This invention relates to a kit of parts and method suitable for use in an impressed current corrosion protection system for an elongate substrate and also in electrical grounding of objects. In particular the invention relates to such kits of parts and methods which include an elongate conductive member which may be connected, in use, by an insulated conductive lead, to a source of electrical current.

It is known to provide impressed current corrosion protection systems in which an elongate conductive substrate such as a pipeline is protected from corrosion by establishing a potential difference between the substrate and a spaced apart electrode. The potential difference is established by connecting the substrate and the electrode to each other, through a power supply of constant sign, and the circuit and an electrochemical cell is completed when electrolyte is present between the substrate and the electrode, so that current flows transversely from the surface ofthe electrode towards the substrate to protect it. Electrolyte is typically provided by soil in which the electrode is buried, or for underwater applications by water. The electrode may be an elongate electrode, known as a long-line electrode or a continuous electrode, or a distributed electrode. Alternatively the impressed current system may comprise a plurality of discrete electrodes, each connected to the power supply. The distributed or discrete electrodes are usually connected to the power supply so that they act as an anode, while the substrate acts as a cathode.

Examples of successful distributed electrodes that are known for use in the impressed current corrosion protection systems are described in EP-A-0067679 (MP769 EPC), GB 941 1787.6 (B265 GB2), and WO930231 1 (RK463). The entire disclosures of these applications, and their corresponding US applications, are incoφorated herein by reference.

EP-A-0067679 describes a distributed electrode comprising:

(i) a continuous elongate core comprising a material having a resistivity at

2 233 CC ooff lleessss tthhaann 55 xx 1100 oohhmm ccmm, and a resistance at 23 °C of less than 0.03 ohm/m (usually a metal) and

(ii) an element which is comprised of a conductive polymer composition which has an elongation of at least 10%, and surrounds and is in electrical contact with the core which is at least 500 microns thick.

GB 941 1787.6 (B265GB2) and WO930231 1 (RK463) describe electrodes which comprise tlie elements of the electrode of EP-A-0067679, and in addition a surrounding mass of particulate carbon (e.g. coke breeze retained within a fabric jacket). WO930231 1 (RK 463) relates in particular to the desired acid and chlorine resistance of that jacket, and GB 941 1787.6 (B265) relates to the use of additional outer tensioning wraps to increase the compaction ofthe carbon particles within the fabric jacket.

As used in the above references, and in the present application, the term "conductive polymer" means a composition which comprises a polymeric component and dispersed in the polymeric component, a particulate conductive filler which has good resistance to corrosion. Examples of suitable conductive fillers are carbon black or graphite.

The entire disclosures of EP-A-0067679, WO930231 1 (RK463) and GB9411787.6 (B265), and their corresponding US applications are incorporated herein by reference.

It is also known to use so called "sacrificial anodes" (that is, discrete anodes that are not connected to a source of electrical power) to protect corrodible substrates. Such anodes typically comprise a metal that is more electrically active than the substrate to be protected. Frequently such discrete anodes comprise zinc or magnesium. The anodes are connected via an insulated lead to the substrate to be

J protected, and the circuit and electrochemical cell is completed by passage of current through an electrolyte (e.g. soil) in which the substrate is positioned.

Where discrete anodes are used, it is known to provide these in a cylindrical configuration, or in a generally dog-bone configuration. The dog-bone configuration is known to provide more constant resistance than a plain cylinder. This is described in "Cathodic Protection" by John Morgan, published in 1987 by NACE, at page 174.

As mentioned above where an elongate electrode is used for an impressed current system, it is connected through a power supply to the substrate to be protected. Practically, the connection to the power supply is effected via an insulated power lead.

The present invention has recognised that, in use, at the point of connection of the electrode to a power lead, the transverse current density, exiting the electrode surface and passing towards the substrate, is greatly increased relative to the current density along the main portions ofthe electrode. This increased current density may lead to problems, for example, for the electrodes described above with reference to EP-A-0067679, WO930231 1 and GB 9411787.6, it may lead to consumption ofthe conductive filler in the electrode, and hence a shortening of he useful life of electrode. The present invention provides a kit of parts that reduces this problem.

