Reduction In Overpressure Research Articles

Louvered jet fire deflector – concept and concept validation for flame length reduction, flame deflection and explosion overpressure reduction

In hydrocarbon processing industries, the standard approach to prevent jet fire escalation to adjacent facilities is to provide a solid fire wall. However, a solid firewall impedes the air flow through the plant, decreasing ventilation and increasing the potential flammable gas cloud size resulting in the generation of higher explosion overpressures if the gas cloud finds an ignition source. The conflicting impact of solid fire walls in preventing jet fire escalates but conversely increasing the potential explosion overpressures is a perennial design issue faced by safety engineers. This paper presents an alternate louvered jet fire deflector design concept; along with the validation work undertaken to demonstrate the explosion overpressure reduction benefits of the louvered wall application. This louvered jet fire deflector concept was subsequently engineered, fabricated, tested and has been incorporated into the plant design. This paper is written to increase the knowledge and awareness of safety engineers of an alternate option to optimise and balance the fire and explosion risk management.

Hydrodynamics in subsurface CO2 storage: Tilted contacts and increased storage security

Hydrodynamic aquifers with horizontal variations in overpressure and brine flow have been reported from sedimentary basins worldwide. In a hydrodynamic aquifer pore-waters flow in the direction of overpressure reduction, whereas trapped hydrocarbons remain static. The main effect of this pressure disequilibrium in the aquifer is a tilt of the free water levels (FWL) in the direction of lower overpressure.Although the impact of hydrodynamics on the petroleum system is established in the oil industry and provides important information for exploration and field development, the interaction of CO2 storage and hydrodynamic flow has hardly been investigated. Supercritical CO2 has a density comparable with oil densities in known hydrodynamic systems in the North Sea. Hence, a tilted CO2-water FWL is expected and has to be taken into account during the planning of CO2 storage. Hydrodynamic spill points will replace structural spill points as a parameter in CO2 storage capacity calculations.Storage security is dependent on CO2 dissolution rates, among other factors. The more effectively CO2 dissolves into brine the more CO2 will be permanently stored in the subsurface. Numerical simulations show that CO2 storage in hydrodynamic aquifers enhances the dissolution of CO2 compared with a static regime. When CO2 dissolves into brine, the brine density increases and the CO2-saturated brine sinks to the bottom of the reservoir and is replaced by under-saturated brine. In a hydrodynamic system the brine saturated with CO2 will be removed more effectively from the CO2-brine interface. Hence, CO2 comes in contact with more under-saturated brine and dissolves at a greater rate.The presence of hydrodynamic flow in a reservoir requires a high degree of understanding but research on oil reservoirs has proven that it is an uncertainty that can be adequately characterized. For long term CO2 storage operations hydrodynamic flow can even be an opportunity for more secure CO2 storage.

Improvement in head blast-protection via the use of polyurea-augmented advanced combat helmet

Purpose – The purpose of this paper is to optimize the design of the advanced combat helmet (ACH) currently in use, by its designers in order to attain maximum protection against ballistic impacts (fragments, shrapnel, etc.) and hard-surface/head collisions. Since traumatic brain injury experienced by a significant fraction of the soldiers returning from the recent conflicts is associated with their exposure to blast, the ACH should be redesigned in order to provide the necessary level of protection against blast loads. In the present work, augmentations of the ACH for improved blast protections are considered. These augmentations include the use of a polyurea (a nano-segregated elastomeric copolymer)-based ACH external coating/internal lining. Design/methodology/approach – To demonstrate the efficacy of this approach, instrumented (unprotected, standard-ACH-protected, and augmented-ACH-protected) head-mannequin blast experiments are carried out. These experimental efforts are complemented with the appropriate combined Eulerian/Lagrangian transient non-linear dynamics computational fluid/solid interaction analysis. Findings – The results obtained indicated that: when the extent of peak over-pressure reduction is used as a measure of the blast-mitigation effectiveness, polyurea-based augmentations do not noticeably improve, and sometimes slightly worsen, the performance of the standard ACH; when the extent of specific impulse reduction is used as a measure of the blast-mitigation effectiveness, application of the polyurea external coating to the standard ACH improves the blast-mitigation effectiveness of the helmet, particularly at shorter values of the charge-detonation standoff distance (SOD). At longer SODs, the effects of the polyurea-based ACH augmentations on the blast-mitigation efficacy of the standard ACH are inconclusive; and the use of the standard ACH significantly lowers the accelerations experienced by the skull and the intracranial matter. As far as the polyurea-based augmentations are concerned, only the internal lining at shorter SODs appears to yield additional reductions in the head accelerations. Originality/value – To the authors’ knowledge, the present work contains the first report of a combined experimental/computational study addressing the problem of blast-mitigation by polyurea-based augmentation of ACH.

