterns E and F. These findings contradict the belief that there is always a connection between reliability and operating age. This belief led to the idea that the more often an item is overhauled, the less likely it is to fail.
Nowadays, this is seldom true. Unless there is a dominant age-related failure mode, age limits do little or nothing to improve the reliability of complex items.
In fact scheduled overhauls can actually increase overall failure rates by introducing infant mortality into otherwise stable systems. An awareness of these facts has led some organizations to abandon the idea of proactive maintenance altogether. In fact, this can be the right thing to do for failures with minor consequences.
But when the failure consequences are significant, something must be done to prevent or predict the failures, or at least to reduce the consequences. This brings us back to the question of proactive tasks. As mentioned earlier, RCM divides proactive tasks into three categories, as follows: scheduled restoration tasks scheduled on-condition tasks.
Scheduled restoration and scheduled discard tasks Scheduled restoration entails remanufacturing a component or overhauling an assembly at or before a specified age limit, regardless of its condition at the time. Similarly, scheduled discard entails discarding an item at or before a specified life limit, regardless of its condition at the time. Collectively, these two types of tasks are now generally known as preventive maintenance.
They used to be by far the most widely used form of proactive maintenance. However for the reasons discussed above, they are much less widely used than they were twenty years ago. On-condition tasks The continuing need to prevent certain types of failure, and the growing inability of classical techniques to do so, are behind the growth of new types of failure management. The majority of these techniques rely on the fact that most failures give some warning of the fact that they are about to occur.
These warnings are known as potential failures, and are defined as identifiable physical conditions which indicate that a functional failure is about to occur or is in the process of occurring.
The new techniques are used to detect potential failures so that action can be taken to avoid the consequences which could occur if they degenerate into functional failures. They are called on-condition tasks because items are left in service on the condition that they continue to meet desired performance standards. On-condition maintenance includes predictive maintenance, condition-based maintenance and condition monitoring. Used appropriately, on-condition tasks are a very good way of managing failures, but they can also be an expensive waste of time.
RCM enables decisions in this area to be made with particular confidence.
Default Actions RCM recognizes three major categories of default actions, as follows: failure-finding: Failure-finding tasks entail checking hidden functions periodically to determine whether they have failed whereas condition-based tasks entail checking if something is failing. This includes modifications to the hardware and also covers once-off changes to procedures. This default is also called run-to-failure.
Its straightforward, plant-based approach makes the book especially well suited to use in centers of highter education. Contents 1.
Introduction to reliability-centered maintenance 2. Functions 4. Failure modes and effects analysis 5.
Reliability-Centered Maintenance, Second Edition
Failure consequences 6. Proactive maintenance 1 : preventive tasks 7.In what way does each failure matter? In recent times, the growth of mechanization and automation has meant that reliability and availability have now also become key issues in sectors as diverse as health care, data processing, telecommunications and building management. Pattern C shows slowly increasing conditional probability of failure, but there is no identifiable wear-out age.
At the same time, most equipment was simple and much of it was over-designed. And potentially introduced a lot of defects that can impact equipment reliability down the line. What causes each functional failure? This chapter provides a brief introduction to RCM, starting with a look at how maintenance has evolved over the past fifty years. If such a task cannot be found then a scheduled failure-finding task must be performed.
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