Compression system check-valve failure hazards

Processes that utilize multistage compression systems (olefins plant compression systems, gas processing, integrated refrigeration systems, etc.) have the potential for overpressure due to single or multiple check-valve failure. Catastrophic equipment failure resulting from overpressure can potentially occur due to compression system discharge, interstage, and/or suction check-valve failure, coincident with compressor shutdown. Depending on system design and application, overpressure values approaching or exceeding 300% of equipment design are possible, while for some equipment, even limited overpressure can result in catastrophic vessel failure due to brittle fracture. Additional hazards associated with compression system fail-to-check scenarios include risks associated with excessive flare loading and compressor rotor reverse rotation. In the case of an ethylene refrigeration compressor at a typical ethylene plant, rotor reverse rotation can potentially exceed overspeed limits.This paper provides risk assessment results based on analyses performed on the three primary compression systems in six ethylene plants. The methodologies used for risk identification screening, detailed risk assessment and evaluation of system dynamics are all presented. Alternative methods for mitigating risks are also discussed, along with check-valve reliability data. An overview of applicable overpressure protection requirements defined in the ASME Boiler and Pressure Vessel Code is provided. This paper will be of interest to anyone who designs or operates multistage compression systems in the chemical, petrochemical or refining industries.     

基于应急避难空间的矿山安全防护体系研究

提出以应急避难空间为基础的煤矿新型安全防护体系,通过在井下布置救生舱、避难所与矿井各系统结合形成救援网络,可在煤矿事故中为被困作业人员提供应急避难空间避难,降低煤矿事故死亡率。提出了救生舱、避难所在矿井中的基本布置原则,并以山西某煤矿为实例进行安全体系建设研究,指出避难室、救生舱在矿井实际条件中的设置原则和方法,以及新型安全防护体系的发展方向,为我国煤矿新型安全防护体系构建提出指导性依据。     

Integration of process control protection layer into a simulation-based HAZOP tool

This paper discusses the framework methodology behind the proposed simulation-based HAZOP tool. Simulation-based approach is one of the many ways to support conventional HAZOP by its automation. Compared to knowledge-based and other approaches, a HAZOP software tool based on deviations simulation is able to examine the investigated process more into detail and so find root causes of hazardous consequences. Another advantage is the ability to identify also potential hazards which did not occur in the past and might be overlooked. The presented framework methodology uses a layer of protection analysis (LOPA) concept of independent protection layers (IPLs) testing. Control system integrated into the raw process design represents the first of various protection layers of the LOPA concept. As a case study, a CSTR chemical production with nonlinear behavior under Proportional-Integral-Derivative (PID) actions as the predominant type of classical feedback control strategy is used. The presented tool identifies hazardous regimes under conditions when control loop introduces hazardous consequences or even acts synergically with existing hazardous events. Risk derived from different consequences is ranked by the risk assessment matrix (RAM) as a part of the conventional quantitative HAZOP study.     

3-Parameters SPW technique: A new method for evaluation of target safety integrity level

Introduced by IEC-61508 standard, safety integrity levels (SIL) have been used for assessing the reliability of safety instrumented functions (SIF) for protection of the system under control in abnormal conditions. Different qualitative, semi-qualitative and quantitative methods have been proposed by the standard for establishing target safety integrity levels amongst which “Risk Graph” has gained wide attention due to its simplicity and easy-to-apply characteristics. However, this method is subject to many deficiencies that have forced industry men and experts to modify it to fit their demands. In this paper, a new modification to risk graph parameters has been proposed that adds more flexibility to them and reduces their subjective uncertainties but keeps the method as simple as before. Three parameters, namely severity (S), hazard avoidance probability (P), and demand rate (W) are used instead of former four parameters. Hence, the method is named SPW. The outcome results of this method can be directly converted to probability of failure on demand (PFD) or risk reduction factor (RRF). The proposed method has been tested on an example case that has been studied before with conventional risk graph and LOPA techniques. The results show that new method agrees well with LOPA and reduces costs imposed by conservative approximations assumed during application of conventional risk graph.     

