This has led to conresponciing growth edged as a secondary function of all devices used to transfer material of in the variety and severity of failure consequences. In an attempt to elirni- any sort - especially fluids. This includes pipes, pumps, conveyors, chutes, nate or at least to reduce these consequences, increasing use is being hoppers and pneumatic and hydraulic systems.
These work in oric of five ways: Conraislment is also an inlportant secondary function of items like gear- to draw the attention of the operators to abnormal conditions wurning boxes and transformers. In this context, note again the remarks on Page 26 lights and audible alarms which respotl i to,fnilur-reflecrs. Anxiety is caused by poorly rn. The best time to deal with these problems is of course at the design stage.
Ifowever, deteric? If the belt were to break in the absence of any protection, the feed mechanism would Appearcrnce drive the stationary cutter into the workpiece or vice versa and cause serious The appeariince of many items embodies a specific secondary function.
This can be avoided in two ways: For instance, the primary function of the paintwork on most industrial by implementing a comprehensive proactive maintenance routine designed to prevent the failure of the belt equipment is to protect it from corrosion, but a bright colour might be by providing protection such as a broken belt detectorto shut down the machine used to enhance its visibility for safety reasons.
Similarly, the main func- as soon as the belt breaks. But thispolicy is only validif the broken belt detector is working, and steps must be taken to ensure that this is so. Functions The rnaintenance of protective devices - especially devices which are not For instance, a car might be expected 'to consume not mare than 6 litres of fuel per km at a constant kmlh, and not more than 4 litres of fuel per i00 km fail-safe - is discussed in much more detail in Chapters 5 and 8.
However, at 60 kmih. This usually happens when equipment has been moctified protective device. So when listing the functions of in for safety reasons, but to items which serve no purpow at all in the con- any asset, we must list the functions of all protective devices. These devices act by exception in other words when gas manifold and a gas turbine.
The original function of the valve was to reduce something else goes wrong , so it is important to describe them correctly. The system was later modified to reduce In particular, protective function statements should include the words 'if' the manifold pressure to 80 psi, after which the valve served no useful purpose.
To remove any ambiguity, the function of and so reduce overall system reliability. To avoid this, they need mainten- a tripwire should be described as follows: ance, which means that they still consume resources. I f they to be capable of relieving the pressure in the boiler if it exceeds psi. This leads them to put a limit on what they are prepared to spend on operating ancl nlaintaining it.
How much they are prepared to spend is A Note on Reliability governed by a cornbination of three factors: There is often a temptation to write 'reliability' l'ictio11 statcrnents such the actual extent of their financial resources as 'to operate 7 days a week, 24 hours per day'.
In fact, reliability is not how much they want whatever the asset will do for them a function in its own right. It is a performance expect;ition which pervades the availability and cost of competitive ways of achieving the same end. It is properly dealt with by dealing appropriately At the operating context level, functional expectations concerning costs with each of the failure modes which could cause each loss of function.
This issue is discussed further in Chapter At the asset Ievel, econornic issues can be adckssed directly by function statements which define what users expect in areas such as fuel economy and loss of process materials. What does matter is that we identify and define all the functions which are likely to be ex- pected by the user.
It also makes it easier to absorb changes trig- what can be done to predict or preverzt each failure? This shows why it is more accurate to define failure in terms of the loss of specific functions rather than the failure of an asset as a whole.
It also This is illustrated in Figure 3. However, ttt complete the 2. Figure 3. A functional failure is defined as the irzability 3. In practice, this definition is vague because it does not distin- different aspects of functional fail- guish clearly between the failed state functional failure and the events which cause the failed state failure modes.
It is also simplistic, because it does not take into account the fact that each asset has more than one function, and each function often has more than one desired standard of performance. The inlplications are explored in the following paragraphs. We have also seen that what anything must do is defined as a func- failure covers complete loss of func- tion and Chat every asset has more than one and often several different tion.
It also covers situations where Figure 3. For instance, the pump in Figure 2. One is to pump For example, the primary function of the pump discussed earlier is 'to pump water water at not less than litreslminute, and the other is to contain the water. It is from tank Xto Tank Y at not less than litreslminute'. Partial failure is nearly always caused by different failure modes from total The function of a crankshaft grinding machine was listed as 'To finish grind main failure, and the consequencesare different.
In some circumstances, this niay not pump in Figure 2. Impeller wear is inevitable, so this capability will decline. As long as it does ing functions of this type. This is illitstrlttect in keep the users satisfied in the context described. However if the capability of the as- Figure 3. Upper and lower limits The previous chapter explained that the performance standards associated with some functions incorporateupper and lower limits.