Where long lengths of substrate are to be protected, it is known to join, end to end, lengths of distributed electrodes ofthe type described above. Joining is done by cutting back the surrounding conductive polymeric sheath and particulate carbon- filled jacket and splicing the central conductors. Again, the transverse current density, exiting the electrode surface towards the substrate at the end-to-end joint, is increased relative to the current density along the main portion of each electrode. The effect is usually less than at the interface between the lead and the first electrode, because of current attenuation along the electrode length. Nonetheless it may present a problem. The kit of parts provided by the invention may also be used to reduce this problem.

Another field of technology in which electrical discontinuities exist at joints is the field of high energy cables. In this field it is known that joints represent a region of high stress, and consequently a region of weakness.

A typical high voltage cable is made up of a conductor, primary insulation and surrounding screen. The screen is at zero potential and contains the current within the cable. At a joint the screen is terminated, and the electrical stress at this point must therefore be controlled to prevent electrical discharge at the joint. Control is typically provided by a stress cone, that is a conical layer that extends the zero potential of the screen along a conicaily tapering surface increasing in diameter from the end ofthe screen.

A first aspect ofthe present invention provides a kit of parts suitable for use in a method of impressed current corrosion protection, or in a method for electrically grounding an object, the kit of parts comprising

(i) an elongate conductive member having first and second ends, and comprising

(a) a continuous elongate core comprising a material having a resistivity at 23°C of less than 5 x 10 ohm cm, and a resistance at 23°C of less than 0.03 ohm/m,

(b) an element which comprises a conductive polymer composition which surrounds and is in electrical contact with the core, and

(c) optional further layers which, if present surround and are in electrical contact with the conductive polymeric element; and

(ii) a generally conicaily shaped member having a passageway extending substantially axially therethrough for receiving at least the core and

conductive polymeric element ofthe first end of the elongate electrode, the passageway being sized and shaped so that it is a push fit over the conductive polymeric element of the first end ofthe elongate electrode, and the conicaily shaped member having a resistivity that is at least as high as the resistivity ofthe conductive polymeric element.

In use, the first end of the elongate conductive member may be connected, via an insulated lead, to a source of electrical current. When so connected, electrical current flows transversely outwards from the elongate conductive member. Similarly in use the second end of the elongate conductive member may be connected to a first end of another identical conductive member.

It is also known to use elongate conductive members in order electrically to ground equipment. The equipment is typically connected to the elongate conductive member via an insulated lead wire.

We have found that the distributed electrode constructions described in EP-A- 0067679, WO930231 1 and GB 941 1787.6 are suitable for use in grounding applications, but are subject to failure by burning due to electrical discharge at the interface between the lead and the electrode. At this interface, the current exiting the electrode into the ground is much larger than along the main body ofthe electrode. We have therefore found that the components of the kit according to the invention are not only suitable for use in an impressed current corrosion protection system, but are also applicable for use in an electrical grounding application. The kit of parts according to the invention may therefore be used, for example, to ground electrically pipelines, high energy switch gear, buildings, and the like.

In both the corrosion protection and the grounding applications, the elongate conductive member can be connected via an electric lead wire to a source of electrical current. In the impressed current corrosion protection method this source of electrical current is a continuous current source, e.g. a power supply. In the grounding

application, the source of electrical current is a transitory current source, e.g. a lightening strike, or electrical discharge from a high energy power line.

During operation of the impressed current corrosion protection system and during discharge in the electrical grounding application, current flows transversely from the elongate conductive member. In a preferred case, the elongate conductive member is generally cylindrical, and the current flows radially outward from the outer surface ofthe elongate conductive member. In the corrosion protection system the current flows towards the substrate to be protected, thereby completing an electrical circuit and electrochemical cell, In grounding applications, current discharges transversely from the surface of the electrode into the surrounding ground. In an impressed current corrosion protection application-using an electrode configuration of the type described with reference to EP-A-0067679, WO930231 1 and GB 9411787.6 the average current density flowing transversely from the electrodes is typically of the order of 50mA/m. In a grounding applications, at discharge using the same electrode configuration, the current density flowing transversely from the electrodes may be of the order of about 300 to 2000 AΛn. In both cases that current density may be about doubled at the interface between the electrode and d e insulated lead, or the interface between an electrode and a joint between that electrode and another electrode. This increased current density may lead to problems, as discussed earlier.

