Predictive Maintenance (PdM) and Preventive Maintenance (PM)

One of the employee ask me, What is the difference between Preventive Maintenance (PM) and Predictive Maintenance (PdM)?

Here's an straight answer:

"The distinction between preventive maintenance (PM) and predictive maintenance (PdM) is that PdM tracks performance based on conditions while PM is a time-based replacement or service process"

The question now is... what is the best between these two?

Preventive Maintenance (PM) Definition

Preventive maintenance (PM) has the following meanings:

1. The care and servicing by personnel for the purpose of maintaining equipment and facilities in satisfactory operating condition by providing for systematic inspection, detection, and correction of incipient failures either before they occur or before they develop into major defects.
2. Maintenance, including tests, measurements, adjustments, and parts replacement, performed specifically to prevent faults from occurring.

While preventive maintenance is generally considered to be worthwhile, there are risks such as equipment failure or human error involved when performing PM, just as in any maintenance operation. PM as scheduled overhaul or scheduled replacement provides two of the three proactive failure management policies available to the maintenance engineer. Common methods of determining what PM (or other) failure management policies should be applied are; OEM recommendations, requirements of codes and legislation within a jurisdiction, what an "expert" thinks ought to be done, or the maintenance that's already done to similar equipment. However Reliability Centered Maintenance, provides the most rigorous and method to determine applicable and effective failure management policies - which may include PM tasks - for an item.

To make it simple:

• Preventive maintenance is conducted to keep equipment working and/or extend the life of the equipment.
• Corrective maintenance, sometimes called "repair", is conducted to get equipment working again.

The primary goal of maintenance is to avoid or mitigate the consequences of failure of equipment. This may be by preventing the failure before it actually occurs which PM and condition based maintenance help to achieve. It is designed to preserve and restore equipment reliability by replacing worn components before they actually fail. Preventive maintenance activities include partial or complete overhauls at specified periods, oil changes, lubrication and so on. In addition, workers can record equipment deterioration so they know to replace or repair worn parts before they cause system failure. The ideal preventive maintenance program would prevent all equipment failure before it occurs.

Source: wikipedia

Predictive Maintenance Program

A Quality Rotating Machinery Predictive Maintenance (PdM) Program for your facility will return your investment many times over. This type of PdM Program is based on periodic vibration measurements of your Rotating Machinery. In many cases, a Return On Investment (ROI) of less than one year (six months typical) is quite common. A Contract PdM Program eliminates the initial capital investment required to conduct your own PdM Program.

There are three classifications of machinery maintenance methods: Breakdown, Preventative, and Predictive Maintenance. Each method has its own associated costs and benefits.

Breakdown Maintenance, by its own nature, is the most expensive method of plant maintenance. This method has no scheduled maintenance until a machine destroys itself, and it must be replaced at great cost. The machine breakdown often brings the production process to an immediate halt. Breakdown Maintenance has high costs in manpower, replacement parts, and lost production.

Preventive Maintenance, the next logical method, relies on a periodic inspection the machines. During the inspection, machine damage is found and corrected. This method requires a large inventory of replacement parts prior to the machine's inspection. Preventative Maintenance has a lower associated cost because manpower can be planned in advance.

Predictive Maintenance involves monitoring the machine's vibration characteristics or symptoms to diagnose its condition. This method relies on the machine's condition to accurately schedule the repair interval. The machine's condition also determines the required replacement parts. Predictive Maintenance has the lowest cost of the three methods with the highest possible savings.

A Machinery PdM Program is beneficial to all industries that have rotating machinery on their site such as:

• Petroleum
• Chemical
• Power Generation
• Co-Generation
• Pulp and Paper
• Water Treatment
• Building Services
• HVAC
• Mining
• Food Processing

Typical Rotating Machinery commonly included in a Machinery PdM Program include but are not limited to the following:

• Electric Motors
• Pumps
• Fans
• Gear Boxes
• Turbines
• Compressors
• Paper Machines
• Reciprocating Machines
• Blowers
• Machine Tools
• Chillers
• Conveyors

Predictive and Preventive Maintenance in a Declining Economy

In a declining economy saving operating expenses has become a priority for most firms. Predictive and preventive maintenance although similar, are two different tools used by facilities managers in order to save precious dollars. Both maintenance systems help keep earnings (the bottom line) stable by avoiding costly repairs and maximizing equipment up-time. Normally cutting expenses for operations means fewer support staff, hiring freezes, and a repair versus replacement strategy on equipment. But what happens when the forecast for low or declining sales does not improve or is mired in a deep recession?

A recent survey conducted by Facilities Planners and Architects, Inc. of facility managers and business owners revealed intended reactions to the current economic situation. The survey highlights are:

• Limiting capital expenditures to sustainability initiatives such as more efficient lighting systems
• More plans to reduce square footage
• Outsourcing non-core services such as janitorial services
• Assessing the condition of the facilities and better strategic planning of their use
• Initiating predictive maintenance programs

Obviously, it is always a good idea to watch your expenses. The results echoes this and indicates a long overdue desire to become more energy efficient, a focus on core responsibilities by outsourcing non-core functions, a strategic look at assets and the initiation of efficiency and savings programs. The survey mentions predictive maintenance as one of the most popular choices for cost saving solutions. It should be noted that predictive maintenance is not the same as preventive maintenance. Successful predictive maintenance starts with preventive maintenance. To better understand let us take a look at both.

