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1、无投影片标题-NCKU Still waters run deep.流静水深流静水深,人静心深人静心深 Where there is life,there is hope。有生命必有希望。有生命必有希望 PurposeThe purpose of an FMEA is to identify single equipment and system failuremodes and each failure modes potential effect(s)on the system or plant.Thisanalysis typically generates recommendation
2、s for increasing equipment reliability,thus improving process safety.Types of ResultsAn FMEA generates a qualitative,systematic reference list of equipment,failure modes,and effects.A worst-case estimate of consequences resulting fromsingle failure is included.The FMEA may be easily updated for desi
3、gn changes orsystem/plant modifications.FMEA results are usually documented in a column-format table.Hazard analysts usually include suggestions for improving safety inappropriate items in the table.Failure and Failure ModeFailure:The termination of an items ability to perform a required function.Fa
4、ilure Mode:The effects by which a failure is observed on the failed item.All technical items are designed to fulfill one or more functions.A failure mode is thus defined as non-fulfillment of one of these functions.Classification of FailuresSudden versus gradual failuresHidden versus evident failure
5、sAccording to effects(critical,degraded or incipient)According to severity(catastrophic,critical,marginal or negligible)Primary failure,secondary failure and command faultClassification of Failure Modes1.Demanded change of state is not achieved.2.Change of conditions or states.1.Fail to open on comm
6、and2.Fail to close on command3.Leakage through the valve in closed position4.Leakage to the environment Examples of Equipment Failure Modes Used in an FMEA Equipment Description Example Failure Modes Pump,normally operating Fails on(fails to stop when required)Transfers off(stops when required to ru
7、n)Seal leak/rupture Pump casing leak/rupture Heat exchanger,high pressure on Leak/rupture,tube side to shell side tube side Leak/rupture,shell side to external environment Tube side,plugged Shell side,plugged Fouling Resource Requirements Using the FMEA approach requires the following data and infor
8、mation sources:(1)a system or plant equipment list or P&ID,(2)knowledge of equipment function and failure modes,and(3)knowledge of system or plant function and responses to equipment failures.FMEAs can be performed by single analysts,but these analyses should be reviewed by others to help ensure com
9、pleteness.Staff requirements will vary with the size and complexity of equipment functions and failure modes and how the failures might affect other portions of the system or plant.The time and cost of an FMEA is proportional to the size of the process and number of components analyzed.On the averag
10、e,an hour is sufficient for analyzing two to four equipment items.As with any HE study of systems with similar equipment performing similar functions,the time requirements are reduced significantly due to the repetitive nature of the evaluations.Table 4.8 lists estimates of the time needed to perfor
11、m an HE study using the FMEA technique.Time Estimates for Using the FMEA TechniqueAnalysis Procedure(1)defining the study problem,(2)performing the review,and(3)documenting the results.STEP 1:Defining the study problem.This step identifies the specific items to be included in the FMEA and the condit
12、ions under which they are analyzed.Defining the problem involves(1)establishing an appropriate level of resolution for the study and(2)defining the boundary conditions for the analysis.A detailed problem definition is a necessary ingredient to performing a thorough and efficient FMEA.(2)Defining the
13、 analysis boundary conditions includes:Identifying the plant and/or systems that are the subject of the analysis.Establishing the physical system boundaries for the FMEA.This includes the interfaces with other processes and utility/support systems.One way to indicate the physical system boundaries i
14、s to mark them on a system drawing that encompasses all equipment within the scope of the FMEA.These boundary conditions should also state the operating conditions at the interfaces.Establishing the system analytical boundaries,including:(1)the failure modes,operating consequences,causes,or existing
15、 safeguards that will not be considered and(2)the initial operating condition or position of equipment.As an example of effects beyond the scope of the study,an analyst may choose not to consider airplane crashes,earthquakes,or tornadoes as causes of failure modes.An example of an initial condition
16、is specifying whether a valve is normally open or closed.Collecting up-to-date reference information that identifies the equipment and its functional relationship to the plant/system.This information is needed for all equipment included within the system boundary and appropriate interfaces with the
17、rest of the plant.Table 6.19 Typical Format for an FMEA WorksheetFMEA-PC (Primatech,Inc,Columbus,Ohio)HAZOOPtimizer (A.D.Little,Cambridge,Massachusetts)SAFEPLAN (Du Pont,Westlake Village,California)Standard word processing and spreadsheet software programs can also help analysts document the results
18、 of FMEA studies.An FMEA study is performed to address safety hazards to plant personnel in a DAP process.The DAP process schematic is presented in Figure 6.7.Each component of the reaction system is evaluated with the relevant information recorded in an FMEA table.The section of the FMEA table for
19、Control Valve B in the phosphoric acid solution line is presented in Table 6.21.ExampleL1F1L1F1PHOSPHORICACID STORAGETANKAMMONIASOLUTION STORAGE TANKUNLOADING STATIONSUNLOADING STATIONSLOADING STATIONSDAP STORAGE TANKENCLOSEDWORK AREAOUTDOORSFigure 6.7 DAP process schemativ for the FMEA example.Diammonium phosphate(DAP)PHOS.ACID excess off-spec.ProductNH3 excess residual NH3 releaseBOTH excess T PTable 6.21 Sample Pages from the FMEA Table for the DAP Process ExampleTable 6.21(contd)Table 6.21(contd)(續)