Stiction webinar 2013


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Stiction webinar 2013

  1. 1. Improving Reliability & SafetyPerformance of Solenoid Valvesby Stroke Testingexida Web SeminarAudio is provided via internet. Please enable your speaker(in all places) and mute your microphone.There is a Q&A tab at the top of your screen. Please use thismechanism to type any questions you may have at any time.Questions will be read and answered.A recording of this session and a copy of the slides will be postedon the exida website and made available for you.Copyright © 2000-2013 exida
  2. 2. Improving Reliability & SafetyPerformance of Solenoid Valvesby Stroke TestingWeb Seminar April 24, 2013Loren L. StewartexidaSellersville, PA USAAudio is providedvia internet.Please enableyour speaker (inall places) andmute yourmicrophone.Copyright © 2000-2013 exida
  3. 3. Loren StewartBioLoren Stewart graduated from Virginia Tech witha BSME.She has 5 years of professional experience. Shecurrently works for exida consulting as a safetyengineer, focusing on the mechanical aspects oftheir customers. Along with assessing the safetyof products and creating FMEDAs and reports,she researches stiction and is creating adatabase for the 2H initiative according to 61508.Copyright © 2000-2013 exida
  4. 4. 4William Goble has over 40 years of professional experience. Hisareas of expertise include safety and high availabilityautomation systems, automation probabilistic analysis, newproduct development and market analysis. He developed manyof the techniques used for probabilistic evaluation of safety andhigh availability automation systems. He was formerly Director,Critical Systems at a successful North American safetycompany where job duties included marketing, research anddevelopment including computer design, software design anddevelopment and engineering project management. He haswritten three books on topics of safety and reliability modeling.He is a fellow member of ISA. He has published many papersand magazine articles. Dr. Goble has a BSEE from Penn State,a MSEE from Villanova and a PhD from Eindhoven University ofTechnology in Eindhoven, Netherlands.Copyright © 2000-2012 exidaDr. William Goble
  5. 5. network of excellence in dependableautomationEuropeAsia PacificNorth AmericaDevelopmentformer Development Managers(Siemens Moore )Instrumentation Engineers(UOP, BAYER, PDVSA, etc.)Application Design + OperationAfricaSafety Certificationformer TÜV Managersformer Safety PLC Product Manager(Siemens)Copyright © 2000-2013 exida
  6. 6. Main Product / Service CategoriesConsultingProcessSafety (IEC61511, IEC62061, ISO26262)AlarmManagementControlSystemSecurity (ISAS99)ProductCertificationFunctionalSafety (IEC61508)ControlSystemCyber-SecurityNetworkRobustness(Achilles)TrainingProcessSafetyControlSystemSecurityOnsiteOffsiteWebSecurityDevelopmentEngineeringToolsexSILentia(PHA Import,SIL SelectionLOPASRSSIL Verification)Safety CaseFMEDASCAReferenceMaterialsDatabasesTutorialsTextbooksReferenceBooksMarketStudiesProfessionalCertificationCFSECFSPControlSystemSecurityExpert(CSSE)Copyright © 2000-2013 exida
  7. 7. Engineering Tools SILAlarm - Alarm Management Tool PHAx – HAZOP Tool / Import SIL Selection Tool Hazard Matrix or Risk Graph Layers of Protection Analysis built-in Cost effectively implement functional safety standards SRS Tool SIL Verification Tool Direct average calculation engine Instrumentation failure database built-in Variables include reality – test coverage, service Proof Test Tool SILStat – Field Data Collection ToolCopyright © 2000-2013 exida
  8. 8. Reference Materialexida authored mostindustry references forautomation safety andreliabilityexida authored industrydata handbook onequipment failure dataexida authored the mostcomprehensive book onfunctional safety in themarket.www.exida.comCopyright © 2000-2013 exida
  9. 9. Improving Reliability &Safety Performance ofSolenoid Valves by StrokeTestingCopyright © 2000-2013 exida
  10. 10. Overview• Mechanical Failure Rates• Cycle Testing – scaling cycle failure values• What is Stiction?• Evidence of Stiction Analyzed• Assessing Solenoid Valve Stroke Testing• Implications of Stroke Testing and Stiction• Recommended Best Practices Copyright © 2000-2013 exida
  11. 11. Mechanical Device Failure Rates• Cycle Testing • Accelerated motion testing until failure or a given number of cycles, used to simulate years• For high or constant demand applications only • FMEDA – Failure Modes Effects and Diagnostic Analysis• Identifies the failure mode within the device which could relate those failures to the operation of the safety instrumented function• For both high and low demand ‐ all applicationsCopyright © 2000-2013 exida
  12. 12. Cycle Testing• Cycle testing is used to estimate failure rates in dynamic (high demand) applications.  • Assumption is that premature wearout is the dominant failure mechanism and that no other failure mechanisms are significant.Copyright © 2000-2013 exida
  13. 13. Cycle Test ScalingCopyright © 2000-2013 exida•A cycle test is done on a set of products(>20) until 10% of the units under test fail.•The number of cycles until failure is calledthe B10 point.
  14. 14. 14Copyright © 2000-2011 exidaB10d Failure Data•Table of examplevalues from ISO13849-1: 2006
  15. 15. Cycle Test ScalingCopyright © 2000-2013 exida•The B10 number of cycles is converted to a timeperiod by knowing the cycles per time period in anyparticular application.•A failure rate is calculated by dividing the 10%failure count by the time period.
