Failure Mode Effect and Criticality Analysis Adam Adgar

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

FMECA ► Failure Mode Effect and Criticality Analysis n 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

What is FMECA ► A set of systemized group activities intended to: n n n ► 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: n n n Brainstorming to identify “all” potential failure causes Assigning numerical priorities to all modes Tracking and documenting corrective actions

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

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

Example CI / RPN ► ► Automobile hydraulic braking system Criticality Index / Risk Priority Number ► ► 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 n = 2 x 9 x 5 = 90 n Value P 1 2 3 4 5 7 8 9 X S D 6 X X 10

Sample FMECA Data Sheet

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

Example: Pressure Cooker ► 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: n n Electric coil heats cooker. Thermostat controls temperature w Switch opens >120 °C. n n n 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.