EP0488995A2 - Korrosionsschutz - Google Patents

Korrosionsschutz Download PDF

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Publication number
EP0488995A2
EP0488995A2 EP92103118A EP92103118A EP0488995A2 EP 0488995 A2 EP0488995 A2 EP 0488995A2 EP 92103118 A EP92103118 A EP 92103118A EP 92103118 A EP92103118 A EP 92103118A EP 0488995 A2 EP0488995 A2 EP 0488995A2
Authority
EP
European Patent Office
Prior art keywords
anode
substrate
electrolyte
tube
ion
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.)
Granted
Application number
EP92103118A
Other languages
English (en)
French (fr)
Other versions
EP0488995B1 (de
EP0488995A3 (en
Inventor
James Patrick Reed
Albert Highe
Michael Masia
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Raychem Corp
Original Assignee
Raychem Corp
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Raychem Corp filed Critical Raychem Corp
Publication of EP0488995A2 publication Critical patent/EP0488995A2/de
Publication of EP0488995A3 publication Critical patent/EP0488995A3/en
Application granted granted Critical
Publication of EP0488995B1 publication Critical patent/EP0488995B1/de
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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
    • C23F13/04—Controlling or regulating desired parameters
    • 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
    • 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
    • C23F13/16—Electrodes characterised by the combination of the structure and the material

