Failure Mode and Effects Analysis (FMEA) is a problem solving method used to identify potential problems (failure modes) in a design, system, or process and to determine the impact (effects) of those problems. An FMEA should answer how likely a design, process, or system is to fail, why the failure would occur, and if a failure occurs, how would it affect the surrounding environment and the safety of the operators.
The goal of an FMEA is to increase reliability, performance, and safety. FMEA also helps to prioritize deficiencies in a design or process and provides an opportunity to correct problems before they occur. Furthermore, FMEA is a practical tool for any risk assessment (e.g. risk-based inspection) and an important element in a reliability centered maintenance program.
How to Do an FMEA
The following outline is a general FMEA procedure meant to provide the minimum requirements of an FMEA. An actual FMEA may be more or less detailed depending on the significance of the project, component, process, or system. Moreover, it’s important in any analysis to develop and implement a solution and measure the results of key changes that were made during the process. Each step should be documented and organized for future failure and risk assessments.
Step 1. Identify Scope of FMEA
The first step is to define the scope of the analysis by asking the following questions:
- Is the analysis for a new design, an existing piece of equipment, a system, or a process?
- What is the purpose of the equipment, system, or process?
- What are the boundary conditions (e.g. external loads, temperature, pressure, hydraulics)?
Step 2. Determine the Cause and Effects of Failure Modes
The second step is to identify all the possible functions of the subject (i.e. component, system, process) and then determine how each of those functions may fail. These are referred to as the possible failure modes. Other methods may be used to supplement an FMEA such as a root cause analysis or a 5 Whys analysis. Once all potential failure modes are identified, the next step is to determine all possible consequences of those failures.
Step 3. Calculate the Risk Priority Number
In this step, the severity of potential failures are prioritized and the most serious problems are treated first. Failure modes are prioritized based on their Risk Priority Number (RPN). The RPN is a numerical scale that quantifies:
- The probability that the failure will happen (occurrence),
- how likely that failure will be detected before it happens (detection), and
- the significance the failure will have on personnel, equipment, and the surrounding environment (severity).
RPN is commonly represented as the product of these three factors: RPN = Occurrence x Detection x Severity.
Step 4. Develop and Implement Strategic Plan
When all failure modes have been assigned an RPN, the goal is to focus on the highest priority risks first. Next, develop a plan to make process changes, design changes, or to establish additional controls that would help mitigate the problem. Delegate tasks to members of the team and set deadlines. It’s important to record any trends as changes are made in a process and measure the results of that change. The results can be measured by re-calculating the RPN.
When to Use FMEA
An FMEA can be used on a new design, system, or process. It can also be used when modifying an existing asset or process. Furthermore, FMEA is a comprehensive failure analysis method that meets Process Hazard Analysis requirements under OSHA’s Process Safety Management standard.
When all high ranking RPN failure modes have been treated, the FMEA process can be applied again at specific intervals determined by the FMEA team.
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