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Since the beginnings of the European American Workshops (EAW) in 1997, the aim was to gather the experts in NDE reliability and discuss burning topics with the aim of identifying crucial problems and suggesting ways to move forward. This was usually achieved during the so-called break-out sessions, in which predetermined topics were discussed. During the 5th EAW, held in Berlin in 2013, this approach was replaced by an Open Space Technology (OST) approach. The benefit of this approach is seen in the freedom of topic choices, i. e., the topics are not predetermined but rather arise at that moment in that space and by the participants choice. The following topics arose: new reliability methods (Bayesian, MAPOD,
), structural health monitoring, definition of requirements of NDE by customer versus provider, what value of POD is good enough?, human factors, manual versus automated inspection, and basic concepts of reliability of NDE. The participants were encouraged to walk from one session to another and openly express their opinions. These were in the end summarized by a chosen group of moderators and presented in this paper.
Der Artikel beschreibt eine arbeitspsychologische Analyse des Einflusses der menschlichen Faktoren auf die Zuverlässigkeit zerstörungsfreier Prüfungen (ZfP). Im Zeitraum von 5 Jahren wurde eine Serie von Untersuchungen zur wiederkehrenden Prüfung in Kernkraftwerken sowie zur Prüfung von Komponenten für die Endlagerung von radioaktivem Abfall durchgeführt. Dieser Beitrag gibt einen Überblick über vier Studien, diskutiert ausgewählte experimentelle Ergebnisse, und schlägt sich daraus ergebende Möglichkeiten zur Optimierung des ZfP-Verfahrens, der Prüfanweisung sowie zur Schulung des Personals vor. Die experimentellen Ergebnisse haben gezeigt, dass sowohl hoher Zeitdruck als auch hohe psychische Arbeitsbeanspruchung die Qualität des Prüfungsergebnisses negativ beeinflussen. Auffällig waren die Einflüsse der Einteilung des Arbeitsplans, der Kommunikation, der Prüfanweisung, der Prüfaufsicht sowie der Demonstrationsübung. Die abgewandelte Fehlermöglichkeits- und Einflussanalyse (Failure Mode and Effects Analysis FMEA) wurde zur Identifizierung potentieller menschlicher Risiken während der Datenaufnahme und deren Auswertung benutzt. Darauf basierend werden verschiedene Präventivmaßnahmen, wie z.B. menschliche Redundanz und Automatisierung vorgeschlagen, sowie sich daraus möglicherweise ergebende Probleme diskutiert. Die experimentellen Ergebnisse haben gezeigt, dass menschliche Redundanz bei kritischen Anwendungen, wie beispielweise der Fehleridentifizierung, zu anderen Fehlerquellen führen kann, wie sozialem Faulenzen bei den Prüfern. Die Verwendung automatisierter softwarebasierter Entscheidungshilfen zur Fehlererkennung bzw. Fehlergrößenbestimmung kann zu übersteigertem Vertrauen in das automatisierte System (automation bias) durch die Prüfer und somit zu Fehlentscheidungen führen. Dadurch kann die Zuverlässigkeit der Prüfung in ungewollter Weise beeinflusst werden. Um die Zuverlässigkeit und Sicherheit der technischen Prozesse zu gewährleisten ist es wichtig, als Hauptfehlerquelle nicht mehr nur das einzelne Individuum zu sehen, sondern ebenfalls die Organisation zu berücksichtigen.
This paper gives an introduction to the field of human factors with the focus on their influence on the reliability of NDT in the nuclear energy production (in-service inspections) and final storage of highly radioactive nuclear waste. A set of methodological tools has been developed in the scope of three projects, namely: 1) a theoretical model describing potential human factors influencing manual ultrasonic inspection performance during inservice inspections in nuclear power plants; 2) a method for identifying potential human errors during acquisition and evaluation of data gathered with mechanized ultrasonic, radiographic and eddy-current systems, as well as visual testing with a remote camera (Failure Modes and Effects Analysis, FMEA); and 3) use of eye tracking methodology to optimize existing procedures and practices. The experimental results have shown that time pressure, mental workload and experience influence the quality of the inspection performance. Noticeable were influences from the organization of the working schedule, communication, procedures, supervision and demonstration task. Implementing human redundancy in critical tasks, such as defect identification, as well as using an automated aid (software) to help operators in decision making about the existence and size of defects, could lead to other kinds of problems, namely social loafing (excerpting less effort when working on tasks collectively as compared to working alone) and automation bias (uncritical reliance on the proper function of an automated system without recognizing its limitations and the possibilities of automation failure) that might affect the reliability of NDT in an undesired manner.
The human factors approach relies on understanding the properties of
human capability and limitations under various conditions and the application of that
knowledge in designing and developing safe systems. Following the principles of
MTO (Man Technology Organization) approach, emphasis should be given to the
way people interact with technical as well as organizational systems.
A model describing human factor influences in relation to the performance shaping
factors and their effect on the manual ultrasonic inspection performance had been
built and a part of it empirically tested. The experimental task involved repeated
inspection of 18 flaws according to the standard procedure under no, middle and
high time pressure. Stress coping strategies, mental workload of the task, stress
reaction and organizational factors have been measured. The results have shown that
time pressure, mental workload and experience influence the quality of the
inspection performance. Organizational factors and their influence on the inspection
results were rated as important by the operators. However, further research is
necessary into the effects of stress.
The human factors approach relies on understanding the properties of human capability and limitations under various conditions and the application of that knowledge in designing and developing safe systems. Following the principles of the MTO (Man Technology Organisation) approach, emphasis should be given to the way people interact with technical as well as organisational systems.
A model describing human factor influences in relation to the performance shaping factors and their effect on manual ultrasonic inspection performance had been built and a part of it empirically tested. The experimental task involved repeated inspection of 18 defects according to the standard procedure under no, middle and high time pressure. Stress coping strategies, the mental workload of the task, stress reaction and organisational factors have been measured. The results have shown that time pressure, mental workload and experience influence the quality of the inspection performance. Organisational factors and their influence on the inspection results were rated as important by the operators. However, further research is necessary into the effects of stress.
Die übergeordnete Zielsetzung unserer Untersuchung bestand darin,
am Beispiel von Prüfungen mit Ultraschall eine belastbare Aussage zum Einfluss der Arbeitsbedingungen des Prüfers auf die Qualität der Ergebnisse von zerstörungsfreien Prüfungen zu ermitteln und Möglichkeiten zur Minimierung ungünstiger Einflussfaktoren aufzuzeigen.
Der Schwerpunkt der Untersuchung wurde auf die manuelle Ultraschallprüfung gelegt und der Faktor 'Zeitdruck' (in drei Stufen variiert) als die zu variierende physische Einflussgröße gewählt. Die Variation des Faktors Zeitdruck wurde gemäß dem Prozessmodell von der Erhebung psychologischer Faktoren, die das Individuum und die Organisation beschreiben, begleitet.
Die Ultraschallprüfungen erfolgten mit zehn Prüfern am Großbehälter und an Vergleichskörpern mit eingebrachten Testfehlern (Nuten, Risse). Die ausgewählten Fehler waren typisch für Prüfaufgaben, die bei wiederkehrenden Ultraschallprüfungen in Kernkraftwerken von den Prüfern zu lösen sind. Die Prüfaufgabe bestand darin, die in den vorgegebenen Prüfabschnitten vorhandenen Reflektoren aufzufinden und deren Amplituden, Ortskoordinaten und Längenerstreckungen zu ermitteln. Als Bewertungsmaßstab für die Qualität der Prüfaussage und für den Einfluss des menschlichen Faktors diente die Präzision der gemessenen Werte. Die Ergebnisse zeigen einen hohen Einfluss des menschlichen Faktors auf das Prüfergebnis und eine Einwirkung des Zeitdrucks besonders auf die Präzision der Messwerte. Hierbei war die Wirkung des individuell wahrgenommenen Zeitdrucks zusammen mit der psychischen Arbeitsbeanspruchung signifikant. Es wurde unter anderem herausgearbeitet, dass durch eine gute Vorbereitung auf die Prüfung, z.B. durch die sorgfältige Einweisung und ein vorgeschaltetes Fertigkeitstraining an Vergleichskörpern, die Zuverlässigkeit der Prüfergebnisse verbessert werden kann.
Insgesamt hatte der Faktor 'Organisation' neben der 'Erfahrung' einen hohen Einfluss auf das Leistungsvermögen der Prüfer.
Die Projektergebnisse wurden im Abschlussbericht des Forschungsvorhabens SR2514 dargestellt, es wurden drei Empfehlungen zur Vorbereitung und Einweisung der Prüfer, zur Stärkung der Verantwortung der Prüfaufsicht und zum 4-Augen-Prinzip formuliert. Die Empfehlungen wurden in der KTA- Regel 3201.4 'Komponenten des Primärkreises von Leichtwasserreaktoren; Teil 4: Wiederkehrende Prüfungen und Betriebsüberwachung (RÄE Fassung 2010-11)', umgesetzt.
