NO854546L - EXPLOSION RESISTANT TANK FOR LIQUID FUEL. - Google Patents

Description

The invention relates to pressure tanks for the storage of liquid or vaporizable fuel, and in particular such tanks which are resistant to explosion.

It is well known that liquid fuel for engines, heating or cooking is easily flammable and thus potentially a source of explosion. Gasoline tanks often explode when a fire causes the gas tank to heat up, increasing the pressure inside the tank until it ruptures and the gas is spewed out to cause an explosion. US 4,149,649 deals with a means of suppressing the above-mentioned type of explosion by filling the inside of the tank with a mass of layers of expanded metal where adjacent layers are arranged so that the direction of inclination of the expanded metal is different in adjacent layers. Although this patented invention has provided some degree of protection against explosions in gasoline tanks, it has not provided ultimate protection and has not been in any way successful with tanks for propane or similar hydrocarbon which is normally a gas but is stored under sufficient pressure to flow the hydrocarbon.

It is an object of this invention to provide an improved explosion-resistant metal tank for liquid fuel. It is another object of this invention to provide an explosion-proof metal tank for liquid propane. It is a still further object of this invention to provide an improved metal tank construction. Other purposes will be apparent from the more detailed description that follows.

This invention relates to an explosion-resistant metal tank filled with liquid fuel in which the tank surrounds a mass of expanded metal 1 . The improvement provided by this invention comprises a metal tank containing a normally vapor hydrocarbon under sufficient pressure to maintain the hydrocarbon in the liquid phase, and a mass of expanded metal sheets packed together to form a structure of substantial thickness adjacent and in heat conducting contact with essentially the entire internal surface of the tank, as the mass has sufficiently high thermal conductivity to transfer heat from the tank to the cool liquid fuel with the filling of the spaces of the mass of expanded metal thereby reducing the tendency for the tank to crack due to a. the high temperature of the tank.

Another embodiment of the invention relates to a method for producing the above-described metal tank by producing two uniform, cup-shaped metal 1 pressure heads which have a cylindrical part joined at one end to a closed essentially hemispherical head part and which terminates at the other end in a circumferential edge portion, attaching a manually operated valve to a pressure head by a line extending from the valve inward relative to the tank along the inner surface of one head and its adjacent cylindrical portion parallel to the longitudinal axis of the tank and past the circumferential tank portion and terminating with an open end at a point on the hemispherical surface of the second printing head adjacent its junction with its respective cylindrical portion, causing the mass of expanded metal sheets to fit neatly against the inner contour of the two heads when joined at their respective peripheral edge parts so that the mass of expanded metal is in hot conductive contact with essentially the entire inner surface of the two pressure heads. To assemble the two pressure heads with the mass of expanded metal enclosed within both heads, to weld the two pressure heads along circumferential edge portions to produce a pressure-tight container, and to stress-relieve the welded joint without melting any substantial portion of the mass of the expanded metal.

The new features which are considered to be characteristic of this invention are specified in particular in the attached claims. However, the invention itself, both in terms of its organization and mode of operation, together with further purposes and advantages thereof, can best be understood with reference to the following description in connection with the attached drawings where: Fig. 1 is a vertical view, partly in cross-section , of the preferred embodiment of the tank according to this invention.

Fig. 2 is a top plan view of the tank in fig. 1.

Fig. 3 is a vertical view of the upper half section

of the tank in fig. 1.

Fig. 4 is a vertical view of the lower half section

of the tank in fig. 1.

Fig. 5 is an enlarged view of a piece of expanded metal. Fig. 6 is a perspective view of a tightly wound coil of expanded metal for use in this invention with the container of Fig. 1. Fig. 7 is a vertical view of a second embodiment of

a tank for use in this invention.

Fig. 8 is a vertical view of a third embodiment

of a tank for use in this invention.

Fig. 9 is a top plan view of the tank in fig. 8.

Fig. 10 is a vertical view of the hood on the inlet to

the pressure relief valve.

Fig. 11 is a top plan view of the cap in fig. 1 0 .

