CA2231867A1 - Corrosion protection and electrical grounding - Google Patents
Corrosion protection and electrical grounding Download PDFInfo
- Publication number
- CA2231867A1 CA2231867A1 CA 2231867 CA2231867A CA2231867A1 CA 2231867 A1 CA2231867 A1 CA 2231867A1 CA 2231867 CA2231867 CA 2231867 CA 2231867 A CA2231867 A CA 2231867A CA 2231867 A1 CA2231867 A1 CA 2231867A1
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- Canada
- Prior art keywords
- conductive
- elongate
- resistivity
- resistive
- electrical contact
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 238000005260 corrosion Methods 0.000 title claims abstract description 27
- 230000007797 corrosion Effects 0.000 title claims abstract description 27
- 238000000034 method Methods 0.000 claims abstract description 35
- 239000000463 material Substances 0.000 claims abstract description 16
- 229920001940 conductive polymer Polymers 0.000 claims abstract description 11
- 239000000758 substrate Substances 0.000 claims description 35
- 239000000571 coke Substances 0.000 claims description 14
- 239000004744 fabric Substances 0.000 claims description 13
- 239000002245 particle Substances 0.000 claims description 13
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 11
- 239000002689 soil Substances 0.000 claims description 11
- 229910052799 carbon Inorganic materials 0.000 claims description 10
- 239000003792 electrolyte Substances 0.000 claims description 10
- 230000001681 protective effect Effects 0.000 claims description 5
- 230000001419 dependent effect Effects 0.000 claims 2
- 239000002184 metal Substances 0.000 description 9
- 229910052751 metal Inorganic materials 0.000 description 9
- WABPQHHGFIMREM-UHFFFAOYSA-N lead(0) Chemical compound [Pb] WABPQHHGFIMREM-UHFFFAOYSA-N 0.000 description 7
- 239000011231 conductive filler Substances 0.000 description 5
- 238000007789 sealing Methods 0.000 description 4
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 3
- 239000004698 Polyethylene Substances 0.000 description 3
- -1 polyethylene Polymers 0.000 description 3
- 229920000573 polyethylene Polymers 0.000 description 3
- 239000004699 Ultra-high molecular weight polyethylene Substances 0.000 description 2
- 239000006229 carbon black Substances 0.000 description 2
- 239000004020 conductor Substances 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 238000009413 insulation Methods 0.000 description 2
- 229920000785 ultra high molecular weight polyethylene Polymers 0.000 description 2
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 1
- 239000004831 Hot glue Substances 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- 238000004210 cathodic protection Methods 0.000 description 1
- 229910052801 chlorine Inorganic materials 0.000 description 1
- 239000000460 chlorine Substances 0.000 description 1
- 238000005056 compaction Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000003487 electrochemical reaction Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000013521 mastic Substances 0.000 description 1
- 229920000098 polyolefin Polymers 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection
- C23F13/02—Inhibiting corrosion of metals by anodic or cathodic protection cathodic; Selection of conditions, parameters or procedures for cathodic protection, e.g. of electrical conditions
- C23F13/06—Constructional parts, or assemblies of cathodic-protection apparatus
- C23F13/08—Electrodes specially adapted for inhibiting corrosion by cathodic protection; Manufacture thereof; Conducting electric current thereto
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Prevention Of Electric Corrosion (AREA)
Abstract
A kit of parts suitable for use in a method of impressed current corrosion protection, and comprising (a) an elongate conductive member comprising a core comprising a material having a resistivity at 23 ~C of less than 5 x 10-4 ohm cm, and a resistance at 23 ~C of less than 0.03 ohm/m, and a conductive polymer element which surrounds and is in electrical contact with the core, and (b) a generally conically shaped member having a passageway extending substantially axially therethrough for receiving at least the core and conductive polymeric element.
Description
W O 97/13890 PCT/~Di'1~303 -.
Corrosion Protection and Flectrical Grolln-lin~
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 gro~mding of objects. In particular the invemion relates to such kits of parts and melhods which include an elongate conductive member which may be connected, in use, by an insulated conductive lead, to a source of electrical current.
~ is known to provide impressed current CO~TOsiOIl 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 trans~ersely from the surface of the electrode towards the subskate 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 aplurality of discrete electrodes. each connçcte~l to the power supply. The distributed or discrete electrodes are usuallv conn~cte~l to the power supply so that they act as an anode, whîle the substrate acts as a cathode.
Examples of successful distributed electrodes that are known for use in the h~ ,s~ed current corrosion protection systems are described in EP-A-0067679 (MP769 EPC), GB 9411787.6 (B265 GB2), and W09302311 (RK463). The entire disclosures of these applications, and their corresponding US applications, are incorporated herein by reference.
