What is criticality analysis?

It is a structured and systematic method of assessing the risk machine failures pose to a business. The criticality of machines relative to each other is ranked by a certain technique. The implementation of targeted plant maintenance strategies proportional to the failure’s impact is supported by this technique. 

The structured process removes considerable subjectivity while optimizing maintenance spending. It helps improve machines' availability and reliability, plant safety, and equipment uptime.

It combines the seriousness and frequency of potential risk and uses that information to rate machines’ criticality levels and determine the priority for performing a maintenance task.

What is the purpose of completing a machine criticality assessment?

Criticality analysis is not just another maintenance gadget to save money. It’s a strategic business process that requires involvement and input from a broad range of company departments if it is to deliver company-wide benefits.

The outputs from a criticality analysis can be used for:

·        Stockpiled optimization: Identifying optimum spares holdings for critical equipment.

·        Capital distribution: Identifying CAPEX investment for critical equipment upgrades or process increase needs while eliminating unnecessary spending.

·        Safety improvements: Decreasing critical failures and eliminating unnecessary maintenance involvement and downtime.

·        Maintenance program optimization: Machines priority rankings for planned maintenance tasks and work order requests. Machines with applying risk reduction strategies such as condition or trend monitoring.

·        Resource optimization: By better understanding machine criticality, maintenance resources are used more effectively.

Sub-optimal approaches to estimating equipment criticality:

Different methods exist for applying criticality classification to machines. However, many lack procedural rigor and miss the mark when it comes to improving maintenance outcomes. 

We will still explain some of them so you get an idea of what is out there. You might also apply them as a band-aid until you have enough resources to conduct a full equipment criticality analysis.

The Pareto principle (a.k.a. the 80/20 rule):

This method is subjective and involves the maintenance manager ranking all machines by their perceived criticality, then focusing most maintenance efforts on the top 20% of the list.

While some machine failure rates improve, others will break down due to a lack of attention, forcing the maintenance team into reactive mode.

Forced ranking

Like the Pareto method, forced ranking assumes a clear staircase of machine criticality, which is not the reality. With scheduled maintenance efforts applied from the top, machines that are towards the bottom half of the list will receive little to no attention, depending on the maintenance team’s workload. 

This method is wildly unpredictable, preventing informed and systematic changes to improve machine availability and measure efficiency.

Maintenance frequency allocation:

The frequency allocation method increases or decreases scheduled maintenance involvements based on machine criticality. However, effective and efficient maintenance is not linked to how often a piece of equipment is looked at, but rather to having the right tasks performed at a predetermined time. 

Frequency distribution often allows less critical machines to run late on scheduled checks or has them canceled completely due to time pressures.

Over-maintaining:

In this scenario, businesses assume that every machine is equally important. Based on the flawed principle that if a little oil is good for something, more must be better, and the business gives all the machines equal attention. 

Apart from being extremely expensive and time-consuming. When a machine fails, as one surely will, management will look at the size of the maintenance budget and assume the maintenance department is unqualified. 

The fact a business is spending a lot of money on maintenance does not mean the maintenance adds value.  

How to determine the criticality of the machine:

The machines' classification system in terms of severity of failure occurrence.
Six criteria are considered:

·        Safety: Dangerous machines, such as presses, can cause serious damage to the health of the operator

·        Product quality: Some machines carry out high precision processes and, in this way, the lowest level of misalignment can result in loss of quality of the manufactured product

·        Impact on production: Failures in production process bottleneck machines can have a strong impact on productivity in the plant. In some cases, they can even lead to full production stops. Therefore, this is an essential criterion in criticality analysis

·        Mean Time Between Failures (MTBF) (Frequency): This criterion deals with the time elapsed between failures in a machine

·        Mean Time to Recovery (MTTR): This criterion represents the average time required to replace or repair a faulty component, or even to restart the machine

·        Maintenance Costs: Money to be spent on repairing a specific machine that may fail. This expense varies according to the failure, but in general, it’s possible to infer if the asset requires high expenses with spare parts and so on.

Each of the analyzed machines must be classified in the six criteria mentioned above, according to three levels of impact:

·        A: high impact

·        B: medium impact

·        C: no impact

By this method, the machines will be classified as follows:

·        A: Highly critical equipment

·        B: Moderately critical equipment

·        C: Equipment of low criticality in the process

Mitigation strategy to be applied to Machines: