Cylindrical-shaped storage tanks with formed outer jacket

A cylindrical-shaped rigid inner storage tank with substantially flattened ends is jacketed in a manner which results in storage tank system capable of holding detecting liquid or being placed under non-atmospheric pressure without structural damage. The rigid inner tank initially has end plates mounted on its flattened ends. Thereafter, a separating agent is applied over the side walls of the storage tank, a layer of fibrous reinforcing material applied on the separating agent and the end plates, and a resinous material applied. The resultant jacket is independent from the side walls of the inner tank. True secondary containment is provided by the jacket. A fail safe containment storage tank system is provided by the use of a leak detection means to monitor the closed space between the storage tank and jacket for tank or jacket leakage.

This invention relates to storage tanks. More particularly, the invention 
relates to underground storage tanks which have a jacket for secondary 
containment means. 
BACKGROUND OF THE INVENTION 
Commercial and industrial storage tanks are widely used for storing a great 
variety of liquids. Some of these liquids are highly corrosive and/or are 
flammable. The service life of a storage tank will vary, depending upon 
environmental conditions, including the liquid being stored. Eventually, 
however, the tank will become corroded and develop leaks. This can result 
in a significant danger to the environment and health of nearby residents. 
For example, storage tanks are commonly used for storing gasoline at 
service stations. Gasoline, of course, is highly flammable and is capable 
of posing a significant health and safety hazard if not properly 
contained. Federal as well as local regulations govern he structure of 
such storage tanks. 
Heightened public awareness of the danger posed by storage tanks 
(particularly underground gasoline storage tanks) has led to additional 
governmental regulations. Recent proposed regulations will soon require 
most storage tanks to have secondary containment means and possibly a fail 
safe design feature to guard against accidental soil, water, and air 
contamination. Secondary containment means must be capable of containing 
leaked liquid from the storage tank. Rigid double walled tanks have been 
suggested as one alternative. While effective for containment purposes, 
such tanks, as presently available, are costly to build and difficult to 
install because of their weight. Such tanks are built by basically forming 
two rigid tanks utilizing different sized, reusable molds and then placing 
one tank inside the other. 
Single and double walled tanks made from fiberglass reinforced resinous 
material are built using a number of distinct time consuming steps. In all 
known methods, a cylindrical-shaped, reusable mold is used to build tank 
halves which are subsequently assembled. Initially, layers of fiberglass 
followed by a resinous coating are applied to the mold or chopped 
fiberglass/resin streams are simultaneously directed onto the mold and 
subsequently cured. Sufficient applications of the fiberglass and resin 
are made until a wall thickness is obtained which has the desired 
strength. Next, support rib molds of cardboard, four to six inches wide, 
are placed completely around the cylinder at approximately sixteen inch 
intervals. Fiberglass and resin are then applied over the cardboard molds 
and onto adjacent areas of the cylinder so as to become an integral part 
of the inner tank shell. The mold is finally removed. The 
cylindrical-shaped wall, including the ribs and one end of the tank, are 
produced in this stage of the method. The above steps are repeated to 
obtain a second half-tank. The two half-tanks are then joined together by 
appropriate sealing means. The resultant single walled tank is capable of 
being installed in the ground and, in fact, is of the type which has been 
extensively used for the past twenty years. 
In more recent years, double walled tanks have been built and used. 
Essentially, these tanks are built by the same method as the single walled 
tanks. An inner, rigid tank is formed in the above described manner. Next, 
a larger diameter reusable mold is used to build a horizontal half-tank. 
The fiberglass/resin is applied in a known manner to the mold and cured to 
form the half-tank. A second horizontal half-tank is formed. Next, the 
completed inner tank is placed into the larger diameter half-tank. The 
ribs on the inner tank are properly dimensioned to act as spacer ribs 
between the two tanks. The second larger diameter half-tank is placed over 
the inner tank, joined and sealed at the seams with its matching halftank. 
The resultant product is a double walled storage tank system comprised of 
essentially two rigid tanks, one inside the other. 
