Impact of common cause failure on reliability performance of redundant safety related systems subject to process demand

Acknowledgments The authors would like to thank the anonymous reviewers for their constructive comments and feedback.Peer reviewedPostprin

Reliability modelling of redundant safety systems without automatic diagnostics incorporating common cause failures and process demand

Sriramula’s work within the Lloyd’s Register Foundation Centre for Safety and Reliability Engineering at the University of Aberdeen is supported by Lloyd’s Register Foundation. The Foundation helps to protect life and property by supporting engineering-related education, public engagement and the application of re-search.Peer reviewedPostprin

Operational Data Framework for Safety Instrumented Systems : A Case Study in Functional Safety and Reliability

In various industries, companies are adopting functional safety measures to address safety concerns, adhere to standards, and manage complex systems. This research is focused on ensuring the reliable operation of Safety Instrumented Systems (SISs) by emphasizing the reliability data. The study examines methodologies for collecting data, classifying failures, mitigating risks, and complying with international safety standards. Through a case study in the energy and marine power industry, a theoretical framework is developed to utilize operational data for assessing SIS performance in the form of a new Engine Safety System (ESS). By complying with IEC standards 61508 and 61511 and incorporating the framework into the ESS's Functional Safety Management Plan, the research addresses key challenges such as data collection, failure analysis, and performance verification. The primary research questions involve determining the type of data to be collected and establishing guidelines for analysing and evaluating that data. A mixed method approach is chosen, with a greater emphasis on qualitative aspects due to the nature of interpreting standards and establishing procedures. The developed framework is presented using tables that outline the required data inputs for reporting actual demands, spurious trips, failures of other barriers, and SIS element failures. Failure report templates are provided, emphasizing the importance of identifying root causes and categorizing failures into Safe or Dangerous failures, as well as Undetected or Detected. The reliability assessment involves comparing actual performance data against the criteria defined in the Safety Integrity Requirements that have been established for the SIS, based on the outcome of the risk assessment. Different risk assessment techniques, such as Layer of Protection Analysis, Fault tree analysis, and risk matrices, are presented in this context, while key performance indicators like demand rates and failure rates are explored to highlight their role in verifying SIS performance. The established framework, designed for the ESS to execute safety functions at Safety Integrity Level 2, is versatile and can serve as a robust foundation for the development of future Functional Safety projects within the organisation and can be applied to other SISs with different Safety Integrity level targets. The study concludes by addressing challenges associated with reliability and various data sources, such as human error and lack of functional safety training, emphasizing the significance of comprehending functional safety when operating with data of SISs

SPURIOUS ACTIVATION ASSESSMENT OF THERMAL POWER PLANT’S SAFETY-INSTRUMENTED SYSTEMS

Safety-instrumented systems (also called technological protections) play the significant role in prevention and mitigating of major accidents that can occur on thermal power plant. Activations of safety-instrumented system turn the power unit into safe state by shutting it down or reducing it productivity. The power generation process operates continuously. Any unplanned outage of generation equipment leads to undersupply of energy and big commercial losses to generation company. In Russia the values of allowed spurious trip rate for safety-instrumented systems are set by regulatory agency. These values are strict to all technological protections and do not take into account the differences in amounts of losses. This paper presents more flexible approach based on the Farmer’s risk criterion. Also risk reduction factor for spurious activation is proposed

A CFD-based Approach for Gas Detectors Allocation

PresentationAccidental gas releases are detected by allocating sensors in optimal places to prevent escalation of the incident. Gas release effects are typically assessed based on calculating the dispersion from releasing points. In this work, a CFD-based approach is proposed to estimate gas dispersion and then to obtain optimal gas sensors allocation. The Ansys-Fluent commercial package is used to estimate concentrations in the open air by solving the governing equations of continuity, momentum, and energy combined with the realizable κ-ε model for turbulence viscosity effects and species convection-diffusion. CFD dynamic simulations are carried out for potential gas leaks, assuming worst-case scenarios with F-stability and 2 m/s wind speed during a 4min releasing period and considering 8 wind directions. The result is a scenario-based methodology to allocate gas sensors supported on fluid dynamics models. The three x-y-z geographical coordinates for the sensor allocation are included in this analysis. To highlight the methodology, a case study considers releases from a large container surrounded by different types of geometric units including sections with high obstacles, low obstacles, and no obstacles. A non-redundant set of perfect sensors are firstly allocated to cover 100% detection for all simulations releases. The benefits of redundant detection via a MooN voting arranging scheme is also discussed. Numerical results demonstrate the capabilities of CFD simulations for this application and highlight the dispersion effects through obstacles with different sizes