Definitions

  • This invention relates to the corrosion protection of pipes, vessels and other corrodible substrates.
  • a corrosion-protecting potential difference between the substrate and a counter-electrode.
  • a DC power source is used to establish the desired potential difference between the substrate as cathode and an anode which is composed of a material which is resistant to corrosion, eg. platinum, graphite, or a conductive polymer.
  • a material which is resistant to corrosion eg. platinum, graphite, or a conductive polymer.
  • the known corrosion systems suffer from serious disadvantages, in particular a failure to obtain sufficiently uniform current distribution on the substrate.
  • This disadvantage can arise from the use of one or more discrete electrodes; or from the use of a distributed electrode, eg a platinum wire, whose radial resistance to the substrate is low, so that at high currents the current density on the anode decreases rapidly as the distance from the power source increases; and/or because the substrate is shielded (including those situations in which the substrate has a complex shape which results in one part of the substrate being shielded by another part of the substrate).
  • the flexible elongate anodes disclosed in U.S. Patents Nos.
  • 4,502,929 and 4,473,450 which comprise a low resistance core surrounded by a conductive polymer coating, are very useful in mitigating this disadvantage, but they cannot be used at the high current densities which are required in certain situations, for example the protection of structures which have no protective coating thereon.
  • Another disadvantage is the relatively short life of anodes (including the electrical connections thereto), especially when exposed to environments which are highly corrosive or which contain oily contaminants (and in the case of platinum anodes, when exposed to fresh potable water), and the difficulty and expense of repairing or replacing the anodes when this becomes necessary.
  • a barrier which lies between the substrate and the counter-electrode, which is spaced part from the substrate and the counter-electrode, and which directs the flow of ions between the substrate and the counter-electrode, and thus provides an improved current distribution on the substrate, and/or enables the counter-electrode to be more easily maintained or replaced, and/or reduces the rate at which the current density on an elongate electrode changes with the distance from the power source, and/or provides a controlled environment around the electrode to improve its efficiency, eg. by reducing contamination or by making it possible to surround the counter-electrode with an electrolyte which is different from the electrolyte which contacts the substrate.
  • the present invention provides an assembly for cathodically protecting an electrically conductive substrate from corrosion, and a method of corrosion protection which makes use of such an assembly, the assembly comprising
  • the present invention provides a method of cathodically protecting an electrically conductive substrate from corrosion by an electrolyte which contacts it, which method comprises establishing a potential difference between the substrate and a discrete anode which is located in an anode chamber containing an electrolyte and having at least one ion-permeable section therein, the electrolyte being fed into the chamber and being driven by hydrostatic pressure from the chamber through said at least one ion-permeable section.
  • the barrier which is used in the present invention modifies the way in which current flows between the substrate and the anode so as to produce one or more of the desirable results noted above. In general, this will result in the resistance between the substrate and the anode being substantially higher than it would be in the absence of the barrier, preferably by a factor of at least 10, for example at least 100, or even more, balancing the resulting advantages against the disadvantage of the higher voltages required as the resistance increases.
  • the barrier preferably comprises a plurality of ion-permeable sections.
  • Preferred ion-permeable sections include simple apertures, for example a hole in the wall of a tube, or an opening at the end of a tube.
  • Ion-permeable sections which are composed of an ion-permeable material, eg. a glass frit, can also be used, especially when it is desired to have the anode contacted by an electrolyte which is different from that which contacts the substrate.
  • the size and/or the spacing of the ion-permeable sections can be uniform or non-uniform, depending upon the desired current distribution on the substrate.
  • the ion-permeable sections are preferably of fixed dimensions.
  • the distance between adjacent ion-permeable sections is preferably less than 10 times, particularly less than 4 times, the distance between the ion-permeable sections and the substrate.
  • An important factor in determining the size of the apertures can be the need to ensure that anodic reaction products, eg gaseous chlorine, do not block the apertures. Unless the conditions of operation are such that anodic reaction products remain dissolved in the electrolyte or can be easily vented, care must be taken to prevent harmful build-up of such reaction products between the anode and the barrier. In some case positive benefit can be derived from such reaction products, eg. to lessen fouling of marine structures.
  • hydrostatic pressure drives the electrolyte through the ion-permeable section(s) towards the substrate.
  • hydrostatic pressure which is typically provided by a pump, can have the alternative and/or additional advantages of (1) reducing the danger that the ion-permeable sections will be blocked by contaminants present in the electrolyte between the barrier and the substrate, for example oily contaminants in the water layer at the bottom of an oil storage tank, and/or (2) making it possible, when it is desired to surround the anode with an electrolyte which is different from the electrolyte which contacts the substrate (eg. when protecting a potable water tank with a platinum anode), to prevent substantial contamination of the anode electrolyte by the substrate electrolyte with minimal contamination of the substrate electrolyte by the anode electrolyte.
  • the barrier must not be electronically connected to the substrate or the anode, and is preferably composed of (including coated by) an electrically insulating material, eg. a plastic.
  • Preferred barriers are in the form of a tube (which may be of round or other cross section) or a plurality of tubes which are joined together to form a branched structure.
  • the branch tubes are preferably of smaller cross-section than the main tube, for example so that the total cross-sectional area of the branch tubes is no greater than the cross-sectional area of the main tube.
  • the tube or tubes can be heated by an internal or external heater to reduce the viscosity of the electrolyte therein (including to prevent it from freezing) and/or to reduce its resistivity.
  • the tube or tubes can be arranged as a continuous loop, so that electrolyte circulates through them, or can simply terminate in an open end (ie. an ion-permeable section) or a closed end.
