Multi-energy Method Research Articles

Head-to-Head Comparison of Dual-Source and Split-Beam Filter Multi-Energy CT versus SPECT/CT for Assessing Lobar Lung Perfusion in Emphysema.

To evaluate dual-source and split-beam filter multi-energy chest CT in assessing pulmonary perfusion on a lobar level in patients with lung emphysema, using perfusion SPECT as the reference standard. Patients with emphysema evaluated for lung volume reduction therapy between May 2016 and February 2021 were retrospectively included. All patients underwent SPECT and either dual-source or split-beam filter (SBF) multi-energy CT. To calculate the fractional lobar lung perfusion (FLLP), SPECT acquisitions were co-registered with chest CT scans (hereafter, SPECT/CT) and semi-manually segmented. For multi-energy CT scans, lung lobes were automatically segmented using a U-Net model. Segmentations were manually verified. The FLLP was derived from iodine maps computed from the multi-energy data. Statistical analysis included Pearson and intraclass correlation coefficients and Bland-Altman analysis. Fifty-nine patients (30 male, 29 female; 31 underwent dual-source CT, 28 underwent SBF CT; mean age for all patients, 67 years ± 8 [SD]) were included. Both multi-energy methods significantly correlated with the SPECT/CT acquisitions for all individual lobes (P < .001). Pearson correlation concerning all lobes combined was significantly better for dual-source (r = 0.88) than for SBF multi-energy CT (r = 0.78; P = .006). On the level of single lobes, Pearson correlation coefficient differed for the right upper lobe only (dual-source CT, r = 0.88; SBF CT, r = 0.58; P = .008). Dual-source and SBF multi-energy CT accurately assessed lung perfusion on a lobar level in patients with emphysema compared with SPECT/CT. The overall correlation was higher for dual-source multi-energy CT.Keywords: Chronic Obstructive Pulmonary Disease, Comparative Studies, Computer Applications, CT Spectral Imaging, Image Postprocessing, Lung, Pulmonary Perfusion© RSNA, 2023.

Study on Overpressure Explosion of Oil and Gas Pipelines and Risk Prevention & Control Measures

In view of the flammable and explosive characteristics of oil and gas pipeline transportation medium, once it leaks, production safety accidents are easy to occur. This study uses explosions with severe consequences caused by natural gas pipeline leakage as an example. The risk factors and accident modes of oil and gas storage and transportation pipelines are analyzed; the explosion load is calculated by a scaling explosion prediction model with the TNO multi-energy method; the relationship between overpressure load and combustible gas cloud radius is studied. The methane-air explosion volume fraction of 9.5% is taken as another example, with which the overpressure attenuation law of explosion wave is obtained. Based on the above research, safety risk prevention and control measures are proposed. The research results can provide technical support for daily management and risk prevention and control of oil and gas storage and transportation pipelines.

The TNO multi-energy method combined to mathematical programming and computational fluid dynamics for optimisation of gas detectors

Gas leakage is a matter of concern for several industries such as oil and gas, mining, food, and healthcare. When the industry considers gas detectors, the main questions are: How many gas detectors are required? Where is the best location to install them? To answer these questions Computational Fluid Dynamics (CFD) simulations and optimisation procedures are employed to calculate the plume location and plume volume to better position the gas detectors. We investigated how the optimisation cell size for the set covering problem can be calculated based on a given explosion overpressure threshold. Resorted by the multi-energy explosion model, we calculate the flammable cloud volume associated with a pre-defined overpressure value. The cloud volume is applied in the solution of the set covering problem and an optimal set for the gas detectors is obtained. The final gas detector network (number and location of the devices) is validated against CFD simulations for small releases. The results provide evidence that the optimal gas detector networks is able to detect gas leaks within a feasible time.

Application of the TNO multi-energy and Baker-Strehlow-Tang methods to predict hydrogen explosion effects from small-scale experiments

Analytical models or abacus are of importance to predict explosion effects in open and congested areas for industrial safety reasons. The goal of this work is to compare overpressure and flame speed values of small-scale deflagration experiments to predicted values from the TNO multi-energy (TNO ME) method and the Baker-Strehlow-Tang (BST) method. Experiments were performed in cylindrical congested volumes of hydrogen – air mixtures varying from 1.77 L to 7.07 L. The reactivity was controlled by the equivalence ratio of hydrogen-air mixtures, ranging from 0.5 to 2.5. The congestion was realized with varying numbers of grid layers and configurations. The influence of the obstacle density and the importance of the mixture reactivity to choose the strength index in order to predict the effects of an explosion has been highlighted for the TNO ME method. Predictive flame speed values from the BST method are in accordance with almost half of the experimental results and the method is conservative in most tested configurations. The use of the TNO ME method has been validated on a small-scale experiment to predict maximal overpressures generated by the deflagration of medium and large-scale H2/air clouds.

