Modeling the performance of coated LPG tanks engulfed in fires

The improvement of passive fire protection of storage vessels is a key factor to enhance safety among the LPG distribution chain. A thermal and mechanical model based on finite elements simulations was developed to assess the behaviour of full size tanks used for LPG storage and transportation in fire engulfment scenarios. The model was validated by experimental results. A specific analysis of the performance of four different reference coating materials was then carried out, also defining specific key performance indicators (KPIs) to assess design safety margins in near-miss simulations. The results confirmed the wide influence of coating application on the expected vessel time to failure due to fire engulfment. A quite different performance of the alternative coating materials was evidenced. General correlations were developed among the vessel time to failure and the effective coating thickness in full engulfment scenarios, providing a preliminary assessment of the coating thickness required to prevent tank rupture for a given time lapse. The KPIs defined allowed the assessment of the available safety margins in the reference scenarios analyzed and of the robustness of thermal protection design.     

Prevention of domino effect: from active and passive strategies to inherently safer design

The possible application of an inherent safety approach to the prevention of domino accidents was explored. The application of the inherent safety guidewords to the definition of effective actions for the prevention of domino events was analyzed. Due to the constraints originated by the conventional approach to process design, the "limitation of effects" guideword resulted the more effective in the identification of inherent safety actions to avoid domino events. Detailed design criteria for the improvement of layout in the framework of inherent safety were identified and discussed. Simple rules of thumbs were obtained for the preliminary assessment of safety distances and of critical inventories with respect to the escalation of fires and explosions. The results evidenced that the integration of inherent safety criteria with conventional passive or active protections seems a promising route for the prevention of severe domino accidental scenarios in chemical and process plants.     

Development of a framework for the risk assessment of Na-Tech accidental events

Natural events impacting on chemical and process plants may cause severe accidents, triggering the release of relevant quantities of hazardous substances. The present study focused on the development of the tools needed to build up a general framework allowing the extension of quantitative risk assessment procedure to include the analysis of the industrial accidents caused by natural events. Specific methods and models were developed to allow the quantitative assessment of risk caused by two categories of “Na-Tech” accidents: accidents triggered by earthquakes and accidents triggered by floods. The approach allows the identification of the different damage modes expected for process equipment and of the accidental scenarios that may be triggered. The damage models developed allow the calculation of the damage probability of equipment items due to the natural events. A specific methodology was issued to take into account the consequences of the possible contemporary failure of several process units due to the impact of the natural event. The procedure allows the calculation of the overall individual and societal risk indexes including the multiple-failure scenarios caused by the impact of natural events. The overall methodology was applied to the analysis of specific case studies.     

The analysis of domino accidents triggered by vapor cloud explosions

Domino effect is a well-known cause of severe accidents in the chemical and process industry. Several studies pointed out that the more critical step in the quantitative assessment of domino hazards is the availability of reliable models to estimate the possibility and probability of the escalation of primary accidents. This work focused on the revision of available models for the quantitative estimation of damage probability to plant equipment caused by pressure waves generated by a primary accident. Available data on damages to process equipment caused by pressure waves were analyzed. Several specific probit functions for different elements of process equipment were obtained from the analysis of failure data. The analysis of blast wave propagation in different types of explosions allowed the estimation of the expected damage probability as a function of distance from the explosion center and of explosion strength. The results obtained were used to assess safety distance criteria and to evaluate the contribution to individual risk of domino effect due to pressure waves.     

The development of an inherent safety approach to the prevention of domino accidents

The severity of industrial accidents in which a domino effect takes place is well known in the chemical and process industry. The application of an inherent safety approach for the prevention of escalation events leading to domino accidents was explored in the present study. Reference primary scenarios were analyzed and escalation vectors were defined. Inherent safety distances were defined and proposed as a metric to express the intensity of the escalation vectors. Simple rules of thumb were presented for a preliminary screening of these distances. Swift reference indices for layout screening with respect to escalation hazard were also defined. Two case studies derived from existing layouts of oil refineries were selected to understand the potentialities coming from the application in the methodology. The results evidenced that the approach allows a first comparative assessment of the actual domino hazard in a layout, and the identification of critical primary units with respect to escalation events. The methodology developed also represents a useful screening tool to identify were to dedicate major efforts in the design of add-on measures, optimizing conventional passive and active measures for the prevention of severe domino accidents.     

