On the thermal rupture of 1.9 m propane pressure vessels with defects in their thermal protection system

This paper describes the results from a series of fire tests that were carried out to measure the effect of defects in thermal protection systems on fire engulfed propane pressure vessels.

In North America thermal protection is used to protect dangerous goods rail tank-cars from accidental fire impingement. They are designed so that a tank-car will not rupture for 100 min in a defined engulfing fire, or 30 min in a defined torching fire. One common system includes a 13 mm blanket of high-temperature ceramic fibre thermal insulation covered with a 3 mm steel jacket. Recent inspections have shown that some tanks have significant defects in these thermal protection systems. This work was done to establish what levels of defect are acceptable from a safety standpoint.

The tests were conducted using 1890 l (500 US gallon) ASME code propane pressure vessels (commonly called tanks in the propane industry). The defects tested covered 8% and 15% of the tank surface. The tanks were 25% engulfed in a fire that simulated a hydrocarbon pool fire with an effective blackbody temperature of 870 °C.

The fire testing showed that even relatively small defects can result in tank rupture if the defect area is engulfed in a severe fire, and the defect area is not wetted by liquid from the inside. A wall failure prediction technique based on uniaxial high-temperature stress rupture test data has been developed and agrees well with the observed failure times.     

The boiling liquid expanding vapour explosion

The boiling liquid expanding vapour explosion (BLEVE) has existed for a long time and for most of this time it has been cloaked in mystery. Several theories have been put forward to explain this very energetic event but none have been proven. This paper describes a series of tests that have recently been conducted to study this phenomenon.

The study involved ASME code automotive propane tanks with nominal capacities of 400 litres. The tanks were exposed to a combination of pool and/or torch fires. These fire conditions led to thermal ruptures, and in some cases these ruptures resulted in BLEVEs. The variables in the tests were the pressure-relief valve setting, the tank wall thickness, and the fire condition.

In total, 30 tests have been conducted, of which 22 resulted in thermal ruptures. Of those tanks that ruptured, 11 resulted in what we call BLEVEs. In this paper, we have defined a BLEVE as the explosive release of expanding vapour and boiling liquid following a catastrophic tank failure. Non-BLEVEs involved tanks that ruptured but which only resulted in a prolonged jet release.

The objective of this study was to investigate why certain tank ruptures lead to a BLEVE rather than a more benign jet-type release. Data are presented to show how wall temperature, wall thickness, liquid temperature and fill level contribute to the BLEVE process.     

An experimental study of an LPG tank at low filling level heated by a remote wall fire

This paper describes an experimental study of 2300 L pressure vessels exposed to remote fire heating by a natural gas fuelled wall fire simulator. The tanks were filled to 15% capacity with commercial liquid propane. The flame intensity and distance were varied to study the effect of different heating levels on the tank and its lading.The fire simulator is first characterized with tests including fire thermocouples, radiative flux meters and thermal imaging. With the appropriate positioning of a target tank it is possible to get very realistic fire heat fluxes at the tank surface.Three tests were conducted with the 2300 L tanks filled to 15% capacity with propane. The tanks were positioned at three different distances from the wall fire resulting in measured average peak heat flux at the tank surfaces ranging between 24 and 43 kW m^?2. The data shows rapid rise in vapour space wall temperatures, significant temperature stratification in the vapour space, and moderate rate of pressure rise. These results provide excellent data for the validation of computer models used to predict the response of pressure vessels exposed to moderate heating from a remote fire.     

Fire and explosion risk assessment for large-scale oil export terminal

Now in Russian Federation and other countries large-scale oil terminals (volume of one tank exceeds 100 000 m³, total volume of tanks exceeds 300 000 m³) are designed and constructed. Therefore fire safety of such objects becomes a very important task, solution of which is hardly possible without detail fire risk assessment. This study is aimed to a solution of this problem. Potential, individual and social risks were calculated. The potential risk was defined as a frequency of occurrence of hazardous factors of fires and explosions in a given point of space (the so-called risk contours). The individual risk was defined as a frequency of injuring a given person by hazardous factors of fires and explosions. Time of presence of this person in hazardous zones (near the hazardous installation) is taken into account during calculations of the individual risk. Social risk was defined as a dependence of frequency of injuring a given number of people by hazardous factors of fires and explosions on this number. In practice the social risk is usually determined on injuring not less than 10 people.

