US3689395A - Cathodic protection system and delay-activation anode - Google Patents

Cathodic protection system and delay-activation anode Download PDF

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US3689395A
US3689395A US835023A US3689395DA US3689395A US 3689395 A US3689395 A US 3689395A US 835023 A US835023 A US 835023A US 3689395D A US3689395D A US 3689395DA US 3689395 A US3689395 A US 3689395A
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anode
anodes
cathodic protection
galvanic
protection system
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US835023A
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Floyd E Blount
Wallace B Allen
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ExxonMobil Oil Corp
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Mobil Oil Corp
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    • 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

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  • the specification discloses an extended lifetime cathodic protection system employing sequentially activated galvanic anodes. All of the anodes are connected by means of an electrical conductor to the metallic structure to be protected so that as one anode is consumed an additional anode or anodes are activated in sequence to provide continuous electrical current flow over any desired period of time.
  • a delay-activation anode is disclosed with a body of anode material enclosed by a hermetic casing which includes a relatively corrodible material such as iron. The corrodible material is chosen to provide a predetermined corrosion rate when immersed in a particular electrolyte, whereby an opening is created to expose the anode material at a desired delay time.
  • This invention relates to a novel method and apparatus for cathodic protection of metallic structures and, more particularly, to a delay-activation galvanic anode and process for making the same.
  • cathodic protection has been used for reducing the corrosion rate of such metallic structures, by making the steady state or corrosion electrical potentials of the metallic structure more electronegative.
  • the method is normally-applied to iron or steel structures but it is also used for lead, aluminum, and other metalcontaining structures.
  • An exposition on cathodic protection is found in Fundamentals of Cathodic Protection by F. E. Blount, University of Oklahoma Corrosion Control Short Course, Proceedings pages C-1C2'9, 1968.
  • galvanic anodes constructed of some material such as magnesium or zinc, are located in the same electrolyte with a metallic structure and are connected by means of an electrical conductor to such structure. Corrosion occurs at the galvanic anodes instead of at the structure being protected. Consequently, when complete consumption of the galvanic anode occurs, the lifetime of the cathodic protection system ceases. Normally, groups of galvanic anodes are connected in series by a single electrical conductor to the metallic structure being protected. These galvanic anodes are activated when first located in the electrolyte and all become consumed at essentially the same time. The lifetime of a cathodic protection system depends on various factors including the anode-to-electrolyte resistivity, but the maximum lifetime ordinarily expected for any environment is about ten years.
  • This invention provides a novel method and apparatus for providing extended lifetime cathodic protection for a metallic structure located in an electrolyte.
  • the method comprises inserting a plurality of galvanic anodes into the electrolyte, each anode being adapted to be activated sequentially. All of these anodes are connected by means of an electrical conductor to the metallic structure to be protected, whereby as one galvanic anode is consumed, an additional anode or anodes are activated in sequence to provide continuous electrical current flow through the conductor connected to the metallic structure. Any desired number of galvanic anodes can be arranged to be adapted at the same time to provide the desired current density for the cathodic protection system.
  • a delay-activation galvanic anode and process for making the same.
  • the process comprises the steps of securing an electrical lead to a body of anode material, such as magnesium, and bonding a piece of corrodible material to the edge of the body of anode material.
  • This piece of corrodible material e.g., iron
  • This piece of corrodible material is chosen to provide a predetermined corrosion rate when immersed in an intended electrolyte, whereby a passageway will be corroded through the piece of corrodible material to expose the body of anode material to the electrolyte.
  • the portion of the body of anode material which surrounds the piece of corrodible material is coated with a coating material which is substantially impervious to corrosive action, thereby providing a hermetic casing around the anode material.
  • FIG. 1 is a schematic cross-sectional view of a cathodic protection system illustrating the present invention in connection with a pipeline underlying a body of water;