Assessment of missile hazards: evaluation of the fragment number and drag factors

An approach was proposed for the assessment of the expected number and drag factor of fragments generated in the collapse of a vessel due to internal pressure. The analysis of a database reporting data on more than 140 vessel fragmentation events allowed the identification of a limited number of fragment reference shapes. The correlation of fragment reference shapes to the vessel credible fragmentation patterns allowed the assessment of the expected number and reference shape of fragments generated. Starting from the fragment reference shapes identified, simplified functions for drag factor calculation were developed, based on few geometrical parameters of the vessel undergoing the fragmentation event. The probabilistic models for the expected shape and number of fragments generated and the simplified drag factor functions developed may constitute an important input for the analysis of the possible fragment trajectories in the framework of missile hazard assessment.     

A multiple shutdown method for managing evacuation in case of major fire accidents in chemical clusters

This paper may be regarded as the second part of a larger article. The basic decision model developed in the first part of the article by Reniers et al. [G.L.L. Reniers, N. Pauwels, A. Audenaert, B.J.M. Ale, K. Soudan, Management of evacuation in case of fire accidents in chemical industrial areas, J. Hazard. Mater., 147 (2007) 478-487] is extended to determine both the optimal time and the optimal mode to stop the ongoing activities in case of a major fire possibly giving rise to an escalating event. Chemical plants have multiple modes to stop their production processes, differing with respect to the resulting costs, and with respect to the required time and personnel to complete the shutdown operations. The existence of an additional and more economic (but slower) shutdown mode might encourage the decision maker to stop the production processes earlier, in a less intervening manner, whereas the availability of an additional faster (but less economic) shutdown procedure might stimulate the decision maker to stop the production processes later, in a more intervening manner.     

DX旋挖挤扩灌注桩在LNG储存罐中的应用

针对场地上部为吹填海砂、下部为粉砂的特殊地层条件,在储存罐的基础中采用了普通直孔灌注桩和三节DX旋挖挤扩灌注桩;通过现场自平衡载荷试验,判定桩的竖向抗压极限承载力和沉降量,分析桩的载荷传递机理,并对桩侧阻力、桩端阻力的分配和发展规律进行研究;同时通过对两种桩的试验结果进行对比,发现DX挤扩灌注桩的极限承载力、桩身沉降明显优于普通直孔灌注桩,而且DX桩的长度明显小于直孔桩。     

Quantifying similarity in reliability surfaces using the probability of agreement

ABSTRACT

When separate populations exhibit similar reliability as a function of multiple explanatory variables, combining them into a single population is tempting. This can simplify future predictions and reduce uncertainty associated with estimation. However, combining these populations may introduce bias if the underlying relationships are in fact different. The probability of agreement formally and intuitively quantifies the similarity of estimated reliability surfaces across a two-factor input space. An example from the reliability literature demonstrates the utility of the approach when deciding whether to combine two populations or to keep them as distinct. New graphical summaries provide strategies for visualizing the results.     

Assessment of statistical responses of multi-scale damage events in an acrylic polymeric composite to the applied stress

Assessments of the statistics of damage ensemble are essential steps to develop accurate modeling and predictions of material failures. Events of random damage constitute a damage system that resides in the microstructures of the materials. Characterization and evaluation of such a system involve assessing the evolving the cascading damage events from hierarchical microstructures of the solids, and there currently lacks an experimental means to do so. To address this need, we established an approach to acquire the events of random damage (ERD) by employing a measureable multi-variate D_A defined in our previous work based on acoustic emission. It was found that the responsive events of random damage created by pure tension and three-point bending correlated strongly across all multiscale column vectors of D_A in spacetime. The correlation strength is much stronger under tension than that under bending, and much stronger in early loading stages across the column scale vectors of the D_A variate. ERD were found to be in clear distinct statistical populations by Andrews' exploratory data analysis plots under tension and bending, and in different stages of loading, which suggests that damage mechanisms are not only “physical”, but also “statistical”. Furthermore, our data showed that the strongly coupled multiscale column vectors of D_A can be transformed orthogonally to becoming decoupled principal components, PCs, which may facilitate the constitutive modeling. However, a PC indexes nearly evenly all scale vectors of D_A, which implicates, in conjunction with the findings of correlation and Andrews' plot, can be unidirectional, bi-directional, and or interwoven, but is a complicated index variable to describe the cascading multiscale damage events in evolving hierarchical microstructures of semicrystalline polymers.     

