US20040200842A1

US20040200842A1 - Containment system for storage systems having discontinuities

Info

Publication number: US20040200842A1
Application number: US10/740,409
Authority: US
Inventors: Gary Low; Collin Watson
Original assignee: Individual
Current assignee: NILEX CONSTRUCTION Inc
Priority date: 2003-04-14
Filing date: 2003-12-22
Publication date: 2004-10-14

Abstract

A system for sealing a liner about an internal member in a structural envelope, such as a liquid storage tank. A mechanical seal is located between the liner's first edge and the structural envelope and forms secondary containment between the structural envelope and the liner. A plate sealably attaches outside the outer perimeter of the mechanical seal to either the inner or outer surface of the structural envelope and forms a continuous envelope extension from the liner to the discontinuity. The plate provides secondary containment between the continuous envelope extension and the structural envelope. Tertiary containment is achievable through use of a liner boot, the outer edge attached to the liner outside the perimeter of the mechanical seal and the inner edge mechanically sealed to the discontinuity.

Description

FIELD OF THE INVENTION

The invention involves methodology and apparatus for providing secondary containment for structural enclosures such as tanks, more particularly for sealing around discontinuities in the tank such as internal structure and penetrations of the structural envelope.

BACKGROUND OF THE INVENTION

This invention relates to storage tanks that contain a variety of fluids and that are lined with impermeable and sealed internal geosynthetic liners. Such liners are also referred to in the art as storage tank bladder seals, as set forth in U.S. Pat. No. 5,558,245, or leakage protection liners as set forth in U.S. Pat. No. 6,431,387.

The tank storage industry has been slow to adopt sealed internal geosynthetic liners because of the difficulty in sealing the liner membrane to or around discontinuities or internal structures that attach to the structural envelope such as to the tank's containing walls including floors. Discontinuities include support beams, sumps, stands, gauge boards, and penetrations in the internal floor or walls such as pipes, manways, heating coils, or other penetrations.

The prior art methodology for sealing internal geosynthetic liners about structures attached to the floor, such as tank columns, consists of three main approaches. The first approach is to extend or bring the liner membrane underneath the tank column, however this places the membrane on the tank floor at risk. The impact of weight and movement of these structures introduces significant uncertainty about the ability of the membrane to withstand the forces of the structure, and the membrane may be cut, crushed or otherwise damaged.

The second approach, if the column is round, is to bring the membrane up to the column, and then to seal a boot (a membrane welded in a cylindrical shape, with a brim attached at one end of the cylinder and extending out from the cylinder), around the column and to the membrane on the floor, and then to seal the throat of the cylinder of the boot to the column, using a form of mechanical clamping or banding to bind the boot to the column. This approach also poses risks to the functioning of the liner. The hand or detail welding of the boot to the membrane on the floor is prone to leak and difficult to test. In addition, clamping or banding systems are often not sufficiently resistant to fluid penetration. This system introduces a weak link in the liner at a penetration which exposes the entire envelope to a breach. As a result of the high failure rates of tanks employing these two liner methods, sealed internal geosynthetic liners have not been widely adopted except in situations where there are few or no tank penetrations or attachments below the liquid level of the tank.

A third, less common, but more effective approach is to use mechanical compression seals for use in sealing the liner directly to the tank floor about or encircling the discontinuity. Mechanical compression systems employ bolts or fasteners attached to the floor of the tank, with a batten or punched bar, to compress a system of gaskets, bonding or adhesive material and the membrane to the floor of the tank, or to a flange on the floor, around the structure or attachment. While this approach can provide a more reliable compression and a better seal than the approaches noted above, the secondary containment is limited to the main envelope and such advantages are lost specifically at the discontinuity, such as where the structures are attached directly to the floor. A fundamental requirement of most modern regulatory schemes is that storage tanks are design to provide dual containment. Regulators will often not approve the omission or loss of dual containment that occurs in selected areas in the tank when this third approach is used.

