US3342716A

US3342716A - Anode for cathodic protection system

Info

Publication number: US3342716A
Application number: US374705A
Authority: US
Inventors: Edward P Anderson; Samuel P Crago
Original assignee: Engelhard Industries Inc
Current assignee: BASF Catalysts LLC; Engelhard Industries Inc
Priority date: 1964-06-12
Filing date: 1964-06-12
Publication date: 1967-09-19
Anticipated expiration: 1984-09-19
Also published as: DE1272681B; SE316964B; NL125196C; GB1063406A; NO115508B; DK116107B; BE665310A; NL6507495A

Description

Sept. 19, 1967 E. P. ANDERSON ETAL 3,342,716

ANODE FOR CATHODIC PROTECTION SYSTEM Filed June 12, 1964 4 24 12 10 M 91% 1/2 I .L V IiL I 5 Pawer aw y INVENTORS Edward i. findersan Samuel 1? Gray ATTORNEY United States Patent 3,342,716 ANODE FOR CATHODIC PROTECTION SYSTEM Edward P. Anderson, Livingston, and Samuel P. Crago, Wyckolf, N.J., assignors to Engelhard Industries, Inc., Newark, N.J., a corporation of Delaware Filed June 12, 1964, Ser. No. 374,705 4 Claims. (Cl. 204-196) The present invention relates to an anode adapted for use in impressed current cathodic protection systems for preventing corrosion of large metal surfaces under water such as the hulls of ships.

Hereafter, the anode of this invention and cathodic protection systems in which it is used are described with reference to ships hulls, but it will be understood that they are equally adapted for use in cathodically protecting any metal surface under water or in damp ground.

Impressed current cathodic protection systems are used on the submerged portions of ships hulls to reduce or eliminate corrosion of the metal of the hull. Metal in water is corroded by the flow of positive ions away from the metal surface toward more negatively charged areas. This galvanic process of corrosion is halted by impressing a charge on the bull to render it more negatively charged. In conventional current cathodic protection systems the negative potential of the hull is built up by means of anodes mounted on the submerged portions of the hull structure. The anodes are electrically insulated from the hull and a source of direct current electric power is connected to the anodes and the hull in a manner to be able to adjust the potential of the hull by regulating the voltage applied to the anodes.

It is a principal object of the present invention to provide an anode which is particularly adapted for use in impressed current cathodic protection systems on the largest ocean-going ships or on other structures having underwater metal surfaces to be protected against corrosion.

It is a further object to provide an anode from which a protective current will be effectively disseminated over a large area with low voltage.

An additional object is to provide such an anode which is of simple, rugged and economical construction and which is mounted easily and inexpensively on a ships hull.

In cathodic protection systems the anodes are normally mounted on the surface to be protected as a matter of convenience and they are, of course, insulated from direct contact with the surface. The anodes are therefore conventionally formed of an electrically conductive metal surface on an electrically insulating support with the insulating support attached to the hull.

In these systems the voltage applied to the anodes is desirably such as to project a protective current for as great an area as possible around each anode. The negative potential built up on the hull will be greatest close to the anode. The level of potential impressed on the hull de creases as the distance from the anode increases and the extent of the area of protection around each anode is determined by the amount of voltage applied. But the amount of voltage which can beneficially be applied is limited since too great a negative potential impressed on a portion of the hull will cause paint on that portion to flake olf. If part of the hull area around an anode is coated with paint and part is bare metal, the difference in the amount of impressed potential required to adequately protect the respective parts may be too great for the amount of power projected from a single anodic surface to provide protection for both the painted part and the bare metal.

Cathodic protection of a large area of submerged surface is conventionally provided by using a number of anodes spaced apart over the submerged area. The hull would normally be pierced at each anode for electrical connection to the source of electric power within the hull. A stufling box or other water-tight seal is required for each connection through the hull and this makes the use of a large number of separate anodes expensive. In addition, the location of bulkheads and other obstructions within the hull may make it difficult or impossible to locate anodes in the best positions to provide even protection over the hull.

An alternative by which the number of connections through the hull is reduced is to use anodes which are in the form of elongated strips of the conductive metal which is used for the anodic surfaces.

The present invention is an anode generally of the strip type but having a novel construction which makes more efficient and economic use of expensive corrosion-resistant metals-such as platinum, palladium and alloys thereof-than previous anode constructions.

In accordance with the invention the anode has a plurality of anodic surfaces spaced apart on the insulating support so that some of the effective anodic surface is further from the electrical connection than if the anodic surface were a continuous strip. In addition, with the anode of this invention the anodic surfaces and insulating support are connected in such a way that the anodic surfaces are firmly anchored and considerably less easily scraped or broken away from the support than with some conventional types of construction, yet the anode has flexibility which enables it to be secured flat against curved surfaces of a ships hull.

The anode of this invention comprises generally a rod of electrically conductive metal embedded in an electrical insulating support member with short portions of the rod exposed at intervals along the rod. In practice the support is an elongated block of insulating material such as glass reinforced polyester and the rod is formed. with a plurality of generally U-shaped portions bent up out of the plane of the rod and arranged in the support so that the top part of each U-shaped portion is exposed to provide an anodic surface. A conventional electrical connection through a stufling box is used to connect the rod to the cathodic protection system power supply within the hull.

