US3156637A

US3156637A - Cathodic protection anode assembly

Info

Publication number: US3156637A
Application number: US340846A
Authority: US
Inventors: Edward P Anderson
Original assignee: Individual
Current assignee: BASF Catalysts LLC
Priority date: 1960-11-14
Filing date: 1964-01-10
Publication date: 1964-11-10
Anticipated expiration: 1981-11-10

Description

Nov. 10, 1964 E. P. ANDERSON 3,156,637

CATHODIC' PROTECTION mom: ASSEMBLY Original Filed Nov. 14. 1960 pf 12 4a g 4 26 e 6 i9 23 .92 'I5 INVENTOR. EDWARD P. ANDERSON laq ATTORNEYS United States Patent 1 Claim. (Cl. 204-196) This invention relates to a high-pressure tight seal for sealing anode assemblies through ship hulls in cathodic protection systems.

This application is a division of co-pending application No. 68,906, now abandoned, entitled High-Pressure Tight Seal, filed November 14, 1960.

Considerable difficulties have been encountered in the design of sealing assemblies capable of resisting highpressure for extended periods of time without corroding when in continuous contact with sea water. Such severe operating conditions exist with anodes in systems for cathodically protecting ship hulls.

In cathodic protection systems, the anode is mounted on the outside of the ship and below the water line. Since it serves as the positive electrode for applying protective current between the anode and the hull, electrical connection must be made from a power supply on board and inside the ship to the anode. Such connection is generally passed through the hull, and the assembly must provide for insulation of the anode from the hull, it must be sufficiently tight to resist the Water pressure, and a further requirement is that the components thereof resist corrosion which may occur under the attack by sea water and its decomposition products appearing in the vicinity of the anode when protective current is applied.

The importance of all these requirements will be appreciated when considering that, with a seal through the hull of a ship, a bore through it cannot be avoided, so that the safety of the ship is seriously endangered in the event that the seal becomes damaged and leakage occurs.

Numerous attempts have been made to provide corrosion-resistant, pressure-tight seals, and heretofore the greatest part of them is based on the well-known principle of compression. This means that the sealing assembly includes one or more resilient members, such as packings, washers or the like, and components for compressing the packing. Such components generally include screw-threaded parts or equivalent arrangements. It is well known, however, that the pressure exerted by this type of assembly automatically releases after a certain time. Furthermore, packings are made generally from materials which, at least after a certain period of time, are attached by sea water or its decomposition products. Since cathodic protection systems are frequently installed on large seagoing vessels which cannot be checked for defects in the anode seals, satisfactory sealing assemblies for the anodes must be reliable under any circumstances for long periods of time, such as months and even years.

Accordingly, it is one of the main objects of the present invention to provide a seal which fulfills the requirements set forth above.

In accordance with the invention, a new type of anode sealing assembly is provided which eliminates the necessity of compressing packings, washers or other equivalent I resilient members by means of mechanical components.

It has been found, that a high-pressure tight seal is obtained When providing an assembly which includes the elements to be sealed together, herein referred to as outer and inner elements, the elements being shaped in such a mannot that they form a space between each other, pressureinjecting a curable plastic into the space, and simultaneously maintaining the injected plastic under pressure and subjecting it to a curing step. Curing is normally associated with solidification and, consequently, provided 3,156,637 Patented Nov. 10, 1964 that the pressure is maintained until the curing step is essentially terminated, the finished seal is formed by elements of the assembly with the cured plastic arranged between the elements and permanently maintained at at least the pressure which prevailed during the curing step. It appears that some of the curable high-polymers, generally referred to as plastics, increase their volume during the curing step, so that the pressure prevailing in the finished product may, under circumstances, exceed the pressure which was actually applied during the injection and curing steps.

High-polymers or plastics of the type useful for producing seals in accordance with the invention are Well known in the art. The term, as used herein, is intended to encompass high-molecular weight artificial materials which, either under the action of heat, of pressure, or by aging are transferred into a permanent state of solidification. By definition, this process is not reversible, i.e., the materials generally become insoluble and heat-resistant; they do not exhibit the properties of a plastic any more. It is generally assumed that the process of curing is associated with the formation of cross-links in the molecular structure of the material. Preferably, self-curing plastics are used and a representative group of such materials are epoxy resins. Other suitable high-polymer compounds are polysulfide rubbers; for example, Acme Wire Companys XK-263 with AL-lSB Activator and AL-77 Hardner; Minnesota Mining and Manufacturing Companys EC1130 resin and EC-776 primer with their accelerator; and Products Research Companys PR-IZOL with PR-1201-A accelerator.

