Societal risk acceptance criteria for gas distribution pipelines based on incident data from the United States

A significant number of pipeline operators use pipeline integrity management (PIM) to improve pipeline safety and reliability. Risk assessment is a critical step in PIM, because it determines the necessity of conducting the following steps in PIM for certain pipelines. Risk acceptance criteria are required in the process of risk assessment. Individual risk and societal risk are most frequently adopted as the two indicators of the risk acceptance criteria. To the best of the authors’ knowledge, quantitative societal risk acceptance criteria, especially for gas distribution pipelines, do not exit. The aim of this paper is to establish the societal risk acceptance criteria for gas distribution pipelines. Hence, FN curves were established using historical incident data from 2002 to 2017 provided by the U.S. Department of Transportation (DOT). Linear regression and the ALARP principle are used in evaluating the limits of the negligible line and intolerable line to obtain a graphical societal risk acceptance criterion for gas distribution pipelines. A line having a slope of −1.224, and an anchor point of (1, 8.413 × 10⁻⁷) is proposed as the negligible line. Further, the intolerable line has a slope of −1.224, and an anchor point of (1, 2.524 × 10⁻⁶). Both the negligible risk and the intolerable risk for the gas distribution pipeline are lower than the current societal risk acceptance criteria for hazardous installations. The reasons for these relatively lower risk acceptance criteria are discussed.     

Quantification of impact of line markers on risk on transmission pipelines with natural gas

The paper presents a model for the assessment of the influence of line markers on risk on transmission pipelines with natural gas. The impact of line markers on risk is determined as a function of the line marker recognisability, which in turn depends on the ability to discern a line marker from a distance. The model is based on physical properties of line markers, especially on their colour, measures and the colour of the environment. These properties served to quantitatively assess the discernability of two most frequently encountered types of line markers. Calculated distances at which a particular line marker is discernible were compared to the average distances between two line markers. Risk reduction factors were derived from the comparison between the calculated results and the data from the appropriate hazardous event database. Results of the model indicated significant dependence of the risk reduction factor due to line markers on the distance between two line markers and the weather conditions. The model shows its flexibility through its distinct dependence on local conditions along the pipeline route. It can serve as a supplement to the existing models for quantitative risk assessment on pipelines used in natural gas transportation.     

Impact assessment of traffic-induced vibration on natural gas transmission pipeline

The purpose of this paper is to present a study of impact assessment of the traffic-induced vibration on a buried natural gas transmission pipeline. The basic assumption in this study is that the traffic on pipeline-transportation route crossing might have a significant impact on natural gas pipeline structural integrity due to the traffic-induced vibration which propagates from the road surface through the soil and excites the buried natural gas pipeline. The resulting dynamic stress causes pipeline material fatigue loading which consequently may cause pipeline failure with the gas release into the environment exposing the population and the buildings in pipeline vicinity to a significant threat. The experiment on operating buried natural gas pipeline was conducted where measurements were performed on the road surface, the two operating buried natural gas pipelines of external diameter 500 mm and 250 mm and on corresponding casing pipes. The measurement data analysis was performed and the results were used for determination of pipeline lifetime period in the model for theoretical estimation of pipeline lifetime which has been exposed to traffic-induced vibration. The findings of the study in this paper show that the traffic-induced vibration on given buried natural gas pipeline is detectable, however this vibration, compared to the other factors which are influencing pipeline's structural integrity, does not have a significant impact on pipeline lifetime period.     

Reducing the risk level for pipelines transporting carbon dioxide and hydrogen by means of optimal safety valves spacing

In many countries where electricity generation is based on their natural resources of fossil fuels a need arises to implement new power engineering technologies that allow carbon dioxide capture. Simultaneously, efforts are made to find new energy carriers which, if fired, do not involve carbon dioxide emissions. Hydrogen is one of such fuels with this future potential which is now becoming increasingly popular. Obviously, this means that the two gases mentioned above – carbon dioxide and hydrogen – will be produced in large quantities in future, which in many cases will necessitate their transport over considerable distances. If a pipeline failure occurs, the transport of the gases may pose a serious hazard to people in the immediate vicinity of the leakage site. This paper presents an analysis of the possibility of reducing the level of risk related to pipelines transporting CO₂ and H₂ by means of safety valves. It is shown that for a 50 km long and a 0.4 m diameter pipeline transporting gas with the pressure of 15 MPa the individual risk level can be reduced from 1·10⁻⁴ to 6.5·10⁻⁷ for CO₂ and from 1·10⁻⁶ to 6·10⁻¹⁰ for H₂. The social risk can be diminished in similar proportions.     

