AU651997B2 - Storage tank having secondary containment - Google Patents

Description

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PCT

OPI DATE 20/05/92 AOJP DATE 25/06/92 APPLN. ID 85490 91 PCT NUMBER PCT/IIS91/07085 INTERNATIONAL (PCT) (51) International Patent Classification 5 (11) International Publication Number: WO 92/06905 90/02, 90/50 Al (43) lnte.national Publication Date: 30 April 1992 (30.04.92) (21) International Application Number: PCT/US91/07085 (81) Designated States: AT (European patent), AU, BE (European patent), CA, DE (European patent), DK (Euro- (22) International Filing Date: 30 September 1991 (30.09.91) pean patent), ES (European patent), FR (European patent), GB (European patent), IT (European patent), JP, NL (European patent), NO, SE (European patent).

Priority data: 596,189 12 October 1990 (12.10.90) US Published With international search report.

(71) Applicant: OWENS-CORNING FIBERGLAS CORPOR- With amended claims and statement.

ATION [US/US]; Fiberglas Tower 26, Toledo, OH 43659 (US).

(-1Inventor: BARTLOW, David, Harvey 272 Bellingrath, Conroe, TX 77301

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(74) Agents: PACELLA, Patrick, P. et al.; Fiberglas Tower 26, Toledo, OH 43659 (US).

(54) Title: STORAGE TANK HAVING SECONDARY CONTAINMENT 4i -t -j Ai (57) Abstract An underground storage tank having secondary containment comprising a self-supporting, semi-rigid thin liner (40) located on the inside of the tank The thin inner liner (40) completely lines the inside of the tank and is structurally independent of the tank.

WO 92/06905 -1- STORAGE iT'K flAfV±PM StEUONL)AKX UCiNiAJJNDE~N .1 PC/US91/07085 i il TECHNICAL FIELD This invention generally relates to storage tanks and more particularly to underground storage tanks with secondary containment.

BACKGROUND ART Environmental protection is becoming increasingly important. As our understanding of contamination of soil and water beneath the surface grows, our efforts to prevent leaks increases. Early efforts resulted in glass fiber reinforced plastic single wall underground tanks. See U.S. Patent No.

3,661,294 issued in 1972. As our awareness grew, our efforts to protect the environment matured into glass fiber reinforced plastic double-wall underground tanks, often equipped with leak detection systems. See U.S.

Patent No. 4,561,292 issued in 1985.

Others have attempted to encase or fit rigid storage tanks with secondary containment systems, often with flexible bladders or jackets. See U.S. Patent No.

4,524,609 issued in 1985. Flexible bladders have obvious problems. For example, flexible inner bladders or flexible outer jackets are very susceptible to damage from cutting, tearing, puncturing, etc.

DISCLOSURE OF THE INVENTION Basically, my invention is a sta sil-gle wall tank (SWT) on the inside of w I have added an FRP smooth inner wall tha not attached to the outer wall. The annula ace between the inner and outer wall may have on-structural porous core such as a thin HDPE transmitting net.

"r IY -2- According to one aspect of the present invention there is provided an underground storage tank comprising: a rigid tank particularly suited for use underground; and an inner wall located on the inside of the tank, the inner wall having sufficient flexibility so that it would substantially collapse if totally unconstrained when the inner wall is lying on its side, but having sufficient rigidity so that it would substantially ;conform, without being attached to the tank, to the shape of the tank when positioned within the tank and when the tank is empty.

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*i p:\wpdocs\dys\85490.spc\dys v rp WO 92/06905 PCT/US91/07085 11 -3- BRIEF DESCRIPTION OF THE DRAWINGS The invention is.more fully explained with reference to the accompanying drawing\in which: v Figure 1 is an elevational view of a single wall tank containing an FRP liner in accordance with the present invention.

Figure 2 is a sectional view taken generally along the line 2-2 of Figure 1; and Figure 3 is a fragmentary perspective of an FRP inner wall panel in accordance with this invention.

BEST MODE OF CARRYING OUT INVENTION Figure 1 shows a tank 20 which employs the FRP inner wall structure of the present invention (not shown). The tank 20 is made up of opposed frusto-conical tank halves 22, connected together by center joint 24.

Wall 26 includes a wall element 25 in combination with a rib 28. Actually, a plurality of ribs 28 are axially spaced along the length of the tank 20. Ribs 28 extend peripherally of the tank 20 and act in the nature of strong hoops against radially inwardly crushing forces.