The oil terminal under consideration includes the following main parts: crude oil storage consisting of three tanks of volume 100 000 m³ each, input crude oil pipeline of diameter 0.6 m, crude oil pumps, output crude oil pipeline of diameter 0.8 m, auxiliary buildings and facilities. The following main scenarios of tank fires have been considered: rim seal fire, pool fire on a surface of a floating roof, pool fire on a total cross-section surface of the tank, pool fire in a dyke, explosions in closed or semiclosed volumes. Fires and explosions in other parts of the terminal are also taken into account. Effects of escalation of accidents are considered.

Risk contours have been calculated both for the territory of the terminal and for the neighbouring space. The potential risk for the storage zone is near 10⁻⁴–10⁻⁵ year⁻¹, and at a distance 500 m from the terminal the potential risk values do not exceed 10⁻⁶ year⁻¹. The values of the individual risk for various categories of workers are in the range of 10⁻⁵–10⁻⁶ year⁻¹. Because of low number of the workers on the terminal and large distances to towns and villages the social risk value is negligible. These risk values are consistent with practice of the best oil companies, and fire hazard level of the terminal can be accepted as tolerable.     

Ammonia large scale atmospheric dispersion experiments in industrial configurations

A programme of large-scale experiments for atmospheric dispersion was carried out by INERIS over a period extending from December 1996 to April 1997. The objectives of the test campaign were to measure anhydrous ammonia concentrations in a range of few meters to 2 km from the release, in order to generate data to be used to improve 2-phase discharge and dispersion modelling.

The discharges were released from a 6-tonne storage tank of pressurised liquid ammonia and through a discharge device with an outlet diameter of 2 in. Fifteen trials were carried out with various release configurations corresponding to industrial situations (impinging jets on the ground and on a wall at various distances, release through a flange without seal…). The quantity of ammonia discharged from the liquid phase varied according to the tests, from 1.4 to 3.5 tons for durations between 7 and 14 min and, therefore, at flow rates between 2 and 4.5 kg/s. Approximately 200 sensors were settled downwind to measure ammonia concentrations and temperature in the plume. These tests showed that for discharges with identical flow rates the distances corresponding to the same concentration vary a lot according to the configurations. These distances tend to be reduced by the presence of obstacles or retention dikes that collected liquid ammonia. In the paper, the main experimental results are presented. In order to enable the comparisons with numerical predictions, more detailed information are given in [Bouet R. (1999). Ammoniac—Essais de dispersion atmosphérique à grande échelle. INERIS rapport, ref INERIS-DRA-RBo-1999-20410 (available at http://www.ineris.fr/recherches/recherches.htm).     

大型原油储罐泄漏隔堤池火灾后果研究

为了研究储罐大孔泄漏后可能产生的隔堤局部面状液池火灾,以10万立方大型原油储罐为例,采用计算流体力学软件FLUENT和火灾模拟软件FDS计算储罐在真实泄漏场景下的液池区域,模拟发生隔堤池火的分布特征及对临罐热辐射影响。研究结果表明:储罐原油泄漏后将在隔堤内形成相对稳定面积的液池,在储罐不同方位处泄漏形成的液池面积与储罐壁距雨水收集槽长度相关;储罐正下方的隔堤池火对储罐造成的热辐射极大;风对临罐受到的池火热辐射强度影响明显,指向罐组中心方向的来风对临罐热辐射强度影响较大。     

