US3037925A - Cathodically protected structure and method of making same - Google Patents

Description

INVENTORS. HARRY P. BONCHER BY WAYNE A. DER/NGER W p /m Attorneys H. P. BONCHER ETAL CATHODICALLY PROTECTED STRUCTURE AND METHOD OF MAKING SAME Filed April 9, 1958 I 5 H 4 m a L MZE W F v 2 a W w U n H m n m m H 1? H in 2 June 5, 1962 23 F I G. 3.

United States Patent 3,037,925 CATHODICALLY PROTECTED STRUCTURE AND METHOD OF MAKING SAME Harry P. Boncher, and Wayne A. Deringer, Milwaukee, Wis., assignors to A. 0. Smith Corporation, Milwaukee,

Wis., a corporation of New York Filed Apr. 9, 1958, Ser. No. 727,350 8 Claims. (Cl. 204-197) This invention relates to a cathodically protected structure employing an anode secured to the wall of the structure to establish cathodic protection of the structure and to a method of welding the anode to the structure. The welding method is particularly adapted for attaching a plurality of distributed anodes in a glasslined hot water heater tank and the like.

Water heater tanks and the like which are made of steel or other similar metal and contain water are subject to corrosion by the free oxygen in the water.

It is known to provide the inner surface of hot water tanks made of steel or other similar metal with a glass coating which is not subject to corrosive attack by oxygen. Further, because it is economically impossible to obtain a perfect glass coating, cathodic protection has been employed to protect the metal of the tank at pinholes and the like which are present in economically applied glass coatings.

The conventional cathodic protection apparatus ineludes an anode of magnesium or the like, which has a higher position in the electromotive series than the steel tanks to which the anode is secured in electrical connection. The anode extends into the water or other oxygen bearing fluid in the tank, and an electrolytic current is established by the difference in the electrical potential of the anode and the tank wall. The current establishes a protective hydrogen barrier at the tank wall which prevents the oxygen from reaching the metal surface of the tank and thereby substantially prevents any corrosion of the tank wall.

Presently, anodes are attached within openings in the tank wall by suitable spud connections into which the anodes are threaded. The anode connection is normally made at the upper end of the tank and the anode extends downwardly to the lower portion of the tank.

The spud type attachment is relatively expensive, and difficult problems are presented in applying a glass coating thereto in glass lined hot water heaters and the like.

The present invention provides an anode and a method to weld the anode to the inner surface of a steel tank or the like without auxiliary openings and connectors. The method of attachment is inexpensive and allows the use of a plurality of short, stubby anodes secured in spaced relation to each other within the tank to provide a distributed cathodic protection system.

The drawing furnished herewith illustrates the best mode presently contemplated by the inventor for carrying out the invention.

In the drawing,

FIGURE 1 is a vertical section of a water heater tank, including anodes attached in accordance with the present invention;

FIGURE 2 is an enlarged, fragmentary perspective view of a portion of FIGURE 1, with the anode components shown in exploded relation to the heater tank;

FIGURE 3 is a fragmentary sectional view, with the anode components located in position for welding;

FIGURE 4 is a view similar to FIGURE 3, with an are established between the anode and the tank; and

FIGURE 5 is an enlarged fragmentary view, in section, showing an attached anode.

Referring to the drawings, and particularly to FIGURE 1 thereof, a water heater tank is shown including a cy- 3,037,925 Patented June 5, 1962 ice lindrical steel body portion 1 having an upper cup-shaped head 2 and a lower cup-shaped head 3 disposed within the opposite ends of the body portion 1. The heads 2 and 3 open outwardly and are welded or otherwise secured to the body portion 1 to provide a water-tight tank. The body and the attached heads 2 and 3 are disposed within a mass of insulation 4 to reduce heat loss from the tank. A decorative enclosure 5 surrounds the insulation to support the insulation and provide an attractive Water heater assembly.

A water inlet 6 is secured within an opening in the upper head 2 by a spud 7. The water inlet extends outwardly through the insulation 4 and the casing 5 to a suitable source of water, not shown, and also interiorly the inlet 6 extends downwardly to the lower port-ion of the tank 1 to supply relatively cold water to the lower portion of the tank.

A water outlet 8 is secured by a threaded spud 9 within an opening in the upper head 2. The water outlet extends outwardly through the insulation 4 and the decorative enclosure 5 to a water distribution system, not shown.

The water heater tank, comprising the body portion 1 and the heads 2 and 3, is generally made of a suitable steel which is therefore subject to corrosion by the free oxygen existing in water 10 which continuously is contained within the tank.

