safety,risk and reliability
mahmoud Shahrokhi; Mohammad Farhadi
Abstract
In combined cycle power plants, instead of releasing gases produced from burning fossil fuels, after turning the gas turbines, they enter into heat recovery steam generator (HRSG) boilers to produce steam. The produced steam by these boilers is used to generate electricity in steam turbines and thus, ...
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In combined cycle power plants, instead of releasing gases produced from burning fossil fuels, after turning the gas turbines, they enter into heat recovery steam generator (HRSG) boilers to produce steam. The produced steam by these boilers is used to generate electricity in steam turbines and thus, electricity generation efficiency is dramatically increased. In this way, the efficiency of electricity production increases significantly. These boilers are made at a great cost and also, any failures of them cause a power plant to stop and create enormous costs, so optimizing their reliability is very important. This paper deals with the modeling of the HRSG feed water system by using a block diagram for two states (i.e., half-time and full load), to evaluate the difference between the proposed alternative designs, by considering their reliability. The method used in this paper can be applied to evaluate and optimize the reliability of many other industrial systems. Introduction In power generation, the reliability of industrial control systems is crucial, as failures can disrupt services, leading to accidents and damages. This study focuses on the reliability of Heat Recovery Steam Generator (HRSG) boilers in combined cycle power plants. These plants optimize electricity generation by redirecting gases from burning fossil fuels into heat recovery steam generators. HRSG boiler reliability is pivotal due to high construction costs and the potential for extensive downtime and expenses in case of malfunctions. Addressing this challenge, the research employs the underutilized Reliability Block Diagram (RBD) model, providing a graphical representation of system components and interactions. Specifically tailored to the needs of the Mapna Boiler Company, the study aims to assess and optimize the reliability of the steam production unit, i.e., the boiler, within combined cycle power plants. Research BackgroundReliability, in conjunction with factors such as availability and safety, stands as a cornerstone in ensuring the practical quality of any system. The application of Reliability Block Diagrams (RBD) is a well-established method for modeling and calculating the reliability of industrial systems. Numerous studies have applied RBDs across diverse domains, ranging from power substation automation and wind turbine reliability to error calculations in intelligent submarine power systems. However, despite the versatility of RBDs, a noticeable gap exists in the literature regarding their use for modeling boiler reliability, especially as a multi-state system. Research MethodologyTo undertake a comprehensive reliability analysis of HRSG boilers, the study focuses on distinct subsystems, including:Feed-Water Storage SystemFeed-Water System (FWS)High-Pressure (HP) SectionLow-Pressure (LP) SectionCondensate SystemChemical Dosing System.The Feed-Water System (FWS) is crucial for immediate boiler operation. The initial design involves a Four-Pump System (A2 design) for the FWS. A modification is proposed, removing one feed-water pump, prompting an examination of its impact on boiler reliability. Critical components are identified based on their role in potential disruptions, emphasizing parts causing immediate boiler shutdowns. Using expert knowledge and diagrams, a Reliability Block Diagram (RBD) is developed, visually highlighting weak points. The RBD assesses FWS reliability, comparing two configurations for optimization. Calculation of HRSG Boiler Reliability as a Multistate SystemConfigurations of three-pump and four-pump setups for the Feed-Water System (FWS) are illustrated and analyzed using the Reliability Block Diagram (RBD). The reliability analysis entails a detailed process of data gathering, failure rate determination, and overall reliability calculation for diverse system configurations. The study incorporates probabilities for various operational states and introduces mathematical formulations to calculate the Mean Time Between Failures (MTBF) for water feed system configurations.Fig1: Configuration of HRSG boiler water supply system in 3 pump modeFig2: Configuration of HRSG boiler water supply system in 4 pump mode Steps of optimizing the operational reliability (OPR)Step 1: Identifying Components Used in FWSStep 2: Determining Failure Rates for Each ComponentStep 3: Drawing a Reliability Block Diagram (RBD)Step 4: Evaluating Component ReliabilityStep 5: Calculating Overall Reliability for Each Configuration. ResultsTables present Mean Time Between Failures (MTBF) for water feed system configurations, offering insights into the trade-offs between complete shutdowns and demi-capacity operations. The analysis suggests that the four-pump configuration, while experiencing fewer complete shutdowns, operates at half capacity more frequently compared to the three-pump configuration. The data-driven