Hydrophilic anode corrosion control system

A method and apparatus for reducing corrosion on the interior and exterior of a fuel storage tank. A galvanic anode assembly is placed within the interior of or exterior to the fuel storage tank and is surrounded by a layer of hydrophilic gel. The hydrophilic gel absorbs water in the fuel storage tank, thus removing it from contact with the tank. The hydrophilic gel also absorbs metal ions produced as the anode is consumed. The hydrophilic gel is maintained around the anode assembly by a porous container. The anode, hydrophilic gel, and porous container are maintained within a flexible container that allows water and fluid contained within the fuel storage tank to contact the hydrophilic gel. In one embodiment, the hydrophilic gel includes a polyacrylamide material.

FIELD OF THE INVENTION 
This invention relates to cathodic protection systems for metallic 
structures, and more specifically to galvanic anode cathodic protection 
systems for use with fuel or other liquid storage tanks. 
BACKGROUND OF THE INVENTION 
Most metals are reactive in electrolytic environments, such as the type of 
environment present in damp soil or water resulting in electrolytic 
corrosion. Electrolytic corrosion presents a particular problem for liquid 
storage tanks formed of metal, because corrosion can create holes, 
allowing the tanks to leak. Electrolytic corrosion is a particularly acute 
problem in metal liquid storage tanks such as the tanks used to store 
petroleum fuels at storage sites or service stations. 
It's estimated that 3 to 5 million metal underground storage tanks are in 
service today. Failure or leakage of such tanks can have dramatic 
ramifications under current local, state and federal government 
regulations. In addition, storage tank failures due to corrosion and the 
resulting replacement costs dramatically impact the costs associated with 
their use and maintenance. Methods to increase the life of metal storage 
tanks and to decrease failures have a large impact on the operating and 
maintenance costs. 
Electrolytic corrosion occurs on both the interior and exterior of fuel 
storage tanks. Basically, a corrosion cell is formed between different 
areas on the internal and external surfaces of the fuel storage tank. 
Variations in electrochemical activity or potential between one area on 
the interior or exterior surface of a tank and another area cause a 
corrosion cell to be formed between the areas. Although corrosion is most 
common on the exterior of a storage tank, it can also be a problem on the 
interior of the storage tank. 
In order to minimize electrolytic corrosion problems, cathodic protection 
systems using either impressed current or galvanic protection are 
connected to the exterior of storage tanks. The galvanic anodes are formed 
of a metal that has a higher Electromotive Force than the material used to 
form the structure of the storage tank. Thus, current passes from the 
galvanic anode to the surface being protected, consuming the anode while 
preventing corrosion of the protected surface. Galvanic anodes used in 
tanks formed of ferrous materials such as steel are commonly formed of 
magnesium or zinc. There are a number of other anode materials that may be 
used, depending upon the application. The best anode material, and thus 
galvanic efficiency, depends upon the application. 
Galvanic anodes are sacrificial elements that slowly corrode or are 
consumed in an electrolytic environment. Galvanic anodes may be consumed 
due to galvanic metal oxidation, which involves oxygen evolution and 
chlorine evolution. Because galvanic anodes are higher in Electromotive 
Force than the metal being protected, the corrosion or breakdown of the 
anode prevents the breakdown of the protected metal. In effect, the 
protected metal becomes a cathode of an electrolytic cell whose anode is 
formed by the sacrificial metal, i.e., "cathodic protection." 
In cathodic protection systems using impressed current, small amounts of 
direct current are passed continuously from sacrificial anodes to the 
metallic structure to be protected. Controlling the amount of current 
passed between the anodes and the metallic surface halts the external loss 
of metal when the tank electrochemically reacts with its environment. 
Instead of the metal surface being protected from corroding, the 
sacrificial anode is corroded or consumed. 
Cathodic protection of the exterior surface of a storage tank helps to 
prevent corrosion on only the exterior surface of the tank, but it does 
not prevent the interior surface of the storage tank from being corroded. 
Thus, to ensure that a storage tank does not fail due to interior 
corrosion, it would be beneficial to cathodically protect the interior 
surface of the tank as well as the exterior surface of the storage tank. 