The water It) is heated by any suitable means such as an electrical heating element 11 which surrounds the body portion 1 to increase the temperature of the water as desired.

The corrosivity of water increases substantially with temperature and consequently the problem of corrosion prevention is substantially increased in hot water heater tanks and the like.

A glass lining 12 completely covers the inner surfaces of the body portion 1 and the heads 2 and 3 to protect the tank from corrosion. However, as previously noted, it is practically and economically not feasible to provide a perfect continuous coating, and small pinholes 13 and the like are present.

To protect such exposed portions 13 of the water heater tank, a pair of cylindrical magnesium anodes 14 and 15 are secured in electrical connection to the respective upper and lower heads 2 and 3 of the water heater tank by corresponding steel anode core rods 16 and 17, extending outwardly from one end thereof.

The core rods extend substantially coextensive with the corresponding anodes and are resistance welded to the inner surfaces of the heads 2 and 3 in the following manner in accordance with a preferred embodiment of the invention.

Referring to FIGURES 2 and 3, the glass lining 12 on the lower head 3 is provided with an opening 18 which is larger than the diameter of the adjacent core rod 17, but somewhat smaller than the diameter of the anode 15. The core rod 17 extends outwardly from the anode 15 into engagement with the tank head 3. The rod is welded to the tank head 2 by mash or stud welding in the following manner.

Substantially all traces of magnesium or other anode material on the extended end of the rod 17 are removed to provide a good bond between the rod 17 and the head 3. As shown in FIGURES 3 and 4, the end of the rod 17 is first placed in engagement with the metal of the head 3 and a welding current is applied from any suitable source, not shown. The rod 17 is then withdrawn, normally about of an inch, from the head 3 by any suitable means, not shown, to establish a predetermined are 19. v

The heat of the are 19 melts the end of the core rod 17 and the inner surface of the head 3 and establishes a puddle of molten metal. After a predetermined period the welding current is discontinued to break the arc 19 and the end of the rod 17 is then forced into the molten puddle. The molten metal rapidly solidifies and bonds to the rod 17 and head 3 to secure the anode 15 to the head 3 as shown in FIGURES l and 5.

Referring to FIGURES 2-4, the rod 17 is provided with a tapered end 20 to establish a relatively blunt point engagement with the head 3. If this is not done, when the rod 17 is first brought into engagement with the head 3, only one portion of the outer edge may contact the head and an erratic arc action results.

A recess 21 is provided in the anode 15 immediately adjacent the rod 17 to receive a ferrule 22 of porcela n or the like. The ferrule 22 encircles the rod 17 and is provided with a lower serrated edge 23 which is adapted to be held in engagement with the head 3. An integral reduced extension 24 of the ferrule 22 partially closes the upper end of the ferrule to substantially enclose the are 19. The ferrule 22 prevents molten metal from being blown out under the action of the arc and the rapid movement of the end of rod 17 into the molten metal. If the metal is allowed to freely escape, insufiicient metal will be present to secure a good bond to the rod 17.

The ferrule 22 also shields the are 19 to prevent oxidation of the molten metal and concentrates the heat of the arc into the head 3.

A small coil spring 25 is disposed between the base of the recess 21 and the upper outer surface of ferrule 22 to hold the ferrule in place during the welding operation. The small spring 25 should be of a relatively light construction to avoid placing any undue force on the ferrule opposing the movement of the anode rod 17 into the molten tank head 3.

The serrated edge 23 allows the arc gases to freely escape, but prevents the molten metal from escaping except for a very small amount of arc spatter which will escape between the spaces of the serrations of edge 23.

As shown most clearly in FIGURE 5, the wall end of the anode 15 is slightly spaced from the glass coating 12 after the welding operation, as at 26, to prevent interference with the complete movement of the extended end of rod 17 into the molten puddle during the welding operation. The spacing 26 also allows welding spatter to pass freely therebetween and therefore eliminates possible interference with the movement of the rod into the weld puddle.

The end of the anode 15 is also provided with a conically tapered surface 27 joining a flat end surface 28 and the side wall of the recess 21. The enlarged recess thus formed immediately adjacent the weld area accommodates any are spatter which cannot pass through the space 26.

If the final spacing 26 is sufficiently great to allow all possible spatter to move freely out of the welding area, the tapered surface 27 can be eliminated. In the normal operation, however, a certain amount of spatter will be of such a diameter that the tapered surface 27 is highly desirable, if not necessary.