Such limits mean that the asset has failed if it produces products which are over the upper limit or below the lower limit. In these cases, the breach of the upper limit usually needs to be identified separately from the breach of the lower limit. This machine has failed: Note that In both of the above cases, not 1'11 of the products produced if it stops altogether hy the processes In questlon wlll bc faded If the breach 1s rnlnor.
Who should set the standard? For example, one function of a hydraulicsystem istocontain oil. How well it should Figure 3. There are pro- Capability breaches upper and lower limits duction managers who believe that a hydraulic leak only amounts to a functional failure if it is so bad that the equipment stops working altogether.
Then again, a safety officer might say that a functional failure has occurred of spec are in a hiled state. The failure modes which can cause these failed if the leak creates a pool of oil on the floor in which people could slip and fall or states are cliscussed in the next chapter.
Chapter7 deals with the implica- which might create a fire hazard. This is illustrated in Figure 3. Chapter 2 men- about failure tioned that upper arid lower limits also apply to the performance standards associated with gauges, indicators, protection and control systems. However access may be denied because the operators think the machine 'is still working OK.
For similar reasons, the maintenance manager might not release a maintenance person to operating context. Th15 means that In the same way that we should not repair a small leak when requested to do so by the safety officer. The real problern not to generalise about functional failures. For example, we saw how the pump shown in Figure 2.
If the This example illustrates three key points: same pump is used to fill a tank from which water is drawn at litresiminute, the second failed state occurs if the throughput drops below IitresJminute. They are coded alphabetically, as shown in Figure 3. Fails to contain the gas A failure mode could be defined as any event which is lrkely to cause an asset or system or process to fail.
It is much tnore precise to distingiiish between a 'functlonal fail- ure' a failed state and a 'failure mode' an rverlt which could cause a failed state. This distinction leads to the followirlg Inore preclse definl- tion of a failure mode:.
A failure mode is arzy everzt which causes a Junctional failure. In particular, the verbs used to describe failure modes should be chosen what is being done to repair it and - sometilnes - what can be cfone to with care, because they strongly influence the subsequent failure man- stop it happening again.
In short, the entire meeting is spent discussing agement policy selection process. The use of more specific verbs makes it possible to select from Sadly, in too many cases, the4e farlure modes are cltscussed, recorded or the fit11 range of failure management options. This in turn means that the failure mode is most likely to occur soon after start up, ln in Figure 4.
This applies as shown in Figure 4. Figure 4. These are Figure 4. The example also suggests that one of the failure modes could be elim- jfailure by: changing? Chapters 5 to 9 describe an orderly approach to deciding what is likely to be the most suitable way of dealing with each failure. For instance we could monitor impeller wear by monitoring the pump perform- ance and only change the impeller when it needs it.
We also need to bear in mind ;failure by: training that adding a screen to the suction line adds three more failure possibilities, which impellers correctly? These points all indicate that the identification of failure modes is one nenon.
As shown in Figure nd of the six failure patterns of the most important steps in the development of any prograin intended n B. So if we know roughly to ensure that any asset continues to fulfil its intended functions. In prac- iequences of the failure are tice, depending on the complexity of the item, its operating context and the his failure by changing the level at which it is being analysed, between one and thirty failure modes are usually listed per functional failure.
There would also be no categories of failure modes ir. So if the consequences level of detail. FMEA Failure h40cfe. Eventually resistance cirops so much that the asset car1 Some people regard tnailltenance as being all about - and only about - no longer deliver the desired perforrnance - in other words, it fails.
Some even go so far as to specify that FMEA's Deterioration covers all forms of 'wear and tear' fatigue, corrosion, carried out on their assets should deal only with failure mode, caused by abrasion, erosion, evapor-ation,degradation of insulation, etc. This is unfortunate, because it often they are thought to be reasonably likely. The level of detail with which transpires that deterioration causes a surprisingly small proportion offail- they need to be recorded is discussed in the next part of this chapter.
In thew cases, restricting the analysis to deterioration only can lead to a woeftilly incomplete maintenance strategy. Failure modes can be in the last two decades. Twenty yeas ago, the majority of lubrication points classified into one of three groups, as follows: were replenished manually. The cost of lubricating each of these points when capability falls below desired performance was tiny compared to the cost of not doing so. It was also tiny compared a when desired performance rises above initial capability to the cost of analysing the lubricatiort requirements of each point in detail.