Predictive vs. Preventive Maintenance:

Preventive maintenance occurs on a pre-determined schedule and is intended to increase efficiencies by reducing the amount of reactive work and increasing the ability of management to manage work. Most importantly, it allows for the early identification of problems and significantly increases the life cycle of equipment, lowers capital expenditure requirements and allows for better planning of capital budgets. In addition, when integrated with handheld technologies and a combination of asset management, work order management and inspections, work flow efficiencies are increased to maximum levels. The data collected through this method becomes the building block for predictive maintenance.

Predictive maintenance does have its benefits in a difficult economy particularly because it can be less labor intensive than preventive maintenance. Predictive maintenance programs are based upon the actual condition of the equipment and a determination of when maintenance should be performed to minimize costs. New technology techniques such as ultrasound, infrared and vibration online testing make predictive maintenance a viable alternative in certain circumstances. However, for most equipment the complex metrics for making educated guesses is provided by preventive programs.

The goal of a facility manager or business owner is to make sure equipment has the highest possible uptime and to extend the life cycle of the equipment as long as possible at the most reasonable economical cost. Some predictive maintenance plans will require a capital investment in higher technology sensing equipment but most will be built upon the foundation and metrics provided by an existing preventive maintenance program. Facility managers should not rely on just a predictive maintenance solution to save expenses especially if dealing with high value equipment or if safety is at stake.

Tough times call for tough decisions as both maintenance programs have their place. The solution may be a combination of the two maintenance programs or it may be dependent on your industry, type of equipment and survival strategy. What is your company going to do?

Source: Mintek | http://EzineArticles.com/?expert=S_W_Smith

Preventive Maintenance As A Clever Cost-Cutting Process

So many managers in factories and hotels treat maintenance as a necessary evil. The cost of engineers and technicians, who look after and repair the equipment, is considered a burden that deprives the entity of extra profit. In these entities, one often finds the maintenance personnel, “fighting fires” all the time. They tend to serve those who either stand high in the hierarchy or those who shout the loudest.

The lack of an organised maintenance effort brings about a lot of wasted time, time that is preciously limited and time that costs a lot of money. Studies taken in such workplaces showed that a maintenance technician only spends around 25 per cent of work-time actually on the job solving problems. The rest of the time (75 per cent) is spent looking for spare parts, going to and from the work-site (several times), getting permits to start work and on other similar non-productive work.

Change is always difficult to make and changing operating procedures and mentality even more so. The change required here is to gradually move from reactive maintenance (fighting fires technique) to proactive maintenance (preventing the fires in the first place). Proactive maintenance is more commonly referred to as Preventive Maintenance. This can be achieved through short- and long-term maintenance planning. Employing the help of software improves the chances of success drastically.

A Computerised Maintenance Management System (CMMS) is software dedicated to improving the efficiency, organisation and effectiveness of the maintenance section. A good CMMS is capable of keeping track of repairs done on equipment or machinery, alerts maintenance personnel on when preventive maintenance is due, plans and schedules jobs to personnel who have the skill to do the job in question, makes sure that required parts are ordered in time for maintenance to take place and other similar organising functionalities.

The use of a CMMS can improve maintenance personnel efficiency to 55 per cent or even more. This means that a maintenance person is capable of doing more than twice the amount of work that used to be done before. It often results that as more time is available to the maintenance section, work that used to be outsourced will be handled in-house, further reducing costs, building better in-house skills while affecting maintenance in a shorter time.

A CMMS application also helps reduce the frustration felt by maintenance persons who might feel that the lack of organisation in their department makes them look inefficient in the eyes of their clients. It creates a pride of being professional through planning and efficient handling of maintenance. It improves production, as downtime is reduced. Maintenance can be planned weeks ahead and the necessary arrangements for reassigning production workers to other chores in the factory can be done with ease.

Long-term benefits of using a CMMS is that equipment and machinery lifetime is extended through the proper implementation of preventive maintenance. This in itself reduces the cost of re-investing earned profit into new machines.

Decision taking is also made easier with the data provided by such an application. Data on each and every machine’s repairs and maintenance is recorded. When the question of whether to repair or replace comes up, a more informed decision can be taken.

With all of these benefits, one wonders why so many entities overlook such an application. Reasons vary from the lack of understanding of the benefits such an application provides to the fear that such an application would cost the earth. On the other hand, while it is true that most CMMS software cost too much to be implemented in SMEs, there exist systems aimed at such entity sizes that are more affordable and still offer a good return on investment .

Technology has come a long way and the use for cost cutting and improved bottom line is a clever way towards moving closer to success.

Source: maltabusinessweekly.com | Carmelo Romano

Predictive Maintenance Technology Using Fluke Ti25 IR Infrared Thermal Imaging Camera

The Fluke Ti25 is an industry leading infrared camera system. The Ti 25 is the ultimate tool for troubleshooting, preventive maintenance and predictive maintenance. This thermal Imager is the perfect tool to add to your problem solving arsenal. Built for tough work environments, this high performance, fully radiometric infrared camera is ideal for troubleshooting electrical installations, electro mechanical equipment, process equipment, HVAC/R equipment and others.

Companies use infrared for both predictive maintenance programs and diagnostics tools. Processing manufacturing has many pieces of equipment that can literally cost thousands of dollars every hour of downtime. With infrared companies can predict well in advance any problems that may be on the horizon. The return on investment for an infrared program is usually meet after only a few detections of potential problems.

