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Preventive Maintenance needs to be carried out without excessive expenditure. A method of doing the same is known as optimized PM. This paper helps one to understand the strictures and apply PM appropriately to the plant assets

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An Allied Reliability Group White Paper

4200 Faber Place Drive Charleston, SC 29405 843.414.5760 www.alliedreliabilitygroup.com

Preventive Maintenance

By: Andy Page, Principal Consultant Carey Repasz, Principal Consultant

March 5, 2014

Reliability… it’s in our DNA.

Contents
Preventive Maintenance Defined .............................1 The History of Preventive Maintenance ..................1 The P-F Curve ..........................................................5 PM Activity Types ....................................................7 PM in the Overall Maintenance Strategy ................9 Business Case for Efficient PM ..............................10 PM Procedures .......................................................11 PM Procedure Hierarchy ...................................11 Procedure Elements ..........................................11 PM Scheduling and Compliance.............................13 PM Evaluation and PM Optimization ....................14 Preventive Maintenance Evaluation .................14 Preventive Maintenance Optimization .............16 Summary and Conclusion ......................................16

Preventive Maintenance Defined
In the most theoretical sense, Preventive Maintenance (PM) is any maintenance activity that is performed to prevent a piece of equipment from failing. Preventive maintenance activities may take several forms, which will be discussed later in this paper, but suffice it to say all of the forms of PM are intended to do one of two things, either prevent the next occurrence of a failure (only reengineering can possibly prevent it forever) or at least detect the presence of an impending failure. Preventive maintenance has another characteristic in that it happens on a very predictable frequency. Preventive maintenance is any maintenance activity that is performed on a fixed interval. Some refer to it as calendar-driven. The interval is usually based on operating time, such as every so many days, weeks, months, or years; however, the interval can also be based on throughput (aka meter-driven), such as every so many gallons of fuel burned, miles driven, or boxes produced. Either way, PM activities occur at fixed intervals. Therefore, any activity that is performed on-demand is not a PM activity. These characteristics of PM have been misinterpreted over the years resulting in PM programs that look very different from one company to the next.

The History of Preventive Maintenance
The oldest version of a PM program entailed a PM person walking around looking at, listening to, and feeling equipment while it ran in an attempt to determine whether the machine was working fine or not. Any discrepancy found during these walk around inspections was either fixed on the fly or during a brief interruption of service, such as a shift change for example. In essence, this person’s job was to ensure that the place kept running. This is where the term millwright came from. In the days when wooden sheaves and leather belts ran off of a

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line shaft running down the center of the shop, the millwright would be in charge of keeping the “mill” “right”, or keeping it running. Any problems were brought to his attention and he would take care of them right then and there. Some companies still subscribe to this style of maintenance. PM mechanics are assigned to constantly survey the machinery in order to detect issues that need correcting. These inspections are usually conducted using their human senses or the most basic of tools, like a long screwdriver or mechanic’s stethoscope to detect problems on bearings for example. Of course, the issue with this style of inspection is that the defect has to be very late in its failure progression to be detected. This creates a scenario where production has to be interrupted to fix the problem and the warehouse has to keep a very large inventory of parts to deal with whatever may arise. In the late 1960s, this style of maintenance was found to be too costly and produce too much non-productive downtime due to not knowing what was going to break next and how long it would take to fix. This scenario gave way to a different PM execution model. In the early 1970s, the concept of time-based replacement came into popularity. There was a belief that all failures were a function of time or throughput and were therefore very predictable. With this predictability, organizations could organize their preventive maintenance strategy to replace parts or components at fixed intervals known well in advance and thereby avoid the problem of not knowing when the next failure would occur. They believed that accurate record keeping and simple statistics would solve their reliability problems. Much to the chagrin of those who followed this philosophy, it did not work. Maintenance costs sky rocketed and system reliability went by and large unchanged. The problem was a lack of understanding of the cause of the problems. When

