CA1150682A - Interior safety device for liquid-containing storage vessels - Google Patents
Interior safety device for liquid-containing storage vesselsInfo
- Publication number
- CA1150682A CA1150682A CA000300037A CA300037A CA1150682A CA 1150682 A CA1150682 A CA 1150682A CA 000300037 A CA000300037 A CA 000300037A CA 300037 A CA300037 A CA 300037A CA 1150682 A CA1150682 A CA 1150682A
- Authority
- CA
- Canada
- Prior art keywords
- vessel
- porous material
- liquefied
- interior
- pressure
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C13/00—Details of vessels or of the filling or discharging of vessels
- F17C13/12—Arrangements or mounting of devices for preventing or minimising the effect of explosion ; Other safety measures
- F17C13/123—Arrangements or mounting of devices for preventing or minimising the effect of explosion ; Other safety measures for gas bottles, cylinders or reservoirs for tank vehicles or for railway tank wagons
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2201/00—Vessel construction, in particular geometry, arrangement or size
- F17C2201/06—Vessel construction using filling material in contact with the handled fluid
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2203/00—Vessel construction, in particular walls or details thereof
- F17C2203/06—Materials for walls or layers thereof; Properties or structures of walls or their materials
- F17C2203/0602—Wall structures; Special features thereof
- F17C2203/0604—Liners
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2203/00—Vessel construction, in particular walls or details thereof
- F17C2203/06—Materials for walls or layers thereof; Properties or structures of walls or their materials
- F17C2203/0634—Materials for walls or layers thereof
- F17C2203/0636—Metals
- F17C2203/0639—Steels
- F17C2203/0643—Stainless steels
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2203/00—Vessel construction, in particular walls or details thereof
- F17C2203/06—Materials for walls or layers thereof; Properties or structures of walls or their materials
- F17C2203/0634—Materials for walls or layers thereof
- F17C2203/0636—Metals
- F17C2203/0646—Aluminium
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2205/00—Vessel construction, in particular mounting arrangements, attachments or identifications means
- F17C2205/03—Fluid connections, filters, valves, closure means or other attachments
- F17C2205/0302—Fittings, valves, filters, or components in connection with the gas storage device
- F17C2205/0323—Valves
- F17C2205/0332—Safety valves or pressure relief valves
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2221/00—Handled fluid, in particular type of fluid
- F17C2221/03—Mixtures
- F17C2221/038—Refrigerants
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C2260/00—Purposes of gas storage and gas handling
- F17C2260/04—Reducing risks and environmental impact
- F17C2260/042—Reducing risk of explosion
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Filling Or Discharging Of Gas Storage Vessels (AREA)
Abstract
Abstract Closed pressurized storage vessels for holding liquefied gases, including non-flammable liquids, and their vapors under pressure are provided on the interior surface with a lining of expanded mesh or other highly heat-conductive porous material for reducing or avoiding the risk of BLEVE of the vessel on accidental exposure of the vessel to a fire hazard. The interior lining serves to disperse and dissipate heat that is absorbed by the vessel and its contents and delays the heating of the wall of the vessel, and thus delays weakening of the vessel wall to the point where it may rupture under the internally-generated pressure.
Description
~1~5~
The present invention relates to arrangements whereby the hazards of so-called "boiling liquid expanding vapor explosion" (BLEVE) may be reduced or avoided. More particularly, the present invention is concernecl with measures for the protection of closed storage vessels for the storage of liquefied gases. Of especial interest are large scale storage vessels for the storage of liquefied flammable gases or non-flammable gases such as liquefied inert gases, e.g. the FREOi~S
and other inert volatile aerosol propellant liquids and refrigerants. The invention is in general applicable to the protection of all closed storage vessels for liquefied gases where the liquefied gas is stored under super-atmospheric pressure and where the wall structure of the vessel is capable of withstanding a significant internal pressure. Amongst other examples may be mentioned closed tanks for the storage of liquefied petroleum gas, liquefied ammonia, and pressure vessels for inert liquefied gases. All such storage vessels are liable to an explosive failure of enormously destructive capability, termed a BLEVE, on accidental exposure to a fire hazard or other source of heating impinging on the surface of the vessel.
As a result of the application of heat, a pressure is built up within the vessel. If the flame and other heat is initially incident on an area of the vessel below the liquid level, the heat will initially be dissipated through conduction through the liquid and eventually the liquid boils, and vapor is released through the pressure-relief valves normally provided as a safety precaution on closed storage systems.