The Fluke Ti25 features Fluke's patented IR fusion capabilities. IR fusion allows the user to blend both the infrared and visual light image. IR fusion ability allows the user to diagnose problems more effectively and efficiently. Other features include; a thermal sensitivity of just 100mk, 160x120 resolution, instant high low spot meters, sixty second voice annotation, seven different color palettes, a six hundred and ninety two degree temperature range, an industry leading two year warranty, and Smart View 2.1 software with all future upgrades of the software for free. This is all backed by Fluke's award winning customer service and un matched product durability.

Recently the Fluke Ti25 recently won an award from Plant Engineering magazine for product of the year. Different manufactures entered several different models, and the Ti25 took the award.

Develop Good Strategies For Effective Preventive Maintenance (1/2)

Experience has clearly shown that some confusion does exist over just what people mean when they use the term preventive maintenance. One significant factor stems from the evidence that a vast majority of our industrial plants and facilities have been operating for extended periods, years in many cases, in a reactive maintenance mode. That is to say that the maintenance resources have been almost totally committed to responding to unexpected equipment failures. Corrective, not preventive, maintenance is frequently the operational mode of the day, and this tends to blur what is preventive and what is corrective.

In one actual extreme case, a plant developed an entire culture that fostered a feeling of pride in people's ability to fix things rapidly and under pressure when a forced outage occurred. Plant personnel viewed their actions as preventive in the sense that they were able to "prevent" a long outage because of their highly efficient and effective reactive and corrective actions. What the plant staff did not consciously recognize (or acknowledge) was that they were the highest cost per unit producer among their peers.
We use the following definition of preventive maintenance (PM):

Preventive maintenance is the performance of inspection and/or servicing tasks that have been preplanned (i.e., scheduled) for accomplishment at specific points in time to retain the functional capabilities of operating equipment or systems.

The word "preplanned" is the key element in developing a proactive maintenance mode and culture. In fact, this now provides us with a very clear and concise way to define corrective maintenance (CM):

Corrective maintenance is the performance of unplanned (i.e., unexpected) maintenance tasks to restore the functional capabilities of failed or malfunctioning equipment or systems.As viewed by the authors, the entire world of maintenance activity is fully encompassed in these two definitions.

However, there are two troubling factors that people frequently question which give rise to some of the confusions over the "PM or CM" discussions. The first of these involves the games that people play with the terminology. These games can be driven by such diverse nontechnical factors as accounting practices or political (regulatory) pressures. For example, some plants, in addition to planned outages and forced outages, have a third category known as a maintenance outage (MO).

The MO occurs as a result of an unexpected equipment problem which hasn't quite yet reached the full failure state but will do so very soon. So the plant management will delay the shutdown until some off-peak period when the plant outage is more tolerable, and hope that the equipment will hold out until then.

Now from an operational point of view, this is a very smart thing to do — but, as a rule, MOs are not counted when it comes to reporting the plant forced outage rate. Somehow they seem to wind up in the preplanned category ("after all, we planned to fix it next Saturday!"). Make no mistake about it, an MO is a forced outage and should be labeled as such when measurements are made. You are only kidding yourself to do otherwise.

Please also read:
Develop Good Strategies For Effective Preventive Maintenance (2/2)

Source: Anthony M. Smith and Glenn R. Hinchcliffe (Plant Engineering - November 1, 2005)

Four Task Categories To Understand In Undertaking Preventive Maintenance (4/4)

Run-To-Failure (RTF)

As the name implies, we make a deliberate decision to allow an equipment to operate until it fails — and the maintenance action occurs only after the failure has occurred. There are some limited cases where such a strategy makes common sense:

1. We can find no PM task that will do any good irrespective of how much money we might be able to spend.

2. The potential PM task that is available is too expensive. It is less costly to fix it when it fails, and there is no safety impact at issue in the RTF decision.

3. The equipment failure, should it occur, is too low on the priority list to warrant attention within the allocated PM budget.

4. Note the distinction between FF and RTF. With FF the failure is hidden and we do not want to be surprised by its occurrence if the failure should happen. With RTF, we have made a deliberate decision not to be concerned about failure occurrence, be it evident or hidden, and will simply correct the failure at our time of choosing should it occur.

Four Task Categories To Understand In Undertaking Preventive Maintenance (3/4)

Condition-Directed (CD)

When we do not know how to directly prevent or retard equipment failure-or it is impossible to do so — the next best thing that we can hope to do is to detect its onset and predict the point in time where failure is likely to occur in the future. We do this by measuring some parameter over time where it has been established that the parameter correlates with incipient failure conditions. When such is done, we call it a condition-directed or CD task. Thus, a CD task would pre-warn us to take action to avoid the full failure event. If the warning comes soon enough, our action can most likely be taken at some favorable timing of our choice.

The CD task, like the TD task, has a periodicity for the measurements, but actual preventive actions are not taken until the incipient failure signal is given. The CD task takes two forms: (1) we can measure a performance parameter directly (e.g., temperature, thickness) and correlate its change over time with failure onset; or (2) we can use external or ancillary means to measure equipment status for the same purpose (e.g., oil analysis or vibration monitoring). With the CD task, all such measurements are nonintrusive. The keys to classifying a task as CD are: (1) we can identify a measurable parameter that correlates with failure onset; (2) we can also specify a value of that parameter when action may be taken before full failure occurs; and (3) the task action is nonintrusive with respect to the equipment.