基于IAHP和灾变链式方法的城市油气管道风险诱因与预警研究

城市油气管道穿越城区街道、建筑和居民区等特殊地段,保障其安全运行具有重要意义。为实现城市油气管道风险早期预警,基于城市与野外长输油气管道风险对比分析,识别城市油气管道风险预警指标;建立城市油气管道风险预警指标体系,采用区间层次分析法对预警指标重要度进行定量排序,确定关键预警监测点;并依据灾变链式理论,构建城市油气管道重大事故灾变链式模型,研究管道风险演化过程,发现灾变前兆进行断链减灾。研究结果表明:“腐蚀”及“第三方破坏”占据城市油气管道失效致因比重最大,风险因子“油气管道与市政管道距离”以及“城市工程施工作业”应作为城市油气管道重点监测点。同时,围绕城市油气管道风险预警需致力于孕源断链。     

Large scale experiments to study fires following the rupture of high pressure pipelines conveying natural gas and natural gas/hydrogen mixtures

As part of the EC funded Naturalhy project, two large scale experiments were conducted to study the hazard presented by the rupture of high pressure transmission pipelines conveying natural gas or a natural gas/hydrogen mixture containing approximately 22% hydrogen by volume. The experiments involved complete rupture of a 150 mm diameter pipeline pressurised to nominally 70 bar. The released gas was ignited and formed a fireball which rose upwards and then burned out. It was followed by a jet fire which continued to increase in length, reaching a maximum of about 100 m before steadily declining as the pipeline depressurised. During the experiments, the flame length and the incident radiation field produced around the fire were measured. Measurements of the overpressure due to pipeline rupture and gas ignition were also recorded. The results showed that the addition of the hydrogen to the natural gas made little difference to radiative characteristics of the fires. However, the fraction of heat radiated by these pipeline fires was significantly higher than that observed for above ground high pressure jet fires (also conducted as part of the Naturalhy project) which achieved flame lengths up to 50 m. Due to the lower density, the natural gas/hydrogen mixture depressurised more quickly and also had a slightly reduced power. Hence, the pipeline conveying the natural gas/hydrogen mixture resulted in a slightly lower hazard in terms of thermal dose compared to the natural gas pipeline, when operating at the same pressure.     

Estimation of safety distances in the vicinity of fuel gas pipelines

In this paper, safety distances around pipelines transmitting liquefied petroleum gas and pressurized natural gas are determined considering the possible outcomes of an accidental event associated with fuel gas release from pressurized transmission systems. Possible outcomes of an accidental fuel gas release were determined by performing the Event Tree Analysis approach. Safety distances were computed for two pipeline transmission systems of pressurized natural gas and liquefied petroleum gas existing in Greece using real data given by Greek Refineries and the Greek Public Gas Enterprise. The software packages chetah and breeze were used for thermochemical mixture properties estimation and quantitative consequence assessment, respectively. Safety distance determination was performed considering jet fire and gas dispersion to the lower flammable limit as the worst-case scenarios corresponding to immediate and delayed cloud ignition. The results showed that the jet fire scenario should be considered as the limiter for safety distances determination in the vicinity of natural and petroleum gas pipelines. Based on this conclusion, the obtained results were further treated to yield functional diagrams for prompt safety distance estimation. In addition, qualitative conclusions were made regarding the effect of atmospheric conditions on possible events. Thus, wind velocity was found to dominate during a jet fire event suppressing the thermal radiation effect, whereas gas dispersion was found to be affected mainly by solar radiation that favors the faster dissolution of fuel gas below the lower flammable limit.     