The container according to the preferred embodiment and best mode of this invention is best shown in fig. 1-4 in the attached drawings. The tank 10 consists of an upper half section 11 and a lower half section 12 which are joined around the middle section by a weld seam 13. The half section 11 comprises a cylindrical part 14 and an upper hemispherical pressure head part 15. Similarly, the half section 12 comprises a cylindrical portion 16 and a lower hemispherical pressure head portion 17. It should be understood that the pressure head portions 15 and 17 need not be completely hemispherical, from a geometrical point of view, but for the purposes of this invention the word "hemispherical" shall be understood to include any convex arched section which may be a suitable shape for the head of an internally pressurized tank. The upper pressure head portion 15 is equipped with one or more valves and/or couplings which are designed to fill the tank, release its contents, and to indicate the internal conditions with respect to pressure and/or temperature. The purge valve is a pressure reducing valve designed to receive liquid from the interior of the tank 10 and to allow it to expand and transform into a gas as it exits the valve 18. A manually operated needle valve is one of the well known types used for this purpose. , because it allows easy adjustment of the rate of discharge for the contents, such as a gas. Another type of valve is a pressure relief valve 19 which automatically opens to relieve an excessively high pressure within the tank 10, preferably from areas close to the inner wall of the container 10, as will be explained in more detail below. The head portion 15 preferably includes a liquid inlet valve 20 which acts as a check valve as it opens to allow liquid flow under pressure to fill the tank 10, but otherwise remains closed. The measuring tube 39 is used in the filling tank 10 to determine when the tank is full, which is when 80% of the internal volume is filled with liquid. The tube 39 extends downwards so that the end of the tube will be at the liquid level for 80% full in the vertical position. Likewise, the pipe 39 is placed so that when the tank 10- is filled in the horizontal position, where the pipe can be at the liquid level when 80$ is full.

To enable the tank 10 to stand vertically with protection for the valves on the pressure head 15, a protection ring 21 is welded on the outside of the hemispherical part 15 and a foot ring 22 is welded on the hemispherical part 17. These two ring parts 21 and 22 allows the tank 10 to stand on end in one direction or the other and to protect the valves 18, 19 and 20 and the pipe 39 from being damaged under use.

The liquid drain line 23 is operationally connected to the drain valve 18 to lead liquid from the inside of the tank 10 to the valve 18 for use by the consumer. The wire 23 extends along the cylindrical portion 14 and the cylindrical portion 16 and terminates as an open end 24 along the hemispherical worm portion 17. The exact location of the end 24 is such that it will indicate to the consumer when the tank is almost empty, i.e. when the remaining liquid is approx. 10% or less of the volume when the tank is filled. when the liquid fuel level reaches 25 when the tank 10 is in a vertical position, there will be a noticeable milling at the liquid inlet end 24. Likewise, when the tank 10 is in the horizontal position and the liquid level reaches 26, the milling noise will occur. Thus, the wire 23 is positioned to lie along cylindrical portions 14 and 16 and generally be parallel to the vertical axis 27 of the tank 10. To keep the wire 23 in a fixed position, it is preferred to attach it by spot welding or by other equivalent means by 28. This also provides a certain ease when assembling the various parts of the tank 10 as it is produced for sale and use.

In fig. 3 and 4 show half sections 11 and 12 before they are assembled. The section 11 has an inner ledge part 29 to provide a good attachment seat when the sections 11 and 12 are placed together and closed by welding.