This meant that it was just 11otworth carrying orit an in-depth analytical excr- Each of these categories is drscussed in the following paragraphs cise to set up a lubrication program.
Falling Capability Nowadays however, 'sealed-for-life' components and centralised lubri- cation systems have become the norrn in most inc1trst1-ies. From with, but then drops below desired the analytical viewpoint, this rneans that it is now cost-effective to: perforrnance after the asset is put into use RCM to analyse centralised lubrication systems in their own right service, as illustrated in Figme 4.
The five principal causes of reduced consider the loss of lubricant in the few remaining rllanitally lilbricated capability are listed below: points as individual failure modes. In some cases, deterioration of the or1 rnay be aggravated by the build- 'capability reducing' hurnari ersors.
These stresses cause the further analysis. It interferes directly with The second category of failure modes occurs when desired performance machines by causing them to block, stick or jam. Dirt can also cause product the capability envelope. As a result, the increase in stress cause5 deterioration to accelerate to the extent that failures caused by dirt should be listed in the FMEA whenever they are the asset becomes so unreliable that it is effectively useless.
An example of the first case occurs if the users of the purnp shown in Figure 2. Under these Distz, setrzbly circumstances, the pump is unable to keep the tank full. These are usually the failure of welds, sol- is 'red-lined' at 6 rpm persists in revving the motor to 7 rpm.
This causes dered joints or rivets due to fatigue or corrosion, or the failure of threaded the engine to deteriorate more quickly than if the user keeps the revs within the components such as bolts, electrical connections or pipefittings which prescribed limits, so it fails more often.
This phenomenon is illustrated in Fig- Also take care to record the functions anti associated failure modes of ure 4. As the name implies, these refer to errors incorrect process material. Sustained, deliberate overloading Examples include manually operated valves left shut causing a process to be In many industries, users quickly give unable to start, parts incorrectly fitted by maintenance craftsmen or sensors set in to the temptation simply to speed in such a way that a machine trips out when nothing is wrong.
In other Fa,,ure Mode Category in the FMEA so that appropriate failure management decisions can be cases, people use assets acquired for rnade later i11the process. Neither of them are 'wrong' - they are sitnply considering the problem from two different points of view.
In these cases, irnplernenting 'better' maintenance procedures will do little or nothing to solve the problem. In fact, maintaming a machine which cannot deliver the desired performance has been likened to rearranging the Figure 4.
In such cases we need to look beyond mainte- nance for solutions. How this occurs is illustrated in Figure 4. The dotted lines represent the capability of each operation. They also upgrade the power supplies to match. This can be seen as an increase in applied stress.
However, it is important to do so, because the level of detail pro- In practice, these 'failure modes' are seldom the result of a failure of the foundly affects the validity of the FMEA and the arnount of time needed asset under review, but are nearly always the effect of a failure elsewhere to do it. Too many failure modes andlor too ent asset. However, acknowledging these failures in the analysis of the much detail causes the entire RCM process to take much longer than it affected asset helps to ensure that they will receive attention when the needs to.
In extreme cases, excessive detail can cause the process to take system which is really causing the problem is analysed. As a result, these two or even three times longer than necessary a phenomenon known as failure modes should be incorporated in the FMEA where they are known analysis paralysis. Initial incapability Causation Chapter 2 explained that for any asset to be maintainable, its desired perforrnance must fall within the envelope of its initial capability.
How- detail, and different levels are appropriate in different situations. The of detail is illustrated in Figure 4. These failure as failure modes in an FMEA. The top level Level 1 is failure of the pump set as a whole. Level 2 recognises Figure 4.
Thereafter failures are considered in progressively more detail. When considering this example, please note that levels have been defined and failure modes allocated to each level for the 4.
They are not any kind of universal classification. The example shows the further one 'drills down' in an FMEA, the larger the nurnber of failure modes that can be listed. For instance,there are five failure modes listed at level 2forthe pump set in Figure 4.
Two more key issues which arise from Figure 4. They are diacussed below. Root causes The term 'root cause' is often used in connection with the analysis uf fail- ures.
It implies that if one drills down far enough, it is possible to arsive at a final and absolute level of causation. In fact, this is selclom the case. For instance, in Figure 4.
If we were to go down one level further, the assembly error might have occurred because the 'fitter was distracted' level 8. He might have been distracted because his 'child was ill' level 9. This failure might have occurred because the 'child ate bad food in restaurant' level The fact that the level which is appropriate varies for different failure modes rneans that we do not have to list all failure modes at the sante level on the Information Worksheet.
