Avoid This Common Mistake: Criticality And Risk Are Not The Same

I see a great deal of reference to Criticality or Criticality Ranking in the same breath as our Risk matrix or even used to represent Risk.

Let's talk about some of the important differences between Equipment Criticality, Equipment Risk and Failure Mechanism Risk.

First, some industry accepted definitions.

Equipment Criticality is a numerical or alphabetical representation of the consequence of failure of that piece of equipment in its current operating environment. It does not consider current or future probability of failure.

Criticality Ranking is the methodology to categorize equipment by importance of consequence of failure and to influence the Maintenance Strategy which in turn will be used to define the corresponding level of effort tools and techniques which will be used to define the resulting work processes and technologies that will be applied.

Criticality Ranking is performed by assessing consequence of failure of each piece of equipment typically in 5 key areas of business impact typically including, Staff and Public Safety, Regulatory and Environmental Compliance, Production, Operations and Maintenance Costs (O&M) and Product Quality.

Risk or equipment risk is a numerical or alphabetical representation of the consequence of failure of that piece of equipment, times the probability of failure of that piece of equipment in its current operating environment, including current failure mechanism controls.

Risk or equipment risk ranking is the methodology to categorize equipment by importance of consequence of failure times probability of failure (APM Risk Matrix) and to assign a current Risk Ranking to the equipment with its current controls. This is used to measure the current risk that a piece of equipment represents in a system, process or plant.

Failure Mechanism Risk is the risk (consequence times probability) that a specific failure mechanism (failure mode) represents to a specific piece of equipment in its current operating environment, including current failure mechanism controls.

Equipment criticality is one of the first steps that we need to undertake when looking at where we are going to spend time and effort regarding developing and implementing equipment specific strategies (including changing existing strategies). This step allows us to categorize equipment based upon consequence of failure and then apply different strategy tools based upon that consequence. These strategy tools include Reliability Centered Maintenance, Failure Modes and Effect Analysis, OEM suggested maintenance templates, industry or customer specific templates or even a run to failure strategy. 

The results of Criticality Ranking allows us to confidently apply the right level of effort around defining the right strategy for each specific piece of equipment with the goal of reducing the probability of failure and hence impacting the Risk a piece of equipment poses to our system, process or plant.

That said, Equipment Criticality is not a static variable. Especially in today’s complex processes and operating scenarios often the Criticality of a piece of equipment can change. This is due to a change in the piece of equipment’s current operating environment. Going from processing sweet to sour crude or going from a base load power plant to a peaking plant are examples. Just keep in mind that the Criticality does not change due to the probability of failure, that is where we define Risk as consequence times probability.

So how do we affect Probability of failure? That is where our Asset Management Strategies come into play. Here we analyze the specific Failure Mechanism Risks by using RCM, and FMEA tools. This can include looking at what existing controls are in place like Time Based PM’s, Condition Monitoring, lubrication routines, operator logs and the like, looking at failure histories, looking at OEM recommendations, looking at existing data sources, adding data sources, looking at current designs and redesigning, looking at current operating procedures and updating or revising, looking at current training and enhancing or enforcing, looking at current redundancy and even looking at current MRO stores or supply chain strategies.

Done right, we should be able to look at a piece of equipment, understand its failure mechanisms, the current risk these failure mechanisms represent to the system (also referred to as Severity), process or plant, understand the current probability (also referred to as Occurrence) of failure and understand the current Detectability. With these three factors we can define the Risk Priority Number (RPN) that each failure mechanism represents to that piece of equipment. Once we understand the RPN we can then start adjusting our strategies with the aim to improve our current controls to positively impact the the three factors of our RPN which are Severity x Occurrence x Detectability. Reducing the RPN is not only done with Detectability (aka analytics, Condition Monitoring data etc) but is also done by addressing Severity and Occurrence. The paragraph above identifies but a few of the things that are looked at when addressing current and future RPN. In APM we use the RPN ratio (current to future) to define the proposed improvement in risk reduction and corresponding costs as a means of justifying adding to or reducing current controls aka adjusting our Intelligent Asset Strategy.

It all starts with understanding your equipment and then understand the Criticality of that equipment and then applying the appropriate level of effort tools like RCM, FMEA and Templates to determine current risk and to make strategy changes to reduce or mitigate that risk. All of this can be done in GE Digital Asset Performance Management (APM).

Don’t mix Criticality and Risk……they are two different things!