Within the tank 10 is placed a mass of expanded metal sheets which are packed together to form a construction of substantial thickness; preferably the mass is a tightly wound coil 30 of expanded metal. An alternative embodiment of the coil

30 is a hollow construction of expanded metal layers tightly packed together, the total thickness of the packed layers being 1-4 inches. The layers may be wrapped around an internal support or attached to the wall of the tank 10 by any suitable means. The position of the coil 30 in the tank 10 is shown in fig. 1 and its original structure is seen in fig. 6. The coil 30 is rolled tightly without breaking the stretched structure of the plate (as seen in Fig. 5) and is made with little or no central space 38 along its vertical axis. The coil 30 is originally made in the form of a cylindrical roll with flat ends (see fig. 6) and is then cut to fit the contour of the inner shape of the tank 10. Cut-out parts for the valves 18, 19 and 20 and for the line 23 are removed from the coil 30. The flat ends of the coil 30 are shaped into a hemispherical contour so that the maximum degree of contact is formed between the tank 10 and the coil 30 as shown in fig. 1. The contact should be a positive contact to provide the maximum heat conduction between the tank 10 and the coil 30. The contoured coil 30 must be placed within the sections 11 and 12 before they are assembled for welding the seam 13. The coil 30 is made of an excellent heat conductor. For this reason as well as due to its availability and low cost, aluminum is preferred. Many other metals, such as stainless steel, titanium, magnesium, copper, silver and various alloys are also excellent conductors of heat and can be used here, but are not preferred on . g. a. the higher cost. which is involved. The thickness of the metal in the coil must be sufficient for the coil to have a certain stiffness in order to keep its shape inside the tank 10 with maximum contact with its inner surface. Aluminum should be approx. 0.0 03 inch thick for this purpose, while stainless steel can be as thin as 0.00 1 inch thick to achieve the same purpose.

As fully explained in US Patent 4. 1 49 . 649, the coil 30 can be made so that adjacent layers of expanded metal sheets in the coil 30 have opposite inclination directions produced by the process for manufacturing the expanded metal. This presumably gives a lower room weight for the coil 30 than would be the case if adjacent layers had the same angle of inclination. As far as the present invention is concerned, the coil 30 can have one or the other orientation and the results of the explosion resistance are essentially the same. In other words, it does not matter whether the coil 30 has adjacent layers of expanded metal with the same or opposite inclination directions.

In order for a welded tank to behave well when internally pressurized, all welded seams must be given a stress-relieving treatment. Normally this is done by heating the welded tank to a high temperature over a short time and then cooling it before it is put into use. The high temperature required for stress relief of the welded steel tank is above the softening point of aluminum (approx.

1 20 0 °F) and thus such a treatment cannot be used for containers according to this invention which have a mass of expanded aluminium. If the tensile metal is stainless steel, other material is more high-melting than aluminum, the stress relief under high temperature is permissible and preferred. Similarly, if the tank is made of aluminum and the tensile metal is also aluminum, the weld can be stress relieved by heat treatment without damaging the tensile metal structure. When the tensile metal is aluminum and the tank is steel, stress relief is best achieved by other means, e.g. ball hammering, which does not involve high temperatures that would soften aluminium.

When the half sections 11 and 12 are welded with the coil 30 inside, there is a localized softening or melting of the coil 30 where it touches the inside of the weld seam and the adjacent portions of the sections 11 and 12. However, this is not harmful to the coil 30, and is assumed on the other hand, to be beneficial. The inner surfaces of the sections 11 and 12 where they meet around the edge 29 (see Fig. 3) extend somewhat inwards and pinch the middle section of the coil 30. This causes a small portion of the inner walls of the sections 11 and 12 adjacent the joined edges at the weld seam 13 to be without physical contact with the coil "30. The welding heat softens a very narrow band around the coil 30 which is sufficient to allow the coil 30 to fit itself more intimately against the contours of the inner wall and thus provides much better heat conduction contact.

Fig-7 shows a previously known tank 31 which has a central cylindrical part 32, an upper hemispherical pressure head part 33 and a lower hemispherical pressure head part 34. This container is formed by rolling a steel plate into a cylindrical shape and welding the meeting edges of the plate along a seam 35. The upper pressure head portion 33 is welded to the cylindrical portion 32 along the seam 36. The lower pressure head portion 34 is welded to the cylindrical portion 32 along the seam 37. This previously known tank is made explosion-resistant by being equipped with an internal mass or coil of expanded metal 30 which is in heat-conducting contact with essentially the entire internal surface of the tank 31. However, the previously known tank is not as strong as the tank 10 in fig. 1. During the high temperature of a fire, both tanks 10 and 31 will have. tendency to bulge outwards due to the increasing internal pressure. Any bulge in the tank can leave a pocket of steam or liquid between the tank wall and the coil 30, and such a pocket is a potential place of explosion. Thus, it is important to make the tank 10 as resistant to buckling as possible. The tank 31 will bulge more than the container 10, because that the seam 13 of the tank 10 provides additional circumferential stiffness that is not found in the tank 31.