A second method of making double walled fiberglass, reinforced, resinous 
tanks is similar to the above method and us just as time consuming and 
costly. In this method, the mold has a design wherein the ribs are formed 
as the fiberglass and resin material is applied. After forming the inner 
tank of which the ribs are an integral part thereof, the mold is removed. 
The interior portion of the tank next has a fiberglass/resin layer applied 
over the rib indentations to result in a smooth cylindrical-shaped 
interior. A second half-tank is formed in the same manner and the two 
halves joined. A cylindrical-shaped outer tank is then formed in 
horizontal halves. The formed inner tank and outer tank halves are 
assembled as in the first method described above to form a double walled 
storage tank system based on two rigid tanks with support ribs 
therebetween. 
As is readily apparent, building a double walled storage tank system by 
known methods is very labor extensive and costly. Recent concerns about 
leaked tanks has heightened the need for an efficient and economical 
manner of building double walled storage tank system. A jacketed storage 
tank system, as disclosed in my U.S. Pat. No. 4,523,454 also provides 
secondary containment means and avoids the problems associated with the 
rigid double walled systems. Additionally, the aforementioned jacket 
system features a fail-safe design due to the fact it provides continuous 
monitoring means whereby the integrity of both the primary and secondary 
containment means are checked to insure that leakage of either containment 
means is known when it first occurs. 
Lacking in current designs of jacketed tanks with flat ends is the ability 
of the jacket to withstand the forces created on the fiberglass jacket's 
ends when the monitoring space is filled with a liquid or pressure is 
applied. To install domed end caps over the end of flat ended tanks is not 
practical or cost effective. Tanks ranging from six feet to eleven feet in 
diameter with domed end caps would require from 500 to 1,000 gallons of 
detection liquid just to fill the end caps. Further the spherical end caps 
would add considerable more length to the tank which is a disadvantage 
with shipping or installation underground 
Currently-built double walled fiberglass tank do not have sufficient 
structural strength to be shipped and installed with the monitor space 
(annular space) filled with liquid. Currently fiberglass tanks are shipped 
with a vacuum in the annular space to hold the inner and outer tank shell 
together preventing separation of either wall from the ribs placed between 
the walls. 
There has now been discovered methods whereby new and used storage tanks 
with flat ends can be provided with a fiberglass jacket of sufficient 
strength in the flat end area of the tank to hold a detecting liquid in 
the space between the storage tank and the newly formed secondary 
containment area commonly called the annular space. The separating 
material is capable of adjusting to the shrinkage encountered with 
fiberglass and resins preventing sealing when the jacket shrinks around 
the tank's cylinder. Used storage tanks are refurbished to a standard 
equivalent to that possessed by a new tank and then upgraded to have a 
secondary containment feature. 
SUMMARY OF THE INVENTION 
A method of adding secondary containment capability to cylindrical-shaped 
storage tanks having substantially flattened ends comprises the steps of 
(a) mounting end plates on each flattened end, (b) applying a separating 
agent to the side walls of the storage tank, (c) applying a layer of a 
fibrous reinforcing material onto the separating agent and the end plates 
of the storage tank, and (d) applying a resinous material onto or with the 
reinforcing material. When the resinous material is cured, a jacket is 
formed which covers the storage tank, thereby providing secondary 
containment for any liquid which may leak from the storage tank. The 
annular space between the storage tank and the end plates with the newly 
formed jacket can be monitored for any leakage.

DETAILED DESCRIPTION OF THE INVENTION 
While the description to follow describes the invention in terms of its use 
with underground storage tanks, it should be understood the invention has 
applicability for other uses as well. However, the invention lends itself 
particularly well to underground storage tanks used for storing liquid 
gasoline and, therefore, this preferred use is described in the following 
paragraphs. 
With reference to FIG. 1, there is shown an underground storage tank 10. 