The rod may be made of an electrically conductive metal and in practice is made of tantalum or titanium over a core of copper or aluminum. Since the exposed portions of the rod are subject to chemical attack by the electrolytic decomposition products of sea water they are normally coated with platinum to render them corrosion resistant.

In one preferred structure of the anode in accordance with the invention two rods are arranged parallel in a single insulating support member and the exposed portions of the rods are in a trough in the top of the support member so as to be below the level of top of the support. The exposed portions of the rods are thus protected from being damaged by underwater floating objects, anchor chains, piers and the like.

In practice the support member is generally rectangular in cross section and the anode may be made long and straight, curved or even circular, in which case it resembles a fiat hoop. It may be made up of one long element or of articulated sections joined by male and female connections.

The invention will be more fully understood from the following detailed description with reference to the accompanying drawings in which:

FIGURE 1 is a top view of an anode in accordance with the present invention;

FIGURE 2 is a section along the line 2-2 of FIG- URE 1;

- 3 FIGURE 3 is a section along the line 33 of FIG- URE 1;

FIGURE 4 is a section along the line 4-4 of FIG- URE 1 showing a suitable stufling box and electrical connector which may be used to connect the anode to a source of electric power within a ships hull; and

FIGURE 5 is a section along the line 5-5 of FIG- URE 4.

Referring now to the drawings, and particularly FIG- URE 3, the anode of the present invention comprises generally a rod of electrically conductive metal which is embedded in a support member 11 of insulating material with portions 12 of the rod 10 exposed to provide anodic surfaces.

In practice the rod 10 is made of titanium or tantalum over a core of copper or aluminum. This combination provides the desired properties of good electrical conductivity, mechanical strength and resistance to corrosion. The portions 12 which are exposed to form the anodic surfaces of the rod 10 are particularly vulnerable to chemical attack by the electrolytic decomposition products of sea Water and are therefore normally plated or sheathed with a layer of platinum or an alloy of platinum or palladium. Tubes of platinum or palladium alloy may he slipped over the rod 10 and swaged in place at the points which will be exposed portions 12 when the rod is embedded in the support member 11.

The support member 11 may be made of any suitable insulating material which is resistant to chemical attack from sea water and electrolytic decomposition products. In addition the support member 11 is preferably flexible to an etxent which will permit the length of a support member 11 to be conformed to the curvature of a ships hull so as to be able to secure the entire length of the member 11 fiat against the hull surface. In practice the support member 11 may be made of glass reinforced polyester and may be any shape suitable for supporting the rod 10 with portions 12 of the rod exposed at spaced intervals as illustrated in FIGURE 3.

The support member 11 will normally be long and narrow to accommodate a single rod 10 or may be made enough wider to accommodate a pair of parallel rods 10 as shown in FIGURES 1 and 2. In practice the sup-port member is generally rectangular in cross-section with a plurality of countersunk holes 14 through it at spaced intervals along its length to receive studs 15 which will normally be welded to a ships hull 16. The studs 15 extend into the holes 14 with nuts 17 threaded on the ends of the studs as means to attach the support member 11, and hence the anode, to the hull 16.

The rods 10 are embedded in the support member 11 so as to leave the portions 12 of the rods exposed at intervals along the length of the rod with the sections of the rods between the portions 12 firmly anchored in the support. This is accomplished by bending a plurality of generally U-shaped portions up out of the plane of the rod and embedding the rod in the support member 11 with the tops of the U-shaped portions exposed to provide the portions 12 which are the anodic surfaces.

As best seen in FIGURE 2 the exposed portions 12 are in a trough 19 in the support member 11 and are below the level of the surface of the support so as to be protected from being scraped or broken by anchor chains, piers, underwater floating objects and the like.

As described subsequently in more detail the rods 10 are connected through a connector pin 20 to an electric power supply 21. A single connection to the power supply 21 thus supplies the power for a plurality of spaced-apart anodic surfaces formed by the exposed portions 12 of the rods 10.

As best seen in FIGURES 2 and 3 a second pair of rods 22 may be connected parallel to and below the rods 10 so as to be in contact with them at spaced intervals along the portion of the rods 10 which are completely embedded in the support member 11.

As shown in FIGURE 3 the rods 22 are held in contact with the bottoms of the U-shaped portions of the rods 10 by pliable bands 24 wrapped around the rods.

The rods 22 serve as bus bars to assure good distribution of power to all the exposed portions 12 along the entire length of the rod 10 and more importantly to provide a by-pass through which electric power will flow to the portions 12 at the ends of the anode if one of the portions 12 intermediate the ends of the anode and the connection to the power source should be severed. In addition the rods 22 add mechanical strength to the anode structure. This is particularly helpful during assembly of the structure when the rods 10 are being embedded in the support member 11.

