FMEA - Failure Modes and Effects Analysis + Criticality ...

1 1 FMEA - Failure Modes and Effects Analysis + Criticality (FMECA)A Core Component of RCMP resented By:Tim BairResearch EngineerThe Applied Research Laboratory at The Pennsylvania State University2 What is the Role of Maintenance? Maintenance helps to ensure that assets continue to fulfill their intended functions: Failure :System completely loses functionality or the operational capability falls below the minimum standarddesired by the user. Minimum Standard: initial designed capability or desired performance below design capability In order to determine the need for maintenance, the function and performance standards for the asset must be defined. Initial CapabilityMargin for DeteriorationAcceptable PerformancePerformanceFailure3 What is a FMEA? Failure Modes and Effects Analysis (FMEA) It is a tool that is an integral part of the RCM Process.

2 The FMEA process is a systematic methodto identify: Primary and secondary functions of the system and the Failure Modes that prevent the system from completing its designed purpose. Process Objective: Identify and prioritize the Failure Modes and the subsequent Effects to the system to help eliminate or minimize catastrophic and critical Failure Modes through the most appropriate type of maintenance methodology. Predictive Maintenance Preventative Maintenance No Scheduled Maintenance4 Sample FMECA Table5 The Major Elements of the Basic RCM Process RCM Establishment and Planning Analysis : Define the function and functional failures of a specific platform, system or component. Then conduct a Failure Modes and Effects Analysis Identify the Failure consequences Determine maintenance tasks and intervals. Analysis Audit Implementation Sustaining the RCM Program: RCM is a Living Program Implement a RCM management, training, benchmarking, and review process to provide feedback and measurement of progress toward asset management goals6 Determine Scope of Analysis The Scope of Analysis is where the systems and sub-systems to be analyzedare identified and a description indicating to what level of detail each will be analyzed.

3 The system will be partitioned, and the level and extent of Analysis necessary to meet program objectives is identified. Define reasonable boundaries so that the system includes the necessary inputs and outputs but is not so large that it is difficult to analyze. Include all Failure Modes that are reasonably likely to cause functional System and Boundaries: Aircraft Hydraulic System A system is a user defined group of: Components Systems Equipment that support an operational requirement. Boundaries are selected to divide a complex system into manageable sub-systems. A boundary or interface should define the inputs and outputs of the and Extent of the Analysis : How Deep Do You Drill Down? Hydraulic SystemHydraulic PumpsControl SurfacesAircraft Cracked Blade Broken Blade Corrosion Shaft Broken Coupling Broken No Coupling Lubrication Splines Broken Bolts Broken Inner Race Failure Outer Race Failure Element Failure Cage Failure Seal Failure Lubrication Failure Viscosity Breakdown Contamination Loss of Lubrication Material Failure Excessive WearRoot Cause of Failure AnalysisThe goal is to isolate the Failure mode to the lowest level that allows for the most effective application of the maintenance policy.

4 ShaftImpellorBearingsLubricationSealsCom ponentsMaintain LevelCBM Level9 Reliability Block Diagram: Fault Tree AnalysisHydraulic Pump/Turbine Engine: Total Loss of Fluid Flow Failure Mode 1 Left Pump Failure 2 Left Engine Failure 3 Shaft FailureBearing SeizureAir FailureFuel Failure010203 4 5 6 11 Fluid Leak 8 Right Pump Failure 9 Right Engine Failure 10 Shaft FailureBearing SeizureAir FailureFuel Failure040506 7 12 14 15 Fluid Leak 1310 Steps for the Analysis Process: Information and System Functions: What does the user need the system to do in its current operating context? Functional Failures: In what way can the system fail (or fail to fulfill its function)? the Failure Modes : What causes the failures? the Failure Effects : What happens when failures occur and what are the symptoms of Failure ? Failure Consequences:How and why does the Failure matter.