Human factors approach to the reliability of NDT in nuclear waste management in Sweden and Finland
(2010)
Nuclear power industry has the responsibility to manage and dispose of all radioactive waste from its
plants. Finnish Posiva and Swedish SKB are leading in the world in the development of disposal of
spent nuclear fuel. Their method consists of encapsulating spent nuclear fuel in copper canisters and
depositing them in the bedrock at a depth of about 500 meters for the next 100 000 years, leaving the
radioactivity to decrease naturally through the decay of the radioisotopes in it. The copper canisters,
consisting of a copper tube, a lid and a bottom (which make the outer shell) and an insert made of a
cast iron, need to be inspected for their structural integrity to ensure no critical defects are present in
the materials and welds that could lead to a leakage of the waste into the environment. Data acquired
by 4 different non-destructive testing (NDT) methods (i.e. UT, ET, RT and VT with a remote camera)
are evaluated by skilled human operators and therefore could be subject to human error.
Human Factors approach lies in identifying potential errors made by the human, their causes
and ways of preventing them. A customized Failure Modes and Effects Analysis (FMEA) was
conducted to anticipate possible human failures during the data evaluation. The results led to
designing several experiments (e.g. diffusion of responsibility within the 4-eye principle, over trust in
automated systems) which are being experimentally tested in ongoing projects. The results are
expected to lead to the optimization of the procedures followed by the NDT operators and
consequently to the improvement of the overall NDT reliability.
Für eine ganzheitliche Betrachtung der Sicherheit bei der zerstörungsfreien Prüfung (ZfP) ist es unvermeidlich neben der Technik auch den Prüfer und die Prüforganisation einzubeziehen. Die Prüfung der Unversehrtheit von Endlagerbehältern ist eine eine sicherheitstechnisch wichtige Anwendung. Die Betreiber der geplanten finnischen und schwedischen Endlager, Posiva und SKB, kapseln den radioaktiven Abfall in Kupferkanistern ein und deponieren die Kanister dann in Felsgestein in einer Tiefe von ca. 500m. Die Kanister bestehen aus einem zylinderförmigen Kupfermantel mit einem Deckel und einem Boden, die zusammen die Außenumhüllung ergeben sowie einer Gusseisenmatrix für die Brennstäbe. Alle Komponenten werden auf ihre Dichtheit bzw. strukturelle Unversehrtheit mittels zerstörungsfreier Prüfmethoden geprüft, um sicher zu stellen, dass im Material und in den Schweißnähten keine kritischen Defekte vorhanden sind, die zu Freisetzungen in die Umgebung führen könnten. Vier ZfP Methoden (Ultraschall-, Wirbelstrom- und radiographische Prüfung, und die visuelle Prüfung anhand einer Kamera) werden mechanisiert durchgeführt, die gewonnenen Daten werden von qualifizierten Fachleuten ausgewertet und bieten so die Möglichkeit, dass Fehler entstehen.
Das 'Human Factor'- Untersuchungskonzept besteht aus der Identifizierung potenzieller menschlicher Fehler, deren Ursachen und Präventionsmethoden. Mit Hilfe einer abgewandelten FMEA (Failure Modes and Effects Analysis) wurden mögliche Risiken identifiziert, die die Wahrscheinlichkeit für das Auftreten menschlicher Fehler bei
der Datenauswertung erhöhen. Einige dieser Risiken sind beispielsweise
Verantwortungsdiffusion beim 4-Augen-Prinzip, Übervertrauen in die Technik bei der automatischen Identifikation von Defekten sowie der Aufmerksamkeitsverlust bei dynamischer Bildbetrachtung. Deren Wirkung wird derzeit experimentell überprüft, um Ansatzpunkte für Optimierungen zu ermitteln und damit die Gesamtzuverlässigkeit des Systems zu verbessern.
Reliability of Routine Radiographic Film Evaluation - an Extended ROC Study of the Human Factor
(2002)
Many radiographic exposures and film evaluations are made daily in a typical industrial NDT laboratory. But questions remain regarding the precise probability of detecting discontinuities, including the reliability of each individual inspector or laboratory. Although most experienced inspectors of the laboratories evaluate each radiograph, the actual quantitative reliability of each of these inspectors remains unknown.
In order to estimate the performance of representative inspectors and laboratories involved in NDE, volunteer laboratories from Croatia and Hungary conducted a series of round-robin inspections using X-ray films of welds. While the RRT is still in progress, the authors try to summarize the results of the second round and discuss the evaluation method. The results of the first round had been reported already. The focus is here to present the new results in terms of additional inspectors and a new more field oriented evaluation scheme.