random failures occurred, the traditional statistical opinion was that not enough data had been collected yet. The companies thought that with enough data, no failure would be random, all would be predictable. While this is actually the case, it was the type of data being collected that was the problem. Simply tracking hours to failure is a lagging indicator and will never point to the nature of the problem. So the system of 100% time-based replacement is not the answer. This realization paved the way for the breakthrough that would be made public in December of 1978. The next style of PM that found some prevalence in the industrial manufacturing world was a hybrid of the previous styles. For years, maintenance people would plan a PM task to go to a piece of equipment, disassemble it, and fix whatever the technician deemed needed fixing. This is probably the most common style seen today. The monthly PM sheet says things like “inspect the following components and repair as needed”. In essence, this is a blank check for the technician to apply whatever level of rigor the technician feels is required in a given situation. Of course, this leads to a high degree of variation in the PM effort as different technicians apply their own idea of how bad is bad enough to work on at that moment. It also means that the degree of inspection is also dependent on how educated, task qualified, and thorough the technician happens to be. This style of PM is not much better than the PM mechanic walking around and working on whatever has the most smoke rolling off of it. The business results for this method reflect that level of efficacy as well. What is interesting is that maintenance managers grow increasingly frustrated with their PM process because of the lack of performance improvement even though piles of money are spent in the PM effort. This leads to action items such as doing more PM, doing it more often, concentrating on technician wrench time, and

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Preventive Maintenance

rewriting all of the procedures in an effort to improve equipment reliability, none of which work because they are not the source of the problem. The source of the problem is a lack of understanding about which failure modes are driven by time or cycles and which ones are random in nature. Nowlan and Heap of United Airlines had developed Reliability Centered Maintenance (RCM) as a failure mode-driven maintenance strategy. In the RCM system, all maintenance tasks are driven by a specific failure mode and have a specific strategy based on the impact of failure and type of failure mode. Failure modes may be random or may wear out with respect to time (see Figure 1).

performed on a machine, such as after initial startup or after maintenance activities, this does not happen after every initial start-up or after every maintenance activity. In fact, sometimes these infant failures happen after start-up or maintenance and sometimes they do not. Hence, there is no specific pattern, which is why they are considered random. Wear out failure modes do not require inspections as frequently as the failure propagation is more predictable. This style of thinking about failure modes, defects, and strategies is perfect for preventive maintenance systems, and though this RCM report is over 30 years old, it remains the gold standard for reliability systems design for maintenance to this day. Some organizations believe that the PM program should start with the precise original equipment manufacturer’s recommendations. They have the belief that no one knows the equipment better than the people who made it. Unfortunately, this is not always the case. The one thing the manufacturer often does not know is the operating context. This is not the case of course for purpose-built equipment, but it is certainly the case for general equipment that can be applied in many applications. Figure 2 shows the results of a reliability analysis based on knowledge of the operating context as compared to the OEM recommendations. Note that some of the task intervals had to be changed and some new tasks had to be initiated. This is a surprise to some people who believe that the manufacturer’s recommendations should be followed to the letter. While this may be the case for purpose-built machines, it is not the case for general machinery. As such, the development of an equipment maintenance plan for a general-purpose machine in a specific application should consider the operating context and the operating environment.

Figure 1: RCM Failure Curves from Nowlan & Heap Random failure modes require inspections and the corrective work is performed based on the condition of the defect at the time of the inspection. A common question is why infant failures are considered random. To answer that question, we must consider the definition of random. Random is literally defined as “having no specific pattern”. While it is true that infant failures happen after work has been

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organization continues to falter while they spend even more on preventive maintenance. The fallacy is that the nature of most problems is random and a time-based replacement strategy is not effective at all in dealing with random problems. To understand this phenomenon, we must first define a few terms. A failure mode is the local effect of a failure mechanism according to the American Society for Testing and Materials (ASTM). An example might be simply “bent”, “broken”, or “leaking”. For the reliability engineer, this is not descriptive enough to identify the problem and solve it. So, a slightly different definition of failure mode will be used for this discussion. A failure mode then shall be described as the part, the problem, and the reason. Example: Bearing – Fatigued – Misalignment. This is read as: The bearing was fatigued due to misalignment. This description of the failure mode gives us all of the information we need to effectively leverage a countermeasure against future failures. This definition will be used for the balance of this paper. Once we understand the failure modes, we can then assign one of the six failure curves found in Figure 1. The A-B-C curves denote an interval-based failure. These are the curves best suited for an interval-based replacement strategy. Curves D-E-F are random failures and an interval-based strategy will not work for them at all. In fact, it will cost significantly more money and will result in no higher availability. Below is a table for a typical motor with a dominant failure mode that is random. The table shows the difference between a timebased strategy applied to a random failure and an inspection-based strategy for the same failure mode. The calculations were made within a Monte Carlo simulation software with typical costs of failure and repair for an electric motor in a typical manufacturing facility.

Figure 2: Failure Modes Analysis of OEM Recommendations Source: OMCS International The litmus test for whether or not a maintenance task remains in the equipment maintenance plan is based mostly on the RCM system. • • • Does the task prevent a failure mode? Does the task detect the presence of a failure mode? Is the task regulatory or statutory in nature?