Once sufficient liquid has evaporated, and the liquid level has dropped below the heated area, the wall of the vessel in the heated area will become rapidly hotter as it is no longer subject to the heat-absorbing contact with the liquid, and the tensile strength of the metal or other material constituting i~ ~
the wall of the vessel will be weakened to a point where the vessel wall ruptures explosively under the internal pressure that has built up within the vessel. The release of energy that accompanies the sudden volatilisation and expansion of the boiling liquid contained within the pressure vessel as the pressure is suddenly released is often enormous and a B~EVE is capable of inflicting catastrophic damage to property and persons across widespread areas.
Although the BLEVE type of explosion is liable to occur not only with pressurised vessels that contain liquefied materials of flammable nature but also with non-flammable materials, the most serious instances have involved accidents to vessels, e.g. railroad tank cars, containing pressurised liquefied fuel gases. In such instances, tank cars remaining intact after an accident may be exposed to flames from fuel spilt from or escaping from ruptured cars. The resultant BL~VES have hurled 15 ton fragments of the tank cars distances of 2800 feet, and personnel have sustained burns at distances as far as 1000 feet from the site of the explosion, as a result of the intensity of the radiant energy generated by the fireball at the moment of explosion.
Another serious problem associated with the BLEVE is that following the initial accident that results in an outbreak of fire, there is a period of unpredictable duration, before the heating is sufficient to weaken the metal skin to the point where the pressure vessel ruptures.
Up to the present invention, there has been no satisfactory way of preventing or adequately deferring the occurrence of a BLEVE.
The present invention provides an arrangement whereby the heat that impinges may be absorbed and dissipated, so that the occurrence of a BLEVE may be preventable or at least may be adequately deferred for a period sufficiently long for the ~. :
appropriate measures to be taken to guard against the possibility of the BLEVE occurring.
The present invention provides a closed storage vessel having a pressure-resistant wall structure comprising a heat-conductive wall material that is sub]ect to loss of strength andmechanical failure under prolonged heating, said vessel holding under super-atmospheric pressure a volume of liquefied gas and its vapor at ambient temperature, the liquefied gas remaining stable at elevated temperature and exerting an increasing vapor pressure with increasing temperature, and the vessel having, at least in selected areas of the interior surface of the wall of the vessel that are exposed to heating hazard, an interior lining in good heat-conductive contact with the vessel wall structure and extending into the liquefied gas contained in the vessel, the lining being composed of heating-resistant, highly-heat conduc-tive porous material having interstices sufficiently large to permit propagation of a flame front through it, said porous material delaying increase in temperature of the vessel wall ; structure when exposed to a heat source located exteriGrly of the vessel, whereby the onset of rupture of the vessel wall structure is deferred or prevented. With the vessel of the invention, the porous material can distribute heat throughout the vessel, whereby the heat incident on a localised area of the exterior of the vessel wall above the liquid level can be dispersed away from the localised area through conduction of heat through the porous material into the volume of liquid within the vessel, which can act as a heat sink, and into areas of the vessel which are not heated, so that the heat may be dissipated into the surroundings.
The interior surface lining thus serves to delay or prevent a rise in temperature of the material of the wall of the vessel to a point where it is sufficiently weakened to undergo rupture under the influence of the internal pressure generated by the heating of the contents.
~, - - : : - , , Any material of appropriately high thermal conductivity, that is heatiny-resistant i.e. it will not lose its structural integrity at elevated temperatures, may be employed for the porous material. The most commonly available high conductivity materials are highly conductive metals and alloys, and these are preferred for the purposes of the present invention. Where the vessel is intended for carrying corrosive and other highly reactive liquids, it is preferable to employ a relatively inert material, e.g. an expanded stainless steel mesh.
The material that is presently preferred, at least in environments that are not highly corrosive, is the expanded thin aluminium foil material as described in Canadian Patent 836,363 in the name J. Szego, dated March 10, 1~70 and more particularly as in Canadian patent application serial no.
283,442 filed July 25, 1~77 in the name Vulcan Industrial Packaging Limited.