In the preferred embodiment, the high-pressure tight seal for cathodic protection systems includes an outer gland open at both ends and adapted to be mounted in a bore through a hull of a ship. Each of the ends of the gland receives an insulating plug fitted into it. The outer plug assumes the function of a support for the electrode serving as the anode and may be maintained in its position with respect to the hull by any suitable means, such as screw studs, or the like. A lead-in conductor connected to the electrode passes through the outer plug, through the space within the gland, and through the inner plug for connection to the power supply on board the ship. The remaining space around the lead-in conductor, delimited by the inner plug surfaces and the inner Wall of the gland, contains a pressurized cured synthetic highpolymer or plastic. As a result of the fact that plastic was pressure-injected and cured, an effective seal is achieved.

Preferably, the gland is provided with radial bores connecting the inner space defined between the plugs with the outer atmosphere. One of the bores may receive a self-sealing filling plug and is used for pressure-injecting the plastic from outside into the space. The other bore serves as a vent at the beginning of the injecting step and can be closed, for example by means of a screw, when the space is entirely filled out, so that the subsequently applied injection-pressure drive the plastic between all mating surfaces to form, upon curing of the material, a seal under permanent pressure.

As stated above, it has been found that seals of the type contemplated herein are particularly useful in cathodic protection systems inasmuch as one of the plugs mentioned above may constitute the support for an electrode serving as the anode. A cathodic protection anode which may readily be adapted for use in connection with the seal disclosed herein is described in US. Patent No. 3,022,243, dated February 20, 1962. However, the anode described in that patent is illustrated therein in connection with a compression seal of which the deficiencies are overcome by the present invention. Consequently, the assembly described herein constitutes a further development of that disclosed in the above-mentioned Patent No. 3,022,243 as far as anode assemblies for cathodic protection systems are concerned. In other words, while the manner in which the electrode is secured to the plastic support forming one plug of the sealing assembly is essentially similar with that described in the above-mentioned patent, and the present invention is directed to a novel seal and a manner of producing it which may be combined, for example, with the cathodic protection anode support shown in the above patent.

Other objects and advantages of the invention will become apparent from the following detailed description and from the accompanying drawing, which is a sectional view through one embodiment of a sealing assembly in accordance with the invention and illustrates its use as a cathodic protection anode assembly.

The assembly shown in the drawing includes a cylindrical gland 10, welded into a bore through the hull l2, and a plastic body 14 which supports the electrode performing as an anode in a cathodic protection system.

The insulating support 14 has a shape similar to that of a mushroom including a flat circular plate 16 and a cylindrical stem 18 attached to its center. A connector pin 20 is axially embedded through the stem 13 and the plate 16. The side of the support plate 16 with the stem 18 thereon faces the hull 12, with an insulating blanket 19 therebetween, while the opposite side carries a corrosion resistant disc or thin plate 22, generally a circular platinum sheet or a similar sheet of a platinum alloy. Good results have been obtained when using an alloy of about 50 percent by weight of platinum with about 50 percent by weight of palladium. The thickness of the disc may be about 0.020 inch. A comparatively narrow circumferential area of the disc is bent out of the plane of the disc and the rim 24 so obtained is embedded in the plate 16 of the support to provide a firm grip all around the circumference of the anode disc.

The disc 22 has one additional area bent out of its plane to form a cup-shaped recess with a perforated annular wall 26 and a bottom 28. The bottom portion is Welded to a flange 30 which, in turn, forms part of the connector pin 20. The cup-shaped recess is filled with plastic material, preferably the same as that from which the support 16 is formed, suitable polytetrafluoroethylene, or any other similar material capable of forming a bond with the material of the support 16. Perforations 32 through the wall portion 26 permit bonding of the plastic material inside the recess with that outside the recess. In the drawing, the plastic material in the recess is shown partly broken away to facilitate illustration of the perforations. Since the perforations 32 are radially arranged through the wall 26, the recessed area is anchored in the support to effectively resist movement in any direction. With the circumferential rim 24 and the central area in the shape of the perforated recess embedded and anchored in the plastic, the annular area of the disc 22 located between them and contacting the outer surface of the support plate 16 is maintained firmly against that surface.

The fiat circular plate 16 is provided with bores and counterbores through which pass threaded studs 34 welded to the hull 12. By means of nuts 36 cooperating with the studs 34, the flat plate 16 and therewith all of the components described to this point are maintained in a fixed position With respect to the hull and to the gland 10, with the cylindrical stem 18 protruding into the gland, as shown in the drawing.

