US3056738A - Impressed current cathodic protection system - Google Patents

Description

H. c. FISCHER 3,056,738

IMPRESSED CURRENT CATHODIC PROTECTION SYSTEM Oct. 2, 1962 4 Sheets-Sheet 1 Filed Feb. 2, 1959 FIG. 4

INVENTOR.

HARRY c. FISCHER FIG. 2

FIG. 3

ATTORNEY 3,056,738 IMPRESSEID CURRENT CATHODIC PROTECTION SYSTEM Filed Feb. 2, 1959 H. C. FISCHER Oct. 2, 1962 4 Sheets-Sheet 2 FIG 9 FIG.5

INVENTOR HARRY C. FISCHER VII ATTORNEY Oct. 2, 1962 H. c. FISCHER 3,056,738

IMPRESSED CURRENT CATHODIC PROTECTION SYSTEM Filed Feb. 2, 1959 4 Sheets-Sheet 5 F|G.l|

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INVENTOR. HARRY c. FISCHER ATTORNEY Oct. 2, 1962 4 Sheets-Sheet 4 Filed Feb. 2, 1959 INVENTOR HARRY c. FISCHER ATTORNEY United States Patent @fiire 3,056,738 INIPRESSEID CURRENT CATHODIC PROTECTION SYSTER l Harry C. Fischer, Lake Valhalla, Montvale, NJ. Filed Feb. 2, 1959, Ser. No. 790,512 Claims. (Cl. 204-496) This invention relates to an impressed current cathodic protection system for hot water heaters, and is particu larly adapted for use with glass-lined hot water heaters.

By impressed current cathodic protection is meant the use of an impressed current to prevent corrosion of a metal in an electrolyte by making such metal the cathode for the impressed current.

In recent years, the use of glass-lined hot water tanks has become prevalent, and while theoretically a coating of glass upon the interior surface will protect the covered metal surface from corrosion, in practice this is not completely accomplished. Minute spots of metal generally are left uncovered, and these bare areas called holidays, corrode, causing the tanks to leak, even though the glass-covered portion of the tank is perfect.

Recently magnesium anodes have been widely used and generally perform satisfactorily in protecting the bare metal areas. A number of difficulties arise with the use of magnesium anodes. First, there is a replacement problem. In some waters the magnesium corrodes very rapidly, While in other waters the magnesium Will not corrode at all, and thus will give no protection. Furthermore, the presence of sulphur in water will result in a bad taste and a disagreeable odor. Local cells caused by impurities in the anode tend to consume it, and thus shorten its protective life. Corrosion products of a magnesium anode fall to the bottom of a hot water tank and may cause a popping noise in gas hot water heaters. When a magnesium anode is consumed, the home owner is generally not aware of it, and since he does not replace it, all protection is lost. Only after a leak develops in a tank, is concern felt for the condition of the interior.

With glass-lined tanks, there is not more than a few square inches at the most of bare metal that requires protection, and with this small area, an impressed current cathodic system is economical when compared with a magnesium anode.

The object of this invention is to provide economical protection for glass-lined hot water heaters over a long period of time.

Another object is to provide means for ascertaining when the protective system is not functioning or requires replacement.

. Still another object is to permit replacement within a hot water tank of that part of the system which may require renewal.

Other objects are apparent from the description which follows.

Embodiments of this invention are disclosed in the accompanying drawings in which:

FIGURE 1 is a cross section in elevation of an electric hot water heater embodying one form of this invention.

FIGURE 2 is a top view of one of the heating elements and protective unit shown in the heater of FIGURE 1.

FIGURE 3 is a side View of the heater and unit of FIGURE 2.

FIGURE 4 is an end view of the heater and unit of FIGURE 2.

FIGURE 5 is a detail of the mounting of the anode used in the protective system shown in the preceding figures.

FIGURE 6 is a wiring diagram for one of the protective units of the heater of FIGURE 1.

3,056,738 Patented Oct. 2, 1962 FIGURE 7 is a cross section in elevation of the upper portion of a gas hot water heater embodying this invention.

FIGURE 8 shows the protective unit assembly used in the gas hot water heater of FIGURE 7.

FIGURE 9 is a wiring diagram of the protective unit of the heater shown in FIGURE 7.

FIGURE 10 is a section at the inlet of a hot water tank showing the employment of a dielectric sleeve.

FIGURE 11 is a cross section in elevation of a gas hot water heater embodying another form of this invention.

FIGURE 12 is a detail, in section, of the mounting of the anode in the inlet of the heater of FIGURE 11.

FIGURE 13 illustrates the mounting of the anode in and around the intake pipe of the heater of FIGURE 11.

