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- Preventive maintenance of critical assets based on degradation mechanisms and failure forecastPublication . Sobral, José; Guedes Soares, CarlosWhen dealing with critical physical assets it is very important to monitor some parameters just to observe and predict the potential time to failure and thus establish a preventive maintenance activity avoiding the unwanted failure occurrence and its consequences. According to periodic (or continuous) data gathered along the time concerning selected parameters it is possible to observe tendencies and determine time to failure, assuming a pre-defined value as the critical one, corresponding to asset failure. The present paper deals with this type of condition monitoring outlining the importance of predicting time to failure and illustrating it with an example where the evolution of a degradation parameter on time for several similar assets is observed and, based on that, the time to failure is determined, allowing to establish the right moment for maintenance for these type of assets operating in these conditions.
- Assessment of the adequacy of safety barriers to hazardsPublication . Sobral, José; Guedes Soares, CarlosThe assessment of safety barriers performance is often achieved through tests or inspections in order to determine their availability or probability of failure on demand (PFD). The ultimate objective of these activities is to observe if the safety barrier is operational and to detect possible hidden failures. However, sometimes due to error in design or changes performed on the installation, the referred safety barrier is not adequate or no longer suitable to face the current level of risk. In the present paper is made a description of safety barriers as important means concerning risky situations and a methodology to evaluate the adequacy of a safety barrier is proposed. This methodology links the safety integrity level of an assessed safety barrier to the probability of occurrence of the hazardous event that it should protect. There is a pre-selection of the classified dangerous undetected safety function failures that will be used to determine the probability of failure on demand (PFD) and the safety barrier adequacy to a specific risk. It will be also possible to estimate the probability of occurrence of a hazardous situation corresponding to the simultaneity of the initiating hazardous event and the safety barrier fault (when a demand occurs).
- Review of condition-based maintenance strategies for offshore wind energyPublication . Kang, Jichuan; Sobral, José; Guedes Soares, CarlosThe existing maintenance strategies of offshore wind energy are reviewed including the specific aspects of condition-based maintenance, focusing on three primary phases, namely, condition monitoring, fault diagnosis and prognosis, and maintenance optimization. Relevant academic research and industrial applications are identified and summarized. The state of art, capabilities, and constraints of condition-based maintenance are analyzed. The presented research demonstrates that the intelligent-based approach has become a promising solution for condition recognition, and an integrated data platform for offshore wind farms is significant to optimize the maintenance activities.
- Repairable items inventory optimization based on maintenance data and risk criteriaPublication . Sobral, José; Guedes Soares, CarlosThe performance of organizations has a strong dependence on the successful operation of their physical assets and this is based on a large scale in the way how assets are managed, where spare parts play an important role. Repairable items, while units that can run an unlimited number of times between the asset (equipment) in which they are installed, the maintenance shop where they are submitted to maintenance activities (preventive or corrective) and the warehouse where they will wait for a demand, are very important elements once they represent a huge part of the inventory. This paper presents a methodology, initially developed in the aeronautics field to determine the optimum quantity of individual repairable items to exist in the warehouse to face their necessity. In the methodology it is taken into account the scheduled maintenance (hard time maintenance) as well as the unscheduled removals and the time of recovery in the maintenance shop. All these elements are gathered from maintenance historic data. The methodology also takes into account the risk by introducing the concept of Service Level. This work also presents a real case study, showing the applicability of the methodology presented and demonstrating its valuable contribution to the maintenance management decision making process.