results highlight the nuances of system reliability and its dynamic nature. Research FindingsThe reliability assessment for boiler construction, considering the failure rates of components over a one-year period, indicates that the four-pump configuration is superior when component reliability is high; otherwise, the three-pump configuration may have an advantage. However, the decision to choose between these configurations necessitates an economic evaluation, accounting for construction costs, shutdown expenses, and half-capacity operation costs. The study underscores the importance of integrating economic considerations with reliability assessments for informed decision-making. Discussion and ConclusionThis research offers valuable insights into vulnerable areas of the HRSG boiler water feeding system, guiding maintenance attention and informing decision-making processes. The study emphasizes the need for future research to consider repair times and incorporate fuzzy reliability values to enhance the robustness of reliability calculations. The holistic approach adopted in this study, combining technical assessments with economic considerations, lays the groundwork for a more comprehensive understanding of system reliability in industrial settings. Suggestions for Future ResearchAs industries evolve, future research should tailor reliability models to specific contexts. Exploring different failure distribution functions beyond the constant-rate assumption opens avenues for investigation. Models like the Weibull mixture model, competitive risk models, compound models, and hybrid models offer promising directions. For instance, the study proposes exploring the application of a compound renewal model, known as complementary risk, for systems with parallel performance and independent components. The limited exploration of this model in the literature presents an opportunity for future research to uncover its potential applications and contributions to reliability modeling.
safety,risk and reliability
Amir Hossein Soltaninia; Mahdi Ravanshadnia; Milad Ghanbari
Abstract
Occupational Health and Safety (OHS) management significantly affects reducing costs, increasing productivity, and the social credibility of construction companies and plays a facilitating role in the transition towards sustainable development. This study aims to identify and quantitatively analyze OHS ...
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Occupational Health and Safety (OHS) management significantly affects reducing costs, increasing productivity, and the social credibility of construction companies and plays a facilitating role in the transition towards sustainable development. This study aims to identify and quantitatively analyze OHS risks in sustainable construction projects in Iran. To do this, first, common OHS risks are identified by conducting library studies. Then, these risks are screened and localized for Iran's sustainable construction projects by surveying 13 experts, selected by the snowball sampling method, in a focus group meeting. Afterward, each risk's importance and priority are determined using the Neutrosophic Group Best-Worst Multi-criteria (NGBWM) method, while applying a weight to each expert's opinion. The Neutrosophic sets theory provides the basis for obtaining accurate and more reliable results by considering the uncertainties in the experts' opinions. The findings showed that "the lack of sufficient safety skills of employees due to not allocating time to specialized safety training," "occupational injuries and diseases," "hazards caused by improper design and layout of the project site," "Weakness and inefficiency of occupational health and safety management personnel," and "Negligence and lack of planning for emergency maneuvers," with weights of 0.052, 0.036, 0.035, 0.032, and 0.028 respectively, are the most critical OHS risks in Iran's sustainable construction projects. Finally, reactive and preventive responses were proposed to face them in detail.IntroductionThe construction industry is one of the most dangerous industries worldwide, and Iran is no exception. According to reports from Iran's official institutions, 30-35% of work-related accidents occur in the construction sector. Furthermore, analysis of construction accidents indicates that 22% of accidents occur in the stages of preparation and demolition, while 61% occur during the construction phase (Alipour-Bashary et al., 2021). Research has revealed that sustainable construction projects pose a greater risk to health and safety than conventional construction processes. The health and safety of workers are essential aspects of social sustainability. However, the importance of health and safety risk assessment in sustainable construction projects is still in its early stages (Onubi et al., 2019). Given the complexity and challenges in the Occupational Health and Safety (OHS) risk assessment environment, it is crucial to develop a suitable mechanism for identifying and measuring safety risks in sustainable construction projects. This would enable finding the best solutions for risks that have a high probability of occurrence and severe consequences. The current research aims to answer the following main question: What are the key OHS risks