US3022243A

US3022243A - Anode assembly for cathodic protection systems

Info

Publication number: US3022243A
Application number: US809565A
Authority: US
Inventors: Edward P Anderson
Original assignee: Engelhard Industries Inc
Current assignee: Engelhard Industries Inc
Priority date: 1959-04-28
Filing date: 1959-04-28
Publication date: 1962-02-20
Anticipated expiration: 1979-02-20
Also published as: DE1209845B; NL127738C; BE590158A; NL250897A

Description

Feb. 20, 1962 E. P. ANDERSON 3,022,243

ANODE ASSEMBLY FOR CATHODIC PROTECTION SYSTEMS Filed April 28, 1959 .L. I v 8 M 16 20 Z2 Z1. 19

CATHODIC PROTECTION POWER SUPPLY INVENTOR. EDWARD P. ANDERSON BY (A [Llgmzzr ATTORNEYS United States Patent Oiiice 3,922,243 Patented Feb. 20, 1962 ANODE ASSEMBLY FOR CATHODIC PRO- TECTION SYSTEMS Edward P. Anderson, Livingston, N.J., assignor, by mesne assignments, to Engelhard Industries, Inc., Newark, N.J., a corporation of Delaware Filed Apr. 28, 1959, Ser. No. 809,565 3 Claims. (Cl. 204196) This invention relates to an anode assembly for cathodic protection systems, and more specifically, for such systems installed on ships.

It is well known that much of the rust and corrosion which attacks the metal hulls, particularly of oceangoing ships, is the result of local electrolytic action. This action may be prevented by the use of cathodic protection systems in which direct current is supplied between the hull of the ship as a cathode and generally a number of anodes in contact with the surrounding water and lo- 'cated near the hull. Usually, such adodes are mounted in openings in the hull and electrical lead-in conductors are sealed through the hull openings by means of stuffing box assemblies, so that the protective current may be fed from a power supply inside the ship to the anodes.

In cathodic protection systems, the anode is therefore the only element which is mounted on the outside of the ship and in contact with the water. Under the pre vailing severe circumstances, anodes must meet special requirements. Since they are subject to chemical attack by the electrolytic decomposition products of sea water, the surfaces must be corrosion resistant. precious metals are the appropriate material for the current-carrying anodic surfaces, and platinum or a platinum alloy is generally used. In practice, either thin foils of thicknesses in the range of about 0.005 to 0.010 inch or a base metal body covered with precious metal form the metallic portion of the anode structure.

In addition to chemical attack, anodes are subject to mechanical damages. These include erosion by particles suspended in the water and metal fatigue due to continu- Therefore, a

ous vibrations produced by the extremely high turbulence in the immediate vicinity of the anode. other factors contribute to" deteriorate precious metal coatings after a certain period of time and, subsequently, the base metal corrodes rapidly.

In the case of precious metal foils, there is no coating that may be destroyed, and therefore such foils are preferred over coated metal structures. However, another difficulty occurs at this point. It is well known that metal cannot be bonded to most of the insulating plastic materials which include organic high polymerization products, such as polytetrafluoroethylene. This material is preferred for cathodic protection anode supports, on account of its insulating properties and its mechanical strength, as well as its resistance to chemical attack. The above-mentioned coated base metal anodes are rigid. Usually made in the shape of heavy wires, bands, or the like, they can be mounted comparatively firmly by partially imbedding them in their insulating supports. However, difliculties are encountered with foils. Generally, they are imbedded in the plastic support along a marginal area while the inside of the central areas is exposed to the water. The backside contacts a fiat surface of the support. Since this comparatively large area cannot efficiently be bonded to the support, and on account of the above-mentioned turbulences in the immediate environment, the foil is subject to slight but continuous vibrations which finally lead to its deterioration. At an earlier stage, with the foil still in good condition, the connections to the lead-in wire may be damaged, thereby rendering the anode completely ineffective.

It is therefore the principal object of this invention to All these and increase the resistance to mechanical failure of anode assemblies for cathodic protection systems. More specifically, the object of the invention is to provide an anode using a precious metal foil mounted in a plastic support in such a manner that it withstands the stress resulting from vibrations due to turbulence in the surrounding water or of any other origin.