Quantitative risk analysis of fire and explosion on the top-side LNG-liquefaction process of LNG-FPSO

Since the massive use and production of fuel oil and natural gas, the excavating locations of buried energy-carrying material are moving further away from onshore, eventually requiring floating production systems like floating production, storage and offloading (FPSO). Among those platforms, LNG-FPSO will play a leading role to satisfy the global demands for the natural gas in near future; the LNG-FPSO system is designed to deal with all the LNG processing activities, near the gas field. However, even a single disaster on an offshore plant would put the whole business into danger. In this research, the risk of fire and explosion in the LNG-FPSO is assessed by quantitative risk analysis, including frequency and consequence analyses, focusing on the LNG liquefaction process (DMR cycle). The consequence analysis is modeled by using a popular analysis tool PHAST. To assess the risk of this system, 5 release model scenarios are set for the LNG and refrigerant leakages from valves, selected as the most probable scenarios causing fire and explosion. From the results, it is found that the introduction of additional protection methods to reduce the effect of fire and explosion under ALARP criteria is not required, and two cases of the selection of independent protection layers are recommended to meet the SIL level of failure rate for safer design and operation in the offshore environment.     

垃圾填埋场渗滤液的防渗措施和地下水的污染防护

本文首先介绍了垃圾填埋场对其附近地下水体的潜在污染危害,着重介绍了为防止地下水体污染填埋场而采用的防渗措施,包括封场后的顶部覆盖层、中间夹层、底部集排系统以及底层和四周的衬层系统.然后介绍了由于防渗措施局部失效或其他原因(如破损、腐蚀等)引起渗滤液污染地下水以后可采用的防护方法(物理和生化技术),主要有隔离措施、地下曝气、反应墙或反应井、人工补给或抽水、水力截获、原位生物修复技术.最后简要介绍了对填埋场污染地下水这一问题的研究现状,并对这一方面的技术研究提出展望.     

Design support for the systematic integration of risk reduction into early chemical process design

Design for safety in the chemical industry is becoming a more explicit and well-organised process. However, it requires additional support tools to enable designers to pay attention to safety from the earliest conceptual design stage and through the subsequent detailing and to design more cost-effectively. This paper presents a more explicit approach called design for safety (DfS), which links with approaches already in use, such as layers of protection approach (LOPA). The method consists of two elements, a technology management environment (TME) aimed at supporting the interaction between the many contributors to safe design and a safety modelling language (SML). This provides a rigorous object-oriented language for conceptualising the requirements for risk control (barriers) and analysing their vulnerability to degradation or attack by other system elements or conditions. The method provides a focus for organising and applying existing knowledge about risk control and systematically learning from new knowledge to be gathered and supplied in supporting databases.     

Planning protection measures against runaway reactions using criticality classes

A systematic approach to the assessment of thermal risks linked with the performance of exothermal reactions at industrial scale was proposed a long time ago. The approach consisted of a runaway scenario starting from a cooling failure and a classification of these scenarios into criticality classes. In the mean time these tools became quite popular and many chemical companies use them. Recently, the international standard IEC 61511 required the use of protection systems with reliability depending on the risk level. Since the criticality classes were developed as a tool for the choice of risk reducing measures as a function of the criticality, it seems obvious that the criticality classes may be used in the context of the standard IEC 61511, which provides a relation between the risk level and the reliability of protection systems.Firstly, the runaway scenario and the criticality classes will be shortly described. Secondly, the assessment criteria for severity and probability of occurrence of a runaway scenario will be described together with the required data and their interpretation in terms of risk. Thirdly, the assessment procedure is exemplified for the different criticality classes. Finally, the design of protection measures against runaway and the required IPL and SIL are based on the risk assessment obtained from the criticality classes. This approach allows minimising the required data set for the safety assessment and for the definition of the protection system designed in order to avoid the development of the runaway.     