  • FIG. 2 is an elevational view of one type of delayactivation galvanic anode
  • FIG. 3 is a sectional view taken along line 33 in FIG. 2;
  • FIG. 4 is a sectional view taken along line 44 in FIG. 2.
  • FIG. 1 illustrates the present invention embodied in a cathodic protection system for a pipeline 10 lying on or embedded in marine bottom 11 beneath the surface of a body of water 12.
  • the cathodic protection system comprises a plurality of galvanic anodes lying on marine bottom 11 at some distance from the pipeline 10. It will be appreciated that the elements of a cathodic protection system are shown schematically and that in an actual embodiment of the invention the usual practices and components of a cathodic protection system will be provided.
  • the galvanic anodes 14a-14e are connected by an electrical conductor 16 to a terminal 18 on the pipeline 10.
  • Galvanic anodes 14a-14e are arranged to be activated sequentially. More particularly, when first located in the water the galvanic anode 14a is arranged to be activated immediately to begin providing galvanic current through the conductor 16 to provide cathodic protection for pipeline 10.
  • the anodes 14b-14c are adapted to have delayedactivation times so that they become activated after the initial anode 14a has been substantially consumed. For example, anode 14b may have a delay time of two years, anode 14c four years, anode 14d six years, and anode 14c eight years. Accordingly, anodes 14b-14c will be activated sequentially so that only after eight years of operation will the anode 14e become activated.
  • FIGS. 2-4 illustrate one type of delay-activation galvanic anode which can be used in the cathodic protection system described in connection with FIG. 1. It will be appreciated that the galvanic anode has a specific shape illustrated which may be varied to fit the particular application required. It will also be appreciated that the galvanic anode assembly may have additional uses besides the cathodic protection system described above; for example, as an element of an electrical power source as dc scribed in copending application Ser. No. 835,022 to the present inventors, filed on June 20, 1969, now US. Pat. No. 3,568,140, entitled Underwater Electrical Power Source and Sonic Beacon.
  • the galvanic anode illustrated comprises a body of anode material 70, such as magnesium, which is encased by a coating 72 of a suitable material such as plastic, which is substantially impervious to corrosive action in the electrolyte intended for use.
  • a plug or plate 74 of some corrodible material, such as iron, forms a closure for an opening in the casing or coating 72.
  • the thickness, size, and properties of the plug 74 are chosen so as to provide a predetermined rate of corrosion when exposed to an electrolyte intended to be used. For example, in order to provide a delay activation of two years, a plate of iron on the order of one-fourth inch thick may be used for an electrolyte of sea water.
  • Embedded in the body of anode material 70 is a metallic core or rod 78 which provides an electrical terminal for the galvanic anode.
  • One process for manufacturing the delay-activation galvanic anode assembly shown in FIGS. 24 comprises casting the body of anode material 70 around the metallic core 78 in any desired molding shape.
  • the plate 74 of corrodible material can then be cast in the recess formed in the side of the body of anode material 70 as shown in FIGS. 2-4.
  • the casing for hermetically sealing the galvanic anode assembly can be formed by coating the body of anode material 70 with a coating material 72 of plastic material such as polyvinylchloride.
  • the coating material can be applied to all the portions of the body of anode material 70 except the corrodible plug 74, which remains exposed to the exterior.
  • a cathodic protection system for a metallic structure located in an electrolyte comprising:
  • each of said galvanic anodes comprising:
  • actuating means comprising a closure means sealed in said opening, said closure means being of a corrodible material and having 4 properties such that corrosion of a passageway through said closure means will occur at a predetermined time after said galvanic anode is exposed to said electrolyte;
  • electrical connector means for connecting each of said plurality of said anodes to said metallic structure whereby said plurality of galvanic anodes may be sequentially activated to provide extended-life cathodic protection for said metallic structure.
  • a cathodic protection system for a metallic structure located in an electrolyte comprising:
  • each of said galvanic anodes comprising:
  • a hermetic casing enclosing said body of anode material, at least a portion of said casing comprising a corrodible material exposed to the exterior thereof, whereby said anode body may become exposed to an electrolyte at a delayed time after location therein;
  • electrical connector means for connecting each of said plurality of said anodes to said metallic structure whereby said plurality of galvanic anodes may be sequentially activated to provide extended-life cath-odic protection for said metallic structure.