Non-linear fusion of dual-energy projections for XCT imaging of challenging components

The imaging of multi-material components having large changes in attenuation behaviour is widely regarded as a limitation of X-ray computed tomographic techniques. The use of Dual Energy X-ray Computed Tomography (DECT) is common in the field of medical imaging, providing many benefits to imaging and characterisation. However, multienergy methods such as DECT remain underutilised in the industrial sector. In this work, a novel measurement based multi-energy image fusion approach was evaluated using two radiographic image stacks acquired under two distinct polychromatic spectra; this fusion was then compared to the results of the individual high and low-energy datasets as well as their average. The implemented approach was tested using a Titanium (Ti) and Carbon Fibre reinforced Polymer (CFRP) double-step lap joint to evaluate performance. Results indicated improvements to contrast in Dual Energy fused radiographs, aiding the interrogation of complex components in 2D. The translation of these benefits into the Reconstructed CT volume showed promise for isolated material regions. It was established that careful parameter selection was needed to achieve optimum fusion results, as it was found that failure to do so, resulted in contrast suppression in regions of mixed materials. The process proposed here acts as a first foundational step into the fusion of multi-energy industrial X-ray computed tomography (XCT) datasets using standard XCT equipment. Further work will aim at refining and comparing it to other projection weighting functions and measures.

The potential for deflagration to detonation transition (DDT) - Lessons from LPG tanker transportation accident

On June 13, 2020, an LPG tanker leaked, followed by a vapor cloud explosion on the highway section near Liangshan Village, Wenling City, China. The accident killed 20 people and injured more than 170, causing severe damage to the surrounding area and significant impact to the society. This work studied the large vapor cloud explosion of the LPG transportation accident in terms of the dynamic phenomena of explosion, building damage level, and mechanism of DDT. The accident analysis indicates that blast shock wave front and reaction front were moving together at a speed higher than the speed of sound; the explosion overpressure of the accident is consistent with the calculation using the detonation approach of TNO multi-energy method; the blockage level and flame acceleration distance caused by the shrubs, and the quantity of release LPG provide enough conditions for DDT occurrence. Therefore, it is believed that DDT has occurred in this accident. The findings of this work also contribute to providing scientific recommendations on preventing DDT accidents, including redesign the vegetation at incident-prone section of the highway to eliminate the condition of DDT occurrence, and optimize the transportation route to avoid highly populated areas.

Influence of obstacle morphology on safety of nuclear hydrogen production system

The safety of the nuclear hydrogen production system is a key issue that cannot be ignored in the future commercialization. The reasonable arrangement of obstacles can effectively improve the safety of the system under accident conditions. In this paper, based on the high-pressure hydrogen storage tank model of a nuclear hydrogenation plant, two mechanisms by which obstacles can effectively improve safety are analyzed. In order to determine the obstacle design scheme with outstanding effect, the response surface methodology is used to study the influence of the structural parameters and spatial position parameters of obstacles of different shapes, and the comprehensive performance of different obstacles is compared by the TNO multi-energy method. The results show that the semi-cylindrical surface can control the separation distance within 141 m at a lower processing cost, which has good engineering utilization value. This study can provide a valuable reference for the design of nuclear hydrogen production systems.

Fire and Explosion Consequence Analysis of Occupied Buildings in an LPG Storage Facility in Southern Nigeria

The purpose of this work was to carry out an evaluation of occupied buildings from the devastating impact of an explosion in a Liquefied Petroleum Gas (LPG) bulk storage facility with the intention to provide information on blast requirements of the buildings and make layout modification as needed using the consequence-based approach. The simulation was done using DNV’s Process Hazard Analysis Software Tool (PHAST) and the process data were obtained from a process plant located in the Niger-Delta region of Nigeria. Three major scenarios; catastrophic rupture, full bore rupture was considered for a 6-inch pipe and fixed duration release of the stored LPG and propane gas using the TNO multi-energy method to determine the Maximum Credible Event on the occupied buildings within the facility From the study, the catastrophic rupture of LPG vessel #18 at 2/F weather category gave the worst impact with an overpressure effect of 0.7barg at a hazard distance of 166.959m. The thermal radiation intensity of 37.5KW/m2 due to Jet fire from the fixed duration release of Propane vessel #22 at 2/F weather category was found to produce the greatest consequence/impact at a hazard distance of 180.72m. The results from this work show that most of the occupied buildings within the location are in the vicinity of the effect zone of both explosion overpressure and Jet fire thermal radiation.

