US3408280A

US3408280A - Anode-assembly for cathodic protection systems

Info

Publication number: US3408280A
Application number: US377632A
Authority: US
Inventors: Herman S Preiser
Original assignee: Hydronautics
Current assignee: Hydronautics Inc
Priority date: 1964-06-24
Filing date: 1964-06-24
Publication date: 1968-10-29
Anticipated expiration: 1985-10-29

Description

Oct. 29, 1968 H. s. PREISER 3,408,280

ANODE-ASSEMBLY FOR CATHODIC PROTECTYON SYSTEMS Filed June 24, 1964 2 Sheets-Sheet 1 id V Y 71 Source INVENTOR ATTORNEY Oct. 29, 1968 H. s. PREISER 3,408,280

' ANODE-ASSEMBLY FOR CATHODIC PROTECTION SYSTEMS Filed June 24, 1964 2 Sheets-Sheet 2 INVENTOR j ermzz if/wiser,

ATTORNEY United States Patent 3,408,280 ANODE-ASSEMBLY FOR CATHODIC PROTECTION SYSTEMS Herman S. Preiser, Ellicott City, Md., assignor to Hydronautics, Incorporated, Laurel, Md., a corporation of Maryland Filed June 24, 1964, Ser. No. 377,632 17 Claims. (Cl. 204-196) ABSTRACT OF THE DISCLOSURE An anode and anode assembly for cathodic protection of a metal having inner and outer skins, the anode being a dome shaped valve metal wall secured to the larger end of an inwardly tapered valve metal connector rod, the rod extending through an opening in the skin and an inwardly tapered tube secured to the skin, insulating means between the rod and tube and co-operating securing and insulatin means on the smaller end of rod watertightly jamming the rod in the tube and insulating it therefrom.

This invention relates to improvements in anode-structures or -assemblies for cathodic protection systems, and more particularly relates to such assemblies for an impressed current system used to protect the outer surface of the metallic hull of a ship against corrosion and deterioration; the term ship being used broadly as denoting any vessel or the equivalent using a cathodic protection system.

In impressed current cathodic protection systems, metallic anodes are used which are connected to an electrical power source so as to be generally electrically positive with respect to the protected metallic structure. Where the metallic structure to be protected is a sea-going ship, a preferred form of cathodic protection utilizes a plurality of anodes watertightly mounted at a plurality of spaced underwater points on the outside of the hull of the ship in such a manner that the anodes can be connected to an electric power source inside the hull. To this end, anode-structures or anode-assemblies are provided of which the anodes form a part.

A prime object of the invention is to provide a simple and rugged anode-assembly of a type described which has a minimum of parts, is low in cost, and is easy to assemble, and when assembled has an improved watertight connection to the hull.

A further object of the invention is to provide an improved anode-assembly of a type described for cathodic protection of a ship, the assembly having an anode'which is readily mounted on the outside of the ships hull below the waterline while the ship either is in drydock or is floatin in the sea; by sea meaning any suitable body of water in which the ship floats. The mounting and also demounting of the anode can be effected with common hand tools. Consequently, repair or replacement of the anode for any reason can also be made under water by divers without the need for taking the ship to a drydock.

A further feature of the invention resides in the novel inert anode and in the connecting rod thereto preferred for the anode-assembly of this invention, the anode being electrolytically long-lived, comparatively inexpensive and light in weight, and well adapted for use in an impressed current cathodic protection systempand the connecting rod providing a simple one-piece member for conducting electric power directly to the anode.

, Other objects, features and innovations of the invention will become apparent from the following description of a preferred embodiment thereof which is to be considered in conjunction with the accompanying drawings in which:

FIG. 1 is essentially a longitudinal or axial cross-sectional view, to scale, except as otherwise noted, of a cathodic-protection anode-assembly in accordance with the invention;

FIG. 2 is a view of a central connecting rod of the anode-assembly;

FIG. 3 is a view of a curved metal anode of the anodeassembly, as viewed from inboard of the hull, looking outboard;

FIG. 4 is a cross-sectional view of FIG. 3; and

FIG. 5 is an axial cross-sectional view of a modified form of nutlocking pin utilized in the anode-assembly.

Referring to the drawings, the reference numeral 6. represents a portion of the metallic skin of a structure provided with a cathodic protection system, and specifically represents a portion of the hull of the ship. The hull 6 is provided with numerous circular openings or holes for anode-assemblies or -structures of the system, one such opening and anode-assembly being shown in FIG. 1.