Failure-Finding (FF)

In large complex systems and facilities, there are almost always several equipment items-or possibly a whole subsystem or system-that could experience failure and, in the normal course of operation, no one would know that such failure has occurred. We call this situation a hidden failure. Backup systems, emergency systems, and infrequently used equipment constitute the major source of potential hidden failures. Clearly, hidden failures are an undesirable situation since they may lead to operational surprises and could then possibly initiate an accident scenario via human error responses. For example, an operator may go to activate a backup system or some dormant function only to find that it is not available and, in the pressure of the moment, fail to take the correct follow-up procedure. So, if we can, we find it most beneficial to exercise a prescheduled option to check and see if all is in proper working order. We call such an option a failure-finding task.

Let's look at a simple example-the spare tire in our automobile. If you are like us, you don't really worry about a flat spare tire because you have AAA coverage, and are never more than 10 to 15 minutes away from an ability to get emergency road service-except for that once-a-year trip with the family into "uncharted lands" (e.g., Death Valley). Again, if you are like us, you do check the spare before you leave — and that is a failure-finding task.

Notice that the only intent in such an action is to determine if the spare tire is in working order or not. We are doing nothing to prevent or retard a flat tire (a TD task) or to measure its incipient failure condition (a CD task). It is or is not in working order. And, if it is not in working order, we fix it. That is the essence of what a failure finding task is all about. (Is it OK? If not, fix it.)

Four Task Categories To Understand In Undertaking Preventive Maintenance (2/4)

This is part 2 of the series Four Task Categories To Understand In Undertaking Preventive Maintenance

Time Directed (TD)
In the not too distant past, virtually all preventive maintenance was premised on the basis that equipment could be periodically restored to like-new condition before it was necessary to discard it for a new (or improved) item. This premise thus dictated that equipment overhauls were about the only way to do preventive maintenance.

Today, we are slowly realizing that this is not always the correct path to pursue. However, in many valid situations we still specify PM tasks at predetermined ("hard time") intervals with the objective of directly preventing or retarding a failure. When such is done, we call it a time-directed task. A TD task is still basically an overhaul action-sometimes very complete, extensive, and expensive (like rebuilding an electric motor), and sometimes very simple and cheap (like alignments and oil/filter replacements). As a rule of thumb, whenever we have a planned intrusion into the equipment (even just to inspect it), we have in essence an overhaul-type action which is labelled a TDI (Time-Directed Intrusive) task. Some time-directed tasks can be non-intrusive, such as simple visual inspections or minor adjustments that do not require a breach of the equipment boundary or housing. In this case, the action is simply labelled as a TD task.

More often than not, time-directed tasks tend to be intrusive. A simple example that everyone can picture is the changing of oil in our automobile. Here, we intrude in the PM action by removing the drain plug (which will leak if not properly reinstalled), by injecting fresh oil (which must be of the correct type, grade, and quantity with the fill cap properly replaced), and by replacing the oil filter (which will leak if the gasket is not properly installed). The "hard time" associated with this action is car mileage, which has been suggested by the manufacturer who has collected years of experience defining excessive engine wear as a function of oil deterioration due to contaminants and loss of viscosity.

Notice that this simple PM task, a TDI task, presents several opportunities for human error to creep into the procedure. The keys to categorizing a task as time-directed are:

(1) the task action and its periodicity are preset and will occur without any further input when the preset time occurs;

(2) the action is known to directly provide failure prevention or retardation benefits; and

(3) the task usually requires some form of intrusion into the equipment.

Four Task Categories To Understand In Undertaking Preventive Maintenance (1/4)

By Mac Smith and Glenn HinchcliffePlant Engineering - December 1, 2005

There are four basic factors behind the decision to define and choose preventative maintenance actions:
1. Prevent or mitigate failure occurrence
2. Detect onset of failure
3. Discover a hidden failure
4. No nothing, because of value limitations

By identifying the four factors for doing preventive maintenance, we have also set the stage for defining the four task categories from which a PM action may be specified. These task categories, by one name or another, are universally employed in constructing a PM program, irrespective of the methodology that is used to decide what PM should be done in the program.

The four task categories are as follows:
1. Time-directed (TD): aimed directly at failure prevention or retardation.
2. Condition-directed (CD): aimed at detecting the onset of a failure or failure symptom.
3. Failure-finding (FF): aimed at discovering a hidden failure before an operational demand.
4. Run-to-failure (RTF): a deliberate decision to run to failure because the others are not possible or the economics are less favorable.

Is Preventive Maintenance Necessary?

Written by William C. Worsham (Senior Consultant and Trainer, Reliability Center, Inc.) Feature article for "Focus on Reliability" Column at MaintenanceResources.com

Reliability Centered Maintenance has changed the way we think about Preventive Maintenance (PM). It has caused some to question whether it is even necessary to do preventive maintenance. The truth is most manufacturing facilities would benefit from a good preventive maintenance program. It would be especially beneficial for those plants that rely on breakdown or run-to-failure maintenance. But, a preventive maintenance program is potentially risky, so it must be administered and performed properly to be successful. This paper will examine both the benefits and risks of preventive maintenance and offer some ideas on how to make it successful. We will start with a definition of preventive maintenance.

What is Preventive Maintenance?