Storage tanks 10 of the type shown in FIG. 1 are well known and are widely 
used, especially in the gasoline service station industry. They are 
typically made of metal or, more recently, a fiberglass reinforced resin 
material. Either type of tank has use in this invention. A typical metal 
storage tank is shown in FIG. 1. Sufficient openings are found in the 
storage tank 10 to allow for various access lines to communicate with the 
interior of the tank. As shown, lines 11, 12, and 13 are a fill pipe, 
dispensing line and vent pipe, respectively. 
The fill pipe 11 provides as its obvious function the means by which 
gasoline can be pumped into the inner tank from an outside source, e.g. a 
tank truck. As illustrated in FIG. 1, fill pipe 11 comprises a line 14 
through which gasoline flows to the inner tank 10 and a space 15 within 
the fill pipe which acts as a vapor recovery line. As gasoline is pumped 
into the inner tank, gasoline vapors which are formed are sucked through 
the space 15 back to the tank truck for recovery. This reduces the amount 
of gasoline vapors which would otherwise be vented to the atmosphere or 
remain in the inner tank preventing the tank from being filled completely 
with gasoline. As used throughout here, the term "fill pipe" connotes the 
pipe by which gasoline is pumped to the tank; it can be a single pipe, but 
more often has vapor recovery means associated with it and is often 
referred to as a vapor recovery fill line. As shown in FIG. 1, line 14 
extends into the inner tank 10 with its end near the bottom. 
Dispensing line 12 is used for withdrawing gasoline and delivering it to 
the consumer through gasoline dispenser 16. While not illustrated in FIG. 
1, a pump is positioned within the inner tank, dispensing line or gasoline 
dispenser for pumping gasoline to the dispenser. The bottom of the 
dispensing line 12 is in close proximity with the bottom of the inner tank 
10. The vent pipe 13 provides means by which gasoline vapors resulting 
primarily from a filling operation can be vented to the atmosphere and 
prevents a vacuum from forming in the tank during a dispensing operation. 
The opening to the atmosphere is normally substantially off ground level 
for safety reasons. All the aforementioned pipes and lines are securely 
attached to the rigid inner tank. Outer jacket 17 provides the secondary 
containment enjoyed by the tanks of this invention while closed annular 
space 18 provides a means by which leakage of the inner tank and jacket 
can be detected. 
End plates 19 are mounted on each flattened end 20 of the inner storage 
tank 10. The end plates are semi-rigid or rigid and serve the purpose of 
strengthening the outer jacket 17. The end plates have a shape which 
approximates the shape and size of the flattened ends of the inner tank. 
It is preerred that the end plates be substantially the same size as the 
flattened ends of the tank. Smaller end plates down to those having an 
area of only 20% of the area of a flattened end can be used. Most 
preferred, however, are hose end plates which have an area equal to about 
90% to about 101% of the area of the tank's flattened end. 
Each end plate is mounted in a manner which results in an open space 21 
between it and the flattened end. Additionally, the open space 21 is in 
communication with space adjacent the side walls of the cylindrical-shape 
inner tank. As discussed more fully below, the open space 21 is used a 
part of the leak detection system of the invention. Spot welds 22 are 
preferably used to hold the end plates 19 to the inner tank 10. The spot 
welds are located around the edges of the end plates or randomly in the 
central portion. The use of the spot welds randomly in the central portion 
has the added effect of strengthening the ends of the total tank system. 
Thus, a composite effect is achieved. Other mechanical means can as well 
be used to hold the end plates to the inner tank. 
A separating agent is applied to the side walls of the storage tank 
extending preferably to the end plates before the jacket is formed. The 
purpose of the separating agent is to insure that a subsequently applied 
fibrous reinforcing material and resinous material which form the jacket 
will not adhere to the inner storage tank or seal closed the annular 
space. It is necessary that the cured jacket over the side walls and the 
storage tank have a space between the two. Such annular space is closed 
and provides secondary containment capability. Still, another function of 
the closed space 18 is to provide a means by which the space therein can 
be monitored for possible tank or jacket leaks. 