In addition to the kit of parts, the present invention also provides methods of cathodically protecting an electrically conductive substrate from corrosion, and a method of electrically grounding equipment.

A second aspect ofthe invention provides a method of cathodically protecting from corrosion, an elongate electrically conductive substrate that is positioned in an electrolyte, the method comprising:

(i) providing an elongate conductive member having a first and second end, and comprising

(a) a continuous elongate core comprising a material having a rreessiissttiivviittyy aatt 2233°°CC ooff lleessss tthhaann 55 .x 10 ohm cm, and a resistivity at 23°C of less than 0.03 ohm/m,

(b) an element which comprises a conductive polymer composition which surrounds and is in electrical contact with the core, and

(c) optional further layers, which if present surround and are in electrical contact with the conductive polymeric element

(ii) positioning a resistive member to surround and to be in electrical contact with the conductive polymeric element ofthe first end ofthe elongate conductive member: and

(iii) connecting a power supply, via an insulated conductive lead, between the substrate and the first end ofthe conductive member, so that a potential difference is established between the substrate as cathode and the elongate conductive member as anode, whereby a protective electrical current flows from the surface of the anodic elongate conductive member to the cathodic substrate, the shape and resistivity ofthe said resistive member being arranged to decrease the protective electrical current flowing from that part of the elongate conductive member that is surrounded by the resistive member.

The shape and resistivity ofthe said resistive member is arranged to decrease the current flowing from the elongate conductive member. The term "decrease the current" is used to mean decrease the current relative to the current that would flow from the elongate conductive member if the resistive member were not present.

As mentioned above the invention may also be used to solve problems at an interface between two elongate conductive members joined end-to-end. Thus another aspect ofthe invention provides a method of cathodically protecting, from corrosion, an elongate substrate that is positioned in an electrolyte, the method comprising:

(i) providing at least two elongate conductive members, each having first and second ends, and each comprising

(a) a continuous elongate core comprising a material having a resistivity at 23°C of less than 5 x 10 ohm cm, and a resistivity at 23°C of less than 0.03 ohm/pi,

(b) an element which comprises a conductive polymer composition which surrounds and is in electrical contact with the core, and

(c) optional further layers, which if present surround and are in electrical contact with the conductive polymeric element;

(ii) positioning two resistive members to surround and to be in electrical contact with the conductive polymeric elements of respective second ends ofthe two elongate conductive members;

(iii) electrically connecting the cores ofthe said second ends ofthe two elongate conductive members, so that the conductive members are in end-to-end arrangement; and

(iv) connecting a power supply, via an insulated conductive lead, between the substrate and the first end of a first ofthe elongate conductive members, so that a potential difference is established between the substrate as cathode, and the elongate conductive members as anode,

whereby a protective electrical current flows from the surface ofthe anodic elongate conductive members to the cathodic substrate.

Preferably a similar resistive element is also positioned to surround and to be in electrical conduct with the conductive polymeric element at the first end of the first elongate conductive member (which is adjacent to and connected to the insulated conductive lead).

A further aspect of the invention provides a method of electrically grounding an object, comprising:

(i) providing an elongate conductive member having a first and second end, and comprising

(a) a continuous elongate core comprising a material having a resistivity at 23°C of less than 5 x 10 ohm cm, and a resistivity at 23°C of less than 0.03 ohm/m,

(b) an element which comprises a conductive polymer composition which surrounds and is in electrical contact with the core, and

(c) optional further layers, which if present surround and are in electrical contact with the conductive polymeric element;

(ii) connecting the first end ofthe elongate conductive member to the object using an insulated electrically conductive lead;

(iii) positioning a resistive member to surround and to be in electrical contact with the conductive polymeric element at the first end ofthe elongate conductive member, the shape and resistivity ofthe said resistive member being arranged to decrease the electrical current

flowing from the surrounded surface ofthe elongate conductive member during grounding; and

(iv) positioning die elongate conductive member and surrounding resistive member in the ground.