As an illustrative embodiment of the invention, an anode assembly for cathodic protection of ships includes a plate-shaped support, a disc of a precious metal foil in contact with one surface of the support and a cupshaped recess formed in the center of the disc. The recess has a plurality of perforations therethrough and is imbedded in the support so that the plastic material fills the cup and continues through the perforations to form a bond with the remainder of the plastic support. Therefore, in accordance with an important feature of this invention, an anode assembly comprises a thin plate of corrosion resistant metal which has a substantially flat main portion and at least one area bent out of its plane to form a recess. The recessed area has a plurality of perforations therethrough and is imbedded in an insulating support so that the recess is filled with plastic material which is bonded to the remainder of the support through the perforations. The area of the metal plate surrounding the recess lies flat against the plastic support and may be retained in this position by imbedding a circumferential area, as described below.

In accordance with another feature of the invention, such a cup-shaped recess is formed at the location, usually in the center of the plate, where connection to a power supply is made, e.g. by welding the bottom portion of the recess in the anode plate to a lead-in conductor extending therefrom and through the support. Since the recess is entirely imbedded, the weld is protected against vibrations or other mechanical or chemical influences so that failure of this connection is precluded.

'It has been found that the combined action of imbedding with the reinforcing action imparted to the foil by providing at least one recessed portion in the foil results, in ananode which remains practically vibration.- free even under continuing severe operating conditions.

The invention will. be further-illustrated by reference to the/accompanying drawing which is asectional'view of one embodiment of the invention.

The hull '6 of a ship has secured thereto an insulating plastic support 8 having essentially the shape of a mush room. Thus, the support 8 includes a flat circular plate 10 and a cylindrical stem 12 attached to its centerj A connector pin 14 is axially embedded through the stem 12 and the plate 10. 'Iheside of the supp'ortplate 10 with the stem 12 thereon facesthe hull 6,-whi1e the opposite side carries a corrosion resistant'disc or thin'plate 16, generally a circular platinum sheet or a similar sheet of a platinum alloy. Good results have been obtained when using an alloy of about percent by weight of platinum with about 20 percent by weight of palladium. The thickness of the disc may be about 0.005 inch. A comparatively narrow circumferential area 18 of the disc 16 is bent out of the plane of the disc and the rim so obtained is imbedded in the plate 10 of the support to provide a firm grip all around the circumference of the anode disc 16.

In accordance with the embodiment of the invention shown in the drawing, the disc 16 has one additional area bent out of its plane to form a cup-shaped recess with an annular wall 20 and a bottom 22. The bottom portion 22 is welded to a flange 24 which, in turn, forms part of the connector pin 14. The pin 14 provides electrical connection to the positive terminal of a power supply 26, suitably by means of a female connector 28.

The cup-shaped recess is filled with plastic material, preferably the same as that from which the support 8 is formed, suitably polytetrafluoroethylene, or any other similar material capable to form a bond with the material 7 of the support 8. The perforations 25 through the wall portion permitbonding of the plastic material inside the recess with that outside the recess. Therplastic'material in the recess is shown broken away in the drawing to facilitate illustration of the perforations 25. Since the perforations are radially arranged through the wall 20, the recessed area" is anchored in the support to as described above, in the hull, the latter is provided with bores and'compression seals or stufling boxes secured in the bores. An example of one suitable seal is illustrated in the drawing. The seal includes a tubular sleeve with an outer thread which is welded into a bore through a the hull. An annular jam nut 32engagesthe threaded sleeve for compressing a packing 34. Thereby a tight seal between the stem 12 and the inner surface of the sleeve 30 is obtained. The aperture through the jam nut 32 leaves sufficient clearance for the protruding connector pin 14 and the female connector 28 engaging its end portion. If desired, the seal described may be re- 7 placed by any other suitable structure such as the assembly disclosed in co-pending application Serial No. 682,- 336, filed September 6, 1957, of Arthur J. Zwanzig. An automatically adjusted power supply which may be used is set forth in co-pending application Serial No. 732,275, filed May 1, 1958, of Eugene M. Fry.

The anode assembly has. been described above as including one single, centrally arranged perforated recess, of which the bottom portion 22 is connected to the pin 14. While good results are obtained with thisr arrangea ment, in the case of larger anode discs a plurality of I recesses may be provided in any desired configuration, for example in circular or in radial arrangements. Rectangular anode foils may also be secured to a support by such arrangements.

