ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part B: Mechanical Engineering

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In the framework of energy transition, a focus is given to the study of the conversion of offshore Oil&Gas (O&G) platforms at the end of their life due to the depletion of the reservoirs on which they operate. Their modular and versatile structure allows the implementation of new processes and innovative sustainable technologies for reducing the environmental impact of a complete decommissioning, especially on the subsea ecosystem that has grown around the jacket, and for guaranteeing cost-saving solutions. Among different conversion options, this paper focuses on the installation on the platform of a system for the production of photovoltaic (PV) energy to be used for seawater desalination and its delivery to other platforms operating in the same area. The project focuses on the definition of technical characteristics of the basic design, on the investigation of the technical feasibility of the conversion process, and on qualitative safety and environmental impact studies. Moreover, the old platform equipment to be decommissioned (i.e., the equipment necessary for hydrocarbons treatment) are identified, and the installation of new equipment is optimized, e.g., the number of PV panels and, therefore, the installed power are maximized. At the same time, decommissioning costs and impacts can be minimized. The basic design is completed with a preliminary structural verification to guarantee that critical situations do not rise, with an indication on the main maintenance activities for the preservation of plant good efficiency and with safety and environmental preliminary analyses for the identification of potential criticalities to be managed at different design levels. This article is available in the ASME Digital Collection at .

Important facilities constructed during last decades of 20th century are near completion of design life. For extending their service life or to evaluate these for new demands (loads), assessment of strength of concrete in existing structure becomes necessary, a task generally performed with nondestructive tests (NDT); ultrasonic pulse velocity (USPV) and rebound hammer being most commonly executed. Compressive strength is estimated using empirical expressions relating NDT to partially destructive tests (PDT) such as core test. For the development of structure-specific expressions, results of adequate number (depending on variability and desired confidence level) of PDT are essential but these might not be available due to operational constraints. Correlation expressions from literature could be used in such cases but having been developed for different ingredients, curing regimes, and environmental exposure conditions, there would be associated uncertainties. A practical method for the estimation of these uncertainties is not readily available in the literature. This article proposes the statistical approach of resampling for quantifying the uncertainty of indirect strength estimates using expressions from literature. Parametric (probability distribution) and nonparametric (bootstrap) tools are employed and demonstrated with a case study from India. Both parametric and nonparametric approaches could capture across-member variability whereas overall uncertainty incorporation, as well as repeatability, was better in nonparametric approach. Parametric approach is traditionally used and well accepted by practitioners in contrast to nonparametric methods, which have certain advantages. The detailed methodology enumerated in the article would be very useful for practitioners across the world. This article is available in the ASME Digital Collection at .

At the end of the nuclear-powered submarines (NS) operational life, they have to be defueled, decommissioned, and their nuclear reactors have to be safely disposed of. Their specific decommissioning process may be adapted to suit the needs of the decommissioning and storage process of small modular reactors (SMR) and reactors installed in floating devices. This paper addresses: 1—the decommissioning of NS, 2—the safe interim storage of their reactor compartments (RC), and 3—proposes a multicriteria decision-making (MCDM) approach for the RC interim storage facility site selection process, all focused on the Brazilian case. This approach is based on the application of the analytic hierarchy process (AHP). This article is available in the ASME Digital Collection at .

The use of neutron noise analysis in pressurized water reactors to detect and diagnose degradation represents the practice of pro-active structural health monitoring for reactor vessel internals. Recent enhancements to this remote condition monitoring and diagnostic computational framework quantify the sensitivity of the structural dynamics to different degradation scenarios. This methodology leverages benchmarked computational structural mechanics models and machine learning methods to enhance the interpretability of neutron noise measurement results. The novelty of the methodology lies not in the particular technologies and algorithms but our amalgamation into a holistic computational framework for structural health monitoring. Recent experience revealed the successful deployment of this methodology to pro-actively diagnose different degradation scenarios, thus enabling prognostic asset management for reactor structures. This article is available in the ASME Digital Collection at .

The integrity assessment of aged or worn out large electromechanical equipment units, such as in hydroelectric generators, for possible life extension has been identified as a growing challenge in the electrical power generation industry worldwide. Although the available recommended practices provide a general assessment process, it is necessary to have more detailed guidelines. This can be achieved by adding relevant theories and models which can capture time-dependent equipment unit degradation more precisely. Seeking to fulfill this gap, this work aims to present a framework that combines several techniques of data analysis, reliability, and decision-making to support engineers, operators, and managers in the often-complex decision process, regarding whether or not to extend the time in service of an equipment or system, thus postponing the moment of a scheduled maintenance shutdown. To demonstrate the application of the proposed framework, a case study is presented considering simulated scenarios based on data and information from a real Hydroelectric Power Plant. The results show how the reliability of the components and the remaining useful life of those in fault can impact the decision-making regarding the in-service life extension of a system. This article is available in the ASME Digital Collection at .