So far the results of a total of 35 inspectors of the different laboratories were evaluated. Those inspectors were selected who have done usually the work of radiographic film interpretation. They have from a half up to 35 years professional experience. For better overview we created four groups: maximum 4 year-experience, from 5 to 12 year-experience, from 15 to 25 year- experience and from 26 to 35 year-experience.
Discussing the circumstances of the RRT with the participants, many of them expressed, they could not exactly follow the prescription of the test. According to their professional experience the small discontinuities can be omitted because of the strictest acceptance level accept them. So the most experienced evaluators did not write the small gases and slags into the list, which yield a wrong reliability of detection. As a consequence we should accomplish two types of evaluation: taking into consideration of all discontinuity and only the bigger once they are over the acceptance level.
In addition we analyzed the true values in a critical review. These developments were made and the new results of the evaluation of the testers were more precise and reliable.
The corresponding results are evaluated and presented in a ROC diagram where the p(TP) is plotted against the p(FP). The p(TP) means the probability of a true positive indication (correct defect finding) and p(FP) means the probability of a false positive (false alarm) indication. From the mean value of all inspectors maximum operation points we can estimate a representative overall reliability in terms of a correct indication rate of about 68 % (64 % new) and a false call rate of about 17 % (8 % new). This is a reasonable result within the strict 1 cm score.
Statistical design of experiments applied to tests of metal detectors used for mine detection
(2006)
Trial Design for Testing and Evaluation of Metal Detectors Used in Humanitarian Landmine Clearance
(2006)
For inspection of thick-walled (50mm) copper canisters for final disposal of spent nuclear fuel in Sweden, ultrasonic inspection using phased array technique (PAUT) is applied. Because thick-walled copper is not commonly used as a structural material, previous experience on Phased Array Ultrasonic Testing for this type of application is limited. The paper presents the progress in understanding the amplitudes and attenuation changes acting on the Phased Array Ultrasonic Testing inspection of copper canisters. Previous studies showed the existence of a low pass filtering effect and a heterogeneous grain size distribution along the depth, thus affecting both the detectability of defects and their "Probability of Detection" determination. Consequently, the difference between the first and second back wall echoes were not sufficient to determine the local attenuation (within the inspection range), which affects the signal response for each individual defect. Experimental evaluation of structural attenuation was carried out onto step-wedge samples cut from full-size, extruded and pierced&drawn, copper canisters. Effective attenuation values has been implemented in numerical simulations to achieve a Multi Parameter Probability of Detection and to formulate a Model Assisted Probability of Detection through a Monte-Carlo extraction model.
The focus of NDT reliability research in the past was in the field of two high risk industries: (atomic) power plants and aircrafts. The responsible organizations have been well aware of the risks and founded projects to understand and optimize critical steps during production, operation and maintenance. But the use of NDT is not limited to these two fields. The risks during operation of chemical plants, trains or windmills are different from the area above but evident. The coverage by legal regulations is relatively low. Instead of this owner responsibility, product liability and financial issues are the driving forces to do inspections and to use non-destructive testing. The different targets and financial issues influence the practice of NDT-inspections. A survey of this practice and its results are shown.
Analyzing the reliability of non-destructive tests using the modular modell - a practical approach
(2016)
Non-destructive testing is an important tool to guarantee the safety of railway traffic.
The infrastructure with tracks, switches and sleepers is regularly tested, the
locomotives and wagons with their wheels, bogies and axles as well. Many years of experience and some events lead in Germany to a good practice in testing the railway components. Now, European authorities are drafting a system of common requirements and standards for the European Railway Market. The German practice combines an intensive training of the NDT-personnel including sufficient time for practical exercises with organizational measures of the companies, responsible for rolling stock and infrastructure. Through the example of UT-testing of railway axles it will be shown, how training and organizational measures influence the reliability of such testing.
How much information do we need? A reflection of the correct use of real defects in POD-evaluations
(2016)
To evaluate the capability of a non destructive testing system the “truth” of the used defects is essential. But what exactly is the truth of a real defect? And how much information is usable for the study? This presentation gives an overview about an advanced use of multiple metallographic cuts for the POD evaluation. In the presentation an approach is shown where information of metallographic studies are reconstructed and weighted to gain the essential information about real defects and which information are important for the detection with radiographic testing equipment. Furthermore, different connection points are discussed were additional knowledge from simulation and artificial defects can be used to gain additional certainty for the result of the evaluation. The methodology is used for the evaluation for the digital radiographic testing system for the testing of electron-beam welds, which is one possible choice to seal the Finnish copper canisters for the final deposit of spent nuclear fuel.
