Pressure Relief System Research Articles

An experience on wheelchair bank management

In this article, we described the wheelchair bank program at a local hospital and our experiences in managing the service over the past 10 years from 1996 to 2005. This article also reported statistical information related to the acquisitions of wheelchairs and adaptive components, including body support and pressure relief systems. The cost benefit of recycling seating and mobility equipments for use by children with neuromuscular diseases was revealed. With the reference of the reported data, the demands on specific types of wheelchairs and adaptive parts were disclosed to facilitate budget planning of similar services.

CHEMICAL BOARD BLASTS BP Merritt

SAFETY RECOMMENDATIONS for petroleum refineries, triggered by a fatal accident in March 2005 at a Texas City, Texas, BP refinery, were issued by the Chemical Safety & Hazard Investigation Board (CSB) on Oct. 31. A day earlier, the board ripped into BP for failing to act on long-running plant safety problems. The board's recommendations focus on a refinery pressure-relief system that failed and resulted in an explosion at the BP plant, killing 15 workers and injuring 180 others. A distillation tower and attached blowdown drum were overfilled with highly flammable liquid hydrocarbons during start-up of the plant's octane-boosting isomerization unit, CSB says. The blowdown drumintended to capture excess hydrocarbons—overflowed and exploded in a geyser of flame as it was vented directly to the atmosphere rather than through a flared, controlled safety system. The board urges the American Petroleum Institute and the Occupational Safety & Health Administration (OSHA) to require refineries to eliminate unsafe bl...

Containment system design

AbstractThis article deals with the design considerations for several plant containment systems that were installed as part of the emergency pressure relief system. In all cases, the quench tank approach with vapor suppression was utilized. The examples presented include: (1) multiple batch reactors handling vinyl monomers, (2) multiple initiator charge vessels, and (3) multipurpose batch reactors with possible Grignard‐type reactions. The design considerations include: quench fluid selection, sizing of the quench tank, fluid mixing, sparging dynamics, vapor condensation efficiency, and post relief heatup. © 2006 American Institute of Chemical Engineers Process Saf Prog, 2006

Modular HTR confinement/containment and the protection against aircraft crash

Does an HTR need a containment – pressure resistant – or is it possible – licensable – to have only a so-called confinement. The answer depends on both the results of the safety analysis of the accidents considered in the design and the acceptance by the licensing authorities and the public of a safety approach only based on severe core damage exclusion. The safety approach to be developed for modular HTRs must describe the application of the defence in depth principle for such reactors. Whatever the requirements on the last confinement barrier could be, a convincing demonstration of the exclusion of any severe core damage is needed, relying on exhaustive and bounding considerations of severe core damage initiators and the use of non-questionable arguments. The paper presents the containment issues for HTRs based on German experience background and considerations for modern modular HTR safety approach including beyond design situations. • For the German HTRs (designed in the 80s), it could be shown in the licensing procedures in Germany that there was no need for a pressure retaining and gas tight containment to enclose radioactive nuclides released from the nuclear heat source. Instead, the confinement envelope acted in conjunction with other barriers to minimize the release of radioactive nuclides and the radiological impact on the environment. • The confinement envelope consisted of the reactor building, a sub-atmospheric pressure system, a building pressure relief system, an HVAC systems isolation and a filtration system. • During a major depressurization accident, unfiltered releases were discharged to the environment. The analyses results show that the environmental impact was far below the dose limits according to the German Radiological Protection Ordinance, even when the effect of filters was not taken into account. • The demonstration strongly relied on the assumptions made for the source term definition, e.g. the fuel particles failure rates (under irradiation and during accidental conditions), the diffusion data, the dust data and the deposition/lift-off mechanisms. • For modern modular HTRs, the last confinement barrier performances will have to be determined in accordance with the set of accidents to be considered in the design including internal and external hazards and the limits targeted for the public and the environment protection. Further more the paper presents an analysis of effects of a deliberate crash of a large commercial airliner on a former German HTR design.