These tests help us determine if a task is valueadding and whether it should remain a part of the maintenance strategy. All too often, these non-value adding (NVA) tasks creep into the program over time and become bigger and bigger problems. The PM program becomes bloated over time and no matter how much bigger it becomes, it is no more effective, and soon becomes a burden to the organization instead of a program that solves problems. The typical scenario that creates such a large program is that upon experiencing a failure, the organization, believing they can PM their way to reliability, immediately assigns more tasks to the PM, at a higher frequency, and with more people. Of course, this does not address the problem for reasons we will discuss in just a moment, and the

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Table 1: Monte Carlo Simulation Results of Task Interval Optimization Maintenance Strategy Run-toFailure Life Time Costs Number of Failures Failure Downtime Maintenance Downtime (planned) $82,250 2.15 8.6 0 IntervalBased Strategy $97,020 2.16 8.64 6.96 InspectionBased Strategy $9,600 0.02 0.08 4.10

It should be obvious from the differences in the runto-failure column and the interval-based strategy column that for a random failure, replacing the component on a fixed schedule does nothing to the availability of the component and only raises the maintenance costs. The answer to random failures is an inspection-based strategy where the component is inspected at some regular frequency and the repair is affected based on the condition of the component, regardless of time. This is a very doable strategy within the PM program. All of the inspections should produce this type of work.

The P-F Curve
No one graphic within the realm of reliability speaks to all of the concepts encompassed in the name reliability so much as the P-F Curve. This graphic says more with fewer words than any other graphic in the field.

Figure 3: P-F Curve

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As defects propagate into a system, the signals these defects give off change as the defect passes through its severity progression cycle. The signals are different early in a defect’s life from what they are later in its life. These signals tell the inspector about the condition of the defect, which makes the planning and scheduling of the defect elimination much easier and more certain. Acting on the defect as close to Point P as possible creates several advantages for the organization. Among those advantages are lower repair costs, longer lead time for planning and scheduling, lower probability of failure, and a lower necessity for keeping spare parts in stock as opposed to ordering them as needed. These advantages embody all that is reliability and it is for these reasons that the P-F Curve is the single most important concept in the field of reliability. The P-F Curve has some implications for the PM and Predictive Maintenance (PdM) programs. As for inspections, whether PM or PdM, the closer to Point P that the inspection can identify the defect, the more advantageous that identification will have been. For example, using ultrasound to find an early bearing defect provides the organization with an average of 90 days to deal with the problem. However, if an equipment owner relied solely on the eyes, ears, and touch of the operators and technicians to find the bearing defect (as is the case with traditional PM programs), then the plant would likely have something more like 5-7 days to effectively plan, schedule, and execute the work before the situation became more dire and the threat of failure was imminent, forcing maintenance to reschedule production and trigger a maintenance outage. A well-designed PM and PdM program then has separated the defects into those that are easily detected with PdM and those that are more appropriate for PM.

The P-F Curve also gives us an excellent indicator about the frequency with which PM and PdM inspections should occur. For random failures, the inspection interval is less than one half of the P-F interval. This ensures that there is sufficient time to effectively reduce the risk to the organization should a defect be found. This rule applies to PM as well as PdM programs. When the defects are no longer random and there is a sufficiently strong wear out mechanism producing the defect, this rule no longer applies and the equipment operator simply has to decide on what degree of risk they are willing to take with the interval-based replacement activity. For non-random failures, the value of the PM program becomes significant, as it is the only failure-preventing task employed against that failure mode. This next statement cannot be over emphasized. The criticality of a piece of equipment has no bearing whatsoever on the inspection frequency. This is a very common error. It is rooted in poor inspection techniques and the organization’s inability to effectively identify the defect. The inspection interval is solely based on the estimated P-F interval. That being said, the criticality of the piece of equipment does determine the number of inspection methods utilized for a given failure mode. The more critical the equipment, the more duplication one could apply to ensure the defect is detected. There is an old rule of thumb that states if an inspection has been conducted six times and nothing has been found, the inspection interval can then be lengthened. This was often presented as a business decision that operators could make to save money on the inspection program and the total maintenance costs once a given level of reliability was achieved. Given the rule about the length of the inspection interval above, this archaic rule about the number of inspections not producing any results likely seems silly. In fact, if the reliability effort is

