RCM Analysis - Criticality Assessment (Step 2)

This aspect of the RCM analysis relates to question five of the seven RCM questions: In what way does each failure matter? This relates to the criticality of the failure mode in the no-maintenance scenario.
The Criticality Assessment is done through entry of the PROBABILITY and CONSEQUENCE of failure, in the second guided step – the Criticality Assessment:

Consequence

Registration of the probability and consequence of failure is done through the Criticality Assessment Matrix, which has a high granularity for the consequences:

Economic

Economic consequence can be entered with a Direct entry, or a Simple entry, or a Detailed entry:

For the Actuator Failure of the valve 1PC01the Failure Effects example the Production losses is 8 hrs 75%: 

Health & Safety 

Health & Safety consequence can be entered with a Direct entry, or a Simple entry, or a Detailed entry:

Environmental 

There is only one Environment consequence screen with a Direct entry:

Direct Entry

A direct entry can also be realized by clicking in the consequence boxes as shown below. If there is no consequence for that category you can select ‘Nothing’ or click the tick-box below:

Recommendation

We recommend for the RCM analysis to apply the following levels of detail:

It is recommended to align the Health & Safety and Economical consequences already in the ToR document of the RCM study, so that there is consistency around aspects like flaring, product leakages and toxic substances – for the various Equipment and Failure Modes involved.

Probability - ETBF 

The probability is specified in the ETBF (Estimated Time Between Failures) and can be entered directly as digits – in years.

It is also possible to click one of the boxes: < 0.5 y /  0.5 - 4.0 y / 4.0 - 20 y / > 20 y. In this case the value "0.5" / "4" / "20" / "25" years will be entered as the ETBF value. It is however recommended to enter a numeric value for the ETBF.

Final Criticality

For the Actuator Failure of the valve 1PC01the Failure Effects example the following consequences where entered: Production losses: 8 hrs 75%, Environment: No and Health & Safety: No. The ETBF of the actuator failure was set to 9 years. With all data provided, the criticality becomes N (negligible):

When done, click Next.

Instruction video

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

Background on the Criticality Matrix:

Using direct entries on the consequence categories drives the 'Price of Non-Conformance' based on the average values of the category boundaries. 

The values of the category boundries are: 10⁵,  10⁶,  10⁷ and 10⁸.  So, for the ‘Low' catagory the value of a direct entry is the average of 10⁵ and 10⁶, being 10^6.5 or 316 k$. 

This is a similar approach for the other ‘middle ranges’. 

But for the ‘Negligible scale’ it is a problem, because the ‘start of the scale’ resembles 0 – which is actually 10^-999 (though: actually a logarithmic scale cannot start with 0 at all - of course…)   

So: what is the average of that scale? In light that the ‘start of the scale’ is 0 it seemed high to put the average on 31.6 k$ – so instead it was set to 10k$.  

A similar aspect might occur in the ‘Extreme’ consequence scale, which however is less used, so less of an issue.