Briefly, an anode-assembly in accordance with the invention comprises a cylindrical steel stufiing tube 8 watertightly secured to the hull at the periphery of said opening. The tube 8 has a tapered axial or longitudinal bore or hole 10 that insulatedly and watertightly receives a one-piece connecting rod 12 that passes through the tube and is insulated therefrom. An anode 14, also insulated from the hull 6 and tube 8, is secured to the outer end of rod 12, and a lug 16 is secured to the inner end of the rod. The lug 16 is part of a conducting circuit connected to one terminal of a suitable electric power source, the other terminal of which is connected to the hull.

The tube 8 is firmly and watertightly secured to the hull by

welds

18 and 20, preferably with the outer end surface of the tube substantially flush with the out side of the hull. The tube extends inward of the ship with its hole 10 tapered convergingly inboard. In a specific embodiment of the invention, a stufiing tube such as tube 8 had an overall length of five inches.

The connecting rod 12 is better shown in FIG. 2. It comprises a tapered main body portion 22; and at its ends it comprises an outer cylindrical threaded stub portion 24 that extends axially from the relatively thicker outer end of the body portion, and an inner cylindrical threaded stub portion 26 that extends axially from the relatively thicker inner end of the body portion. The main body portion 22 is tapered in the manner of the tapered hole 10 of stuffing tube 8, except for a short portion 28 comprising the outer end of the main body portion. This portion 28 is cylindrical so as to better fit circular holes of the same size, for clearance purposes primarily.

When the connecting rod 12 is jammed in the stufling tube 8, the threaded

stubs

24 and 26 and the end portion 28 of the rod extend beyond the end faces of the tube as shown in FIG. 1. Note that the junction of inner stub 26 and main portion 22 lies inside bore or hole 10 of tube 8.

For making this fit between rod 12 and tube 8 watertight at all times, in spite of possible distortion or inaccuracies of the tapers, and at the same time insulating the rod 12 from the tube 8 and hull 6, the main body portion 22 of rod 12 is covered or jacketed with any; suitable resilient non-water-porous insulating material that provides an adhering layer or jacket 30 thereon. In the preferred embodiment, the material of the jacket 30 was non-porous machinable polyvinyl chloride. The rod 12 may be provided with a plurality of axially-spaced sandblasted for better anchoring the jacket to the rod.

For coating the rod 12 with polyvinyl chloride, the rod was first preheated to about 300 degrees F. and coated to an adequate thickness of about A, and then the combination heat-cured at about 365 degrees F. for several hours to desired hardness. The coating on the rod was then machined to form and size. In FIG. 2, the broken lines paralleling the outer lines of the body portion 22 indicate the outer surface of the finished size of the rod 12 with its outer insulating jacket 30'.

When the anode-assembly is first assembled, the jacketed rod is placed into the tube 8 from outside the ship. In view of the construction provided by this invention, however, a good degree of tolerance and misalignment is permissible in the concentricity and shapes of the coated rod 12 and the hole in tube 8. This feature is highly desirable when a weld joint is used to secure tube 8 to hull 6 because the welding may distort the tube noticeably.

The jacketed rod 12 is drawn watertightly into tube 8 by a fastening means on inner stub 26. The fastening means comprises a nut 34, a washer 36 of insulating material, preferably a rigid polyvinyl chloride, and a washer 38 of metal. The washer 36 and jacket 30 maintain the connecting rod 12 electrically insulated from the stufiing tube 8 and hull 6. The inner stub 26 is long enough to receive the power lug 16 which is held thereon in good contact with nut 34- by a second metal nut 40 screwed on the stub, which nut also serves as a lock nut for nut 34.

In an impressed current cathodic protection system, the lug 16 is usually connected to be positive with respect to the hull; and the electric power delivered to the lug 16 passes through the connecting rod 12 to the anode 14 which is a valve metal. For impressed current cathodic protection systems, in which there is a forced positive current flow from the anode into the sea and to the ships hull, the metals preferred for anodes should be long-lived while exposed in the sea. To this end, certain properties are sought in the metals, including the property of being adequately low in electrical resistance for desired current flow; and the property of being inherently inert in the sea or of being capable of developing a thin surface coating that insulates the metal against flow of current in one direction only with respect to an electrolyte but not with respect to other metal in contact therewith. In the last case it conducts in both directions. The latter metals are known as valve metals; and titanium, tantalum, and columbium are examples. These metals are comparatively costly; and the present invention seeks to provide an anode made essentially from a metal of this expensive variety with a minimum of cost but without loss of the desirable operating characteristics and strength for use as an anode on a ship.