in sustainable construction projects in Iran and the appropriate response and preventive actions for them?Literature eviewReviewing previous research shows that while risk management in construction projects is not a new concept, the focus on the safety of construction projects in recent years is a relatively recent development. Furthermore, with leading international companies in the construction industry increasingly embracing sustainable development, there is a growing interest in integrating safety risk management with sustainable practices, making this perspective unique and novel. Previous studies on the safety risks of construction projects have typically categorized these risks within the dimensions of Health, Safety, and Environment (HSE), often neglecting other dimensions of safety risks. In contrast, the current research proposes to combine the three aspects of sustainable development (economic, social, and environmental) with the dimensions of HSE, thereby offering a more comprehensive framework for organizing the safety risks of construction projects. A significant research gap in this field lies in the evaluation and quantitative analysis of identified risks. To address this gap, the current research employs the Neutrosophic Group Best-Worst Multi-criteria (NGBWM) method, which involves weighting experts' perspectives to provide a more robust and reliable assessment of safety risks.MethodologyThe current research was applied with a purposeful and descriptive survey approach. Data were collected from 13 project managers and executive officials in Iran's sustainable construction projects, sampled using the snowball method. Semi-structured interviews and two researcher-made questionnaires were employed to gather the required data. The research objectives were pursued through a proposed methodological framework comprising five main phases. In this study, Occupational Health and Safety (OHS) risks in sustainable construction projects were evaluated and analyzed within a neutrosophic space and through group decision-making. Following the identification of the final risks, the Neutrosophic Group Best-Worst Multi-criteria (NGBWM) method was applied using the General Algebraic Modeling System (GAMS) to measure importance and determine high-ranked risks. The group decision-making approach aimed to mitigate bias in results and enhance decision accuracy by leveraging collective wisdom. Implementing the NGBWM method in the neutrosophic space helped reduce uncertainty in subjective judgments and enhance decision accuracy through the use of three or four-point estimates and consideration of possibility functions for experts' opinions. ResultsAccording to the results, 45 Occupational Health and Safety (OHS) risks were identified for Iran’s sustainable construction industry. The application of the Neutrosophic Group Best-Worst Multi-criteria (NGBWM) method revealed that risks such as "lack of sufficient safety skills of employees due to not allocating time to specialized safety training," "occupational injuries and diseases," "hazards caused by improper design and layout of the project site," "Weakness and inefficiency of OHS management personnel," and "Negligence and lack of planning for emergency maneuvers," respectively, had the most significant importance and the highest ranks, with weights of 0.052, 0.036, 0.035, 0.032, and 0.028.DiscussionThe inadequacy of specialized training programs in the field of safety has been identified as the root cause of many OHS risks in Iran’s sustainable construction projects. The role of the human resources unit in enhancing and nurturing a skilled and knowledgeable workforce in the principles and standards of safety in sustainable construction projects is more crucial than ever. It is imperative to prioritize the quality of work and personal life of human resources. Designing an efficient incentive system, providing health insurance for employees, conducting periodic check-ups, and offering comprehensive training programs can serve as preventive measures to mitigate the occurrence of injuries and occupational diseases. These proactive steps not only enhance workplace safety but also contribute to the overall well-being and productivity of the workforce in sustainable construction projects.ConclusionThe occurrence of safety risks in sustainable construction projects is multifaceted and does not solely stem from individual carelessness or unexpected accidents. Instead, these risks originate from various areas including social, managerial, structural, and health domains. Consequently, solely focusing on OHS risks in a one-dimensional manner and lacking a systematic and comprehensive view of this issue hinder managers and decision-makers from accurately understanding and analyzing the main sources of risks and implementing appropriate preventive measures.
safety,risk and reliability
Seyedeh Sara Khorashadizadeh; Jalal Haghighat Monfared; Mohammadali Afshar Kazemi; Shahram Yazdani
Abstract
In this study, a comprehensive classification for supply chain risks in the pharmaceutical industry is presented using the Bailey’s classical strategy method and the four-stage Collier method. Initially, through the examination of texts related to the main hazard groups, supply chain elements, ...