Preventive maintenance is planned maintenance of plant and equipment that is designed to improve equipment life and avoid any unplanned maintenance activity. PM includes painting, lubrication, cleaning, adjusting, and minor component replacement to extend the life of equipment and facilities. Its purpose is to minimize breakdowns and excessive depreciation. Neither equipment nor facilities should be allowed to go to the breaking point. In its simplest form, preventive maintenance can be compared to the service schedule for an automobile.

A bona fide preventive maintenance program should include:

• Non-destructive testing
• Periodic inspection
• Preplanned maintenance activities
• Maintenance to correct deficiencies found through testing or inspections.

The amount of preventive maintenance needed at a facility varies greatly. It can range from a walk through inspection of facilities and equipment noting deficiencies for later correction up to computers that actually shut down equipment after a certain number of hours or a certain number of units produced, etc.

Many reasons exist for establishing a PM program. Listed below are a few of these. Whenever any of these reasons are present, a PM program is likely needed.

Reasons for Preventive Maintenance

• Increased Automation
• Business loss due to production delays
• Reduction of insurance inventories
• Production of a higher quality product
• Just-in-time manufacturing
• Reduction in equipment redundancies
• Cell dependencies
• Minimize energy consumption (5% less)
• Need for a more organized, planned environment

Why Have a PM Program

• The most important reason for a PM program is reduced costs as seen in these many ways:
• Reduced production downtime, resulting in fewer machine breakdowns.
• Better conservation of assets and increased life expectancy of assets, thereby eliminating premature replacement of machinery and equipment.
• Reduced overtime costs and more economical use of maintenance workers due to working on a scheduled basis instead of a crash basis to repair breakdowns.
• Timely, routine repairs circumvent fewer large-scale repairs.
• Reduced cost of repairs by reducing secondary failures. When parts fail in service, they usually damage other parts.
• Reduced product rejects, rework, and scrap due to better overall equipment condition.
• Identification of equipment with excessive maintenance costs, indicating the need for corrective maintenance, operator training, or replacement of obsolete equipment.
• Improved safety and quality conditions.

If it cannot be shown that a preventive maintenance program will reduce costs, there is probably no good reason other than safety to have a PM program.

The Law of PM Programs:
There are many advantages for having a good preventive maintenance program. The advantages apply to every kind and size of plant. The law of PM programs is that the higher the value of plant assets and equipment per square foot of plant, the greater will be the return on a PM program. For instance, downtime in an automobile plant assembly line at one time cost $10,000 per minute. Relating this to lost production time an automobile manufacturer reported that the establishment of a PM program in their 16 assembly plants reduced downtime from 300 hours per year to 25 hours per year. With results such as this no well-managed plant can afford not to develop a PM program.

Preventive Maintenance Program Risks
As mentioned in the beginning of this report, preventive maintenance does involve risk. The risk here refers to the potential for creating defects of various types while performing the PM task. In other words, human errors committed during the PM task and infant mortality of newly installed components eventually lead to additional failures of the equipment on which the PM was performed. Frequently, these failures occur very soon after the PM is performed. Typically, the following errors or damage occur during PM’s and other types of maintenance outages.

• Damage to an adjacent equipment during a PM task.
• Damage to the equipment receiving the PM task to include such things as:
• Damage during the performance of an inspection, repair, adjustment, or installation of a replacement part.
• Installing material that is defective, incorrectly installing a replacement part, or incorrectly reassembling material.
• Reintroducing infant mortality by installing new parts or materials.
• Damage due to an error in reinstalling equipment into its original location.

Especially disturbing about these types of errors is the fact that they go unnoticed – until they cause an unplanned shutdown. There is some published data that illustrates this point. It comes from the fossil-fuel power industry.

A review of the data from fossil-fueled power plants that examined the frequency and duration of forced outages after a planned or forced maintenance outage reinforces this concept. That data showed that of 3146 maintenance outages, 1772 of them occurred in less than one week after a maintenance outage. Clearly, this is pretty strong evidence that suggests that in 56% of the cases, unplanned maintenance outages were caused by errors committed during a recent maintenance outage.

Having performed and supervised many industrial PM’s, I also support this concept. I can remember many instances where it would take days after a PM was performed to get everything back to normal. This was particularly true when many components that came in contact with the product being produced were replaced. I remember working with the quality people on many occasions to insure that every position on a multiple position machine was once again producing first quality product. Many times it required adjusting and/or replacing components that were adjusted or replaced on the PM.

How to Have a Successful PM Program
The key to a successful Preventive Maintenance (PM) program is scheduling and execution. Scheduling should be automated to the maximum extent possible. Priority should be given to preventive maintenance and a very aggressive program to monitor the schedule and ensure that the work is completed according to schedule should be in place.

Preventive Maintenance Execution:
Traditional preventive maintenance was based on the concept of the bathtub curve. That is, new parts went through three stages, an infant mortality stage, a fairly long run stage, and a wear-out stage. The PM concept was to replace these parts before they entered the wear-out phase. Unfortunately, Reliability Centered Maintenance based on research done by United Airlines and the rest of the aircraft industry showed that very few non-structural components exhibit bathtub curve characteristics. Their research showed that only about 11% of all components exhibit wear-out characteristics, but 72% of components do exhibit infant mortality characteristics. These same characteristics have been shown to apply in Department of Defense systems as well as power plant systems. It is very likely that they apply universally as well. Therefore, they should be taken into account when configuring preventive maintenance on industrial equipment.

