《船舶安全与可靠性理论》课程教学课件（英文讲义）Safety and Reliability Analysis Lecture 2/5

SafetyandReliabilityAnalysisLecture2Yiliu LiuDepartment of Production and Quality EngineeringNorwegian Universityof ScienceandTechnologyyiliu.liu@ntnu.noNTNU- TrondheimNorwegian University ofScience and Technologywww.ntnu.edu

1 Safety and Reliability Analysis Lecture 2 Yiliu Liu Department of Production and Quality Engineering Norwegian University of Science and Technology yiliu.liu@ntnu.no

FAILUREANALYSISNTNU-TrondheimNorwegian University ofScience and Technologywww.ntnu.edu

2 FAILURE ANALYSIS

3Failures relatedErrorisadiscrepancybetweenacomputed,observedormeasuredvalueorconditionFailureistheeventwhenareguiredfunctionisterminatedFaultishenceastateresultingfromafailureoTarget valueTErrorAcceptabledoviatiorActualperformanceFallure(event)Fault(state)TimeNTNU-Trondheim?Norwegian University ofScience and Technologywww.ntnu.edu

3 Failures related • Error is a discrepancy between a computed, observed or measured value or condition • Failure is the event when a required function is terminated • Fault is hence a state resulting from a failure

WhatisFMECAFailure modes,effects,and criticality analysis (FMEcA):A methodologyto identify andanalyze:AllpotentialfailuremodesofthevariouspartsofasystemTheeffectsthesefailuresmayhaveonthesystemHowto avoid thefailures,and/ormitigate theeffects of thefailures on the systemFMEcA isatechnigueusedto jdentify.prioritize.andeliminatepotential failuresfrom thesystem,designorprocessbeforetheyreachthecustomer.-Omdahl(1988)FMECA is a technique to"resolve potential problems ina system before theyoccur"Initially,theFMECAWascalledFMEA(Failuremodesandeffectsanalysis).TheCinFMECAindicatesthat the criticality(or severity)ofthe variousfailure effects are considered andranked.NTNU-TrondheimNorwegian University ofScience and Technologywww.ntnu.edu

4 What is FMECA Failure modes, effects, and criticality analysis (FMECA): A methodology to identify and analyze: • All potential failure modes of the various parts of a system • The effects these failures may have on the system • How to avoid the failures, and/or mitigate the effects of the failures on the system FMECA is a technique used to identify, prioritize, and eliminate potential failures from the system, design or process before they reach the customer. – Omdahl (1988) FMECA is a technique to “resolve potential problems in a system before they occur.” Initially, the FMECA was called FMEA (Failure modes and effects analysis). The C in FMECA indicates that the criticality (or severity) of the various failure effects are considered and ranked

5WhatcanFMECAbeusedforAssist inselectingdesignalternativeswithhighreliabilityandhighsafetypotential duringtheearlydesignphasesEnsurethatall conceivablefailuremodesandtheireffectsonoperationalsuccessofthesystemhavebeenconsideredListpotential failures and identifythe severity oftheir effectsDevelopearlycriteriafortestplanningandrequirementsfortestequipmentProvidehistorical documentation forfuturereference to aid in analysis of field failuresandconsiderationofdesignchangesProvideabasisformaintenanceplanningProvideabasisforquantitativereliabilityandavailabilityanalysesNTNU-TrondheimNorwegian University of梦Science and Technologywww.ntnu.edu

5 What can FMECA be used for • Assist in selecting design alternatives with high reliability and high safety potential during the early design phases • Ensure that all conceivable failure modes and their effects on operational success of the system have been considered • List potential failures and identify the severity of their effects • Develop early criteria for test planning and requirements for test equipment • Provide historical documentation for future reference to aid in analysis of field failures and consideration of design changes • Provide a basis for maintenance planning • Provide a basis for quantitative reliability and availability analyses

FMECAbasicquestionsHowcaneachpartconceivablyfail?Whatmechanismsmightproducethesemodesoffailure?Whatcouldtheeffectsbeifthefailuresdidoccur?Isthefailureinthesafeorunsafedirection?How is the failure detected?What inherentprovisionsareprovided inthedesigntocompensateforthefailure?NTNU-TrondheimNorwegian University of梦Scienceand Technologywww.ntnu.edu

6 FMECA basic questions • How can each part conceivably fail? • What mechanisms might produce these modes of failure? • What could the effects be if the failures did occur? • Is the failure in the safe or unsafe direction? • How is the failure detected? • What inherent provisions are provided in the design to compensate for the failure?