The usefulness and purpose of evaluating nondestructive testing (NDT) systems and their capabilities has changed in the last decade. The conventional method of simply applying a familiar statistical algorithm to say whether the system is usable for the tasks is history.
Nowadays, multiple parameter methods which describe the probabilities of detection (POD) of different systems or real defects need new characteristics and a broader variety of statistical models to describe the true system behaviour. The appraisal of the NDT system involves diverse departments within a company (engineering, NDT-operators, and statisticians), but is, at the same time, more needed and requested than in the past. In this article, an approach is discussed in which professionals from different fields worked well together, accomplishing cost-intensive metallographic studies in correlation with well-understood physical behaviour of NDT-methods as well as deep-discussed mathematical methods to create a holistic evaluation of the technical reliability for a specific radiographic testing (RT) equipment. The first part of the publication will show the comparison between metallographic grinding and the RT indications. An essential innovation over past evaluation methods was the use of a multi-scale smoothing algorithm, which describes physical parameters, which were not used in evaluation like the POD in this way in the past.
In the second part the statistical requirements for the POD take the focus. It can often be hard to make significant statements; especially in the case where only a small amount of data is available. The combination of data and the use of knowledge from simulations are essential. One possible solution will be shown for the RT evaluation. The methodology is used for evaluating the digital RT system for the inspection of electron-beam welds, which was method considered to seal the Finnish copper canisters for the final deposit of spent nuclear fuel.
Die Fehlerauffindwahrscheinlichkeit oder 'Probability of Detection' ist zu einer wichtigen Qualitätskennzahl von zerstörungsfreien Prüfsystemen geworden. Die Einschätzung von nur künstlichen Fehlern ist jedoch als Bewertungsgrundlage meist nicht ausreichend. Die später verwendeten Prüfobjekte mit den real vorkommenden Fehlern sind die zu betrachtende Basis, für die der Endanwender eine gültige Qualitätseinschätzung der angewandten zerstörungsfreien Prüfung fordert. Jedoch ist bei dem Fall, dass die Datenmenge gering ist, auch die Aussage der POD beschränkt. Es muss daher eine Zwischenlösung gefunden werden, in der die Informationen von beiden Prüfungen kombiniert werden. Die Mathematik ermöglicht mit der Bayes'schen Statistik, diese Informationen miteinander zu kombinieren und somit beide Informationen in die Bewertung einfließen zu lassen. Dabei spielt jedoch der Zusammenhang zwischen Signal und Fehlerausprägung eine wichtige Rolle. Praktisch angewendet und erprobt wird diese Vorgehensweise für die Bewertung der zerstörungsfreien Prüfungen der Firma POSIVA, die sich mit dem Bau eines Endlagers für hochradioaktiven Abfall in Finnland beschäftigt.
Die statistische Qualitätskennzahl 'Probability of Detection (POD)' hängt von der Anzahl der zugrunde liegenden, brauchbaren Ergebnisse ab. Ist die Datenmenge niedrig, so ist auch die Aussage der POD eher beschränkt. Dennoch heißt eine große Zahl von Daten, nicht gleichzeitig, dass die POD für den realen Einsatz in der Produktion genügt. Es muss unterschieden werden, auf welcher Basis unter welchen konkreten Bedingungen - die Daten erhoben wurden. Als wichtigste Ergebnisse zählen die Messergebnisse aus der Produktion der später verwendeten Prüfobjekte für den konkreten Einsatz. Noch bevor die zerstörungsfreien Prüfmethoden zuverlässig in der Produktion eingesetzt wurde, muss jedoch nachgewiesen werden, dass die real vorkommenden Fehler gefunden werden können. Das bedeutet, zu einem Zeitpunkt, an dem noch nicht ausreichend Daten vorhanden sind. Während für die realistische Prüfung die notwendige Anzahl der verschiedenen Fehler meist nicht erreicht wird, so fehlen bei der Bewertung der künstlichen Fehler wichtige Parameter und Einflussgrößen. Es muss somit eine Zwischenlösung gesucht werden, in der die Informationen von beiden Prüfungen kombiniert werden. Mit der Bayesschen Statistik ermöglicht die Mathematik diese Informationen miteinander zu kombinieren und somit beide Informationen mit in die Bewertung einfließen zu lassen.