Fuel tanks which are filled only with fuel and which have an internal mass of expanded metal explode easily when exposed to fire. The fire heats the tank and its fuel, which increases its vapor pressure until the tank ruptures. Steam and liquid are ejected and ignited explosively, blowing the fuel in all directions and sucking ambient air into the vacuum produced by the explosion to support the violent combustion. Furthermore, there is no flame barrier to prevent the flame from spreading to the inside of the tank. In the case of a fuel, such as propane, which is kept liquid in a pressure tank, the explosive properties are even worse than for petrol because the high internal pressure that is normally in the tank. Such tanks are expected to contain 450-500 psi in normal use and have a burst strength of approx. 90 0-1 0 0 0 psi . In the event of a fire, the propane tank will eventually burst the pressure relief valve and release steam into the surrounding fire, and normally steam cannot be released fast enough to keep the internal pressure from rising even higher. Finally, the tank will burst and a violent explosion will occur. When the tank is filled with a mass of expanded metal, it will hold approximately 98% of the volume of liquid propane held in a tank without any expanded metal structure. The tensile metal structure provides good heat conduction between the top and bottom of the tank, reducing the potential for a violent explosion. The top of the tank in a fire is hot because the burning steam escaping. The bottom of the tank is cooler due to the evaporation of liquid propane into steam .. The heat that is conducted through the internal structure of expanded metal reduces the temperature in the walls of the tank which reduces the potential cracking of the walls and causing an explosion. Also, when there is an opening in the tank walls, whether it be a pressure relief valve vent, a crack in the wall, or the like, the escaping liquid and steam will cause the expanded metal to plug that vent or crack allowing some outward leakage of steam and liquid, but the small openings in the expanded metal are an effective flame barrier. Even if vapor and liquid escape and burn, the potential for explosion is virtually completely eliminated due to f the lamb barrier characteristic. As air cannot flow into the tank, the fuel will not burn until it escapes from the tank. This is considered to be the explanation for the explosion resistance characteristic of this invention, but it is not intended that this invention be limited to this.

The third embodiment of the tank is shown in fig. 8 and 9 as a tank which is essentially spherical. This embodiment comprises upper hemispherical pressure head 40 and lower hemispherical pressure head 41 which are joined by a circumferential weld seam 42. An upper guard 43 and lower footing 44 allow the spherical container to stand on a flat surface. This container has a single multi-purpose valve 45 that serves as a liquid inlet, gas outlet, pressure relief valve and the metering tube for filling. As in the case of the previously described embodiments, there is a liquid discharge line 23, an inlet line 46 to the pressure relief valve, and a cap on the inlet line 46. A spherical tank is the strongest form of an internally pressurized container and in use it is in all essentially free of bulges that are potential explosion sites.

In fig. 1 0 and 1 1 there is shown a cap 47 on the inlet pipe 46 which leads to the pressure relief valve 19 on the tank 10. The reason for having the pipe 46 is to cause any gas flow through the valve 19 to come from near the inner surface of the tank 1 0 . The flow of gas from the lower part of the tank to the upper pressure head of the tank provides a certain cooling effect which is desirable to reduce the explosion potential. The upper pressure head will be hot from any external flame-burning fuel emitting from that head, while liquid and vapor in the lower part of the tank are much cooler. Also, if there is any bulge in the walls of the tank 10, steam from lower in the tank will flow upwards along the path of least resistance, which will be along the inside surface of the walls where the coil 30 has been pulled away from the wall.

