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  Cathodic protection system for underground storage tankUSPTO Application #: 20060070871Title: Cathodic protection system for underground storage tank Abstract: There is provided a method for implementing a cathodic protection system for an underground storage tank. A DC voltage source provides a test current between the installed anode and storage tank resulting in the flow of electrical current. If the output is above a defined value, an automatic control DC power supply has sufficient voltage capacity to deliver the required current. If the anode test currents fall below the required minimum current, additional anode(s) are installed as set forth in a pre-engineered table. The method allows for the installation of a cathodic protection system by technicians and other non-experts. (end of abstract) Agent: Joseph E. Waters, Esq. Fay, Sharpe, Fagan, Minnich & Mckee, LLP - Cleveland, OH, US Inventors: James B. Bushman, N. Dennis Burke, William P. Carlson USPTO Applicaton #: 20060070871 - Class: 204196010 (USPTO) Related Patent Categories: Chemistry: Electrical And Wave Energy, Apparatus, Electrolytic, Object Protection The Patent Description & Claims data below is from USPTO Patent Application 20060070871. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND [0001] The present exemplary embodiments relate to a cathodic protection system and method. It finds particular application in conjunction with underground storage tanks, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications. [0002] Metallic surfaces, such as are common in the field of pipelines and related structures, such as buried tanks and distribution systems, are adversely affected by numerous corrosive electrolytic fluids that contact these surfaces. For example, in the natural gas and petroleum industries, corrosion occurs extensively on the outer surface of both buried and above-ground pipelines. [0003] In order to reduce, or preferably eliminate, this undesirable metallic surface corrosion, anti-corrosion protective coatings have been extensively used in the underground storage tank industry. These ubiquitous anti-corrosion protective coatings frequently take the form of a helically-applied tape-like protective outer wrapping. The tape-like protective component may be applied directly over an unprepared tank's outer surface, or may, in fact, be overlaid onto a primer-coated, pretreated tank outer surface. Other forms of protective coatings also exist, including coal tar epoxy, asphalt, and fusion bonded epoxy coatings. Despite the use of such coating compositions and materials, external corrosion of underground tanks is still a concern when there is a breach of the coating or when such coatings have been poorly applied or not applied at all. [0004] Thus, to protect against external corrosion, underground storage tanks (and other buried metallic structures) are typically cathodically protected, either in addition to or in lieu of being coated as described above. The cathodic protection (hereafter alternatively referred to as "CP") system is designed to protect the tank and associated buried pipe where coating defects occur. Cathodic protection, as it is used here, refers to the phenomenon and practice of applying a small potential to a metallic tank that is buried in the ground. This imparted cathodic potential of the buried tank will tend to limit or protect against corrosion attacking the metal surface. [0005] Cathodic protection provides corrosion protection to any bare metal areas exposed to soil due to coating defects by causing direct current to flow from the soil into the structure, thereby polarizing the structure as a cathode. Protection is ensured by modifying the environment around the steel as well as reducing the dissolution rate of the steel by reducing the anodic overpotential. The required direct current output of the cathodic protection system varies both with the existence and quality of any coating and the soil moisture and chemical contents. For example, a good quality coating substantially reduces the bare metal area of the structure exposed to soil thus reducing the amount of metal that has to be protected by cathodic current flow. [0006] Two cathodic protection systems are generally in use for corrosion protection of metal structures. The first, termed an impressed current cathodic protection system, consists of a DC power supply, insulated wires connecting the plus terminal of the DC power supply to a buried anode (for instance graphite cylinders), insulated wire connecting the negative terminal of the DC power supply to the protected structure, and test stations installed at the structure. The test stations typically consist of a pipe or a valve box with one or more insulated wires attached to the structure, typically by brazing, and a terminal board for termination of the wires. The test stations are used for monitoring the corrosion protection levels by measuring potentials between the structure and a reference electrode in an electrical contact with ground above the structure. The reference electrode usually consists of a copper rod fixed in a plastic body filled with saturated copper-sulfate solution, and having a porous plug to facilitate electrical contact with the ground. [0007] The second, termed a sacrificial (galvanic) cathodic protection system, consists of magnesium or zinc anodes buried next to the structure and often directly connected by an insulated wire to the structure. The protective current is generated by the potential difference between the structure and the anode. The structure with sacrificial anodes also has test stations for the cathodic protection testing and evaluation of its corrosion protection effectiveness. [0008] Details of different cathodic protection systems and of the pipeline potential measurements can be found in W. von