Improvement of Charge Strength Guideline for Multi-Energy Method by Comparing Vapor Cloud Explosion Cases

Improvement of Charge Strength Guideline for Multi-Energy Method by Comparing Vapor Cloud Explosion Cases

Investigation and modeling of the LPG tank truck accident in Wenling, China

In this study, the liquefied petroleum gas (LPG) accident in Wenling, Zhejiang Province, China, on June 13, 2020, was analyzed and simulated. An LPG tank truck overturned and collided with the concrete guardrail; the subsequent explosion of the tank released 25.36 t LPG. Shortly afterward, the LPG tank was shot into the air, and the gas cloud ignited, thereby triggering a fire and vapor cloud explosion (VCE). This accident killed 20 people, injured 175 people, and caused significant property loss. The accident timeline was established based on multiple accident images, and the accident process was discussed in detail. The distribution of tank debris, evaporation and spreading of the LPG pool, dispersion of the LPG gas cloud, and VCE were simulated with the EFFECTS and ALOHA software. The images of the accident scene helped to determine and analyze the accident process. In the particular case in which a tank is shot into the air with a continuous two-phase jet, the actual flight distance of the tank is much greater than the prediction of the debris distribution model. The gas cloud distribution simulated with the SLAB model approximately corresponds to a major part of the severely damaged zone. In this accident, the TNO multi-energy method and ALOHA provide relatively consistent predictions with the actual building damage distribution when models use a specific confined explosive mass.

A quantitative correlation of evaluating the flame speed for the BST method in vapor cloud explosions

In recent decades, vapor cloud explosions (VCEs) have occurred frequently and resulted in numerous personnel injuries and large property losses. As a main concern in the petrochemical industry, it is of great importance to assess the consequence of VCEs. Currently, the TNT equivalency method (TNT EM), the TNO multi-energy method (TNO MEM), and the Baker-Strehlow-Tang (BST) method are widely used to estimate the blast load from VCEs. The TNO MEM and BST method determine the blast load from blast curves based on the class number and the flame speed, respectively. To quantitatively evaluate the flame speed for the BST method, the experimental data is adopted to validate the confinement specific correlation (CSC) for the determination of the class number in the TNO MEM. As a bridge, a quantitative evaluation correlation (QEC) between CSC correlation and the flame speed is established and the blast wave shapes corresponding to different flame speeds are proposed. CFD software FLACS was used to verify the quantitative correlation with the numerical models of three geometrical scales. It is found that the calculated flame speeds by the QEC are in good agreement with the simulated ones. A petrochemical plant is selected as a realistic scenario to analyze the TNT EM, TNO MEM, BST method and FLACS simulations in terms of the positive-phase side-on overpressure and impulse at different distances. Compared with the flame speed table, the predicted overpressure from BST curves determined by the proposed QEC is closer to that from FLACS and more conservative. Furthermore, the predicted results of different methods are compared with each other. It is found that the estimated positive-phase side-on overpressure and impulse by the TNO MEM are the largest, and the estimated impulse by the TNT EM is the smallest. Moreover, the estimated overpressure and impulse are larger in the higher reactivity gas.

Dynamic vulnerability assessment of process plants with respect to vapor cloud explosions

Vapor cloud explosion (VCE) accidents in recent years such as the Buncefield accident in 2005 indicate that VCEs in process plants may lead to unpredicted overpressures, resulting in catastrophic disasters. Although a lot of attempts have been done to assess VCEs in process plants, little attention has been paid to the spatial-temporal evolution of VCEs. This study, therefore, aims to develop a dynamic methodology based on discrete dynamic event tree to assess the likelihood of VCEs and the vulnerability of installations. The developed methodology consists of six steps: (i) identification of hazardous installations and potential loss of containment (LOC), (ii) analysis of vapor cloud dispersion, (iii) identification and characterization of ignition sources, (iv) explosion frequency and delayed time assessment using the dynamic event tree, (v) overpressure calculation by the Multi-Energy method and (vi) damage assessment based on probit models. This methodology considers the time dependencies in vapor cloud dispersion and in the uncertainty of delayed ignitions. Application of the methodology to a case study shows that the methodology can reflect the characteristics of large VCEs and avoid underestimating the consequences. Besides, this study indicates that ignition control may be regarded as a delay measure, effective emergency actions are needed for preventing VCEs.