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  • 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

THE SPECIFICATION DISCLOSED AN EXTENDED LIFETIME CATHODIC PROTECTION SYSTEM EMPLOYING SEQUENTIALLY ACTIVATED GALVANIC ANODES. ALL OF THE ANODES ARE CONNECTED BY MEANS OF AN ELECTRICAL CONDUCTOR TO THE METALLIC STRUCTURE TO BE PROTECTED SO THAT AS ONE ANODE IS CONSUMED AN ADDITIONAL ANODE OR ANODES ARE ACTIVATED IN SEQUENCE TO PROVIDE CONTINUOUS ELECTRICAL CURRENT FLOW OVER ANY DESIRED PERIOD OF TIME. A DELAY-ACTIVATION ANODE IS DISCLOSED WITH A BODY OF ANODE MATERIAL ENCLOSED BY A HERMETIC CASING WHICH INCLUDES A RELATIVELY CORRODIBLE MATERIAL SUCH AS IRON. THE CORRODIBLE MATERIAL IS CHOSEN TO PROVIDE A PREDETERMINED CORROSION RATE WHEN IMMERSED IN A PARTICULAR ELEC-

TROLYTE, WHEREBY AN OPENING IS CREATED TO EXPOSE THE ANODE MATERIAL AT A DESIRED DELAY TIME.