EP-A-0067679 describes a distributed elect~ode comprising:
SUBSTITUTE SHEET (RULE 26) W O 97/13890 PCT/~Lr./~303 (i) a continuous elongate core comprising a material having a resistivity at23 C of less than S x 10 1 ohm cm, and a r~ t~nce 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 9411787.6 (B265GB2) and W09302311 (RK463) describe electrodes which comprise the elemenLs of the electrode of EP-A-OG67679, and in addition a surrounding mass of particulate carbon (e.g. coke breeze retained within a fabric jacket). W09302311 (RK 463) relates in particular to the desired acid and chlorine reci~t~n~e of that jacket, and GB 9411787.6 (B265) relates to the use of additional outer tensioning wraps to increase the compaction of the 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, W09302311 (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 anodesthat 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 thesubstrate to be protected. Frequently such discrete anodes comprise zinc or m~nesium. The anodes are connected via an in~ tt~l lead to the substrate to be SUBSTITUTE SHEET (RULE 26) CA 0223l867 l998-03-l2 W O 97/13~90 PCT/~'5.'~2~03 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 conn~cte-l 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 ofthe 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 of the electrode. This increased current density may lead to problems, for example, for the electrodes described above with reference to EP-A-0067679, W093023 1 1 and GB 941 1787.6, it may lead to consumption of the conductive filler in the electrode, and hence a shortening of the useful life ofelectrode. 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 toend, lengths of distributed electrodes of the 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 ~tt~nnzltion along the electrode length. Nonetheless it may present a problem.
The klt of parts provided by the invention may also be used to reduce this problem.
SUBSTITUTE SHEET (RULE 26) CA 0223l867 l998-03-l2 W O 97/13890 PCT/GB96tO2303 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 ,el,iesent a region of high stress, and consequently a region of w.o~kn~ss 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 terrnin~tetl and the electrical stress at this point must therefore be controlled to prevent electrical discharge at the joint. Control is typicallv provided by a stress cone, that is a conical layer that extends the zero potential of the screen along a conically tapering surface increasing in diameter from the end of the screen.
A first aspect of the 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 S x 10 ~ ohm cm, and a rPci.ct~n~.e 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 uith 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 conically shaped member having a passageway Çxt~nc~ing substantially axially therethrough for receiving at least the core and SUBSTITUTE SHEET (RULE 26) W O 97tl3890 PCT/GB96/02303 s conductive polymeric element of the 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 of the elongate electrode, and the conically shaped member having a resistivity that is at least as high as the resistivity of the conductive polymeric element.
In use, the first end of the elongate conductive member may be connecteA 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, W093023 1 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 imo the ground is much larger than along the main body of the 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 partsaccording 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 ai continuous current source, e.g. a power supply. In the grounding SUBSTITUTE SHEET (RULE 26) -CA 0223l867 l998-03-l2 W O 97/13890 PCT/GB~G~'~2303 application, the source of electrical current is a transitory current source, e.g. a li~htening strike, or electrical discharge from a high energy power line.
During operation of the h~ es~d current corrosion protection system and during discharge in the electrical grounding application, current flows transversely from the elongate conductive member. In a ~lcr lled case, the elongate conductive member is generally cylindrical, and the current flows radially outward from the outer surface of the 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~sing an electrode configuration of the type described with reference to EP-A-0067679, W093023 11 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 A/m. In both cases that current density may be about doubled at the interface between the electrode and the insulated lead, or the int~ e 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 of the 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 SUBSTITUTE SHEET (RULE 26) _ -(a) a continuous elongate core comprising a material having a resistivity at 23~C of less than 5 x 10 1 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 of the first end of the elongate conductive member; and (iii) cormecting a power supply, v ia an insulated conductive lead, between the substrate and the first end of the 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 of the said resistive member being arranged to decrease the p~o~eclive electrical current flowing from that part of the elongate conductive member that is surrounded by the resistive member.
The shape and resistivity of the 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.
SUBSTITUTE SHEET (RULE 26) _ -As mentioned above the invention may also be used to solve problems at an int~rf~r.e between two elongate conductive members joined end-to-end. Thus another aspect of the 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 m~tt~ri~l having a resistivity at 23~C of less than S x 10 ohm cm, and a resistivity at 23~C of less than 0.03 ohm~rn, (b) an element which comprises a conductive polymer composition which surrounds and is in electrical contact with the core, and (c~ optional further layers, ~vhich 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 of the hvo elongate conductive members;
(iii) electrically connecting the cores of the said second ends of the 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 of the elongate conductive members, so that a potential difference is established between the substrate as cathode, and the elongate conductive members as anode, SUI~ 111 UTE SHEET tRULE 26) _ whereby a protective electrical ctlrrent flows from the surface of the 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 oblect, comprlslng:
(i) providing an elongate conductive m~mber having a first and second end, and comprising (a) a continuous elongate core comprising a m~t~ l having a resistivity at 23~C of less than ~ x 10~ ohm cm, and a resistivity at 23~C of less than 0.03 ohrnJm, (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 eiectrical contact with the conductive polymeric element, (ii) connPcting the first end of the 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 of the elongate conductive member, the shape and resistivity of the said resistive member being arranged to decrease the electrical current SUBSTITUTE SHEET (RULE 26) flowing from the surrounded surface of the elongate conductive member during grounding; and (iv) positioning the elongate conductive member and surrounding resistive member in the ground.