Referring to the drawings in which the same number refers to the same or a similar part wherever shown, FIGURE 1 illustrates in section, an electric hot water heater. The heater consists of a glass-lined metal tank 1, having a dielectric or cold water inlet 2 and a hot water outlet 3. Within the tank, near the bottom and also near the top, are glass-coated steel heating elements 4, which are subject to the control of thermostat 5. Instead of steel, glass coated, these heating elements may be of copper, provided they are electrically insulated from the tank wall. Ground 6 is attached to the cold water inlet 2, but, of course, may be attached at any other convenient location, or a suitable ground may be had through the metal plumbing system.

FIGURE 2 is a top view of one of the U-shaped heating elements 4, secured to a mounting plate 11, to which is affixed an electric terminal mounting member 9. Beneath heating element 4, as may best be seen in FIGURE 3, is a platinum wire anode 7, attached to tantalum lead in wire 8, supported at its end by member 10 which extends more than halfway across the tank, both wire 8 and member 10 being mounted on plate 11. Plate 11 is atfixed to the outer surface of tank 1, and through holes in the wall of the tank, the heating element and anode assembly project into the tank. Outwardly the end view of the complete assembly is as seen in FIG- URE 4.

FIGURE 5 illustrates in detail the mounting of wire anode 7, and supporting member 10. Anode 7 may be platinum or platinum-clad tantalum Wire, the latter having the advantage of economy. Lead in wire 8 is tantalum or a metal having similar properties. An anode holder 12, threaded at one end, is embedded at the other end in the base of member 10. Member 10 passes through an opening in plate 11, and completely insulates anode 7 and wire 8 from plate 11. Nuts 13 firmly attach the anode assembly to plate 11.

Mounted on the outer end of anode holder 12 and on member 9 is diode half wave rectifier and resistor housing 14, as best seen in FIGURES 2 and 3. Wire 15 supports and connects housing 14 with anode holder 12 and wire 16 secures it to member 9. In FIGURES 2 and 4, terminal posts 19 and 20 are visible and to these are connected the wires leading to a power source.

FIGURE 6 illustrates the wiring for the heating and the protective unit shown in the preceding figures. A 220 volt alternating current power source is connected through thermostat 5 to resistance heating wires 4', encased in heating element 4. Taken from the hot lead of the power source is wire 16 connected through the resistor 18 and diode half-wave rectifier 17 to anode 7.

In conventional electric utility practice the potential between wire 16 and the grounded tank is about volts, and in order to reduce the flow of direct current in the protective system to a value sufiicient to overcome the corrosion producing current, suitably designed resistor 18 is included in the circuit. Five milliamperes has been found suflicient to protect up to from 36 to 72 square inches of bare metallic area from corrosion and in most glass-lined domestic water heaters, this area of bare metal is seldom exceeded. An isolating transformer may be added if a larger current is desired for protective purposes than that supplied with the circuit as shown.

In designing resistor 18, the internal resistance through the water in the tank must be considered. In most waters this resistance will be low by comparison with the resistance of resistor 18. In analyzing the effect of this internal resistance, if

E=line voltage to ground (110 to 125 volts) l=current in amperes R =resistance of resistor 18 (approximately 12,000

ohms) R =internal resistance through water between anode and tank E =voltage across R when system is in operation then E=I (R plus R If R, is insignificant, as it will be in most waters, then the current I will remain relatively constant, depending largely upon the R selected for resistor 18.

If in unusual waters an extremely high R is found to exist, then the value of I will be decreased. In such cases, the voltage drop, E across the resistor 18, is reduced. If the current flow and, therefore, the voltage are not high enough to light a neon indicator lamp, the external resistance, R must be reduced so that the sum of the internal and external resistances will allow the desired current of not greater than 5 milliamperes to flow. Use of a milliammeter will determine the current flow.

It is obvious that with the circuit as shown, a minute flow of electrons may be passed through the water in the tank from the holidays to the platinum anode.

FIGURE 7 illustrates the application of this protective system to a gas hot water heater. In FIGURE 7, glasslined tank 22, adapted for use with a gas heating element not shown, is provided in the threaded opening, conventionally found in the top of such a tank, with protective unit assembly 21. This unit is connected with a 115 volt alternating current power source by a cord containing wires 23 and 24. Platinum wire anode 7 and lead in wire 8, mounted on elongated dielectric support member 10, project into tank 22, with the extreme end portion of said anode secured to the end portion of said support, as in FIG. 3.