In order to have a successful PM program, the message is clear. The PM should focus on cleaning, lubrication, and correcting deficiencies found through testing and inspections. When there is a need to adjust or replace components, it should be done by highly trained and motivated professionals. Predetermined parts replacement should be minimal and done only where statistical evidence clearly indicates wear-out characteristics. In the absence of data to support component replacement, an age exploration program or the collection of data for statistical analysis to determine when to replace components should be initiated. Borrowing from the Japanese, lubrication points should be clearly marked with bright red circles to ensure that lubrication tasks are not missed. Cleaning should be carried our to remove dust, dirt, and grime because these things mask defects that can cause unplanned maintenance outages.

Motivating Preventive Maintenance Workers:
A quality preventive maintenance program requires a highly motivated preventive maintenance crew. To provide proper motivation, the following activities are suggested:

• Establish inspection and preventive maintenance as a recognized, important part of the overall maintenance program.
• Assign competent, responsible people to the preventive maintenance program.
• Follow-up to assure quality performance and to show everyone that management does care.
• Provide training in precision maintenance practices and training in the right techniques and procedures for preventive maintenance on specific equipment.
• Set high standards.
• Publicize reduced costs with improved up-time and revenues, which are the result of effective preventive maintenance.

In addition to explaining the importance of a good preventive maintenance program and the benefits that can be derived from it, training is probably the most effective motivational tool available to the maintenance supervisor. Maintenance and training professionals have estimated that a company should spend $1200 per year for training of supervisors and $1000 per year for each craftsperson. In fact, due to advances in technology, if the company has not provided any training for craftspeople in the past 18 months, their skills have become dated.

Conclusion
It is possible to have a successful preventive maintenance program. From a cost reduction viewpoint it is essential, but it does entail risk. When the proper care is taken, the risks, however, can be minimized. In order to minimize risk, preventive maintenance has to be carefully planned and carried out by well-trained and motivated workers. The biggest benefits of a PM program occur through painting, lubrication, cleaning and adjusting, and minor component replacement to extend the life of equipment and facilities.

Preventive Maintenance: Replacing Incandescent Lamps with LEDS

Currently, there is interest in high efficiency, long-life, light emitting diode (LED) lamps for use in factories, institutional, and commercial applications, because the costs of electricity for lighting and labor for bulb replacement are significant. The goal of the LED manufacturers is to build a very high-brightness white LED that is economical and efficient enough to be used for illumination. To gain widespread acceptance as a legitimate light source for general lighting, LEDs must be able to economically and reliably deliver illumination levels of white light of a quality within today's acceptable standards.

Theory of operation

An LED is a PN junction semiconductor that emits photons when forward biased. The emission of light occurs when minority carriers recombine with carriers of the opposite type in the band gap of the diode. The wavelength of the emitted light — which determines its color — varies according to the semiconductor material.

LEDs are processed in wafer form similar to silicon integrated circuits, and broken out into dice. The simplest packaged LED is the indicator lamp. Typically, LEDs have a mean time between failures (MTBF) of more than 100,000 hr.

Today's ultrabright LEDs exceed the light output of incandescent and halogen lamps. They don't have the maintenance requirements associated with filament lamps. LEDs can be dimmed using a pulse-width modulation (PWM) circuit, which delivers energy in pulses of varying duty cycle.

History of LEDs

The first reports of a device with properties similar to LEDs dates back to 1906 when Henry Round reported electroluminescence while experimenting with carborundum. However, LEDs didn't become commercially available until the early 1960s. Texas Instruments sold an infrared (IR) device for $130 and GE distributed red LEDs through the Allied Radio catalog for $260. They were expensive and sold in low volumes.

IBM used LEDs as on-off indicator lights on circuit boards in a mainframe computer constructed around 1964, which marks the first time LEDs were used to replace incandescent lamps. LEDs used less power, could be mounted directly on the circuit board, and had a much longer life expectancy, which made using LEDs attractive from a maintenance perspective.

In the mid 1980s, the U.S. military began gradually replacing tungsten filament indicators with LEDs, and they began appearing in elevator cars. As with the IBM application, LEDs were designed into pieces of equipment. They were mounted on printed circuit boards (PCBs), mounted in equipment panels and face plates using specific mounting bezels with wires soldered to their leads, and plugged into sockets made specifically for LEDs.

LED performance made a leap in the early 2000s. Companies started manufacturing flashlights using LEDs instead of the traditional incandescent bulb. As improvements were made in brightness and color, LEDs moved farther into tungsten territory. They appeared in traffic signals, home entertainment, and decorative lighting.

Today, LEDs are used in many industries from automotive to architectural lighting applications. Industrial plants are discovering the benefits of replacing traditional bulbs with LED lamps. For example, hundreds of incandescent lamp part numbers now have direct LED-based replacements. Most LED suppliers have extensive cross-reference literature and databases. Standard lamp bases are available, allowing LED lamps to replace incandescent lamps without having to retrofit equipment.

Flashlights continue to get brighter. Some currently available flashlights suitable for industrial use boast as much as 1800 foot-candles (fc) of white light. LED floodlights, work lights, and luminaires for general-purpose lighting applications are available as well.

Benefits

LEDs have enjoyed continued success because they use considerably less power and last much longer than tungsten filament incandescent bulbs. LED lamps use only 10% to 20% of the energy consumed by equivalent incandescent lamps. An average LED life span can exceed 100,000 hr — more than 11 yr.

