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Identification of component performance degradations caused by ageing using expert panels

Identification of component performance degradations caused by ageing using expert panels. MIRELA NITOI, MARGARIT PAVELESCU*, DUMITRU CRISTEA mirela.nitoi@nuclear.ro. OVERVIEW. Ageing considerations Ageing Failure Mode and Effect Analysis Case study Conclusions. Background.

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Identification of component performance degradations caused by ageing using expert panels

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  1. Identification of component performance degradations caused by ageing using expert panels MIRELA NITOI, MARGARIT PAVELESCU*, DUMITRU CRISTEA mirela.nitoi@nuclear.ro

  2. OVERVIEW • Ageing considerations • Ageing Failure Mode and Effect Analysis • Case study • Conclusions ICSI, Calimanesti-Caciulata, 29-31 October 2008

  3. Background Any facility has thousands of different components, all of them being affected to some degree by ageing It is not desirable nor necessary to evaluate ageing of all individual components A systematic screening process can identify and prioritize the components for which ageing impact should be evaluated ICSI, Calimanesti-Caciulata, 29-31 October 2008

  4. Technical issues • which components are susceptible to ageing degradation that could adversely affect facility safety? • what are the degradation processes of materials and components that could, if unchecked, affect facility safety? • are current methods for testing, inspection, surveillance, maintenance and replacements adequate to detect and mitigate ageing problems before they significantly affect facility safety? • what kinds of records and documentation are needed to support these kind of analyses? ICSI, Calimanesti-Caciulata, 29-31 October 2008

  5. Expert opinions – identification of significant safety components, possible root causes and equipment problems which can be caused by ageing, as the effects that ageing phenomenon have on component performances. ICSI, Calimanesti-Caciulata, 29-31 October 2008

  6. Expert assessment • expertise in a full spectrum of relevant technical areas: PSA, component reliability, materials behavior and failure analyses, in-service inspection, operations and maintenance, safety, regulatory, ageing and life extension issues. Necessary information for a clear judgment (list of components, prioritization criteria, prioritization methodologies, and technical support material) • assess the effects of plants ageing • prioritize the components taking into account their risk significance of ageing • incorporate an understanding of ageing and its effects (define the list of components susceptible to ageing and the contribution of SSC ageing to plant risk) • assess the adequacy of current practices for managing component ageing within acceptable levels of risk ICSI, Calimanesti-Caciulata, 29-31 October 2008

  7. Methods evaluate the potential of ageing degradation to cause component failure It involves another screening process, related to ageing mechanism, and requires knowledge of material degradation properties and operating stressors for a specific component Screening after the component susceptibility to age related failure ICSI, Calimanesti-Caciulata, 29-31 October 2008

  8. JRC APSA Network Incorporating Ageing Effects into Probabilistic Safety Assessment (APSA)- operating under the JRC FP-6 Institutional Work Program “Analysis and Management of Nuclear Accidents” by Sector of Probabilistic Risk and Availability Assessment of Energy Systems, IE, Petten • Evaluation of available methods and approaches on incorporation of ageing effects into PSA; • Identification of necessary information on ageing issues to be addressed in PSA tools for specific PSA applications; • Demonstrations of the impact of different levels of ageing information included in a PSA model on the overall PSA results; • Discussion of reliability models and data to be used for modeling of ageing effects in PSA models; • Institute for Nuclear Research Romania is partner since September 2004. to develop and operate a network of interested partners (operators, industry, research, academia) on the topic of incorporating ageing effects into PSA and use of APSA applications. ICSI, Calimanesti-Caciulata, 29-31 October 2008

  9. Ageing Failure Mode and Effects Analysis (AFMEA) • study the results or effects of item failure caused by ageing, on system operation and classify each potential failure according to its severity • permits identification of stress factors and provides recommendation for their decreasing • specifies ageing failure modes for a particular component • identifies failure effects caused by ageing • prioritizes system vulnerabilities to ageing • identifies the modalities in which the ageing failure can be detected • provides justification for improving testing and maintenance activities All recommended actions which result from the FMEA shall be evaluated for implementation or documented justification for no action. ICSI, Calimanesti-Caciulata, 29-31 October 2008

  10. AFMEA Procedure System overview –Grouping of components -Identification of stress factors for each component and associated ageing mechanism Identification of all potential ageing failure modes of each component -Specification of their effect on the immediate function or item, on the system, and on the mission to be performed –Determine failure detection methods Evaluation of each ageing failure mode in terms of the worst potential consequences which may result Prioritization of components, Recommend actions Documentation of analysis ICSI, Calimanesti-Caciulata, 29-31 October 2008

