FMECA

1. FMECA Failure Modes, Effects and Criticality Analysis Mehmet YILMAZ May 2009

2. FMECA • What is FMECA? • Why to perform FMECA? • How to perform FMECA? • Conclusions

3. FMECA Definition • Failure Modes = Incorrect behavior of a subsystem or component due to a physical or procedural malfunction. • Effects = Incorrect behavior of the system caused by a failure. • Criticality = The combined impact of • The probability that a failure will occur • The severity of its effect • Failure Modes Effects and Criticality Analysis (FMECA) = a step-by-step approach for identifying all possible failures in a design, a manufacturing or assembly process, or a product or service.

4. Evolution of FMECA • FMEA was originally developed by NASA to improve and verify the reliability of space program hardware. • MIL-STD-1629 establishes requirements and procedures for performing FMECA

5. Purpose of FMECA • Select the most suitable design with high reliability and high safety potential in the design phases. • List potential failures and identify the severity of theireffects in the early design phases. • Develop criteria for test planning and requirements. • Provide necessary documentation for future design andconsideration of design changes. • Provide a basis for maintenance management. • Provide a basis for reliability and availability analyses.

6. Basic Questions of FMECA • Why failures will happen (Failure mode)? • What is the consequence when the failure occurs (Failureeffect)? • Is the failure in the safe or danger direction (FailureCriticality)? • How to remove the failure or reduce its frequency?

7. Benefits of FMECA • FMECA is one of the most important and most widely used tools of reliability analysis. • The FMECA facilitates identification of potential design reliability problems • Identify possible failure modes and their effects • Determine severity of each failure effect • FMECA helps • removing causes of failures • developing systems that can mitigate the effects of failures. • to prioritize and focus on high-risk failures

8. Benefits of FMECA • It provides detailed insight about the systems interrelationships and potentials of failures. • Information gained by performing FMECA can be used as a basis for • troubleshooting activities • maintenance manual development • design of effective built-in test techniques.

9. The results of the FMECA • Rank each failure mode. • Highlight single point failures requiring corrective action • Identify reliability and safety critical components

10. FMECA Techniques • The FMEA can be implemented using a hardware (bottom-up) or functional (top-down)approach • Due to system complexity, it isperformed as a combination of the two methods.

11. FMECA Techniques • Hardware Approach : • The bottom-up approach is used when a system design has been decided already. • Each component in the system on the lowest level is studied one-byone. • Evaluates risks that the component incorrectly implements its functional specification.

12. FMECA Techniques • Functional Approach : • Considers the function of each item. Each function can be classified and described in terms of having any number of associated output failure modes. • The functional method is used when hardware items cannot uniquely identified • This method should be applied to when the design process has developed a functional block diagram of the system, but not yet identified specific hardware to be used.

13. FMECA Procedure • FMECA pre-requirements • System structure and failure analysis • Preparation of FMECA worksheets • Team review • Corrective actions to remove failure modes

14. FMECA Prerequisites • Define the system to be analyzed • System boundaries. • Main system missions and functions. • Operational or/and environmental conditions. • Collect available information that describes the systemfunctions to be analyzed. • Collect necessary information about previous andsimilar designs.

15. Functional Block Diagram • Functional block diagram shows how the different parts of the system interact with each other. • It is recommended • to break the system down to different levels. • to review schematics of the system to show how different parts interface with one another by their critical support systems to understand the normal functional flow requirements. • to list all functions of the equipment before examining the potential failure modes of each of those functions. • to include operating conditions (such as; temperature, loads, and pressure), and environmental conditions in the components list.

16. Functional Block Diagram

17. Rate the Risks Relatively • A systematic methodology is used to rate the risks relative to each other.  The Risk Priority Number is the critical indicator for each failure mode.   • RPN = Severity rating X Occurrence rating X Detection rating • The RPN can range from 1 to 1,000 • Higher RPN = higher priority to be improved.

18. Severity Classification • A qualitative measure of the worst potential consequences resulting from a function failure. • It is rated relatively scaled from 1-10.

19. Severity Classification

20. Probability of Occurrence • Probability that an identified potential failure mode will occur over the item operating time. • It is rated relatively scaled from 1-10.

21. Occurrence Classification

22. Detection rating • A numerical ranking based on an assessment of the probability that the failure mode will be detected given the controls that are in place. • It is rated relatively scaled from 1-10.

23. Detection rating

24. FMECA CASE STUDY • Component = D1 • Function = restricting the direction of current • Failure = short • Cause = Physical Damage • Effect = Reverse current

25. FMECA CASE STUDY • Severity = 7 • Occurrence = 5 • Detection = 9 • RPN = 7*5*9 = 315

26. FMECA Worksheet

27. Corrective Actions • RPN reduction: the risk reduction related to a correctiveaction.

28. FMECA Checklist • System description/specification • Ground rules • Functional Block Diagram • Identify failure modes • Failure effect analysis • Worksheet (RPN ranking) • Recommendations (Corrective action) • Reporting

29. Summary

30. References • MIL-P-1629 “Procedures for performing afailure mode, effects and criticality analysis • http://www.fmeca.com/