Effect on Risk Based Inspection of spatio-temporal dependence of ROC curves: Study of the corrosion of steel harbour structures
Owners of civil infrastructures base their maintenance decisions schemes mainly both on structural integrity assessment and consequence analysis. Some inputs come from information collected by non-destructive or destructive tools. Uncertainties and noise of measurements can lead to bad decisions but are rarely integrated into the process of decision. Nowadays, Risk Based Inspection (RBI) provides the basic concepts for optimizing the maintenance plans of existing structures while insuring a good safety and availability conditions during service life of structures. In this paper, concepts are applied on a steel sheet pile seawall submitted to uniform corrosion where spatio-temporal dependence of performance of ROC (Receiver Operating Characteristic) curves is studied. Résumé Les gestionnaires d’infrastructures de génie civil basent leurs schémas décisionnels de maintenance essentiellement à partir de l’évaluation de l’intégrité structurale des ouvrages et de l’analyse des conséquences en cas de défaillance. Certaines données d’entrée proviennent de contrôles destructifs ou non destructifs. Les incertitudes et le bruit sur les mesures peuvent conduire à de mauvaises décisions mais sont rarement pris en compte dans les processus de décision. Actuellement, les méthodes RBI (Risk Based Inspection) donnent les fondamentaux pour aboutir à des plans de maintenance optimisés tout en garantissant la sécurité et la disponibilité des ouvrages en service. Dans cet article, ces concepts sont appliqués à un quai constitué par un rideau de palplanches soumis à la corrosion uniforme et la dépendance spatio-temporelle de la performance des courbes ROC (Caractéristique Opérationnelle du Récepteur) est étudiée.
A unifying review of NDE models towards optimal decision support
Non-destructive evaluation (NDE) inspections are an integral part of asset integrity management. The relationship between the condition of interest and the quantity measured by NDE is described with probabilistic models such as PoD or ROC curves. These models are used to assess the quality of the information provided by NDE systems, which is affected by factors such as the experience of the inspector, environmental conditions, ease of access, and the precision of the measurement device. In this paper, we review existing probabilistic models of NDE and show how they are connected within a unifying framework. This framework provides insights into how these models should be learned, calibrated, and applied. We investigate and highlight how the choice of the model can affect the maintenance decisions taken on the basis of NDE results. In addition, we analyze the impact of experimental design on the performance of a given NDE system in a decision-making context.
Reliability of inspection for fatigue cracks in offshore structures
Offshore structures are subject to wind and wave loading, which-eventually causes fatigue crack growth. The rate of growth of cracks depends on the load history, environment, design of joint and structure. In order to check for this growth the structure is periodically inspected with the inspection schedule designed to detect cracks before they are a danger to the structural integrity. The capability of an inspection method to detect cracks of a certain size is therefore an important aspect in establishing the schedule and maintaining the structural integrity. Also important is the capability of equipment to size the cracks, as this will determine the actions which may be taken in the event of a crack detection. The types of inspection reliability information required therefore includes probability of detection (POD), probability of false calls (spurious) and accuracy of sizing. Inspection reliability information can be obtained in a number of ways. These include anecdotal (inspection experience with particular equipment), manufacturers information, experimental determination and modelling. Each of these has its advantages and disadvantages. The offshore industry decided to explore an experimental inspection programme which led to the ICON project. The programme and the ICON project are briefly described.