Even if you have an asset maintenance program that helps increase productivity and optimize assets, a lack of expertise in asset failure could cause your critical risks to spiral out of control. FMECA is a powerful tool to improve product and process designs. It results in increased reliability and higher quality.
FMECA can be used to determine the need for maintenance programs (for items that are not easily maintained) and to contribute to quality control procedures. This knowledge base provides information on failure modes and the associated corrective actions. It is helpful for training, troubleshooting, and Root Cause Failure Analysis.
How to perform Failure Mode, Effects & Criticality Analysis (FMECA).
First of all, Perform FMEA
FMEA can be used as a starting point for the FMECA. FMEA permits creative inputs from multi-disciplined engineering teams. FMEA is the first step in a design change process and can help jumpstart the risk mitigation process. FMEA data is then transferred to the FMECA Criticality Worksheet. The data that will be transferred from the FMEA worksheet include:
- Item Identification Number
- Item/Function
- Specific Function and Requirements
- Failure Mechanisms and Failure Causes
- Sometimes, the Mission Phase or Operational Mod (DoD-specific) is closely related to the Effects of Failure.
Determine The Severity Level
Next step to perform FMECA analysis is to determine the severity level for each Effect of Failure. There are many severity tables available. These are used in some aerospace and medical activities. You can modify the descriptions to suit any product or process design. These are the four levels of severity:
Catastrophic: Can cause death, permanent total disability or loss exceeding $1M, or irreversible environmental damage in violation of law or regulation.
Major/High Impact: Permanent partial disablement, occupational illnesses, and injuries that result in 3 or more people being hospitalized, loss of $200K or less than 1M, or irreversible environmental damage that causes a violation or violation of law or regulation.
Minor Impact: This could result in an injury or occupational illness that results in one or more days lost, loss exceeding $10K but under $200K, or mitigating environmental damage.
Low Impact: Cause minor injury or illness that does not result in lost workdays, loss exceeding $2K, but less than 10K, or minimize environmental harm.
Probability of Failure
FMECA can assign a Beta value to the probability of failure in some cases. FMECA analysts may use engineering judgment to determine the Beta value.
Probability of Occurrence (Quantitative).
This refers to the selected data source for information on how to assign probability values for each Failure Mode. If the failure mode probability has been listed (functional approach), several columns may be skipped from the FMECA Criticality Sheet. You can calculate Criticality (Cr) directly. If you need to know the failure rates of failure modes or contributing components, each component can be assigned a detailed failure rate.
Next, you need to assign the Component Failure Rate (lambda). The failure rate source document contains the Failure Rates for each component. The FMEA qualitative values are used in cases where there is no failure rate. FMEA can also be used for innovative or new designs.
Operating Time (t), also known as the expected life expectancy of an item or component, is the amount of time it will take to reach that point. This refers to the regular duty cycles.
Calculate Criticality and Plot
FMECA calculates criticality in two ways
The Modal Criticality (each failure mode, all causes) = Cm
Cr = Criticality of the Item (all failure types summarized).
This explanation does not include formulae for each.
Risk Mitigation and Design Feedback
Risk mitigation is a discipline essential for reducing possible failure. The substitute for failure is the identified risk in the criticality matrix and must be considered in the same way as a customer returned item or test failure. FMECA requires that there be a change in the risk levels or criticality following mitigation. An acceptable defect detection strategy may be required in proportion to the risk level. The following are acceptable risk management strategies:
- Mitigation actions targeted at combinations of Highest Probability and Severity
- Any risk that cannot be mitigated is eligible for Mistake Proofing and Quality Control to protect the customer/consumer from potential failure.
- The failure modes are first, and then the individual causes if they cannot be shipped or accepted.
- For each unwanted risk, action logs and “risk lists” are kept with revision history.
You can also consider these FMECA mitigation strategies:
- Design changes. Design change. Change components, review duty cycles or take a new direction in design technology.
- Selecting a component with a lower failure rate (lambda) If this is not identified in Product Development early, it can become costly.
- The component can be physically redundant. This option places redundant components in parallel. Failure mode can only occur if both components fail simultaneously. This option can be used if there is a safety concern.
- Software redundancy. An addition of sensing circuit that can alter the product’s state. This option reduces the severity by protecting components and reducing input stress.
- Alert system. To avoid failure or its effect, an operator or analyst must take action.
- Inspection or testing to detect and remove the possibility of failure. Inspection effectiveness must be proportional to the severity and criticality.
Perform a Maintainability Analysis
Maintainability Analysis identifies the most dangerous items and predicts when they will fail. Cost and availability of parts are also taken into consideration. This analysis may affect the placement of components or items during the design phase. When serviceability is more critical, it’s essential to plan for easy access.
- Easy to remove access panels allow for service of identified parts and items. This will reduce downtime for necessary machinery.
- Typically, a spare parts list is created from the maintainability analysis.