Description

Stpt. 5, 1972 v BLOUNT ET AL 3,589,395
CATHODIC PROTECTION SYSTEM AND DELAY-ACTIVATION ANQDE Filed June 20. 1969 PIPELINE GALVANIC ANQDES ifi LI] ghs h,
FIG.2
72 FLOYD E. BLOUNT WALLACE B. ALLEN INVENTORS 70 BY 13mm ATTORNEY FIG.4
Patented Sept. 5, 1972 4 Claims ABSTRACT OF THE DISCLOSURE The specification discloses an extended lifetime cathodic protection system employing sequentially activated galvanic anodes. All of the anodes are connected by means of an electrical conductor to the metallic structure to be protected so that as one anode is consumed an additional anode or anodes are activated in sequence to provide continuous electrical current flow over any desired period of time. A delay-activation anode is disclosed with a body of anode material enclosed by a hermetic casing which includes a relatively corrodible material such as iron. The corrodible material is chosen to provide a predetermined corrosion rate when immersed in a particular electrolyte, whereby an opening is created to expose the anode material at a desired delay time.
BACKGROUND OF THE INVENTION This invention relates to a novel method and apparatus for cathodic protection of metallic structures and, more particularly, to a delay-activation galvanic anode and process for making the same.
It is well known that a metallic structure, such as a pipeline, when buried in the ground or immersed in a body of water, is subject to corrosion by galvanic action with the ground or water-forming an electrolyte. A techniquecalled cathodic protection has been used for reducing the corrosion rate of such metallic structures, by making the steady state or corrosion electrical potentials of the metallic structure more electronegative. The method is normally-applied to iron or steel structures but it is also used for lead, aluminum, and other metalcontaining structures. An exposition on cathodic protection is found in Fundamentals of Cathodic Protection by F. E. Blount, University of Oklahoma Corrosion Control Short Course, Proceedings pages C-1C2'9, 1968.
In cathodic protection, galvanic anodes, constructed of some material such as magnesium or zinc, are located in the same electrolyte with a metallic structure and are connected by means of an electrical conductor to such structure. Corrosion occurs at the galvanic anodes instead of at the structure being protected. Consequently, when complete consumption of the galvanic anode occurs, the lifetime of the cathodic protection system ceases. Normally, groups of galvanic anodes are connected in series by a single electrical conductor to the metallic structure being protected. These galvanic anodes are activated when first located in the electrolyte and all become consumed at essentially the same time. The lifetime of a cathodic protection system depends on various factors including the anode-to-electrolyte resistivity, but the maximum lifetime ordinarily expected for any environment is about ten years.
SUMMARY OF THE INVENTION This invention provides a novel method and apparatus for providing extended lifetime cathodic protection for a metallic structure located in an electrolyte. The method comprises inserting a plurality of galvanic anodes into the electrolyte, each anode being adapted to be activated sequentially. All of these anodes are connected by means of an electrical conductor to the metallic structure to be protected, whereby as one galvanic anode is consumed, an additional anode or anodes are activated in sequence to provide continuous electrical current flow through the conductor connected to the metallic structure. Any desired number of galvanic anodes can be arranged to be adapted at the same time to provide the desired current density for the cathodic protection system.
By another feature of the present invention, there is provided a delay-activation galvanic anode and process for making the same. The process comprises the steps of securing an electrical lead to a body of anode material, such as magnesium, and bonding a piece of corrodible material to the edge of the body of anode material. This piece of corrodible material, e.g., iron, is chosen to provide a predetermined corrosion rate when immersed in an intended electrolyte, whereby a passageway will be corroded through the piece of corrodible material to expose the body of anode material to the electrolyte. The portion of the body of anode material which surrounds the piece of corrodible material is coated with a coating material which is substantially impervious to corrosive action, thereby providing a hermetic casing around the anode material.
BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further described with reference to certain specific embodiments thereof and the accompanying drawings in which:
FIG. 1 is a schematic cross-sectional view of a cathodic protection system illustrating the present invention in connection with a pipeline underlying a body of water;
FIG. 2 is an elevational view of one type of delayactivation galvanic anode;
FIG. 3 is a sectional view taken along line 33 in FIG. 2; and
FIG. 4 is a sectional view taken along line 44 in FIG. 2.
DESCRIPTION OF SPECIFIC EMBODIMENTS Referring more specifically to the drawings, FIG. 1 illustrates the present invention embodied in a cathodic protection system for a pipeline 10 lying on or embedded in marine bottom 11 beneath the surface of a body of water 12. The cathodic protection system comprises a plurality of galvanic anodes lying on marine bottom 11 at some distance from the pipeline 10. It will be appreciated that the elements of a cathodic protection system are shown schematically and that in an actual embodiment of the invention the usual practices and components of a cathodic protection system will be provided.
The galvanic anodes 14a-14e are connected by an electrical conductor 16 to a terminal 18 on the pipeline 10. Galvanic anodes 14a-14e are arranged to be activated sequentially. More particularly, when first located in the water the galvanic anode 14a is arranged to be activated immediately to begin providing galvanic current through the conductor 16 to provide cathodic protection for pipeline 10. The anodes 14b-14c are adapted to have delayedactivation times so that they become activated after the initial anode 14a has been substantially consumed. For example, anode 14b may have a delay time of two years, anode 14c four years, anode 14d six years, and anode 14c eight years. Accordingly, anodes 14b-14c will be activated sequentially so that only after eight years of operation will the anode 14e become activated.