Experimental Determination of Two-Phase Flow Rates of Hydrocarbons Through Restrictions

Accurate prediction of flow rate through a given restriction is important in the design of pressure relief and blowdown systems. While this prediction is well understood for single-phase gases and liquids, it is much less well understood for two-phase gas-liquid flows. We report here a large number of measurements conducted on highly volatile mixtures of hydrocarbons (mainly C1 to C10) at pressures up to 100 bar and flow rates of up to 4 kg s−1. For mixtures in which the liquid mass fraction is below about 0.8, we find that the homogeneous equilibrium model (HEM) provides a good approximation: the discharge coefficient varies from 0.90 for pure single-phase gas flow to about 0.98 when the upstream liquid fraction is 0.8. For flows of compressed volatile liquid, we find that the incompressible-flow model provides a good approximation, with a discharge coefficient of 0.60: however, preliminary experiments indicate that this simple model progressively breaks down as the volatile gas content increases. We also find that, in a number of circumstances, the widely-used recommendations of the American Petroleum Institute (API) can significantly over- or under-predict flow rates through restrictions if misapplied.

Fire Versus Non-Fire Contingencies: A Study of Pressure-Relief Device Sizing Risks

There are tens of thousands of industrial manufacturing facilities operating throughout the world. Each chemical plant, petroleum refinery, pharmaceutical plant and other manufacturing facility has equipment and piping systems that operate under pressure. In the event of excessive overpressure, equipment or piping failures could result in economic loss to business, environmental contamination, and health and safety risks. To reduce such risks, equipment and piping systems that operate under pressure must be protected from excessive overpressure. This is accomplished with the installation of pressure-relief devices, which must be properly sized and specified for the intended service conditions. More specifically, overpressure protection is provided by pressure-relief devices that are sized, selected, specified and installed for the postulated governing overpressure contingency. To adequately size a pressure-relief device to provide overpressure protection for equipment and piping, several relief event scenarios always should be considered. In the U.S.A., federal and state regulations require operating industrial facilities to have risk management programs in place that include the design basis for safety-relief systems installed to protect pressurized equipment from overpressure. For new installations, the pressure-relief system design philosophy should be established during the project design phase. However, for process facilities that have been in operation for many years, the original design basis and calculations for the safety-relief devices often are no longer available. For existing pressure-relieving installations, fitness-for-service assessments should include verification of the relief device size and specification, and review and substantiation of required documentation. This paper presents results from a study intended to examine which overpressure relief contingency, if any, most often governs the size of relief devices that are used to protect equipment and piping systems. The required elements of a pressure-relieving system sizing and documentation program are described. The author emphasizes seven relief contingencies to be considered when sizing pressure-relief devices. Some restrictions and limitations of the codes and standards that are applied for design guidance of pressure-relieving systems are challenged. For this study, relief device sizing data was compiled from a number of chemical and petrochemical project applications to provide a reasonable sample of contingencies that governed the sizes of existing and new safety-relief valves and rupture disks. The study results show that a significant number of pressure-relief devices presently installed in the U.S.A. likely are undersized. This further suggests that, worldwide, an alarming number of pressure-relief devices may be undersized.

Pilot-Scale Evaluation of the Inhibition of Exothermic Runaway

Even if an emergency pressure relief system successfully prevents catastrophic failure of a chemical reactor, there may be a significant release of toxic or flammable material. For these and other reasons, reaction inhibition is being considered as an alternative or additional measure. In this study, reaction inhibition system design methodology was evaluated at a facility specially designed for investigating runaway reactions on a scale which is reasonably representative of industrial installations. Experimental results on the polymerization of styrene initiated by benzoyl peroxide and subsequently inhibited by the addition of tertiary butyl catechol are reported. These 340 litre pilot-scale runaway polymerization tests were supported by 1 litre laboratory-scale runaway reaction experiments and adiabatic calorimetry. The pilot-scale experiments on the polymerization of styrene have demonstrated that with a simplified kinetic model and analysis of heat and mass transfer it is possible to predict the conditions which will lead to runaway on large-scale. The influence of varying agitation speed on the effectiveness of reaction inhibition is discussed.