The anode of the preferred embodiment is shown in more detail in FIGS. 3 and 4. It comprises a one-piece semi-finished casting of commercially pure-grade titanium having its exposed surface subsequently coated or plated with a thin layer 42 of platinum which may be porous. The layer is shown exaggerated in FIG. 1. As first cast, the titanium casting comprises a circular outer rim 44, a curved or dome-shaped main wall 46 having a cylindrical central well 48 with a central hole 50 in its bottom, and a plurality of radial orthogonally-related reinforcing ribs 52 that extend along the inner side of wall 46 from the rim to the well. After being cast, the casting is faced with the inboard faces of the well 48 and the rim 44 gen erally in a plane. The ribs 52, as cast, preferably have free inboard faces short of the plane so that no machining is required on them except to provide each with a flow-hole 54. The inside bottom of the well may also be spot faced to provide a good seat for a nut.

The hole 50 in well 48 is preferably of a size to just about fit around outer stub 24 of rod 12 which passes through the hole; and a threaded second hole 56 is machined in the bottom of well 48 near its periphery for receiving a nut-looking pin, subsequently described, in the nature of a set screw.

The dome-shaped main wall 46 of anode 14 preferably follows the shape of a hollow segment of a sphere or an ogive; but the dome-shaped wall obviously may be of any other shape, with a'smoothly curved streamlined shape bein preferred. This surface receives the platinum coating 42 for completing the metal anode 14.

The metal anode 14 may be said to be hollow or skeletonized, but reinforced for strength by the well 48 and ribs 52. By making the anode as described, the cost and amount of metal required to make the anode is kept at a minimum without significant sacrifice in its resistance to mechanical damage, and without significant sacrifice to the total working-surface area of the dome-shaped wall. The thicknesses of the well-walls and the dome-shaped wall should be adequate to provide low-resistance for current-flow from the connecting rod 12 to the surface of the anode. The ribs 52 aid in this respect.

The cavity in the metal anode is substantially filled with a filler 61 of any suitable comparatively inexpensive inert material in order to prevent water from being trapped in the assembly. A polyester resin filled with native chalk has been found satisfactory as well as other materials.

A gasket-like disc 62 is cemented to the filled side of the anode. The disc may be of the same material as filler 61 and, optionally, can also be sheet acrylonitrile, butadiene, polystyrene copolymer such as Royalite, or commercial sheet polyvinyl chloride, or a cast polyester resin reinforced with saturated glass-fiber mats. With some such alternate materials, the final filling of the anode-cavity and the addition of the disc are left until mounting in position on the hull. The holes 54 in ribs 52 of the anode facilitate flow of the filler in the cavity before it hardens. Excess filler is squeezed out during assembly and excess material wiped off the working outer surface of the anode.

All excess material on the anode surface is wiped off except for a covering bead at the joining edge of the metal rim of the anode. This bead, completely covering the circular rim edge, has been found to increase the life of the edges of the metal when the anode is part of a cathodic protection system operating at a maximum or near maximum voltage of about 12 volts D.C.

Also before the anode is placed in the assembly, the hull receives an insulating or dielectric shield 64 (thickness shown exaggerated in FIG. 1) and receives a gasketlike dielectric mat or cushion 65 as a seat for the anode.

The purpose of the shield 64 is to decrease the possibility of a short-circuit or low-resistance leakage path from the metal anode directly to the hull. To this end, the shield should, when feasible. extend from the rod 12 radially in all directions for a substantial distance beyond the edge of anode 14.

In some instances, as for example when the disc 62 is made relatively thick, the cushion 65 may be omitted. In general, the material for the filler 61, disc 62, and cushion 65 in the completed assembly should be resilient, waterproof, inert to sea water, acid-resistant to oxychlorides, an electrical insulator.

Polyester resins, especially when containing fillers such as for example chopped or mat fiberglass or the equivalent, are suitable. Such materials are referred to also in column 2 of U.S. Patent No. 3,101,311 of Aug. 20, 1963, to Preiser et al., and are recommended for the filler 61 and disc 62. Elastomeric materials, such asfor example neoprene, are recommended for the cushion 65.