In the methods according to d e invention, the resistive member may have any suitable shape. In one embodiment the resistive member is a generally conically-shaped member as used in the kit of parts according to the invention. Where such a resistive conically-shaped member is used in a kit of parts, or in methods according to the present invention, the resistivity ofthe conicaily shaped member is preferably at least as high as the resistivity ofthe cβnductive polymeric element ofthe elongate conductive member. Preferably the resistivity of the conicaily shaped member is higher than the resistivity ofthe conductive polymeric element ofthe elongate conductive member. Preferably the resistivity ofthe material ofthe conicaily shaped member is at least twice, preferably at least five times, or at least ten times as high as the resistivity of the conductive polymeric element of the elongate conductive member.

Where a conicaily shaped resistive member is used in the methods according to the invention, the cone is preferably positioned on the elongate conductive member so that the wider end, rather ian the narrower end, ofthe conicaily shaped resistive member is nearer to the end ofthe elongate conductive member.

The conicaily shaped member provides a mass of resistive material surrounding the end ofthe elongate conductive member. It therefore acts to reduce die current exiting transversely at the end ofthe elongate conductive member. The conical shaping acts to reduce the current more at the wider end ofthe cone, than at the narrower end ofthe cone. The current density reduction preferably decreases progressively towards the narrower end ofthe cone.

The resistivity ofthe conicaily shaped member is preferably uniform throughout its body. However, it may be non-uniform, to optimise current flow properties as desired. The way this could be done would be evident to the man skilled in the art.

In preferred methods according to the present invention, the resistive member is generally conicaily shaped, and has a passageway therethrough for receiving the elongate conductive member. The passageway preferably extends axially ofthe cone, and conveniently may take the form of a generally cylindrical bore extending axially ofthe cone. The outer surface of the resistive member is generally conical, and die member is otherwise preferably a substantially solid mass, except for the passageway therethrough. The term "generally conicaily shaped" is also used herein to include shapes having frustoconical outer surface shape as well as those having an outer surface shape that is a complete cone.

In other embodiments of methods according to the invention, the resistive member may take other shapes. As an example it may comprise a wrapped tape. In this case the resistivity of the wrapped tape is preferably greater than, preferably at least twice or even five times the resistivity ofthe medium surrounding the elongate conductive member. In the methods of cathodically protecting an elongate electrically conductive substrate this medium will be the electrolyte. For example, for buried substrates and elongate conductive members, the medium surrounding the conductive member may be soil, or loose coke particles buried in the soil. In the method of electrically grounding equipment, the medium surrounding the elongate conductive member may similarly be, soil or loose coke particles buried in the soil.

The elongate conductive member used in all aspects ofthe present invention is preferably cylindrical. In one preferred embodiment it comprises a metal conductive core, a conductive polymeric jacket, typically having a resistivity of about 1.5 ohm cm. and an outer permeable jacket containing carbon particles, e.g. coke, between it and the conductive polymeric jacket. The outer permeable jacket may be a fabric.

Elongate conductive members ofthe type described above, which incoφorate conductive polymeric materials, are known for use in impressed current corrosion protection systems, and such use is described EP-A-00067679, WO930231 1 and GB941 1787.6. Such conductive members are also useful for grounding applications. Unlike bare metal wires, which are typically used as grounding rods, the elongate conductive members comprising conductive polymeric elements are not susceptible to rusting when buried in the ground. Also a bare metal wire used as grounding wire will discharge most of its current at its end nearest to its connection point with the object being grounded. This is due to the low radial resistance of such a wire. In contrast, an electrode comprising a conductive polymeric element has a higher radial resistance than a bare metal wire. Therefore current discharge tends to be distributed further along the length of grounding member comprising conductive polymeric material, than along a bare metal wire grounding member. This may both enhance the lifetime of the grounding member, and avoid electrical stress concentration at points directly beneadi the objects being grounded.