  11. AFMEA WORKSHEET INFORMATION • General administrative information (system, analyst) • Identification number/ Item name • Operational Phase • Failure mode • Failure cause/ failure mechanism • Failure effect • Risk assessment (Severity / Probability / Risk) • Action required / remarks ICSI, Calimanesti-Caciulata, 29-31 October 2008

  12. TRIGA Reactor - Secondary Cooling Circuit Function: • transports the heat from the primary cooling circuit – by means of transfer surfaces of the heat exchangers – to cooling towers, where is dissipated into the atmosphere. ICSI, Calimanesti-Caciulata, 29-31 October 2008

  13. Questions to be answered For each components group • What stress factors are you consider as specific for this group? • What are the corresponding ageing mechanisms, which can be induced by this kind of stressors? • What failure modes are induced by these ageing mechanisms? • What are the effects caused by the ageing failures? • What is the manner of discovery for the ageing failures (detection issues)? • How effective are, in your opinion, current activities dedicated to mitigation of ageing effects (maintenance, replacement and repair)? ICSI, Calimanesti-Caciulata, 29-31 October 2008

  14. Active component-types of failures considered Critical failures - loss of function of the component • change of state without the command • failure to function on demand Degraded failures: erratic output, slow operation, improper response (partially open/close, oscillations) Incipient failures • local inspection (case of overheating, leaks, noise, vibration, cracks) • testing (case of output above or below specified limits while in standby mode of operation) • monitoring ICSI, Calimanesti-Caciulata, 29-31 October 2008

  15. Passive component-types of failures considered Critical failures • breach of pressure or static fluid boundary (major leaks) • loss of energy transport or exchange capability (blocked or stopped flow, loss of heat transfer capability) • loss of structural integrity Degraded failure: minor leaks, restricted flow, reduced heat transfer capability Failures are discovered through: • testing (case of failure of diminished ability to transmit or retain energy) • local inspection (case of leaks, vibration, odor, cracks) • monitoring ICSI, Calimanesti-Caciulata, 29-31 October 2008

  16. The consequences of failure were evaluated by three criteria and associated indices: • severity of potential ageing failure (S), • likelihood of occurrence of a potential ageing failure (O) • the chance of detection within the process (D) Each index ranges from 1 (lowest risk) to 10 (highest risk). For each index were developed tables for allocation of value. • The overall risk of each failure - Risk Priority Number (RPN) RPN = S × O × D ICSI, Calimanesti-Caciulata, 29-31 October 2008

  17. Results list of components which are sensitive to ageing (the components are prioritized considering the severity of components failure, the probability of failure occurrence and also the probability of detection). Ageing sensitivity: HIGH– high RPN value (higher then 150) - High value for remaining sensitivity to ageing, after considering the maintenance effects- very sensitive component (high degradation rate) MEDIUM – RPN value between 100 and 150 - ageing has a moderate impact on component operability LOW – low RPN value (lower then 100) - LOW value for remaining sensitivity to ageing, after considering the maintenance effects - ageing has a low impact ICSI, Calimanesti-Caciulata, 29-31 October 2008

  18. The cables and trays are subject to ageing by loosening of cable tray supports, cable insulation ageing and loosening of cable terminations or connectors. Thermal ageing causes decrease in strength properties, hardness, ductility and toughness. Cable loss could result in associated equipment being out of operation. Cable - Includes cable and terminations to equipment. Stress factors: Electrical stress Ageing mechanisms: Thermal ageing Insulation ageing Possible failures: DEFORMED OPEN CIRCUIT SHORT CIRCUIT SHORT TO GROUND Ageing effects: EXAMPLE Ageing maintenance practice: There are no direct means to determine a cables true life expectancy (before insulation total break down). No maintenance practice. Routine inspections. Replacement of certain cables may be required based on inspection. ICSI, Calimanesti-Caciulata, 29-31 October 2008

  19. Pump Fails while running – HIGH RPN Fails to start and Inadequate Flow – MEDIUM RPN External leaks – LOW RPN Medium detection probability index, low occurrence probability failure index (due to maintenance activities). ICSI, Calimanesti-Caciulata, 29-31 October 2008

  20. Conclusions • the highest susceptibility to ageing was identified for the following components: manual valves, cables, pipes, fan motors • some components could appear as being sensitive to ageing degradation (due to stressors), but they are classified as MEDIUM or LOW sensitive due to maintenance efficiency and easily detection of ageing signs (performance monitoring) • maintenance is very important issue to be taken into account, even if not always preventive maintenance programs are sufficient to control the kinetic of ageing mechanism ICSI, Calimanesti-Caciulata, 29-31 October 2008

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