环氧丙烷储罐空气泡沫灭火试验研究

环氧丙烷为低沸点水溶性可燃液体,由于其饱和蒸汽压大,灭火困难,此前,国内外未对环氧丙烷进行过大型工程应用灭火试验研究。为研究空气泡沫对环氧丙烷储罐的灭火性能,分别对环氧丙烷进行了0．25m^2油盘探索性试验、1．73m^2油盘泡沫灭火剂选型试验和直径3．5m储罐工程应用灭火试验。试验结果表明,空气泡沫难以扑灭环氧丙烷储罐火灾,在直径3．5m储罐上,虽然采用了灭火性能较好的泡沫液,且使用了较大的供给强度和较长的供给时问,但仍难灭火。在试验基础上,对环氧丙烷储罐的消防要求提出了建议。     

High-temperature stress-rupture data for the analysis of dangerous goods tank-cars exposed to fire

This paper contains tension and stress-rupture test data on sample railroad tank-car steels at room temperature and temperatures between 500 and 720 °C. The paper describes the test facility, applicable standards, and procedures that were followed during the tests of tension and stress rupture. The paper also contains a simple correlation for the data and gives examples of how it can be used to predict tank failure times when exposed to fire heating.The stress-rupture testing was conducted at constant load (tensile force) conditions. A sample was heated to a specified temperature and the load was applied. The time to failure was then recorded. This testing was needed due to a general lack of available data for the high-temperature stress rupture of tank-car steels. These data are needed for the purposes of predicting tank failure when tank-cars are exposed to heating by fire. The steel samples were obtained from a recent train derailment in Ontario, Canada, and the steel samples included both new and older steels. Samples were cut in both the hoop and longitudinal directions to see if the stress-rupture properties were isotropic.Excellent data were obtained with very little data scatter in each sample. The results show that stress-rupture properties vary from sample to sample. Some older steels were as good as new steels, and some were not. However, all samples were nearly isotropic when it came to high-temperature stress rupture.     

硫铁化物氧化自燃的动力学分析

为研究含硫油品储油罐中硫铁化物的自燃倾向性，采用STA8000同步热分析仪对10，15，20℃/min等不同升温速率和15，20，25 mL/min等不同空气流量下的硫铁化物进行试验，并通过获得的TG-DSC曲线研究试样的自燃特性；在此基础上，根据Coat模型，利用不同反应机理函数对热重数据进行分析。结果表明:该试验条件下，硫铁化物的氧化进程符合三级反应动力学机制；得出了硫铁化物在不同升温速率和空气流量下的表观活化能；在560～746℃温度区间内，随着升温速率的增加，空气流量的加大，活化能数值明显减小，自燃倾向性增大。研究结果可为预防和控制因硫铁化物自燃引发的火灾、爆炸事故提供理论参考。     

Fire tests on defective tank-car thermal protection systems

Many railway tank-cars carrying hazardous materials are thermally protected from fire impingement by thermal insulation and a steel jacket applied to the outside of the tank-car shell. Over time, it is possible that the thermal insulation will sag, rip, degrade, or be crushed under the steel jacket. A thermographic technique to determine whether or not a tank has insulation deficiencies has been developed, but it is necessary to determine which thermal deficiencies do not affect a tank’s survivability in a fire and which thermal deficiencies must be repaired. In order to develop a guideline in assessing thermal defects, a thermal model and experimental data would be beneficial.A series of fire tests were performed on a quarter-section tank-car mock-up to assist in developing a guideline and to provide validation data for a thermal model. Twelve fire tests, with constant, credible, simulated pool fire conditions, were performed on the tank-car mock-up with various insulation deficiencies. An infrared thermal imaging camera was used to measure the tank wall temperature. The thermal images were useful in determining the temperature profiles across the defects at different times and the transient temperature behaviour at different locations.It was seen that the properly installed thermal protection system significantly reduced the heat transfer from the fire to the tank wall. It was also seen that the steel jacket alone (i.e. 100% defect) acted as a radiation shield and provided a significant level of protection. With small defects, it was observed that the surrounding protected material provided a cooling effect by thermal conduction. A square defect greater than about 40 cm on each side should be considered significant, because unlike smaller defects, there is little benefit from the surrounding material as far as the peak defect temperature is concerned.     