Numerical investigation of surface conduit parallel gas pipeline explosive based on the TNT equivalent weight method

With the rapid development of petroleum industry, the transport pipelines of oil and gas are increasingly constructed to minimize land use conflicts. Therefore, the parallel pipelines are unavoidable in order to save land resource, reduce the pipeline construction and maintenance costs. The economy and security of pipeline laying and running is the primary problem considered in pipeline construction, which the parallel spacing plays a decisive role to. The leakage of natural gas is very serious and dangerous due to its flammable and combustible. The explosive of leak gas causes impact failure to parallel pipeline. Specific to the surface conduit parallel gas pipeline, numerical simulation of leak natural gas explosive was carried out based on TNT equivalent weight method. Explosive damage degree of pipeline decreased with the pipeline distance increasing. Consulting with the pipeline ovalization strain design criteria and the combustion effect, the safety parallel natural gas pipeline space maybe at least 4 m to ensure the surface conduit parallel pipeline safely and steadily operation.     

城区天然气管道泄漏数值模拟与爆炸危害分析

在人口密度为三级和四级的城区内,密集的高建筑物对天然气管道泄漏后的扩散和流场形成产生重要影响。本文以某城市的实际情况为例,建立多建筑物的空间几何模型,采用k-ε湍流方程,SIMPLE算法,模拟了在三种不同风流速度、三种不同压力条件下,城区天然气管道泄漏气体在多建筑物地形中的扩散情况。根据模拟结果,依据天然气的爆炸极限,对模拟结果及其火灾爆炸危害的范围进行了对比分析。结果表明,CH4气体的泄漏扩散同时受管道压力、风流速度和周围建筑物的影响;同时受当地风速的影响,泄漏气柱在风流作用下会发生偏折,造成阻挡风流的建筑物内侧危险气体浓度升高,大大增加建筑物周围环境的危险性。研究结果对城区天然气管道的建设具有一定的指导意义。     

Towards more detailed determination of third party impact on risk on natural gas pipelines: Influence of population density

The paper presents a refined way to quantify the effects of third party interference on risk that is posed on people by transmission pipelines for natural gas. The main focus is set on the influence of population density on risk. Using the interdisciplinary approach, the presented study combines the knowledge from relevant risk assessment recommendations, physical consequences of hazardous events, existing history databases of hazardous event frequencies and urban planning. A quantitative boundary between two most populated types of area was established. A flexible risk coefficient was determined for a suburban type of populated area that is dependent on average population density. Consequently, a new approach for determination of a hazard distance from the pipeline and area boundaries for calculation of average population density was presented. This differs from the established methods described in some guidelines, but is based on results of applied quantitative risk assessment. The final result is more accurate determination of risk levels in suburban areas. Described methods may serve as a supplement to the existing models for quantitative risk assessment on pipelines used in natural gas transportation and may be used by pipeline operators as well as policy- and decision makers.     

基于FLACS CFD的不同气油比油气混输管道泄漏火灾后果对比

不同气油比的油气混输管道泄漏后果危害形式和风险差异的准确判断对于管道泄漏应急处置至关重要。以中国西部某油田集输管道为研究对象,针对不同气油比管道泄漏的火灾危害进行了对比分析,构建了FLACS CFD模型,并研究了油气混输管道原油泄漏形成池火的火灾特征和影响范围,以及天然气泄漏形成喷射火的高温分布和影响规律。研究结果表明:应急处置应考虑不同气油比下池火与喷射火危害的差异。在油气混输管线泄漏10 min形成稳定火焰的场景中,气油比低于100 m3/t时,原油池火为火灾危险的主要影响因素;气油比高于200 m3/t时,天然气喷射火为主要影响因素;气油比超过250 m3/t,高温覆盖距离不再明显增加;40 m为此场景下混输油气泄漏喷射火致死距离上限,120 m为温度影响上限。     