In summary, the anode 15, ferrule 22 and spring 25 are located over an opening 18 with the tapered end 20 of rod 17 disposed in engagement with the head 3. The current is turned on and the anode 15 withdrawn to establish are 19. The spring 25 maintains the ferrule 22 in shielding relation over the are 19. After a predetermined period, the welding current is discontinued and the end of rod 17 forced into the molten puddle which solidifies forming a weld 29, shown in FIG. 5, which rigidly secured the core rod 17 to the tank head 3.

The opposite anode 14 is welded to head 2 by welding core rod 16 to the head 2, as described above.

In operation, the anodes 14 and 15 establish an electrolytic current flow from the corresponding anode to exposed portions 13 of the tank wall which arise due to defects in the glass coating 12. The electrolytic current positively prevents attack by the free oxygen in the water.

The method can be employed regardless of the length of the anode. However, a relatively long anode such as presently employed in hot water heaters has a relatively long moment arm about the point of securement to the tank wall or the like and the anode may tend to break away from the tank during shipment and handling. To eliminate the necessity of providing an auxiliary supporting means, the anodes 14 and 15 are therefore preferably relatively stubby anodes, having a length to diameter ratio preferably Within the range of 5 to 10 for a conventional water heater assembly.

In a water heater tank and the like, the total electrolytic current includes effective currents flowing from the anode to the tank wall and local cell currents which circulate on the anode surface. Only the effective current which is determined by the area of the tank exposed, acts to cathodically protect the structure. The local cell currents are wasted energy which destroy the anode. The local cell currents are proportional to the anode surface in the tank.

A single, long anode longitudinally supported in the water heater tank is first destroyed at the ends adjacent the greater area of tank surface due to the greater effective current concentration. However, the local cell currents continuously erode the entire anode including the central portion which is ineffective until the end portions are substantially destroyed.

By employing distributed, stubby anodes, an equally distributed effective current is obtained with a substantially reduced surface area and resultant decreased local cell currents. The effective current is then a greater proportion of the total current and the efficiency is correspondingly increased.

The present anode construction is adapted to resistance welding and particularly stud welding of an anode to the tank wall by a simple, rapid and reliable method without auxiliary spuds and the like. Because the method and apparatus is generally inexpensive, a plurality of relatively small anodes can be economically employed and distributed throughout the inner portion of the tank to provide a distributed cathodic protection and thereby insure protection of all surfaces.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

1. An anode to be welded to the surface of a metal tank or the like comprising an elongated body of material having a higher position in the electromotive series than the metal of the tank and having an axial recess formed in one end thereof, and a steel core axially secured within the body and in electrical connection therewith and having an end extending within the recess and projecting a substantial distance beyond said end of the body, said core having a substantially smaller diameter than the diameter of said recess to provide a generally annular clearance between the core and the wall of the recess with said clearance adapted to receive a ferrule during welding.

2. An anode adapted to be flash welded to the surface of a ferrous tank or the like comprising an elongated body having an axial recess formed in one end thereof, and a steel core axially secured within the body and in electrical connection therewith and having an end extending within the recess and projecting a substantial distance beyond said recessed end of the body, said core having a substantially smaller diameter than the diameter of said recess to provide a generally annular clearance between the core and the wall of the recess with said clearance adapted to receive a ferrule during welding, and the projecting end of the core having a generally tapered tip to improve the arcing characteristics when the core is welded to the tank.

3. An anode adapted to be flash welded to the surface of a ferrous tank or the like comprising an elongated body having an axial recess formed in one end thereof and having a generally flat transverse end surface disposed radially outward of the recess and having a tapered surface extending between the end surface and the recess, and a steel core axially secured within the body and in electrical connection therewith and having an end extending within the recess and projecting a substantial distance beyond the recessed end of the body, said core having a substantially smaller diameter than the diameter of said recess to provide a generally annular clearance between the core and the wall of the recess with said clearance adapted to receive a ferrule during welding, and said end of the core having a generally tapered tip to improve the arcing characteristics when the core is welded to the tank.

4. An anode to be stud welded to the surface of a ferrous tank or the like comprising an elongated magnesium body having an axial recess formed in one end thereof, and a steel core axially secured within the body and having an end extending within the recess and projecting a sufficient distance beyond said end of the body to permit stud welding of the core to the ferrous tank without effecting direct engagement of the body to the tank, said core having a substantially smaller diameter than the diameter of said recess to provide a generally annular clearance between the core and the wall of the recess with said clearance adapted to receive and contain a ferrule during and after welding and said end of the core having a generally pointed tip to improve the arcing characteristics when the core is welded to the tank.