TwoapproachesinFMECAThebottom-upapproachThebottom-upapproachisusedwhenasystemconcepthasbeendecided.Eachcomponentonthelowestlevel of indentureisstudiedone-by-one.Thebottom-upapproachisalsocalledhardwareapproach.Theanalysisiscompletesinceall componentsareconsidered.Top-downapproachThetop-down approach is mainlyused in an early design phase before the whole systemstructure is decided.The analysisis usuallyfunctionoriented.The analysis startswith themain system functions-and howthesemay fail.Functional failures with significant effectsare usually prioritized in the analysis.The analysis will not necessarily be complete.The top-downapproachmayalsobeusedonanexistingsystemtofocusonproblemareas.NTNU-TrondheimNorwegian University ofScienceand Technologywww.ntnu.edu

7 Two approaches in FMECA • The bottom‐up approach The bottom‐up approach is used when a system concept has been decided. Each component on the lowest level of indenture is studied one‐by‐one. The bottom‐up approach is also called hardware approach. The analysis is complete since all components are considered. • Top‐down approach The top‐down approach is mainly used in an early design phase before the whole system structure is decided. The analysis is usually function oriented. The analysis starts with the main system functions ‐ and how these may fail. Functional failures with significant effects are usually prioritized in the analysis. The analysis will not necessarily be complete. The top‐ down approach may also be used on an existing system to focus on problem areas

8FMECAworksheetSystem:Perlormed by:Date:Ref.drawing no.:Page:ofDescription ofunitEffectoffailureDescriptionoffailureRiskOpera-FallureOntheFailureRel.FailureDetectionOntheSeverityreducingsystemtionalcauseormodeoffailuresubsystemnoFunctionCommentsraterankingmodemechanismfunctionmeasures(4)(5)(6)(7)(8)(9)(10)(11)(12)(1)(2)(3)NTNU- TrondheimNorwegian University ofScience and Technologywww.ntnu.edu

8 FMECA worksheet

OFMECAworksheet1.Inthefirstcolumnauniquereferencetoanelement(subsystemorcomponent)isgiven2.Thefunctions of the element are listed.It is importantto list all functions.A checklistmaybeusefultosecurethatallfunctionsarecovered3.Thevariousoperationalmodesfortheelementarelisted.Exampleofoperational modesare:idle,standby,andrunning4.Foreachfunctionandoperational modeof anelementthepotentialfailuremodeshavetcbeidentifiedand listedThefailuremodesidentified incolumn4arestudied one-by-one.Thefailuremechanisms5.(e.g.,corrosion,erosion,fatigue)thatmayproduceorcontributetoafailuremodeareidentifiedand listed.Otherpossiblecausesofthefailuremodeshouldalsobelisted.6.The various possibilities for detection ofthe identifiedfailure modes are listed.Thesemayinvolvediagnostictesting,differentalarms,prooftesting,humanperception,andthelikeNTNU-TrondheimNorwegianUniversityofScienceand Technologywww.ntnu.edu

9 FMECA worksheet 1. In the first column a unique reference to an element (subsystem or component) is given 2. The functions of the element are listed. It is important to list all functions. A checklist may be useful to secure that all functions are covered. 3. The various operational modes for the element are listed. Example of operational modes are: idle, standby, and running 4. For each function and operational mode of an element the potential failure modes have to be identified and listed. 5. The failure modes identified in column 4 are studied one‐by‐one. The failure mechanisms (e.g., corrosion, erosion, fatigue) that may produce or contribute to a failure mode are identified and listed. Other possible causes of the failure mode should also be listed. 6. The various possibilities for detection of the identified failure modes are listed. These may involve diagnostic testing, different alarms, proof testing, human perception, and the like

10FMECAworksheet7.Theeffectseachfailuremodemayhaveonothercomponentsinthesamesubsystemandonthesubsystemassuch(localeffects)arelisted.8.Theeffectseachfailuremodemayhaveonthesystem(globaleffects)arelisted9.Failureratesforeachfailuremodeare listed1o.Theseverityof afailuremode isthe worstpotential (but realistic)effect ofthefailureconsideredonthesystemlevel(theglobaleffects)11.Possibleactionsto correctthefailureand restorethefunctionorprevent seriousconsequencesarelisted.Actionsthatarelikelytoreducethefrequencyofthefailuremodesshouldalsoberecorded.12.Thelast column may be used to record pertinent information not included in theothercolumns.NTNU-TrondheimNorwegian University ofScienceandTechnologywww.ntnu.edu

10 FMECA worksheet 7. The effects each failure mode may have on other components in the same subsystem and on the subsystem as such (local effects) are listed. 8. The effects each failure mode may have on the system (global effects) are listed. 9. Failure rates for each failure mode are listed. 10. The severity of a failure mode is the worst potential (but realistic) effect of the failure considered on the system level (the global effects). 11. Possible actions to correct the failure and restore the function or prevent serious consequences are listed. Actions that are likely to reduce the frequency of the failure modes should also be recorded. 12. The last column may be used to record pertinent information not included in the other columns