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Preventive Maintenance

doing its job, then the inspections are not going to return any defects. So then the business mind wonders: “If the inspections are not finding anything, why do we keep doing it? It seems nonvalue adding.” If we remove the concept of risk from our mindset, the business mind’s questions are relevant. However, it is the mitigation of risk that represents the core of the field of reliability to begin with, so the prudent reliability mind cannot remove risk from the paradigm. Risk must remain a part of the decision matrix. With risk planted firmly in our minds, the fact that six consecutive inspections have yielded nothing should give us cause for celebration

as evidence of a job well done. This six-inspection rule does have one caveat. If six inspections have yielded no results, then the nature of the inspections and the inspection criteria should be evaluated to ensure accuracy. This is the only caveat, leave the inspection interval alone. Six inspections without finding anything simply means that the I-P interval (I = Point of Installation, so the I-P interval is the failure-free period) has lengthened (see Figure 4), it does not mean that the P-F interval has changed. It is the P-F interval that determines inspection frequency, not the length of the I-P interval.

Figure 4: I-P-F Interval

PM Activity Types
There are six PM activity types. They are: clean, inspect, adjust, replenish, rebuild, and replace. These six activity types may be completed by anyone in the organization, not just a maintenance technician. Operators and engineers may also play a role in PM. Cleaning involves keeping the machinery clean enough for two things to occur. First, the machine has to run efficiently, and reliably. It cannot do so if the machine is dirty. Second, the operator has to be able to identify easily any defect or unacceptable condition with the machine. Therefore, operational personnel and not maintenance normally handle cleaning. The only caveat to this is where significant machinery disassembly is required, and then maintenance typically does the cleaning.
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Inspection is the heart of any maintenance program. Inspections may fall into one of two major categories, quantitative and qualitative. Qualitative inspections do not require the use of measurement tools, such as feeler gauges, micrometers, or dial indicators. Permanently mounted instruments like gauges are technically measurement tools, but they do not require a special skill set to read, so for this discussion, reading a gauge is considered qualitative, not quantitative. Quantitative inspections are those inspections requiring a measurement tool and/or a special skill set. As a rule of thumb, qualitative inspections should be assigned to machinery operators and quantitative inspections to maintenance technicians.

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Some components and parts need adjustments over time. Operators can perform some of these adjustments as long as the proper set points have been marked by a skilled craftsman. The most common example of this is center-lining. Some machines have different settings depending on the mode of operation or the product they are running, which require the machine to be configured differently. These different settings are marked to indicate the proper positions for different pieces of the machine. Operators often make these machinery moves themselves without the assistance of a maintenance technician. Other adjustments may include things like calibration, where the technician measures something, compares the measurement results to a known standard, and then adjusts the item to bring it back into calibration. Additionally, some adjustments are made based on wear. For example, if material hits a wear plate, the plate thins over time. To maintain a given clearance, the position of the plate must be moved. This is a classic example of an adjustment activity as a PM task. Replenish simply means to put back what has been consumed. Lubrication is the most common replenishment task, but not all replenish tasks are related to lubrication. Another example might be coolants that are consumed in the process. Not all lubrication tasks require someone highly trained and skilled in contamination control techniques. Some lubrication tasks require only basic skills that operators can perform. As long as the lube process has been well defined such that the proper amount and type of lubricant is delivered at the proper frequency, there is no reason why anyone cannot perform the task. Replace can be as simple as replacing a filter based on the number of hours it has been in service, like air filters or water filters. Replace can also be as complex as replacing catalyst elements based on the number of hours in service. But what they both have in common is that the replacement was based on a fixed interval; it was not based on waiting for

the system to malfunction in some way only to find out that a replacement had not been made. At this point, the replacement is an emergency and not preventive maintenance. Rebuild is essentially like replace. If the failure mode is known and the failure mode is a clear wear out mechanism, and the interval is known, then rebuild may very well be the correct PM strategy. The important factor here is that the rebuild takes place on a regular and fixed interval. Rebuilds that are performed on an as-needed basis are not considered PM, they are simply repairs or corrective work. It only counts as PM if the activity is performed on the interval. Additionally, major repairs found and corrected during a PM do not count as PM. Some organizations do this to avoid the increase in any emergency maintenance metrics and also to avoid the Mean Time Between Failure (MTBF) of the machine/system from being negatively affected. Some of these same PM activity types can be performed in the storeroom just like they are performed out in the manufacturing or production environment. Motor and pump shafts should be turned on a regular basis. Bearings and seals should remain in their original packaging. V-belts should be stored flat and not hung on hooks. Parts made from raw metals should be protected from oxidation. Items that are sensitive to dust and moisture should be sealed and protected. Bearings should be stored on anti-vibration mats to protect them from false brinneling. These tasks should be assigned within the Computerized Maintenance Management System (CMMS) and executed at a set frequency, just like the tasks performed on the installed equipment. Stores PM activities are not much different. There should be inspections, cleaning, and adjustments.

