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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).