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Preventive Maintenance

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Presentation on theme: "Preventive Maintenance"— Presentation transcript:

1 Preventive Maintenance
Buddhika Lewangama Marriott School November 2006

2 Agenda Definition of Preventive Maintenance (PM)
Reasons for the increased need of PM Advantages of a PM system Risks of running a PM system When to use a PM system The law of PM Guide to a successful PM system Execution process Conclusion Readings

3 What is Preventive Maintenance?
Preventive maintenance is a schedule of planned maintenance actions aimed at the prevention of breakdowns and failures. The primary goal of preventive maintenance is to prevent the failure of equipment before it actually occurs. It is designed to preserve and enhance equipment reliability by replacing worn components before they actually fail. Preventive maintenance activities include equipment checks, 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. 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. If the automobile is not maintained properly, it might break down at an unexpected time. Likewise, when the machinery in a firm breaks down unexpectedly, it could result in lost business and halts in production which could be very costly.

4 Reasons for the need of a PM system
Increased Automation Business loss due to production delays Production of a higher quality product Just-in-time manufacturing Need for a more organized, planned environment Increased automation of production facilities has caused a higher need for a PM system for a successful and continuous flow of activities. A halt in the process would cause business losses due to production delays. Since production delays will have an adverse effect on Just In Time (JIT) manufacturing, the need for a PM will be vital in such an environment.

5 Advantages of a PM system
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. Timely, routine repairs circumvent fewer large-scale repairs. 1.Reduced production downtime will be the result of proper maintenance of the equipment. 2.Conservation of assets -When equipment is properly maintained it would increase and maintain the life expectancy of a certain asset. This concept can be understood through the simple example of a automobile maintenance. When a car is maintained properly it would run smoothly, if not it would start causing problems half way through of its life cycle. 3.Timely routine repairs - One other argument for a PM system is that, routine checks and repairs would be less expensive than large scale repairs which would require intensive repairs causing longer system break-downs.

6 Continued - Reduced cost of repairs by reducing secondary failures. When parts fail in service, they usually damage other parts. Better quality products Identification of equipment with excessive maintenance costs Improved safety and quality conditions. 4.Better Quality Products - Reduced product rejects, rework, and scrap due to better overall equipment condition. 5. Identification of equipment with excessive maintenance costs - This would indicate the need for corrective maintenance (maintenance technique which takes a reactive approach), comprehensive operator training, or replacement of obsolete equipment.

7 Brainstorming Exercise
Are there any risks of running a PM system? Let the trainees name some of the risks involved in running a PM system. Let them brainstorm for a minute and try to get different and out of the box answers. Once the trainees name some of the risks make them weigh the risks with the advantages and let them name some situations where a PM system would be advantageous for a firm. This slide is specifically for the interaction with the trainees, therefore give them time to come up with creative ideas. If there are risks when would it be a good time to use PM?

8 Potential errors or damage of a PM system
Damage to an adjacent equipment during a PM task. Reintroducing infant mortality by installing new parts or materials. Damage due to an error in reinstalling equipment into its original location. One potential risk of PM would be the damage that might occur to the adjacent equipment that is around the equipment that is being maintained. These kind of errors might occur due to accidents such as oil leaks, re-connection errors and etc. Every time new parts are being installed, the equipment goes through the infant stage where it will either fail or succeed. This uncertainty of the new part of working properly is referred to as the infant morality. Since, reintroduction of a new part reintroduces infant morality to that particular equipment, it is considered as a potential risk of PM. A lot of the errors that occur due to PM, occur as a result of errors in reinstalling equipment into its original location. To emphasize this point, you can the ask the trainees of situation where they had taken something apart and wasn’t able to put it back to its original form.

9 A real life example of a PM error
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 our point. The data collected from those plants 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. Get more examples from the trainees where they had been involved in such situations. Then prepare them for the next slide by posing the question “when would it make sense to implement PM?”

10 When Does Preventive Maintenance Make Sense
This is a logical choice that considers two conditions #1. The component in question has an increasing failure rate. #2. The overall cost of the preventive maintenance action must be less than the overall cost of a corrective action. If both of these conditions are met PM would make sense PM should be implemented when and only the equipment or component under consideration has an increasing failure rate which means the failure rate should increase with time, implying wear out. PM of a component that has a constant rate of failure would not be sensible because such components could be replaced without the implementation of a PM system. We can just replace such components just by monitoring the duration of use since it has a constant failure rate. 2. In the overall cost for a corrective action, one should include ancillary tangible and/or intangible costs, such as downtime costs, loss of production costs, lawsuits over the failure of a safety-critical item, loss of goodwill, etc.

11 The Law of PM Higher the value of the plant assets and equipment per square foot of plant, the greater will be the return on a PM program. E.g. - 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. Now that you have discussed when to use a PM program it is important to talk about the law of PM. However, keep in mind that no matter how big the value of the assets would be, in order for the PM to be successful you need to fulfill the two conditions mentioned earlier. It is important to remind the trainees about those two points because those two points basically decide whether or not to implement a PM program.