A fuzzy logic and probabilistic hybrid approach to quantify the uncertainty in layer of protection analysis

Layer of protection analysis (LOPA) is a widely used semi-quantitative risk assessment method. It provides a simplified and less precise method to assess the effectiveness of protection layers and the residual risk of an incident scenario. The outcome failure frequency and consequence of that residual risk are intended to be conservative by prudently selecting input data, given that design specification and component manufacturer's data are often overly optimistic. There are many influencing factors, including design deficiencies, lack of layer independence, availability, human factors, wear by testing and maintenance shortcomings, which are not quantified and are dependent on type of process and location. This makes the risk in LOPA usually overestimated. Therefore, to make decisions for a cost-effective system, different sources and types of uncertainty in the LOPA model need to be identified and quantified. In this study, a fuzzy logic and probabilistic hybrid approach was developed to determine the mean and to quantify the uncertainty of frequency of an initiating event and the probabilities of failure on demand (PFD) of independent protection layers (IPLs). It is based on the available data and expert judgment. The method was applied to a distillation system with a capacity to distill 40 tons of flammable n-hexane. The outcome risk of the new method has been proven to be more precise compared to results from the conventional LOPA approach.     

生态城市环境管理经济方法体系研究

针对生态城市的特征,根据整体最优的原则,通过政府、企业、公众的互动,整合了排污收费、排污权交易、生态补偿、资源费、激励机制、环保银行等经济方法,并与法律、行政、技术、教育等手段相结合,建立了一套完整的生态城市环境管理经济方法体系.以厦门市九龙江流域生态补偿为案例,简要分析了该方法体系实施后的效益.结果表明,该方法体系的应用将产生可观的社会、经济和环境效益,进一步可实现生态城市的高效环境管理.     

Reliability analysis of subsea blowout preventer control systems subjected to multiple error shocks

Two configurations of subsea blowout preventer (BOP) distributed control systems, which are triple modular redundancy (TMR) control system and double dual modular redundancy (DDMR) control system, are presented. With respect to common-cause failures, the performances of the two systems are evaluated by using Markov method with multiple error shock model. Due to the complexity, each system is split into three independent modules, and the corresponding Markov models are proposed subsequently. The probability of failure on demand, availability and reliability of the systems are evaluated by merging the independent Markov modules by Kronecker product approach. The results indicate that a same safety integrity level of SIL3 can be attained for the two configurations, which satisfies the requirement of subsea BOP control system, even though both of them have some advantages and shortcomings. In addition, for TMR control system, the effects of multiplicity distribution of multiple error shock and mean time to repair on reliability performances are studied.     

Investigation of oil vapor emission and its evaluation methods

In oil operations such as storage, loading, and unloading, there are many chances for oil vapor to be emitted from tanks, tankers or truck tanks into the air. Oil vapor emission (OVE), having serious harmful effects on people and the environment, is always an important research topic for scientists, engineers or managers engaged in the fields of oil production and transportation, fire prevention, and environmental protection. As the second greatest oil consuming country in the world, China has particular interests in investigating ways to better methods to realize and then control the OVE. In this paper, three evaluation methods for the OVE are introduced and summed up. In particular, a set of self-founded OVE’s appraisement methods, which work by theoretical deduced equations integrated with both a software PELES-2.0 and a simple correction method, was systematically investigated. This appraisement system can conveniently and accurately be applied to evaluate the OVE, and further it can also provide base references and/or guides for the law makers, enterprise managers and equipment developers in controlling OVEs.     

自动消防水炮的喷水强度分布特性及其控火性能研究

喷水强度是决定自动喷水灭火系统性能的重要参数.自动消防水炮在火灾早期可以快速响应,探测火源位置并自动喷水扑灭火灾.但如果由于某些因素不能及时响应,控制火灾的发展就是该系统的主要目标.传统的自动消防水炮研究只考虑射程和流量,没有考虑喷水的强度分布特性.本文将喷水强度引入自动消防水炮的控火性能研究,通过实验研究其在不同射程处的喷水强度分布特性,并参照不同危险等级的场所控制火灾所需的喷水强度参数来推算其有效保护区域和可控制的最大火源功率.研究结果表明:自动消防水炮在有效射程内,不同射程点的喷水强度、有效保护面积有所不同,喷水强度分布具有不均匀性.自动消防水炮应在火灾发展到最大有效保护面积之前自动或手动启动,才能达到有效控制火灾的目的.对于本文研究的某特定类型水炮,在20m至40m的射程范围内,应用于不同火灾危险等级场所,最大有效保护区域面积和可控制的最大火源功率均随射程增加而增加;而在40m至50m的射程范围内,应用于轻危险等级场所,最大有效保护区域面积随射程增加而增加,而其它危险等级场所的最大有效保护区域面积随射程增加而降低.     