The prior art for sealing internal geosynthetic liners around penetrations through tank walls and through the internal geosynthetic membrane covering such walls, such as around pipes for incoming or outgoing fluid, consists of several methods. A first method is applied in the case of tanks having penetrations at the point where pipes attach to the tank. Pipes are fitted with a flange that attaches to a flange on the tank. The geosynthetic membrane is sandwiched between the flanges with the conventional gasket for sealing therewith around the flange. There are several limitations with this approach. The penetration of the pipe at the flange itself is not covered. Any movement of the pipe attached to the flange exerts considerable leverage on the gasket and membrane, deforming the membrane and breaking the seal, and contaminating the interstitial containment space. In addition, leaking can occur behind the flange, again contaminating the interstitial space.

A second method, more often used with tanks having welded in place penetrations, is to fabricate a boot that seals to the membrane on the inner wall, and then to seal the constricted throat of the boot around the pipe penetration using a form of clamps or bands to bind the geosynthetic membrane to the pipe. This approach has limitations similar to liner boot seals about columns as discussed above. Hand or detail seams for boots are less reliable than machine wedge or dielectric seams, and more prone to leakage and failure. Clamping or banding systems are not necessarily sufficiently resistant to fluid penetration.

A problem unique to pipe penetrations is that a boot system for pipe penetrations on the tank wall does not protect the interstitial space (the isolated area between the tank and the geosynthetic membrane) from leaking that may occur at the junction of the pipe and the tank wall behind the membrane. In the event of such leaks, the entire interstitial area between the geosynthetic membrane and the inner tank surface becomes contaminated with fluid. If the interstitial space is monitored, the monitor will indicate a leak, even though the membrane may not have been the cause of the leak. In addition, because of the movement of incoming pipes, or shifting of the membrane on the inner tank surfaces, the boot can be stretched and damaged by these forces, resulting in liner failure. These types of penetration seals cannot be isolated, and are difficult to test. These design problems contribute to the perception of unreliability of sealed internal geosynthetic liners.

Finally, a third method to deal with penetrations is to adhere the geosynthetic membrane to the wall of the tank around the penetration, using both an adhesive material, and compressing the material to the wall, using bolts or fasteners attached to the wall of the tank, with a batten or punched bar to compress a system of gaskets, bonding or adhesive material and the membrane to the wall of the tank, around the pipe penetration. While this method provides a stronger and more reliable seal, it suffers from the same limitations of this same approach when used on a tank floor. The dual containment provided by the first two approaches is lost in this third approach where the point of penetration, which is the most susceptible to leaks, loses dual containment, and may not be acceptable where regulatory or environmental requirements require dual containment. In addition, the metal in this unprotected area of the tank and penetration is not protected from corrosion from the fluids in the tank.

There is a need for a system which enables an internal geosynthetic liner to seal effectively and reliably around attachments, structures and penetrations while providing secondary or tertiary containment including at such discontinuities.

SUMMARY OF THE INVENTION

The objects of the invention are achieved through a system that provides for sealing an internal geosynthetic liner around or over discontinuities in the structural envelope so as to form dual or tertiary containment at the internal members, attachments or other discontinuities including columns, manways, pipes, stands, and gauges. A more reliable and stronger seal is the result.

Accordingly, in one broad aspect of the invention, a system seals a liner about a discontinuity at a structural envelope for containing fluid. The liner forms secondary containment between the liner and an inner surface of the structural envelope. The system comprises: an opening in the liner for forming a first edge about the discontinuity; a mechanical seal circumscribed at an outer perimeter about the discontinuity and located between the liner's first edge and the structural envelope for forming secondary containment between the structural envelope and the liner; and a secondary seal attached at a perimeter attachment to one of the inner or an outer surface of the structural envelope at the discontinuity, the perimeter attachment being outside the outer perimeter of the mechanical seal for forming a continuous envelope extension from the liner to the discontinuity and for forming secondary containment between the continuous envelope extension and the structural envelope.

In another aspect, the system comprises a plate sealably attached at its perimeter attachment to the inner surface of the structural envelope. The plate spaces the discontinuity from the structural envelope and is sealably attached to the structural envelope by a discontinuous weld at the plate's perimeter attachment. The mechanical seal seals the plate to the liner.

In yet another aspect, the system comprises a discontinuity penetrating the structural envelope at a first penetration and attached to the structural envelope at the first penetration. The plate is sealably attached at its perimeter attachment to the outer surface of the structural envelope. The discontinuity penetrates the plate at a second penetration and is sealably attached at the second penetration. The mechanical seal seals the liner to the inner surface of the structural envelope.