Since they are of high tensile strength, they also absorb tensile stresses to which the tank 20 may be subjected.

It is important to note that the ribs 28 add to the stiffness of the wall 25; also, they provide protective buffers during handling.

The ribs 28 are spaced apart a sufficient distance so that fill and Vent fittings 30 and 32 can be installed between the ribs. Optional positions 34 for fittings are thus provided all along the length of the tank 20. In an actual 6,000-gallon capacity tank of 8 feet nominal diameter, and approximately 20 feet length, ia spacing of 16 1/2 inches between rib enters was WO 92/06905 PCT/US91/07085 -4employed and this provided adequate space for the installation of the fittings 30 and 32.

U.S. Patent No. 3,661,394 fully describes ribbed, single wall tank construction.

Figure 2 shows FRP inner wall 40 on the inside of wall element 25. Figure 2 also shows annular space 43 between wall 40 and wall element 25. Space 43 is partially filled with porous core 44.

Figure 3 shows a panel of FRP inner wall detached from tank Typically, one can use any molding process or spray up equipment to make FRP inner wall 40. One can achieve this by placing mold release (Mylar) on a conventional SWT mold, spraying up thin FRP inner liner including end cap, curing the FRP, placing another sheet of Mylar on top of liner 40 and then carrying out the conventional construction of SWT, for example, as described in U.S. Patent No. 3,661,394.

FRP inner wall 40 preferably is made of unsaturated polyester compounds. The practice of this invention, however, is not restri co unsaturated polyesters.

These compositions, intended to polymerize when molded under heat and pressure, are generally combined with fillers and chopped glass, to produce products having appearance surfaces with a minimum of irregularities.

The use of chopped glass as reinforcement in such molding compounds is well known. The chopped glass is produced in the form of individual strands which are sized, gathered into rovings, chopped to the desired length and incorporated into the resin composite prior to molding.

o WO 92/06905 PCT/US91/07085 1 The sizes generally comprise a lubricant, film formers and the like and are extremely important in imparting to the reinforcing glass its ability to be wetted out by the molding compound. These sizes are also important in that they protect the glass in it handling subsequent to being sized and are influential in minimizing the amount of fuzz and fly which is produced on the glass, the fuzz and fly having a decided affect upon the appearance surface of the molded product.

The sized glass fibers generally are employed as reinforcement for sheet molding compounds (SMC) and bulk molding compounds (BMC).

Unsaturated polyesters useful in this invention typically contain a polyesterification product of one or more ethylenically unsaturated dicarboxylic acids or anhydrides such as maleic or fumaric with one or more glycols such as ethylene or propylene glycol and, sometimes, minor proportions of other aromatic or aliphatic mono- or dicarboxylic acids or anhydrides and/or other mono- or polyhydroxyl compounds. They also typically contain an ethylenically unsaturated monomer, such as styrene, copolymerizable with the unsaturated polyester for curing.

The glass fibers preferably are glass fibers, well known to those skilled in the art. See U.S.

Patent No. 2,334,961.

As I stated above, porous core material 44 may fill space 43. Examples of porous core materials 44, are mattings, nets, screens, and meshes. Specific examples are high density polyethylene (HDPE) net, jute, polyurethane foam, polyester foam, fiberglass matting, cotton matting, nylon matting and corrugated cardboard.

I Z .i ,i WO 92/06905 PCT/US91/07085 1 -6- INDUSTRIAL APPLICABILITY The following table summarizes the advantages of my invention over other alternatives:

TABLE

THIN WALL FRP INNER TANKS VS OTHER ALTERNATIVES Self-Supporting Low Permeability to Fuels Internal Wall of Primary Containment Corrosion-Resistant to Alcohol Blend, Fuels, Water External Wall of Primary Containment Corrosion Resistant to Water Independent (unconnected) From Outer Wall Able to Determine the

INVENTION

THIN STAINLESS FRP INNER STEEL WALL 1/10" Yes Yes Yes Yes Yes Yes Yes Yes

CONTROL

CARBON CARBON FLEXIBLE STEEL STEEL RUBBER-IIKE I1/4" 1/10" BLADDER Yes Yes No Yes Yes No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No location of teaks An alternative embodiment comprises FRP inner wall 40 sections small enough to fit inside a tank through manway openings. Typically the panels are up to 8 feet in length and range from 2 to 4 feet in width.