  • the tube (or at least one of the tubes where a plurality of tubes are joined together) surrounds an elongate anode, for example one whose length is at least 100 times, preferably at least 1000 times, its smallest dimension, typically a metal wire, especially a platinum or platinum-coated wire, having for example a diameter of at least 0.01 inch (0.025 cm), preferably 0.02 to 0.3 inch (0.05 to 0.075 cm).
  • the internal diameter of the tube containing the wire anode is preferably P times the diameter of the wire, where P is 2 to 100, eg. 5 to 30, for example a diameter of 0.125 to 0.6 inch (0.36 to 1.5 cm).
  • the tube containing the wire anode comprises ion-permeable sections, or there are branch tubes comprising ion-permeable sections attached thereto, or both.
  • the branch tubes can comprise perforations and/or can have an open end, which may be fitted with a nozzle. In this way, it is possible to obtain a much more uniform current density on the anode, and hence also on the substrate, than in the absence of the barrier. This desirable result is achieved because the resistance between the substrate and the elongate anode is much greater than it would be in the absence of the tube or tubes, preferably by a factor of at least 10, for example at least 100 or even higher. This is especially valuable when it is desirable to provide a high current from a distributed anode.
  • anode comprising a metal core and a conductive polymer jacket, because such anodes cannot support the high current densities required.
  • a platinum wire anode or the like; such anodes will support very high current densities, but at the currents needed in such circumstances, the current density on the anode decreases rapidly as the distance from the power source increases, as demonstrated for example in Example 2 below.
  • the anode is a discrete electrode which is placed in a vessel remote from the substrate, and electrolyte is pumped (or gravity fed) from the anode vessel to the vicinity of the substrate via one or more tubes which constitute the barrier and which contain (including terminate in) ion-permeable sections.
  • the resistivity of the electrolyte is preferably less than 50 ohm.cm, particularly less than 20 ohm.cm, so that the tubes can be of a convenient size.
  • the main tube or tubes conveying electrolyte from the anode chamber to the vicinity of the substrate may for example have an equivalent inner diameter (ie. of cross-section equal to a circle of that diameter) of 1 to 12 inches (2.5 to 30.5 cm), and the branch tubes may for example have an equivalent diameter of 0.5 to 3 inches (1.25 to 7.5 cm).
  • the voltage of the power source is preferably less than 100 volts, particularly less than 50 volts, with the system being designed with this preference in mind.
  • electrolyte When there is a net transfer of electrolyte through the ion-permeable section(s) of the barrier, electrolyte must be supplied to the anode, and this can be done by recycling electrolyte from the vicinity of the substrate and/or by supplying fresh electrolyte.
  • electrolyte When build-up of electrolyte in the vicinity of the substrate must be avoided, eg. in the bottom of an oil storage tank, means must be provided for removing excess electrolyte; the excess electrolyte can be recycled to the anode, if desired or necessary after filtering or otherwise treating it to remove harmful contaminants.
  • Preferred uses for the present invention include the protection of city water tanks, ballast tanks in ships, oil rigs, cooling tanks for power stations, water tanks for secondary recovery in oil wells, oil storage tanks, heat exchangers, condensers, heater treaters, and buried pipes, in particular pipes buried below the permafrost line, for example oil pipes in frozen tundra.
  • each of Figures 1 and 2 shows a DC power source 1 which is connected to an anode 2 and a corrodible substrate 3 which is a cathode.
  • Anode 2 and substrate 3 are separated by a barrier 4 which comprises ion-permeable sections 45, and are connected by electrolyte 5 through sections 45.
  • a positive hydrostatic pressure is maintained from the interior of the barrier 4 across the ion-permeable sections 45 by means of pump 6.
  • Figure 1 is a diagrammatic side view which shows the corrodible substrate 3 within a vessel 7 containing the electrolyte 5.
  • the anode 2 is an elongate anode
  • the barrier 4 is a perforated tube containing the anode.
  • FIG. 2 is a diagrammatic side view in which the substrate 3 is an oil storage tank in which the electrolyte 5 is a highly corrosive aqueous mixture covered by oil 8.
  • the anode is a discrete anode which lies within an anode chamber 21.
  • the barrier 4 comprises, in addition to the part of the anode chamber which lies between the anode and the tank 3, a tube 41 which leads from anode chamber 21 to the center of tank 3 and branch-tubes 42 which communicate with tube 41, which are of relatively small diameter, and which contain perforations 45. Means not shown removes excess electrolyte from the tank 5. Pump 6 maintains a positive pressure across the perforations 45 and thus reduces the danger that they will become blocked by oily contaminants in the water layer.
  • Figure 3 shows in diagrammatic plan view an alternative way of protecting a vessel 3.
  • Tube 44 surrounds the vessel and contains elongate anode 2.
  • Branch tubes 42 communicate with tube 44, pass through the wall of the vessel, and terminate in open ends or nozzles 45 which can point in one or more desired directions.
  • Figure 4 shows in diagrammatic side view a system for protecting a pipe 3 which is buried in the earth or immersed in the sea or other electrolyte.
  • the anode 2 lies within an anode chamber 21 and is surrounded by electrolyte 3.
  • Barrier 4 comprises a tube 41 which extends downwards from the anode chamber 21 and branch tubes 42 which communicate with and extend horizontally from the tube 41 under the pipe 3, and which comprise nozzles 45 covered by protective caps.
  • Tube 41 contains a heater 9 which may be used to prevent the electrolyte from freezing or reduce its viscosity, for example when the tube 41 passes through a layer of earth which is frozen or liable to freezing, and/or to decrease its resistivity.
  • a positive hydrostatic pressure is maintained across the nozzles 45, and the electrolyte lost in consequence is replaced from electrolyte storage tank 23.
  • Figure 5 shows a tube with perforations therein through which ion-containing electrolyte can emerge; the perforations shown are uniformly spaced and of uniform size, but they could be of different sizes and separations in order to provide desired current distribution.
  • Figure 6 shows a tube composed of an ion-conducting membrane through which ions can pass, but non-ionic material cannot.
  • Figure 7 shows a perforated tube which is covered by an ion-conducting membrane.
  • Figure 8 shows a part of a perforated tube in which each perforation is covered by an ion-conducting membrane.
  • Figure 9 shows an open-ended tube through the open end of which ion-containing electrolyte can emerge.
  • Figure 10 shows in open-ended tube whose open end is covered by a porous plug.
  • Figure 11 shows a tube having a plurality of branch nozzles mounted thereon.
  • Figure 12 shows the arrangement of the tube in Example 1, as described below.
  • procedures (A) and (B) are comparative examples and procedure (C) is an example of the invention.