In a final aspect of the invention the system comprises a tertiary seal. The tertiary seal is a liner boot with an outer edge attached to the liner outside the perimeter of the mechanical seal and extends inward to an inner edge. A second mechanical seal between the liner boot's inner edge and the discontinuity forms secondary containment between the continuous envelope extension and the structural envelope.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a typical prior art boot welded to a liner and banded to a penetration through a barrier such as a wall or a floor; [0017]
FIG. 2 is a sectional view of a tank lined with a prior art methodology showing a sealing extending under the base of a central column; [0018]
FIG. 3 is a sectional view of a tank lined with a prior art methodology having a boot welded to the liner and extending significantly up the column; [0019]
FIG. 4 is a sectional view of a prior art compression seal practiced by the applicants for sealing about a penetration through a structural envelope; [0020]
FIG. 5[0021] a is a cross sectional view of a sealing system according to one embodiment of the invention, showing a mechanical seal to a plate under a column the plate being supported on a structural envelope or barrier such as a tank floor and forming a continuous envelope extension with the liner;
FIG. 5[0022] b is a close-up cross-sectional view of the mechanical seal at the periphery of the plate of FIG. 5a;
FIG. 6[0023] a is a cross sectional view of a sealing system according to another embodiment of the invention, showing a mechanical seal to a plate under a column and a boot seal about the mechanical seal, the plate being supported on a structural envelope or barrier such as a tank floor;
FIG. 6[0024] b is a close-up cross-sectional view of the mechanical seal at the periphery of the plate of FIG. 6a;
FIG. 7[0025] a is a cross sectional view of a sealing system according to another embodiment of the invention, showing a mechanical seal to the structural envelope with an exterior plate, or secondary plate on the exterior surface of the structure, opposite and surrounding the mechanical seal;
FIG. 7[0026] b is a cross sectional view of a sealing system according to another embodiment of the invention, showing a mechanical seal to the structural envelope adjacent a penetration and a boot seal about the mechanical seal;
FIG. 8 is a cross section of a plastic boot; [0027]
FIG. 9 is a plan view of sectional compression bars applied to mechanical seals around any discontinuity; and [0028]
FIG. 10 is a cross sectional view of a sealing system according to another embodiment of the invention, showing a mechanical seal to the structural envelope adjacent a penetration, secondary containment provided by a plate sealably attached to the exterior of the structural envelope, and a boot seal about the mechanical seal. [0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the prior art, attempts have been made to seal structural enclosures or envelopes with a lining. These envelopes are typically storage tanks made of steel and are configured to support hydrostatic loading of liquids contained therein. Steel envelopes are subject to corrosion and all envelopes including those of plastic are prone to leaks. Such enclosures are fit with a liner when possible. [0030]
With reference to FIG. 1, a prior art system illustrates a [0031] structural envelope 10, or storage tank 12, which is sealed to a discontinuity 16 using a liner 18 extended to fit to the discontinuity with a boot 20. FIG. 2 illustrates a further prior art situation where the liner 18 runs directly under the discontinuity 16 resting on the floor of the storage tank 12. FIG. 3 illustrates yet another alternate prior art approach, illustrating a very tall boot 20 extending upwards, preferably above an expected liquid level. None of these approaches have garnered widespread acceptance.
With reference to FIG. 4, one prior art approach to improve the sealing and security of the [0032] liner 18 to the structural envelope 10, practiced by the Applicants, includes bringing the liner 18 adjacent to the discontinuity 16, and mechanically sealing the liner 18 with means such as a compression device 30. As shown in FIG. 5b, a compression bar 32 is placed over a threaded stud 34 affixed to a plate 60. Gaskets 36 sandwich the liner 18 while a washer 38 and a nut 40 are tightened onto the threaded stud 34 to compress and completely seal the liner 18. However, referring back to FIG. 4, Applicants recognize that no secondary containment results at the discontinuity 16. Thus, the discontinuity 16 is subjected directly to the internal environment and any leak that develops would be directed to the outside environment.
Further, the [0033] structural envelope 10 of fluid-containing walls including floor surfaces of storage tanks 12 generally require seals around discontinuities 16 in the structural envelope 10. Discontinuities 16 include structures that penetrate through a surface 42 of the structural envelope 10, as well those that attach to the surface 42.