This material comprises uniform mesh strands of thin aluminium foil interconnected with one another and forming diamond-shaped mesh openings. It resembles the conventional expanded metal material. Typically, however, the widths of the strands forming the mesh may be from 1/32 to 7/32 of an inch, and advantageously in the range 1/32 to 1/8 inch, and the foil thickness is usually in the range of from about 0.0005 to 0.012 inches, more typically about 0.001 to 0.010 inches and preferably about 0.001 to 0.005 inches. When layers of the expanded mesh are laid together to form a mass, the interstices of the mesh provide open passageways through which the liquids contained in the vessel can flow freely, and because of its highly expanded state, the metal mesh does not significantly detract from the volumetric capacity of the interior of the vessel. Typically, the mesh occupies less than about 2 percent of the interior volume of the vessel. The packing density of ~3~ 6~2 the mesh within the vessel will typically be from about 1 to 5 lbs per cu. ft., more usually 2 to 4 lbs. per cu. ft. and preferably about 3 to 4 lbs. per cu. ft. This known expanded foil mesh material is flame-permeable, i.e. in contrast to flame arrestors it has pores or interstices sufficiently large to permit propagation of a flame front through it when it is exposed to a combustible air/vapor mixture and the mixture is ignited.
Typically, the vessels to which the invention will be applied will be closed vessels provided with a pressure relief valve adapted to vent the interior of the vessel to the ambient atmosphere through a valve opening when the super-atmospheric pressure within the vessel exceeds a predetermined limit.
The accompanying drawings show a graph plotting internal pressures generated within a pressure vessel exposed to a heating source and also plotting the pressure required to rupture the vessel, calculated from the fall in tensile strength of the wall material with the rise in temperature of the wall.
In the examples from which the data illustrated in the graph were obtained, 0.2 cu. ft. cylindrical tanks were employed. The tanks had a carbon steel pressure-resistant tank wall. The tanks were filled to an extent of 15~ of their volume with liquefied FREON-22, (trade mark for a normally - gaseous halogenated alkane that is liquefiable under super-atmospheric pressure at ordinary temperatures) and were equipped with thermocouples to measure the wall temperature, and an internal pressure measuring device.
In the tests the tanks were exposed to an external heat source provided by a propane/air blow torch.
Results plotted in the graph in broken lines and labelled "Protected", are applicable to tanks filled with an internal filler mass of expanded aluminium foil material.
~, ' ?
~ ' ' ' . , : ' The testing was also conducted with identical tanks con-taining no filler mass. The results are indicated in the solid lines in the graph, labelled "Unprotected".
From the measured wall temperatures, the tensile strengths S of the wall material at these temperatures was obtained from standard tables, and the pressures required to burst the wall ~ere obtained therefrom. The results are shown in the upper plots in the graph and indicate the ~eakening of the tank wall with increasing temperature on continued exposure. The lower plots are of the measured pressure values, and indicate the rise in internal pressure.
The tanks under test were provided with a pressure relief valve set to vent at 275 psig and therefore pressures above that value in the graph are obtained by extrapolation. It may be seen, however, that with the unprotected tank a point of failure, at which the pressure generated is sufficient to rup-ture the weakened tank wall, would be obtained after about 1 8 mins. exposure to the heating, while with the protected tank a rupture point is not reached during the period of test.
In the practice of the invention, the vessels that may be protected will typically be storage vessels of large capacity, having an uninsulated metal wall exposed directly to the sur-roundings on its outer side. In order to conduct heat away from the surface of the protected vessel, and defer or prevent a hazardous rise in temperature of the vessel wall and the ` vessel contents, the vessels need not be completely filled throughout their interior volume with the expanded mesh or other porous material, and a protection can be obtained by lining the inner surface of the vessel. In order to economise on the amount of mesh material employed and on the weight added to a vessel, it may be desired to apply the interior lining only at those areas that are especially liable to im-pingement of flame or other heat hazard in the event of an ; accidental outbreak of fire. Thus, in the case of a railway tank car or other vessel where there is little likelihood of flame impinging on the bottom or lower surface of the vessel~
the interior lining may be applied only on the side and top interior surfaces of the wall of the vessel, and as will be ," ~
`~
, .. . : ` ' 6~32 appreciated in such case the interior porous material occupies only part of the internal volume of the vessel and defines within the vessel an empty void free from the porous material.
For convenience, or in order to provide a firm and secure positioning and support of the mesh material inside the vessel, it may however be preferable to completely fill the interior of the vessel, so that there are substantially no interior voids.