Elongate conductive members as used in the present invention are preferably at least 25m, more preferably at least 50m, or at least 75m long. The conductive members may even be at least 80m or at least 100m long. For certain applications length ranges of at least 200m, at least 300m or at least 500m may be appropriate. Where the length of conductive member required is longer than 50m, this may be provided by a single elongate conductive member, or by joining several conductive members end-to-end.

A preferred elongate conductive member according to the invention comprises a metal core, a conductive polymeric sheath surrounding the core, and carbon particles around the conductive polymeric sheath and contained within an outer jacket, which is preferably a fabric. This preferred elongate conductive member is preferably used in combination with the generally conicaily shaped resistive member described hereinbefore. When this combination is used, d e methods ofthe invention preferably comprise inserting the conicaily shaped resistive member within the outer fabric

jacket, and preferably also securing the jacket over the outer surface of the conicaily shaped member. The conicaily shaped member is preferably surrounded by coke within the outer jacket. In order to insert the conically-shaped member within the outer jacket, it may be necessary to displace some ofthe coke from widiin the jacket.

Examples of materials that may be used for the conicaily shaped resistive member, or other resistive member include polymeric materials containing a conductive filler, for example polyolefins such as polyethylene, and sintered ultra high molecular weight polyethylene, containing a conductive filler such as carbon. A particularly suitable material comprising sintered ultrahigh molecular weight polyethylene containing carbon is described in WO8806517 (MP1180PCT) and US89/02738 (MP1180 PCT3).

Embodiments of the present invention will now be described, by way of example, widi reference to the accompanying drawings, wherein

Figure 1 shows an impressed current corrosion protection system and Figure 2 shows an electrical grounding application for the present invention;

Figure 3 is an enlarged longitudinal sectional view ofthe dotted region III shown in Figures 1 and 2 showing the current densities that would be present without tiie use of a resistive member according to the invention;

Figure 4 is a longitudinal section view similar to that of Figure 3, showing the addition of a resistive cone as provided by the present invention;

Figure 5 is a longitudinal sectional view showing the use of resistive cones at an end-to-end joint between two elongate conductive members; and

Figure 6 is a longitudinal sectional view showing the use of resistive tape at the end of an elongate conductive member.

Referring to the drawings, Figure 1 shows an impressed current corrosion protection system in which the present invention is applicable. The substrate, in the form of pipeline 1, is connected to an elongate conductive member 3 via a power supply 5. The elongate conductive member is a distributed anode, and is connected to the positive terminal ofthe power supply 5. The substrate pipeline 1 is connected to the negative terminal ofthe power supply 5. The connections to the power supply 5 are made via insulated conductive wire lead 7. The electrical circuit, and an electrochemical cell, are completed through an electrolyte in which both the pipeline 1 and distributed anode 3 are positioned. The electrolyte might typically be soil. Electrochemical reactions occur at the surface of both pipeline 1 and die distributed anode 3, and result in a nett transfer of current to the pipeline 1. Corrosion ofthe pipeline 1 is therefore substantially prevented.

Figure 2 shows another application of the present invention, in this case to ground an object such as a building 9. A building 9 is connected via an insulated lead wire 7 to an elongate conductive member 3. The insulated lead 7 and die conductive member 3, together with the base ofthe building 9, are buried in soil 11. The elongate conductive member 3 is about 100m in length, and is conveniently buried generally parallel to the soil surface.

The construction of the elongate conductive member 3. and the insulated lead 7, and die connection between them are die same for both of embodiments shown in Figures 1 and 2, and shown in more detail in Figure 3.

Referring now to Figure 3, the elongate conductive member 3 comprises a generally cylindrical metal core 13, preferably copper, and a surrounding sheath of conductive polymeric material 15 that is in electrical contact with the core. The elongate conductive member 3 additionally comprises an outer fabric jacket 17, and particulate coke 19 contained within the outer fabric jacket 17 between that jacket and

the conductive polymeric sheath 15. The insulated lead 7 comprises a conductive core of copper 23 and a polyethylene insulation 25.