Suppression of vortex shedding and its mitigation effect in gas explosions: an experimental study

This paper reports occurrence of vortex shedding behind bluff-bodies in gas explosions, methods to suppress them using passive flow control techniques, and their overall impact on explosion overpressures. The pressure-time histories from a series of explosion tests, using an initially quiescent propane-air mixture in a vented channel of dimensions 1.5 m × 0.28 m × 0.3 m, are presented. Selected high-speed video frames visualizing the flame propagation are also presented. Three different bluff-obstruction scenarios are considered: 1) a reference case with a single smooth circular cylinder of diameter D = 0.0157 m, 2) a single cylinder identical to that in the reference case, mounted with a splitter plate of varying length from 5.13D to 0.26D, width 17.8D and thickness 0.06D, and 3) a single helically wired cylinder with wire diameter 0.1D and pitch 4D or 8D. All circular cylinders had a length of 17.8D and were mounted normal to the direction of the flow, spanning the channel cross-section 0.5 m downstream of the ignition point. The obstructions were inserted in the rig using a unique experimental setup. The peak overpressure generated by the explosion is of main interest. Both vortex shedding suppression techniques 2) and 3) yielded significant reduction in maximum overpressures when compared to the reference cylinder case 1). While all splitter plate configurations successfully reduced the maximum explosion overpressure, the splitter plates with length 1.02D and 0.51D were the most efficient, with an average reduction in overpressure of 32 ± 3%. The helical steel wire configurations also had a significant effect, with 25 ± 3% and 20 ± 3% reduction in the maximum overpressure for pitch 4D and 8D, respectively. The high-speed video visualization further buttressed the quantitative findings in the pressure measurements and clearly showed vortex shedding suppression. The current observations imply that the contribution from vortex shedding, i.e. apart from turbulence effects, to the overpressure generation in gas explosions is significant. The modelling community must consider this while preparing their simulators.

Influence of barrier material and barrier shape on blast wave mitigation

This paper investigates means for increasing the effectiveness of a blast barrier using various types of surfacing. It builds on previous research on the blast effect mitigation properties of rigid concrete blast barriers. Previous research has studied barriers with a smooth surface. The effectiveness of rigid smooth barriers in reducing shock wave overpressure has been proven to be low. Their main contribution is in absorbing flying debris or shrapnel created by an explosion, and thereby reducing the risk of injury to the occupants of a building. This paper suggests ways to achieve greater safety by increasing the blast mitigation properties of barriers. It studies the influence of various materials and shapes on the effectiveness of a barrier, and proposes methods for providing increased overpressure reduction while keeping the same overall dimensions. A barrier of this kind provides additional security for the occupants of a building without disrupting the functionality of the interior with a massive obstacle. The use of a deformable porous material is compared with the use of rigid durable ultra-high performance fibre-reinforced self-compacting concrete (UHPFRSCC), developed by the authors especially for application in blast-resistant structures. The results of an original experimental program are used to determine the influence of barrier shape and barrier material on blast wave mitigation. The effect of uneven barrier surfacing on a shock wave is demonstrated on a finite element numerical model calculated using LS-DYNA. Results of the analysis proved that the use of uneven surface has a positive effect on blast mitigation properties of a barrier without affecting its shrapnel absorption capabilities. All experiments and FEM models consistently proved that a barrier has significant overpressure reduction effect in the area directly behind the barrier. The comparison of experimental measurements of rigid and deformable barrier material showed no drastic increase in mitigation properties of deformable barrier.