On exposure of the vessel to a fire hazard, where the flame impinging on the vessel is below the level of the liquid inside the vessel, in the case of an unprotected vessel or in the case of a vessel protected in accordance with the invention, at least initially heat may be dissipated by conduction through the liquid inside the vessel, and with further heating the liquid will boil and vaporised liquid will be vented through the pressure-relief valve conventionally provided as a safety measure on pressurised storage vessels.
When the liquid level in the tank has fallen as a result of evaporation, or if the tank is initially mostly empty, the - liquid level will then lie below the area of the tank wall on which theheat and flame impinges, and in such case heat will no longer be absorbed through conduction into the liquid or by vaporisation of the liquid, but with the vessel in accordance with the invention heat will be dispersed and absorbed through the heat-conductive porous material.
In the case of the unprotected vessel, however, heat of the impinging flame is not conducted away and the wall of the vessel will rapidly become heated, so that the strength of the wall ~:-` will be rapidly reduced to a point where the BLEVE will occur.
It may be noted that since with the unprotected vessel there is a high rate of increase of internal temperature of the vessel, the rate of vaporisation of liquid within the vessel may be in excess of the maximum flow of vapor that can escape through the relief valve, so that a pressure in excess of the relief valve pressure can be generated within the vessel at the time of its rupture and the occurrence of the BLEVE.
As one preferred example of porous material may be men-tioned a foil mesh material obtained from aluminium foil of 0.003 inch thickness, which is slit through a rotary-slitting ;~1 - ;
~ ' f3~82 procedure and is expanded in accordance with the procedures des-cribed in Canadian patent application serial no. 285,777 filed August 30, 1977 in the name Vulcan Industrial Packaging Limited.
The mesh strand width is 0.055 inches, and the expansion of the slit foil is from an original slit and unexpanded width of 14 inches to an unexpanded width of 39 inches. The packing density of the expanded foil within the vessel approximates to 3 lbs.
per cu. ft.
As examples of storage vessels to which the interior .....
' :
' '' .
.' . "' , ', ;' ', , ' ,' linings or fillings described above in detail may be applied there can be mentioned railroad and road vehicle pressurized tank cars, and stationary storage vessels, especially large capacity storage vessels for the storage of liquefied normally gaseous materials. Typically, the liquids that may be stored in the storage vessels will include flammable liquefied gases e.g. liquefied petroleum gas, or :inert, non-flammable liquefied gases such as FREONS i.e. halogenated lower alkanes including chlorinated, brominated and/or fluorinated methanes, ethanes and butanes, as well as other aerosol propellant liquids, volatile inert dry cleaning fluids, blowing agents, inert fire extinguishing agents, and other gases that can be stored in liquefied form under super-atmospheric pressures and at ordinary atmospheric temperatures.
_ g ; , .
6~3Z
SUPPLEMENTARY DISCLOSURE
Examples of other porous, heating-resistant, heat-conductive materials that may be employed for the porous, heat-conducting lining in the vessels of the invention include materials of honeycomb sandwich construction e.g.
metal honeycombs available under the trade mark HEXCEL from Hexcel Corporation, Dublin, California, and knitted wire mesh products available under the trade mark METEX from Metex Corporation, Edison, New Jersey.
The present invention relates to arrangements whereby the hazards of so-called "boiling liquid expanding vapor explosion" (BLEVE) may be reduced or avoided. More particularly, the present invention is concernecl with measures for the protection of closed storage vessels for the storage of liquefied gases. Of especial interest are large scale storage vessels for the storage of liquefied flammable gases or non-flammable gases such as liquefied inert gases, e.g. the FREOi~S
and other inert volatile aerosol propellant liquids and refrigerants. The invention is in general applicable to the protection of all closed storage vessels for liquefied gases where the liquefied gas is stored under super-atmospheric pressure and where the wall structure of the vessel is capable of withstanding a significant internal pressure. Amongst other examples may be mentioned closed tanks for the storage of liquefied petroleum gas, liquefied ammonia, and pressure vessels for inert liquefied gases. All such storage vessels are liable to an explosive failure of enormously destructive capability, termed a BLEVE, on accidental exposure to a fire hazard or other source of heating impinging on the surface of the vessel.
As a result of the application of heat, a pressure is built up within the vessel. If the flame and other heat is initially incident on an area of the vessel below the liquid level, the heat will initially be dissipated through conduction through the liquid and eventually the liquid boils, and vapor is released through the pressure-relief valves normally provided as a safety precaution on closed storage systems.