The principles and design of Applicants' solution are applicable whether addressing either type of [0034] discontinuity 16 identified above. In practice, most penetrating discontinuities 16 occur through the wall of the tank 12, and involve the piping of fluids in and out of the tank 12, or manways. Other discontinuities 16 involve such things as columns, gage boards, or pipe stands attached to the structural envelope 10.
Turning then to one embodiment of the present invention in FIGS. 5[0035] a, 5 b, a system for sealing the liner 18 about the discontinuity 16 is shown. A discontinuity 16, such as an internal member 44, bears against or is attached to the surface 42 of the storage tank 12. As shown in FIG. 5a, an opening formed in the liner 18 of geosynthetic membrane allows the liner 18 to cover an inner surface of the tank 46, and extending up to a first edge 50 circumscribed about the discontinuity 16. The compression device 30 seals the liner 18 to the structural envelope 10. Accordingly, secondary containment is provided in an interstitial space 56 formed between the liner 18 and the structural envelope 10 and terminating at the compression device 30 and first edge of the liner 50.
As seen in FIG. 5[0036] b, interstitial material 57 is placed preferably between the liner 18 and the structural envelope 10. The interstitial material 57 is fluid-transmissive and is typically applied to enable fluid flow between the liner 18 and the structural envelope 10. Examples of suitable interstitial materials 57 are geotextiles and geogrids, commonly used in construction and landscaping applications.
Herein, geosynthetic membranes (geomembranes) are understood generally to be impermeable sheets composed of synthetic materials including PVC, fluorothermoplastic, urethane, polypropylene, or high-density polyethylene (HDPE). Geomembranes are commonly used as landfill liners, pond liners and in capping applications. Geotextiles are porous, synthetic fabrics, made of woven or non-woven fibers. Geogrids are molded rigid, porous matts made from high-density polyethylene (HDPE) or other synthetic resins. Geogrids are generally more resistant to pressure than geotextiles, but more difficult to work with, and more expensive. [0037]
For completing secondary containment including at the [0038] discontinuity 16, the plate 60 is provided which separates the discontinuity 16 from the structural envelope 10. The discontinuity 16 is initially separated from the surface 42, and the plate 60, typically of a material complementary with the structural envelope 10, is inserted therebetween. The plate 60 has a support area larger than the area of the contact point of the internal member 44 (preferably providing a perimeter of about 12 inches around the contact point) and extends to a perimeter outside the perimeter of the mechanical seal. The plate 60 is secured to the structural envelope 10 such as through welding (metal or plastics) or is otherwise attached to the surface 42, preferably without further penetration of the surface 42. An interstitial area 58 is formed between the plate 60 and the structural envelope 10. The composition of the material of the plate 60 may depend on whether the plate 60 will come in contact with the fluid of the tank 12, and the corrosive nature of such fluids.
The [0039] plate 60 is attached to the inner surface 46 using a welding pattern that is continuous or discontinuous. If the welding pattern is discontinuous the interstitial area 58 is in communication with the liner's interstitial space 56. If a plate is optionally attached outside the inner surface 46 then the welding pattern would be continuous.
The addition of the [0040] plate 60 provides a number of advantages. The plate 60 allows the attachment of almost any kind of internal member 44 thereto and compensates for seams and other imperfections on the surface 42, providing a smooth clean surface 42 for a weld 62 and provides sufficient workman's assess and a surface 42 for the attachment of the liner 18 of geosynthetic membrane. The use of a stitch weld, or any other attachment process, that allows fluid to flow from the interstitial area 58 under the plate 60 to the liner's interstitial space 56 accomplishes secondary containment under the internal member 44. A preferred configuration of the plate 60 is to maintain a rectangular plate with rounded corners, allowing for the use of standard sized rectangular, mechanical compression pieces and corners, with sides of varying lengths.
Best seen in FIG. 5[0041] b and FIG. 9, the preferred compression device 30 is a series of threaded studs 34, preferably with 2 inch spacing from centre to centre, welded to and extending from the plate 60. An opening is cut in the liner 18 so the liner is formed around the discontinuity 16 to form the first edge 50 which is punched with a plurality of holes corresponding and aligning with the spacing of the studs 34. The compression bar 32 is also punched in a pattern that matches the series of threaded studs 34 welded to the top of the plate 60. The bar 32 is placed over the threaded studs 34 and gaskets 36. The washer 38 and nut 40 are tightened to compress the device 30 onto the liner 18 creating a mechanical seal 54.