Some key effects on the failure assessment of weld repairs in CrMoV pipelines using continuum damage modelling

Some typical results obtained from finite element (FE) creep and continuum damage mechanics analyses, for assessing weld repair performance, are presented. The work outlines some developments in failure analyses of repaired welds in pressurised, thick-walled, main steam circumferential pipe weldments made of CrMoV steels. Methods involved in determining the material properties for constitutive equations are briefly described. Results presented cover a range of analyses, taking account of the effects of repair profiles/dimensions, geometry change during creep, end (system) loading, reheating effects in the weld metal of partial repair welds and initial damage level, etc., on the failure life of the repaired welds. The potential uses and limitations of the damage analysis for weld repair performance assessment are discussed.     

The importance of the time factor in fire and rescue service operations in Sweden

The aim of the paper is to measure the benefits and costs for the society if the fire and rescue service is delayed by 5 and 10 min respectively. A 5 min longer turn-out time is often the difference between a full-time and a voluntary crew. A 10 min difference may represent what happens if a voluntary crew on the outskirts of the municipality is closed down and their services are taken over by the centrally located full-time staff. In Sweden a full-time staff costs USD 180,000 more per year and man on duty. When it comes to the costs of a longer turn-out time three items dominates: fires in buildings; road transport accidents; and drowning cases. These three account for 38% of the alarms but 97% of the damage increase if the rescue operation is delayed, whether it is for 5 or 10 min. For all these three items we have carried out calculations based on our own empirical material. To be allowed to fight fires using breathing apparatus Swedish legislation requires a minimum crew of five. For a municipality in Sweden with the average number and distribution of alarms a full time crew of five is not economically justifiable until it reaches a population of 30,000.     

A quasi-static indentation test to elucidate the sequence of damage events in low velocity impacts on composite laminates

Any attempt to achieve composite laminates with improved damage tolerance to low velocity impacts must depart from the understanding of the sequence of damage mechanisms taking place. To this purpose, a series of quasi-static indentation experiments was conducted on AS4D/TC350 carbon/epoxy specimens. The induced damage at different indenter displacements was characterized using electron microscopy and C-scan, while the residual indentation profiles were captured with a 3D surface roughness machine. The indentation depth was shown to have relaxed after the test, reaching a steady value after 14 days. For the conditions explored, the relaxation was not dependent on the damage extent. The results showed that matrix cracking is in fact the crucial damage mechanism as it is responsible for the first sudden loss of load capacity and triggers the progressive growth of delaminations.     

The influence of some blasting techniques on the probability of ignition of firedamp by permissible explosives

The ignition of firedamp by permissible explosives is assessed by means of gallery testing conducted by the Bruceton up-and-down method. Six test series were made in order to analyze the influence of several blasting practices in long-holes coal blasting, namely: use of slotted PVC pipes, detonating cord, salt cartridges and double (top and bottom) initiation. The parameters of the distributions of the probability of ignition are determined by the maximum likelihood method; normal, logistic, lognormal and Weibull distributions have been used. Confidence bands for the probability points are obtained both from the asymptotic standard errors of the parameters and by a bootstrap-like technique. The four distributions used give similar results in a rather ample probability range; discrepancies in the probability points are within 2% and in the confidence limits within 10% in a range of probability [0.1, 0.9] in most of the cases. The use of detonating cord is found to affect significantly the probability of ignition; the double initiation does also have an influence though not statistically significant at a 95% level; the use of salt cartridges, in the amount tested, has little effect in the ignition probability; the use of PVC pipe shows no effect.     