Galvanic anodes have not been commonly or effectively used inside storage 
tanks for a number of reasons. Sacrificial galvanic anodes release metal 
ions which can combine with water to form corrosive salts as the anodes 
break down. These corrosive salts can contaminate the liquid in a storage 
tank. If the liquid is refined fuel, the corrosive salts can make the fuel 
unusable for internal combustion engines. Specifically, corrosive salts 
can cause significant damage to the engine. Because the interior of a 
metal fuel storage tank is not cathodically protected, it is highly 
susceptible to interior corrosion, which can lead to fuel leakage, and 
thus costly environmental concerns. 
As the petroleum industry becomes more environmentally conscious, there is 
increasing pressure to eliminate metal fuel storage tanks that may be 
susceptible to interior and exterior corrosion, and thus to possible 
petroleum leaks into the surrounding soil. This has led the petroleum 
industry to replace some underground metal fuel storage tanks at service 
stations and other locations with nonmetallic storage tanks formed of 
plastic or another polymerized or non-corrosive material. Nonmetallic fuel 
storage tanks are generally not as damage-tolerant or forgiving as metal 
fuel storage tanks, especially during earthquakes. 
Because galvanic anodes must be replaced when the anode metal becomes 
sufficiently consumed, an anode within a storage tank should be easily 
replaceable. Further, in order to be effective, a galvanic anode must be 
positionable in the region where water accumulates in a storage tank, 
namely at the bottom of the tank. More specifically, because water is 
heavier than petroleum products, water tends to accumulate at the bottom 
of a storage tank underneath any fuel in the tank. In order for a galvanic 
anode to work efficiently, it should be located in direct contact with any 
water in the tank. Only by being located in the water will a 
low-resistance electrical circuit be created. If a low-resistance 
electrical circuit is not formed between the galvanic anode and the 
interior surface of the fuel tank, the galvanic anode will not effectively 
prevent the corrosion of the interior surface of the fuel tank. 
Thus, there exists a need for cathodic protection systems that reduce or 
eliminate corrosion problems on the exterior and interior surfaces of 
metal fuel storage tanks such as those used at fuel storage sites or 
service stations. Such protection systems would allow fuel storage tanks 
formed of metal to be safely used without worry of corrosion, thus 
reducing the need for expensive and less damage tolerant plastic fuel 
storage tanks. As will be better understood from the following discussion, 
the invention provides a cathodic anode assembly that addresses some of 
the problems discussed above. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a galvanic anode assembly 
suitable for use inside of metal storage tanks, particularly above or 
below ground petroleum metal storage tanks, is provided. The anode 
assembly includes standard materials, such as magnesium or zinc, as 
sacrificial anode elements to prevent corrosion on the interior of a metal 
storage tank. The sacrificial anode element material is surrounded by a 
hydrophilic gel that maintains a layer of water around the sacrificial 
anode element material. The hydrophilic gel surrounding the sacrificial 
anode element contains metal ions produced during consumption of the 
sacrificial anode element. Because metal ions are absorbed by and 
maintained within the hydrophilic gel, they do not combine to form 
corrosive salts that can contaminate fuel contained within the storage 
tank. 
The hydrophilic gel is maintained around the exterior surface of the 
sacrificial anode element by a porous bag or other porous structure that 
is capable of maintaining the hydrophilic gel around the anode element, 
while allowing water to pass through the bag and into the hydrophilic gel. 
The combined anode elements, hydrophilic gel, and porous bag may in turn 
be placed within a flexible, protective structure, such as a plastic pipe 
containing holes. The resulting galvanic anode assembly is easily 
insertable through the fuel filling tube on a fuel storage tank. 
Maintaining a layer of water around the anode material has the advantage 
of increasing the efficiency of the anode assembly by providing a 
low-resistance electrical path between the anode assembly and the interior 
surface of the storage tank near the anode. The increased efficiency of 
the sacrificial anode helps improve galvanic corrosion prevention. 
In accordance with other aspects of the invention, the galvanic anode 
assembly is lowered into a fuel storage tank so as to rest on the bottom 
of the storage tank where water is located if the tank contains any water. 