In the methods according to the 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 of the conically shaped member is preferably at least as high as the resistivity of the c~nductive polymeric element of the elongate conductive member. Preferably the resistivity of the conically shaped member is higher than the resistivity of the conductive polymeric element of theelongate conductive member. Preferably the resistivity of the m~ten~l of the conically 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 conically 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 than the narrower end, of the conically shaped resistive member is nearer to the end of the elongate conductive member.
The conically shaped member provides a mass of resistive material surrounding the end of the elongate conductive member. It therefore acts to reduce the current exiting transversely at the end of the elongate conductive member. The conical shaping acts to reduce the current more at the wider end of the cone, than at the narrower end of the cone. The current density reduction preferably decreasesprogressively towards the narrower end of the cone.
SUBSTITUTE SHEET (RULE 26) CA 0223l867 l998-03-l2 The resistivity of the conically 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 conically shaped, and has a passageway therethrough for receiving the elongate conductive member. The passage~ ay preferably extends axially of the cone, and conveniently may take the form of a generally cylindrical bore e~cten~ling axially of the cone. The outer surface of the resistive member is generally conical, and the member is otherwise preferably a substantially solid mass, except for the passageway therethrough. The term "generally conically shaped" is also used herein to include shapes having frustoconical outer surface shape as ~ell as those having an outersurface 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 of the 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 ofelectrically grounding eqllipm~nt~ 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 of the present invention is preferably cylindrical. In one preferred embodiment it comprises a metal conductive core, a conductive polymeric jacket, typicallv having a resistivity of about 1.5 ohm cm~ and an outer permeable jacket cont~ining carbon particles, e.g. coke, between it and tne conductive polymeric jacket. The outer permeable jacket may be a fabric.
SUBSTITUTE ''I .__ I (RULE 26) CA 0223l867 l998-03-l2 Elongate conductive members of the type described above, which incorporate conductive polymeric materials, are known for use in il,.ples~ed current corrosion protection systems, and such use is described EP-A-00067679, W09302311 and GB9411787.6. 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 wirewill discharge most of its current at its end nearest to its connection point with the object being grounded. This is due to the lo-v radial resistance of such a wire. In contrast, an electrode comprising a conducti- e 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 beneath 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 conductivemembers mav even be at least 80m or at least 100m long. For certain applicationslength 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 conically shaped resistive member described hereinbefore. When this combination is used. the methods of the invention preferably comprise inserting the conically shaped resistive member within the outer fabric SUBSTITUTE SHEET (RULE 26) CA 0223l867 l998-03-l2 W O 97/13890 PCT/~,5./~303 jacket, and preferably also seC~ n~ the jacket over the outer surface of the conically shaped member. The conically 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 of the coke from within the jacket.
Examples of materials that may be used for the conically shaped resistive member, or other resistive member include polymeric materials cont~ining a conductive filler, for example polyolefins such as polyethylene, and sintered ultra high molecular weight polyethylene, cont~ining a conductive filler such as carbon. A
particularly suitable material comprising sintered ultrahigh molecular weight polyethylene cont~inin~ carbon is described in W08806517 (MP1180PCT) and US89/02738 (MP1180 PCT3).
Ennbotlimenr~ of the present invention will now be described, by way of example, with 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 of the dotted region III
shown in Figures 1 and 2 showing the current densities that would be present without the use of a resistive member according to the invention;
Figure 4 is a longitudinal section view similar to that of Figure 3, showing theaddition of a resistive cone as provided by the present invention;
Figure S 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.
SlJ~ JTE SHEET (RULE 26) CA 0223l867 l998-03-l2 W O 97/13890 PCT/~L~ 03 Referring to the drawings, Figure 1 shows an hllpl~ssed 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 terrnin~l of the power supply 5. The substrate pipeline 1 is connected to the negative terminal of the power supply 5. The connections to the power supply S
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 the distributed anode 3, and result in a nett transfer of current to the pipeline I . Corrosion of the 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 in~nl~ted lead wire 7 to an elongate conductive member 3. The in~ ed lead 7 and the conductive member 3, together with the base of the building 9, are buried in soil 11. The elongate conductive member 3 is about 1 OOm in length, and is conveniently buried generally parallel to the soil surface.