Monitoring the damage evolution of flexural fatigue in unidirectional carbon/carbon composites by electrical resistance change method

This paper reported simultaneous monitoring damage evolution of flexural fatigue in unidirectional carbon-fiber-reinforced carbon composites (C/C composites) by electrical resistance change (ERC) methods. The degree of irregularity in electrical resistance changes increased with stress levels increasing. The shapes of electrical resistance change rate–fatigue cycle curves can reflect stress levels and damage types of tested samples: sawtooth shapes reflected delamination at a higher stress level; and “peak” shapes reflected inner damages in one fiber bundle at the fatigue limit stress level. In addition, the similarity of initial electrical resistance–fatigue life curve and S–N curve was observed clearly. In summary, ERC methods can monitor the damage evolution and qualitatively estimate the fatigue life of unidirectional C/C composites.     

On the influence of the unilateral damage behaviour in the stability of cracked beam/columns

This paper deals with the buckling analysis of cracked beam-columns. The crack is modelled with a unilateral elastic bending-stiffness behaviour, represented by a unilateral rotational spring. This model takes into account the crack closure effect associated with the phenomenon of breathing crack. The rotational spring may model a one-sided crack (or a unilateral joint for other applications in biomechanics or civil engineering). The unilateral elastic constitutive law of the crack is introduced from a variational procedure based on energy arguments. It is shown that this constitutive law can be formulated as a function of a physically-based damage parameter. A one-crack and a two-crack hinged-hinged beam-column are theoretically investigated to illustrate the unilateral effect of the crack behaviour on the buckling load. It is shown that the open crack analogy can be adopted for the one-crack beam-column, whereas this simplified assumption cannot be retained for the two-crack beam-column. In this last case, the crack closure effect strongly affects the buckling load, with respect to the open crack analogy of the same problem. More specifically, the crack-closure phenomenon tends to increase the buckling load, with respect to the open crack assumption mainly retained in the literature.     

The effect of thin deployable construction elements of the international space station on the probability of its hull penetration by meteoroids and orbital debris

When calculating the probability of hull penetration by meteoroid and orbital debris (M/OD) for some of the International Space Station (ISS) modules (e.g. FGB, Service module, cargo vehicle “Progress”), one has to take into account their additional shielding produced by ISS deployable construction elements (such as solar panels, radiators), which decrease M/OD penetrating probabilities. The lack of developed calculation methods of accounting for this effect has arisen the necessity to investigate the law— governed nature of particle fragmentation process accompanying high velocity penetration of thin barriers, as well as to elaborate techniques for correct calculation of the probability of no penetration (PNP) of module pressure wall. The results of thorough analysis of the theoretical and experime ntal published data as well as of data obtained in joint NASA and RSA experimental program on particle fragmentation are presented in this report in the form of normalized analytical correlation between the fragment maximum size and impact parameters. On the basis of above mentioned particle fragmentation law, the method of module hull ballistic limit curves (BLC's) recalculation is determined, which include the effect of thin barriers greatly distanced from the module hull. This BLC's are used for module PNP calculations with the help of modified version of NASA BUMPER code. The special subroutines accounting for PNP changes due to the particle collisions with ISS deployable construction elements are introduced in the BUMPER algorithm. The results of the Service module PNP calculations with account for its “shadowing” by solar panels and radiators are presented.     

Characterisation of the damaging micromechanisms in a pearlitic ductile cast iron and damage assessment by acoustic emission testing

The damaging micromechanisms in a pearlitic (EN‐GJS700‐2) ductile cast iron (DCI) are investigated by means of scanning electron microscope (SEM) analysis and acoustic emission (AE) testing. Monotonic uniaxial tensile tests are performed on microtensile specimens under strain control. SEM analysis is applied under in situ conditions by means of a tensile holder. The multiple damaging micromechanisms are identified, and their evolution along with the mechanical response is characterised. The traditional AE features are found to be qualitatively correlated to the onset of the fracture damage over the elastic behaviour. The information entropy of the AEs evaluated according to both Shannon and Kullback‐Leibler formulations is proven to be well correlated to the ongoing damage and the incipient failure. Tentative failure criteria are finally proposed. The assessment approach is found to be promising for structural health monitoring purposes.