5 Frequency of occurrence Severity of the Failure modeReference: TACOM ILSC CBM+, Reliability Centered Maintenance Process Overview, C1061-03-000411 Defining Function What are the functions and associated desired standards of performance of the asset in its present operating context? Identify all primary and secondary functions of the asset or system in terms of performance. Primary Functions:Speed, Output, Storage Capacity, Product Quality Secondary Functions:Safety, Control, Containment, Comfort, Economy, Environmental Compliance Functional statements should contain a verb, an object and a performance standard. The turbine engine is designed to provide 65000 lbsof thrust @ 21000 rpm. The platform is designed to transport 100 soldiers and 10,000 lbs. of cargo at an maximum speed of 650 mph. Performance standards should be at a level desired for the operational Function Operating Context The operating context may influence the primary and secondary functions.

6 Operating Environment: The operating environment may be unique for one type of equipment, which may be different than other (like) equipment. Safety and Environmental Standards: Equipment may have different safety and environmental standards based on how they are operated with respect to humans. Regular or Intermittent Use: Does the equipment or platform deploy regularly or is it only used for unique circumstances ( cold weather kits, bridge layer platforms)? System Redundancies: With backup systems, one piece of equipment may operate continuously and the redundant system may be on FunctionPerformance Standard Many systems will have multiple performance standards. The engine must operate at 3000 RPM and 1000 HP continuously. Quantitative vs. Qualitative: be as precise as possible when defining a performance standard. Absolute standard: exact specification To contain 40 gallons of fluid or to contain fluid.

7 Variable standard: mean with upper and lower limits To contain an average of 40 gallons of fluid +/-1 gallon. Example: Hydraulic PTO Pump What is its function in its operating context? To be able to move hydraulic fluid on demand at a flow rate ranging from 550 to 650 cfm, at a pressure range from 600 to 2000 psig and at a temperature ranging from -50 F to +220 Function Hidden Function A function whose Failure does not become apparent to the operating crew under normal circumstances. Equipment Protective Devices (Safety) Provide a warning indicator of an abnormal condition Shut down for equipment in case of Failure (avoidance of catastrophic Failure ) Provide redundant control in case of primary control Failure Guards to prevent physical harm Example:Hydraulics What are the hidden functions? Relief valve must activate at 2000 psi (OEM setting for maximum payload) as a safety device from overloading the system.

8 Relief Valve Failure Mode: Due to normal valve wear (spring sag) the relief valve will begin to activate at 1600 psi, which will limit the maximum lift capability. This will result in a functional Failure of the hydraulic Functional Failure In what ways can a system fail to fulfill its function to the standard of performance required by the user? Performance standards for the asset must be well defined and agreed upon by operations and maintenance. Functional Failure : Once the function of the asset has been established, the inability of the asset to perform to the defined standard constitutes a Failure . List all failed states associated with each function. Total and Partial Failures Limit Exceedence (Operational Performance) Operational Metric Displays (Gauges and Indicators) Example: What are the Pump Functional Failures? loss of flow2.

9 No indication of operational parameters3. Flow below required rate4. Unable to contain fluid5. Fluid pressure out of range6. Inability to control pump operation7. Fluid temperature above require range16 Defining Failure Modes What causes each functional Failure ? List all Failure Modes reasonably likely to cause each functional Failure . Decreasing Capability: Deterioration: fatigue, corrosion, wear and tear Lubrication Failures: root cause of many failures Contamination: causes excessive wear Human Errors: manual devices not properly operated Desired Performance exceeds Capability: Intentional or Unintentional Sustained or Intermittent17 Defining Failure Modes Failure Modes should be defined in enough detail to select the most appropriate Failure management policies. Failure Modes should be identified in terms of cause and effect if possible.

10 Bearing Failure : caused by manufacturing defect or lubrication loss need to address both separately. List Failure Modes with the highest probability of occurrence. Start with Failure Modes that have occurred on similar equipment Use experience to estimate which Failure Modes are most likely to occur. List Failure Modes that result in the most severe consequences. Engine coolant pump Failure is more severe than the AC pump Failure . Do not get bogged down with too many Failure Modes . SAE Standard Stipulates: Only Failure Modes that are likely to occur in the operating context. Example: What are the Pump Failure Modes for Total Loss of Flow1. Pump Shaft Failure2. Failure of Lubrication(foreign material in the fluid)3. Pump Impellor of the Seal 5. PumpBearing Seizure (manufacturing defect)18 Defining Failure Effects What are the functional consequences when each Failure mode occurs?