Mitigation of blast loadings on structures by an anti-blast plastic water wall

Seven in-situ tests were carried out in far field to study the blast mitigation effect of a kind of water filled plastic wall. Test results show that the mitigation effect of water filled plastic wall is remarkable. The maximum reduction of peak reflected overpressure reaches up to 94.53%, as well as 36.3% of the minimum peak reflected overpressure reduction in the scaled distance ranging from 1.71 m/kg1/3 to 3.42 m/kg1/3. Parametric studies were also carried out. The effects of the scaled gauge height, water/charge scaled distance (the distance between the explosive charge and the water wall), water wall scaled height and water/structure scaled distance (the distance between the water wall and the structure) were systematically investigated and compared with the usual rigid anti-blast wall. It is concluded that these parameters affect the mitigation effects of plastic water wall on blast loadings significantly, which is basically consistent to the trend of usual rigid anti-blast wall. Some formulae are also derived based on the numerical and test results, providing a simple but reliable prediction model to evaluate the peak overpressure of mitigated blast loadings on the structures.

Water hammer in the pump-rising pipeline system with an air chamber

Water hammer following the tripping of pumps can lead to overpressure and negative pressure. Reduction in overpressure and negative pressure may be necessary to avoid failure, to improve the efficiency of operation and to avoid fatigue of system components. The field tests on the water hammer have been conducted on the pump rising pipeline system with an air chamber. The hydraulic transient was simulated using the method of characteristics. Minimizing the least squares problem representing the difference between the measured and predicted transient response in the system performs the calibration of the simulation program. Among the input variables used in the water hammer analysis, the polytropic exponent, the discharge coefficient and the wave speed were calibrated. The computer program developed in this study will be useful in designing the optimum parameters of an air chamber for the real pump pipeline system. The correct selection of air chamber size and the effect of the inner diameter of the orifice to minimize water hammer have been investigated by both field measurements and numerical modeling.

Testing parameters affecting gas analysis value of particleboard

The gas analysis method according to EN 717 part 2 is a well-known technique to measure the formaldehyde emission of plywood and coated wood-based materials for quality control purposes. There is an increasing interest to apply this method also for uncoated wood-based panels compared to the perforator method (EN 120: 1992) owing to many reasons. As there is still limited experience in testing particleboard with this method, it is the aim of this study to evaluate the effect of some parameters to ensure correct and precise testing using the gas analysis method. Furthermore, the study aimed to show how the m.c. of panels before testing affects the Gm, and to calculate an m.c. correction factor from these results for particleboard with modern bonding systems at a low emission level. Gas analysis value and m.c. show a very good correlation. Based on this correlation an m.c. correction factor can be determined, which facilitates an m.c. correction of Gm data. This may help to improve the quality of Gm data for quality control and data comparison (i.e. for round robin tests). Combining the sampling for hour 3 and 4 as well as 2, 3 and 4 has no significant effect on the level of formaldehyde emission tested. Also the accuracy of testing was not reduced. Consequently, the change in sampling procedure may lead to a reduction on the required number of water analyses needing to be performed in the laboratory, and therefore to a reduction in consumption of chemical consumables and expenditure of human labour. The reduction of overpressure during gas analysis did not have a major effect on the values as such, but increased the coefficient of variation. Also, an increase in air flowrate did not affect the Gm at lower emission levels.