Baeckmann et al., Handbook of Cathodic Corrosion Protection, Theory and Practice of Electrochemical Protection Processes 3.sup.rd Ed., Gulf Publishing Co., 1997, the entire disclosure of which is incorporated herein by reference. [0009] Even when cathodic protection is used, corrosion and defects usually still occur. Coating defects generally take the form of either exposed bare steel or a disbandment where the coating remains intact but a gap is formed between it and the bare steel. CP systems effectively deliver current to defects directly exposed to soil or water and therefore mitigate corrosion. [0010] The above described cathodic protection methods are often complex and cumbersome to install, typically requiring specialized equipment and personnel to be present during the installation of a tank and for detailed filed surveys or soil testing to be performed, thereby adding to the cost of such a system. Thus, despite the above-described methods and materials for protecting a buried tank from corrosion, and for monitoring any corrosion that may occur, improvements in the industry are still desired. For example, there is a continued need for a simpler and less costly cathodic protection system and a method for installing such a system that can be performed by a general tank installer contractor especially where the buried tank(s) and piping are of smaller capacity. Such conditions exist on buried tanks and piping used to store and deliver fuel oil to home and small apartment building heating systems and for diesel and gasoline storage for emergency electrical generating systems. BRIEF DESCRIPTION [0011] In accordance with one aspect of the present exemplary embodiments, there is provided a cathodic protection system for an underground storage tank. The system includes a constant current DC power supply of sufficient capacity to provide corrosion mitigation up to a given size tank system in any common environment regardless of the coating condition. Connected to the positive terminal of the power supply are one or more anodes placed in the ground an appropriate distance from the storage tank. The negative terminal of the power supply is connected to the tank. [0012] In accordance with a second aspect of the present exemplary embodiments, there is provided a method for implementing a cathodic protection system for an underground storage tank. The method includes the steps of installing an anode at preset locations adjacent to the storage tank, using a DC voltage source to provide a test current between the installed anode and storage tank resulting in the flow of electrical current. [0013] If the output is above a defined value, the as yet to be installed automatic control DC power supply has sufficient voltage capacity to deliver the required current. If the anode test currents fall below the required minimum current, additional anode(s) are installed as set forth in a pre-engineered table. BRIEF DESCRIPTION OF THE DRAWINGS [0014] FIG. 1 is a diagram showing the steps needed for determining the appropriate number of anodes required for any particular HOUST system. [0015] FIGS. 2A and 2B are graphs showing the number of anodes necessary based on the test current measured for a HOUST system. [0016] FIG. 3 is a diagram of the installed cathodic protection for a HOUST system. DETAILED DESCRIPTION [0017] The present exemplary embodiments relate to a system and method for providing impressed current cathodic protection to an underground storage tank or pipe. By way of example, the exemplary embodiments will be described with reference to an underground heating oil storage tank for home or residential use, which applicants envision as the primary market for the present invention. However, the invention is in no way limited to such tanks but in fact can be extended to any underground storage tank or pipe for holding or transporting a material. For convenience, applicants may make reference herein when describing the present embodiments to a HOUST system, which is an acronym for Home Oil Underground Storage Tank. The present described embodiments can be employed in conjunction with both new and existing HOUST systems. In addition, although the described embodiments make reference to underground tanks, above ground metallic structures in need of cathodic protection are also amenable to the present process. [0018] Typical HOUST's are usually small and of only two general sizes (500 to 550 gallon and 1000 to 1100 gallon). Because of their relatively small size, the total current required for cathodic protection for such tanks is also small, generally being less than 1/2 ampere. Since they are all typically bare steel, a standardized design for all such systems may be supplied, thereby eliminating the need to do expensive field surveys or testing prior to installation of the present system. [0019] Generally, the only variable that significantly impacts the cathodic protection system design is the soil resistivity. That is, the higher the soil resistivity, the more difficult it is to deliver current to the HOUST to be protected. Measuring the resistivity at each site can be expensive and, in some case, misleading if not measured by a person expert in making these measurements. [0020] Additionally, it has become standard practice for larger UST (under-ground storage tank) systems such as those found at fuel dispensing locations (service stations) to conduct a detailed corrosion evaluation study as outlined in the ASTM standard practice for Testing UST prior to upgrading with Cathodic Protection (ASTM G158-98). Continue reading... Full patent description for Cathodic protection system for underground storage tank Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Cathodic protection system for underground storage tank patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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