Metallic Liner System

Abstract

A liner system for retaining liquid in a storage tank. The liner system includes a continuous metallic liner which has sides which are substantially coextensive with the sidewalls of the tank and a bottom which is substantially coextensive with the floor of the tank. Upright expansion joints, provided in the sides of the liner, compensate for expansion and contraction of the sides in a circumferential direction and expansion joints, provided in the bottom of the liner, compensate for expansion and contraction in the bottom of the liner. Hanger members are secured to the upper portion of the tank and are resiliently mounted thereto. The upper end of the sides of the liner engage the resiliently mounted hangers so as to compensate for expansion and contraction of the liner in a vertical direction.

Description

BACKGROUND OF THE INVENTION - FIELD OF THE INVENTION

AND DESCRIPTION OF THE PRIOR ART

This invention relates to a liner system for retaining liquid in a storage tank and it particularly relates to such a liner system which is particularly useful in storing liquid gas at cryogenic temperatures.

Normally the only problem that is encountered with the storage of liquids at atmospheric pressure is the prevention of the liquid from escaping from the container in which it is stored, a large storage tank, for example. Problems of retaining liquid in a storage tank are normally greater when storage is at superatmospheric pressures, but nevertheless, significant problems are encountered even when the liquid is stored at atmospheric pressure. Such problems include the selection of a construction material which will not permit the passage of the liquid by seepage. For example, storage tanks are often constructed of concrete and the inside of the tank must be treated so as to prevent any loss of the liquid from the tank. Such loss of liquid can be caused by the permeability of the material from which the tank is constructed, by stresses imparted to the storage container or a liner material which ultimately will cause cracks or apertures to form, or by a combination of these two factors.

Particularly difficult problems are encountered in the storage of large quantities of liquid gas stored at cryogenic temperatures and at atmospheric pressures. Because of the extremely cold cryogenic storage temperatures which must be withstood by the storage tank material and because of the insulation which must be used in such tank structures, separate liners for the interior of the storage tanks are used in order to prevent the loss of the stored liquid gas from the tank. In U.S. Pat. application Ser. No. 526,983, now U.S. Pat. No. 3,418,812, there is shown and described an insulating system for a storage tank for retaining liquid natural gas at cryogenic temperatures. In this particular insulating system the insulation is of a porous, foamed material. The innermost surface of the material is formed of separate blocks of insulated foam which are joined together in close proximity. Because of the porosity of the material and because of the spaces between the individual blocks, it is essential that a liner be used in the interior surface of the blocks to prevent the egress of the stored liquid from the cryogenic storage tank. A flexible liquid and gas barrier or liner is formed as an integral part of the insulating panels wherein such liners may be a laminated material of MYLAR (polyethylene terephthalate fiber) having a backing of lightweight fiber cloth and aluminum foil. Although once installed, this material is quite satisfactory, great care must be exercised during this installation of the laminate so as to prevent creasing of the material, which will ultimately form pinholes therein. Such small holes cannot be tolerated because it will cause leakage of the liquid gas from the tank.

Because of the discussed inherent problems with the plastic film-metal film-fibrous laminate, metal liners, such as aluminum foil, may be used on the inside of a tank for retaining the liquid. Although the aluminum or metallic liners are not subject to the same difficulties encountered with the laminated type of liner, other difficulties are encountered. The interior of the cryogenic tanks must be capable of withstanding temperatures cycling between extreme cold and normal temperatures. Thus, means must be provided for compensating for expansion and contraction of the metal liner while it is within the storage tank. If any undue stress is set up in the material during use, cracks may develop and the liquid natural gas can escape from within the liner. It is therefore necessary to construct the metallic liner in such a manner that it will avoid stresses of expansion and contraction of the liner so as to avoid cracks forming. In prior metallic liner systems, the expansion joints have been of complex and expensive design. For example, it has been necessary to use a complex three-dimensional expansion joint at the intersections between the sides and floor.