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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)
  • Preventing Corrosion Or Incrustation Of Metals (AREA)
  • Internal Circuitry In Semiconductor Integrated Circuit Devices (AREA)
  • Thermistors And Varistors (AREA)
EP92103118A 1986-07-18 1987-07-17 Korrosionsschutz Expired - Lifetime EP0488995B1 (de)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US88819886A 1986-07-18 1986-07-18
US888198 1986-07-18
EP87306336A EP0253671B1 (de) 1986-07-18 1987-07-17 Korrosionsschutz

Related Parent Applications (1)

Application Number Title Priority Date Filing Date
EP87306336.6 Division 1987-07-17

Publications (3)

Publication Number Publication Date
EP0488995A2 true EP0488995A2 (de) 1992-06-03
EP0488995A3 EP0488995A3 (en) 1992-07-01
EP0488995B1 EP0488995B1 (de) 1995-10-25

Family

ID=25392719

Family Applications (2)

Application Number Title Priority Date Filing Date
EP92103118A Expired - Lifetime EP0488995B1 (de) 1986-07-18 1987-07-17 Korrosionsschutz
EP87306336A Expired - Lifetime EP0253671B1 (de) 1986-07-18 1987-07-17 Korrosionsschutz

Family Applications After (1)

Application Number Title Priority Date Filing Date
EP87306336A Expired - Lifetime EP0253671B1 (de) 1986-07-18 1987-07-17 Korrosionsschutz

Country Status (7)

Country Link
EP (2) EP0488995B1 (de)
JP (1) JPS6333587A (de)
AT (2) ATE129529T1 (de)
CA (1) CA1331160C (de)
DE (2) DE3781735T2 (de)
ES (1) ES2033852T3 (de)
NO (1) NO177355C (de)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ES2119692A1 (es) * 1996-07-12 1998-10-01 Lopez Calleja Lopez Jose Luis Dispositivo, sistema y procedimiento para aislar electricamente la estructura metalica de una embarcacion de una masa externa.
DE102014203659A1 (de) * 2014-02-28 2015-09-03 Siemens Aktiengesellschaft Kühlvorrichtung für einen Konverter einer Hochspannungs-Gleichstrom-Übertragungsanlage

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB9426216D0 (en) * 1994-12-23 1995-02-22 Cathelco Ltd Descaling ships ballast tanks

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3022242A (en) * 1959-01-23 1962-02-20 Engelhard Ind Inc Anode for cathodic protection systems
NL247246A (de) * 1959-12-17 1900-01-01
GB1108692A (en) * 1964-04-17 1968-04-03 Gordon Ian Russell Method for installing cathodic protection against corrosion
NL6612237A (de) * 1966-08-31 1968-03-01
JPS5137263B1 (de) * 1968-10-28 1976-10-14
US4171254A (en) * 1976-12-30 1979-10-16 Exxon Research & Engineering Co. Shielded anodes
US4318787A (en) * 1980-02-22 1982-03-09 Conoco Inc. Sacrificial anode composition in cathodic protection process
US4457821A (en) * 1983-01-17 1984-07-03 Pennwalt Corporation Cathodic protection apparatus for well coated metal vessels having a gross bare area

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ES2119692A1 (es) * 1996-07-12 1998-10-01 Lopez Calleja Lopez Jose Luis Dispositivo, sistema y procedimiento para aislar electricamente la estructura metalica de una embarcacion de una masa externa.
DE102014203659A1 (de) * 2014-02-28 2015-09-03 Siemens Aktiengesellschaft Kühlvorrichtung für einen Konverter einer Hochspannungs-Gleichstrom-Übertragungsanlage

Also Published As

Publication number Publication date
NO873015D0 (no) 1987-07-20
ATE129529T1 (de) 1995-11-15
EP0488995B1 (de) 1995-10-25
ES2033852T3 (es) 1993-04-01
DE3751575D1 (de) 1995-11-30
EP0253671A2 (de) 1988-01-20
NO177355B (no) 1995-05-22
EP0488995A3 (en) 1992-07-01
DE3751575T2 (de) 1996-06-27
DE3781735D1 (de) 1992-10-22
JPS6333587A (ja) 1988-02-13
EP0253671A3 (en) 1988-08-03
EP0253671B1 (de) 1992-09-16
DE3781735T2 (de) 1993-04-22
ATE80674T1 (de) 1992-10-15
NO177355C (no) 1995-09-06
NO873015L (no) 1988-01-19
CA1331160C (en) 1994-08-02

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