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PM in the Overall Maintenance Strategy
In the past, most maintenance managers have believed that the PM program was the heart of the maintenance effort. While this is still mostly true, we have to consider the PM program and the PdM program separately to ensure that we get the right balance of activity types. The general expectation of the PM program should be inspection of equipment that requires some degree of disassembly and that cannot be performed by some PdM technology, and it should include all of the activities that prevent defects from entering the system.

The proper balance between PM and PdM is found in Figure 5. Preventive maintenance should consume 15% of the total maintenance labor. This is not a minimum, and 35% is not better than 15%. The PM activities should generate some work. The corrective work as a result of the PM activities should consume another 15% of the total maintenance labor force. Again, this is not a minimum or maximum, it is the target. PdM inspections should consume 15% of the total maintenance labor force. These inspections will generate corrective work as well. The corrective work as a result of the PdM inspections should consume 35% of the maintenance labor force.

Figure 5: Proactive Workflow Model

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Business Case for Efficient PM
There are two reasons why PM procedures should be well-designed work procedures. Number one, to eliminate the probability of human error in the execution of the procedure. Number two, to improve the wrench time of the work force. See Figure 6 for a chart on probability of human error. According to the chart, a person working independently, under stress, and without a well-defined work procedure is 30,000 times more likely to commit an error than

someone who is working with a well-designed procedure and with a team. Of course, one of the issues is that we make errors every day and over time we have become accustomed to these errors and no longer see them as problems to be overcome. We simply see them as part of our everyday lives. These are known as institutionalized losses, as we have made them part of our daily expectations. Well-defined work procedures are intended to eliminate as many of these as possible.

Figure 6: Human Error Rates Source: A Guide to Practical Human Reliability Assessment, by Barry Kirwin The second reason well-defined work procedures are so important pertains to manpower utilization, namely wrench time. The more comprehensive the job packet, the more efficient the work. There is a lot of value to an organization for getting the wrench time up to a respectable level. For example, if an organization has 60 technicians, 15% of the 60 technicians (9) should be working on PM at any given time. If the wrench time for this group of
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technicians is 29% (North American average) and through better procedures and more complete job packets, the wrench time was shifted to 55% (considered by many to be the upper limit of possibilities), then the organization would effectively realize an 89.65% increase in productivity without hiring any additional personnel.

Preventive Maintenance

Some craftsmen have a negative reaction to this line of logic. They believe that doubling the output means they have to double their efforts, and the doubled effort is expected at no additional increase in compensation. If these were the only elements in the equation, one could see this as a demotivator. However, more efficient work means easier work. The definition of efficient after all is “results divided by effort”. So, if I can get better results with less effort, I get an increase in efficiency. The less effort part comes from not looking for parts, not waiting to get a machine down, not waiting for a permit, and not wondering how to do the job or having to invent a way to do the job. A wellconstructed job packet contains all of these things; therefore, the technician expends less effort while getting more work accomplished. This is wrench time logic that creates a significant portion of the business case for improved PM procedures.

Project 1 Job(s) 2 Task(s) 3 Step(s) 4 Instructions 5 Figure 7: Procedure Taxonomy A common procedure hierarchy or taxonomy ensures that everyone uses the same terms to describe aspects of the procedures and there are no lapses in understanding due to different terms.

PM Procedures
PM Procedure Hierarchy
To ensure everyone uses the same terminology for procedures, Figure 7 contains a standard taxonomy for procedure construction. • • • • Projects contain one or more jobs Jobs contain one or more tasks Tasks contain one or more steps Steps may or may not have instructions

Procedure Elements
A procedure is much more than a task list. Task lists are what normally appear in a PM job plan. Figure 8 is an example of a task list that is supposed to pass for a PM procedure: **Safety** Follow all company guidelines for safety 1) Check pump for normal operations 2) Check bearings for excessive heat, vibration, and unusual noises 3) Check seals for leaks 4) Ensure all bolts and fasteners are tight and properly torqued 5) Check coupling for any problems 6) Check impeller for any wear, damage, and proper balance Record any deficiencies in the space below and report them to your supervisor. Figure 8: Typical PM Task List