Coupled multiphase flow and geomechanics model for analysis of joint reactivation during CO2 sequestration operations

The initial and primary trapping mechanism for long term subsurface sequestration of CO2 is structural trapping beneath a low permeability caprock layer. Maintaining caprock integrity during injection operations is paramount to successful sequestration. Evaluation of jointed/fractured caprock systems is of particular concern to CO2 sequestration because creation of fractures or reactivation of joints can lead to enhanced pathways for leakage.In this work, a joint model is introduced to describe joint reactivation during injection of CO2. The model assumes equally spaced anisotropic joint sets with non-linear normal stiffness and linear shear stiffness. Normal displacement of the joints is mapped into a dynamically evolving effective anisotropic permeability tensor, assuming a cubic law for fracture permeability as a function of joint aperture. A model problem is presented to demonstrate features of the joint model and how it affects the coupled geomechanics and flow during injection of CO2 into deep saline aquifers. The model is used to demonstrate injection reservoir properties and injection rates that have potential for inducing leakage through the caprock due to overpressures associated with CO2 injection.In situations where pore pressure approaches or exceeds lithostatic pressure under a constant-rate, 30 year injection, the model indicates between 16 and 20% of injected CO2 could leak past the primary caprock after 50 years. The model also indicates a concomitant overpressure reduction that could signal caprock leakage during the injection.

Modelling the mitigation of hydrogen deflagrations in a nuclear waste silo ullage by depleting the oxygen concentration with nitrogen

It is expected that significant transient releases of hydrogen could occur during the decommissioning of a nuclear waste storage plant that would result in a transient flammable atmosphere. Interest has been expressed in the use of nitrogen dilution in a vented silo ullage space in order to reduce the oxygen level and thereby mitigate the overpressure rise should a hydrogen–air deflagration occur.In the work presented here the data characterising the influence of oxygen depletion via nitrogen dilution upon the burning velocity of hydrogen–air mixtures have been obtained using the COSILAB code (and also compared with experimental test data). These data have then been used with the FLACS-HYDROGEN CFD-tool to try to predict the potential explosion overpressure reduction that might be achieved using oxygen depletion (via nitrogen dilution), for a transient hydrogen bubble sudden gaseous release (SGR) scenario occurring in a silo ullage type geometry.The simulation results suggest that using nitrogen dilution to deplete the oxygen levels to 12.5% or 9.9% would produce only a relatively modest reduction in the predicted peak overpressure. However, with an oxygen depletion level of 7%, the rate of pressure rise is more substantially slowed and the predicted maximum pressure rise is significantly reduced.

Quantification of hydrodynamic effects on capillary seal capacity

Whether a reduction in overpressure across a hydrocarbon column and its seal will reduce the column height that the seal is capable of supporting has been much debated. Recent studies have focused on measuring water relative permeability at high capillary pressure, and have concluded that hydrocarbon columns may be sufficiently permeable to water for the seal capacity to be unaffected by hydrodynamic flow in most situations. A new method for estimating the capillary seal capacity is developed which properly takes into account viscous as well as gravity and capillary forces. A reassessment of existing analyses indicates that hydrodynamic flow has a greater influence on the seal capacity than previously thought. Sets of sensitivity models, including a range of reservoir and seal geometrical and petrophysical characteristics, indicate that – as a general rule – hydrodynamic flow should not be neglected when assessing capillary seal capacity. The sealing capacity of thick top seals above reservoirs with a basal aquifer are least likely to be affected by hydrodynamic flow. The sealing capacity of membrane fault seals, irrespective of whether they have a basal or edge aquifer, may be influenced by realistic overpressure differences. Simple end-member equations define the possible influence of hydrodynamic flow in a particular situation, and only if this is significant should a more comprehensive evaluation be considered.

Modelling the mitigation of a hydrogen deflagration in a nuclear waste silo ullage with water fog

During the decommissioning of certain legacy nuclear waste storage plants it is possible that significant releases of hydrogen gas could occur. Such an event could result in the formation of a flammable mixture within the silo ullage and, hence, the potential risk of ignition and deflagration occurring, threatening the structural integrity of the silo. Very fine water mist fogs have been suggested as a possible method of mitigating the overpressure rise, should a hydrogen–air deflagration occur. In the work presented here, the FLACS CFD code has been used to predict the potential explosion overpressure reduction that might be achieved using water fog mitigation for a range of scenarios where a hydrogen–air mixture, of a pre-specified concentration (containing 800L of hydrogen), uniformly fills a volume located in a model silo ullage space, and is ignited giving rise to a vented deflagration. The simulation results suggest that water fog could significantly reduce the peak explosion overpressure, in a silo ullage, for lower concentration hydrogen–air mixtures up to 20%, but would require very high fog densities to be achieved to mitigate 30% hydrogen–air mixtures.

