DE69015260T2 - Method for electrically connecting non-corrodible anodes to the corrodible core of a power-supplying power supply cable insulated with standard insulating material. - Google Patents

Abstract

An improved method of connecting one or more non-corrodible valve metal anodes, the surfaces of which have been activated by a deposit of a non-passivatable material, to the corrodible core of an insulated power supply in order to produce a flexible anode assembly to be used for the cathodic protection of metallic structures. In the inventive method, a plurality of ductile metal bushings (7, 8, 9) are disposed over a tubular valve metal anode (6) provided with a corrosion resistant outer surface. The power supply cable (2) is passed through at least one piece of an elastomeric tubing (5a, 5b) having an inner diameter slightly larger than the cable insulation and an outer diameter slightly smaller than the inner diameter of the anode. The cable and tubing is passed through the anode until a segment of the cable, previously stripped of its insulating sheath, and supplied with a highly conductive split collar (4a, 4b) having a thickness substantially similar to the combined thickness of the cable insulation and elastomeric tubing, is underneath one of the bushings, and at least one piece of the tubing is located on at least one side of the stripped cable segment and underneath at least one of the bushings. After the anode is in place, the circumference thereof is reduced at positions corresponding to the bushings by cold-heading. The inventive method can be used to form a seal between the anode and cables insulated with low cost and chemically resistant non-elastomeric insulating materials.

Description

BACKGROUND OF THE INVENTION Field of the invention

The present invention relates to a method for producing a sealed electrical connection between a non-corrodible anode and the corrodible core of a power supply cable. In particular, the invention relates to a method for producing a sealed electrical connection between the anode and the core of a power supply cable which is insulated with a conventional, low-cost, chemically resistant insulating material.

Description of the state of the art

The use of cathodic protection as a means of controlling corrosion of metal structures operating in natural environments, such as seawater, freshwater or underground, is well known and widely used. Such systems work by means of electrochemical reduction of oxygen located near the surface of the structure to be protected. Corrosion of the metal is prevented because the oxygen near the surface of the structure is removed.

Cathodic protection can be achieved by using sacrificial electrodes or alternatively by applying current. In the method of applying current to which the present invention relates, the structure to be protected is cathodically polarized by connecting the structure to the negative pole of an electrical current source. The anode is connected to the positive pole of the same current source. The resulting circulating current causes a reduction of oxygen at the cathode, while an oxidation of anions at the anode.

The anodes used for cathodic protection of buried or submerged metal structures by the current injection technique must often be located a long distance from the surface of the structure to be protected in order to ensure an even distribution of the current over the entire structure. Therefore, the electrical current must be supplied to the anodes using power cables with a low ohmic voltage drop. Such cables are usually made of insulated copper or aluminum. However, these highly conductive metals are rapidly anodically dissolved when they come into contact with the medium, either water or soil, in which the anodes operate.

The introduction of permanent anodes, i.e. anodes made of material that is resistant to anodic corrosion and dissolution, represents an important technological improvement because these anodes offer a practically unlimited service life or at least a much longer service life than conventional anodes used in the current injection process, for example made of graphite, cast iron silicon chromium, magnetite, etc. Permanent anodes are usually made with a base of valve metal, such as titanium, tantalum, niobium, hafnium, tungsten, zirconium or their alloys. The anode surface is at least partially coated with a layer of a corrosion-resistant and anodically non-passivable material, such as a noble metal from the platinum group, such as platinum, iridium, rhodium, ruthenium, palladium, osinium or, more preferably, an oxide thereof, individually or mixed with other materials, or as mixed crystals with oxides of valve metals or other metals, preferably other transition metals.

With the advent of new permanent electrodes, which allow extremely long operating periods, the guarantee that all parts forming the anode structure have a reliability and durability equivalent to that of the anode itself. In particular, the most important requirement to be met is to provide a suitable electrical connection to the power supply cable which is durable and absolutely protected from contact with the medium in which the anode structure operates.

Various solutions have been proposed. Among them, U.S. Patent No. 3,134,731 describes a connection method using glands and sealing wax. U.S. Patent No. 2,841,413 describes a connection method using a sleeve welded to one end of the anode, the conductive wires of the power cable are inserted into the sleeve, which is then crimped onto the wires. The electrical connection is protected by an impermeable adhesive tape. However, the use of additional sealing material does not always achieve perfect reducibility and reliability of the seal. In addition, the materials used to seal the connection gradually lose their characteristic properties and effectiveness, and the performance of the anode structure often depends on the effective life of these aids.