One desired separating agent is a wax material which can be subsequently 
heated and optionally removed so as to destroy any adhesion between the 
jacket and the underlying storage tank and consequently form the annular 
space. Another is a solid material which acts as a separating agent as 
well as a corrosion inhibiting agent, e.g. grease. Another preferred 
separating agent, shown in FIGS. 1 and 2, is a gas pervious material 25. 
Such materials are foraminous or porous and can take on various physical 
shapes and structures. Examples of such materials are mattings, nets, 
screens, and meshes. Specific examples are jute, polyurethane foam, 
polyester foam, fiberglass matting, cotton matting, nylon matting, 
corrugated cardboard, and asbestos. A heat seal or sealing material, e.g. 
a polymeric coating or film such as Mylar or a polyethylene, is used on 
one surface of the gas pervious material when needed to prevent 
substantial saturation by a subsequently applied resinous material as 
discussed in the following paragraphs. Another solid material which acts 
as a separating agent is a sheet material with surface irregularities 
placed towards the inner tank shell. A porous standoff material can also 
be placed on the tank shell and then wrapped with a solid material such as 
tape. Sheets or rolls of fiberglass reinforced resin or metal can also be 
utilized as a separating agent. 
Jacket 17 is a fibrous reinforced resinous material. It is formed by first 
applying a layer of fibrous reinforcing material on separating agent 25 
found on storage tank 10. The fibrous reinforcing material can take on 
many different physical shapes and structures variously referred to as 
mattings, nets, screens, meshes, filament winding strands, and chopped 
strands. Examples of fibrous materials include fiberglass, nylon, and 
other synthetic fibrous materials. The fibrous material, if in a sheet 
form, can be laid onto the storage tank as a continuous matting. 
Once the fibrous reinforcing material is applied, a resinous material is 
next applied to the reinforcing material and thereafter cured. Several 
different resinous materials are known for the purpose of reinforcing 
fibrous material. Such materials include polyesters, e.g. vinylesters, 
isophthalic polyesters, polyethylene, polypropylene, polyvinylchloride, 
polyurethane, and polyepoxide. The listed resinous materials used in the 
construction of this jacket are not all inclusive, but only illustrative 
of some of the resinous materials which can be used. As an alternative, 
and in fact preferably, the fibrous material is applied in the form of 
chopped strands with the resinous materials described in the previous 
paragraph. That is, the chopped strand and resinous material are sprayed 
from separate nozzles of the same spray gun and the jacket formed 
therefrom on the separating agent as the resin cures. Still another method 
of forming the jacket uses filament windings. Continuous reinforcing 
fibrous strands are impregnated with the resinous material and then 
wrapped around the separating material-covered inner tank in a crossing 
pattern. Other known methods of forming a fibrous reinforced resin 
substrate can be used. 
The shape of the resultant jacket is such that it encases the side walls of 
rigid inner storage tank to form a closed space 18. The jacket also 
completely covers the end plates 19 and is preferably securely adhered 
thereto. The jacket formed around the cylinder part of the tank is 
preferably less than about 2 inches from the inner tank cylinder, more 
preferably from about 1/2 inches to about 1/32 of an inch. The jacketed 
end plate is preferably less than about 12 inches from the inner tank's 
flattened end, more preferably from about 1/2 inch to less than about 1/32 
of an inch thereby allowing just enough space for detection of any leaked 
liquid which is stored in the storage tank. The jacket itself is capable 
of containing any liquid which is stored in the storage tank and which has 
leaked therefrom. The strength of the jacket has sufficient structural 
integrity to withstand external or internal load forces normally 
encountered by underground storage tanks without suffering cracking or 
collapsing. As used herein, cracking is defined to means the jacket 
structurally tears apart to the extent a liquid will at least seep there 
through. Slight surface deformations can be tolerated; however, 
deflections of greater than about two inches from the norm would be 
considered a collapse. Preferably, the jacket is rigid and will not 
noticeably crack or collapse when external or internal load forces are 
encountered during normal use. 