Corrective measures based on pressure control strategies for CO 2 geological storage in deep aquifers

A prerequisite to the wide deployment at an industrial scale of CO 2 geological storage is demonstrating that potential risks can be efficiently managed. Corrective measures in case of significant irregularities, such as CO 2 leakage, are hence required as advocated by the recent European directive on Carbon Capture and Storage operations. In this regard, the objective of the present paper is to investigate four different corrective measures aiming at controlling the overpressure induced by the injection operations in the reservoir: stopping the CO 2 injection and relying on the natural pressure recovery in the reservoir; extracting the stored CO 2 at the injection well; extracting brine at a distant well while stopping the CO 2 injection, and extracting at a distant well without stopping the CO 2 injection. The efficiency of the measures is assessed using multi-phase fluid flow numerical simulations. The application case is the deep carbonate aquifer of the Dogger geological unit in the Paris Basin. A comparative study between the four corrective measures is then carried using a cost-benefit approach. Results show that an efficient overpressure reduction can be achieved by simply shutting-in the well. The overpressure reduction can be significantly accelerated by means of fluid extraction but the adverse consequences are the associated higher costs of the intervention operations.

Effect of pressure vessel size on the formation of gas hydrates

A Seafloor Process Simulator (SPS) has been used for mesoscale experiments investigating the nature of hydrate nucleation and dissociation. The SPS is a 72 L vessel which establishes the pressures and temperatures required for methane and carbon dioxide hydrate stability. This paper describes the experiments that have been performed in the SPS and have been duplicated in the smaller Parr vessel (450 mL). It was found that experiments in the SPS resulted in hydrates consistently forming at lower overpressures and in shorter induction times than equivalent experiments in the Parr vessel. The variability of pressure and/or induction time for hydrate formation was not eliminated by using the SPS, but it appeared to be less dramatic (small coefficients of variation) when compared with a 450 mL Parr vessel. Based on the experiments performed using the SPS this reduction in overpressure and/or induction time required for the accumulation of hydrates may be attributed to increased bubble surface area, increased gas concentration, increased lifetime of bubbles, increased total volume of the SPS, or a combination of the above. Mesoscale experiments, such as those in the SPS, may perhaps be more representative of hydrate accumulation in the natural environment.

Geochemistry of formation water and its implication on overpressured fluid flow in the Dongying Depression of the Bohaiwan Basin, China

This study of the geochemistry of formation waters in the Dongying Depression of the Bohaiwan basin, East China, unravels a close relationship between vertical zonality and overpressured fluid flow. The zones have distinctive original pore waters because the sediments formed under different climate conditions. The highest value of the total dissolved solid in the formation water occurs in the ES4 member of Shahejie Formation due to the dissolution of halite and gypsum beds. In the overlying ES3 and ES2 members, low salinity water occurs, except for near syndepositional fault zones where a significant increase in salinity of formation water and a reduction in overpressure were observed. This fact indicates strong overpressured fluid flow where thermal anomalies have been observed, as evidenced from thermal gradient and fluid inclusion homogenization temperatures. The results indicate that the geochemistry of pore water may be used to help identify the main migration pathways for overpressured fluid flow with hydrocarbons.

Modelling the effects of transient overpressure on the petroleum systems of the UK North East Atlantic Margin and northern North Sea areas: implications for the deep water South Atlantic and Gulf of Mexico