The Effect of Reduced Design Margin on the Fire Survivability of ASME Code Propane Tanks

In the 1999 addenda to the 1998 ASME pressure vessel code, Section VIII, Div. 1 there was a change in design margin for unfired pressure vessels from 4.0 to 3.5. This has resulted in the manufacture of propane and LPG tanks with thinner walls. For example, the author has purchased some new 500 gallon ASME code propane tanks for testing purposes. These tanks had the wall thickness reduced from 7.7 mm in 2000 to 7.1 mm in 2002 and now to 6.5 mm in 2004. These changes were partly due to the code change and partly due to other factors such as steel plate availability. In any case, the changes in wall thickness significantly affects the fire survivability of these tanks. This paper presents both experimental and computational results that show the effect of wall thickness on tank survivability to fire impingement. The results show that for the same dank diameter, tank material, and pressure relief valve setting, the thinner wall tanks are more likely to fail in a given fire situation. In severe fires, the thinner walled tanks will fail earlier. An earlier failure usually means the tank will fail with a higher fill level, because the pressure relief system has had less time to vent material from the tank. A higher liquid fill level at failure also means more energy is in the tank and this means the failure will be more violent. The worst failure scenario is known as a boiling liquid expanding vapor explosion and this mode of failure is also more likely with the thinner walled tanks. The results of this work suggest that certain applications of pressure vessels such as propane transport and storage may require higher design margins than required by Section VIII ASME code.

Technological advances in powered wheelchairs.

During the last 40 years, there have been revolutionary advances in power wheelchairs. These unique wheelchair systems, designed for the physically immobile patient, have become extremely diversified, allowing the user to achieve different positions, including tilt, recline, and, more recently, passive standing. Because of this wide diversity of powered wheelchair products, there is a growing realization of the need for certification of wheeled mobility suppliers. Legislation in Tennessee (Consumer Protection Act for Wheeled Mobility) passed in 2003 will ensure that wheeled mobility suppliers must have Assistive Technology Supplier certification and maintain their continuing education credits when fitting individuals in wheelchairs for long-term use. Fifteen other legislative efforts are currently underway in general assemblies throughout the US. Manufacturers, dealers, hospitals, and legislators are working toward the ultimate goal of passing federal legislation delineating the certification process of wheeled mobility suppliers. The most recent advance in the design of powered wheelchairs is the development of passive standing positions. The beneficial effects of passive standing have been documented by comprehensive scientific studies. These benefits include reduction of seating pressure, decreased bone demineralization, increased bladder pressure, enhanced orthostatic circulatory regulation, reduction in muscular tone, decrease in upper extremity muscle stress, and enhanced functional status in general. In February 2003, Permobil, Inc., introduced the powered Permobil Chairman 2K Stander wheelchair, which can tilt, recline, and stand. Other companies are now manufacturing powered wheelchairs that can achieve a passive standing position. These wheelchairs include the Chief SR Powerchair, VERTRAN, and LifeStand Compact. Another new addition to the wheelchair industry is the iBOT, which can elevate the user to reach cupboards and climb stairs but has no passive standing capabilities. In addition, the physically immobile patient must be seated on an ERGODYNAMIC Seating System 2000, which is inflated by the alternating pressure compressor 8080. This seating system has a deep center seam between the two ischial-support chambers, which provides a recess for the coccyx. The pre-ischial crossbar compartment inflates during each cycle to prevent the pelvis from slipping forward. It is essential that the physician of the immobile patient order two ERGODYNAMIC Seating Systems 2000 because the patient must have an additional seating system in the case one leaks. Moreover, two compressors are necessary because each compressor must be serviced after 2500 hours of use. For the protection of the consumer, these pressure relief systems must be supplied and serviced by a Certified Rehabilitation Technology Supplier such as Wheelchair Works Inc. Despite the indisputable scientific evidence of the medical benefits of passive standing for the immobile user, few individuals have access to these revolutionary wheelchairs. Consequently, it is mandatory that the medical community, headed by specialists in physical and occupational therapy as well as rehabilitation medicine, CRTS, and manufacturers collaborate in a national education campaign to convince Medicare/Medicaid and all commercial insurance companies to approve immediately these assisted technologies. This program is essential so that the physically immobilized patient can achieve the undisputed physical benefits of passive standing.