SUMMARY OF THE INVENTION

It is therefore an important object of this invention to provide an improved liner system for the inside of storage tanks for storing liquids wherein the liner system avoids problems of prior art liner systems.

It is also an object of this invention to provide an improved liner system for the interior of storage tanks used for storing liquid natural gas at cryogenic temperatures wherein the liner is of a metal material so as to provide durability and ease of construction, but at the same time substantially avoids complex expansion joints normally required with other metal liner systems.

It is another object of this invention to provide an improved liner system for storing liquid natural gas at cryogenic temperatures wherein the liner system compensates for vertical expansion and contraction by the use of special hangers resiliently mounted to the upper portion of the storage tank.

It is yet another object of this invention to provide an improved liner system for storing liquid natural gas at cryogenic temperatures wherein expansion joints are located in an upright position along the sides of the liner and in ringlike configuration in the bottom of the liner and the upper end of the sides of the liner are resiliently mounted.

Further purposes and objects of this invention will appear as the specification proceeds.

The foregoing objects are accomplished by providing a liner system which comprises a continuous liner having sides which are substantially coextensive with the sidewalls of the storage tank and having a bottom which is substantially coextensive with the floor of the storage tank, first upright expansion joint portions in the sides of the liner to compensate for expansion and contraction of the sides, second expansion joint portions in the bottom of the liner to compensate for expansion and contraction of the bottom, hanger members resiliently secured to the upper portion of the tank, and means secured to the upper end of the sides of the liner to engage the hanger members to compensate for vertical expansion and contraction, whereby the sides are suspended in a position substantially coextensive with the sidewalls and the bottom is maintained in a position substantially coextensive with the floor.

BRIEF DESCRIPTION OF THE DRAWINGS

Particular embodiments of the present invention are illustrated in the accompanying drawings wherein;

FIG. 1 is a top plan cross-sectional view through a tank using our improved liner system;

FIG. 2 is a vertical cross-sectional view taken through a tank construction of the type shown in FIG. 1;

FIG. 3 is an enlarged fragmentary plan view showing the expansion joints used in a liner system;

FIG. 4 is a cross-sectional view taken along the line 4-4 of FIG. 3 showing a detailed view of the expansion joints of the liner;

FIG. 5 is a detailed cross-sectional view taken along the line 5-5 of FIG. 4;

FIG. 6 is a fragmentary cross-sectional view taken along the line 6-6 of FIG. 3;

FIG. 7 is an alternate embodiment of our liner system, when the tank structure is located entirely below the ground;

FIG. 8 is an enlarged cross-sectional view taken along the line 8-8 of FIG. 7;

FIG. 9 is an enlarged detailed view showing the construction of the hanger member used in the embodiment of FIG. 7; and

FIG. 10 is a fragmentary detailed view taken along the line 10-10 of FIG. 8 .

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The liner system for retaining liquids in a storage tank, which will be hereinafter described in detail, may be used in any type of tank used for the storage of liquids. The tank structure may be entirely above the ground, partially above the ground and partially below the ground, or completely below the ground. The tank structure may store liquids at atmospheric conditions, at atmospheric pressure and cryogenic temperatures, etc. It is to be understood, however, that the greatest utility of the liner systems described hereinafter is in the storage of liquid gases at cryogenic temperatures because of the various expansion joints and resilient hangers used in our liner system to compensate for expansion and contraction of the liner.

Liquid natural gas is commonly stored in large storage containers at substantially atmospheric pressures but at cryogenic temperatures. The purpose of the storage of liquid natural gas at these conditions is to store the maximum quantity of gas in a minimum space so that on peak demand days, such as during cold weather, sufficient gas is available for heating purposes. It is in such storage tanks that our liner system finds its greatest utility.

In the accompanying drawings, two preferred embodiments of our liner system are illustrated. In the first embodiment, shown in FIGS. 1--6, hanger members, used for suspending the liner, project upwardly from the upper portion or top of the tank when the tank structure is either completely above the ground or partially above the ground. In the embodiment of FIGS. 7--10, the tank structure is completely below the ground so that the hanger members are located entirely within the tank and are suspended downwardly from the top or upper portion of the tank. Each of these embodiments will be described in detail below.