Some failure niocles might be identified at level 2, others at level 7, and the rest somewhere in between. For instance, in one particular context, it may be appropriate to list only those failure modes shaded in grey in Figure 4.
In another context, it may be appro- priate for an entire FMEA for an identical pump set to consist of the single failure mode 'pump set fails'. Another context may call for yet another selection.
Obviously, in order to be able to stop at an appropriate level, the people doing such analyses need to be awzu-e of of the fit11 range of Lulure manage- ment policy options. These are discussed at length in Chapters 6 to 9. Other factors which influence the level of detail are considcrcd in the rest of this part of this chapter and again in part 7. Hurnan t7rrc r However, a revlew of exlstlng schedule5 shoulcl only be carrred out Part 3 of this chapter mentioned a number of general ways in which as a final check after the rest of the KCM analyils hai been completed human error could cause machines to fail.
This has been done in Figure 4. Others may be extretnely improbable, with mean tirnes between occur- any otherfailure nzode. Identifying and clecidlng how to deal sions rtlust be made continuously as to what failure modes are so unlikely wlth failures which have not happened yet is an es5entlal feature of pro- that they can safely be ignored. A list of 'reasonably likely' fail- pump shown in Figure 4. This means that the likelihood of lubrication failure ure modes should include the following: is low - so low that it would not be included in most FMEA's.
On the other hand, failure due to lack of lubricant probably would be included in FMEA's prepared failurrs which have occurred before on the same or similar assets. As discussed later, sources of information about these failures include people who know the asset well your own employees, vendors or other Consequences users of the same equipment , technical history records and data banks.
However, if the routirzes, and so which would occur if no proactive maintenance was pump were pumping something really nasty in a nuclear installation, this failure being clone. One way to ensure that none of these failure modes have mode is more likely to be taken seriously even though it is still highly improbable.
Another example from Figure 4. This failure mode Similarly, a vehicle operating in the Arctic would be subject to different failure is likely to be dismissed on the grounds of improbability in most situations.
Even modes from the same make of vehicle operating in the Sahara desert. Similarly, if it does occur, the consequences may be so trivial that it is excluded from the a gas turbine powering a jet aircraft would have different failure modes from the FMEA. On the other hand, if it could occur and it does matter - especially in cases same type of turbine acting as a prime mover on an oil platform.
These differences mean that great care should be taken to ensure that the operating context is identical before applying an FMEA developed in one Cause vs Effect set of circumstances to an asset which is used in another. Note also the comments regarding the use of generic FMEA's in part 6 of this chapter. Care shoulct be taken not toconfuse causes andeffects when listing failure The operating context affects levels of analysis as well as the causes modes. This is a subtle mistake most often made by people who are new and consequences of failure.
As discussed earlier, it rnight be appropriate to the RCM process. Initi- ally, the following failure modes were recorded for one of these gearboxes: Gearbox bearings seize Gear teeth stripped.
The failures did not affect safety but they did affect production. What is more, no-one could recall that any of the gearboxes had failed if they had been Note that failure effects are not the same as failure consecluenccs. A properly lubricated. As a result, the failure mode was eventually recorded as: failure effect answers the question "what happens'?
This underlined the importance of the obvious proactive task, which was to check consequence answers the question " how does it matter? This is not to suggest that all gearboxes should be ana- A description of failure effects should include all the infonation needed lysed in this way.
Some are much more complex or much more heavily loaded, to support the evaluation of the consequences of the failure. Specifically, and so are subject to a wider variety of failure modes. In other cases, the failure when describing the effects ofa hilure, the following should be recorded: consequences may be much more severe, which would call for a more defensive view of failure possibilities. This is also true of failure modes in what must be done to repair the failure. Evidence of Failure Safety and Environmental Hazards.
It should electrocution also state whether the machine shuts down as a result of the failure. Tank Y low levelalarm vehicle accidents or derailinents soundsafter20minutes, and tank runs dry after30 minutes. Downtime required exposure to sharp edges or moving inachinery to replace the bearings 4 hours. These the collapse of strtictures deposits could be partially removed by the periodic injection of special materials the growth of bacteria into the air stream, a process known as 'jet blasting'.
Exhaust temperature is displayed on the local control panel and in the central control room. If no action is taken, failure has safety consequences" or 'fthis failure affects the environmetlt". A high exhaust Simply state what happens, and leave the evaluation of the consequences gas temperature alarm annunciates on the local control panel and a warning to the next stage of the RCM process.
