for the case where no PM tasks are done at all -- that is the Run-To-Failure or RTF case
for the case where the world-class recommended PM tasks are performed, all at their recommended task frequencies (called the baseline case), and
for the custom case designed by the user, in which any of the recommended tasks can be deleted or have its task interval changed by the user.
Furthermore, the user can reset the baseline at any time, most often so that it represents his current PM program. In this mode he is comparing his current program with a proposed change to it.
Second, all the calculations are not only functions of the component type and the selected PM activities and their frequencies, but also are functions of the duty cycle and the in-service stressors that the user chooses to impose (-- see White paper
"Pro-M Failure Rate Methodology." NOTE: MIDAS is undergoing a name change to Pro-M for trademark reasons. We
apologize for the delay in updating all of our materials.)
Connecting Component Failure To Production Losses
The calculated failure rate is obviously at the heart of the cost estimates, but so is the information that connects the failure of the component to its impact on production. The link between loss of component function and its production impact is taken from the rapid checklist that the user fills out in order to assess and automatically document the functional criticality of the component. Examples of production impacts that he might select are: Production line or plant unavailable, Reduction in production rate between 66% and 100%, Reduction in production rate between 33% and 66%, Reduction in production rate between 10% and 33%, and Reduction in production rate less than 10%. When combined with plant settings that include parameters such as Maximum production rate in units/hour, Average production capacity factor, Cost of one lost unit of production, Ramp time to 100% production, and Cost of a maintenance man hour, these enable plant-level impacts to be estimated from component-level failures.
Elements Of Equipment Downtime
The equipment downtime when an in-service failure occurs is composed of several parts. The time taken to diagnose the problem, obtain tools, instructions, and replacement parts, and to initiate repair activities is referred to as the Planning Time. The time taken to tag the equipment out of service before repair work is initiated and to lift the tags after the repair work is completed is referred to as the Tag Out and Return To Service Time. Values for these two elements of the equipment downtime are suggested to the user. The hands-on time taken to repair the equipment (Wrench Time) depends on the specific failure mechanism by which the failure occurred. Consequently, an average value for this quantity is calculated by averaging over the specific wrench times for each failure mechanism in the component data table, weighting each with its likelihood of occurrence. These three elements of the downtime are each editable by the user to take account of his special circumstances. A fourth downtime element affects the production process but not the component itself. This is the time taken to restore production back to 100% after it has been reduced by the component failure. This is taken from a straight line estimate using the production impact of the failure and the ramp time to 100% production, described above.
Forced Outages Triggered By Predictive Maintenance
In addition to the forced outage impacts of in-service component failures, Pro-M also estimates a contribution that arises from the successes of predictive maintenance tasks wherein a monitoring activity such as oil sampling and analysis may give advanced warning of an impending failure. These successes of preventive maintenance will not be able to avoid taking a planned outage of the equipment to effect repairs. However, such a planned outage will be less expensive than a normal forced outage because it may be able to be taken at a time when there is no impact on production. Even if the event can not be prevented from causing a loss of production it will usually be less expensive than a true forced outage because planning and logistics elements (getting access, erecting scaffolding, obtaining spare parts etc) of the equipment downtime can usually be done before the equipment is taken out of service. Pro-M includes a rough estimate of these effects by inserting an estimated proportion of the failure rate that is due to the predictive tasks. This proportion has been evaluated by prior analysis and is contained within the Pro-M data.
Production Losses Caused By Performing PM Tasks
The user is presented with typical hours the component type is made unavailable in order to perform each PM task, as well as with the man hours needed to perform the task and the cost of replacement parts and materials required. The user can edit these values to take account of special circumstances, e.g. where access to the equipment requires lengthy preparation. In addition, if the user's enterprise system has accumulated statistics on these quantities, they can be downloaded to Pro-M for use in these calculations. The factor by which component unavailability influences production losses is taken from the criticality checklist, in the same way as is done for forced outages. In addition, most PM component unavailability that would otherwise affect production can normally be prevented from doing so by adequate planning and scheduling. The likelihood that this can be achieved successfully is a parameter controlled by the user, and he has quick recalculation capability to vary this parameter and draw conclusions on solutions that would be practical and achievable in his plant.
Direct Costs Of Maintenance
Man hours required for PM activities and related stores costs are taken from core data for each task, editable as described above. Similar values for forced outage repair are calculated using the wrench time and a man loading parameter, also editable by the user. Direct repair costs for forced outages and the "triggered" forced outages obviously also involve the calculated failure rate.
Calculated Costs
Costs are calculated for the following quantities with positive values representing costs:
Annual Direct Cost Of Maintenance
PM Man-Hours and Stores
Repair Man-Hours and Stores
Total Direct Cost To Maintenance
Annual Cost Of Lost Production
Production Loss Because Of PM
Production Loss Because Of Failures
Total Production Loss
Annual Total Cost = Total Direct Cost To Maintenance + Total Production Loss
The difference between each of these values for the baseline and custom calculations is also presented with positive values as savings:
Saving = Baseline Cost - Custom Cost
Return On Investment
Two values are presented for return on investment. The most often used is the ROI for the change proposed between the Baseline and Custom calculations:
ROI (for any PM changes) =
Change in (Total Direct Cost To Maintenance + Total Production Loss)
Change in (PM Man Hours and Stores Cost)
The ROI obtained by comparing the Custom case with Run-To-Failure shows the bottom line benefit of each dollar spent on the Custom PM program for the component as a whole:
ROI (Benefit Of This PM Program) =
Change in (Custom Annual Total Cost - RTF Annual Total Cost)
Change in (Custom PM Man Hours and Stores Cost)
