Preventive Maintenance - Revision history

Lisa Hacker at 21:04, 18 September 2023

2023-09-18T21:04:41Z

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	<noinclude>{{Banner BlockSim Articles}}{{Navigation box}}		<noinclude>{{Banner BlockSim Articles}}{{Navigation box}}
	''This article~~, which discusses preventive maintenance in BlockSim,~~ also appears in the [~~[Introduction_to_Repairable_Systems#Preventive_Maintenance_2\|~~System ~~Analysis Reference]~~] ~~book~~.''		''This article also appears in the [https://help.reliasoft.com/reference/system_analysis System analysis reference].''
	</noinclude>		</noinclude>
	Preventive maintenance (PM) 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. Recent technological advances in tools for inspection and diagnosis have enabled even more accurate and effective equipment maintenance. The ideal preventive maintenance program would prevent all equipment failure before it occurs.		Preventive maintenance (PM) 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. Recent technological advances in tools for inspection and diagnosis have enabled even more accurate and effective equipment maintenance. The ideal preventive maintenance program would prevent all equipment failure before it occurs.

Sharon Honecker: /* The Fallacy of "Constant Failure Rate" and "Preventive Replacement" */

2017-02-08T21:17:37Z

The Fallacy of "Constant Failure Rate" and "Preventive Replacement"

← Older revision		Revision as of 21:17, 8 February 2017
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	'''Case 2''': The component's reliability from 50 to 60 hours:		'''Case 2''': The component's reliability from 50 to 60 hours:
	*With preventive maintenance, the component was replaced at 50 hours, so this is solely based on the reliability of the new component for a mission of 10 hours, or <math>R(t=10)=90.48%\,\!</math>.<br>		*With preventive maintenance, the component was replaced at 50 hours, so this is solely based on the reliability of the new component for a mission of 10 hours, or <math>R(t=10)=90.48%\,\!</math>.<br>
	*Without preventive maintenance, the reliability would be the conditional reliability of the same component operating to 60 hours, having already survived to 50 hours, or <math>{{R}_{C}}(T=~~60\|~~50)=R(60)/R(50)=90.48%\,\!</math>.		*Without preventive maintenance, the reliability would be the conditional reliability of the same component operating to 60 hours, having already survived to 50 hours, or <math>{{R}_{C}}(t=10\|T=50)=R(60)/R(50)=90.48%\,\!</math>.

	As can be seen, both cases — with and without preventive maintenance — yield the same results.		As can be seen, both cases — with and without preventive maintenance — yield the same results.

Richard House: /* Determining Preventive Replacement Time */

2015-12-22T22:11:34Z

Determining Preventive Replacement Time

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	The following figure shows the Cost Per Unit Time vs. Time plot and 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, as we let a component operate for longer times, 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; if you do PM too often, the costs increase. 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.		The following figure shows the Cost Per Unit Time vs. Time plot and 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, as we let a component operate for longer times, 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; if you do PM too often, the costs increase. 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.

	[[Image:costpertime.png\|center\|~~450px~~\|Cost curves for preventive and corrective replacement.]]		[[Image:costpertime.png\|center\|500px\|Cost curves for preventive and corrective replacement.\|link=]]

	===Optimum Age Replacement Policy===		===Optimum Age Replacement Policy===

Richard House: /* The Fallacy of "Constant Failure Rate" and "Preventive Replacement" */

2015-12-22T22:10:46Z

The Fallacy of "Constant Failure Rate" and "Preventive Replacement"

← Older revision		Revision as of 22:10, 22 December 2015
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	Even though we alluded to the fact in the last section, it is important to make it explicitly clear that if a component has a constant failure rate (i.e., defined by an exponential distribution), then preventive maintenance of the component will have no effect on the component's failure occurrences. To illustrate this, consider a component with an <math>MTTF\,\!</math> = <math>100\,\!</math> hours, or <math>\lambda =0.01\,\!</math>, and with preventive replacement every 50 hours. The reliability vs. time graph for this case is illustrated in the following figure, where the component is replaced every 50 hours, thereby resetting the component's reliability to one. At first glance, it may seem that the preventive maintenance action is actually maintaining the component at a higher reliability.		Even though we alluded to the fact in the last section, it is important to make it explicitly clear that if a component has a constant failure rate (i.e., defined by an exponential distribution), then preventive maintenance of the component will have no effect on the component's failure occurrences. To illustrate this, consider a component with an <math>MTTF\,\!</math> = <math>100\,\!</math> hours, or <math>\lambda =0.01\,\!</math>, and with preventive replacement every 50 hours. The reliability vs. time graph for this case is illustrated in the following figure, where the component is replaced every 50 hours, thereby resetting the component's reliability to one. At first glance, it may seem that the preventive maintenance action is actually maintaining the component at a higher reliability.

	[[Image:7i2.png\|center\|~~400px~~\|Reliability vs. time for a single component with an <math>MTTF =100\,\!</math> hours, or <math>\lambda =0.01\,\!</math>, and with preventive replacement every 50 hours.]]		[[Image:7i2.png\|center\|500px\|Reliability vs. time for a single component with an <math>MTTF =100\,\!</math> hours, or <math>\lambda =0.01\,\!</math>, and with preventive replacement every 50 hours.\|link=]]

	However, consider the following cases for a single component:		However, consider the following cases for a single component:

Harry Guo: /* Optimum Age Replacement Policy */

2013-11-27T22:41:39Z