Process Failure Mode Effects Analysis (PFMEA) Explained

Operating processes within  service or manufacturing organizations are never perfect. On any given day, challenges can surface that cause the organization to deviate from its target objectives. Knowing that uncertainty exists, the key to successful Operations Management lies in appropriate preparedness which involves building contingencies in place, that facilitate your organization’s restoration. In its usual systematic fashion, Six Sigma Methodology offers a tool called Process Failure Mode Effects Analysis (PFMEA) to achieve this objective.

PFMEA is a step-wise means of analyzing a process, in order to identify and rate its critical failure modes. The tool is best utilized during the design phase of a project, and should be refreshed as the existing system is optimized. Once all the critical system failure modes, and their associated consequences are identified and weighted, the organization can arrange itself to facilitate appropriate elimination, or frequency reduction of these opportunities based on the highest priority. Appropriate documentation of the potential system failures and their associated risks, facilitates the implementation of continuous improvement efforts such as engineering controls. Once built into the system, guarantees of improved robustness can be facilitated.

As the old adage states: “Teamwork makes the dream work”. An effective PFMEA assessment requires a cross functional team with a combination of both fresh and experienced eyes to ensure that varying perspectives are being accounted for. In a manufacturing process for instance, you would want to engage with your Operations Staff at varying levels (operators and supervisors), process engineers, process control team and reliability team of electrical and mechanical engineers in order to ensure that all bases are covered in the identification of critical system weaknesses.

With an appropriate identified system scope, visual representations of the system are then generated, and appropriate indicators of the points of weakness should be placed on the diagram. Visual representations of the process can be simple process flow diagrams, or more sophisticated views. Continue to dissect the process into process units until an appropriate level of detail is identified, and ask critical questions to ensure that the function of each phase is clearly identified, along with its risks.  A suitable format for documenting the failure modes is highlighted below:

Table 1. PFMEA Analysis Example

Table 1. PFMEA Analysis Example

For each process function, identify the critical failure modes. The example above focuses on a process pump. The first column of the PFMEA template captures the function. Moving from left to right, failure modes are identified. For simplicity, only one is highlighted in this example. For an operating pump, an easily identified failure of the pump is a blocked discharge chute. The associated consequence or severity(S) of this condition is identified on a scale of 1-10, with ten being the highest severity.

A root cause analysis of the problem is then executed. An occurrence rating (O) is generated based on the possibility of the identified root cause(s). Once again, a rating for the root cause is determined on a scale of 1-10, with 10 being the highest order of occurrence.

Thirdly, existing system controls are then identified and rated. The detection rating (D) is an indicator of the existence of control. The scale 1-10 is used for the detection rating, but the meaning of the values is reversed, indicating that a value of 10 means no controls are in place.

With the appropriate ratings in place, two additional variables are calculated according to the following formulae:

Risk Priority Number RPN = S x O x D

Criticality = S x O

Once calculated and tabulated, priority risks are identified based on the order of magnitude of the risk priority number and the criticality. The higher the numbers, the more attention should be paid to the risk. A suitable action plan then accompanies the action, and the organization can allocate funding in order to eliminate or mitigate against the risk. An organization that remains ready for challenges, will always be ahead of the game. PFMEA is an appropriate tool to add to your arsenal of operations optimization tools.