Referring to the embodiment of FIGS. 1--6, the storage tank 10 is located partially above the ground. In the description of this embodiment, as well as in the description of FIGS. 7--10, the walls of the tanks will be shown as being of solid concrete construction. It is to be understood, however, that in the storage of liquid natural gas at cryogenic temperatures the walls will generally comprise an outer supporting concrete section, an outer liner which acts as a water barrier, and multiple layers of insulating material, such as foamed polyurethane (not shown). Specific examples of tanks having such construction are found in U.S. Pat. application Ser. No. 526,983, now U.S. Pat. No. 3,418,812, U.S. Pat. application Ser. No. 527,158, now U.S. Pat. No. 3,407,606, U.S. Pat. application Ser. No. 702,293, filed Feb. 1, 1968, and U.S. Pat. application Ser. No. 702,471, filed Feb. 1,1968. Since the liner system used for the retention of the liquid is the subject of the present invention, the tank structure 10 will only be described in general terms.

The tank 10 includes upwardly extending outer walls 12, a roof 14, and a floor 16. The liner, generally 18, is supported inside the tank and retains the liquid in place within the tank 10 so as to prevent the egress thereof from the tank.

The liner 18 has a bottom 20 which is substantially coextensive with the floor 16 of the tank 10 and also has upright sides 22 which are maintained substantially coextensive with the walls 12 of the tank 10. The upper end of the sides 22 includes integral strap members 24 which engage a resiliently mounted ringlike support member 26.

Because the liner 18 is designed particularly for use with tanks for storing liquid natural gas at cryogenic temperatures, the liner 18 is constructed to avoid stresses which may be caused by expansion and contraction of the liner material, when the tank 10 is cycled between cryogenic temperatures for storing the liquid gas and higher normal temperatures when the tank 10 must be repaired or serviced. The liner 18 is designed so as to compensate for expansion and contraction of its bottom 20 and of its sides 22, both circumferentially and vertically.

In the preferred embodiment, the bottom 20 of the liner 18 is formed by integrally joining planar sections, such as the central portion 28, with a plurality of expansion joints 30 and 32. The planar portions, such as the central portion 28 are formed by integrally joining, as by welding, sheets of metal such as from rolls of aluminum or steel sheeting. As shown in FIGS. 3 and 5, the expansion joints 30 are integrally joined, as by welding, to the planar portions of the bottom 20. The expansion joints 30 generally comprise thermal expansion metal which has the general configuration of corrugated sections. The corrugated expansion joints 30 expand when the temperature in the tank is raised and contract when the temperature is lowered, so that regardless of the temperature, the bottom 20 of the liner 18 remains substantially coextensive at all times with the floor 16 of the tank 10 without undue stresses being set up in the liner bottom. Preferably, a multiplicity of expansion joints 30 are provided in the bottom 20. The bottom expansion joints are preferably ringlike and substantially concentric with each other such as shown in FIG. 1.

The sides 22 of the liner 18 are maintained in close proximity to the walls 12 of the tank 10 and generally comprise a plurality of substantially planar upright sections 32 which are spaced apart by a plurality of upright expansion joints 34. The expansion joints 34 extend from the upper edge of the liner sides 22 downwardly to the intersection between the bottom 20 and the sides 22. Preferably, the lower or terminal portion of the upright joints 34 is brought into intersecting, united relationship with the outermost ringlike expansion joint 36 in the bottom 20. The intersection between the upright joints 34 and the outermost joint 36 provides a far simpler construction than structures used in the prior art, which involve using three dimensional expansion joints for avoiding excessive stresses at the intersection of a vertical liner section with the floor liner section. The intersection between the upright expansion joint 34 and the floor joint 36 is accomplished by a V-shaped intersection between these joints 34. As shown clearly in FIGS. 3 and 5, the planar sections 32 are joined to the upright expansion joint section 34 by suitable means, as by welding at the joint 38. A plurality of metal sheet sections may be welded or joined together by other suitable means to form the planar sections 32 in a manner similar to that used for forming the central portion 28 of the bottom 20 of the liner 18. The upright expansion joints 34 compensate for circumferential expansion and contraction of the sides of the liner 22.