The cushion or mat 65 has a central hole which loosely encompasses the adjacent part of rod 12; and any space in the hole may be filled with an insulating putty 66 such as silicone grease, if desired. i

For completing the anode-assembly, the anode 14 is placed on cushion 65 withouter stub 24 of connecting rod 12 extending through the hole of well 48. The extreme end of stub 24 is inward of the outer face of the anode 14; and the anode is held in place by tightening of a jam nut 68 screwed on stub 24. As the nut 68 is tightened, the anode is pressed toward the hull, and because of the anodes rigidity it tends to compress the cushion 65 and insulating shield 64 so that a watertight seal is provided. However, with valve metal in the anode, connecting rod 12, and nut 68, it is not essential for this anode seal to be watertight for the cathodic protective system to be fully and properly operative.

Tightening of the nut 68 cannot destroy the watertight joint between tube 8 and rod 12, because the nut 34 and washers 36 and 38 at the other end of the rod are already tightly against the inner end of the tube, and the insulating material of jacket 30 is in a compressed state insuring that the watertight joint will remain that way. Moreover, it is not necessary to draw the nut up to a maximum to insure locking the anode securely to the hull; and the nut 68 may even be backed up slightly where necessary to leave the second hole 56 in well 48 uncovered so as to receive a locking pin or stud 70 which prevents the nut 68 from Working loose on the stub 24. Only a slight back turning should be made so as to maintain the action of nut 68 to provide a good electrical connection between connecting rod 12 and anode 14.

The assembly is then completed by filling or plugging the remaining space in well 48 with a filler 72 of any suitable material such as for example a polyester thixotropic compound. The surface of this filler may be smoothly finished to merge into the streamlining of the anode.

The anode-assembly described is usually initially put on a ship while in drydock; and the assembly can be renovated in any way thereto. However, the structure provided permits the anode 14 or other seaside parts of the assembly to be repaired or replaced while the ship is waterborne. A diver merely removes or chips away the filler 72, removes locking pin 70, and jam nut 68 so that the anode can be pried loose. The repairs or replacement can then be made.

The locking pin 70 need not be immediately replaced; but should this step be desired a pin 74 shown in FIG. 5 should be used. The pin 74 has a through axial hole 76 through which Water in hole 56 of well 48 may escape as the pin is tightened in hole 56.

In the preferred embodiment, the connecting rod 12, the nuts 34 and 68 on its ends, the washer 38 abutting the nut 34, and the locking pin 70 (or 74) were made of commercially pure titanium. Similarly, the metal of anode 14 is also commercially pure titanium except for its outer exposed working surface which is platinized.

Obviously, modifications and variations of the preferred embodiments and parts therefor as herein described may be made without departing from the scope of the invention.

I claim:

1. An anode-assembly for a cathodic protection system for a metallic structure having a two-sided skin with an opening comprising, a tube secured to said skin at said opening and extending from a first side of the skin, said tube having a tapered hole, the taper diverging inwardly from the skin; an anode on the other side of said skin; means insulating said anode from said skin; and conducting means for conducting electricity to said anode from said first side of said skin, said conducting means including a valve metal tapered connecting rod in said tapered hole of said tube, said rod projecting from the tube at each end thereof, means insulating the rod from the interior of the tube, the anode being connected to the rod at one end, and removable means at the other end for watertightly jamming the rod in the tube and insulating it therefrom.

2. An anode-assembly for a cathodic protection system comprising: a metallic stufiing tube having a longitudinally tapered hole; a valve metal connecting rod having a tapered main body portion, said rod having a pair of end portions; an insulating jacket around said main body portion; said jacketed main body portion being tightly in said tapered hole and insulated from said'tube; the conecting rod end portion at the smaller end of the taper receiving an electricity conductor, cooperating means at said smaller end for securing the electricity conductor, watertightly jamming the rod in the tube and insulating it therefrom; an anode; and securing means conductively securing said anode to the other of said end portions.

3. An anode-assembly for a cathodic protection system for a ship having a metallic hull provided with an opening, comprising, a metallic stuffing tube watertightly secured to said hull at said opening and extending inwardly, said tube having a hole tapering convergingly inboard, a metallic connecting rod having a tapered main body portion and an inner and an outer end portion extending from the ends of said body portion, said body portion being in said tapered hole, insulation between said body portion and tube, means associated with said inner end portion watertightly jamming said body portion of said rod in said hole with said rod insulated from said tube and said hull, an anode on said hull, insulation for the inboard side of said anode, and means cooperating wtth said outer end portion of said rod holding said anode on said hull with said insulation interposed, and conductively connecting said anode to said rod.