To avoid the need for glands, sealing tapes and other devices, U.S. Patent No. 4,526,666 proposes the use of a continuous cable covered with an elastomeric material such as ethylene propylene rubber (EPR) or chlorinated polysulfonated polyethylene (HYPALON, manufactured by DuPont de Nemours) which is passed through tubular anodes. The anodes are placed over the areas of the cable where the insulation has been previously stripped and the anode ends have been pressed onto the insulation to form a seal between the anode and the insulating jacket. A slotted sleeve of conductive material placed over the exposed area of the cable provides adequate electrical connection between the anode and the cable.

Although the method described above obviates the need for additional sealants by using the elastomeric material sheath to form the necessary seal, this method is not without its drawbacks. Due to the high cost of cables insulated with elastomeric insulating material, it is not feasible to develop anode systems that have only one anode per cable and therefore, to reduce costs, a large number of anodes must be connected along a single cable. The arrangement of many anodes on a single cable is considered disadvantageous because if several anodes are installed on the same cable, the failure of one anode on the cable will automatically break the electrical circuit of all anodes on the cable located below (downstream) the inoperative anode. In addition, these elastomeric insulation materials are not very resistant to chemicals and if the cables are buried, for example, the environment will quickly degrade the insulation, at which point the cable underneath will begin to corrode. Elastomeric insulation materials are particularly known for their poor resistance to wet chlorine, which often occurs when the anodes are used in sea water. These materials decompose very quickly in the presence of chlorine, leaving the copper conductor of the power cable exposed to the aggressive environment.

TASK OF THE INVENTION

The present invention directly addresses the above-mentioned problems and provides a method for connecting an anode to a power cable insulated with a conventional, inexpensive, chemically resistant insulating jacket in a leak-proof and permanent manner without relying on glands, sealing tapes and other additional sealing means.

SUMMARY OF THE INVENTION

The method of the present invention is particularly well suited to connecting one or more anodes arranged at fixed spaces along the insulated power supply cable which is passed coaxially through the anode or anodes and which serves both as a holding means and as a current conducting means from one anode to the other.

The method of the invention for producing a sealed electrical connection between anodically insoluble tubular valve metal anodes and a corrodible core of an insulated power cable insulated by an insulating jacket comprises

(a) fitting a number of ductile metal sleeves over the tubular valve metal anode having a corrosion resistant outer surface;

b) passing the insulated cable through the tubular anode to a segment of the cable from which the insulating layer has been previously stripped and which has a slotted sleeve of highly conductive metal around the conductive core of the cable, the sleeve being located under one of the sleeves and;

c) plastically reducing the circumference of the anode in the area of the external sleeves by cold heading the valve metal anode around the slotted sleeve arranged on the conductive core in the area of one of the sleeves and in the area of the sleeve(s) arranged on at least one side of the sleeve located in the area of the slotted sleeve, and

characterized in that the method between step a) and step b) further comprises the following step:

Passing the insulated power cable through at least one piece of elastomeric tubing, the inner diameter of which is slightly larger than the outer diameter of the insulating jacket and the outer diameter of which is slightly smaller than the inner diameter of the anode; wherein in the following step b) the insulating cable and the elastomeric tubing or tubings are passed through the tubular anode such that at least one piece of tubing is arranged on at least one side of the stripped cable segment and under at least one of the sleeves, the thickness of the sleeve being substantially equal to the total thickness of the cable insulation and the elastomeric tubing; and wherein in step c) the cold heading of the valve metal anode is effected in the region of the sleeve(s) arranged on at least one side of the sleeve located in the region of the slotted sleeve directly around the piece or pieces of tubing.

The cable is flexible and consists of braided or stranded wires of a conductive metal such as copper, tinned copper, aluminum and/or steel. The cable may be insulated with any commonly suitable insulating material. Several cable insulating materials have recently been developed specifically for use in cathodic protection. These materials include double-layer insulation in which the outer layer is made of high molecular weight polyethylene (HMWPE) and the inner layer is made of KYNAR (polyvinylidene difluoride, manufactured by Pennwalt Corp.) or HALAR (fluoropolymer, manufactured by Allied Chemical Corp.). These materials exhibit superior resistance to the acidic and sometimes chlorine-saturated environments in which the anodes often operate and their use is preferred. Other suitable insulating materials include HMWPE, KYNAR, HALAR, TEFLON (polytetrafluoroethylene manufactured by E.I. DuPont de Nemours & Co.), combinations of HMWPE and KYNAR, HMWPE and HALAR, and HMWPE and TEFLON.