Numerical Investigation on the Long-term System Transient Response of a SWR Event in a LMR

In order to investigate the later phase of a sodium-water reaction (SWR) event, the code SELPSTA (Sodium-water reaction Event Later Phase System Transient Analyzer) has been developed and the analysis for the long-term system dynamic responses of a SWR event in KALIMER (Korea Advanced Liquid MEtal Reactor) has been made. The SELPSTA code uses the very simple analysis model applied only to the reaction period characterized by a bulk motion, and makes the very quick and concise computation possible. The code reasonably predicts the quasi-steady system transients and has the superiority in the aspect that the various design parameters or operational characteristics are flexibly applicable. In the long-term period of a SWR event, the system dynamic responses analyzed by the code totally depend on the system design parameters such as the breaking pressure of the rupture disk, the variation of the steam injection rate and the sodium drain tank pressure,etc. Based on these analyses results, it is expected that the numerical quantification method of the SELPSTA code is practicable for the long-term system transient analysis and also makes the design of a pressure relief system against a SWR event in a liquid metal reactor (LMR) possible.

Passive speaker system

A passive radiator and method is disclosed which improves frequency response linearity and greatly reduces the possibility that wobble of a passive radiator which will occur without the displacement limitations of a spider containing speaker structure. Two substantially fiat surfaced speaker diaphragms are tied together and supported by two sets of surrounds oriented in opposite directions to reduce the non-linearity in the surround spring rate Hand improve low frequency sound generation. A vent (pressure relief system is provided to improve the frequency response and range of motion of the passive speaker system. A progressive surround roll arrangement provides for improved sound quality by utilizing localized position based extension while maintaining the range of maximum travel during resonance.

Numerical Investigation on the Long-term System Transient Response of a SWR Event in a LMR

In order to investigate the later phase of a sodium-water reaction (SWR) event, the code SELPSTA (Sodium-water reaction Event Later Phase System Transient Analyzer) has been developed and the analysis for the long-term system dynamic responses of a SWR event in KALIMER (Korea Advanced Liquid MEtal Reactor) has been made. The SELPSTA code uses the very simple analysis model applied only to the reaction period characterized by a bulk motion, and makes the very quick and concise computation possible. The code reasonably predicts the quasi-steady system transients and has the superiority in the aspect that the various design parameters or operational characteristics are flexibly applicable. In the long-term period of a SWR event, the system dynamic responses analyzed by the code totally depend on the system design parameters such as the breaking pressure of the rupture disk, the variation of the steam injection rate and the sodium drain tank pressure,etc. Based on these analyses results, it is expected that the numerical quantification method of the SELPSTA code is practicable for the long-term system transient analysis and also makes the design of a pressure relief system against a SWR event in a liquid metal reactor (LMR) possible.

Kinetics of the reactions of ethylene oxide with water and ethylene glycols

AbstractThis study of the water‐contamination reactions of ethylene oxide was conducted by Arthur D. Little, Inc. with funding from, and under the auspices of, the Ethylene Oxide Industry Council, part of the American Chemistry Council. Significant experimental and technical contributions were also made by staff from Shell Chemicals' Westhollow Technology Center in Houston, Texas, and Union Carbide Corporation's Research Center in South Charleston, West Virginia. Unique fourth‐order kinetics for the reactions of ethylene oxide with water, and ethylene oxide with ethylene glycols were derived and validated, as were kinetics for the reactions of neat ethylene oxide and the decomposition of ethylene glycols. The latter data was incorporated into a reaction model useful for the determination of ethylene oxide storage stability and pressure relief system design under water‐contamination scenarios.

Dynamic simulation of the behaviour of pressure relief systems

Pressure relief of near critical processes working at two phase region is simulated dynamically. The design procedure for pressure relief devices is demonstrated by an example. The example shows that the required relieving area of the safety valve depends on time and scenario. This is the basis for the selection of the type and the size of safety valve. When the process relieves through the selected valve the outflow and the pressure of the protected vessel varies dynamically. This phenomenon cannot be discovered by the static approach that is normally used in the design of pressure relieving devices. The traditional sizing equations, API 520 and DIERS, are also difficult to apply in near critical region and they include coefficients that are sometimes difficult to obtain. The sensitivity may be so large that a different size of the relieving device is selected depending on the model. Usage of two common models, API 520 and DIERS, in the region of two phases is discussed.