Limit Capabilities of Identifying Materials by High Dual- and Multi-Energy Methods

A method is considered for identifying materials in large-sized test objects by high dual- and multi-energy methods based on assessment of effective atomic number. An algorithm is presented for processing original images produced by dual- and multi-energy methods. The algorithm allows one to determine the effective atomic number of the material of the test object and its fragments. It is proved by a computational experiment that the ADC digit capacity and the mass thickness and effective atomic number of the test-object material have a significant effect on the quality of material identification. The necessity of prefiltering bremsstrahlung to ensure the prescribed identification quality for small thicknesses of fragments of studied objects is substantiated. An algorithm is provided for assessing the limit capabilities of the proposed method in material identification. The fundamental possibility of distinguishing between the following materials has been experimentally proved by numerical modeling: light organics ($$Z = 6$$); mineral materials ($$Z = 9$$); light metals ($$Z = 13$$); calcium ($$Z = 19$$); metals ($$Z = 26$$); heavy metals ($$Z > 50$$).

Specific Features of Material Recognition by the Multi-Energy X-Ray Method

The specific features of recognizing materials of test objects and their structural fragments by the multi-energy method are considered. An approach to the combined usage of the methods of level lines and multiple energies with the aim to improve the accuracy of estimating the effective atomic number is demonstrated. An algorithm is described for the formation and processing of information in the multi-energy method, which allows one to highly accurately measure the effective atomic number and mass thickness of fragments in the test object. The simulation technique has demonstrated the effectiveness of using the material-identification method being analyzed.

Flammable Substances in Korea Considering the Domino Effect: Assessment of Safety Distance.

Benzene, toluene, and xylene (BTX) are flammable substances used in a wide range of raw materials and products. Chemical accidents caused by flammable substances are different from leakage accidents of toxic materials. Initial explosions and fires may cause secondary or tertiary explosions, or fires with nearby flammable materials. This is called the domino effect. In cases of leakage accidents, it is possible to prevent accidents through early control of the leakage to the outside or by bypassing, but it is difficult to cope with explosions because they occur instantaneously. To prevent explosions due to the domino effect, a safety distance must be set. Safety distances vary widely by country. In the case of the United States (US) or the European Union (EU), safety distances are set in various ways depending on the chemical industry and the amount of flammable substances being handled. However, countries such as Korea, Taiwan, and Dubai have comprehensive regulation, and the safety distances are small. In this study, we simulated the range of overpressure at which other chemical equipment could explode when an explosion occurs in a flammable BTX storage tank. There are three types of analysis methods of vapor cloud explosion. PHAST (Process Hazard Analysis Software Tool) and ALOHA (Areal Location of Hazardous Atmosphere) were selected to model explosions using three methods (trinitrotoluene equivalence method, the Netherlands Organization multi-energy method, and Baker-Strehlow-Tang method). The results indicated that the safety distances in the US and EU showed low probability of a domino effect, but those in Korea, Dubai, and Taiwan could lead to a secondary explosions. Therefore, it is necessary to propose a reasonable method to determine safety distances considering the amount and physicochemical characteristics of the flammable substances being used.

Failure of reinforced concrete and tuff stone masonry buildings as consequence of hydrogen pipeline explosions

Pipelines are the most efficient method of transporting large quantities of hydrogen, and the low volumetric energy density of gaseous hydrogen requires that the gas must be compressed to extremely high pressure to be used as a transport fuel. The failure of high pressure hydrogen gas pipelines and subsequent explosion may induce heavy damage to buildings. In this paper, such an issue is addressed for existing reinforced concrete framed buildings and tuff stone masonry buildings. Physical features such as the gas jet release process, flammable cloud size, blast generation and propagation, and explosion effects on structural components of buildings are considered and evaluated through the SLAB integral model, Multi-Energy Method and pressure‒impulse diagrams. Damage to both types of structural components was evaluated and the maximum distance of blast damage was derived in several environmental conditions, contributing to land-use planning and performance-based design/assessment of pipelines and buildings.

Assessing risk and resilience of critical infrastructures in the fuel and energy economy involving failure cascading effects

A practical procedure of risk and resilience assessment, with cascading failures occurring in the fuel and energy economy, is proposed. It is based on the threshold values and multi-energy methods. The probability analysis of the equipment damage is carried out using vulnerability models for various equipment classes and in the process the probit-functional analysis is applied. Resilience indices-criteria are used for assessing the resilience of plants as complex mechanical systems. The procedure proposed enables calculating threshold values of cascading failure; safe distances for equipments; probability assessment of failure propagation. It also adds to identifying the facilities triggering cascading effects; probability of the equipment damage; to assessing the amount of damage and the damage loss rate. The strategy (procedure) allows ranking the equipment as related to the risk of domino effects’ occurrence; analyzing consequences for each cascade direction and the possibility of its propagation on to the following level; evaluating the resilience state of the plant as a technical system. The damage amount and damage loss rate are evaluated comparing the load received and predetermined threshold values of cascading failure for various equipment classes. The strategy (procedure) developed will allow judging about safety of one or other type of a tank farm containing hydrocarbons; the results obtained in the process and the actual data converge. This strategy (procedure) is strongly recommended to be applied by experts in the field of industrial safety in developing industrial safety manifests, safety justification as well as in developing safety registration certificates of critical infrastructures.