ExSys-LOPA for the chemical process industry

The chemical process industries are characterized by the use, processing, and storage of large amounts of dangerous chemical substances and/or energy. Among different missions of chemical plants there are two very important ones, which: 1. provide a safe work environment, 2. fully protect the environment. These important missions can be achieved only by design of adequate safeguards for identified process hazards. Layer of Protection Analysis (LOPA) can successfully answer this question. This technique is a simplified process of quantitative risk assessment, using the order of magnitude categories for initiating cause frequency, consequence severity, and the likelihood of failure of independent protection layers to analyze and assess the risk of particular accident scenarios. LOPA requires application of qualitative hazard evaluation methods to identify accident scenarios, including initiating causes and appropriate safeguards. This can be well fulfilled, e.g., by HAZOP Studies or What-If Analysis. However, those techniques require extensive experience, efforts by teams of experts as well as significant time commitments, especially for complex chemical process units. In order to simplify that process, this paper presents another strategy that is a combination of an expert system for accident scenario identification with subsequent application of LOPA. The concept is called ExSys-LOPA, which employs, prepared in advance, values from engineering databases for identification of loss events specific to the selected target process and subsequently a accident scenario barrier model developed as an input for LOPA. Such consistent rules for the identification of accident scenarios to be analyzed can facilitate and expedite the analysis and thereby incorporate many more scenarios and analyze those for adequacy of the safeguards. An associated computer program is under development. The proposed technique supports and extends the Layer of Protection Analysis application, especially for safety assurance assessment of risk-based determination for the process industries. A case study concerning HF alkylation plant illustrates the proposed method.     

Layer of Protection Analysis – Quantifying human performance in initiating events and independent protection layers

Layer of Protection Analysis (LOPA) is widely used within the process industries as a simplified method to address risks and determine the sufficiency of protection layers. LOPA brings a consistent approach with added objectivity and a greater degree of understanding of the scenarios and risks as compared to purely qualitative studies such as Process Hazard Analyses. LOPA can be used to address a wide range of risk issues and serves as a highly effective aid to decision making.Incorporation of human performance within LOPA is recognized as an important, though often challenging, aspect of the analysis. The human role in potential initiating events or within human independent protection layers is important throughout the process industries, and becomes even more critical for batch processing facilities and in non-routine operations. The human role is key to process safety and the control of risks, necessitating the inclusion and quantification of human actions in independent protection layers for most companies. Human activities as potential initiating events and human performance within independent protection layers are reviewed and methods for quantification outlined. An extension into Human Reliability Analysis (HRA) is provided, including methods to develop Human Error Probabilities specific to the process safety culture and operations at a given plant site.     

Dynamic risk assessment using failure assessment and Bayesian theory

To ensure the safety of a process system, engineers use different methods to identify the potential hazards that may cause severe consequences. One of the most popular methods used is quantitative risk assessment (QRA) which quantifies the risk associated with a particular process activity. One of QRA's major disadvantages is its inability to update risk during the life of a process. As the process operates, abnormal events will result in incidents and near misses. These events are often called accident precursors. A conventional QRA process is unable to use the accident precursor information to revise the risk profile. To overcome this, a methodology has been proposed based on the work of Meel and Seider (2006). Similar to Meel and Seider (2006) work, this methodology uses Bayesian theory to update the likelihood of the event occurrence and also failure probability of the safety system. In this paper the proposed methodology is outlined and its application is demonstrated using a simple case study. First, potential accident scenarios are identified and represented in terms of an event tree, next, using the event tree and available failure data end-state probabilities are estimated. Subsequently, using the available accident precursor data, safety system failure likelihood and event tree end-state probabilities are revised. The methodology has been simulated using deterministic (point value) as well as probabilistic approach. This Methodology is applied to a case study demonstrating a storage tank containing highly hazardous chemicals. The comparison between conventional QRA and the results from dynamic failure assessment approach shows the significant deviation in system failure frequency throughout the life time of the process unit.     

