EP0285747B1 - Process and apparatus for sustaining the cathodic protection of metal surfaces - Google Patents

Process and apparatus for sustaining the cathodic protection of metal surfaces Download PDF

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Publication number
EP0285747B1
EP0285747B1 EP88100558A EP88100558A EP0285747B1 EP 0285747 B1 EP0285747 B1 EP 0285747B1 EP 88100558 A EP88100558 A EP 88100558A EP 88100558 A EP88100558 A EP 88100558A EP 0285747 B1 EP0285747 B1 EP 0285747B1
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EP
European Patent Office
Prior art keywords
time
switched
current
potential
protective
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Expired - Lifetime
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EP88100558A
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German (de)
French (fr)
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EP0285747A1 (en
Inventor
Hans Prof. Dr. Rickert
Günther Dr. Holzäpfel
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RWE Energie AG
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VEREINIGTE ELEKTRIZITAETSWERKE WESTFALEN AG
Vereinigte Elektrizitatswerke Westfalen AG
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Priority to AT88100558T priority Critical patent/ATE59414T1/en
Publication of EP0285747A1 publication Critical patent/EP0285747A1/en
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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
    • C23F13/04—Controlling or regulating desired parameters

Definitions

  • the invention relates to a method for maintaining cathodic corrosion protection for metallic surfaces in contact with an electrolyte, with external current using an inert electrode as external current anode and a potentiostat, the protective current being switched off periodically and the existing potential (ice) directly between
  • the external current anode acting as reference electrode in this phase and the surface to be protected are measured and compared with the protective potential (Es o il) set on the potentiostat, and the difference (Eist-Esou) is used directly as a control variable for the protective current.
  • the object of the invention is therefore to provide a solution with which it is achieved that the protective potential just prevailing in each case can be measured and thus readjusted independently of the protective current which has flowed.
  • this object is achieved according to the invention in that the potential (ice) is measured after a slight time interval as a waiting phase after switching off and is used as a control variable in the control phase for the protective current flowing in the switch-on time.
  • the invention makes use of the knowledge that after switching off it was not as previously assumed, e.g. Platinized titanium anode has a very stable constant potential immediately and for a longer period of time, but that after switching off, the potential corresponding to the ohmic voltage drop at the electrode drops immediately, and that there is another relatively rapid potential drop connects, which depends on the level of the previous polarization and thus on the current flowing in the switch-on interval.
  • the stable potential to be measured is only reached after a certain time, which the invention exploits.
  • the procedure in one embodiment provides that the total switch-off time, i.e. the sum of the waiting phase and control phase is less than or equal to 10 ms, the invention also providing that the switch-on phase of the protection potential is a multiple of this total switch-off time.
  • the invention also provides a device which is characterized in that it is provided with an electronic delay element in order to delay the start of the measurement after the protective potential has been switched off.
  • the delay element can be designed such that the delay is in the range of 30 microseconds, in particular in the range of 25-50 microseconds.
  • the device also has a control element, by means of which the switch-off time for determining the controlled variable for the protective current can be limited to a maximum of 10 ms, wherein a control element can also be provided, by means of which the activation time of the protective current can be extended to a multiple of the total switch-off time .
  • the potential-time curve shown as an example in FIG. 1 shows the course of the potential after switching off the current at two different current intensities. These are currents that flowed through a platinum-coated titanium anode during the switch-on time.
  • the potential is only reached after a time of approx. 40 ⁇ s.
  • the surface 1 to be protected is in contact with an electrolyte 2, for example sea water in a ship's hull or household water in a hot water boiler or the like.
  • the surface 1 to be protected is connected to a setpoint voltage generator 3 with which the protection potential (Esou) should be set.
  • the target voltage generator 3 is connected to an isolation amplifier 5, one output 6 of which is part 7 of a double scarf ters 8 applied.
  • the other part of the double switch 8 is designated 9.
  • An integrator 10 is located between the two parts 7 and 9 of the double switch 8.
  • the double switch 8 as can be seen in FIG. 2, is actuated by a control element 11, which once comprises a timer and performs the functions "on / off".
  • a current amplifier 12 is connected behind part 9 of the double switch 8, one output of which is connected via line 13 to an electrode 14 immersed in electrolyte 2.
  • the electrode 14 in turn is also connected to the isolation amplifier 5 via the line 15.
  • an electronic delay element 17 is provided.
  • the possibility of regulating and maintaining the protection potential is drawn from a power supply unit 16, the inputs and outputs of which are labeled with the corresponding voltage designations, which correspond to those of the inputs and outputs of the protection system.
  • the mode of operation of the device is as follows: The protective current flows during a switch-on time that can be defined by the control element 11. If it is now to be regulated, the protective current is switched off via the control element 11 and, after a waiting phase, which is determined by the delay element 17, the potential (Eist) between the electrode 14, which acts as a reference electrode in this switching state, and the surface 1 to be protected is compared, the surface to be protected lies on ground. Any existing control deviation (E ist -E Soll ) is integrated several times by the integrator 10 in the control phase, the integrated voltage being used to control the protective current which is subsequently switched on again. This process is repeated periodically.