FIGS. 2-4 illustrate one type of delay-activation galvanic anode which can be used in the cathodic protection system described in connection with FIG. 1. It will be appreciated that the galvanic anode has a specific shape illustrated which may be varied to fit the particular application required. It will also be appreciated that the galvanic anode assembly may have additional uses besides the cathodic protection system described above; for example, as an element of an electrical power source as dc scribed in copending application Ser. No. 835,022 to the present inventors, filed on June 20, 1969, now US. Pat. No. 3,568,140, entitled Underwater Electrical Power Source and Sonic Beacon.
The galvanic anode illustrated comprises a body of anode material 70, such as magnesium, which is encased by a coating 72 of a suitable material such as plastic, which is substantially impervious to corrosive action in the electrolyte intended for use. A plug or plate 74 of some corrodible material, such as iron, forms a closure for an opening in the casing or coating 72. The thickness, size, and properties of the plug 74 are chosen so as to provide a predetermined rate of corrosion when exposed to an electrolyte intended to be used. For example, in order to provide a delay activation of two years, a plate of iron on the order of one-fourth inch thick may be used for an electrolyte of sea water.
Embedded in the body of anode material 70 is a metallic core or rod 78 which provides an electrical terminal for the galvanic anode.
One process for manufacturing the delay-activation galvanic anode assembly shown in FIGS. 24 comprises casting the body of anode material 70 around the metallic core 78 in any desired molding shape. The plate 74 of corrodible material can then be cast in the recess formed in the side of the body of anode material 70 as shown in FIGS. 2-4. The casing for hermetically sealing the galvanic anode assembly can be formed by coating the body of anode material 70 with a coating material 72 of plastic material such as polyvinylchloride. The coating material can be applied to all the portions of the body of anode material 70 except the corrodible plug 74, which remains exposed to the exterior.
The invention claimed is:
1. A cathodic protection system for a metallic structure located in an electrolyte comprising:
a plurality of galvanic anodes located in said electrolyte,
each of said galvanic anodes comprising:
a body of anode material;
an electrical lead secured to said body of anode material;
a casing surrounding said body of anode material and said electrical lead, said casing being impervious to corrosion and having at least one opening; and
a means for actuating said anode at a difierent time with respect to the others of said plurality of anodes, said actuating means comprising a closure means sealed in said opening, said closure means being of a corrodible material and having 4 properties such that corrosion of a passageway through said closure means will occur at a predetermined time after said galvanic anode is exposed to said electrolyte; and
electrical connector means for connecting each of said plurality of said anodes to said metallic structure whereby said plurality of galvanic anodes may be sequentially activated to provide extended-life cathodic protection for said metallic structure.
2. A cathodic protection system as defined in claim 1 wherein said casing comprises a coating of plastic material on said body of anode material.
3. A cathodic protection system as defined in claim 1 wherein said closure comprises a plate secured to the exterior of said body of anode material.
4. A cathodic protection system for a metallic structure located in an electrolyte comprising:
a plurality of galvanic anodes located in said electrolyte,
each of said galvanic anodes comprising:
a body of anode material;
an electrical lead secured to said body of anode material; and
a hermetic casing enclosing said body of anode material, at least a portion of said casing comprising a corrodible material exposed to the exterior thereof, whereby said anode body may become exposed to an electrolyte at a delayed time after location therein; and
electrical connector means for connecting each of said plurality of said anodes to said metallic structure whereby said plurality of galvanic anodes may be sequentially activated to provide extended-life cath-odic protection for said metallic structure.
References Cited UNITED STATES PATENTS 2,752,308 6/ 1956 Andrus 204-197 2,941,935 6/ 1960 Miller et a1. 204-197 3,108,939 10/1963 Sabins 204-196 3,146,182 8/1964 Sabins 204-197 3,308,046 3/ 1967 I Suleski 204196 2,856,342 10/ 1958 Van der Hoeven et a1. 204-197 3,383,297 5/1968 Eberius 204-197 3,403,090 9/1968 Tajiri et a1. 204 3,421,990 1/1969 Penix -l. 204197 3,451,917 6/1969 Laborde et al. 204196 3,516,917 6/1970 Maurin 204-196 3,354,063 11/1967 Shutt 204-148 TA-HSUNG TUNG, Primary Examiner 11.8. C1. X.R.
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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4544464A (en) * 1983-12-23 1985-10-01 Oronzio De Nora S.A. Ground anode prepacked with backfill in a flexible structure for cathode protection with impressed currents
US4855027A (en) * 1986-01-10 1989-08-08 Mccready David F Carbosil anodes
US4863578A (en) * 1988-04-25 1989-09-05 Corrosion Service Company Limited Corrodible link for cathodic protection systems
US6103097A (en) * 1997-09-30 2000-08-15 Russell; Larry L. Method and apparatus for lead contamination control
US7186327B1 (en) 1997-09-30 2007-03-06 Russell Larry L Method and apparatus for scaling control and in-situ cathodic protection

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4544464A (en) * 1983-12-23 1985-10-01 Oronzio De Nora S.A. Ground anode prepacked with backfill in a flexible structure for cathode protection with impressed currents
US4855027A (en) * 1986-01-10 1989-08-08 Mccready David F Carbosil anodes
US4863578A (en) * 1988-04-25 1989-09-05 Corrosion Service Company Limited Corrodible link for cathodic protection systems
US6103097A (en) * 1997-09-30 2000-08-15 Russell; Larry L. Method and apparatus for lead contamination control
US6423208B1 (en) 1997-09-30 2002-07-23 Larry L. Russell Method and apparatus for lead contamination control
US7186327B1 (en) 1997-09-30 2007-03-06 Russell Larry L Method and apparatus for scaling control and in-situ cathodic protection

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