Praktisch angewandt und erprobt wird die Vorgehensweise gemeinsam mit der Firma POSIVA, die sich mit dem Bau eines Endlagers für hoch-radioaktiven Abfall in Finnland beschäftigt. Hier wird als eine der technischen Barrieren ein Kupferbehälter für die Aufbewahrung der verbrauchten Brennstäbe genutzt. Dieser Kupferbehälter wird mit mehreren zerstörungsfreien Prüfmethoden geprüft. Anhand von Radiographiedaten wird gezeigt, dass die Aussagekraft der realistischen Fehlerdaten mit Hilfe der künstlichen Referenzfehlerdaten untermauert werden kann.
POD is the most often used approach for the evaluation of the reliability of non-destructive testing methods in critical areas. But especially for those cases the requirements for a sufficient amount of data, adequate type of defects and the statistical requirements are high. The claim for checking these requirements is not new, but never the less often ignored. Especially the large amount of data for critical real defects seems too often to be not really solvable. In this presentation we show an approach to use real defect data with knowledge from former testing results with the same equipment, in a useful adequate way. Furthermore we introduce a method to evaluate the real defect description parameters for the radiographic testing. This approach was used for a joint project with the company POSIVA, which is building a final depository for spent nuclear fuel in Finland. Radiographic testing is one of the NDT-methods they use to test the electron beam weld of the copper canister. The copper canister will be used in the deposit as a corrosion barrier within the deposit concept. Through the high sophisticated manufacturing methods of the canister there are almost no material defects, which could be used for reliability evaluation. In this context the idea of Bayesian Updating of the POD with real defect data with former results from artificial defect data was born to get a useful evaluation.
The report 'Probability of Defect Detection of Posiva's electron beam weld' describes POD curves of four NDT methods radiographic testing, ultrasonic testing, eddy current testing and visual testing. POD-curves are based on the artificial defects in reference blocks. The results are devoted to the demonstration of suitability of the methods for EB weld testing. Report describes methodology and procedure applied by BAM.
Report creates a link from the assessment of the reliability and inspection performance to the risk assessment process of the canister final disposal project. Report ensures the confirmation of the basic quality of the NDT methods and their capability to describe the quality of the EB-weld.
The probability of detection curves are determined based on the MIL-1823 standard and it's reliability guidelines. The MIL-1823 standard was developed for the determination of integrity of gas turbine engines for the US military.
In the POD-process there are determined as a key parameter for the defect detectability the a90/95 magnitudes, i.e. the size measure a of the defect, for which the lower 95 % confidence band crosses the 90 % POD level. By this way can be confirmed that defects with a size of a90/95 will be detected with 90 % probability. In case the experiment will be repeated 5 % might fall outside this confidence limit.
The Probability of Detection (POD) is used to evaluate the detectability of non-destructive testing (NDT) systems. The POD is highly dependent on the amount of available data. The Bayesian approach provides a solution to compute POD-curves in case of a small amount of real defects without losing the necessary information. The result contains the needed information for the computation of POD-curves for real defects with an acceptable amount of information, even for sparse amount of data. In this paper is shown limitations of the Bayesian approach and how it can be applied to NDT. The Bayesian approach is applied in this case to the evaluation of radiographic testing. Bayesian approach is applied to determine POD-curves for the inspection techniques of nuclear fuel disposal canisters. The reason for using Bayesian approach is the high safety demands and also the low amount of real defects due to the high quality of the reliable production techniques.
Proposals for Performance Demonstration and Modular Reliability Assessment for Humanitarian Demining
(2003)
Proposals for perfomance demonstration and modular reliability assessment for humanitarian demining
(2003)
Konzepte zur Quantifizierung des Restrisikos bei der Minensuche und in der zerstörungsfreien Prüfung
(2003)
Proposals for perfomance demonstration and modular reliability assessment for humanitarian demining
(2003)
Acceptance Tests
(2003)
POD evaluation of NDT techniques for CU-canisters for risk assessment of nuclear waste encapsulation
(2006)
The paper will give an overview of new methodology for evaluating the reliability of NDE systems
accurately, reliably and efficiently in accordance with the specific requirements of industrial
application. After a review of the substantive issues from the status in 2002, the go forward guidance
from these interactions is considered.
At the beginning of the reliability analysis, the actual safety demands have to be defined in
order to fit the investigation to the level of risk when the component would fail. Next, all the essential
influencing parameters need to be documented and transferred to an appropriate design of
experiments (DOE) to determine the reliability in terms of a qualitative assessment for lower risk or in
terms of a quantitative probability of detection (POD) or ROC (Receiver Operating Characteristics)
curves for higher safety demands. A new paradigm is offered to consider the POD or reliability of the
system as a function of the configuration of input variables and use it for optimisation rather than for a
final judgement. An advantage for the end user is also to sample all single PODs to an integral
Volume POD of a part.