The sacrificial anode is electrically connected to the storage tank. 
In accordance with further aspects of this invention, the galvanic anode 
assembly includes a porous structure that maintains the hydrophilic gel 
around the sacrificial anode element so that the hydrophilic gel absorbs 
metal ions produced during consumption of the anode. 
In accordance with still other aspects of this invention, the porous 
structure is a porous bag that houses both the anode elements and the 
hydrophilic gel. 
In accordance with still further aspects of this invention, the galvanic 
anode assembly includes a flexible plastic pipe and the porous bag is 
located in the flexible plastic pipe. The plastic pipe includes a series 
of slits or holes that allow water to enter the plastic pipe, flow through 
the porous bag, and be absorbed by the hydrophilic gel. 
In accordance with still other aspects of this invention, a series of 
sacrificial anode elements are electrically connected together to form an 
anode assembly of any desired length for use in tanks of varying sizes. 
In addition to being used as a galvanic anode in the interior of a tank, 
the present invention may also be used in either a galvanic or impressed 
current configuration to prevent corrosion on the exterior surface of a 
storage tank. In one embodiment of this application, a galvanic anode 
assembly is buried in the ground in the proximity of the storage tank and 
is electrically connected to the exterior surface of the storage tank. A 
layer of hydrophilic gel is mixed with the soil around the anode assembly. 
The hydrophilic gel attracts and maintains water around the anode, thus 
increasing its efficiency. 
In another embodiment, the anode assembly is buried in the ground in the 
proximity of the storage tank and is electrically connected to a DC power 
source. A layer of hydrophilic gel is mixed with the soil around the anode 
assembly to create an improved electrolyte and ensure an efficient 
low-resistance electrical path between the anode assembly and the 
surrounding soil. The DC power source is in turn electrically connected to 
the storage tank. The power source provides a driving force that helps 
move current between the anode assembly and the exterior surface of the 
storage tank.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 illustrates a fuel storage tank 10 in combination with an interior 
14 and an exterior 24 galvanic anode assembly formed in accordance with 
the present invention. The fuel storage tank 10 shown is a cylindrical 
fuel storage tank formed of metal, such as iron, and is typical of the 
type of underground fuel storage tanks used to store fuel at service 
(i.e., gas) stations, etc. The storage tank 10 includes a venting tube 11 
and a fuel filler tube 12 that extend upwardly from the fuel tank to the 
surface of the ground 20 in which the tank is buffed. 
Although the invention is illustrated for use with underground fuel storage 
tanks, it may be used with either underground or above-ground fuel storage 
tanks. In addition, the invention may be used in tanks used to store 
substances other than fuel. 
Corrosion of the interior surface of the storage tank 10 is prevented by 
the interior galvanic anode assembly 14, which is placed inside the 
storage tank and electrically connected to the tank by an electrical cable 
16. More specifically, one end of the cable 16 is connected to one end of 
the galvanic anode assembly 14. The other end of the cable is electrically 
connected to a metal tube 17. The tube 17 passes through the filler tube 
12 extending from the top of the fuel filler tube 12 downward at least 
partially into the interior of the tank 10. The tube 17 is electrically 
conductive and is electrically connected to the storage tank 10 by being 
connected to the filler tube 12. The galvanic anode assembly is sized to 
be inserted into the tank 10 via the filler tube 12. The electrical cable 
16 is long enough to allow the galvanic anode assembly 14 to be lowered to 
the bottom of the tank and to lie along the bottom, as shown. 
The external anode assembly 24 is buried below the surface of the ground 20 
in the proximity of the storage tank. In the preferred embodiment 
illustrated, one end of the exterior anode assembly 24 is connected by 
electrical cable 22 to one terminal of an option DC power supply 18. The 
other terminal of the DC power supply 18 is in turn electrically connected 
to the exterior surface of the tank 10 by an electrical cable 23 connected 
to filler tube 12. The exterior anode assembly 24 helps to prevent 
corrosion of the exterior of the tank 10. 