LEDs are solid-state devices, which make them virtually immune to electrical and mechanical shock — unlike incandescent lamps, which have filaments that are very susceptible to electrical and mechanical shock. Electrical shock comes from constant on-off transitions, transients, and surges; mechanical shock comes from bumping, jarring, and other forms of vibration. Also, LEDs produce very little heat, making them an attractive alternative to incandescent lamps in applications where heat is an issue, such as biotechnology, chemical, and food processing.

Issues

LEDs had to overcome physical and technological issues to get where they are today. The primary hurdles have been drive current, packaging, color, and price. Although these issues have been addressed, they still exist to some degree. Drive current directly affects LED lamp output and lamp life. LEDs are inherently robust. They are capable of delivering high output at high current, as long as heat is extracted properly.

Packaging issues include thermal management, current handling capability, and color. Advanced device packaging allows adequate heat dissipation and increased current capacity. Packaging also affects color, which is extremely important in applications that require white light. Use of LEDs as illumination sources requires white light with a degree of "warmth." This requirement must be met if LEDs are to make any headway in replacing incandescent lamps for general-purpose illumination. Fluorescent lighting addressed this issue. And it appears that LEDs are rising to meet the challenge as well.

The cost-effectiveness of LEDs depends on the application. Today, the system price is high for replacing conventional incandescent lamps with LED-based technology. However, for established LED applications, such as control panel indicators and annunciator lamps, LEDs are more cost effective. Although the unit price is higher, the lower power consumption and longer lamp life help offset the initial purchase price. Some plants can justify the higher cost of LEDs for this application based on lower maintenance costs alone.

Source: Plant Engineering Magazine - January 1, 2005

Preventive and Predictive Maintenance

by Ken Staller, Senior Maintenance Consultant

If you ask ten people what their definition of Preventive Maintenance is, you will get ten different answers. The tasks range from very simple to fairly complex. What's more, the manner in which they are performed and the depths to which they are carried out vary considerably. For the purpose of this guide to Preventive Maintenance (PM) and Predictive Maintenance (PDM), I will use the following definition: PM and PDM are a series of tasks and company policies that, if followed, improve and keep business profits as high as possible. This is achieved by adhering to three general guidelines.

• Maintain the production equipment and plant utility systems equipment as close to brand new condition as possible and have all equipment ready to start up and run with no unplanned shutdowns.
• Maintain the production equipment and plant utility systems equipment in the best possible operating condition for the purpose of producing quality manufactured goods while the machines are in service.
• Complete all PM and PDM work on a regularly scheduled basis without exceeding the "Point of Diminishing Returns on Investment" for the labor, tools and materials required to perform the work.

The difference between Preventive and Predictive Maintenance is that Preventive Maintenance tasks are completed when the machines are shut down and Predictive Maintenance activities are carried out as the machines are running in their normal production modes.

With PM and PDM systems – as in all systems and processes of work – there are the Who, What, When, Where and Why questions to answer before any actual work begins. With the above three guidelines we have already defined the "Why" question.

The "Who" question relates to several different types of members of the PM and PDM team.

• Someone who has an abundance of maintenance and plant engineering experience should write the individual tasks. To receive the expected results from the investments made in the PM and PDM protocol, the person writing the details of what needs to be done must have a deep understanding of the many aspects of machines. Aging, wear, component material fatigue patterns, effects of dirt and other contaminants, heat/cold, humidity, effects of chemical contact, vibration, lubrication practices, measurement processes, maximum safety methods, work efficiency standards, work scheduling, people skills, and plant processes are all factors that must be carefully considered.
• The mechanics and electricians that perform the PM and PDM work must be of high caliber and possess the skill levels of a maintenance department. On average, 85% to 90% of PM and PDM work orders call for machine inspection work and only 10% to15% lubrication work. The people performing these tasks must fully understand machine and machine component operations before they can effectively inspect for specific problems and negative operating trends.
• The management person directly responsible for the people performing the PM and PDM work must understand the work to be accomplished and set the performance standards, goals and expectations. They must be able to monitor the quality and quantity of work completed as well as measure the results. Also, they should be able to make on going changes and improvements to the individual PM tasks as part of an overall continuous improvement effort. These changes are dictated by the results of measurements and changes in the plant processes and equipment. Finally, the management person should also be able to complete component failure analyses. Determining why and how a component failed is the first step in determining how to prevent subsequent failure.
• The plant upper management must view the PM and PDM work system as required constant work practices that are just as important to the production process as any other function. This will require a minimal planned downtime of equipment to accomplish all PM and PDM work.
• Production employees also are a significant part of PM systems. They can be, and many times are, the first to see changes in the equipment they operate. Total Productive Maintenance (TPM) represents the active participation of all production employees in various machine set-ups, inspections and, in some cases, the lubrications of machinery. The amount of participation in TPM varies with the complexity of the equipment, the types of processes involved and the overall skill levels of the work force. Training the work force and the setting its expectations varies with the philosophies of the plant management of each facility.
• Contractors should be included in some PM work, especially the PDM work involved. Many contractors can supply cost effective services in some of the more specialized inspections and tests required. For example, many plants do not have trained refrigeration mechanics and they hire contractors to do the scheduled PM on Heating Ventilation and Air Conditioning (HVAC) units for the plant systems. Other contractor applications may be for air compressor and air dryer PM. In addition, vibration and ultra sonic analyzing is highly specialized aspect of PDM and requires extensive training and high test equipment purchase and upkeep costs.