Among the influencing parameters, the human factor is the most important one. A systematic
psychological approach shall help to find out where the bottlenecks are but most importantly to
provide best possible working conditions for the human inspectors.
The aim of all the effort devoted to NDE reliability is to evaluate the reliability accurately, reliably and efficiently, in accordance with the specific requirements of industrial application taking into account the very different nature of influencing factors. The set up of the Modular Reliability Model in 1997 was a big step forward in the understanding of influencing mechanisms in terms of the three different main elements, i.e. the intrinsic capability (IC), the application parameters (AP) and the human factors (HF). The intrinsic capability stands for the pure physical-technological process of the signal detection caused by the waves or the rays from a material defect in the presence of noise (caused by the material and the devices). This intrinsic capability is the upper bound of the possible reliability. Already when measuring this intrinsic capability for thick walled components the original one-parameter POD should be extended to a multi-parameter POD, where, in addition to the defect size, a number of additional physical parameters, such as the grain size distribution (or attenuation), defect depth, and angle or surface roughness, must be considered. For real life cycle assessments it is necessary to evaluate the signal response from real defects. The industrial application factors, e.g. coupling conditions, limited accessibility, heat and environmental vibrations, diminish the reliability. The amount of reduction can be determined quantitatively, if the underlying conditions are controlled. In case they are not controlled it is necessary to count for a (unknown) fluctuation in the reliability in the field anyway. The third group of important influencing factors are the human factors, which do not only cover the individual performance capability of the inspectors but also the design of the working place, the procedure, the teamwork quality, interaction with systems, the organization, and finally, the relationship between the companies involved in the inspection process and to which extend the responsible parties are aware of it. Both the internal and external organizational context, affect not only the HF but also the IC and AP. After having analysed the single factors separately it is necessary to look how everything is interconnected. When comparing an “ideal inspection” with a “real inspection” it is worthwhile to look at the existing practices, rules and standards. How do they really support reliable testing? With respect to the industrial end user, it needs to be shown how the level of reliability of NDE, influenced by the different factors and their interaction, has an impact on acceptance or rejection of safety critical parts. The approach of analysis and synthesis will be illustrated by examples of the reliability investigation of the inspection of copper canisters for nuclear fuel deposit in Sweden and Finland and German Railway inspections (hollow axle testing).
The paper will give an overview of new methodology for evaluating the
reliability of NDE systems accurately, reliably and efficiently in accordance with the
specific requirements of industrial application. After a review of the substantive
issues from the previous workshops, the go forward guidance from these
interactions is considered.
At the beginning of the reliability analysis, the actual safety demands have to
be defined in order to fit the investigation to the level of risk when the component
would fail. Next, all the essential influencing parameters need to be documented and
transferred to an appropriate design of experiments (DOE) to determine the
reliability in terms of a qualitative assessment for lower risk or in terms of a
quantitative probability of detection (POD) or ROC (Receiver Operating
Characteristics) curves for higher safety demands. A new paradigm is offered to
consider the POD or reliability of the system as a function of the configuration of
input variables and use it for optimisation rather than for a final judgement. An
advantage for the end user is also to sample all single PODs to an integral 'Volume
POD' of a part.
Among the influencing parameters, the human factor is the most important one.
A systematic psychological approach shall help to find out where the bottlenecks are
but most importantly to provide best possible working conditions for the human
inspectors.
Using the Modular Reliability Model the three different main influencing elements, i.e. intrinsic capability (IC), application parameters (AP) and the human factors (HF), are, in the first instance, investigated separately. The intrinsic capability stands for the pure physical-technological process of the signal detection caused by the waves or the rays from a material defect in the presence of noise (driven by the material and the devices). This intrinsic capability is the upper bound of the possible reliability. Already when measuring this intrinsic capability for thick walled components the original one-parameter POD must be extended to a multiparameter POD, where, in addition to the defect size, a number of additional physical parameters, such as the grain size distribution (or attenuation), defect depth, and angle or surface roughness, must be considered. For real life cycle assessments it is necessary to evaluate the signal response from real defects. The industrial application factors, e.g. coupling conditions, limited accessibility, heat and environmental vibrations, diminish the reliability. The amount of reduction can be determined quantitatively, if the underlying conditions are controlled. In case they are not controlled it is necessary to count for a fluctuation in the reliability in the field anyway. The third group of important influencing factors are the human factors, which do not only cover the individual performance capability of the inspectors but also the design of the working place,the procedure, the teamwork quality, interaction with systems, the organization, and finally, the relationship between the companies involved in the inspection process and to which extend the responsible parties are aware of it. When comparing an “ideal inspection” with a “real inspection” it is worth while to look how the existing practices, rules and standards support reliable testing and where the “delta” is. In the context of vigor, with respect to the industrial end user, it needs to be shown how the level of reliability of NDE, influenced by the different factors, has an impact on acceptance or rejection of safety critical parts.