Once sufficient liquid has evaporated, and the liquid level has dropped below the heated area, the wall of the vessel in the heated area will become rapidly hotter as it is no longer subject to the heat-absorbing contact with the liquid, and the tensile strength of the metal or other material constituting i~ ~
the wall of the vessel will be weakened to a point where the vessel wall ruptures explosively under the internal pressure that has built up within the vessel. The release of energy that accompanies the sudden volatilisation and expansion of the boiling liquid contained within the pressure vessel as the pressure is suddenly released is often enormous and a B~EVE is capable of inflicting catastrophic damage to property and persons across widespread areas.
Although the BLEVE type of explosion is liable to occur not only with pressurised vessels that contain liquefied materials of flammable nature but also with non-flammable materials, the most serious instances have involved accidents to vessels, e.g. railroad tank cars, containing pressurised liquefied fuel gases. In such instances, tank cars remaining intact after an accident may be exposed to flames from fuel spilt from or escaping from ruptured cars. The resultant BL~VES have hurled 15 ton fragments of the tank cars distances of 2800 feet, and personnel have sustained burns at distances as far as 1000 feet from the site of the explosion, as a result of the intensity of the radiant energy generated by the fireball at the moment of explosion.
Another serious problem associated with the BLEVE is that following the initial accident that results in an outbreak of fire, there is a period of unpredictable duration, before the heating is sufficient to weaken the metal skin to the point where the pressure vessel ruptures.
Up to the present invention, there has been no satisfactory way of preventing or adequately deferring the occurrence of a BLEVE.
The present invention provides an arrangement whereby the heat that impinges may be absorbed and dissipated, so that the occurrence of a BLEVE may be preventable or at least may be adequately deferred for a period sufficiently long for the ~. :
appropriate measures to be taken to guard against the possibility of the BLEVE occurring.
The present invention provides a closed storage vessel having a pressure-resistant wall structure comprising a heat-conductive wall material that is sub]ect to loss of strength andmechanical failure under prolonged heating, said vessel holding under super-atmospheric pressure a volume of liquefied gas and its vapor at ambient temperature, the liquefied gas remaining stable at elevated temperature and exerting an increasing vapor pressure with increasing temperature, and the vessel having, at least in selected areas of the interior surface of the wall of the vessel that are exposed to heating hazard, an interior lining in good heat-conductive contact with the vessel wall structure and extending into the liquefied gas contained in the vessel, the lining being composed of heating-resistant, highly-heat conduc-tive porous material having interstices sufficiently large to permit propagation of a flame front through it, said porous material delaying increase in temperature of the vessel wall ; structure when exposed to a heat source located exteriGrly of the vessel, whereby the onset of rupture of the vessel wall structure is deferred or prevented. With the vessel of the invention, the porous material can distribute heat throughout the vessel, whereby the heat incident on a localised area of the exterior of the vessel wall above the liquid level can be dispersed away from the localised area through conduction of heat through the porous material into the volume of liquid within the vessel, which can act as a heat sink, and into areas of the vessel which are not heated, so that the heat may be dissipated into the surroundings.
The interior surface lining thus serves to delay or prevent a rise in temperature of the material of the wall of the vessel to a point where it is sufficiently weakened to undergo rupture under the influence of the internal pressure generated by the heating of the contents.
~, - - : : - , , Any material of appropriately high thermal conductivity, that is heatiny-resistant i.e. it will not lose its structural integrity at elevated temperatures, may be employed for the porous material. The most commonly available high conductivity materials are highly conductive metals and alloys, and these are preferred for the purposes of the present invention. Where the vessel is intended for carrying corrosive and other highly reactive liquids, it is preferable to employ a relatively inert material, e.g. an expanded stainless steel mesh.
The material that is presently preferred, at least in environments that are not highly corrosive, is the expanded thin aluminium foil material as described in Canadian Patent 836,363 in the name J. Szego, dated March 10, 1~70 and more particularly as in Canadian patent application serial no.
283,442 filed July 25, 1~77 in the name Vulcan Industrial Packaging Limited.