In order to produce a high-pressure tight seal in accordance with the invention, the other, inner end of the gland is closed by means of a plug 38 of insulating, preferably plastic material threadably engaging the inner gland wall. The plug 38 is provided with an axial bore receiving a metallic cap 40 which, in turn, has a threaded bore through it, through which passes the protruding portion of the pin 20. The cap is preferably shaped in such a manner that its portion protruding from the plug 38 forms a terminal 42 adapted and dimensioned for receiving a female connector of any suitable type (not shown) to provide current flow through the pin 20 to the platinum foil 22.

As illustrated in the drawing, the plug 38 on one side, and the cylindrical stem 18 on the other side, are dimensioned sufficiently short so that an initially empty space remains within the gland 10. A pair of bores is provided through the gland at locations adjacent the empty space, so that connection is made between the space and the outer atmosphere. A self-sealing, unidirectional-valve filling plug '4, for example of the well known type provided with a stop valve, is mounted in one of the bores, and the other bore 46 is closed by means of a screw 48.

The assembly, as described to this point, is ready for the steps necessary to form the seal in accordance with this invention. At first, the screw 48 is removed and the filling plug 4 is connected to conventional pressure-injection equipment of any suitable type (not shown). Subsequently, this equipment is started to operate, whereby the space defined Within the gland between the inner surface of the plug 38 and of the cylindrical stem 13, and around the pin 20, as well as the inner protruding portion of the cap 40, is filled out with the plastic. Injection is continued until the material appears outside the bore 46 which, during this portion of the injection step, performs as a vent through which air escapes from the space inside the gland into the outer atmosphere. The outflow of material indicates that the space is entirely filled with plastic material. Now the screw 48 is reinserted into the bore 46, so that the space within the gland 10 is completely closed. Upon further operation of the pressure-injection equipment, the plastic within the gland 10 is subject to pressure; this pressure remains, even when the injection step is terminated and upon removal of the injection equipment, since the filling plug 44 is provided with a stop valve. As noted above, the pressure forcibly drives the plastic into all possibly existing cracks and between mating surfaces of all of the components involved and in contact with it. The subsequent curing step then operates to solidify the plastic in situ, which means when in intimate contact with all of the surfaces involved. A certain wetting action, due to molecular forces present and active between some plastics and metal surfaces, assists in the formation of an extremely intimate contact under the described conditions.

The nature of the curing step depends on the highpolymer plastic material selected for the specific purpose. Preferably, a self-curing plastic is used, so that solidification and transformation into a non-plastic insoluble material occurs automatically after a certain time. In a specific instance, an epoxy resin commercially designated as Union Carbide ERL 2774 with Lancast A accelerator has been used, which is a self-curing plastic. After a time period of about 30 to 45 minutes curing was terminated, resulting in a high-pressure tight, corrosionresistant seal, suitable for use as an anode in cathodic protection systems.

Although the method for producing the seal is described in the foregoing in connection with a self-curing plastic, other curable plastics may be used, and the manner in which curing is effected depends on the properties of the selected material. Generally speaking, any type of curable high-polymer may be used, provided that the curing is performed in situ, i.e., that the plastic is pressurized between the mating surfaces to be sealed during the curing step.

It will be understood that the pressure injection and curing steps may be performed either before or after mounting the assembly into the hull of a ship.

It will be appreciated that certain modifications may be made in the structure described without departing from the spirit or scope of the present invention defined in the following claim.

What is claimed is:

An anode assembly in a cathodic protection system for a ships hull comprising an open ended tubular gland 5 member fixed through the hull, an anode element having a plate portion fixed to the outside of the hull, said anode element having a stem portion extending into one end of the gland member and a connector pin embedded in said stem portion and extending through said gland member, a plug fixed in and closing the other end of the gland member, said connector pin extending through the plug, said stem portion and the plug being spaced apart to provide a space between them within the gland member, a

pair of bores opening through the side of the gland mern- 10 her into said space, a filling plug threaded into one of said bores, and an air vent screw threaded into the other of said bores, said space being filled with a synthetic plastic which has been injected into the space under pressure and cured in situ.

References Cited in the tile of this patent UNITED STATES PATENTS 2,910,419 Preiser et a1 Oct. 27, 1959 2,926,128 Flower Feb. 23, 1960 2,949,417 Preiser et a1 Aug. 16, 1960