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In this study, a comprehensive classification for supply chain risks in the pharmaceutical industry is presented using the Bailey’s classical strategy method and the four-stage Collier method. Initially, through the examination of texts related to the main hazard groups, supply chain elements, considering resources and functions, and categorizing upstream supply chain organizations, primary industry, and downstream supply chain organizations within the industrial and market environment, infrastructural environment, and external macro environment were modeled. In the next stage, criteria related to the security and safety of the supply chain were identified. In the final stage, a two-dimensional matrix classification for the identification of supply chain risk factors was proposed through the cross-tabulation of supply chain elements with security and safety criteria. Based on this classification and utilizing the exemplification method through a synthetic framework, a detailed list of risk factors was compiled. The aim of this study is to propose a comprehensive risk classification for pharmaceutical industries.MethodBailey’s classical strategy method has been used to develop a comprehensive classification of supply chain risks in pharmaceutical industries. In order to review the existing knowledge about supply chain risk groups, a systematic review of literature was performed. In the first stage, to find articles related to supply chain risks in the pharmaceutical industry, different combinations of related keywords have been used to search for articles in relevant databases. The selected articles were examined in three stages: extracting and classifying the main risk groups of the supply chain (the first dimension of the conceptual framework of classification), extracting and classifying criteria for a low-risk supply chain (the second dimension of the conceptual framework of classification), and applying the two-dimensional framework of classification to identify and classify risk factors of the supply chain.ResultsA total of 77 articles were selected for review. Based on the analysis of these articles, 83 risk groups were identified. These risk groups were arranged into a model including upstream supply organizations, the main industry, and downstream supply organizations, considering the relationships between supply chain’s resources, functions, and outcomes in the industry and market environment, infrastructural environment, and external macro environment. In the next step, 30 criteria for a safe and secure supply chain were identified. These criteria are divided into two general categories: criteria for the security of the internal supply chain environment (criteria of resistant supply chain resources and criteria of resilient supply chain functions) and criteria for the safety of the external supply chain environment (criteria of safety of market and industry, criteria of safety of infrastructural environment, and criteria of safety of external macro environment). In the last stage, through cross-tabulation of resource groups with resource resistance criteria, function groups with function resilience criteria, and peripheral environment elements with peripheral environment safety criteria, a model for identifying risk factors in the industrial environment was proposed. Based on this model, 372 risk factors of the supply chain of the pharmaceutical industry were identified.ConclusionIn this study, a new classification for supply chain risks of the pharmaceutical industry has been presented. The proposed classification is highly comprehensive, and the number of risk groups counted in this study is more than all the studies that have been done in this field so far. Most existing risk taxonomies are incomplete and do not follow a specific theoretical model. The classification of risk groups identified in this study has been done based on a model that considers the relationship between assets, functions, and outcomes of the supply chain. The risk groups identified in this study cover from the upstream of the supply chain to the main industry and the downstream of the supply chain. Many risk taxonomies focus on the pharmaceutical industry and do not cover the entire supply chain from raw material production to customers. In this study, cross-tabulation of resource groups with resource resistance criteria, function groups with function resilience criteria, and peripheral environment elements with peripheral safety criteria create an ideal model for identifying risk factors in the industrial environment. The classification proposed in this study can be used to evaluate the resistance and resilience of the supply chain. This model can also provide a suitable basis for identifying and evaluating risks in the supply chain environment. In addition, results of this study provide a very practical guide for choosing supply chain risk management strategies.
safety,risk and reliability
Amir Yousefli; reza Norouzi; Amir Hosein Hamzeiyan
Abstract
Reliability Redundancy Allocation (RRA) is one of the most important problems facing the managers to improve the systems performance. In the most RRA models, presented in the literature components’ reliability used to be assumed as an exact value in (0,1) interval, while various factors might affect ...
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Reliability Redundancy Allocation (RRA) is one of the most important problems facing the managers to improve the systems performance. In the most RRA models, presented in the literature components’ reliability used to be assumed as an exact value in (0,1) interval, while various factors might affect components’ reliability and change it over time. Therefore, components reliability values should be considered as uncertain parameters. In this paper, by developing a discrete - continuous inference system, an optimization - oriented decision support system is proposed considering the components’ reliability as stochastic variables. Proposed DSS uses stochastic if - then rules to infer optimum or near optimum values for the decision variables as well as the objective function. Finally, In order to evaluate the efficiency of the proposed system, several examples are provided. Comparison of the inferred results with the optimal values shows the very good performance of the developed stochastic decision support system.