This material comprises uniform mesh strands of thin aluminium foil interconnected with one another and forming diamond-shaped mesh openings. It resembles the conventional expanded metal material. Typically, however, the widths of the strands forming the mesh may be from 1/32 to 7/32 of an inch, and advantageously in the range 1/32 to 1/8 inch, and the foil thickness is usually in the range of from about 0.0005 to 0.012 inches, more typically about 0.001 to 0.010 inches and preferably about 0.001 to 0.005 inches. When layers of the expanded mesh are laid together to form a mass, the interstices of the mesh provide open passageways through which the liquids contained in the vessel can flow freely, and because of its highly expanded state, the metal mesh does not significantly detract from the volumetric capacity of the interior of the vessel. Typically, the mesh occupies less than about 2 percent of the interior volume of the vessel. The packing density of ~3~ 6~2 the mesh within the vessel will typically be from about 1 to 5 lbs per cu. ft., more usually 2 to 4 lbs. per cu. ft. and preferably about 3 to 4 lbs. per cu. ft. This known expanded foil mesh material is flame-permeable, i.e. in contrast to flame arrestors it has pores or interstices sufficiently large to permit propagation of a flame front through it when it is exposed to a combustible air/vapor mixture and the mixture is ignited.
Typically, the vessels to which the invention will be applied will be closed vessels provided with a pressure relief valve adapted to vent the interior of the vessel to the ambient atmosphere through a valve opening when the super-atmospheric pressure within the vessel exceeds a predetermined limit.
The accompanying drawings show a graph plotting internal pressures generated within a pressure vessel exposed to a heating source and also plotting the pressure required to rupture the vessel, calculated from the fall in tensile strength of the wall material with the rise in temperature of the wall.
In the examples from which the data illustrated in the graph were obtained, 0.2 cu. ft. cylindrical tanks were employed. The tanks had a carbon steel pressure-resistant tank wall. The tanks were filled to an extent of 15~ of their volume with liquefied FREON-22, (trade mark for a normally - gaseous halogenated alkane that is liquefiable under super-atmospheric pressure at ordinary temperatures) and were equipped with thermocouples to measure the wall temperature, and an internal pressure measuring device.
In the tests the tanks were exposed to an external heat source provided by a propane/air blow torch.
Results plotted in the graph in broken lines and labelled "Protected", are applicable to tanks filled with an internal filler mass of expanded aluminium foil material.
~, ' ?
~ ' ' ' . , : ' The testing was also conducted with identical tanks con-taining no filler mass. The results are indicated in the solid lines in the graph, labelled "Unprotected".
From the measured wall temperatures, the tensile strengths S of the wall material at these temperatures was obtained from standard tables, and the pressures required to burst the wall ~ere obtained therefrom. The results are shown in the upper plots in the graph and indicate the ~eakening of the tank wall with increasing temperature on continued exposure. The lower plots are of the measured pressure values, and indicate the rise in internal pressure.
The tanks under test were provided with a pressure relief valve set to vent at 275 psig and therefore pressures above that value in the graph are obtained by extrapolation. It may be seen, however, that with the unprotected tank a point of failure, at which the pressure generated is sufficient to rup-ture the weakened tank wall, would be obtained after about 1 8 mins. exposure to the heating, while with the protected tank a rupture point is not reached during the period of test.
In the practice of the invention, the vessels that may be protected will typically be storage vessels of large capacity, having an uninsulated metal wall exposed directly to the sur-roundings on its outer side. In order to conduct heat away from the surface of the protected vessel, and defer or prevent a hazardous rise in temperature of the vessel wall and the ` vessel contents, the vessels need not be completely filled throughout their interior volume with the expanded mesh or other porous material, and a protection can be obtained by lining the inner surface of the vessel. In order to economise on the amount of mesh material employed and on the weight added to a vessel, it may be desired to apply the interior lining only at those areas that are especially liable to im-pingement of flame or other heat hazard in the event of an ; accidental outbreak of fire. Thus, in the case of a railway tank car or other vessel where there is little likelihood of flame impinging on the bottom or lower surface of the vessel~
the interior lining may be applied only on the side and top interior surfaces of the wall of the vessel, and as will be ," ~
`~
, .. . : ` ' 6~32 appreciated in such case the interior porous material occupies only part of the internal volume of the vessel and defines within the vessel an empty void free from the porous material.
For convenience, or in order to provide a firm and secure positioning and support of the mesh material inside the vessel, it may however be preferable to completely fill the interior of the vessel, so that there are substantially no interior voids.