The resiliently mounted support member 26 is desirably a ringlike structure which is rigidly joined at a plurality of spaced locations to upright rods or tubes 40. The hanger members 42 are mounted on the upper surface of the roof 14 of the tank 10. The hangers 42 are located in direct alignment above the support member 26. The support member 26 is constructed so as to be in close proximity to the walls 12 of the tank 10 and so as to provide assurance that the sides 22 of the liner 18 remain substantially coextensive with the tank walls 12 at all times.

The hanger members 42 each include a flange portion 44 which is rigidly secured on the upper surface of the roof 14. An outer tubular member 46 is threadably secured to the threaded portion of the flange 44 and extends upwardly therefrom. The upper end of the tube 46 is closed by a cap 48 which is threadably secured to the upper end of the tube 46. The tubular member 46 defines a housing for a compression spring 50 which is located in the annular space between an upright rod or tube 40 and the outer tube 46. A collar 52 is removably secured to the upper end of the upright tube 40 by means of a pin 54. The upper end of the compression spring 50 engages the collar 52 and the lower end of the compression spring 50 engages the upper end of the flange 44.

The hanger members 42 thereby provide resilient support for the support member 26 and thereby for the liner 18. The weight of the liner 18 and the weight of the liquid contained within the liner 18 cause downward movement of the support member 26. This downward movement compresses the spring 50 because the spring 50 is trapped between the collar 52 and the flange 44. The compression springs 50 provide resilient mounting of the liner 18 and thus compensate for vertical expansion and contraction of the sides 22 to accommodate for height variation depending upon the depth of the liquid contained within the liner 18, without creating any significant stresses in the liner material which could ultimately cause breaks to form therein. Preferably a packing gland 56 is interposed between the flange 44 and the outer surface of the upright tube 40 so as to prevent gas leakage from the tank storage area.

The compression spring 50 is designed so as to allow for the contraction of the liner material. Thus, with the proper spring constant, when the wall material cools and contracts or heats and expands, excessive stresses will not be set up in the material which can ultimately lead to failure of the liner. The compression spring has a load due to the weight of the liner material itself and due to the weight of the liquid contained therein, and it also has a load due to the contraction of the wall material. The spring constant is chosen so that the force required to compress the spring an amount necessary to allow for the contraction of the wall material is only a relatively small percentage of the proportional stress limit of the material. Since the loading due to contraction is only a small percentage of the loading due to the material weight, the compression spring is relatively long. In order to keep the length of the total assembly within reasonable limits, it is desirable to precompress the spring to about 90--95 percent of the material weight load before it is installed.

Referring now to the embodiment of FIGS. 7--10, the tank 70 shown therein is located entirely below the ground so that the upwardly projecting hanger members 42 of the embodiment of FIGS. 1--6 cannot be used. The essential differences between the embodiment of FIGS. 1--6 and the embodiment of FIGS. 7--10 lie in the construction of the hanger members, although it is to be understood that the principle of both liner systems is substantially the same. The construction of the liner 72 in the tank 70 is substantially the same as liner 18 for the tank 10. The only difference between the embodiment of FIGS. 7--10 and of FIGS. 1--6 is that the liner 72 uses a different type of strap member 74 for engaging the ringlike support 76, which is resiliently mounted from a plurality of hanger members 78. It is noted that each strap 74 is elongated and constitutes a continuation of the liner material which is folded upon itself and welded in place over the ringlike support 76.