After the panels are in place inside the tank, one uses a hand lay-up procedure on the seams of each panel to form FRP inner wall Basically, the procedure involves building up a combination of chopped glass fibers and a hardenable liquid resin and, if desired, a sand filler.

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WO 92/06905 PCT/US91/07085 1 Complete wetting of the chopped glass fibers is desirable and can be accomplished, as is well known in the art, by rolling out the resin and glass and sand mixture. After the seams are fabricated, heat or the passage of time cures the resin. One can use any spray device or combination of spray devices to apply the resin and chopped glass fibers. Often the resin contains an accelerator or catalyst to speed up the curing process.

As shown in Figure 3, the panels and FRP inner liner 40 preferably have the same curvature as wall element 25. Preferably inner FRP liner 40 is thin and typically is 1/3 to 1/4 of an inch thick.

Access to the inside of the tank 20 is provided by a flanged manway fitting 54 (Figure 1) communicating with the inside thereof, and a double-flanged extension normally covered by a cover 56. Hand lay-up secures manway fitting 54 to tank 20 by application of hardenable resin, chopped glass strand and filler such as sand. The hand lay-up procedure is much the same as that used to connect the panels of FRP inner wall The thin FRP inner liner that I use is unique in that it is: Self Supporting Corrosion resistant Offers lower permeability In one embodiment, the thin inner liner is structurally independent of the tank for the entire circumference except for a narrow width centered at the top of the bank. For these narrow widths, the inner liner is bonded to the rigid primary tank, thus allowing easy manufacture and installation of tank accessories such as fittings and manways. Alternately, the inner liner can end near the WO 92/06905 PCT/US91/07085 -8top of the tank resulting in only one wall at the top of the tank.

Claims (14)

1. An underground storage tank comprising: a rigid tank particularly suited for use underground; and an inner wall located on the inside of the tank, the inner wall having sufficient flexibility so that it would substantially collapse if totally unconstrained when the inner wall is lying on its side, but having sufficient rigidity so that it would substantially conform, without being attached to the tank, to the shape of the tank when positioned within the tank and when the tank is empty.

2. The tank of Claim 1 wherein the inner liner is structurally independent of the tank.

3. liner. The tank of Claim 2 wherein an annular space exists between the tank and inner rt f

4. The tank of Claim 3 including gas porous material in the annular space between the tank and inner liner. The tank of Claim 4 wherein the gas pervious material is high density polyethylene net.

6. The tank of Claim 3 wherein the inner liner is glass fiber reinforced plastic.

7. The tank of Claim 2 wherein the inner linear is glass fiber reinforced pla2:-tic from 0.020" to 0.250" thick.

8. The tank of Claim 2 wherein the inner liner is stainless steel or other metallic imaterial from 0.010" to 0.125" thick.

9. The tank of Claim 1 wherein the inner liner would collapse an amount more than about 90 percent of its manufactured diameter when totally unconstrained, but would Sremain at a height of at least 93 percent of its manufactured diameter when positioned within the tank. ~PILlcq) \~P IA. I U' Iv V p:\wpdocs\dys85490.sp\dys i~.Ya*Rna~ Ilra~ P: The tank of Claim 9 wherein the inner liner structurally independent of the tank.

11. The tank of Claim 10 wherein the inner would collapse an amount more than about 25 percent of its manufactured diameter when totally unconstrained, but would remain at a height of at least 98 perceio. of its manufactured diameter when positioned within the tank.

12. liner. The tank of Claim 10 wherein an annular space exists between the tank and inner LAL

13. The tank of Claim 12 including gas porous material in the annular space between the tank and inner liner.

14. The tank of Claim 13 wherein the gas porous material is a high density polyethylene net. The tank of Claim 10 wherein the inner liner is glass fiber reinforced platic.

16. The tank of Claim 10 wherein the inner liner is glass fiber reinforced plastic from 0.020" to 0.250" thick.

17. The tank of Claim 19 wherein the inner liner is stainless steel or other metallic material from 0.010" to 0.125" thick. Dated this 2nd day of June, 1994 OWENS-CORNING FIBERGLAS CORPORATION By its Patent Attorneys DAVIES COLLISON CAVE p:\wpdocs\dys\85490.sp\dys