It will be obvious that many more modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. r a

What is. claimed is:

1. An anode assembly comprising a substantially plateshaped insulating plastic support, a circular thin plate of corrosion resistant metal serving as the anode and having one surface in contact with one circular surface of said support, a circumferential area and a central circular area'of said thin metal plate being bent out. of the plane of the plate to form a rim and a cup-shaped recess,

respectively, said recess having a bottom portion and a substantially annular side wall, a plurality of perforations through said side wall, said recess and said rim being imbedded in the insulating support, the recess being filled with plastic material, which filling material forms a bond with the remainder of the support through said perforations, electrical connecting means secured to the bottom portion of the cup-shaped recess and extending through the insulating support to protrude therefrom at the other surface.

2. An anode assembly comprising an insulating plastic support, a corrosion resistant metal'sheet serving as the anode mounted on said support and'in contact therewith,

the sheet having a circumferential area and at least one portion of its inner area bent out of its plane, the circumferential area forming a rim and the inner area forming a cup-shaped recess, the recess having at least one perforation therethrough, and both the rim and the recess being imbedded in the insulating support, the recess being filled with plastic material, which filling material forms a bond with the remainder of the support through said perforation.

3. In combination, a hull of a ship, a cathodic protection power supply'having its negative terminal connected to the hull, an anode assembly including a substantially mushroom-shaped insulating plastic support having a fiat portion and a cylindrical stem portion, a circular thin plate of corrosion resistant metal serving as the anode and having one surface in contact with the surface of the flat support portion opposite the stem portion, a circumferential area and a central circular area of said thin metal plate being bent out of the plane of the plate to form a rim and a cup-shaped recess, respectively, said recess having a bottom portion and a substantialy annular side wall, a plu rality of perforations through said side wall, said recess and said rim being imbedded in the insulating support, the recess being filled with plastic material which filling material forms a bond with the remainder of the support through said perforations, a connector pinsecured to the bottom portion of the cup-shaped recess and extending through the stem portion of the support to protrude therefrom, means for connecting the protruding pin portion to the positive terminal of the cathodic protection system, the hull having an aperture therethrough,'and compression sealing means mounted insaid aperture and engaging the stem portion of said insulating support to secure the anode assembly to the hull.

References Cited in the file of this patent UNITED STATES PATENTS 393,072 Marquand Nov. 20, 1888 799,061 Kellner Sept.. 12, 1905 994,405 James June 6, 1911 1,302,959 Page May 6, 1919 1,788,904 Zdanski Jan. 13, 1931 1,900,011 Durham Mar. 7, 1933 2,910,419 Preiser et a1. Oct. 27, 1959 2,910,420 Preiser Oct. 27, 1959 FOREIGN PATENTS 4,251 Great Britain June 13, 1912 of 1912 a

Claims

1. AN ANODE ASSEMBLY COMPRISING A SUBSTANTIALLY PLATESHAPED INSULATING PLASTIC SUPPORT, A CIRCULAR THIN PLATE OF CORROSION RESISTANT METAL SERVING AS THE ANODE AND HAVING ONE SURFACE, IN CONTACT WITH ONE CIRCULAR SURFACE OF SAID SUPPORT, A CIRCUMFERENTIAL AREA AND A CENTRAL CIRCULAR AREA OF SAID THIN METAL PLATE BEING BENT OUT OF THE PLANE OF THE PLATE TO FORM A RIM AND A CUP-SHAPED RECESS, RESPECTIVELY, SAID RECESS HAVING A BOTTOM PORTION AND A SUBSTANTIALLY ANNULAR SIDE WALL, A PLURALITY OF PERFORATIONS THROUGH SAID SIDE WALL, SAID RECESS AND SAID RIM BEING IMBEDDED IN THE INSULATING SUPPORT, THE RECESS BEING FILLED WITH PLATIC MATERIAL, WHICH FILLING MATERIAL FORM A BOND WITH THE REMAINDER OF THE SUPPORT THROUGH SAID PERFORATIONS, ELECTRICAL CONNECTING MEANS SECURED TO THE BOTTOM PORTIONS OF THE CUP-SHAPED RECESS AND EXTENDING THROUGH THE INSULATING SUPPORT TO PROTRUDE THEREFROM AT THE OTHER SURFACE.