Preventive Maintenance, Third Edition

Joseph Patton, J.D. Patton, Jr.

• Publisher: International Society of Automation
• Year: 2016
• Print ISBN: 9781556178757
• eBook ISBN: 9781941546147
• Topic: Technology & Engineering
• Subtopic: Automation in Engineering
• Index: Technology & Engineering

This third edition of a best-selling classic shows how the investment in a preventive maintenance program repays a company in longer equipment life, smoother operation, planning, and scheduling. It includes information on computerized PM systems, enhanced techniques, and insights into preventive maintenance. The latest technology has improved equipment quality, reliability and dependability by fault-tolerance, redundant components, self-adjustments, and replacement of hydraulic and mechanical components by more reliable electronic and optical operations. Many components, however, still wear out, corrode, become punctured, vibrate excessively, become overheated by friction or dirt, or can even be damaged by humans. Fortunately, modern sensors and computers for condition monitoring and detection enable equipment to "call home" to report they need PM before they fail. The preventive maintenance advantage is that you will pay less now to do planned work when production is not pushing versus very expensive emergency repairs that may be required under disruptive conditions causing production to halt and loss of revenue. Good PM saves money over a product's life cycle. The book addresses major types of maintenance; advantages and disadvantages of PM; designing a PM program; economics of PM; nondestructive testing; scheduling; metrics; data issues; and much more. - See more at: https://www.isa.org/store/products/product-detail/?productId=116165#sthash.KmAbLW8z.dpuf

CHAPTER 1

Major Types of Maintenance

There are three main types of maintenance and three major divisions of preventive maintenance, as illustrated in Figure 1-1.

Figure 1-1

Structure of Maintenance.

IMPROVEMENT MAINTENANCE

Picture these divisions as the five fingers on your hand. Improvement maintenance efforts to reduce or eliminate entirely the need for maintenance are like the thumb, the first and most valuable digit. We are often so involved in maintaining that we forget to plan ahead and eliminate the need at its source. Reliability engineering efforts should emphasize elimination of failures that require maintenance. This is an opportunity to preact instead of react.

For example, many equipment failures occur at inboard bearings that are located in dark, dirty inaccessible locations. The oiler does not lubricate those bearings as often as he lubricates those that are easy to reach. That is a natural tendency. One can consider reducing the need for lubrication by using permanently lubricated, long-life bearings. If that is not practical, at least an automatic oiler could be installed. A major selling point of new automobiles is the elimination of ignition points that require replacement and adjustment, introduction of self-adjusting brake shoes and clutches, and extension of oil change intervals.

CORRECTIVE MAINTENANCE

The little finger in our analogy to a human hand represents corrective (emergency, repair, remedial, unscheduled). At present, most maintenance is corrective. Repairs will always be needed. Better improvement maintenance and preventive maintenance, however, can reduce the need for emergency corrections. A shaft that is obviously broken into pieces is relatively easy to maintain because little human decision is involved. Troubleshooting and diagnostic fault detection and isolation are major time consumers in maintenance. When the problem is obvious, it can usually be corrected easily. Intermittent failures and hidden defects are more time-consuming, but with diagnostics the causes can be isolated and then corrected. From a preventive maintenance perspective, the problems and causes that result in failures provide the targets for elimination by PM. The challenge is to detect incipient problems before they lead to total failures and to correct the defects at the lowest possible cost. That leads us to the middle three fingers–the branches of preventive maintenance.

PREVENTIVE MAINTENANCE

On-Condition

On-condition maintenance is done when the equipment needs it. Inspection through human senses or instrumentation is necessary, with thresholds established to indicate when potential problems start. Human decisions are required to establish those standards in advance so that inspection or automatic detection can determine when the threshold limit has been exceeded. Obviously, a relatively slow deterioration before failure is detectable by condition monitoring, whereas rapid, catastrophic modes of failure may not be detected. Great advances in electronics and sensor technology are being made.

Also needed is a change in human thought process. Inspection and monitoring should disassemble equipment only when a problem is detected. The following are general rules for on-condition maintenance:

— Inspect critical components.

— Regard safety as paramount.

— Repair defects.

— If it works, don’t fix it.

Condition Monitor

Statistics and probability theory are the basis for condition monitor maintenance. Trend detection through data analysis often rewards the analyst with insight into the causes of failure and preventive actions that will help avoid future failures. For example, stadium lights burn out within a narrow range of time. If 10 percent of the lights are burned out, it may be accurately assumed that the rest will fail soon and should, most effectively, be replaced as a group rather than individually.