The construction of the elongate conductive member 3, and the in~ te~l lead 7, and the connection between them are the same for both of embo-lim~n~ shown inFigures 1 and 2, and shown in more detail in Figure 3.
~eferring 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 SUBSTITUTE Sl ~__ I (RULE 26) CA 0223l867 l998-03-l2 1~
the conductive polymeric sheath l 5. The in~ tPcl lead 7 comprises a conductive core of copper 23 and a polyethylene insulation ~ 5 .
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 bv a crimp 27. Any other joining method could be used. An insulating and moisture sealing sheath is then provided over the insulating layer 25 of the lead 7 and the outer fabric jacket l 7 of the elongate conductive member 3. This sheath might be for example in the form of a heat ~hrink~hle polymeric sleeve 29. The sleeve 29 is provided with a lining of a moisture sealing layer 3~, such as a mastic or adhesive, e.g. a hot melt adhesive. The moisture sealing layer 30 may instead be provided separatel~r 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 l 7 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 of the resistive cone or member is indicated by the arrowed lines, labelled j ~ and j2. The length of the arrowed lines j I and j7 indicates schem~tically the relative current density along the length of the 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 disadvantageouslv lead to consumption of the coke particles l 9 in the impressed current corrosion protection system of Figure l, or failure by burning in the case of the grounding application shown in Figure 2(current densities typically being higher in grounding applications than in illlp.essed current corrosion protection systems).
SUBSTITUTE SHEET (RULE 26) Figure 4 is the same as Figure 3, except that is includes a resistive cone according to the invention. A cone 31 is posilioned 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 of the elongate conductive member. The cone 31 has an axially ext~n~ling cylindrical bore therethrough, and is positioned around the conductive polymeric sheath 15 of the conductive member 3, but within the fabric jacket 17.Coke 19 is displaced to make space for the cone 31. The free end of the 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, generall- conically shaped merAber 31 typically has a resistivit~of about 30 ohm cm. A particularly preferred material for the resistive cone 31 is sintered ultra-high molecular ~ ~eight polyethylene cont~ining carbon black particles.
The resistive cone 31 acts to reduce the higher current densities j2 which wouldotherwise 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 ~ shows another application of the resistive cone 31, at a junction between two elongate conductive members 3. Such a junction might be required, for example, where ver~ long lengths of distributed electrode 3 are used in an impressed current corrosion protection s- stem. 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 of the elongate conductive members 3. The wider end of the cone is positioned closer than the point of the cone to the end of the 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 SUcs~ 111 UTE SHEET (RULE 26) CA 0223l867 l998-03-l2 W O 97/13~90 PCT/GB96/02303 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 wTapped 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 of the tape 3 is about twice that, or more, than that of the 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 invention that the resistive cones 31, andresistive 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.
SUBSTITUTE SHEET (RULE 26)
Corrosion Protection and Flectrical Grolln-lin~
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 gro~mding of objects. In particular the invemion relates to such kits of parts and melhods which include an elongate conductive member which may be connected, in use, by an insulated conductive lead, to a source of electrical current.
~ is known to provide impressed current CO~TOsiOIl 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 trans~ersely from the surface of the electrode towards the subskate 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 aplurality of discrete electrodes. each connçcte~l to the power supply. The distributed or discrete electrodes are usuallv conn~cte~l to the power supply so that they act as an anode, whîle the substrate acts as a cathode.
Examples of successful distributed electrodes that are known for use in the h~ ,s~ed current corrosion protection systems are described in EP-A-0067679 (MP769 EPC), GB 9411787.6 (B265 GB2), and W09302311 (RK463). The entire disclosures of these applications, and their corresponding US applications, are incorporated herein by reference.
EP-A-0067679 describes a distributed elect~ode comprising:
SUBSTITUTE SHEET (RULE 26) W O 97/13890 PCT/~Lr./~303 (i) a continuous elongate core comprising a material having a resistivity at23 C of less than S x 10 1 ohm cm, and a r~ t~nce 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 9411787.6 (B265GB2) and W09302311 (RK463) describe electrodes which comprise the elemenLs of the electrode of EP-A-OG67679, and in addition a surrounding mass of particulate carbon (e.g. coke breeze retained within a fabric jacket). W09302311 (RK 463) relates in particular to the desired acid and chlorine reci~t~n~e of that jacket, and GB 9411787.6 (B265) relates to the use of additional outer tensioning wraps to increase the compaction of the 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, W09302311 (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 anodesthat 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 thesubstrate to be protected. Frequently such discrete anodes comprise zinc or m~nesium. The anodes are connected via an in~ tt~l lead to the substrate to be SUBSTITUTE SHEET (RULE 26) CA 0223l867 l998-03-l2 W O 97/13~90 PCT/~'5.'~2~03 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 conn~cte-l 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 ofthe 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 of the electrode. This increased current density may lead to problems, for example, for the electrodes described above with reference to EP-A-0067679, W093023 1 1 and GB 941 1787.6, it may lead to consumption of the conductive filler in the electrode, and hence a shortening of the useful life ofelectrode. 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 toend, lengths of distributed electrodes of the 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 ~tt~nnzltion along the electrode length. Nonetheless it may present a problem.