4. An anode-assembly for a cathodic protection system for a ship having a metallic hull provided with an opening, comprising, a metallic stuffing tube watertightly secured to said hull at said opening and extending into said hull, said tube having a tapered hole converging inboardly, a titanium connecting rod having a main body portion in said hole and having an inner portion extending from said main body portion, insulation around said body portion, said inner end portion havin a threaded part protruding beyond an end face of said tube, means comprising a metallic nut on said threaded part and cooperating with said end face for jamming said rod insulatedly and watertightly in said tube, a platinized titanium anode on the outside of said hull, an insulating cushion between said anode and said outer side of said hull, and means for securing said anode on said hull with said cushion therebetween, and for conductively connecting said anode to said rod, the last said means comprising a titanium nut.

5. An anode-assembly for a cathodic protection system for a ship having a metallic hull provided with an opening, comprising, a metallic stufiing tube watertightly secured to said hull at said opening and extending inwardly, said tube having a tapered hole converging inboardly, a metallic connecting rod having a tapered main body portion in said tapered hole and having inner and outer end portions extending from the ends of said body portion, insulation between said body portion and said tube; said inner end portion having a threaded part protruding beyond said tube, means comprising a first nut threaded on said threaded part and pressing on an end face of said tube for jamming said rod insulatedly and watertightly in said tube, a skeleton anode on the outside of said hull, an insulating cushion between said anode and hull, said anode comprising an outer rim, a domeshaped Wall from said rim, and a plurality of reinforcing ribs inside said dome-shaped wall, said wall having a central well with a bottom wall having a hole, said cushion having a hole, said outer end portion of said rod having a threaded part extending through said holes in said bottom Wall and cushion, and means comprising a second nut threaded on the last said threaded part for watertightly holding said anode on said bull in conductive relation to said rod.

6. An anode-assembly as defined in claim 5 but characterized, by said well having a second hole and locking means in said second hole for said second nut.

7. An anode-assembly as defined in claim 5 but characterized by means on, the first said threaded part for conducting electric power to said rod.

8. An anode-assembly as defined in claim 5 characterized by said rod and said first and second nuts being essentially of titanium.

9. An anode-assembly as defined in claim 8 but characterized by said anode being essentially titanium but with a platinized surface for its dome-shaped wall.

10. An anode-assembly as defined in claim 9 but characterized by a filler in said well with its surface blended to that of said dome-shaped wall.

11. An anode for a cathodic protection system comprising aone-piece valve-metal casting having an outer rim, a dome-shaped wall extending from said rim, and reinforcing ribs inside said dome-shaped wall.

12. An anode as defined in claim 11 wherein said casting is essentially titanium.

13. An anode as defined in claim 11 wherein the outer edge of said rim is covered with a plastic.

14. An anode as defined in claim 11 wherein the outside surface of said dome-shaped wall is platinized, and the inside contains filler.

15. An anode for a cathodic protection system comprising a one-piece valve-metal casting having an outer rim, a dome-shaped wall extending from said rim, said wall having a central well provided with a bottom Wall having a hole, and reinforcing ribs inside said domeshaped wall extending substantially from said well to said rim.

16. A connecting rod means for use in an anode-assembly for a cathodic protection system, comprising a onepiece circular valve metal rod having a tapered main body portion, inner and outer end portions extending from the end portions of said body portion, said inner and outer portions having threaded parts and a machinable resilient insulation jacket jacketing the outside of said body portion.

17. A connecting rod means as defined in claim 16 wherein the said jacket is made of a polyvinyl chloride plastic, and said body portion having grooves filled with said plastic.

References Cited UNITED STATES PATENTS 1,506,306 8/1924 Kirbaldy 204--196 2,169,967 8/193'9 Smith 174152 2,486,871 11/ 1949 Osterheld 204197 2,6613 89 12/1953 Presswell 17477 2,816,069 12/1957 Andrus 204-196 3,075,911 1/ 1963 Anderson 204-196 FOREIGN PATENTS 944,715 12/ 1963 Great Britain.

HOWARD S. WILLIAMS, Primary Examiner.

T. TUNG, Assistant Examiner.