  16. 16. High Demand CertificationsSome certificationsare based on failuredata derived from“cycle testing” orother methods thatrequire frequentmovement ofelectro-mechanicalproducts. Thisassessment is notvalid for typical lowdemand processapplications.Copyright © 2000-2013 exida10 demandsper year =870 hours percycle
  17. 17. What time period is valid? Copyright © 2000-2013 exida•A failure rate is calculated by dividing the 10%failure count by the time period.•One year? 8760 hrs.•One month? 730 hrs.•One week? 168 hrs.•How long can a device with a seal remainmotionless before other failure mechanismsbecome significant such that premature wearoutno longer dominates?
  18. 18. What is Stiction?• Stiction – Static + Friction• The resistance to the start of motion usually measured as the difference between the external force being applied in order to over come the static friction and the force to maintain movement between the two contacting or working surfaces.• Can result from: corrosion, cold welding, break down of lubrication, build‐up of deposits, chemical reactions, breakdown of the sealing components…Copyright © 2000-2013 exida
  19. 19. Who cares about Stiction?• Started studying stiction to determine the maximum time period before stiction impacts failure rates.  • This is the maximum time period for scaling cycle test results.Copyright © 2000-2013 exida
  20. 20. Evidence of Stiction Analyzed• Expert Knowledge• Technicians and engineers routinely work on valves• Stiction occurring after a month or more• O‐ring Manufacturers Guides• Stationary between 1 week and 1 month• “Delay between cycles” plateaus at approximately 300 hours • Experimental Study • Studies conducted on lubrication thickness in magnetic thin‐filmed disks. • As equilibrium rest time increases, stiction increases to a plateau or around 275 hours, depending on lubrication type • ISO 13849• “Valve must be operated at least once per week or once per shift to insure the intended function” Copyright © 2000-2013 exida
  21. 21. Impact of Stiction • We discovered that stiction becomes significant after one week therefore never scale cycle test results beyond 275 hours.• We also realized that improvements in safety and reliability can be obtained with stroke testing.Copyright © 2000-2013 exida
  22. 22. Solenoid Background• Solenoid ValvesOpen Solenoid Valve Closed Solenoid ValveCross section of an open and closed solenoid valve, showing how the plunger movement directly controls the process fluid flow. Copyright © 2000-2013 exida
  23. 23. Copyright © 2012 LLCAssessing Solenoid Valve Stroke TestingPFDavg
  24. 24. Impact of Stiction • We also discovered that once stiction is overcome via movement, bonds creating the binding are destroyed and must start reforming.• Even with a small movement.Copyright © 2000-2013 exida
  25. 25. Assessing Solenoid Valve Stroke TestingValues of failure rates from the solenoid valve(manufacturer X, model Y) used in computing PFDavg( ) p g gParameter failures/109hrs operationλDstiction 103.7λDnon-stictionDetectable 84.3λDnon-stictionUndetectable 1.9Copyright © 2000-2013 exida
  26. 26. Assessing Solenoid Valve Stroke Testing• Case 1: No Valve Stroke Testing• λD = λDStiction + λDnon-StictionDetectable + λDnon-StictionUndetectable• λD = 103.7 + 84.3 + 1.9 = 189.9 fits• Case 2: Infrequent Valve Stroke Testing• λD = λDStiction + λDnon-StictionDetectable + λDnon-StictionUndetectable• λD = 103.7 + 84.3 + 1.9 = 189.9 fits• Case 3: Frequent Valve Stroke Testing• λD = λDnon-StictionDetectable + λDnon-StictionUndetectable• λD = 84.3 + 1.9 = 86.2 fitsCopyright © 2000-2013 exida
  27. 27. Implications of Stoke Testing and StictionCase 1: proof testing every 2 yearsCase 2: valve stoke testing performed once every 6 monthsCase 3: valve stoke testing performed once every weekCopyright © 2000-2013 exidaPFDPFDavg
  28. 28. Implications of Stoke Testing and StictionCase 3: valve stoke testing performed once every week0.00E+002.00E‐044.00E‐046.00E‐048.00E‐041.00E‐031.20E‐030 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6PFD avg (t)Time in yearsCase 3Upper Limit SIL 3Copyright © 2000-2013 exida
  29. 29. Implications of Stroke Testing and StictionCopyright © 2000-2013 exida
  30. 30. Recommended Best Practices• Implement automatic or semi‐automatic stroke testing in final element designs.• Make certain that the movement in actuator‐valve assemblies is small so as to not cause process disturbances.• Do not let actuator pressure drop too far as stiction bonds might let loose can cause a false trip.Copyright © 2000-2013 exida
  31. 31. Recommended Best Practices• Begin valve stroke testing on a weekly basis unless maximum cycle ratings are below 52 * useful life (years)• After a few months of testing, if the number of times the valve is found stuck, cut the testing period in half• Repeat the testing procedures until an optimum test interval is identified.Copyright © 2000-2013 exida
  32. 32. Recommended Best Practices• Valve stroke testing can have significant beneficial impacts on safety • Most beneficial practice would be a frequent valve stroke testing of once per week or more.• We believe there is a reduction in false trip rate as well but need more research.Copyright © 2000-2013 exidaFuture Web Seminar: Design Options forPartial Stroke Testing of Final ElementAssemblies, May 2013
  33. 33. Questions ? Comments?More Information:1. Free Web Seminars – see www.exida.com2. White Papers3. Safety Automation Equipment List – www.sael-online.com4. Books:, www.exida.comEmail me at: Lstewart@exida.comCopyright © 2000-2013 exida
  34. 34. Copyright © 2000-2013 exida
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