The klt of parts provided by the invention may also be used to reduce this problem.
SUBSTITUTE SHEET (RULE 26) CA 0223l867 l998-03-l2 W O 97/13890 PCT/GB96tO2303 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 ,el,iesent a region of high stress, and consequently a region of w.o~kn~ss 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 terrnin~tetl and the electrical stress at this point must therefore be controlled to prevent electrical discharge at the joint. Control is typicallv provided by a stress cone, that is a conical layer that extends the zero potential of the screen along a conically tapering surface increasing in diameter from the end of the screen.
A first aspect of the 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 S x 10 ~ ohm cm, and a rPci.ct~n~.e 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 uith 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 conically shaped member having a passageway Çxt~nc~ing substantially axially therethrough for receiving at least the core and SUBSTITUTE SHEET (RULE 26) W O 97tl3890 PCT/GB96/02303 s conductive polymeric element of the 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 of the elongate electrode, and the conically shaped member having a resistivity that is at least as high as the resistivity of the conductive polymeric element.
In use, the first end of the elongate conductive member may be connecteA 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, W093023 1 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 imo the ground is much larger than along the main body of the 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 partsaccording 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 ai continuous current source, e.g. a power supply. In the grounding SUBSTITUTE SHEET (RULE 26) -CA 0223l867 l998-03-l2 W O 97/13890 PCT/GB~G~'~2303 application, the source of electrical current is a transitory current source, e.g. a li~htening strike, or electrical discharge from a high energy power line.
During operation of the h~ es~d current corrosion protection system and during discharge in the electrical grounding application, current flows transversely from the elongate conductive member. In a ~lcr lled case, the elongate conductive member is generally cylindrical, and the current flows radially outward from the outer surface of the 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~sing an electrode configuration of the type described with reference to EP-A-0067679, W093023 11 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 A/m. In both cases that current density may be about doubled at the interface between the electrode and the insulated lead, or the int~ e 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 of the 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 SUBSTITUTE SHEET (RULE 26) _ -(a) a continuous elongate core comprising a material having a resistivity at 23~C of less than 5 x 10 1 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 of the first end of the elongate conductive member; and (iii) cormecting a power supply, v ia an insulated conductive lead, between the substrate and the first end of the 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 of the said resistive member being arranged to decrease the p~o~eclive electrical current flowing from that part of the elongate conductive member that is surrounded by the resistive member.
The shape and resistivity of the 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.
SUBSTITUTE SHEET (RULE 26) _ -As mentioned above the invention may also be used to solve problems at an int~rf~r.e between two elongate conductive members joined end-to-end. Thus another aspect of the 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 m~tt~ri~l having a resistivity at 23~C of less than S x 10 ohm cm, and a resistivity at 23~C of less than 0.03 ohm~rn, (b) an element which comprises a conductive polymer composition which surrounds and is in electrical contact with the core, and (c~ optional further layers, ~vhich 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 of the hvo elongate conductive members;
(iii) electrically connecting the cores of the said second ends of the 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 of the elongate conductive members, so that a potential difference is established between the substrate as cathode, and the elongate conductive members as anode, SUI~ 111 UTE SHEET tRULE 26) _ whereby a protective electrical ctlrrent flows from the surface of the 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 oblect, comprlslng:
(i) providing an elongate conductive m~mber having a first and second end, and comprising (a) a continuous elongate core comprising a m~t~ l having a resistivity at 23~C of less than ~ x 10~ ohm cm, and a resistivity at 23~C of less than 0.03 ohrnJm, (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 eiectrical contact with the conductive polymeric element, (ii) connPcting the first end of the 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 of the elongate conductive member, the shape and resistivity of the said resistive member being arranged to decrease the electrical current SUBSTITUTE SHEET (RULE 26) flowing from the surrounded surface of the elongate conductive member during grounding; and (iv) positioning the elongate conductive member and surrounding resistive member in the ground.