Referring to FIGURE 8, the details of assembly 21 will be seen. Mounting bushing 25 is threaded to fit the threaded hole in the top of glass-lined tank 22. Within it are held the base of an anode-support member 10, flexible or rubber O-ring 26, nylon bushing 27, washer 28, anode support holder 12 for the base of said support with a stem passing through the bushing and washer, and a nut 29 threaded on the end portion thereof. Supported on it is casing mount 30 and casing 31 seated thereon. Within the casing mount and easing are diode rectifier 17, resistors 33 and 34 and neon glow lamp 35, a portion of the latter projecting out of the top of the casing of assembly 21 through bushing 32 for observation by an attendant. The substantially straight wire anode 7 extends approximately coaxial of the bushing 25 from an end portion connected to that part of the support adjacent said bushing to its other end portion connected to the free end portion of said support, as viewed in FIGURES 1, 2 and 3.

- Referring to FIGURE 9, a wiring diagram of the pro t'ective system of FIGURE 8 is illustrated. It will be noted that in the circuit there is included the anode 7, wire 8, diode rectifier 17, neon glow lamp 35 and four resistors 33- and 34, connected as shown. In this arrangement neon glow lamp 35 is in the center of a bridge circuit, and it will remain lighted while the system is functioning or be completely extinguished when no current is flowing. The resistors are designed to control or permit such minute flow of current as the size of the tank may require. For example, resistors 33 may be 12,000 ohm resistance while 34 are 125,000 ohms. In this circuit the input to the diode rectifier is the center tap of a resistance between the two leads of the volt circuit so that irrespective of the manner in which the plus is inserted in a receptacle, a voltage will result between the rectifier and ground.

A neon lamp may also be included in the system used for electric hot water heaters, to serve as an indicator to show that the system is functioning. Furthermore, if desired or required by any electrical code, an isolating transformer may be introduced in the system. This requirement generally exists if the current for the system is in excess of five milliamperes.

FIGURE 10 shows how a sleeve for pipe connections to heater tanks may be used to protect metal at these critical areas. Sleeve 36 of nylon or other suitable plastie, is friction fitted within the connecting pipe for a short distance from tank 1. Thus, the areas not glass-coated may be protected with the same low current that protects the rest of the tank.

FIGURES 11, 12 and 13 illustrate a protective system incorporated in the inlet pipe connection of a gas hot water heater. Open end plastic tube 37 commonly known as a dip tube, extends downward into glass-lined tank 22, being supported at its upper end within T 38. T 38 is mounted on the outside of tank 22 by nipple 39. Flue 42 for conducting heat from the fell gas to the heater extends therethrough.

An inlet pipe, not shown, may be connected to threaded opening '40 or T 38. Water enters T 38 and enters hole 41 in wall of tube 37 near its upper end and thence goes through tube 37 and into tank 22.

Tube 37 and the protective system are removably attached to T 38 as best shown in FIGURE '12. Tube 37 is threaded to mounting bushing 43, which in turn is threaded into T 38. Nylon bushing 44 provides electrical insulation, and O-ring 26 insures a water-tight fit. The lamp, resistors and rectifier may be contained in mounting bushing 43, or may be separately housed, as for example in a combination housing and plug that can be inserted in an ordinary 110 volt outlet and connected by cord 48 to the anode. The figures do not show the remote housing.

Referring to FIGURE 13, it will be seen that hole 49 in tube 37 affords a passage through which tantalum lead in wire 46 may pass from within to outside of tube 37. This wire and the active platinum-coated tantalum wire sections 47 and an additional section of tantalum wire 46, spliced as shown, are spirally wound about the tube, being secured at their lower end in holes 50.

It has been found economical to make the anode of platinum-clad tantalum wire '47, adjacent to the top of the tank and adjacent to the bottom as shown, using tantalum wire 46 for the rest of the anode length. Thus, in FIGURE 13, a central portion of the anode is shown as a piece of tantalum wire 46. The lead in portion of the anode is likewise of tantalum wire 46. Tantalum anodizes completely in water when used as an anode and its oxide coating then resists the further flow of current from its surface.

It should be noted that in this system, it is not necessary to concentrically locate the anodes in the tanks. In fact, their disposition may be made to combat the most sensitive areas in a tank.

Various modifications may be made in the system illustrated, and I do not by the illustration given herein, limit the scope of this invention.

What I claim is: i

1. An electrical protective device for the prevention of corrosion in hot water heaters and adapted to be removably secured in a threaded opening in an electrical- 1y grounded hot water heater tank, comprising a bushing threaded to fit such threaded opening in the tank wall; an anode secured to such bushing and adapted to project into the tank; a casing mounted on the bushing and adapted to lie outside the tank; a half wave rectifier and a resistor within the casing both connected in series with the anode; and a conductor from said resistor to the exterior of the casing.