In order to form the connection between the insulated lead 7 and the elongate conductive member 3, all the layers surrounding the copper cores 13 and 23 are cut back. The cores 23 and 25 are then joined by a crimp 27. Any other joining method could be used. An insulating and moisture sealing sheath is then provided over the insulating layer 25 ofthe lead 7 and the outer fabric jacket 17 of the elongate conductive member 3. This sheath might be for example in the form of a heat shrinkable polymeric sleeve 29. The sleeve 29 is provided with a lining of a moisture sealing layer 30, such as a mastic or adhesive, e.g. a hot melt adhesive. The moisture sealing layer 30 may instead be provided separately from the sleeve. The sleeve 29 is heated, causing it to shrink into contact with the crimp 27 and the outer jacket 25 of lead wire 7 and the outer jacket 17 of the conductive member 3. During this heating the sealing layer 30 is urged into any voids in the connection region, thereby effecting a moisture seal.

In Figure 3 the resistive cone, or other resistive member, as required by the present invention is not shown. The current density exiting transversity from elongate conductive member in the absence ofthe resistive cone or member is indicated by the arrowed lines, labelled j, andj ₂ . The length of the arrowed lines j, andj ₂ indicates schematically the relative current density along the length ofthe elongate conductive member 3. As can be seen, the current density at the ends of the elongate conductive member is about twice that along the main length of the elongate conductive member 3. This non-uniform current density could disadvantageously lead to consumption of the coke particles 19 in the impressed current corrosion protection system of Figure 1, or failure by burning in the case ofthe grounding application shown in Figure 2 (current densities typically being higher in grounding applications than in impressed current corrosion protection systems).

Figure 4 is the same as Figure 3, except that is includes a resistive cone according to the invention. A cone 31 is positioned at one end of the elongate conductive member 3 so that the wide end of the cone is nearer than the point of the cone to the end ofthe elongate conductive member. The cone 31 has an axially extending cylindrical bore therethrough, and is positioned around the conductive polymeric sheath 15 ofthe conductive member 3, but within the fabric jacket 17. Coke 19 is displaced to make space for the cone 31. The free end ofthe fabric jacket 17 of the conductive member 3 is positioned on the cone 31, and may be secured thereto. Then the heat shrinkable sleeve 29 is shrunk into place over the end of fabric jacket 17 and cone 31.

The resistive, generally conicaily shaped member 31 typically has a resistivity of about 30 ohm cm. A particularly preferred material for the resistive cone 31 is sintered ultra-high molecular weight polyethylene containing carbon black particles. The resistive cone 31 acts to reduce the higher current densities j ₂ which would otherwise be present at the end of elongate conductive member 3 at the junction with the insulated lead 7, as described hereinbefore with reference to Figure 3.

Figure 5 shows another application ofthe resistive cone 31, at a junction between two elongate conductive members 3. Such a junction might be required, for example, where very long lengths of distributed electrode 3 are used in an impressed current corrosion protection system. In this drawing like reference numerals refer to like parts as used in the previous Figures. A resistive cone 31 is included at the connected end, of each ofthe elongate conductive members 3. The wider end of the cone is positioned closer than the point of the cone to the end ofthe conductive member 3 in each case.

Another possible arrangement (not shown) that is similar to Figure 5 would be to use a lead wire between the adjoining ends of the two elongate conductive members, in conjunction with a "T"shaped crimp to connect the lead wire to the core

of each elongate conductive member, and a "T" shaped heat shrinkable moulded sheath.

Figure 6 shows another embodiment according to the present invention. In this case the resistive cone is replaced by wrapped tape 33. The resistivity of this tape is preferably greater than the resistivity of the coke particles 19 in which it is embedded. Preferably the resistivity ofthe tape 3 is about twice that, or more, than that ofthe coke particles surrounding it. For simplicity the connection of core 13 of the elongate conductive member 3 to the lead wire 7 is not shown. It would be as in the embodiment of Figure 4.

It is also envisaged according to the invenUon that the resistive cones 31, and resistive tape 33 could be used on other elongate conductive members. In particular they could be used on a structure similar to that shown in these Figures but without the additional outer fabric jacket 17 and coke particles 19.