Das Ziel des Artikels ist es eine Übersicht über neue methodische Ansätze und Verfahren zur Bewertung der Zuverlässigkeit von ZfP-Systemen in Übereinstimmung mit den spezifischen Anforderungen verschiedener industrieller Anwendungen zu geben. Nach einem Überblick über die in den vergangenen Jahrzehnten erreichten Fortschritte, wird der Fokus auf die gegenwärtigen Entwicklungen gerichtet. Für hohe Sicherheitsanforderungen wurde die quantitative Fehlerauffindwahrscheinlichkeit (probability of detection, POD) basierend auf 'hit/miss'- oder 'Signal-Response'-Analysen und die ROC-Analyse (Receiver Operating Characteristics) als typische Werkzeuge entwickelt. Im Rahmen des modularen Modells für die ZfP-Zuverlässigkeit unterscheidet man zwischen den rein physikalisch-technischen Einflussfaktoren, den industriellen Anwendungsfaktoren und den menschlichen Faktoren. Es hilft zum Beispiel zu erkennen, welche dieser Faktoren man in Modellierungsrechnungen bzw. mittels offenen oder Blindversuchen untersuchen kann. Ein neues Paradigma wird für die Betrachtung der POD als eine Funktion der gewählten Systemparameter und somit als Optimierungswerkzeug verwendet, anstelle sie für die endgültige Beurteilung zu nehmen. Zur Handhabung der Zuverlässigkeitsuntersuchung von realen Defekten in einer realistischen Umgebung werden ökonomisch vertretbare, aber dennoch präzise genug arbeitende Methoden, wie der Ansatz von Bayes oder modellbasierte Methoden vorgestellt. Die menschlichen Faktoren sind oft von ausschlaggebender Wichtigkeit für die Gesamtzuverlässigkeit. Hier hilft ein systematischer psychologischer Ansatz die Engpässe und Verbesserungsmöglichkeiten zu finden.
New methodologies for evaluating the reliability of NDE systems are discussed in accordance with the specific
requirements of industrial application. After a review of the substantive issues from the previous decades, the go
forward guidance is concluded.
For high safety demands a quantitative probability of detection (POD) created from hit miss
experiments or signal response analysis and ROC (Receiver Operating Characteristics) are typically created. The
modular model distinguishes between the influence of pure physics and technique, industrial application factors
and the human factor and helps to learn what factors are covered by modelling, open or blind trials. A new
paradigm is offered to consider the POD or reliability of the system as a function of the configuration of input
variables and use it for optimisation rather than for a final judgement. New approaches are considered dealing
with real defects in a realistic environment, affordable but precisely like the Bayesian approach or model assisted
methods.
Among the influencing parameters, the human factor is of high importance. A systematic psychological
approach helps to find out where the bottlenecks are and shows possibilities for improvement.
The paper will give an overview of new methodology for evaluating the
reliability of NDE systems accurately, reliably and efficiently in accordance with the
specific requirements of industrial application. After a review of the substantive
issues from the previous workshops, the go forward guidance from these
interactions is considered.
At the beginning of the reliability analysis, the actual safety demands have to
be defined in order to fit the investigation to the level of risk when the component
would fail. Next, all the essential influencing parameters need to be documented and
transferred to an appropriate design of experiments (DOE) to determine the
reliability in terms of a qualitative assessment for lower risk or in terms of a
quantitative probability of detection (POD) or ROC (Receiver Operating
Characteristics) curves for higher safety demands. A new paradigm is offered to
consider the POD or reliability of the system as a function of the configuration of
input variables and use it for optimisation rather than for a final judgement. An
advantage for the end user is also to sample all single PODs to an integral 'Volume
POD' of a part.
Among the influencing parameters, the human factor is the most important one.
A systematic psychological approach shall help to find out where the bottlenecks are
but most importantly to provide best possible working conditions for the human
inspectors.