Accordingly, secondary containment is also provided by the [0042] interstitial area 58 at the discontinuity 16 formed between the plate 60 and the structural envelope 10.
Typically, the [0043] mechanical seal 54 further comprises flexible gaskets 36. The gasket material is a compressible material punched with corresponding stud holes that creates constant and uniform pressure when compressed. It is preferable that the gasket material have a memory to maintain constant pressure over time. While it may in some instances be preferable to place only the gaskets 36 between the liner 18 and the plate 60 or structural envelope 10, adhesive and sealant 64 are preferably also applied to both sides of the gaskets 36. As gaskets 36 also come in contact with the fluids, it is recommended they be selected to provide chemical resistance to the fluids.
Adhesive or [0044] sealant 64 can be applied between the liner 18 and the plate 60 to aid in sealing small channels that may exist where membrane seams overlap, or deal with surface imperfections. The sealant 64 can take the form of applied liquids or gels, tapes, or mastics. Materials with adhesive qualities have the added advantage of providing a sealing grip between the plate 60 and the liner 18 in the event of the failure or weakness in the mechanical seal 54. As adhesive or sealant 64 will come in contact with tank fluids, it is recommended they be selected to provide chemical resistance to the fluids.
The [0045] mechanical seal 54 provides a reliable seal of the liner 18 about internal members 44, structures, attachments, and other discontinuities 16 generally of all shapes and sizes. Further, the interstitial area 58 under the plate 60 becomes a continuation of the sealed area or interstitial space 56 that exists under the liner 18, and the plate 60 serves as a sealed continuation of the liner surface, or continuous envelope extension, which passes under the discontinuity 16, and thereby provides secondary containment.
With reference to FIGS. 6[0046] a and 6 b, in another embodiment, a boot 20 (as seen in isolation in FIG. 8) provides third layer of containment, or tertiary seal, and provides a redundant seal that must be challenged before the mechanical seal 54 and plate 60 come in contact with the fluids leaking from the tank 12. The additional seal of the boot 20 also provides protection to the various metal components of the system, such as the plate 60, the studs 34, washers 38, nuts 40 and the compression bar 32.
Accordingly, in this embodiment, this alternate design adds the [0047] flexible geosynthetic boot 20 to cover the mechanical seal 54, the base of which has an outer edge 66 which extends beyond the perimeter of the mechanical seal 54 and is fused or adhered directly to the liner 18. An inner edge 68 is sealed to the discontinuity 16 using a second mechanical seal for creating an additional barrier to liquid entry at the discontinuity 16. Further, mechanical stress on the liner 18 such as that imposed by shifting or pulling is now absorbed by the robust mechanical seal 54 and thereby relieves stress on the more fragile boot 20 which has points of inherent weakness including the welding at seams.
This [0048] boot 20 becomes an additional continuous envelope extension, extending to the liner 18 and can be prefabricated such as that formed from two planes of liner 18 material. One plane involves a large flat membrane that is circular or rectangular with rounded corners, and with a circular hole in the centre of the liner 18, the outer perimeter forming the boot's outer edge 66. The second plane is a rectangular membrane fused or adhered into a cylindrical shape, the upper extremity forming the boot's inner edge 68. One end of the cylinder membrane is fused or adhered to the circular hole in the first flat membrane creating a single boot 20, with a throat 70 through which the discontinuity 16 can pass.
The upper extremity or [0049] throat 70 of the boot 20 is then sealed to the discontinuity 16 with a single or multiple circular bands of steel 72, or other banding material which provide a further barrier to liquid entry where the geosynthetic material throat 70 meets the discontinuity 16. A preferred configuration of banding consists of three stainless bands around the discontinuity 70. Adhesive or sealant 64 can also be added to provide the necessary seal to the boot 12 and the discontinuity 16.
If the cross-section of a [0050] discontinuity 16 is irregular, other fastening techniques, particularly glues or adhesives 64, can be used to connect the throat 70 of the boot 20 and seal therebetween. This additional boot 20 provides a barrier through which liquid must pass before it can come in contact with the mechanical seal 54.
The fabrication techniques of the [0051] boot 20 include the use of geosynthetic adhesives, or hand welding equipment, ensuring a continuous liner 18 without any channels or holes.
With reference to FIG. 7[0052] a, another embodiment of the invention addresses discontinuities 16 such as those which penetrate through the surface 42 of storage tanks 12 where the geosynthetic liner 18 covers the inner surface of the tank 46.