The "What" and "Where" of PM consists of what equipment is to be inspected and lubricated and to what extent and detail the work is to be performed. Typically detailed PM and PDM procedures are written for all production equipment to insure that all machine components are inspected and lubed for maximum sustained operation. This process should also be applied to other plant equipment systems, such as machines that supply the plant utilities including air compressors, air dryers, boilers, electrical sub-stations, motor control centers, and wastewater treatment. Plant safety systems also should be included, including natural and propane gas systems, tanks, fire alarms and suppression systems, emergency lighting, overhead cranes and hoists, and ceiling mounted items such as lights, fans, and piping. Many plants also choose to include PM work on HVAC systems, overhead door and dock plates, forklifts, company vehicles, truck fleets, roof leak detection, air emissions and other systems usually not considered until there is a problem.

The detail and extent of the PM and PDM work varies with the type of equipment involved. The written PM procedure is the document that tell workers what needs to be done. This document needs to contain all of the tasks that will provide the most thorough inspections and lubrications of machines in planned down time, without exceeding the point of diminishing ROI. Generally, the PM inspections of most machines are one of two types. The first is for any thing that moves or causes some other machine part to move. This needs to be inspected for damage, wear, loose and missing fasteners, etc., and proper lubrications performed. The second is the inspection of static, non-moving machine components such as wiring, plumbing lines and hoses, structural support members, etc., for damage, cracked welds, loose and missing fasteners, etc. These procedures may be lengthy or simple, depending on the type of machines involved. The main concern is that the person writing the procedures is very experienced in plant maintenance and plant engineering. This person must understand and be experienced in all phases of static and dynamic machine principals and actual machine degradation analysis.

"When" PM should be performed depends on several factors. Some machines are simple in design and function and some are not. Typically, there are items to be inspected and lubricated on a daily basis. Other inspections and lubes are progressively more detailed and regularly performed on a bi-weekly, monthly, quarterly, semi-annual and/or annual basis, depending on what is required.

In addition to the machine design and basic function, several other factors help in determining the best time interval between PM tasks. One is the amount of time the machine runs between regularly scheduled shutdowns and/or how much time is available for PM. Does the machine run 24 hours per day, seven days per week, or eight hours per day five days per week? Another factor is the environment in which the machine runs. Is it humid and damp, or extremely hot and dry? Does the machine receive shock loads or run with moderate to high vibration levels? Is the machine subject to chemical spillage or leakage, ultra violet light, etc? Good operating and cleaning practices, or the lack of them, have a significant impact on PM scheduling. In addition, planned shutdowns for plant expansions, machine rebuilds, inventories, vacations, etc., also dictate when some of the more involved PM work can be accomplished.

Predictive Maintenance 101

Most of the above information relates to Preventive Maintenance procedures that are completed on machines while shut down. There are other tasks that are considered Predictive Maintenance (PDM) practices. One of these, usually done while the equipment is shut down, is oil sampling and analysis. Oil samples are taken and sent out to laboratories that specializing in analyzing industrial oils. The cost is relatively inexpensive and provides much valuable information. This process identifies the lubricating ability of the oil; its stability; contents of water, wear metal particles, and dirt; among other aspects.

Another extremely important PDM procedure is vibration analysis. Using a portable vibration analyzer, readings are taken from many points on machines. These readings are direct and extremely accurate measurements of the vibration amounts and frequencies produced by the moving parts of the machine. These vibration amounts and frequencies are used to tell if any parts need replacing or adjustment, and exactly what internal parts are causing problems. Bad bearings, excessively worn gears, and poor coupling alignment can cause excessive vibration, weakened mounting fasteners and many other mechanical problems. Vibration analysis also can tell you if pumps have loose impellers, air cavitation, faulty valves, or mounting problems. In addition, it reveals trending information. When vibration readings are taken, they provide a base number to use as a gauge to determine if and how much internal machine changes are taking place between inspections. This is the very best tool for detecting the correct health of machines and for trending the internal activities inside motors, gearboxes, pumps, large fans, compressors, and many other machine components. There is no better way to detect machine problems before they cause an unplanned shutdown due to a component failure. What's more, the fact that vibration analysis is done while the machines are running in their production modes allows the testing to be done at any time and is especially important for any plant that runs 24 hours per day, seven days per week.

A Comprehensive View of Preventive & Predictive Maintenance

There are many aspects of maintenance and other plant functions that have an effect on the number of machine breakdowns and the length of downtime. Some of these considerations are not normally associated with the term Preventive Maintenance, but nonetheless contribute to equipment failure. Therefore, they should be considered as a part of comprehensive approach to Preventive & Predictive Maintenance.

• Proper start-up protocols. Start-up operations; changeover and set-up; and shutdown procedures should be carefully planned and consistently implemented on all machines.
• Procedures lists for unplanned shutdowns. Outline what is to be done when an unplanned power outage occurs and what to do before the power comes back on.
• Emergency management plans for floods, fire, etc.
• Machine component rebuild programs to insure quality and consistency.
• Machine cleaning practices and procedures.
• Available informational equipment manuals for maintenance personnel.
• Solid troubleshooting skills by all maintenance personnel

The above information provides an outline of a comprehensive PM and PDM system. This approach is unassuming and leaves little, if nothing, to chance. While there are many variables to take into consideration, if properly designed, instituted and operated, the PM and PDM system will help to ensure dependable and predictable performance from all serviced equipment, machines, and related processes.