Blast overpressures from medium scale BLEVE tests

The measured blast overpressures from recent tests involving boiling liquid expanding vapour explosions (BLEVE) has been studied. The blast data came from tests where 0.4 and 2 m³ ASME code propane tanks were exposed to torch and pool fires. In total almost 60 tanks were tested, and of these nearly 20 resulted in catastrophic failures and BLEVEs. Both single and two-step BLEVEs were observed in these tests. This paper presents an analysis of the blast overpressures created by these BLEVEs. In addition, the blast overpressures from a recent full scale fire test of a rail tank car is included in the analysis.The results suggest that the liquid energy content did not contribute to the shock overpressures in the near or far field. The liquid flashing and expansion does produce a local overpressure by dynamic pressure effects but it does not appear to produce a shock wave. The shock overpressures could be estimated from the vapour energy alone for all the tests considered. This was true for liquid temperatures at failure that were below, at and above the atmospheric superheat limit for propane. Data suggests that the two step type BLEVE produces the strongest overpressure. The authors give their ideas for this observation.The results shown here add some limited evidence to support previous researchers claims that the liquid flashing process is too slow to generate a shock. It suggests that liquid temperatures at or above the Tsl do not change this. The expansion of the flashing liquid contributes to other hazards such as projectiles, and close in dynamic pressure effects. Of course BLEVE releases in enclosed spaces such as tunnels or buildings have different hazards.     

Scale considerations for fire testing of pressure vessels used for dangerous goods transportation

Fire protection of pressure vessels for transport and storage of dangerous goods is an active topic of research around the world. In many cases, organizations are conducting theoretical analysis followed by fire testing of thermal protection systems to determine how long they delay thermally induced failure, or if they eliminate failure. In most recent cases the organizations chose to do small scale fire testing because of the obvious cost savings.The question then is – are small scale experiments representative of highway tank truck and rail tank car scales? This paper discusses the scale issues involved. It goes on to show how identical fire heating conditions can give dramatically different failure times and modes of failure for small and large scale tanks if the conditions are not truly similar.     

储罐两环段喷淋圈管对供给强度的影响

国内储罐火灾爆炸事故时有发生,储罐消防冷却系统实施有效的冷却是控制火势和扑救初期火灾的主要因素之一。为了研究油罐消防喷淋系统在灭后冷却中的影响,本文选取4座5×10~3内浮顶罐组,开展消防冷却水系统喷洒实验,通过测试分析发现:实际的冷却水供给强度不满足规范的要求,并探讨了储罐固定冷却水系统供给强度不足的原因,结合分析的原因建议对规范中着火罐和临近罐供水强度要求统一均为2.5 L/(min·m^2),其冷却水喷淋圈管设置应为四段以上。     

蒙德法在火电厂液氨储罐评价单元的应用

火电厂液氨储罐单元存在大量高纯度的液氨,一旦发生火灾、爆炸,后果极其严重。为了研究液氨储罐的火灾爆炸危险性及毒性,在对火电厂液氨储罐危险性辨识的基础上,依据液氨储罐单元的主要参数,运用蒙德法分别确定评价中需要的各种危险性系数,从而进行各项指标计算,查询危险性等级表,将各项指标进行等级划分,结论表明各项危险等级都很高。在得出结论基础上,进行安全措施补偿评价,补偿后的各种危险等级均降低,可见采取补偿措施后能够一定程度的降低火灾、爆炸、毒性的危险性,防止事故的发生。     

液化石油气储运容器不同受热条件下的温度压力的估算

提出了液化石油气储运容器在不同受热条件下,容器内的温度和压力的简化的计算方法,可用于此类火灾原因的分析认定、安全分析等,对火灾的扑救也具有十分重要的意义。     

Thermal interaction analysis in pipeline systems: A case study

The assessment of the consequences of high pressure releases of flammable gases is a fundamental requirement for the safe design and operation of industrial installations, plants and pipework. A scenario of interest concerns a high pressure jet-fire following the ignition of a gas jet release which results in a thermal loading to the surroundings and possibly leads to accident escalation.