FIGS. 3 and 4 illustrate alternative end plates which can be used. In FIG. 
3, end plate 30 has a flange 31 which extends from the periphery of the 
end plate. The flange itself is spot welded (see spot welds 32) to the 
inner tank. Depending on the length of the flange, an open space of from 
about 2 inches to about 12 inches is provided. The flange can abut up 
against the very outer rim of the flattened end or, as shown in FIG. 4, an 
end plate 33 with flange 34 can overlap the side walls of the inner tank. 
Spot welds 35 hold the end plate to the inner tank. Ease of installation 
dictates which end plate alternative is used. 
With reference to FIG. 5, the space between the jacket 17 and the storage 
tank 10 is monitored. As shown an access tube 36 extends from ground level 
through the jacket so as to be in communication with the closed space. Any 
of well known and commercially available monitor means are used. For 
example, the closed space is filled with a detecting liquid. This 
detecting liquid can be placed in the closed space by the manufacturer of 
the tank due to the fact the closed space between the storage tank and 
jacket occupies a small volume, e.g. about 25-100 gallons detecting liquid 
is sufficient for use with a 20,000 gallon storage tank. At the end of the 
access tube is a sight glass 37. Whenever leakage occurs, a change in the 
level or color of a detecting liquid will occur and will be readily 
observed in the sight glass. Instead of the sight glass and visual 
observation of a change in level or color of detecting liquid, non-visual 
leak detection means such as pressure transducers or float controls can be 
used to detect a change in level. 
Alternatively, the closed space is placed either under a non-atmospheric 
pressure, i.e., a positive or negative air pressure. Detection means 
associated with the closed space is capable of detecting any change in 
pressure resulting from the leak in the jacket or the storage tank. A 
conventional air pump or vacuum pump, together with an associated pressure 
regulator are used. A pressure change sensor is a part of the detection 
means. A pressure gauge serves this purpose adequately. Optionally, an 
alarm system is electronically linked with the pressure sensor to audibly 
or visually warn of a preset significant pressure change. Gas pervious 
material 25 maintains a spaced relationship between the inner tank and the 
jacket when a vacuum is used as well as serves as the separating agent. 
Preferably, an access tube with strategically spaced holes extends from 
the air or vacuum pump to the lower portion of the closed space. 
Another embodiment of the detection means utilizes an analyzer capable of 
detecting the liquid being stored. Thus, the detection means comprises the 
analyzer which is in communication with the closed space. Preferably, a 
vacuum means for withdrawing gaseous material from the closed spaced is 
used for the purpose of obtaining a sample. Thus, an analyzer capable of 
detecting selected liquids is used instead of a pressure change sensor. 
Still another detection means utilizes a probe which extends through an 
access tube so as to monitor for leakage, preferably at or near the bottom 
of the closed space. The probe is capable of detecting pre-selected 
liquids or gases. In this embodiment, the separating agent can be a gas 
pervious material whereby leakage will ultimately seep to the bottom of 
the closed space and be detected or a solid which is stored liquid-, e.g., 
gasoline-soluble or water-soluble. Such solid separating agents will 
ultimately be solubilized and the leakage detected by the probe. 
Fittings as illustrated in U.S. Pat. No. 4,653,312 (specifically shown in 
FIGS. 6 and 7) can be used. The disclosure of this patent with regard to 
the fittings is hereby incorporated by reference. 
All the leak detection means discussed above can be electronically linked 
with an alarm system to audibly or visually warn of a pre-set significant 
change in the closed spaces. The leak detection means and secondary 
containment means allow for an early warning of a deterioration of either 
the primary or secondary containment means thereby permitting the 
necessary repair work to be done before any significant soil or water 
contamination has occurred. 
The invention herein has been described with particular reference to the 
drawings. It should be understood other variations of the invention are 
within the scope of coverage. For example, inner storage tanks with a 
manway are useful herein. The manway can be used to accommodate the 
various access liner, including a line for leak detection purposes.