Failure Mode Effect and Criticality Analysis

1. Failure Mode Effect and Criticality Analysis Adam Adgar School of Computing and Technology

2. FMECA • Failure Mode Effect and Criticality Analysis • Detailed study of a system to determine which parts are most critical to operation under various failure modes • Developed in USA in 1950’s • Objective is to prevent failures • Can be used at design stage or process stage • Different Industries have different standards but all are very similar in philosophy and procedures

3. What is FMECA • A set of systemized group activities intended to: • recognize and evaluate the potential failure of a product or process and its effects • identify and prioritize actions which could eliminate or reduce the chance of the failure occurring • document the process • It involves: • Brainstorming to identify “all” potential failure causes • Assigning numerical priorities to all modes • Tracking and documenting corrective actions

4. Definitions • Failure Mode Analysis • Incorrect behavior of a subsystem or component due to a physical or procedural malfunction • Failure Effect Analysis • Incorrect behavior of the system caused by a failure • Failure Criticality Analysis • The combined impact of • The probability that a failure will occur • The severity of its effect

5. Stage 1 Identify all components, assemblies etc of the system under consideration Stage 2 Make an exhaustive list of all possible FMs of each component Stage 3 Establish the effects that each FM would have on the overall system or process Stage 4 Make a list of all possible causes of each FM Stage 5 Assign a numerical value to each occurrence for each of the following FM criteria P = Probability of FM S = Seriousness/Criticality of FM D = Difficulty of detecting FM Stage 6 Determine criticality indexor risk priority number (PSD) for each FM Stage 7 Determine corrective action needed to avoid FM Stage 8 Rank the RPN for the whole system so action may be taken using resources available FMECA Stages

6. Automobile hydraulic braking system Criticality Index / Risk Priority Number = 2 x 9 x 5 = 90 Criteria sometimes ranked on a scale of 1 – 4. (4 = worst) Each level may have detailed verbal description harder to misrepresent a threat minimizes impact of “judgment” on numerical value Example CI / RPN

8. Sample FMECA Data Sheet

9. Summary of FMECA • Is a formalized group-based problem solving method • Similar to design review standards in many industries • Uses brainstorming to try to identify “all” risks • Has become an industry-standard approach • Is revised and improved based on experience • Attempts to define a general “best known method” • Tries to accomplish the following: • Identify risks • Prioritize them • Define and track corrective actions and their effects • Document the entire decision process

10. OPERATOR: 1. loads cooker 2. closes/seals lid 3. connects power 4. observes pressure 5. times cooking at prescribed pressure 6. offloads dinner. SYSTEM DESCRIPTION: Electric coil heats cooker. Thermostat controls temperature Switch opens >120°C. Spring-loaded Safety Valve opens on overpressure. Pressure Gauge red zone indicates overpressure. High temperature/pressure cooks/sterilizes food — tenderizes and protects against botulin toxin. Prepare an FMEA at component level for cooking (after loading/ closing/ sealing). Targets are personnel (P), product (R), and the pressure cooker itself (E). Ignore facility/kitchen and energy consumption. Food is for private use. Example: Pressure Cooker