The structure of the internal galvanic anode assembly 14 will now be 
described with reference to FIG. 2. The internal galvanic anode assembly 
14 includes one or more sacrificial anode elements 36 that are 
electrically connected to the cable 16. More specifically the anode 
elements 36 are electrically connected in series by connecting cables 19, 
as shown in FIG. 2. One of the outer anode elements 36 of the series is 
electrically connected to one end of the cable 16. The number of anode 
elements 36 used, and the size and shape of the anode elements, are 
determined by the geometry of a protective container 28 (described below) 
in which they are placed and the geometry of the fuel tank 10 in which the 
galvanic anode assembly 14 is used. 
Each anode element 36 is surrounded by a layer of hydrophilic material 38. 
Since hydrophilic material absorbs water, the layer of hydrophilic 
material 38 maintains a layer of water around the anode elements 36 if 
there is any water in the interior of the tank 10. The layer of water in 
the hydrophilic material 38 around the anode elements 36 establishes a 
low-resistance electrically conductive pathway between the anode elements 
36, the water surrounding the galvanic anode assembly 14, and the interior 
surface of the fuel tank 10. In the preferred embodiment of the invention, 
the hydrophilic material consists of 99.5% polyacrylamide and less than 
0.05% acrylamide. One exemplary hydrophilic gel is sold under the trade 
name Terr Sorb Ag by Industrial Services International, Inc. 
The water absorbed by the hydrophilic material 38 creates an electrolyte 
around the anode elements 36. The hydrophilic material 38 also helps to 
absorb metal ions produced as the anode elements 36 are consumed. As a 
result, the metal ions do not combine with water to form corrosive salts 
that can enter and contaminate fuel within the tank 10. 
In alternate embodiments, hydrophilic materials having different amounts of 
polyacrylamide or other hydrophilic materials may be used. The chosen 
hydrophilic material should absorb water to remove the water from contact 
with the metal interior surface of the tank and lower the resistivity 
around the sacrificial anode. It is also advantageous that the hydrophilic 
material absorb the metal ions produced as the anode elements are 
consumed. The anode elements 36 are, of course, formed of a metal that is 
higher on the electromotive scale, i.e., higher Electromotive Force than 
the metal used to form the tank 10. If the tank is formed of a ferrous 
material, suitable metals for forming the anode elements include zinc and 
magnesium. 
The hydrophilic material 38 is maintained around each anode element 36 by a 
porous container or bag 40 that surrounds each anode element 36. The bags 
40 are formed of a porous material that allows water to pass through the 
bags into the hydrophilic material 38, but prevents the hydrophilic 
material from moving through the bag 40 and contaminating fuel within the 
storage tank 10. 
The entire structure consisting of anode elements 36, hydrophilic material 
38, and porous bags 40 is contained in a protective container 28. 
Preferably, the protective container 28 is cylindrical and includes two 
endcaps 32 and 34 that maintain the anode elements 36 within the interior 
of the container 28. The protective container 28 includes a plurality of 
holes, preferably in the form of slots 30 spaced along its length. The 
slots 30 allow water and fuel to enter the interior of the container 28 
while maintaining the anode elements 36 and bags 40 within the container. 
The container 28 may be formed from a wide variety of different materials, 
however, it is advantageous for the container to be formed of a flexible 
electrically insulating material, such as a plastic or rubber tube. 
Forming the container 28 of a flexible material and maintaining the length 
of each individual anode element 36 relatively short allows the entire 
anode assembly 14 to be flexible over its length. A flexible anode 14 is 
easier to insert through the fuel filler tube 12 into the fuel storage 
tank 10 than is a rigid assembly. 
In addition to protecting the anode elements 36, bags 40, and hydrophilic 
gel 38 from damage during insertion or withdrawal, the container 28 also 
prevents the anode elements 36 from directly contacting the interior of 
the storage tank 10. This ensures that an electrical connection is not 
established directly between the interior of the fuel storage tank 10 and 
the anode elements 36. The container 28 also prevents any water within the 
hydrophilic gel 38 from contacting the metal interior surface of the tank, 
thus helping to prevent corrosion. 
In order to insert the interior anode assembly 14 into the fuel storage 
tank 10, the tube 17 is first withdrawn from the storage tank. The anode 
14 is then electrically connected to the tube 17 by cable 16 and lowered 
into the storage tank through the filler tube 12. When it is necessary to 
withdraw the anode assembly 14 for repair or replacement, it is withdrawn 
through the filler tube 12. 