5. A cathodically protected structure, comprising a metallic body adapted to have a surface thereof exposed to a corrosive fluid medium, a glass coating for said surface, an anode body having a metallic core embedded axially thereof and having a recess circumferentially of the end of the core facing said metallic body, a weld between the end of said core and said metallic body through an opening in said coating, and a porcelain ferrule in said recess and surrounding said weld and the exposed end portion of said core.

6. A cathodically protected structure comprising a metallic tank to contain a fluid, a glass coating covering a surface of the tank to be protected from corrosion by the contained fluid and having a plurality of spaced open ings therein to expose spaced portions of the tank through the openings, at corresponding plurality of stubby anodes each including a body of material having a higher position in the electromotive series of metals than the metal of the tank and a steel core axially secured within said body, each of said bodies having an axial recess formed in one end and the corresponding core extending within the recess and having the outer end thereof projecting beyond said recessed end of the body, said cores having a substantially smaller diameter than the diameter of said recesses to provide a generally annular clearance between each core and the wall of each recess, a plurality of ceramic ferrules disposed one each within each clearance and around the core and disposed in contact with the tank surface exposed through the opening in the glass coating, and welds joining the outer end of each core to the tank surface exposed through the corresponding opening in said glass coating.

7. A cathodically protected structure comprising a tank to contain a fiuid, a glass coating covering a surface of the tank to be protected from corrosion by the contained fluid and having an opening therein to expose a portion of the tank through the opening, an anode including a magnesium body and a steel core axially secured within said body, said body having an axial recess formed in one end and the core extending within the recess and having the outer end thereof projecting beyond said recessed end of the body, said core having a substantially smaller diameter than the diameter of said recess to provide a generally annular clearance between the core and the wall of the recess, a ceramic ferrule disposed within the clearance and around the core and disposed in contact with the tank surface exposed through the opening in the glass coating, resilient means disposed within the recess for urging the ferrule outwardly toward the tank surface, and a weld joining the outer end of the core to the tank surface exposed through the opening in said glass coating.

8. A eathodically protected structure comprising a metallic tank to contain a fluid, a glass coating covering a surface of the tank to be protected from corrosion by the contained fluid and having an opening therein to expose a portion of the tank through the opening, an anode including a magnesium body having a greater diameter than the opening and having a steel core axially secured within said body, said body having an axial recess formed in one end and the core extending within the recess and having the outer end thereof projecting beyond said end of the body, said core having a substantially smaller diameter than the diameter of said recess to provide a generally annular clearance between the core and the wall of the recess, a ceramic ferrule disposed within the clearance and around the core and disposed in contact with the tank surface exposed through the opening in the glass coating, a Weld joining the outer end of the core to the tank surface exposed through the opening in said glass coating, and a space between the glass coating and the adjacent end of the magnesium body.

References Cited in the file of this patent UNITED STATES PATENTS 2,268,416 Nelson Dec. 30, 1941 2,416,204 Nelson Feb. 18, 1947 2,486,871 Osterheld Nov. 1, 1949 2,762,771 Preiser Sept. 11, 1956 2,775,685 Webster Dec. 25, 1956 2,805,987 Thorn Sept. 10, 1957 FOREIGN PATENTS 527,360 Belgium Apr. 15, 1954 489,984 Canada Jan. 27, 1953 520,285 Canada Jan. 3, 1956

Claims (1)

1. AN ANODE TO BE WELDED TO THE SURFACE OF A METAL TANK OR THE LIKE COMPRISING AN ELONGATED BODY OF MATERIAL HAVING A HIGHER POSITION IN THE ELECTROMOTIVE SERIES THAN THE METAL OF THE TANK AND HAVING AN AXIAL RECESS FORMED IN ONE END THEREOF, AND A STEEL CORE AXIALLY SECURED WITHIN THE BODY AND IN ELECTRICAL CONNECTION THEREWITH AND HAVING AN END EXTENDING WITHIN THE RECESS AND PROJECTING A SUBSTANTIAL DISTANCE BEYOND SAID END OF THE BODY, SAID CORE HAVING A SUBSTANTIALLY SMALLER DIAMETER THAN THE DIAMETER OF SAID RECESS JTO PROVIDE A GENERALLY ANNULAR CLEARANCE BETWEEN THE CORE AND THE WALL OF THE RECESS WITH SAID CLEARANCE ADAPTED TO RECEIVE A FERRULE DURING WELDING.

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