2. An electrical protective device for the prevention of corrosion in hot Water heaters and adapted to be removably secured in a threaded opening in an electrically grounded hot water heater tank, comprising an anode; a bushing fixed to and surrounding the anode adjacent one end thereof and externally threaded to fit the threaded opening in the tank; a housing insulated from and mounted on the bushing; a half-wave rectifier and a resistance within the housing, both connected in series with the anode; a neon glow lamp and a resistance mounted Within the housing and connected in series with the rectifier and the anode; and terminal means on the exterior of the housing for connecting the device with one side of an alternating current source, the other side of which is grounded.

3. An electrical protective device as set forth in claim 1, wherein there is a glow lamp in series with a resistor, connected across said first-mentioned resistor and projecting from said casing.

4. An electrical protective device for the prevention of corrosion in hot water heaters, adapted to be removably secured in a threaded opening in the electrically grounded tank of such a heater, comprising a mounting bushing threaded to fit said opening, a casing mount with a shouldered end portion secured to and a portion projecting outwardly from said bushing, an elongated dielectric anode-support member with a base secured to the shouldered portion of said casing mount, a flexible ring engaging said base and disposed inside the shouldered end portion of the casing mount, a second bushing engaging the other side of said ring and said shouldered end portion, a holder for said base having a stem passing through said second bushing, a nut threaded on the end portion of said stem for securing the ring, bushing, holder and base in place on said shouldered portion, a lead from said holder projecting through said base, a wire anod extending from the free end portion of said lead to the baseremote portion of said support member, a casing seated on and projecting outwardly from said mount, and a diode rectifier, resistors and a neon glow lamp enclosed in said casing and connected to said anode, with a portion of the lamp projecting out of the top thereof for observation by an attendant.

5. In combination with a metal hot water heater tank having a threaded opening, a metal bushing threaded into said opening, an insulating electrode support carried by said bushing, With a portion offset from the axis thereof and extending therefrom into said tank for a distance more than halfway from the bushing to the opposite wall of said tank, and a substantially straight wire anode spaced from and disposed generally parallel to said offset portion while extending approximately coaxial of said bushing from an end portion connected to that part of the support adjacent said bushing to its other end portion connected to the free end portion of said support.

References Cited in the file of this patent UNITED STATES PATENTS 1,846,765 Semenitz Feb. 23, 1932 2,128,331 Schlotter Aug. 30, 1938 2,752,308 Andrus June 26, 1956 2,863,819 Preiser Dec. 9, 1958 2,908,623 'Doring Oct. 13, 1959 FOREIGN PATENTS 665,313 France May 6, 1929 657,392 Great Britain Sept. 19, 1951

Claims (2)

1. AN ELECTRICAL PROTECTIVE DEVICE FOR THE PREVENTION OF CORROSION IN HOT WATER HEATERS AND ADAPTED TO BE REMOVABLY SECURED IN A THREADED OPENING IN AN ELECTRICALLY GROUNDED HOT WATER HEATER TANK, COMPRISING A BUSHING THREADED TO FIT SUCH THREADED OPENING IN THE TANK WALL; AN ANODE SECURED TO SUCH BUSHING AND ADAPTED TO THE TANK; A CASING MOUNTED ON THE BUSHING AND ADAPTED TO LIE OUTSIDE THE TANK; A HALF WAVE RECTIFIER AND A RESISTOR WITHIN THE CASING BOTH CONNECTED IN SERIES WITH THE ANODE; AND A CONDUCTOR FROM SAID RESISTOR TO THE EXTERIOR OF THE CASING.

5. IN COMBINATION WITH A METAL HOT WATER HEATER TANK HAVING A THREADED OPENING, A METAL BUSHING THREADED INTO SAID OPENING, AN INSULATING ELECTRODE SUPPORT CARRIED BY SAID BUSHING, WITH A PORTION OFFSET FROM THE AXIS THEREOF AND EXTENDING THEREFROM INTO SAID TANK FOR A DISTANCE MORE THAN HALFWAY FROM THE BUSHING TO THE OPPOSITE WALL OF SAID TANK, AND A SUBSTANTIALLY STRAIGHT WIRE ANODE SPACED FROM AND DISPOSED GENERALLY PARALLEL TO SAID OFFSET PORTION WHILE EXTENDING APPROXIMATELY COAXIAL OF SAID BUSHING FROM AN END PORTION CONNECTED TO THAT PART OF THE SUPPORT ADJACENT SAID BUSHING TO ITS OTHER END PORTION CONNECTED TO THE FREE END PORTION OF SAID SUPPORT.

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