In one aspect, the lack of secondary containment in the case of the prior art illustrated in FIG. 4 is overcome through the addition of means for secondary containment on an outer surface of the [0053] tank 74. Accordingly, the liner 18 is sealed internal to the envelope 10 and up to the penetrating discontinuity 16, and a containment means such as a plate 60 sealably connected to the outer surface of the tank 74, forms secondary containment.
The [0054] mechanical seal 54 is used to obtain secondary containment at the penetration point by the installation of the plate 60 installed on the outer surface of the tank 74 and about the discontinuity 16. The plate 60 has an opening in its interior for the discontinuity 16 to pass through. If there were no penetration, the plate 60 would be continuous. The plate 60 is sealed around its outer periphery so as to provide a sealed area extending beyond the perimeter of the mechanical seal 54 on the inner surface of the tank 46, on the outer surface of the tank 74. The plate 60 is sealed around its inner periphery to the discontinuity 16. The combination of secondary containment on the outer surface of the tank 74 in the penetration region, with the secondary containment on the inner surface of the tank 46 around the penetration region, provides the liner 18 with secondary containment that includes the penetrating discontinuity 16.
There exists an opportunity to monitor isolated interstitial regions separately for leaks using a [0055] monitoring device 80, giving rise to variations of the invention, where a mechanical seal 54 results in the establishment of interstitial regions that are isolated from other interstitial regions. FIG. 10 shows the simple hole 82 and plug 84 that can be opened to monitor for leaks in interstitial area 58, between the outer surface of the tank wall 74 and the plate 60. Interstitial spaces sealed and isolated by boot systems around wall penetrations can be monitored directly through simple valve openings through the tank surface 42. Any fluid leak into the interstitial area 58 can be detected by opening the valve. When the tank 12 is in service the pressures against the boot 20 will provide a flow of fluid through the tank surface 42.
With reference to FIG. 7[0056] b, another embodiment of the invention addresses the discontinuity 16 that pass through the wall of storage tanks 12 where the geosynthetic liner 18 covers the inner surface of the tank 46. While the design is similar, the fact that the pipe penetrates the wall means that secondary containment is now completed by the use of the boot 20 embodiment that covers the penetration, as opposed to the plate 60 according to FIG. 7a.
With reference to FIG. 10 another embodiment is a hybrid of FIG. 6[0057] a and FIG. 7b, the plate 60 may also be used as shown in FIG. 6a, yet the discontinuity 16 sealably penetrates the plate 60. The boot 20 is then applied as in FIG. 7b to provide tertiary containment. The boot 20 added to the mechanical seal 54 is particularly advantageous over prior art systems including those shown in FIGS. 1-4.
The design of the [0058] boot 20 is the same as FIG. 6a, 6 b. The design of the mechanical seal 54 is the same as that in FIG. 6a except that the threaded studs 34 are welded onto the inner surface of the tank 46, as opposed to the plate 60. The flexible geosynthetic boot 20 has a base which extends beyond the perimeter of the mechanical seal 54 on the tank's inner surface 46, and is described in detail in respect of the mechanical seal 54 above. This boot 20 is fused or adhered directly to the liner 18 on the tank's 12 penetrated surface 42. The throat 70 of the boot 20 is then sealed to the discontinuity 16 with single or multiple circular bands of steel 74, or other material, and/or with chemical adhesive 64 or bonding, providing a further barrier to liquid entry where the geosynthetic throat 70 meets the discontinuity 16.
Like the [0059] mechanical seal 54 for discontinuities 16 shown in FIG. 6a, 6 b, this also creates a distinct and isolated interstitial area 58 around the penetration point, an area which is at higher risk for leaks. This distinct and isolated interstitial area 58 can be monitored and is useful for detecting a leak around the joint before the main interstitial space 56 is contaminated, meeting secondary containment requirements at the joint. The boot 20 covers, and protects the metal mechanical seal 54 from corrosion from tank fluids, and provides an additional or second barrier to liquid entry. An alternative embodiment adds to the foregoing a hole 82 with a removable plug 84 in the exterior plate 60, to allow for the monitoring of the mechanical seal 54 around the discontinuity 16.
Thus, it is apparent that there has been provided, in accordance with the invention, a system for sealing a [0060] structural envelope 10 that fully satisfies the objects, aims and advantages set forth above. While the invention has been described in conjunction with specific embodiments such as a storage tank 12, it is evident that it is equally applicable to any discontinuity 16 of an envelope 10 including many alternatives, modifications and variations which will be apparent to those skilled in the art and in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit of the appended claims.