燃气管网定量风险分析方法综述

以城市燃气管网的风险为研究对象,分析并提出一种可用于城市燃气管网定量风险分析的新思路,包含了不同事故后果及其物理模型的分析即事故可能性分析、后果分析和风险评价,分为失效事故假定、泄漏率计算、物理效应计算、致死率计算、风险值计算、风险评价等环节;整理、研究城市燃气管网定量风险分析所涉及的多种物理模型,并通过比较不同模型的特点,分析各个模型的不足之处;最后针对国内外研究现状及燃气管网风险的特点,指出研究发展方向:研究风险在燃气管网内的传播,提出燃气管网相继失效的风险分析方法。所提出的分析思路、计算方法可与工程应用相结合。     

Risk analysis for oil & gas pipelines: A sustainability assessment approach using fuzzy based bow-tie analysis

Vast amounts of oil & gas (O&G) are consumed around the world everyday that are mainly transported and distributed through pipelines. Only in Canada, the total length of O&G pipelines is approximately 100,000 km, which is the third largest in the world. Integrity of these pipelines is of primary interest to O&G companies, consultants, governmental agencies, consumers and other stakeholder due to adverse consequences and heavy financial losses in case of system failure. Fault tree analysis (FTA) and event tree analysis (ETA) are two graphical techniques used to perform risk analysis, where FTA represents causes (likelihood) and ETA represents consequences of a failure event. ‘Bow-tie’ is an approach that integrates a fault tree (on the left side) and an event tree (on the right side) to represent causes, threat (hazards) and consequences in a common platform. Traditional ‘bow-tie’ approach is not able to characterize model uncertainty that arises due to assumption of independence among different risk events. In this paper, in order to deal with vagueness of the data, the fuzzy logic is employed to derive fuzzy probabilities (likelihood) of basic events in fault tree and to estimate fuzzy probabilities (likelihood) of output event consequences. The study also explores how interdependencies among various factors might influence analysis results and introduces fuzzy utility value (FUV) to perform risk assessment for natural gas pipelines using triple bottom line (TBL) sustainability criteria, namely, social, environmental and economical consequences. The present study aims to help owners of transmission and distribution pipeline companies in risk management and decision-making to consider multi-dimensional consequences that may arise from pipeline failures. The research results can help professionals to decide whether and where to take preventive or corrective actions and help informed decision-making in the risk management process. A simple example is used to demonstrate the proposed approach.     

An integrated quantitative risk analysis method for natural gas pipeline network

Natural gas industry is developing rapidly, and its accidents are threatening the urban safety. Risk management through quantitative assessment has become an important way to improve the safety performance of the natural gas supply system. In this paper, an integrated quantitative risk analysis method for natural gas pipeline network is proposed. This method is composed of the probability assessment of accidents, the analysis of consequences and the evaluation of risk. It is noteworthy that the consequences analyzed here include those of the outside and inside gas pipelines. The analysis of consequences of the outside pipelines focuses on the individual risk and societal risk caused by different accidents, while those of the inside pipelines concerns about the risk of the economic loss because of the pressure re-distribution. Risk of a sample urban gas pipeline network is analyzed to demonstrate the presented method. The results show that this presented integrated quantitative risk analysis method for natural gas pipeline network can be used in practical application.     

天然气管道完整性管理探析

通过对国内外天然气管道事故的统计和分析,指出了对天然气管道进行完整性管理的重要性;在此基础上,简要介绍了管道完整性管理方法,着重探讨了天然气管道完整性管理的流程和环节,包括管道潜在危害辨识、管道数据信息搜集与分析、管道风险评价、管道完整性评价、完整性评价响应和减缓措施,并进一步说明了天然气管道完整性管理的实施方法;最后,给出了在我国开展天然气管道完整性管理的必要性和建议.     