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What is sad is that this is a very typical PM procedure, and there are so many problems with this procedure that it is borderline comical. A well-defined procedure has the following elements: 1. Warning – warnings alert the technician to the possibility of injury during the execution of the procedure. Cautions – cautions alert the technician to the possibility of equipment damage and/or environmental incidents during the execution of the procedure. Tasks and Steps – these are the specific actions to be taken in order to accomplish the objective of the procedure. Instructions – some steps require instructions, some do not. Instructions are the specific element actions required to accomplish a step. Resources – these are all of the things that help accomplish the procedure. Examples of resources include: parts, tools, consumables, permits, departmental coordination notes, and outside services. Constraints and Impediments – these are all of the things that may interfere with the completion of the procedure. Examples include: interference from other machines and structures, production schedules, weights of components, location of components, and specific disassembly requirements. Notes – notes are additional details that are included for clarity, or may be conditional steps added for special circumstances. Performance standards – these are special constraints that are added to ensure that the step meets the desired quality consideration. Examples include: alignment tolerances, torque values, clearance values, and indicators of proper fits.

This list differentiates a task list from a procedure. Most organizations want a procedure, but only invest the time to produce task lists, and then wonder why they experience so much variation and error in the results of the procedures, often blaming this variation and error on the technicians when the blame lies with the quality of the procedure. The nature of the tasks and steps should be quantifiable and repeatable. Quantifiable can also be said as measureable. PM tasks should either require measuring tools to be accomplished or at least have the ability to be measured when complete. This element of the procedure ensures that the task can be quality checked for completeness at some point in the process. If the task is not quantifiable, then the task has some inherent variation within it, as will the results of the task. Additionally, the task has to be worded such that it is repeatable. Repeatability has to do with getting the same results from the same person twice in a row or getting the same results from multiple people completing the same procedure. Wording the procedure properly means taking the time and effort to write the task, step, or instruction to ensure that only one meaning can be interpreted. This is easier said than done, but the time and effort spent doing this is money well spent. There has always been some issue with what degree of instruction to put into a procedure. One school of thought says that the degree of instruction should be targeted at the least experienced technician in the organization. Of course, this method means that the very experienced technician has a large amount of instructions to sift through that they may not need. Another school of thought posits that instructions should never infringe on the skill of the craft and should therefore be minimalistic. Of course, this means that the unskilled crafts person may find the procedure lacking and have to pause the job to go looking for answers. One way to think of how many instructions to put into a procedure is to place the amount of detail in there that

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guarantees consistency of execution. Granted, this is easier said than done if the planner or engineer decides to attempt to build this procedure alone in their office. However, there is a way to accomplish this while garnering a high level of participation from the crafts personnel, and that is to simply involve the technicians in the creation and editing of the procedure. This creates ownership, and it also ensures that the degree of instruction is useful and not overbearing. Yes, sometimes the easiest answer to the age old question of “how detailed should the instructions to the technicians be” is to simply ask them. Some consideration should be given to standard procedures as well. Some procedures are the same regardless of the machine for which they are designed or for the size of the component. These standardized procedures make the construction of new procedures more efficient. For example, shaft alignment for direct coupled machines using rolling element bearings is the same regardless of the machine type or size. Having a standardized procedure for shaft alignment removes a great deal of work from the procedure author. Sheave alignment also falls into this category. Another example is the removal, installation, and inspection of a grid coupling. This procedure is the same regardless of the size of the coupling. Having these standardized procedures to pull from and drop into new procedures under development makes the whole process more efficient while maintaining consistency in critical processes across different jobs. In the maintenance world, one of the biggest complaints has been the lack of useful feedback from technicians about the quality and usefulness of a job procedure, and PM job procedures are certainly no exception. For years, the planners and engineers complained that mechanics and electricians never give any feedback at all or that the feedback they do give is useless. This lack of feedback is usually rooted in two different issues, and it is almost never one or the other. It is usually
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both. Reason number one, the technicians have no ownership in the procedure. They did not help write it, they do not agree with it, and therefore they do not use it. The effect of these three characteristics is that they feel no compelling reason to offer any feedback of substance. As for the treatment for this particular problem, the answer is participation, which we covered previously in this very paper. Reason number two, previous feedback has been habitually ignored to the point there is no use in wasting any more time in providing feedback because it has been made readily apparent that either no one is reading it or no one is acting on what has been read. All feedback deserves to be considered and a response offered on the feedback within a week. When people know that you are listening, and that you care, and that they can count on you to follow through, they will more eagerly participate with you in a process. It is as simple as this: “show me you do not care what I say and fairly soon I will stop saying anything at all.” All work procedure feedback deserves someone coming back to the person who offered the feedback and providing either the evidence that the feedback was integrated or the rationale for why it was not.