In the methods according to the 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 of the conically shaped member is preferably at least as high as the resistivity of the c~nductive polymeric element of the elongate conductive member. Preferably the resistivity of the conically shaped member is higher than the resistivity of the conductive polymeric element of theelongate conductive member. Preferably the resistivity of the m~ten~l of the conically 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 conically 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 than the narrower end, of the conically shaped resistive member is nearer to the end of the elongate conductive member.
The conically shaped member provides a mass of resistive material surrounding the end of the elongate conductive member. It therefore acts to reduce the current exiting transversely at the end of the elongate conductive member. The conical shaping acts to reduce the current more at the wider end of the cone, than at the narrower end of the cone. The current density reduction preferably decreasesprogressively towards the narrower end of the cone.
SUBSTITUTE SHEET (RULE 26) CA 0223l867 l998-03-l2 The resistivity of the conically 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 conically shaped, and has a passageway therethrough for receiving the elongate conductive member. The passage~ ay preferably extends axially of the cone, and conveniently may take the form of a generally cylindrical bore e~cten~ling axially of the cone. The outer surface of the resistive member is generally conical, and the member is otherwise preferably a substantially solid mass, except for the passageway therethrough. The term "generally conically shaped" is also used herein to include shapes having frustoconical outer surface shape as ~ell as those having an outersurface 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 of the 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 ofelectrically grounding eqllipm~nt~ 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 of the present invention is preferably cylindrical. In one preferred embodiment it comprises a metal conductive core, a conductive polymeric jacket, typicallv having a resistivity of about 1.5 ohm cm~ and an outer permeable jacket cont~ining carbon particles, e.g. coke, between it and tne conductive polymeric jacket. The outer permeable jacket may be a fabric.
SUBSTITUTE ''I .__ I (RULE 26) CA 0223l867 l998-03-l2 Elongate conductive members of the type described above, which incorporate conductive polymeric materials, are known for use in il,.ples~ed current corrosion protection systems, and such use is described EP-A-00067679, W09302311 and GB9411787.6. 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 wirewill discharge most of its current at its end nearest to its connection point with the object being grounded. This is due to the lo-v radial resistance of such a wire. In contrast, an electrode comprising a conducti- e 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 beneath 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 conductivemembers mav even be at least 80m or at least 100m long. For certain applicationslength 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 conically shaped resistive member described hereinbefore. When this combination is used. the methods of the invention preferably comprise inserting the conically shaped resistive member within the outer fabric SUBSTITUTE SHEET (RULE 26) CA 0223l867 l998-03-l2 W O 97/13890 PCT/~,5./~303 jacket, and preferably also seC~ n~ the jacket over the outer surface of the conically shaped member. The conically 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 of the coke from within the jacket.
Examples of materials that may be used for the conically shaped resistive member, or other resistive member include polymeric materials cont~ining a conductive filler, for example polyolefins such as polyethylene, and sintered ultra high molecular weight polyethylene, cont~ining a conductive filler such as carbon. A
particularly suitable material comprising sintered ultrahigh molecular weight polyethylene cont~inin~ carbon is described in W08806517 (MP1180PCT) and US89/02738 (MP1180 PCT3).
Ennbotlimenr~ of the present invention will now be described, by way of example, with 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 of the dotted region III
shown in Figures 1 and 2 showing the current densities that would be present without the use of a resistive member according to the invention;
Figure 4 is a longitudinal section view similar to that of Figure 3, showing theaddition of a resistive cone as provided by the present invention;
Figure S 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.
SlJ~ JTE SHEET (RULE 26) CA 0223l867 l998-03-l2 W O 97/13890 PCT/~L~ 03 Referring to the drawings, Figure 1 shows an hllpl~ssed 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 terrnin~l of the power supply 5. The substrate pipeline 1 is connected to the negative terminal of the power supply 5. The connections to the power supply S
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 the distributed anode 3, and result in a nett transfer of current to the pipeline I . Corrosion of the 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 in~nl~ted lead wire 7 to an elongate conductive member 3. The in~ ed lead 7 and the conductive member 3, together with the base of the building 9, are buried in soil 11. The elongate conductive member 3 is about 1 OOm in length, and is conveniently buried generally parallel to the soil surface.
The construction of the elongate conductive member 3, and the in~ te~l lead 7, and the connection between them are the same for both of embo-lim~n~ shown inFigures 1 and 2, and shown in more detail in Figure 3.
~eferring 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 SUBSTITUTE Sl ~__ I (RULE 26) CA 0223l867 l998-03-l2 1~
the conductive polymeric sheath l 5. The in~ tPcl lead 7 comprises a conductive core of copper 23 and a polyethylene insulation ~ 5 .