Multi criteria risk analysis of a subsea BOP system

The Subsea blowout preventer (BOP) which is latched to a subsea wellhead is one of several barriers in the well to prevent kicks and blowouts and it is the most important and critical equipment, as it becomes the last line of protection against blowout. The BOP system used in Subsea drilling operations is considered a Safety – Critical System, with a high severity consequence following its failure. Following past offshore blowout incidents such as the most recent Macondo in the Gulf of Mexico, there have been investigations, research, and improvements sought for improved understanding of the BOP system and its operation. This informs the need for a systematic re-evaluation of the Subsea BOP system to understand its associated risk and reliability and identify critical areas/aspects/components. Different risk analysis techniques were surveyed and the Failure modes effect and criticality analysis (FMECA) selected to be used to drive the study in this thesis. This is due to it being a simple proven cost effective process that can add value to the understanding of the behaviours and properties of a system, component, software, function or other. The output of the FMECA can be used to inform or support other key engineering tasks such as redesigning, enhanced qualification and testing activity or maintenance for greater inherent reliability and reduced risk potential. This thesis underscores the application of the FMECA technique to critique associated risk of the Subsea BOP system. System Functional diagrams was developed with boundaries defined, a FMECA were carried out and an initial select list of critical component failure modes identified. The limitations surrounding the confidence of the FMECA failure modes ranking outcome based on Risk priority number (RPN) is presented and potential variations in risk interpretation are discussed. The main contribution in this thesis is an innovative framework utilising Multicriteria decision making (MCDA) analysis techniques with consideration of fuzzy interval data is applied to the Subsea BOP system critical failure modes from the FMECA analysis. It utilised nine criticality assessment criteria deduced from expert consultation to obtain a more reliable ranking of failure modes. The MCDA techniques applied includes the technique for order of Preference for similarity to the Ideal Solution (TOPSIS), Fuzzy TOPSIS, TOPSIS with interval data, and Preference Ranking Organization Method for Enrichment of Evaluations (PROMETHEE). The outcome of the Multi-criteria analysis of the BOP system clearly shows failures of the Wellhead connector, LMRP hydraulic connector and Control system related failure as the Top 3 most critical failure with respect to a well control. The critical failure mode and components outcome from the analysis in this thesis is validated using failure data from industry database and a sensitivity analysis carried out. The importance of maintenance, testing and redundancy to the BOP system criticality was established by the sensitivity analysis. The potential for MCDA to be used for more specific analysis of criteria for a technology was demonstrated. Improper maintenance, inspection, testing (functional and pressure) are critical to the BOP system performance and sustenance of a high reliability level. Material selection and performance of components (seals, flanges, packers, bolts, mechanical body housings) relative to use environment and operational conditions is fundamental to avoiding failure mechanisms occurrence. Also worthy of notice is the contribution of personnel and organisations (by way of procedures to robustness and verification structure to ensure standard expected practices/rules are followed) to failures as seen in the root cause discussion. OEMs, operators and drilling contractors to periodically review operation scenarios relative to BOP system product design through the use of a Failure reporting analysis and corrective action system. This can improve design of monitoring systems, informs requirement for re-qualification of technology and/or next generation designs. Operations personnel are to correctly log in failures in these systems, and responsible Authority to ensure root cause analysis is done to uncover underlying issue initiating and driving failures

Safety assessment of next generation nuclear systems: methodology development and case studies on fission and fusion devices

L'abstract è presente nell'allegato / the abstract is in the attachmen

Studies of the NERVA program Third quarterly report, Apr. - Jun. 1965

Developments in nuclear engine for rocket vehicle program - engine and propellant feed systems, thrust chamber, radiation effects, ground support equipment, instrumentation, and exhaus