Electricity: measuring and testing – Determining nonelectric properties by measuring electric...
Reexamination Certificate
2001-02-26
2003-08-26
Oda, Christine (Department: 2858)
Electricity: measuring and testing
Determining nonelectric properties by measuring electric...
Reexamination Certificate
active
06611133
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention.
The present invention relates to anode rods used to prevent corrosion of a metal tank. More particularly, the present invention relates to a depletion indicator for anode rods contained in the tank of a pressure vessel, such as a water heater or boiler.
2. Description of the Related Art.
It is known in the art that an average residential water heater should last approximately 10 to 12 years. Almost all of the components of a water heater can be repaired or replaced except for the tank. Once the tank rusts through and leaks water, there is no way to repair the water heater. Replacement is the only solution.
A water heater has an internal sacrificial anode rod to protect the tank from rusting. An anode's sole purpose is to corrode so that the steel of the tank does not corrode, i.e., rust.
The following is an incorporation of a detailed explanation of anode rods and cathodic protection in residential water heaters as provided in Technical Service Bulletin #1201, updated Sep. 24, 1998, issued by the Rheem-Ruud Manufacturing Company:
“Corrosion can be defined as the destructive attack of a metal by an electrochemical reaction with its environment. Steel exposed to moisture and oxygen will rust and corrode. Corrosion is defined as the “eating away” of metal by electrochemical means. There are four main factors affecting water's ability to corrode:
1. Acidity
Water is made acidic by naturally occurring dissolved gases such as carbon dioxide.
2. Temperature
Higher temperatures speed up the corrosive process.
3. Electrical Conductivity
The more dissolved mineral solids in the water, the greater its ability to carry electrical current. When dissimilar metals are in the water, electrical current flows between the metals. One of the metals gradually corrodes faster than the other.
4. Amount of dissolved oxygen
Free oxygen dissolved in the water promotes corrosion.
Dissimilar metals are present in the interior steel tanks surfaces of all water heaters in several forms such as the drain nipples, heating elements, immersion thermostats, inlet and outlet nipples. These metals, and others present in the water itself, combined with the oxygen content of the water and heat, establish an environment conductive to corrosion. The dissimilar metals create a corrosion cell that is enhanced by the conductivity of the water. The anode is put in to overcome (neutralize) the corrosive cell.
In a water heater, corrosion is protected by a glass (actually a porcelain enamel) lining in the steel tank, and the use of auxiliary anode rods. During the manufacturing process, the inside water tank and both the top and bottom heads are sprayed with a slurry of glass material. This material is fired in a furnace, and when cooled, resembles a glass coating called porcelain. This glass provides a long life to the steel tank; otherwise the tank would fail or corrode in a relatively short time. Every glass-lined water tank, no matter how carefully it is manufactured, has some bare metal exposed. This is due to the inability to effectively cover sharp corners and the radius around the fittings. There is a chance that a crack or chip in the porcelain lining will allow the water to come in contact with the steel tank. Over time, water, a universal solvent that becomes more aggressive with temperature, slowly dissolves the interior tank lining. Thus, the exposed bare metal will create conditions for corrosion, starting as pin holes in the tank and finally tank failure.
Cathodic protection is accomplished in the glass-lined water heater through the use of an auxiliary magnesium anode. Due to the relative position of magnesium to steel in the electromotive series of metals, magnesium will corrode, producing an abundance of electrons which flow (much the same as electrical current) to the exposed steel surface and maintaining it in the electro-negative state. As current flow takes place, the anode rod reacts chemically to corrode at a rate faster than the steel inner tank. This process stops tank corrosion by substituting the sacrificial magnesium anode rod in place of the steel tank. As long as the magnesium anode rod remains in the tank, in an active state, there will be no corrosion of the minute areas of exposed steel inside the tank.
The life of the anode, in turn, depends on water temperature, amount of water used, and the quality of the glass lining. However, the most important factor in the life of the anode rod is the water chemistry, the hardness or softness of the water. Also check the manufacture and installation date of the water heater. If the heater is more than five (5) years old, and the anode rod has not been replaced, inspect the anode rod. The anode should be replaced when there is six (6) inches or more exposed core wire at either end.”
Additionally, in Rheem-Rudd's Technical Service Bulletin #1401, “Standing Pilot Gas Water Heater Maintenance,” updated Sep. 24, 1998, Section 2, “Anode Rod Inspection,” it states that:
“The anode rod should be removed from the water heater's tank annually for inspection and replaced when more than 6″ of core wire is exposed at either end of the rod. Refer to your Use and Care Manual for anode rod location. Make certain [the] cold water supply is turned off before removing anode rod.”
Virtually all water heater manufacturer's inspection and maintenance instructions recommend that the anode rod be removed from the hot water heater tank annually for inspection by the homeowner or a technician, as the case may be. Since many consumers have little knowledge of this recommendation and therefore fail to inspect the condition of the anode rod, or fail to have a trained technician inspect the condition of the anode rod, there has been a long felt need for a way to determine when the anode rod requires replacement without any complicated and costly inspection procedures.
Moreover, a recently published (January 2001) brochure from PSE&G, New Jersey's electric and gas company, advises customers to be aware of the telltale signs of failing water heaters, including, among other things, that water is leaking from the tank, that the hot water is discolored or rusty, or that the water heater is over ten years old.
It is clear from PSE&G's brochure advising customers of these signs of water heater failure and suggesting that customers replace their tanks based solely on the age of the tank, that customers are not periodically inspecting/replacing the anode rod as recommended by the manufacturer.
Homeowners, however, should not rely upon these occurrences to detect a problem with the water heater. Indeed, once water is leaking from the tank and/or hot water is discolored, enormous and costly damage may have occurred or will occur shortly.
Thus, there has been a long-felt need in the industry for a way to preserve the structural integrity of the fluid tank in a pro-active manner, rather than in a reactive manner (from age, rusty water or leaks), to replace the often-neglected annual inspection of the anode and to save the consumer the enormous costs that can be associated with water heater failure.
The present inventors under took an assessment of the recommended inspection procedures to determine whether the common-place neglect of the annual inspection could be due to the difficulty of complying with the procedures.
The results showed that the requirements and procedures of annually inspecting the anode rod are unrealistic, overly complex, and difficult for the typical homeowner in the following ways:
The removal of an anode rod for inspection is a highly technical task requiring competence, physical dexterity, expertise, skill, and tools. The primary problem is the lack of headroom in almost all installations. For example, the length of a Rheem-Rudd replacement anode rod is approximately 44 inches, but it could be any length or diameter according to need. The hot water heater must be tilted if there is insufficient headroom for a direct removal and replacement of the anode ro
Cugliari Matthew
Kean James G.
Atlantic Professional Services Inc.
Klauber & Jackson
LeRoux Etienne P.
Oda Christine
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