The arrangement described in this application can be used in all types of cathodic protection facilities, such as deep ground foundations, horizontal ground foundations, shallow vertical ground foundations, coastal facilities, water tanks and others. The use of such arrangements is particularly advantageous in applications where the anodes are difficult to replace, such as in deep ground foundations, and in ground foundations or in sea water where wet chlorine gas is likely to come into contact with the cable insulation. The placement of all anodes on one cable is not recommended where anode installation is difficult and expensive because failure of one anode breaks the electrical circuit to all downstream anodes. The ability of the arrangement of the invention to operate with relatively inexpensive power cables allows the economical use of many cables.

In the method of the invention, a number of ductile metal sleeves are placed over a tubular valve metal anode sleeve having a corrosion resistant outer surface. The anode may be made of any valve metal base such as titanium, tantalum, niobium, hafnium, tungsten, zirconium or alloys thereof, with or without a conductive coating. Preferably, the anode is made of titanium with a conductive mixed metal oxide catalytic coating. Preferably, the mixed metal oxide catalytic coating is made of a non-passivable material such as a platinum group noble metal such as platinum, iridium, rhodium, ruthenium, palladium, osmium or mixtures thereof. More preferably, an oxide of one of these materials or a mixture thereof or other transition metals are used.

The power supply cable is passed through at least a piece of the elastomeric hose, the hose having an inner diameter slightly larger than the cable insulation and an outer diameter slightly smaller than is the inner diameter of the anode. Preferably, the hose is made of an elastomeric EPDM (diene-modified ethylene-propylene copolymer rubber) hose. Other suitable hose materials include EPR (ethylene-propylene copolymer), neoprene and natural rubber. The cable and hose are guided through the anode to a segment of the cable from which the insulating layer has previously been stripped and which has a highly conductive, slotted sleeve whose thickness corresponds essentially to the total thickness of the cable insulation and the elastomer hose, the sleeve being located under the sleeves and at least a piece of the hose being arranged on at least one side of the stripped cable segment and under at least one of the sleeves.

The slotted sleeve is preferably made of silver-plated copper, but may also be made of non-plated copper, tinned copper, aluminum, a nickel alloy, a valve metal or other conductive material. The sleeves are preferably made of copper, but may also be made of iron or other materials. The sleeves may have a wall thickness of between 0.1 and 10 mm and a length that is substantially equal to or greater than the length of the slotted sleeve attached to the conductive core of the power cable.

After the required positioning, fixation is carried out by inserting the prepared anode assembly into a segmented circular saddle of a forging press and closing the saddle around the outer sleeves, forging the valve metal tube onto the slotted sleeve and the conductive core of the power cable (by cold heading) so that a strong electrical connection is made between the anode and the cable. The ductile outer sleeves suffer inevitable wrinkling on the surface due to the action of the circular forging saddle and allow a more uniform reduction in cross-section without significant wrinkling of the underlying valve metal.

The sealing is accomplished by arranging the additional sleeves near the two ends of the anode at locations overlying the elastomeric tubing and by cold heading the additional sleeves as described above. Thus, the valve metal tube is plastically crimped onto the elastomeric tubing, which in turn is crimped onto the insulating jacket of the power cable, thus ensuring a perfect fluid seal.

The process of the invention is further advantageous because the uniform plastic contraction of the anode above the elastomeric tube is achieved without creating noticeable wrinkling of the valve metal tube itself which could cause microcracks or expose the valve metal to possible localized stress corrosion. In addition, the unusually uniform contraction of the anode below the ductile sleeves prevents pinching of the elastomeric tube which could otherwise cause failures in the fluid seal.

The ductile outer sleeves can be removed after assembly is complete, for example by means of a trimming machine, or they can be left in place. The sleeves can also be made of a valve metal resistant to anodic dissolution or, more preferably, they can be made of an anodically soluble material such as copper, aluminum, iron (ARMCO-iron) or copper-nickel alloys. In the latter case, the sleeves are left in place and become an integral part of the anode, being anodically decomposed during the initial phase of operation.

Furthermore, the use of soluble sleeves made of copper or copper-nickel alloy represents, through their dissolution, an effective source of inhibitory agents, essentially in the form of copper ions, against the biofouling of the surface of the structure to be protected during the initial conditioning of this surface.

The tool means used for the forging process comprises a tool body into which a segmented, pierced saddle is fitted, the diameter of the bore being variable by suitably replacing the segments forming the saddle. The tool body is mounted on the platen and ram of a press. The press is preferably hydraulic and has a capacity of about 100 to 200 tons. The hydraulic system of the press may advantageously be designed to allow a fast approach speed at low pressure followed by a slower high pressure closing speed at which the assembly is forged. The forging process is completed in one cycle by closing the saddle around the sleeves on the outside of the tubular valve metal anode.