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 bv a crimp 27. Any other joining method could be used. An insulating and moisture sealing sheath is then provided over the insulating layer 25 of the lead 7 and the outer fabric jacket l 7 of the elongate conductive member 3. This sheath might be for example in the form of a heat ~hrink~hle polymeric sleeve 29. The sleeve 29 is provided with a lining of a moisture sealing layer 3~, such as a mastic or adhesive, e.g. a hot melt adhesive. The moisture sealing layer 30 may instead be provided separatel~r 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 l 7 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 of the resistive cone or member is indicated by the arrowed lines, labelled j ~ and j2. The length of the arrowed lines j I and j7 indicates schem~tically the relative current density along the length of the 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 disadvantageouslv lead to consumption of the coke particles l 9 in the impressed current corrosion protection system of Figure l, or failure by burning in the case of the grounding application shown in Figure 2(current densities typically being higher in grounding applications than in illlp.essed current corrosion protection systems).
SUBSTITUTE SHEET (RULE 26) Figure 4 is the same as Figure 3, except that is includes a resistive cone according to the invention. A cone 31 is posilioned 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 of the elongate conductive member. The cone 31 has an axially ext~n~ling cylindrical bore therethrough, and is positioned around the conductive polymeric sheath 15 of the conductive member 3, but within the fabric jacket 17.Coke 19 is displaced to make space for the cone 31. The free end of the 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, generall- conically shaped merAber 31 typically has a resistivit~of about 30 ohm cm. A particularly preferred material for the resistive cone 31 is sintered ultra-high molecular ~ ~eight polyethylene cont~ining carbon black particles.
The resistive cone 31 acts to reduce the higher current densities j2 which wouldotherwise 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 ~ shows another application of the resistive cone 31, at a junction between two elongate conductive members 3. Such a junction might be required, for example, where ver~ long lengths of distributed electrode 3 are used in an impressed current corrosion protection s- stem. 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 of the elongate conductive members 3. The wider end of the cone is positioned closer than the point of the cone to the end of the 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 SUcs~ 111 UTE SHEET (RULE 26) CA 0223l867 l998-03-l2 W O 97/13~90 PCT/GB96/02303 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 wTapped 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 of the tape 3 is about twice that, or more, than that of the 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 invention that the resistive cones 31, andresistive 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.
SUBSTITUTE SHEET (RULE 26)
Claims (13)
1. 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 conically shaped member having a passageway extending substantially axially therethrough for receiving at least the core and conductive polymeric element of the 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 of the elongate electrode, and the conically shaped member having a resistivity that is at least as high as the resistivity of the conductive polymeric element.
2. A kit of parts according to any of claim 1, wherein the conically shaped member has a resistivity that is higher than the resistivity of the conductive polymeric element of the elongate conductive member.
3. A kit of parts according to claim 2, wherein the conically shaped member has a resistivity that is at least twice as high as the resistivity of the conductive polymeric element of the elongate conductive member.
4. 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 resistivity at 23°C of less than 5 x 10-4 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 of the first end of the elongate conductive member; and (iii) connecting a power supply, via an insulated conductive lead, between the substrate and the first end of the 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 of the 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.
(ii) positioning a resistive member to surround and to be in electrical contact with the conductive polymeric element of the first end of the elongate conductive member; and (iii) connecting a power supply, via an insulated conductive lead, between the substrate and the first end of the 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 of the 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.
5. 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 10-4 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 of the 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 of the elongate conductive member, the shape and resistivity of the said resistive member being arranged to decrease the electricalcurrent flowing from the surrounded surface of the elongateconductive member during grounding; and (iv) positioning the elongate conductive member and surrounding resistive member in the ground.
(a) a continuous elongate core comprising a material having a resistivity at 23°C of less than 5 x 10-4 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 of the 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 of the elongate conductive member, the shape and resistivity of the said resistive member being arranged to decrease the electricalcurrent flowing from the surrounded surface of the elongateconductive member during grounding; and (iv) positioning the elongate conductive member and surrounding resistive member in the ground.
6. A method according to claim 4 or 5, wherein the resistive member is a generally conically shaped member having a passageway extending substantially axially therethrough, the resistive member, having a wider end and a narrower end, and the step of positioning the resistive member to surround and to be in electrical contact with the said first end of the elongateconductive member is carried out so that the wider end of the conically shaped member is nearer than the narrower end of the conically shaped member to the said first end of the elongate conductive member.
7. A method according to claim 4 or 5, where the resistive member is in the form of tape wrapped around the said first end of the elongate member.
. A method according to claim 7, wherein the elongate conductive member is embedded in carbon particles, preferably coke, in soil, and the resistivity of the tape is higher than the resistivity of the surrounding carbon particles in the soil.
9. A kit of parts or method according to any preceding claim, wherein the elongate conductive member additionally comprises, (i) an outer ion - permeable jacket spaced from the conductive polymeric element. and (ii) carbon-rich particles, preferably coke, contained between the permeable jacket and the conductive polymeric element.