Methods of resisting hydrostatic uplift in substructures

Many underground structures are constructed for use as car parks and shops in basements of buildings and as mass rapid transit stations, depressed roadways and civil defense shelters in cities located in coastal areas where the ground is level and the elevations are low, with an attendant high groundwater table. This paper discusses the various methods of resisting hydrostatic uplift. These include the use of tension piles and the installation of a water pressure relief system under the base slab of the basement. A case history in Singapore employing a pressure relief system below a three-level basement is presented.

Analysis identifies deficiencies in existing pressure relief systems

AbstractThis article presents a statistical analysis showing that the pressure relief systems on nearly half of the equipment in the oil, gas, and chemical industries lack adequate overpressure protection as defined by recognized and generally accepted good engineering practice. This analysis was based on data collected from a large number of government mandated (per OSHA 1910.119) pressure relief system design audits per‐formed by an independent contractor. The vast majority of these deviations from good practice were not identified during conventional process hazard analyses (PHA) performed on these same facilities. Most of the units had also been designed by reputable design firms.The authors conclude that, as a practical matter, conventional PHA methods are ineffective tools for evaluating pressure relief systems. They also conclude that the pressure relief system design process could be improved. Specifically, the authors recommend that, in order to reduce this deficiency rate in the future, that the industry adopt an equipment based approach to pressure relief system design and maintenance.

Conceptual design of pressure relief systems

Abstract Conceptual design of pressure relief systems is an important stage in the design of a safe process plant. The conceptual design stage consists of the following steps: deciding on the location of pressure relief devices, selecting the general type of pressure relief device for each identified location, i.e. safety valve and/or bursting disc (rupture disc), or other relief device, and selecting the special features for the chosen device type. Some regulations, codes and standards, and a decision tree for the selection of a relief device have been described in the literature. This paper presents four decision trees that have been developed for the different steps in the conceptual design stage. Only positive pressure in pressure vessels is considered here.

Using constant slip ratios to model non‐flashing (frozen) two‐phase flow through nozzles

AbstractThe TPHEM computer program, supplied with the recently published AIChE / CCPS book “Guidelines for Pressure Relief and Effluent Handling Systems”, can be used to reproduce a range of two‐phase flow data through nozzles. The ability to predict data and design emergency relief systems using simple models is important to the practicing engineer.

An experimental study of viscous flows in contractions

The need to improve the methods used when designing emergency, pressure-relief systems on polymerisation reactors, has made the flow of highly viscous fluids in pipeline fittings highly topical. This paper investigates the flow processes involved in single-phase, viscous flows in nozzles and orifice plates. These fittings were chosen because they would give an insight into the behaviour of highly viscous flows in other geometries, such as the flow upstream of the seat in a pressure relief valve. Experimental data are presented for a pipe, two conical nozzles and a sharp-edged orifice plate for laminar flows in the Reynolds number range 50–400 and for turbulent flows. The volume flow rate—pressure drop characteristics are presented for both nozzles and the orifice plate. The discharge momentum flow rate for the pipe, a nozzle and the orifice plate are also given. Analysis of the data shows that nozzles and orifice plates that are geometrically similar have a similar resistance to flow. It is also shown that the contraction coefficient for an orifice plate tends to unity at low Reynolds numbers.

Pressure relief system documentation: Equipment based relational database is key to OSHA 1910.119 compliance

AbstractUnder OSHA 1910.119, all Process Safety Management (PSM) facilities are required to keep their pressure relief system design information current. This article demonstrates why a pressure relief system design verification effort must be based on an equipment list, rather than a relief device list, in order to ensure that every piece of equipment is adequately protected. The formerly common practice of simply checking the design bases of all existing relief devices is deficient is deficient since this technique does not systematically ensure that every piece of equipment is protected.The “Berwanger Method” is a step by step process for designing or analyzing a pressure relief system to meet OSHA 1910.119 Process Safety Information (PSI) and Process Hazard Analysis (PHA) mandates. The method uses a relational database which tracks the relationships between protected equipment, potential overpressure scenarios, and protective devices.The challenge facing an operating company does not end once the design basis has been “verified”—the design basis information must also be maintained and be readily accessible to avoid costly reinvention of the wheel down the road. The “Berwanger Method” also addresses these maintenance issues.