Scheduled

Scheduled, fixed interval PM should generally be used only if there is an opportunity for reducing failure that cannot be detected in advance, or if dictated by production requirements. The distinction should be drawn between fixed interval maintenance and fixed interval inspection that may detect a threshold condition and initiate condition monitor PM. Examples of fixed interval PM include 3,000-mile oil changes, and 48,000-mile spark plug changes on a car, whether it needs the changes or not. This may be very wasteful since all equipment and their operating environments are not alike. What is right for one situation may not be right for another.

SUMMARY

The way we think about PM holds the opportunity for great improvement. Preventive maintenance can provide major benefits, if it is properly applied and if it truly prevents failures, reduced costs, and downtime, and improves uptime, productivity, and profits.

The five-finger approach to maintenance emphasizes elimination and reduction of maintenance need wherever possible, inspections and detection of pending failures before they happen, repair of defects, monitoring of performance conditions and failure causes, and accessing the equipment on a fixed interval basis only if no better means exist.

CHAPTER 2

Advantages and Disadvantages

On the balance, preventive maintenance (PM) has many advantages. It is beneficial, however, to overview the advantages and disadvantages so that the good may be improved and the negative reduced. Note that in most cases the advantages and disadvantages vary with the type of PM used. Use of on-condition or condition monitor techniques is usually better than fixed intervals.

ADVANTAGES

Management Control

Unlike repair maintenance, which must react to failures, PM can be planned ahead. This means “proactive” instead of “reactive” management. Work loads may be scheduled so that equipment is available for PM at reasonable times.

Overtime

Overtime can be reduced or eliminated. Surprises are reduced. Work can be performed when convenient.

Work Load

Work loads can be balanced to either spread the demand over the available resources, or to hire additional personnel and equipment to meet the demand.

Equipment Uptime

While PM may require an investment of as many maintenance hours as were required previously for corrective maintenance, equipment should certainly perform better and with much higher availability when it is needed. It is a truism that failures are rarely found until equipment is put to use. PM, done properly, will often detect failures that have occurred but that would not otherwise be found until that equipment is needed for a rush job.

Production

Naturally, production will be happy because downtime, shutdowns, scheduling, and personnel problems will be reduced. Access to equipment is often restricted to specific times dictated by production requirements. PM helps assure best possible use of revenue producing functions.

Standardization

The “one best way” to do PM tasks should be determined. Because of the repetitious nature of PM, the procedures may be improved upon and skills may be finely honed. Maximum learning should be established early if the same persons are consistently used to conduct PM. Like any task done frequently with proper guidance, PM can reach a high level of productivity. This also permits more accurate planning because the times will evolve into a relatively narrow target range. Costs, like most insurance policies, are predetermined within small limits.

Part Inventories

Since PM permits planning of which parts are going to be required and when, those material requirements may be anticipated to be sure they are on hand for the event. A smaller stock of parts is required to organizations that emphasize PM compared to the stocks necessary to cover breakdowns that would occur when PM is not emphasized.

Standby Equipment

With high demand for production and low equipment availability, reserve, standby equipment is often required in case of breakdowns. Some backup may still be required with PM, but the need and investment will certainly be reduced.

Safety and Pollution

If there are no PM inspections or built-in detection devices, equipment can deteriorate to a point where it is unsafe or may spew forth pollutants. Performance will generally follow a saw-tooth pattern, as shown in Figure 2-1, which does well after maintenance and then degrades until the failure is noticed and it is brought back up to a high level. A good detection system catches degrading performance before it ever reaches too low a level.

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Table of contents

• Cover
• Title Page
• Copyright
• Dedication
• Contents
• Preface and Acknowledgements
• Chapter 1. Major Types of Maintenance
• Chapter 2. Advantages and Disadvantages
• Chapter 3. Designing a PM Program
• Chapter 4. Economics of PM
• Chapter 5. Nondestructive Inspection
• Chapter 6. On-Condition Maintenance
• Chapter 7. Condition Monitoring Prediction
• Chapter 8. Scheduled Preventive Maintenance
• Chapter 9. Lubrication
• Chapter 10. Calibration
• Chapter 11. Data and Information
• Chapter 12. Planning and Estimating
• Chapter 13. Shutdown Planning
• Chapter 14. Scheduling
• Chapter 15. Computerized PM Systems
• Chapter 16. PM Metrics
• Chapter 17. Motivation
• Chapter 18. Implementing a New PM Program
• Chapter 19. Special Concerns
• True or False Questions
• Answers
• Selected Readings