PM Scheduling and Compliance
There is a difference between adherence and compliance, at least in the PM world. PM Compliance is the percentage of PM tasks that were completed as per the schedule. For example, if the CMMS showed 212 PM tasks scheduled for August and only 203 of them were completed, the PM Compliance for August would be 95.7%, which is good because the goal should be >95% for PM Compliance. While there is no benchmark data to backup the claim of 95% as a target, it is a generally accepted target. Each organization should establish its own target. When evaluating the PM Compliance metric, manpower should be considered as well. If the 212

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PM tasks scheduled for August represented 488 labor-hours, the 95.7% compliance should have consumed something close to that same percentage of labor-hours. This is not always exact as some PM tasks take longer than others, but it should be within the realm of believability. However, if the 95.7% PM Compliance only consumed 54% of the labor-hours that were scheduled, there is a problem. If this happens, the PM completion process should be evaluated, as there is likely someone completing PM on paper and not actually doing the work or the PM completion labor is being charged to something other than the PM. Either way, there is a problem. PM Route Adherence is another measure altogether. Route adherence is the measure of how closely the PM task was completed within its call window. The call window is the allotted time for the timely completion of the task and ideally should only allow for early completion - 10% . For example, the monthly PM was due on 14-October. As it is a monthly PM, the window is 3 days. So, the PM could be completed as early as 11-October, but no later than its due date of 14-October to receive full adherence credit. If the PM is completed outside of the window, it is still checked as being completed, but the degree of how early it was completed determines the degree of route adherence. If it was completed outside of that window, the interval between it and the previous completion (if early) or the next completion (if late) is being infringed upon. Therefore, when measuring the PM program, we want to evaluate PM compliance both from a percentage of task completion, the percentage of labor-hours consumed, as well as the degree of route adherence. Leaving one of these metrics out of the equation opens the organization to some degree of risk with respect to the efficacy of the PM program. PM schedules should be load-leveled across the balance of the scheduled time. For example, I do not want to have 70% of my PM labor-hours in the first week of the month with the other three weeks

having 10% each. The reason I do not want this is that machinery failures and other emergency work may disrupt which machines I have available for PM work and it thus impacts the rest of the month. Not to mention, it puts all of the missed PM at risk to miss the - 10% adherence rule. Evenly distributing the PM load across the month, the quarter, or the year makes the management of the PM effort much easier. Mean Time To Implement is another useful metric for PM program management. The average time it takes to complete the corrective work generated from the PM inspections is the MTTI, or Mean Time To Implement. The idea of this metric is to drive the timely completion of the corrective work identified during the PM inspections. Like all inspection data, there is a best-if-used-by date on all information. Inspections that yield defects have to be corrected in a timely manner lest the defects turn into equipment failures. Failing to act quickly enough begs the question of why inspect it at all if you are not going to act on the information. All corrective work from PM inspections should be completed with a less than 30-day MTTI.

PM Evaluation and PM Optimization
Two processes are used to evaluate and modify PMs to add more value to a Reliability Based Maintenance implementation. The two processes are PM Evaluation (PME) and PM Optimization (PMO). These have been developed over time to replace the time-consuming tasks associated with the RCM practices. These are both described here to compare and contrast their unique processes.

Preventive Maintenance Evaluation
PME takes a Total Productive Maintenance (TPM) approach to evaluating the current PM system, sorting them based on type, and then determining if the task steps should be replaced, deleted, done

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Preventive Maintenance

differently, or left as is. It is based on evaluating the steps of the task list individually and determining if the task step meets certain criteria. The result is a recommended action for each step. This serves as a fairly fast method to go through tasks, but does not evaluate overall effectiveness of the task list or frequency of performance.



Is it good as written?

The evaluator, based on the answer, then assigns one of the following recommendations: □ □ □ □ □ □ No Value Added Reassign: Lubrication Route Reassign: Operator Care Replace with PdM (specify type(s)) Reengineer – with comment(s) No Modification Required

Overview of PME Process
PME takes each task step and asks the following questions: □ □ □ □ □ Does the step add value? Can it be replaced by PdM methods? Should it be on a lubrication route? Could it be assigned to operator care? Does the step need to be written differently (reengineered)?

PME Example
When the PME questions are used to evaluate traditional PM programs, the typical results are as shown in the chart in Figure 9.