Reliability can be predicted by a limit-state function, which may vary with time and space. This work extends the envelope method for a time-dependent limit-state function to a time- and space-dependent limit-state function. The proposed method uses the envelope function of time- and space-dependent limit-state function. It at first searches for the most probable point (MPP) of the envelope function using the sequential efficient global optimization in the domain of the space and time under consideration. Then the envelope function is approximated by a quadratic function at the MPP for which analytic gradient and Hessian matrix of the envelope function are derived. Subsequently, the second-order saddlepoint approximation method is employed to estimate the probability of failure. Three examples demonstrate the effectiveness of the proposed method. The method can efficiently produce an accurate reliability prediction when the MPP is within the domain of the space and time under consideration. This article is available in the ASME Digital Collection at .

Freight rail networks serve a key role in transporting bulk goods to accommodate changing market demands and to serve public needs. Network analyses of such systems can provide important insights into enhancing transportation efficiency and system resilience. This paper develops and investigates a topological analysis model for network efficiency, which is associated with the connectedness of a network's nodes by its links and their corresponding network attributes. This model allows analyzing network topologies with or without assigned weights to their nodes and links based on different attributes. Key attributes may include physical length of links, commodity types and volume of goods transported through links, and dwell-time at nodes, and origination termination volumes of goods, types of goods moved, and origins and destination of goods. The model presented here enables (1) defining distinctions that may be employed for the assignment of node and link weights, (2) gaining an understanding of node and link criticality, and (3) providing methods for objectively maintaining and enhancing network performance. Such analyses can inform rail managers and executives in planning expansions, route or freight changes, or preparations for potential node or link failures. A case study of an aggregate U.S. freight rail network along with other example topologies is presented to demonstrate the use of selected network attributes and their influence on connectedness efficiency and the impacts of node and link failures on the overall transport efficiency. This article is available in the ASME Digital Collection at .

An approach is proposed for the evaluation of the probability density functions (PDFs) of the modal parameters for an ensemble of nominally identical structures when there is only access to a single structure and the dispersion parameter is known. The approach combines the Eigensystem realization algorithm on sets of dynamic data, with an explicit nonparametric probabilistic method. A single structure, either a mathematical model or a prototype, is used to obtain simulated data or measurements that are employed to build a discrete time state-space model description. The dispersion parameter is used to describe the uncertainty due to different sources such as the variability found in the population and the identification errors found in the noisy measurements from the experiments. With this approach, instead of propagating the uncertainties through the governing equations of the system, the distribution of the modal parameters of the whole ensemble is obtained by randomizing the matrices in the state-space model with an efficient procedure. The applicability of the approach is shown through the analysis of a two degrees-of-freedom mass-spring-damper system and a cantilever system. The results show that if the source of uncertainty is unknown and it is possible to specify an overall level of uncertainty, by having access to a single system's measurements, it is possible to evaluate the resulting PDFs on the modal parameters. It was also found that high values of the dispersion parameter may lead to nonphysical results such as negative damping ratios values. This article is available in the ASME Digital Collection at .

The Brazilian decommissioning industry faces challenges in the onshore and offshore environments that could potentially lead to operational safety problems and environmental impacts. In 2020, the Brazilian regulators brought innovations to the decommissioning plans, implementing a new resolution. On the economic aspect, this instrument aims to promote the sector's business conditions and to have it adapted to recognized internationally decom technical standards. On the regulatory side, it aims to compare alternative solutions for decommissioning facilities adopting at least technical, environmental, social, safety, and economic criteria. The existing framework was discussed with different stakeholders, involving industry, society, and academics. Several improvements and opportunities for the sector were identified, suggesting the necessity of improving the local decom infrastructure and technological enhancements to extend the lifecycle of fields. The adoption of Conceptual Installation decommissioning program (IDP) and Executive IDP by the resolution allowed the operator to determine the general lines of actions related to the decommissioning, allowing better planning, and reducing project uncertainties. As seen, the IDP requires the consideration of a multicriteria analysis and the need to be cautionary. The Conceptual IDP ensures a better field development and the best decommissioning planning in initial stages. The new resolution established well-defined rules aimed at field life extension and the recovery factor, lowering costs, and preventing premature decommissioning of the field in a safe manner, minimizing risks to people and the environment, in addition to establishing that the operator must evaluate the possibility of using the asset for another purposes. This article is available in the ASME Digital Collection at .

Decommissioning is expensive and can be a complex operation involving a series of distinct phases, including cessation of operation, site preparation, decontamination, dismantling (demolition) and disposal. Each decommissioning phase has associated risks, which need to be identified, controlled, and minimized as far as reasonably practicable. A risk-based approach has been recognized, both for ensuring safety and reducing the total decommissioning period with cost savings. A traditional hazard and operability (HAZOP) study can be conveniently extended to decommissioning HAZOP, which is a guideword-based collective multidisciplinary study identifying types of risks associated with decommissioning and allocates actions to the contractor and specialists departments for implementation. A decommissioning HAZOP enables to address the hazards and risks of decommissioning activities holistically, addresses all major contingencies, and results in safe decommissioning within budget. The presented decommissioning HAZOP study itself was completed ahead of time, without accidents. While there are other methods, decommissioning HAZOP and risk assessment was recognized as one of the effective methods for achieving the safety and project cost objectives. This article is available in the ASME Digital Collection at .