The cap 47 has a plurality of inlet holes around its periphery to provide no significant resistance to the flow of steam therethrough. Because of. the possibility of pieces of the coil 30 plugging the entrance to the tube 46, it has been found desirable to use the cap 47 which has many inlet holes 48. Any of the holes 48 can be plugged, but due to the large number of these holes, it is not likely that the entire flow into pipe 46 will be plugged in this way.

The fuel used in the tank according to this invention is any flammable liquid that exists in the gas phase at ambient temperatures and pressures. The most commonly known of such fuels is propane. Other fuels for which the tanks according to this invention are usable include natural gas, methane, ethane, butane, acetylene, cutting gases of various compositions, etc.

The preferred metal for the tank 10 is steel because its strength, availability and cost. Aluminum is also a metal for the tank 10 which has the advantage of being light in weight and allowing stress relief of welds at temperatures which will not melt the internal mass of tensile metal. Many other metals can be used, consider far too expensive for everyday use, e.g. titanium and various alloys.

Although the invention has been described with respect to particular embodiments, it will be understood that many modifications and changes may be made by those skilled in the art without departing from the spirit of the invention. It is therefore the purpose of the appended claims to cover all such modifications and changes that fall within the true spirit and scope of the invention.

Claims (34)

1. Explosion-resistant metal tank filled with liquid fuel in which the container encloses a mass of expanded metal, characterized in that said tank is a pressure vessel for a fuel normally in gaseous form under sufficient pressure to keep the fuel in the liquid phase, and a mass of expanded metal plates that are tightly packed together to form a structure of substantial thickness adjacent to and in heat-conducting contact with essentially the entire internal surface of said tank, said mass having a sufficiently high thermal conductivity to transfer heat from the tank to the cool evaporating liquid fuel that fills the spaces in said mass to thereby reduce the tendency for the tank to crack due to the high temperature of the tank. 2. Tank as specified in claim 1, characterized in that said tensile metal is aluminium. 3. Tank as specified in claim 1, characterized in that the tensile metal is stainless steel. 4. Tank as specified in claim 1, characterized in that said mass essentially fills the internal volume of the tank while spaces are left in said mass for said fuel in the size of approx. 98% of the tank's volume. 5. Tank as specified in claim 4, characterized in that the said mass is a tightly rolled coil with adjacent layers of expanded metal that slope in different directions relative to each other. 6. Tank as specified in claim 1, characterized in that alternating layers of said mass are oriented at right angles to each other to provide a more curved path for the flow of fuel through said mass. 7. Tank as set forth in claim 1, characterized in that it consists of two deep-drawn half sections of metal each having a hemispherical pressure head portion and a circumferential edge portion, said sections being welded together along their respective circumferential edge portions, and then stress-relieved by means of which does not produce any significant melting of said tensile metal. 8. Tank as specified in claim 7, characterized by a valve-equipped line through a pressure head thereof, said line extending inside the tank along the inner wall thereof substantially parallel to its longitudinal axis through said pressure heads, the line being attached to said one head adjacent to said circumferential edge portion and partially extending along the inner hemispherical worm-like surface of the second head. 9. Tank as stated in claim 8, characterized in that the end of said line in said second head is placed at the liquid level in the tank, regardless of horizontal or vertical position, which represents approx. 10% of the liquid volume when the tank is filled. 1 0 . Tank as specified in claim 7, characterized in that said tank is made of steel and said mass is made of aluminium. 1 1 . Tank as specified in claim 7, characterized in that said means of stress relief is ball hammering of said weld. 12. Container as stated in claim 7, characterized by a central cylindrical part with a hemispherical pressure head part at each end of said cylindrical part, said half sections being a uniform, deep-drawn, cup-shaped metal object. 13. Tank as specified in claim 7, characterized by a pressure relief valve in said one pressure head and which has a line which is operationally connected to said valve inside the tank, said line extending laterally to an open end close to the inner surface of said head. 14. Tank as stated in claim 13, characterized in that said open end closure is covered with a cap which has a plurality of separate openings through it which communicates with the inside of said wire. 15. Tank as stated in claim 1, characterized in that it is essentially spherical in shape. 