10. A method according to claim 9, when dependent on claim 6, wherein the step of positioning the conically shaped resistive member in electrical contact with the said end of the elongate conductive contact member is carried out by positioning the conically shaped member to surround the conductive polymeric element, but to lie within the outer permeable jacket.
11. A method according to claim 9, when dependent on claim 7, wherein the step of positioning the resistive tape in electrical contact with the elongate conductive member is carried out by wrapping the tape to surround the conductive polymeric element, but to lie within the outer fabric jacket.
12. A method according to claim 10 or 11, including the step of securing the outer permeable jacket of the elongate conductive member to the outer surface of resistive member, after the resistive member has been positioned around the conductive polymeric element of the elongate conductive member.
13. 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 10-4 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 two resistive members to surround and to be in electrical contact with the conductive polymeric elements of respective second ends of the at least two elongate conductive member;
(iii) electrically connecting the cores of the said second ends of the two elongate conductive members so that the conductive members are in end-to-end arrangement;
(iv) connecting a power supply via an insulated conductive lead, between the substrate and the first end of a first of the 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 of the anodic elongate conductive members to the cathodic substrate.
(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 10-4 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 two resistive members to surround and to be in electrical contact with the conductive polymeric elements of respective second ends of the at least two elongate conductive member;
(iii) electrically connecting the cores of the said second ends of the two elongate conductive members so that the conductive members are in end-to-end arrangement;
(iv) connecting a power supply via an insulated conductive lead, between the substrate and the first end of a first of the 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 of the anodic elongate conductive members to the cathodic substrate.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GBGB9520588.6A GB9520588D0 (en) | 1995-10-09 | 1995-10-09 | Corrosion protection and electrical grounding |
| GB9520588.6 | 1995-10-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2231867A1 true CA2231867A1 (en) | 1997-04-17 |
Family
ID=10782011
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2231867 Abandoned CA2231867A1 (en) | 1995-10-09 | 1996-09-20 | Corrosion protection and electrical grounding |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPH11512148A (en) |
| CA (1) | CA2231867A1 (en) |
| GB (1) | GB9520588D0 (en) |
| RU (1) | RU2153027C2 (en) |
| WO (1) | WO1997013890A1 (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2777573B1 (en) * | 1998-04-20 | 2000-06-23 | Atlantic Soc Fr Dev Thermique | DEVICE FOR THE CATHODE PROTECTION OF A WATER HEATER TANK |
| FR2792654B1 (en) * | 1999-04-23 | 2001-08-03 | Atlantic Soc Fr De Dev Thermiq | DEVICE FOR THE CATHODIC PROTECTION OF A WATER HEATER TANK, A HOT WATER PREPARER OR THE LIKE |
| JP2006004847A (en) | 2004-06-21 | 2006-01-05 | Sankosha Corp | Grounding conductor |
| CA2720002C (en) * | 2008-03-31 | 2013-10-01 | Michael Steven Georgia | Polymeric, non-corrosive cathodic protection anode |
| US7959454B2 (en) | 2009-07-23 | 2011-06-14 | Teledyne Odi, Inc. | Wet mate connector |
| US8968018B2 (en) | 2009-08-05 | 2015-03-03 | Teledyne Instruments, Inc. | Electrical penetrator assembly |
| BR112012002580A2 (en) | 2009-08-05 | 2020-03-10 | Teledyne Instruments, Inc. | ELECTRIC PENETRATOR UNIT AND ELECTRIC PENETRATOR ASSEMBLY |
| RU2706344C2 (en) * | 2018-01-18 | 2019-11-18 | Константин Васильевич Ермаков | Method of protection of technical devices in explosion hazardous areas from static electricity without shunting of cathodic protection potential |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB9116114D0 (en) * | 1991-07-25 | 1991-09-11 | Raychem Ltd | Corrosion protection system |
-
1995
- 1995-10-09 GB GBGB9520588.6A patent/GB9520588D0/en active Pending
-
1996
- 1996-09-20 JP JP9504020A patent/JPH11512148A/en active Pending
- 1996-09-20 CA CA 2231867 patent/CA2231867A1/en not_active Abandoned
- 1996-09-20 RU RU98108613A patent/RU2153027C2/en active
- 1996-09-20 WO PCT/GB1996/002303 patent/WO1997013890A1/en active Search and Examination
Also Published As
| Publication number | Publication date |
|---|---|
| JPH11512148A (en) | 1999-10-19 |
| RU2153027C2 (en) | 2000-07-20 |
| GB9520588D0 (en) | 1995-12-13 |
| WO1997013890A1 (en) | 1997-04-17 |
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