The method according to the invention can perhaps be better explained with reference to the series of drawings shown schematically in the attached figures and the following description of the preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE CHARACTERS

Fig. 1 is a partial view of the power supply cable prepared for connection to an anode.

Fig. 2 is a view of a tubular anode slid onto the cable of Fig. 1.

Fig. 3 is a schematic representation of the forging saddle used to reduce the diameter of the anode of Fig. 2.

Fig. 4 shows the tubular anode from Fig. 2 after the forging process.

Fig. 5 shows the anode from Fig. 4 after removal of the sleeves used for pressing or after the anodic dissolution the same is completed.

Fig. 6 shows an end anode with one end of the anode sealed with a titanium end cap.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

According to the invention, the location or locations of the anodes are marked on a cable 1. For example, the user may wish to use two tubular anodes 6 with outside diameters of 2.5 cm and inside diameters of 2.3 cm and lengths of 100 cm mounted on a HMWPE insulated No. 10 AWG (American Wire Gage) cable 1 with a total length of 70 m, with the anodes spaced 6 m from center to center. The cable 1 is marked so that each anode 6 can be placed in the correct location on the cable 1. A mark is made for the end anode as shown in Fig. 6 at 1 m from the end of the cable 1 and marks for the intermediate anodes as shown in Fig. 5 are made at 6 and 7 m from the end of the cable. Additional markings are located at 0.47 m, 0.53 m, 6.47 m and 6.53 m from the end of the cable.

The cable insulation 3 is then removed from the power supply cable 1 between the 0.47 m and 0.53 m marking and between the 6.47 m and 6.53 m marking.

The elastomeric hose 5a, 5b is then placed on the cable. The hoses would have an inner diameter of about 3/8 inch and an outer diameter of about 7/8 inch. Four hoses with lengths of 0.47 m would be necessary. One hose would be pushed down the cable so that it extends from the 6.53 m to the 7 m point from the end of the cable. The following hose would extend from the 6.0 to the 6.47 m point from the end of the cable. The third hose would extend from the 0.53 to the 1.0 m point and the fourth from the 0.00 to the 0.47 m point. Metal collars 4a, 4b are placed around the bare cable wire 2. Two silver plated collars approximately 0.04 m long would be placed around each 0.6 m long section of previously exposed cable wire.

Figure 1 shows the arrangement for the intermediate anode at this point in the operation. The cable insulation 3 has been removed a short distance so that the metal sleeves 4a and 4b can be placed around the exposed cable wire 2. Two pieces of EPDM elastomeric tubing, 5a and 5b, have been pushed onto the cable 1, one piece being placed on each side of the exposed section of the cable. The tubular anode 6 is then pushed onto the cable. The anode 6 would be pushed on so that the intermediate anode would extend from the 6 to the 7 m mark from the end of the cable and the end anode would extend from the 0 to the 1 m mark from the end of the cable. The intermediate anode is a hollow tube open at each end. The terminal anode is open at one end at the 1 m mark, but covered by an end cap at one end at the 0 m mark on the cable. The terminal end of the terminal anode can also be sealed by arranging the terminal anode and the end piece of an elastomeric tube so that they extend beyond the end of the cable and driving a rod of non-elastomeric plastic, the diameter of which is substantially equal to the inside diameter of the elastomeric tube, into the elastomeric tube and pressing the rod into place.

The sleeves are slid into pre-marked locations on the tubular anodes. The 28 mm OD x 26 mm ID x 4 cm long copper sleeves would be located at 6.95 to 6.99 m, 6.48 to 6.52 m, 6.01 to 6.05 m, 0.95 to 0.99 m, 0.48 to 0.52 m and 0.01 to 0.05 m from the end of the cable. Figure 2 shows the location for the intermediate anode at this point in the process. Cable 1 has been inserted into the coated titanium anode 6. The anode tube is positioned so that the central metal sleeve 7 is over the metal sleeves 4a and 4b and the outer metal sleeves 8, 9 are arranged above the pieces of elastomer hose 5a and 5b.

The assembly is inserted laterally into the tool body shown schematically in Figure 3, which comprises a tool body 10 into which is fitted a segmented, pierced saddle consisting of a series of sliding segments 11. The saddle is shown schematically in Figure 3 in its closed position at the stop limit of the pressing stroke. Three successive forging operations are carried out corresponding to the sleeves 7, 8 and 9 respectively, so as to ensure electrical connection and sealing of the connection with respect to the external environment as previously shown. The sleeves are pressed so that the outside diameter of the sleeve after pressing is 24.5 cm. As shown in Figure 4 after pressing, ductile longitudinal folds 12 are formed along the outer surfaces of the metal sleeves 7, 8 and 9. The sleeves 7, 8 and 9 are then removed either mechanically or by anodic dissolution during the initial phase of operation in the working environment. At this point the anode is shown in Figure 5.