Claims

The embodiments for which an exclusive property or privilege is claimed are defined as follows:

1. A system for sealing a liner about a discontinuity at a structural envelope for containing fluid, the liner forming secondary containment between the liner and an inner surface of the structural envelope, the system comprising:

an opening in the liner for forming a first edge about the discontinuity;

a mechanical seal circumscribed at an outer perimeter about the discontinuity and located between the liner's first edge and the structural envelope for forming secondary containment between the structural envelope and the liner; and

a secondary seal attached at a perimeter attachment to one of the inner or an outer surface of the structural envelope at the discontinuity, the perimeter attachment being outside the outer perimeter of the mechanical seal for forming a continuous envelope extension from the liner to the discontinuity and for forming secondary containment between the continuous envelope extension and the structural envelope.

2. The system of claim 1 wherein the secondary seal is a plate.

3. The system of claim 2 wherein the plate is sealably attached at its perimeter attachment to the inner surface of the structural envelope for spacing the discontinuity from the structural envelope, the mechanical seal being between the plate and the liner.

4. The system of claim 3 wherein the plate and the structural envelope are sealably attached by a discontinuous weld at the plate's perimeter attachment.

5. The system of claim 3 wherein the plate and the structural envelope are sealably attached by a continuous weld at the plate's perimeter attachment.

6. The system of claim 2 wherein the plate and the structural envelope are sealably attached by a continuous weld at the plate's perimeter attachment.

7. The system of claim 2 wherein the discontinuity penetrates the structural envelope at a first penetration and is attached to the structural envelope at the first penetration, and wherein:

the plate is sealably attached at its perimeter attachment to the outer surface of the structural envelope;

the discontinuity penetrates the plate at a second penetration and is sealably attached at the second penetration; and

the mechanical seal being between the liner and the inner surface of the structural envelope.

8. The system of claim 7 wherein the structural envelope is a wall of a tank.

9. The system of claim 2 wherein a monitoring device is added to between the structural envelope and the plate for detection of a breach of the secondary containment.

10. The system of claim 1 wherein the structural envelope is a floor of a tank.

11. The system of claim 5 wherein the structural envelope is a floor of a tank.

12. The system of claim 1 further comprising:

a tertiary seal having a liner boot with an outer edge attached to the liner outside the perimeter of the mechanical seal, the liner boot extending inward to an inner edge; and

a second mechanical seal between the liner boot's inner edge and the discontinuity for forming tertiary containment between the continuous envelope extension and the structural envelope.

13. The system of claim 5 further comprising:

14. Apparatus for sealing a liner about a discontinuity at a structural envelope for containing fluid, the liner forming secondary containment between the liner and an inner surface of the structural envelope, the system comprising:

a mechanical seal circumscribed at an outer perimeter about the discontinuity and located an opening in the liner for forming a first edge about the discontinuity, the liner's first edge and the structural envelope for forming secondary containment between the structural envelope and the liner;

a plate attached at a perimeter attachment to one of the inner or an outer surface of the structural envelope at the discontinuity, the perimeter attachment being outside the outer perimeter of the mechanical seal for forming a continuous envelope extension from the liner to the discontinuity and for forming secondary containment between the continuous envelope extension and the structural envelope.