The blades can be partially cleaned by jet blasting, and jet blasting takes about 30 minutes. The average description of a failure effect usually amounts to between twenty and sixty words. In this context, downtime means the total amount of time the asset In addition to downtime, any other ways in which the failure could have would norrnally be out of service owing to this failure, from the moment a significant effect on the operational capability of the a s m jhould be it Pails until the nioment it is fully operational again.
As indicated in listed. Possibilities include: Figure 4. Since it is consequences which are of most interest Downtime to clear the blockage and reset the trip switch about 30 minutes to us, the downtime recorded on the information worksheet should be Downtime to strip the turbine and replace the disc about 2 weeks.
For instance, if the downtime caused by a failure which occurs late on a weekend night shin is usually much longer than it is when the failure occurs on a normal day 4. It is of course possible to reduce the operational consequences of a failure When considering where to get information needed to draw up a rcason- by taking steps to shorten the downtime, most often by reducing the time ably comprehensive FMEA, remember the need to be proactive.
This it takes to get hold of a spare part. Widely recognized by maintenance professionals as the most cost-effective way to develop world-class World-class manufacturing Jim Todd Snippet view — Reliability-centered maintenance RCM is a process to ensure that systems continue to do what their user require in their present operating context.
The second edition includes more than pages of new material on: Views Read Edit View history. Widely recognized by maintenance professionals as the most cost-effective way to develop world-class maintenance strategies, RCM leads to rapid, sustained and substantial improvements in plant availability and reliability, product quality, safety and environmental integrity.
My library Help Advanced Book Search. Today companies can use this standard to ensure that the processes, services and software they purchase and implement conforms with what maintemance defined centerred RCM, ensuring the best possibility of achieving the many benefits attributable to rigorous application of RCM.
Levels of criticality are assigned to the consequences of failure. In some cases these were misleading and inefficient, while in other cases they were even dangerous. Reliability centered maintenance is an engineering framework that enables the definition of a complete maintenance regimen.
This page was last edited on 1 Decemberat Moubray spent his early career developing and implementing maintenance management systems, forst as a paint engineer then as a consultant. Although a voluntary standard, it provides a reference for companies looking to implement RCM to ensure they are getting a process, software package or service that is in line with the original report. Reliability-centered maintenance is a process used to determine — systematically and scientifically — what must be done to ensure that physical assets continue to do what their users want them to do.
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. Successful implementation of RCM will lead to increase in cost effectiveness, machine uptime, and a greater understanding of the maintenancf of risk that the organization is managing.
Successful implementation of RCM will lead to increase in cost effectiveness, reliability, machine uptime, and a moubrwy understanding of the level of risk that the organization is managing. The result was the propagation of many methods that called themselves RCM, yet had little in common with the original concepts. It is generally rellability to achieve improvements in fields such as the establishment of safe minimum levels of maintenance, changes to operating procedures and strategies and the establishment of capital maintenance regimes and cenhered.
This page was last edited on 23 Augustat This book will be of immense value to maintenance managers, and to anyone else concerned with the reliability, productivity, safety, and environmental integrity of physical assets.
By using this site, you agree to the Terms of Use and Privacy Policy. Amazon Giveaway allows you to run promotional giveaways in order to jogn buzz, reward your audience, and attract new followers and customers. Highly recommend 1 to those who wish to have a good understanding of RCM and 2 for your library. Customers who viewed this item also viewed. These sites include all types of manufacturing especially automobile, steel, paper, petrochemical, pharmaceutical, and food manufacturingutilities water, gas, and electicityarmed forces, building services, mining, telecommunications, and transport.
World-class manufacturing Jim Todd Snippet view crm Failure modes and effects analysis 5. This description echoed statements in the Nowlan and Heap report from United Airlines. The late John Moubray, in his book RCM2 characterized reliability-centered maintenance as a process to establish the safe minimum levels of maintenance. Modern RCM gives threats to the environment a separate classification, though most forms manage them in the same way as threats to safety.
RCM emphasizes the use of predictive maintenance PdM techniques in addition to traditional johj measures. The participant will gain the knowledge and understanding of how RCM2 is applied to physical asset management, but how RCM2 can be applied at your location. This website uses cookies to improve your experience while you navigate through the website. Out of these cookies, the cookies that are categorized as necessary are stored on your browser as they are as essential for the working of basic functionalities of the website.
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