12 How to determine the optimum age of replacement?
The above diagram shows the Cost Per Unit Time vs. Time plot. In this figure, it can be seen that the corrective replacement costs increase as the replacement interval increases. In other words, the less often you perform a PM action, the higher your corrective costs will be. Obviously, the longer we let a component operate, its failure rate increases to a point that it is more likely to fail, thus requiring more corrective actions. The opposite is true for the preventive replacement costs. The longer you wait to perform a PM, the less the costs; while if you do PM too often, the higher the costs. If we combine both costs, we can see that there is an optimum point that minimizes the costs. In other words, one must strike a balance between the risk (costs) associated with a failure while maximizing the time between PM actions Source : Reliasoft corporation.

13 How to determine the optimum age of replacement?
A more technical approach. Where: R(t) = reliability at time t. CP = cost of planned replacement. CU = cost of unplanned replacement CPUT(t) = The optimum replacement time The optimum replacement time can be found by minimizing the cost per unit time, CPUT(t). By solving for ‘t’ on the above equation we can find the optimum replacement time interval.

14 The key for a successful PM system
Scheduling – Should be automated to the maximum extent possible Execution – Should be done before the actual break down occurs. 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. If the scheduling of PM isn’t sort out properly it could cost the firm a great deal in lost sales plus an inefficient PM program. Therefore, through automation we can make sure proper maintenance takes place in due time. Execution – Without proper execution, the PM program will not provide the desired results which would result in the same consequences as a failure in scheduling. This will be discussed in detail in the next slides.

15 Execution The Bath Tub Model – Three stages of new parts
Infant morality stage A fairly long run stage Wear out stage Traditional View according to Bath Tub Model – Replace components just before they entered wear out stage Reliability specialists often describe the lifetime of a population of products using a graphical representation called the bathtub curve. The bathtub curve consists of three periods: an infant mortality period with a decreasing failure rate followed by a normal life period (also known as "useful life") with a low, relatively constant failure rate and concluding with a wear-out period that exhibits an increasing failure rate.

16 Execution Traditional view says –
Wear out stage = Increased rate of failure. Point to Ponder – Since, wear out stage represents increased rate of failure, wouldn’t it be plausible to execute the PM program at this stage? Earlier we discussed of the two conditions for considering a PM system one of which was to have a increasing rate of failure. So would it be practical to use a PM system every time a component has an increasing rate of failure? Give the trainees some time to think over. This is not a theoretical question but a practical implication of PM. Theoretically, every time there is an increasing rate of failure it would be best to use PM. But would it be so practically?

17 Execution United Airlines Research
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. If we just decide to take a traditional approach to PM, it would be advisable to use PM during wear out stage but according to the research results presented in the slide it seems like failure could occur at point of an equipments life cycle. So the next question would be, what can be done to overcome and ensure a good PM system?

18 What really should PM focus on?
Cleaning Found through testing Lubrication and inspection And correcting deficiencies In order for a successful PM system, the system should focus mainly on cleaning, lubrication and correcting deficiencies that are found through testing and inspecting the equipment. Without proper testing and inspection, it would not be possible to decide whether to implement a PM program or when to implement it. For cost reduction purposes and efficiency of the program, it’s vital to keep the predetermined part replacement to a minimal and done only where statistical evidence clearly points out wear-out characteristics. If the components are not yet in a wear-out stage its best to continue with a PM system to extract the maximum life from it given that the component has an increasing failure rate and the cost of PM is less than corrective control. Predetermined parts replacement should be minimal and done only where statistical evidence clearly indicates wear-out characteristics

19 In the absence of data Age exploration programs Statistical analysis
Cost shouldn’t be a primary factor in deciding against data collection for a PM Age exploration programs – When prior data is absent to make the decision on PM, a firm should engage in age exploration programs to determine life expectancy, find out critical times in component life cycle, comparisons with similar products to identify problem points of the component. Statistical Analysis – Is the use of statistical methods to decide when to implement a PM system. This requires the action of an age exploration to collect the data that is needed to come with the analysis. When prior data is absent, implementing a PM system would be more costly because of the money that needs to be spent on information collection. However, if a company decides not to implement PM just because of the extra cost, it is very likely that they would incur more costs as a result of sudden system breakdowns.

20 Motivating Preventive Maintenance Workers
Training programs – most effective Establish inspection and preventive maintenance as a recognized, important part of the overall maintenance program. Assign competent, responsible people to the preventive maintenance program. Ask your trainees of some of the motivational elements that could be implemented to ensure that the PM program is being valued by employees. Then discuss the importance of each of these motivational factors and how they apply to your firm. Emphasis the importance of a motivated set of employees for a successful PM program.

21 Continued - 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 Continue with the same directions given for the previous slide

22 Summary PM is not difficult to achieve.
It is an essential part for cost reduction There is an element of risk involved in PM Careful planning and execution will reduce the risk of PM 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. Briefly tie these concepts together one last time

23 Readings John M Gross, “Fundementals of Preventive Maintenance”, American Management Association, Pg 228 Richard D Palmer, “Maintenance Planning and Scheduling Handbook”, ch1-pg.30 “Is Preventive Maintenance Necessary?”, 28 Nov.2006 < “The Reliability Hotwire, the eMagazine for the Reliability Professional”, Issue 21, Nov “Preventive Maintenance”, Reliasoft Coporation, 28 Nov 2006http:// "Core Competencies." QuickMBA. Internet Center for Management and Business      Administration, Inc. 18 Nov <      core-competencies/>.

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