Full-Scale Experimental Verification of the Explosion Shock Wave Model of a Natural Gas Pipeline

As developments in natural gas pipelines increasingly incorporate higher grades of steel, larger diameters, and higher pressures, the consequences of an accident caused by leakage, explosion, or ignition become progressively more severe. Currently, major technical obstacles include the quantification of the impact of an explosion shock wave of a high-strength, large-diameter natural gas pipeline, and the selection of a reasonable shock wave overpressure model appropriate to the operating conditions. In this paper, six models of shock wave overpressure theories, namely, the TNT equivalent method, the TNO method, the multienergy method, the British Gas method, the Shell method, and the Lee formula, were compared and analyzed to determine their applicability. A shock wave model adapted to the characteristics of a full-scale test was proposed, and the model verification of a full-scale blasting test was conducted on pipelines with diameters of 1422 mm and 1219 mm, respectively. Subsequent results indicated that the modifications to the TNT equivalent and the test parameters correlated with changes in the suitability of the model. Henrych’s formula calculation model of the British Gas method was found to correspond strongly with the measured value, in which the absolute value of the relative error was less than 30% and the absolute error within the range of 78 m to 800 m was no more than 0.05 MPa. Thus, the Henrych formula was adopted as the primary model formula for the shock wave overpressure calculations in this study. To further correct the error of the model, the trend between the curve obtained by the Henrych formula and the fitting curve of the measured value was compared and analyzed. The positive and negative compensations of the shaded area before and after the intersection point were carried out, and the new error correction overpressure model formula was obtained by fitting, with the error controlled within 15%.

Far-field pressure prediction of a vented gas explosion from storage tanks by using new CFD simulation guidance

Abstract An extension of previous work to predict the far-field overpressures of vented gas explosions from small-medium scale storage tanks is presented. Four actual vented explosion experiments with different methane-air mixture concentrations were conducted. The recorded internal and external pressures from the tests were compared with the predictions from the Multi-Energy Method (MEM) model and Baker–Strehlow–Tang (BST) model. The limitations of these two empirical models in predicting the vented gas explosion pressures are discussed. Compared to the empirical model predictions, a combined CFD modelling approach (FLACS simulation plus ANSYS Fluent simulation) yields respectable accuracy in far-field overpressure prediction. The flame speed and initial mechanical energy, which are incorrectly assumed in the MEM and BST models, are taken into account in this study. Furthermore, this study simplifies previous work by using FLACS simulations for internal pressure estimation and a newly derived correlation for far-field pressure estimation. In addition to the peak pressure estimation, the equations to calculate the pressure-time history duration and shape are proposed. Computational efficiency and prediction accuracy are both achieved in the proposed approach for far-field overpressure predictions.

Influence of geometrical shapes on unconfined vapor cloud explosion

The vapor cloud explosion (VCE) usually results in large financial and environmental damages. There are many methods to evaluate the consequences of VCE and one of them is the TNO Multi-Energy method (MEM). In the practical applications, the MEM has some weaknesses. For example, it is assumed that the explosion model is hemispherical, which is usually inconsistent with the actual situations. In order to examine the effect of the geometrical shapes on explosion characteristics, a constant volume of clouds with different height-width ratios and length-width ratios were studied. For the vapor cloud with a given volume (32 m3), the geometrical shapes have a great influence on the explosion overpressure, but little on the explosion temperature. When the height-width ratio is 0.5 (the corresponding geometrical shape is 4 m × 4 m × 2 m), the explosion peak overpressure reaches the maximum of 1.57 bar, which is 3.6 times of that (0.44 bar) for the 2 m × 2 m × 8 m vapor cloud. For a constant volume of clouds with the four different height-width ratios in this paper, the MEM predictions correspond to three different initial explosion strengths. As effect of the geometrical shapes on the vapor cloud explosion was not taken into account in the MEM, its predicted results have a greater deviation, especially in the far field. For the scenarios calculated in this study, the relative error for the explosion overpressure predicated in the MEM reaches 150%.