On exposure of the vessel to a fire hazard, where the flame impinging on the vessel is below the level of the liquid inside the vessel, in the case of an unprotected vessel or in the case of a vessel protected in accordance with the invention, at least initially heat may be dissipated by conduction through the liquid inside the vessel, and with further heating the liquid will boil and vaporised liquid will be vented through the pressure-relief valve conventionally provided as a safety measure on pressurised storage vessels.
When the liquid level in the tank has fallen as a result of evaporation, or if the tank is initially mostly empty, the - liquid level will then lie below the area of the tank wall on which theheat and flame impinges, and in such case heat will no longer be absorbed through conduction into the liquid or by vaporisation of the liquid, but with the vessel in accordance with the invention heat will be dispersed and absorbed through the heat-conductive porous material.
In the case of the unprotected vessel, however, heat of the impinging flame is not conducted away and the wall of the vessel will rapidly become heated, so that the strength of the wall ~:-` will be rapidly reduced to a point where the BLEVE will occur.
It may be noted that since with the unprotected vessel there is a high rate of increase of internal temperature of the vessel, the rate of vaporisation of liquid within the vessel may be in excess of the maximum flow of vapor that can escape through the relief valve, so that a pressure in excess of the relief valve pressure can be generated within the vessel at the time of its rupture and the occurrence of the BLEVE.
As one preferred example of porous material may be men-tioned a foil mesh material obtained from aluminium foil of 0.003 inch thickness, which is slit through a rotary-slitting ;~1 - ;
~ ' f3~82 procedure and is expanded in accordance with the procedures des-cribed in Canadian patent application serial no. 285,777 filed August 30, 1977 in the name Vulcan Industrial Packaging Limited.
The mesh strand width is 0.055 inches, and the expansion of the slit foil is from an original slit and unexpanded width of 14 inches to an unexpanded width of 39 inches. The packing density of the expanded foil within the vessel approximates to 3 lbs.
per cu. ft.
As examples of storage vessels to which the interior .....
' :
' '' .
.' . "' , ', ;' ', , ' ,' linings or fillings described above in detail may be applied there can be mentioned railroad and road vehicle pressurized tank cars, and stationary storage vessels, especially large capacity storage vessels for the storage of liquefied normally gaseous materials. Typically, the liquids that may be stored in the storage vessels will include flammable liquefied gases e.g. liquefied petroleum gas, or :inert, non-flammable liquefied gases such as FREONS i.e. halogenated lower alkanes including chlorinated, brominated and/or fluorinated methanes, ethanes and butanes, as well as other aerosol propellant liquids, volatile inert dry cleaning fluids, blowing agents, inert fire extinguishing agents, and other gases that can be stored in liquefied form under super-atmospheric pressures and at ordinary atmospheric temperatures.
_ g ; , .
6~3Z
SUPPLEMENTARY DISCLOSURE
Examples of other porous, heating-resistant, heat-conductive materials that may be employed for the porous, heat-conducting lining in the vessels of the invention include materials of honeycomb sandwich construction e.g.
metal honeycombs available under the trade mark HEXCEL from Hexcel Corporation, Dublin, California, and knitted wire mesh products available under the trade mark METEX from Metex Corporation, Edison, New Jersey.
Claims (21)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A closed storage vessel having a pressure-resistant wall structure comprising a heat-conductive wall material that is sub-ject to loss of strength and mechanical failure under prolonged heating, said vessel holding under super-atmospheric pressure a volume of liquefied gas and its vapor at ambient temperature r the liquefied gas remaining stable at elevated temperature and exerting an increasing vapor pressure with increasing temperature, and the vessel having, at least in selected areas of the interior surface of the wall of the vessel that are exposed to heating hazard, an interior lining in good heat-conductive contact with the vessel wall structure and extending into the liquefied gas contained in the vessel, the lining being composed of heating-resistant, highly-heat conductive, porous material having inter-stices sufficiently large to permit propagation of a flame front through it, said porous material delaying increase in temperature of the vessel wall structure when exposed to a heat source located exteriorly of the vessel, whereby the onset of rupture of the vessel wall structure is deferred or prevented.
2. A vessel as claimed in claim 1 having sides and an upper sur-face and wherein the porous material covers the interior surface of the sides and upper surface.
3. A vessel as claimed in claim 1 wherein the porous material occupies only part of the internal volume of the vessel and de-fines within the vessel an empty void free from the porous material.
