Equipment criticality analysis

In one line

Criticality = failure frequency × failure consequence. The list, sorted from highest to lowest, tells maintenance where to put effort and money first.

What it is

Huerta Mendoza defines criticality analysis as a methodology for ranking systems, facilities and equipment by their overall impact, to make decision-making easier. It starts from a practical reality: there are rarely unlimited financial and human resources to improve human, process, design and maintenance reliability across all areas at the same time. The analysis answers "how do you establish that one piece of equipment is more critical than another?" with a weighted list, from the most critical element to the least critical, and with three zones: high, medium and low criticality.

Mathematically, criticality is expressed as frequency × consequence. Frequency is tied to the number of events or failures of the system or process being evaluated; consequence, to the operational impact and flexibility, repair costs, and safety and environmental impacts. The article lists the fundamental criteria: safety, environment, production, costs (operating and maintenance), mean time to repair and failure frequency.

What it is for

With the ranked list you can prioritize, according to the article:

• Maintenance: which programs and plans (predictive, preventive, corrective) to address first, and even the priority of work orders.
• Inspection: where it is worth inspecting and at what interval (see risk-based inspection).
• Materials: which spare parts to keep in the central and plant warehouses, to fit the stock to what is really needed.
• Projects and plant availability: where to invest in renovations, starting with the area of greatest impact.
• Personnel: which technical training to prioritize, starting with the most critical areas.

How it is applied

Huerta Mendoza asks first that the scope and purpose of the analysis be defined. His basic model follows four steps: set the evaluation criteria, select the method, apply the procedure and obtain the ranked list. In practice:

1. Build the asset hierarchy: facility, process, system, equipment, part. The number of elements to evaluate grows as you go down a level.
2. Form a working team with a facilitator (who knows the method) and people from operations, maintenance and the specialties, from all levels (management, supervision, operators). The more people take part, the more points of view and the greater the acceptance of the results.
3. Gather the information: ideally accurate statistical data, but since quality history is rarely available, the method allows you to work with ranges (the most and least favorable condition of each criterion) and from the participants' knowledge.
4. Score each piece of equipment with a simple survey and calculate frequency times consequence.
5. Sort from highest to lowest and chart it as bars (similar to a Pareto chart): the three zones generally appear easily, and the effort is concentrated on the high-criticality one.

One combination rule used in the article by Meneses Ramírez and colleagues in their risk-based inspection example, and which this site adopts: when consequences are evaluated in several areas (economic, health and safety, environment), the one with the greatest severity determines the consequence class entered in the matrix.

Try it

For each piece of equipment, the tool calculates criticality as frequency times the worst of the four consequences (safety, environment, production, cost), on scales of 1 to 5, and sorts the list. The 1-to-5 scales and the zone cutoffs (A from 15, B from 6 to 14, C up to 5) are conventions of this site. Huerta Mendoza's formula uses a table of criteria with weights specific to the company in the case (PDVSA), which the article shows as an image: each plant must define its own.

Real example

The master's thesis from the Universidad de Sevilla, which builds maintenance indicators with a BI tool for an integrated water cycle management company, starts from the data of the company's maintenance management system (CMMS) and uses the ABC criticality indicator of equipment and technical locations to prioritize. For example, it defines the "scheduled maintenance effectiveness on criticality A equipment" as the percentage of equipment and locations with criticality A that have not suffered breakdowns out of the total of those technical objects, and it counts the breakdowns of priority equipment separately from the rest. It is an example of how, once the analysis is done, the classification is loaded into the system and turned into an indicator. The thesis does not reproduce the scores of each piece of equipment.

An illustrative (made-up) example, with the tool above: an air compressor with frequent failure (3) and a maximum consequence of 5 (for the whole plant) has criticality 15, zone A; a washing pump with infrequent failure (2) and a maximum consequence of 2 has criticality 4, zone C. With that, the compressor goes first into the RCM program and predictive maintenance, and for the pump a basic preventive plan is enough.

Template to use

The criticality Excel spreadsheet has the same logic, with editable zone cutoffs and a sheet for defining what each value of the scale means. Before scoring, it is worth agreeing as a team on what each level means in your plant (for example, "frequency 5 = more than one failure per month").

Benefits

• It puts a shared criterion where there used to be opinions: the team talks about the same criteria.
• It concentrates resources where the impact is greatest and justifies priorities with numbers.
• It is the starting point for RCM, predictive maintenance, the spare parts policy and risk-based inspection.

Limitations to keep in mind

• The result is only as good as the scales and the people scoring: without agreed criteria, two groups get different lists.
• It is a ranking, not a diagnosis: it does not say why something fails or what to do about it.
• Frequency is based on failure history: if breakdowns are not recorded, the values are estimates.
• The worst-consequence rule is simple and conservative; it does not distinguish equipment with one extreme consequence from equipment with four moderate ones.

In summary

Criticality is frequency times consequence. It is scored by a mixed operations and maintenance team, sorted from highest to lowest, and the effort is concentrated on the high zone. It is the first filter of maintenance management: before deciding how to maintain each piece of equipment, you have to decide which ones matter most.