Figure 9: PM Evaluation Results Table

© 2014 Allied Reliability Group

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In traditional PM programs, these questions normally produce the following results. Rows 1 through 3 typically sum to 30%. Rows 4 and 5 normally sum to 30% each, leaving Row 6 as 10%. These numbers mean that most PM programs are larger than they should be and are typically not producing the results everyone thinks they should. Cleaning up that PM program by reallocating the labor to the correct location can go a long way to making the PM program produce the desired results and save a considerable amount of labor expense provided the labor cannot be reassigned to other value-added work, like creating an internal PdM program, performing root cause analysis, or building work procedures. Someone should be assigned to frequently and regularly pick a selection of PM tasks and ask the PME questions. This will keep the PM program from getting bloated and becoming more of a burden on the organization rather than a process that solves machinery problems.

Overview of PMO Process
PMO takes each task list and PM and evaluates them in light of equipment history and functional failure prevention/alleviation. It asks the following questions: □ □ □ Validity: Does it prevent or mitigate a failure? Method: Can it be replaced with PdM or something non-intrusive? Cost Effectiveness: Is it cheaper to replace than maintain? (Include cost of down equipment impact.) Frequency: Is the frequency based on actual needs or just “the way it has always been done”?



Based on the results of these questions, possible recommendations/actions include: □ □ □ □ Failure does not need to be prevented. Failure prevention is not cost effective. Task list can cause damage to equipment – reengineer. Frequency of PM needs to be changed.

Preventive Maintenance Optimization
The PMO evaluates the task based on whether it prevents a failure, the failure needs to be prevented, and there is a better way to do it. Unlike RCM, it primarily approaches the asset evaluation based on the existing PM. By looking at the PPM as a whole, and the asset history, it can also address failure modes not properly identified in past PM implementations. This process is essentially a targeted simplified Failure Mode and Effects Analysis and will require more time than the PME portion of the analysis. This is also more focused on where the equipment is being used. The same model motor in a heating system may not be as important as one in a process line, and therefore not cost effective to maintain.

Summary and Conclusion
Preventive Maintenance has been the heart and soul of professional maintenance efforts in a manufacturing and production environment, and it should always remain so. However, to accomplish the asset reliability required to enable high levels of availability, the PM program has to be streamlined in several ways. • Our expectations of what PM alone can accomplish have to be modified to only include those failure modes that are interval-based or wear out failure modes. We can no longer expect to combat random failures with an intervalbased replacement. • Our expectations of the effectiveness of sensory inspections have to be adjusted as well. Sensory

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inspections identify the defect very low on the PF curve, allowing only a short amount of time to respond correctly and efficiently. We have to ensure that the inspection techniques we employ find the defect as high on the P-F curve as possible. Our expectations of what drives the PM program have to be adjusted. Failures do not drive the PM program. This is reactive thinking. The reasonable and likely failure modes for a piece of equipment drive the PM program. Our expectations for the frequency of PM inspections have to be adjusted. The only factor in the equation for calculating the PM interval for random failures is the length of the P-F curve. The fact that you have conducted the PM inspection six times and not found anything is irrelevant to the inspection frequency. This is what happens when the reliability effort begins to work correctly. This does not mean the machine is now exempt from random failures. Our expectations of what constitutes a proper procedure have to be adjusted. A task list is not a procedure. Procedures have enough detail to drive consistent execution of the PM regardless of who executes the work. Our expectations of what good compliance and adherence look like have to be adjusted. There is a finite time window for each PM; miss the window and you expose the asset to unnecessary liability.

If these expectations are successfully adjusted, then the organization can begin to expect that the PM effort will only take about 15% of the total maintenance labor and it will drive an additional 15% of labor utilization against corrective work found during the PM inspections. These numbers indicate a healthy mixture of PM into the maintenance scheme without wasting any money and without exposing the asset base to unnecessary risk. Accomplishing this is a major step in the direction of improving asset reliability and Overall Equipment Effectiveness (OEE).

© 2014 Allied Reliability Group

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About Allied Reliability Group
Allied Reliability Group (ARG) offers best-inindustry maintenance, reliability, and operational consulting and services, training, staffing, and integrated software solutions servicing the industrial and manufacturing sector. Reliability… it's in our DNA.

For more information about Allied Reliability Group, please contact: Glo ba l H ea dqu ar ter s 843.414.5760 [email protected] www.alliedreliabilitygroup.com

© 2014 Allied Reliability Group

Preventive Maintenance

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