In the manufacture of the anode the support member 11 is extruded from a suitable material such as glass reinforced polyester. The trough 19 may be provided for in the extrusion or it may be routed out later. The countersunk holes 14 are drilled and a pair of parallel channels (indicated by dotted lines 26 in FIGURE 2) are routed out to receive the rods 10. The rods 10 are formed to the desired configuration, and, if rods 22 are to be included, the rods 22 are attached by means of bands 24. The rods 10 are set in the channels to the desired depth and a thermoplastic material such as glass-reinforced polyester is heated until it is viscous and packed into the channels around the portions of the rods 10 to be embedded. The plastic is then allowed to cool and harden. Self-curing plastic resin such as polyvinyl chloride are also quite suitable.

The cured plastic around the

rods

10 and 22 anchor the rods securely in the support member 11, but additional anchoring means may be provided by inserting pegs 27 through the sides of member 11 to extend at right angles over the embedded portions of the rods as illus trated in FIGURES 2 and 3.

As previously mentioned the connection of the rods 10 (and 22) to the power supply 21 is through a connector pin 20. The connector pin 20 may be electrically connected to the

rods

10 and 22 by any convenient means such as welding or by a clamping arrangement such as illustrated in FIGURES 4 and 5.

The clamping arrangement shown is provided by a flange 28 threaded onto the upper portion of the connector pin 20. A pair of lugs 29 project upward from opposite edges of the flange 28 and as best seen in FIGURE 5 the portions of the

rods

10 and 22 adjacent the connector pin 20 are bent inward and passed around the lugs 29 which thus hold the rods across the flange 28. The rods are held clamped against the flange 28 by a nut 30 and Washer 31. The washer 31 rests on top of the

rods

10 and 22 and is held down by the nut 30 which is threaded onto the connector pin 20.

In the construction of the anode a suitable well, indicate-d by dash lines 32, for the connection between the

rods

10 and 22 and connector pin 20 is drilled out of the support member 11. When the connection is assembled it is then embedded in the support member by filling the well with a self-curing plastic.

The bottom of the pin 20 extends out through a cylindrical boss or stem 33 on the bottom of the support member 11. The stem 33 is sealed through the hull 16 in a manner described below and the connector pin 20 extends inside the hull 16. A female connector 34 fitting on the end of the connector pin 20 is on the end of a conductor 35 which is connected to the positive terminal of the power supply 21. The negative terminal of the power supply is connected to the hull 16 through suitable connections as indicated in FIGURE 4 by a conductor 36 to the hull 16.

The seal for the conection through the hull 16 may be formed in any conventional manner. As shown in FIG- URE 4 the seal is conveniently formed by sleeve 38 welded into a bore through the hull. The cylindrical stem 33 of the support member 11 fits snugly into the sleeve 38 which is counterbored as shown to provide space for compression packing rings 39 between the inside of the sleeve 38 and the stem 33. A jam nut 40 having an aperture 41 through the end for the connector pin 20 and female connector 34 is threaded on the sleeve 38 to compress the packing rings 39 and complete the seal.

The above is a detailed description of a preferred embodiment of the anode of this invention and it will be appreciated certain modifications of the structure and arrangement may be made Without departing from the scope and spirit of the invention defined by the following claims.

What is claimed is:

1. An anode assembly for use in a cathodic protection system for underwater metal structures comprising, a support member of electric insulating material, a rod of electrically conductive metal, said rod being embedded in the support member with portions of the rod exposed outside the support member at spaced intervals along the length of the rod, and means for supplying electric power to the rod, said means including a second rod of electrically conductive metal completely embedded in the support member parallel to and in contact wtih the first mentioned rod.

2. An anode assembly for use in a cathodic protection system for underwater metal structures comprising, an

electrically insulating support member, a rod of electrically conductive metal having a plurality of generally U-shaped portions bent up out of the plane of the rod, said rod being anchored and embedded in the support member with top parts of the U-shaped portions exposed outside the support member, and means for supplying electric power to the rod.

3. An anode assembly according to claim 2 including a second rod of electrically conductive metal complete-1y embedded in the support member parallel to and in contact with the first mentioned rod.

4. An anode assembly according to claim 3 in which the support member has surface areas at one side depressed below the plane of that side and in which said exposed portions of the rod are in said depressed surface areas and do not extend above the plane of said side.

Claims

1. AN ANODE ASSEMBLY FOR USE IN A CATHODIC PROTECTION SYSTEM FOR UNDERWATER METAL STRUCTURES COMPRISING, A SUPPORT MEMBER OF ELECTRIC INSULATING MATERIAL, A ROD OF ELECTRICALLY CONDUCTIVE METAL, SAID ROD BEING EMBEDDED IN THE SUPPORT MEMBER WITH PORTIONS OF THE ROD EXPOSED OUTSIDE THE SUPPORT MEMBER AT SPACED INTERVALS ALONG THE LENGTH OF THE ROD, AND MEANS FOR SUPPLYING ELECTRIC POWER TO THE ROD, SAID MEANS INCLUDING A SECOND ROD OF ELECTRICALLY CONDUCTIVE METAL COMPLETELY EMBEDDED IN THE SUPPORT MEMBER PARALLEL TO AND IN CONTACT WITH THE FIRST MENTIONED ROD.