In the present paper, a case study is presented: two parallel-laid natural gas pipelines have been considered, the accidental scenarios which may possibly occur as a consequence of a pipeline failure have been discussed and the thermal effects caused by the jet-fire developing from different rupture sizes have been assessed.

Three scenarios have been analyzed, considering the pipelines being within a highly congested area: (i) large failure and vertical jet with detached flame; (ii) small failure with jet fire directly impinging on the parallel pipeline; (iii) small failure with pipeline engulfed within fire.

Once the temperature gradient through the pipeline wall has been found, the stresses deriving from pressure load and steel differential expansion have been analytically calculated and compared with the yielding stresses at the temperature achieved by the pipeline wall.

In the first scenario the pipeline is able to resist without major problems; in the second case the pipeline rupture is likely to occur; in the third scenario the pipeline resists to the applied loads but with a low margin to yielding.

It is understood that the analysis results are very much dependent on the utilized hypotheses, therefore a sensitivity analysis was performed in order to assess the variation of the results as a function of the variation of problem data; this analysis identifies the large influence of the parameters on the final result.     

A posteriori hazard analysis and feedback information of an accidental event in the grains storage of an agrochemical product

The present study concerns a hazardous event which occurred in an industrial storage tank of a ground insecticide. A preliminary post-accident approach of the hazard evaluation is performed. The rapid report of the presence of an unstable functional group in the active product and of its potential thermal instability (CHETAH indices) has led to complete this examination by an experimental study of thermal analysis using isotherm exposition measurement (DTA) or with temperature programming by differential scanning calorimetry (DSC) and oxidability tests (BAM). The apparent kinetics of decomposition of the active matter of the ground insecticide has been represented by a global Arrhenius law.

A model designed for the simulation of heterogeneous thermal runaways based on the numerical solution of the transient mass and energy balances has been further applied to define the critical conditions of the storage and simulate its behavior.

The results obtained during this analysis with the experienced feedback allowed us on one side to explain the hazardous event and especially on the other side to modify the operating protocol of the conditions of formulation of the active matter on the inert mineral support.     

Fire and explosion hazard analysis during surface transport of liquefied petroleum gas (LPG): A case study of LPG truck tanker accident in Kannur,Kerala, India

This paper presents an analysis and simulation of an accident involving a liquefied petroleum gas (LPG) truck tanker in Kannur, Kerala, India. During the accident, a truck tanker hit a divider and overturned. A crack in the bottom pipe caused leakage of LPG for about 20 min forming a large vapor cloud, which got ignited, creating a fireball and a boiling liquid expanding vapor explosion (BLEVE) situation in the LPG tank with subsequent fire and explosion. Many fatalities and injuries were reported along with burning of trees, houses, shops, vehicles, etc. In the present study, ALOHA (Area Locations of Hazardous Atmospheres) and PHAST (Process Hazard Analysis Software Tool) software have been used to model and simulate the accident scenario. Modeling and simulation results of the fireball, jet flame radiation and explosion overpressure agree well with the actual loss reported from the site. The effects of the fireball scenario were more significant in comparison to that of the jet fire scenario.     

LNG加气站槽车卸车直供过程泄漏后果分析*

为研究LNG加气站槽车直接供液过程泄漏后果严重程度,采用HAZOP辨识槽车供液和储罐供液典型泄漏场景,基于PHAST分析不同泄漏场景下LNG液池半径、蒸汽云扩散距离及积聚时长、爆炸超压和池火热辐射影响范围,定量评价槽车供液可能造成的事故后果扩大程度。结果表明:槽车供液泄漏事故的LNG液池最大半径、蒸汽云最大扩散距离、爆炸超压最大影响半径和池火热辐射最大半径,分别为储罐供液的5.7,1.7,2.3,7.9倍;槽车在无人值守条件下泄漏形成的LNG液池最大半径和蒸汽云积聚时长,分别为有人值守下的1.85,56倍;日供液量较大加气站不宜采用槽车直接为汽车供液模式,而应采用先卸车入罐、再储罐供液的模式;应落实槽车卸车轮班值守制度,并与周边社区建立有效的应急联动方案。