16. Tank as specified in claim 15, characterized in that it has in a pressure head thereof a valve-equipped line through said head and arranged for filling the tank with liquid, for draining gas from the tank and for functioning as a pressure relief safety valve. 17. Explosion-resistant metal tank filled with liquid fuel in which the tank encloses a mass of expanded aluminum, characterized in that the tank is a pressure vessel comprising two half-sections, each of which has a hemispherical pressure head and a circumferential edge portion, said sections being joined along their circumferential edge portions by by means of a weld that is stress-relieved by means of means that do not melt any substantial part of said mass of stretched aluminum, said mass of stretched aluminum, said mass of stretched aluminum comprising a plurality of layers of stretched aluminum plates which are compressed to to form a structure of significant thickness in heat-conducting contact with essentially the entire internal surface of said tank, one of said pressure heads having a valve-equipped line through it with the line running inside said tank along its inner wall essentially parallel to the longitudinal axis of the tank again about both pressure heads, the wire extending past said weld and partly along the inner surface of the other of said heads, the wire being attached to said one pressure head adjacent to said weld. 18. Tank as specified in claim 17, characterized in that said tank is made of steel. 19. Tank as specified in claim 17, characterized in that said stress relief means is ball hammering. 20 . Method for manufacturing a metal tank for storing hydrocarbon in the liquid phase which is emitted from the tank in the gas phase, the tank enclosing therein a mass of expanded metal plate, characterized by providing two uniform, cup-shaped pressure heads of metal each having a cylindrical portion which is joined by a end to a closed substantially hemispherical portion and terminating at the other end in a circumferential edge portion, to attach a manually operated valve to a pressure head with a line extending from the valve into the tank along the inner surface of one head and with its adjacent cylindrical portion parallel to the longitudinal axis of the tank and past the circumferential edge portion and terminating in an open end at a point on the hemispherical surface of the second pressure head adjacent its junction with its respective cylindrical portion, to cause the mass of expanded metal sheet to fit neatly against the internal contours a v the two heads are joined at their respective circumferential edge portions so that the mass of expanded metal is in heat-conducting contact with substantially all of the internal surfaces of the two heads, to align the two pressure heads with the mass of expanded metal enclosed within both heads, to weld the two heads along the circumferential edge portions to produce a pressure-tight container, and to stress relieve the welded joint without melting any substantial portion of the mass of expansion metal. 21 . Method as stated in claim 20, characterized in that the step for stress relief takes place by ball hammering. 22 . Method as stated in claim 21, characterized in that the mass of expanded metal is aluminium. 23. Method as stated in claim 21, characterized in that the pressure heads are made of steel. 24. Method as stated in claim 23, characterized in that the mass of expanded metal is aluminium. 25. Method as stated in claim 20, characterized in that the pressure heads are made of steel. 26 . Method as stated in claim 25, characterized in that the mass of expanded metal is steel. 27. Method as stated in claim 20, characterized in that the mass of expanded metal is aluminum. 28. Method as stated in claim 27, characterized in that the pressure heads are made of aluminum and the stress relief step takes place by heating the manufactured tank without melting the pressure heads. 29. Method as stated in claim 20, characterized in that the mass of tensile metal is placed with adjacent layers of said tensile metal with the opposite inclined stretching direction. 30 . Method as stated in claim 20, characterized in that the mass of tensile metal is placed with adjacent layers of tensile metal oriented at right angles relative to each other with regard to the tensile orientation. 31 . Method as set forth in claim 20, characterized by the steps of welding to the outside of each hemispherical worm pressure head an annular ring capable of holding said tank in an upright position when resting on a flat surface. 32. Method as stated in claim 20, characterized in that the mass of expanded metal is a tightly wound coil of one or more sheets of expanded metal. 33. Method as stated in claim 32, characterized in that said tensile metal is aluminium. 34. Method as stated in claim 32, characterized in that said tensile metal is stainless steel.