The forged sections or segments of the anode made of titanium or other valve metal, which correspond to the central connection or the sealing of the two ends, are substantially cylindrical and have no folds. The two ends are sealed without the need to use a power cable with an insulating elastomeric material. The method according to the invention does not use any means for sealing the electrical connection. Rather, the seal is made directly between the valve metal tube and the elastomeric hose and the cable insulation. This seal creates an exceptionally good and durable connection, which is perfectly protected against corrosion.

Other advantages of the method according to the invention are the perfect reproducibility of the quality of the connection, which is quickly completed due to the essentially automated process, reducing the probability of faulty connections or inadequate sealing due to poor manufacturing. In addition, the two sealing forgings on the insulating cable at the two ends of the tubular anode improve the strength of the assembly and effectively prevent direct mechanical stress on the electrical connection during transport, installation and use of the anode assembly.

Claims (16)

1. A method of making a sealed electrical connection between anodically insoluble tubular valve metal anodes and a corrodible core of a power cable insulated by an insulating jacket, the method comprising the steps of: (a) fitting a number of ductile metal sleeves over the tubular valve metal anode having a corrosion resistant outer surface; b) passing the insulated cable through the tubular anode to a segment of the cable from which the insulating layer has been previously stripped and which has a slotted sleeve of highly conductive metal around the conductive core of the cable, the sleeve being located under one of the sleeves and; c) plastically reducing the circumference of the anode in the area of the external sleeves by cold-forging the valve metal anode around the slotted sleeve arranged on the conductive core in the area of one of the sleeves and in the area of the sleeve(s) arranged on at least one side of the sleeve located in the area of the slotted sleeve, characterized in that the method between step a) and step b) further comprises the following step: Passing the insulated power supply cable through at least one piece of elastomeric tubing, the inner diameter of which is slightly larger than the diameter of the insulating jacket and the outer diameter of which is slightly smaller than the inner diameter of the anode; wherein in the following step b) the insulating cable and the elastomeric tubing or the -hoses are passed through the tubular anode such that at least a piece of the hose is arranged on at least one side of the stripped cable segment and under at least one of the sleeves, the thickness of the sleeve being substantially equal to the total thickness of the cable insulation and the elastomeric hose; and wherein in step c) the cold heading of the valve metal anode is effected in the region of the sleeve(s) arranged on at least one side of the sleeve located in the region of the slotted sleeve directly around the piece or pieces of hose. 2. The method of claim 1, wherein the external ductile metal sleeves consist of an anodically soluble metal from the group comprising copper, aluminum, iron, copper-nickel alloys and mixtures thereof. 3. A method according to claim 1, wherein three sleeves are arranged over the anode, one being arranged substantially centrally on the anode and the others near the two corresponding ends of the anode. 4. A method according to claim 1, wherein the power cable is insulated with a double insulating layer comprising an outer layer of high molecular weight polyethylene and an inner layer of polyvinylidene difluoride or fluoropolymer. 5. The method of claim 1, wherein the power cable has high molecular weight polyethylene insulation. 6. The method of claim 1, wherein the elastomer tube is made of diene-modified ethylene-propylene copolymer rubber. 7. The method of claim 1, wherein the sleeve is made of silver plated copper. 8. A process according to claim 1, wherein the anode is made of titanium and is coated with a catalytic layer of a conductive mixed metal oxide. 9. A method according to claim 2, wherein the sleeves are removed after step c) by anodic decomposition during the initial phase of anode operation under operating conditions. 10. A method according to claim 2, wherein the sleeves are mechanically removed after step c) before use. 11. Intermediate anode obtainable by the process according to claim 3. 12. A terminal anode obtainable by the process according to any one of claims 1, 2 or 4 to 8, wherein a first sleeve is arranged substantially centrally on the anode and a second sleeve is arranged at one end of the anode, the terminal end of the anode being sealed. 13. The terminal anode of claim 12, wherein an end cap is welded onto the terminal end. 14. The end anode of claim 13, wherein the end cap is made of coated titanium. 15. End anode according to claim 11, wherein a rod of non-elastomeric plastic, the diameter of which is substantially equal to the inner diameter of the elastomer tube, is driven into the tube and wherein the titanium anode is pressed at the location of the introduction of the rod. 16. Use of an anode obtainable by the process according to one of claims 1 to 10 for the cathodic corrosion protection of metallic structures.