It is advantageous that the anode assembly 14 be placed adjacent to the 
bottom of the tank 10. In fuel storage tanks, water is heavier than the 
fuel and thus accumulates at the bottom of the tank. Placing the anode 
assembly 14 at the bottom of the tank ensures that the hydrophilic gel 
will absorb water within the bottom of the tank, thus removing the water 
from contact with the metal interior surface of the tank. 
A second embodiment of the porous bag 40 is illustrated in FIG. 3. In the 
second embodiment, instead of using individual bags 40 surrounding 
individual anode elements 36, a continuous bag is placed over all of the 
anode elements 36. The portions of the bag 40 located between individual 
anode elements 36 are tied off using ties 42 to establish individual 
sealed compartments around each anode element 36. Although it is preferred 
to maintain individual compartments around each anode element 36 to ensure 
that hydrophilic material 38 surrounds each anode element 36, alternate 
configurations can be used. For example, a single, undivided bag could 
surround all the anode elements 36. In other alternate embodiments, the 
bag 40 could be eliminated altogether, and the interior of the container 
28 could be filled with a hydrophilic material. In such an embodiment, the 
size of the holes or slots 30 and size of hydrophilic material 38 would 
have to be tailored to ensure that the hydrophilic material does not pass 
through the slots 30 and contaminate fuel within the storage tank 10. 
The structure of the external anode assembly 24 shown in FIG. 1, could be 
the same as the structure of the interior anode assembly 14 described 
above. Alternatively, the anode assembly 24 could be of existing anode 
designs. The efficiency of the anode assembly 24 is increased by 
surrounding the anode with a hydrophilic gel 26, such as a polyacrylamide 
material in a gel or crystal form. The hydrophilic gel 26 could be mixed 
with the soil surrounding the anode assembly 24, for example. The 
surrounding soil will act as a container that maintains the hydrophilic 
gel around the anode assembly 24. Alternatively, the hydrophilic gel could 
be contained around the exterior anode assembly 24 through the use of a 
porous bag (not shown) in a manner similar to that described with respect 
to the interior anode assembly 14 described above. 
The hydrophilic gel 26 surrounding the anode assembly 24 absorbs and holds 
water within the soil in the vicinity of the anode. As the hydrophilic gel 
26 absorbs water, it creates an improved electrolyte and ensures an 
efficient low-resistance electrical path between the anode assembly 24 and 
the surrounding soil. The hydrophilic gel provides the anode assembly 24 
with a uniform environment for low-resistance contact to the earth, thus 
increasing the efficiency of the electrical path. 
The exterior anode assembly 24 may be connected in a galvanic protection 
configuration or an impressed current configuration. In a galvanic 
configuration, the anode assembly is directly electrically connected (not 
shown) to the exterior of the storage tank 10 using an electrical cable or 
other means. 
Alternatively, the efficiency of the exterior anode assembly 24 may be 
increased by connecting it to an optional DC power source 18 in an 
impressed current configuration, as shown in FIG. 1. The power source 18 
is in turn electrically connected to the storage tank 10 through the use 
of an electrical cable 23 as described above. The power source 18 provides 
a driving force that helps move current between the anode assembly 24 and 
the exterior surface of the storage tank 10. The current provided by the 
power source assists in moving current between the anode assembly 24 and 
exterior surface of the storage tank 10, thus ensuring that the anode 24 
corrodes and is consumed as opposed to the exterior surface of the storage 
tank. 
In alternate embodiments of the invention, the anode elements 36 could be 
formed of other materials than those described above. In addition, 
hydrophilic materials other than those specifically described above can be 
used. Further, geometry of and materials used to form the container 28 can 
also be altered without departing from the invention. In still other 
alternate embodiments, the container 28 can be eliminated altogether and 
other methods used to prevent the anode elements 36 and hydrophilic 
material from contacting the interior of the tank 10. While the preferred 
embodiment of the invention has been illustrated and described, it will be 
appreciated that various changes can be made therein without departing 
from the spirit and scope of the invention.