基于模糊保护层的池火灾事故风险分析

为计算引发池火灾事故的风险值,提高事故风险的量化水平,判断现有风险控制措施是否满足风险容忍度的要求,为制定减缓风险措施提供依据,给出了新的池火灾风险评估模型。基于传统的保护层分析模型(LOPA),结合模糊集合理论,引入模糊风险矩阵进行风险评估,构建适用于引发池火灾事故的模糊保护层(fL OPA)风险分析模型。该模型的特点是将模糊逻辑和保护层分析结合,减少了传统保护层分析方法计算过程中的不确定性因素,引入严重度减少指数(SRI)概念,使严重度计算、风险评估更加准确。运用该模型对原油储罐泄漏池火灾事故风险进行分析,给出风险决策方案,判断现有保护措施是否能控制风险在可容忍范围内,实例验证了模型的可行性。     

A reliability evaluation method based on the weakest failure modes for side-by-side offloading mooring system of FPSO

Offshore structures are complex systems, and numerous failure modes must be taken into consideration when reliability analysis in different loads and environment conditions are conducted on them. It is difficult to obtain structural system reliability with respect to complicated systems with numerous failure modes and dependency consideration among them. This paper applies the combination of the weakest failure modes theory with structural reliability theory to conduct reliability analysis on of side-by-side offloading mooring system of FPSO. Firstly, the numerical simulation of the system in different conditions is addressed to acquire the statistical data of time-history stress of components including hawsers, fenders and yoke, based on which, the reliability indexes of all the failure modes and correlation coefficient matrix are derived. Then the weakest failure modes, i.e. the representative failure modes that have significant impact on the system, are located through Probability Network Evaluation Technique. The probability of structural system is estimated through the weakest failure modes by considering the system as series. The analysis results indicate that two environment conditions (0°&0°&0° and 0°&30°&45° in combinations of wave, wind and current) are relative dangerous, which is in good correspondence with the practical expertise. The method is verified to be an effective and convenient evaluation approach for structural reliability analysis in terms of complex systems. It is beneficial for the identification of structure indicators from the weakest failure mode group and conduct optimum of structural system configurations in the design stage.     

Integrating human factors and systems engineering to reduce the risk of operator “error”

Introducing safety devices does not always reduce the frequency of accidents. Operators adjust their response to technological improvements. Protection mechanisms may be used to support “unsafe” working practices so that the net risk of failure remains unchanged or may even rise. Regulatory bodies have reacted against this risk compensation. Rules and procedures have been imposed upon the day-to-day operation of protection equipment. Unfortunately, these constraints often fail to preserve the safety of an application. Inattention, fatigue, poor training and willful neglect can lead to rules and guidelines being ignored. In this paper alternative means of reducing threats posed by risk compensation are explored. In particular, it is argued that designers must exploit an integrated approach to the development of high-risk applications. By this we mean that both human factors and systems engineering must be recruited to support the development of protection equipment.     

Coordinability and consistency: Application of systems theory to accident causation and prevention

Recent works in the safety literature report several fruitful attempts to introduce mathematically rigorous results from systems and control theory to bear upon accident prevention and system safety. Previously, we discussed the implications on safety of the systems theoretic principles of coordinability and consistency, and we identified the lack of coordinability and/or consistency as fundamental failure modes in hierarchical multilevel systems. In this work, we further develop system safety analysis techniques based on these principles. We demonstrate that these principles not only provide a domain-independent vocabulary for expressing the results of post-mortem accident analyses, but they can also be applied to guide design and operational choices for accident prevention and system safety. We develop these ideas with the help of an illustrative case study. This case study represents a broad class of systems where operational policies and procedures of individual stakeholders in the system interact with physical processes such that new system behaviors emerge, and unanticipated safety issues arise. We argue, and illustrate our arguments using this case study, that the coordinability and consistency principles can be developed to deliver a threefold impact on accident analysis and prevention: firstly, these principles provide domain-independent procedural templates and vocabulary for post-mortem accident analysis. Secondly, these principles provide theoretical safety specifications to be met during system design and operation. Finally, these safety specifications can precipitate the formulation of a series of questions directly related to safety-oriented choices in the design, operation, and control of systems.