Transient fluid overpressure development appears to be a major control on the contrasting petroleum systems of Faroe–Shetland Basin (FSB) on the UK North East Atlantic margin and the northern North Sea North Viking Graben (NVG). Middle and Upper Jurassic shales are the main source rocks in both the NVG and the FSB, but the hydrocarbons within these basins differ significantly. Oil is predominant with only minor associated gas in the FSB while the NVG has a significantly higher proportion of dry gas. Both are rifted basins but the amount of rifting, heat flow and depth of burial were all considerably greater in the FSB, and consequently higher maturity hydrocarbons should be present in the FSB than in the NVG. The difference in hydrocarbon type between the basins arises from the different Cenozoic burial and, importantly, pressure histories in the two basins. Oil generation commenced during the early Cretaceous in both basins and some Mesozoic reservoirs may have been charged at this time. Rapid burial of thick argillaceous sediments in both basins from the late Cretaceous into the Tertiary led to overpressure development. The thermodynamic effect of this fluid overpressure in the source rocks was the retardation of hydrocarbon generation. In the NVG, regional uplift during the Tertiary resulted in transient overpressure reductions in the source rocks such that hydrocarbon generation, which had ceased prior to the uplift events, restarted due to the pressure reduction outstripping the effects of reduced temperatures. Although the source rocks were cooler than those in the FSB, the reduction in overpressure was sufficient to result in gas generation from both the Middle Jurassic and lower part of the Upper Jurassic source rocks. Conversely, although the FSB was also uplifted during short-lived Paleogene and Neogene events, the greater thickness of argillaceous late Cretaceous sediments reduced the transient overpressure loss in the source kitchens compared with the NVG. The maturity of the source rocks in the FSB was therefore held in the late oil window and, as a consequence, oil is the predominant hydrocarbon phase in this basin. The importance of overpressure development (or lack of it) and its subsequent release has major implications for petroleum prospectivity of basins. This is illustrated using the NE Kwanza Basin (Angola) and the Mississippi Fold Belt in the Gulf of Mexico (GoM). Whereas there are no commercial hydrocarbon discoveries in the deepwater Kwanza Basin due to lack of regional seal between the oil mature Pre-Salt source and the overlying migration conduit into the shelf, significant oil reserves occur in the deepwater GOM where the source rock depth (∼10 km) might be expected to preclude the presence of oil. The key to the release of oil from the source kitchens is the salt movement that occurs during the Neogene with the formation of salt canopies. As the salt moves vertically, it reduces the overpressure, thereby enabling oil generation to restart and migrate vertically along faults.

Overpressure and noise due to multiple airbag systems in a passenger car

Multiple airbag systems in passenger cars can generate overpressure and noise that may be hazardous to human hearing. Overpressure is compression of the air inside a closed compartment caused by deployment of the bags. Noise results from the action of the gas inflating the bags. SAE J247 provides a standard for measuring the combination of overpressure and noise in a passenger compartment. A special microphone has recently been developed that meets this standard, which operates down to a fraction of a hertz. Details of the microphone are given. Little appears to have been published on the overpressure and noise of modern multiple airbag systems, but early results [R. Hickling, ‘‘The noise of the automotive safety air cushion,’’ Noise Control Eng., May–June, 110–121 (1976)] provide a basic understanding of the phenomenon. Spectral data shows that peak overpressure occurs at about 2 to 3 Hz. A significant reduction in overpressure and noise can be achieved with an aspirating airbag, originally developed at General Motors, whose outer structure is inflated with gas from the inflator, and whose inner structure draws in air from the passenger compartment through one-way cloth valves. Tests have shown that such bags function well when impacted.

Cook-off in aircraft guns

During the decommissioning of certain legacy nuclear waste storage plants it is possible that significant releases of hydrogen gas could occur. Such an event could result in the formation of a flammable mixture within the silo ullage and, hence, the potential risk of ignition and deflagration occurring, threatening the structural integrity of the silo. Very fine water mist fogs have been suggested as a possible method of mitigating the overpressure rise, should a hydrogen–air deflagration occur. In the work presented here, the FLACS CFD code has been used to predict the potential explosion overpressure reduction that might be achieved using water fog mitigation for a range of scenarios where a hydrogen–air mixture, of a pre-specified concentration (containing 800 L of hydrogen), uniformly fills a volume located in a model silo ullage space, and is ignited giving rise to a vented deflagration. The simulation results suggest that water fog could significantly reduce the peak explosion overpressure, in a silo ullage, for lower concentration hydrogen–air mixtures up to 20%, but would require very high fog densities to be achieved to mitigate 30% hydrogen–air mixtures.