RCM Analysis - MEI Calculation (Step 5)

This aspect of the RCM analysis relates to question six (last part) of the seven RCM questions: What can be done to predict or prevent each failure? Note: This relates to the economics in terms of MEI and risk reduction (and residual risk).

This is the last of the 5 guides steps to verify if the suggested preventive maintenance tasks actually do drive value and reduce the probability of negative effects of the equipment failure.

There are two ways to determine if preventive maintenance is driving value:

1. Determine if the "Do-maintenance" situation is beneficial compared to the "No-maintenance" situation.
2. Determine if the risk reduction - driven by the preventive maintenance - has more value than the cost of the preventive maintenance. This last approach is the Maintenance Efficiency Index (MEI) calculation.

In both situations the same data is used, of which one element is the residual risk. The residual risk relates to the question: "With the preventive maintenance executed will there be no equipment failure at all - anymore?"
The probability that will be involved in case equipment failures do occur after all - is called Estimated Time Between Consequences (ETBC).

To visualize if the preventive maintenance strategy is beneficial (for the Actuator Failure on 1PC01 example) both the calculation methods are used:

In this RCM analysis we saw that the cost of failure was 23.64 k$ and the probability: 9 yrs, so the monetary annual value of the base risk (or annual PONC) is 2.63 k$/yr.

The maintenance package costs 3.64 k$ and was executed once every 8 years, driving to an annual cost (or POC) of: 0.45 k$/yr.

Would the "No-maintenance" situation of actuator failure causing production loss, never occur anymore? Perhaps after 3 repairs it may happen again: say once every 26 years. So the monetary annual value of the residual risk will than be 23.64 / 26 = 0.91 k$/yr.

A comparison of the "Do-maintenance" versus the "No-maintenance" situations gives us:

"Do-maintenance"= 0.45 + 0.91 = 1.36 k$/ yr versus "No-maintenance" = 2.63 k$/yr

We see the "Do-maintenance" situation is significantly lower than the "No-maintenance" situation, so it shows a good preventive maintenance plan!

In IMS–RCM we prefer to use the Maintenance Efficiency Index or MEI.
Calculating the MEI is done looking at the improvement in lowering the risk by the maintenance package:

(Base risk - Residual risk)/ Maintenance cost = (2.63-0.91)/0.45 = 3.78

In MEI calculations a maintenance strategy with an MEI above 1 is beneficial, though the more powerful maintenance strategies are found with MEI’s above 2. A MEI of 3.78 is therefore definitely beneficial!

Basically in the last step of the RCM analysis's 5 guided steps, you only need to enter the ETBC value.

Below it shows that in the Recommended Tasks section the financial aspects are shown (3.64 k$ POC and 0.45 k$ annual POC). Note: In this example there was just one task where multiple tasks can be involved with multiple costs incurred.

Next, in the MEI calculations section, the financial aspects of the criticality and tasks are already shown like Total annual POC (0.45 k$) and Total economic risk without maintenance (2.63 k$/yr).

Entering the ETBC value will drive the calculations of the other financial elements, like Total economic risk with maintenance’ (0.91 k$/yr) and Total annual cost with maintenance (1.36 k$/yr).

Also the residual risk is determined (N) and the MEI is calculated; when above the threshold (in the example the threshold is "1") the analysis is automatically Approved, see the tick box. 

When done, click Finish to complete the guided steps.

Note that when the maintenance task is flagged as IsMandatory that the analysis automatically Approved as well.

Low MEI Investigation

At the end of an RCM analysis, users might be confused if the MEI calculation is low or zero. The data fields shown below are than relevant:

Low MEI values typically originate from:

• The criticality in terms of Annual value ($k/yr) is low, note that one can spend about 1/3 of that value on maintenance (annual value).
  • In above example 1/3 of the criticality (2.63 $k/yr) is 0.88 $k/yr, where we actually spend 0.45 $k/yr, so looks promising. 
• The Annual Maintenance cost (POC) is high - or zero.
  • High Annual maintenance cost should be checked at the task data regarding task cost and frequency
  • Zero task cost causes zero MEI - often due to missing task data like no frequency/ interval.
• High Residual Risk Annual value - driven by Low ETBC. It is expected that the ETBC is quite larger than the ETBF.

MEI Threshold

Clients may wish to apply different levels of MEI to approve a RCM analysis. Where the basic approval is when MEI is 1 or above, experience has shown that MEI levels of 2 and above are the more robust RCM analysis. Some businesses have decided to even apply a MEI >5 for RCM approval.

In IMS RCM the MEI threshold can be set at Unit level and at Site level.
It can be configured in Settings \ Company \ Toplevel when a unit is selected in the site hierarchy tree. (See below for HDS Unit 100.)

If there is no configuration on the unit level the threshold of the Site will be used.
If there is a configuration on the unit level then this is indicated in the RCM analysis calculation area at the MEI Unit threshold, see below.
If there is no configuration on the site level a threshold of 1 will be used.
If there is a configuration on the site level then this is indicated in the RCM analysis calculation area at the MEI Site threshold.

There is functionality to track the progress of the analyses through a Status setting.

In case the MEI is below the threshold but there are strong reasons to still put the maintenance strategy in practice, you can "Manually approve" the analysis. There is a track list available to explain and a free text field for more background.

The MEI Calculation type is normally "Include Operator and Engineering costs". However, an option is provided where the MEI will is calculated differently. It will exclude the hours for Operator, Staff and Craftsmen on all tasks of the failure mode for the Price of Conformance in the MEI calculation.

One final aspect of the RCM analysis relates to question seven of the seven RCM questions: What should be done if a suitable proactive task cannot be found? Note: This relates to the situation when the residual risk is too high and additional actions are required.

preferably the residual risk should be on the "M" level or lower, so when the residual risk is "MH" or higher, additional actions are required, like for instance a redesign of the local asset situation with other Equipment involved. Such recommendations can be provided in the free text screen of the MEI calculation area, and should be echoed also in the end report of the RCM study.

When copying Analyses from another Tag

When an RCM Analysis is copied from one tag to another tag, an option to replace the Failure Mode and Task PLE with the PLE of the target System is offered. If checked, the MEI is calculated based on the PLE of the target System. If the option is left unchecked, the PLE from the original tag is used, and the MEI is calculated based on it.

Instruction videos

For more information on the execution of RCM analysis in Guides Steps see instruction video: RCM Analysis Guided Steps Episode 7 Video.