1种城市燃气管道风险评估模型及其应用研究

为科学评估燃气管道在复杂且敏感的城市环境中个人风险可接受情况，促进城市和谐稳定。以燃气管道泄漏射流火灾为事故场景，在常规评估基础上结合管道地区特点，构建基于公众可接受伤亡风险标准的评估模型，并通过案例分析，开展城市燃气管道个人风险定量评估研究。结果表明:我国城市燃气管道个人死亡风险、个人受伤风险可接受标准的建议值分别为5.00×10-6和2.74×10-5，其在一般情况下的公众可接受风险标准建议值范围为5.00×10-7~5.50×10-5和2.74×10-6~4.11×10-4；公众的伤亡风险感知偏差将直接影响风险评估结果，及时有效地对目标群体进行风险疏导以改善其风险认知，有助于避免公众风险感知偏差引发的负面社会效应。     

A review of quantitative risk assessment of onshore pipelines

This paper reviews and analyses frequency and consequences of failure of onshore pipelines transporting oil, refined products and natural gas. Generally accepted risk levels are indicated and a desirable risk range is proposed.Pipeline failure statistics from the United States (US), Canada, Europe and Brazil are compared. Failure rates for internal and external corrosion, human action and natural forces are analyzed and the expected failure rate for each failure mechanism is indicated. The effects of relevant construction and environmental factors on the failure frequency are studied and mean trends are obtained. Furthermore, the sizes of the holes indicated at different databases are compared and a typical distribution of failure sizes is proposed for each mode of failure. Finally, the frequency of ignition after a loss of containment is studied for gas and liquid pipelines.Historical data on consequences of the accidental loss of containment of onshore pipelines is reviewed. Property damage and environmental reparation costs are evaluated directly from pipeline failure data. Straightforward regression models are proposed to quantify these types of consequence taking into account the released fluid and the characteristics of the environment. Societal impact is evaluated by combining simple fire models, heat versus mortality correlations and population density.Finally, values for the desired risk level are evaluated by three methods: i) a risk value representing the good engineering practice; ii) the risk associated to the most relevant codes and regulations concerning pipeline risk assessment and/or construction and operation; iii) an analytically derived optimal risk level. The risk values obtained by the three methodologies are similar and a desirable risk range is proposed.     

城市天然气管道风险特征与肯特法的改进

根据城市高压天然气管道特点,将适合于城市天然气管道风险分析的肯特评分法加以改进,包括调整评分项目和事故因素权重,使其成为适于城市天然气管道的风险分析法。将改进后的肯特评分法应用于常州21km高压天然气管道的风险评价,得出8个相对高风险管段,其分析结果可作为安全管理人员合理分配维护资源的理论依据。工程应用实例证明:改进后的肯特法具有较强的可行性,是城市高压天然气管道风险评估的有效工具。     

Dynamic probability assessment of urban natural gas pipeline accidents considering integrated external activities

Urban gas pipelines usually have high structural vulnerability due to long service time. The locations across urban areas with high population density make the gas pipelines easily exposed to external activities. Recently, urban pipelines may also have been the target of terrorist attacks. Nevertheless, the intentional damage, i.e. terrorist attack, was seldom considered in previous risk analysis of urban gas pipelines. This work presents a dynamic risk analysis of external activities to urban gas pipelines, which integrates unintentional and intentional damage to pipelines in a unified framework. A Bayesian network mapping from the Bow-tie model is used to represent the evolution process of pipeline accidents initiating from intentional and unintentional hazards. The probabilities of basic events and safety barriers are estimated by adopting the Fuzzy set theory and hierarchical Bayesian analysis (HBA). The developed model enables assessment of the dynamic probabilities of consequences and identifies the most credible contributing factors to the risk, given observed evidence. It also captures both data and model uncertainties. Eventually, an industrial case is presented to illustrate the applicability and effectiveness of the developed methodology. It is observed that the proposed methodology helps to more accurately conduct risk assessment and management of urban natural gas pipelines.     

城市天然气管道半定量风险评估方法研究

以实现天然气管道风险评估资源的合理分配，确定天然气管道定量风险评估的重点为目标，改进燃气管道风险评估方法的肯特模型，探求城市天然气管道的半定量风险评估方法；分析了城市埋地天然气管道失效可能性与失效后果的影响因子，并研究其评分标准；分别给出了城市天然气管道失效可能性与失效后果的等级划分标准，并运用半定量风险矩阵进行燃气管道单元的风险初步排序，以确定高风险管道单元；对城市天然气管道进行半定量风险评估，可为识别管道沿线高风险后果区域、风险动态排序、风险预警及制定事故应急预案等提供科学依据和方法指导，具有重要的工程应用价值。