A peripheral beam 80 is rigidly secured to the underside of the roof 82 of the tank 70 by use of bolts 84. The underside of the peripheral ringlike beam 80 has a plurality of downwardly extending tubes or rods 86 projecting therefrom. These tubes are equally spaced at a plurality of locations therearound. The lower end of the tube 86 includes a bearing plate 88 which is rigidly secured thereto by suitable means, as by welding. An outer tubular member or housing 90 is slidably mounted around the downwardly extending tube 86. An upper bearing plate 92 is threadably secured to the upper end of the tubular housing 90. A compression spring 94 is interposed between the bearing plate 92 and the bearing plate 88 and is contained within the annular space between the tubular member 86 and the outer housing 90.

The lower end of the tubular housing 90 is rigidly secured, as by welding, to the ringlike support member 76 around which the strap members 74 are passed to provide support for the liner 72. It is thus seen that the compression springs 94 provide for the same type of support for the liner 72 as is provided by the compression springs 50 for the liner 18. As the liquid depth is varied within the liner 72, less load is applied to the resiliently mounted support 76 and the compression springs 94 tend to lift the support 76 upwardly through the outer housing 90 and the bearing plate 92. The hanger members 78 thus compensate for vertical expansion and contraction of the sides of the liner 72.

It is seen from the foregoing description that we have provided a liner system of relatively simple construction which compensates for expansion and contraction thereof due to great variations in temperature. The construction provides for expansion joints in the floor for radial expansion and contraction. Both the embodiments also provide for circumferential expansion and contraction of the sides, and provide for vertical expansion and contraction of the sides. All this is accomplished in a relatively simple, but highly effective manner. The same basic principles are used in the support of the liner regardless of whether the tank structure is contained entirely above the ground or partially above the ground and partially below the ground. The only variation is in the specific design of the hanger members which are supported by the roof of the tank for the purpose of vertically supporting the liner sides in a resilient manner.

Claims

We claim:

1. A system for retaining liquid in a storage tank structure, said system comprising a storage tank having an upper portion, sidewalls, and a floor, continuous liner means having sides substantially coextensive with said sidewalls and having a bottom substantially coextensive with said floor, upright expansion joint sections integrally joined to said sides of said liner means compensating for circumferential expansion and contraction of said sides, ringlike expansion joint sections integrally joined to said bottom of said liner means compensating for expansion and contraction of said bottom, hanger members resiliently secured to said upper portion of said tank structure, and means secured to the upper end portions of said sides of said liner means for engaging said hanger members whereby said sides are suspended in a position substantially coextensive with said sidewalls and said bottom is maintained in a position substantially coextensive with said floor.

2. The system of claim 1 wherein said upright expansion joint sections in said sides extend to intersect said ringlike expansion joint sections in said bottom so as to allow for movement of said liner means in all directions at the intersection between said side and said bottom.

3. The system of claim 1 wherein the upper portion of said storage tank is above the ground and said hanger members extend outwardly above said upper portion.

4. The system of claim 1 wherein the upper portion of said storage tank structure is below the ground and the said hanger members are enclosed within said storage tanks and extend downwardly from said upper portion.

5. The system of claim 1 wherein said hanger members include spring means for resiliently supporting said sides in a vertical direction to compensate for vertical expansion and contraction of said sides of said liner means.

6. The system of claim 5 wherein said upright expansion joint sections and said ringlike expansion joint sections intersect so as to compensate for expansion and contraction in all directions at the intersection of said side and said bottom, thereby avoiding excessive stresses in said bottom of said liner means.

7. The system of claim 1 wherein said liner means is a flexible metallic material, said expansion joint means generally comprising corrugated sections.

8. The system of claim 1 wherein the said liner means comprise a plurality of planar substantially flexible metallic material sections welded together in a desired configuration so as to provide continuous liner means, and said expansion joint sections comprises unitary corrugated metallic members united to the planar portions of said liner means.

9. The system of claim 1 wherein said first expansion joint sections comprise substantially upright metallic corrugations, said second expansion joint sections integrally joined to said bottom of said liner means, said upright corrugations extend into said ringlike sections, and the outermost of said ringlike portions intersect the said extending portions of said upright corrugations in said sides.

10. The system of claim 1 wherein said hanger members comprise support members resiliently mounted in a vertical direction to compensate for expansion and contraction of said sides in a vertical direction.