4. A vessel as claimed in claim 1 wherein substantially the whole of the interior of the vessel is filled with the porous material.
5. A vessel as claimed in claim 1, 2 or 3 wherein the porous material comprises expanded metal foil.
6. A vessel as claimed in claim 1 wherein the porous material comprises expanded aluminium foil mesh.
7. A vessel as claimed in claim 6 wherein the expanded aluminium foil mesh comprises mesh strands of width from about 1/32 to 7/32 inch and of thickness from about 0.0005 to 0.012 inches.
8. A vessel as claimed in claim 7 wherein said width is from 1/32 to 1/8 inch and said thickness is from about 0.001 to 0.010 inches.
9. A vessel as claimed in claim 8 wherein said thickness is from about 0.001 to 0.005 inches.
10. A vessel as claimed in claim 1 wherein the porous material comprises expanded stainless steel material.
11. A vessel as claimed in claim 1 wherein the vessel has a metallic pressure-resistant wall structure.
12. A vessel as claimed in claim 11 wherein the wall structure is of steel.
13. A vessel as claimed in claim 1 including a pressure-relief valve adapted to vent the interior of the vessel to the ambient atmosphere through a valve opening when the super-atmospheric pressure within the vessel exceeds a pre-determined limit.
14. A vessel as claimed in claim 1, 2, or 3 wherein the in-terior of the vessel is loaded with a flammable liquefied gas.
15. A vessel as claimed in claim 1, 2 or 3 wherein the in-terior of the vessel is loaded with liquefied petroleum gas.
16. A vessel according to claim 1 wherein the interior of the vessel is loaded with a liquefied non-flammable gas.
17. A vessel according to claim 16 wherein said liquefied gas is a liquefied aerosol propellant.
18. A vessel according to claim 16 wherein said liquefied gas is liquefied refrigerant.
19. A vessel according to claim 16 wherein the liquefied gas is a halogenated lower alkane.
20. A vessel according to claim 1, 2 or 3 wherein the vessel has an uninsulated metal wall structure exposed directly to the surroundings on its outer side.
Claim Supported by Supplementary Disclosure
Claim Supported by Supplementary Disclosure
21. A vessel as claimed in claim 1, 2, or 3 wherein the porous material comprises metal honeycomb material or a knitted wire mesh material.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000300037A CA1150682A (en) | 1978-03-30 | 1978-03-30 | Interior safety device for liquid-containing storage vessels |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000300037A CA1150682A (en) | 1978-03-30 | 1978-03-30 | Interior safety device for liquid-containing storage vessels |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1150682A true CA1150682A (en) | 1983-07-26 |
Family
ID=4111110
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000300037A Expired CA1150682A (en) | 1978-03-30 | 1978-03-30 | Interior safety device for liquid-containing storage vessels |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1150682A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0129653A2 (en) * | 1983-06-22 | 1985-01-02 | Udo Poschinger | Gas reservoir |
| EP0175694A1 (en) * | 1984-03-15 | 1986-04-02 | Atlantic Cylinder Tek Corporation | Explosion resistant tank for liquid fuel |
| US4921118A (en) * | 1987-09-04 | 1990-05-01 | Courtney P. Grover, III | Manufacture of filling material |
| US5000336A (en) * | 1987-09-04 | 1991-03-19 | Grover-Turtur Venture | Explosion protection system for a container |
-
1978
- 1978-03-30 CA CA000300037A patent/CA1150682A/en not_active Expired
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0129653A2 (en) * | 1983-06-22 | 1985-01-02 | Udo Poschinger | Gas reservoir |
| EP0129653A3 (en) * | 1983-06-22 | 1985-12-04 | Udo Poschinger | Gas reservoir |
| EP0175694A1 (en) * | 1984-03-15 | 1986-04-02 | Atlantic Cylinder Tek Corporation | Explosion resistant tank for liquid fuel |
| EP0175694A4 (en) * | 1984-03-15 | 1986-07-17 | Atlantic Cylinder Tek Corp | Explosion resistant tank for liquid fuel. |
| US4921118A (en) * | 1987-09-04 | 1990-05-01 | Courtney P. Grover, III | Manufacture of filling material |
| US5000336A (en) * | 1987-09-04 | 1991-03-19 | Grover-Turtur Venture | Explosion protection system for a container |
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