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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

For corrosion protection of metallic surfaces in contact with an electrolyte by an external current, using an inert electrode as the external current anode, and a potentiostat, the protective current being periodically switched off and the actual potential (Eact) being measured directly between the external current anode acting in this phase as reference electrode and the surface to be protected and being compared with the protective potential (Eset) set on the potentiostat, and the difference (Eact-Eset) being utilised directly as the control variable for the protective current, it is intended that the protective potential just prevailing at the time is measurable and hence readjustable independently of the protective current which has flowed through. This is achieved when the potential (Eact) is measured after a slight time interval after switching-off and is utilised in the control phase as the control variable for the protective current flowing during the switched-on time. <IMAGE>

Description

Die Erfindung richtet sich auf ein Verfahren zur Aufrechterhaltung eines kathodischen Korrosionsschutzes für metallische, mit einem Elektrolyten in Berührung stehende Flächen, mit Fremdstrom unter Verwendung einer inerten Elektrode als Fremdstromanode und eines Potentiostaten, wobei der Schutzstrom periodisch abgeschaltet und das vorhandene Potential (Eist) direkt zwischen der in dieser Phase als Bezugselektrode wirkenden Fremdstromanode und der zu schützenden Oberfläche gemessen und mit dem am Potentiostaten eingestellten Schutzpotential (Esoil) verglichen wird und die Differenz (Eist-Esou) direkt als Regelgröße für den Schutzstrom herangezogen wird.The invention relates to a method for maintaining cathodic corrosion protection for metallic surfaces in contact with an electrolyte, with external current using an inert electrode as external current anode and a potentiostat, the protective current being switched off periodically and the existing potential (ice) directly between The external current anode acting as reference electrode in this phase and the surface to be protected are measured and compared with the protective potential (Es o il) set on the potentiostat, and the difference (Eist-Esou) is used directly as a control variable for the protective current.

Ein derartiges Verfahren ist aus der DE-PS 29 16 934 der Anmelderin bekannt. Dieses Verfahren hat sich im vielfachen Einsatz in der Praxis bewährt.Such a method is known from DE-PS 29 16 934 by the applicant. This method has proven itself in multiple use in practice.

Forschungsergebnisse haben nun gezeigt, daß das bekannte Verfahren noch verbessert werden kann, und zwar insbesondere dahingehend, daß die Messungen möglichst stromunabhängig durchgeführt werden.Research results have now shown that the known method can still be improved, in particular in that the measurements are carried out as independently of the current as possible.

Aufgabe der Erfindung ist daher die Schaffung einer Lösung, mit der erreicht wird, daß das jeweils gerade herr schende Schutzpotential unabhängig von dem geflossenen Schutzstrom meßbar und damit nachregelbar ist.The object of the invention is therefore to provide a solution with which it is achieved that the protective potential just prevailing in each case can be measured and thus readjusted independently of the protective current which has flowed.

Mit einem Verfahren der eingangs bezeichneten Art wird diese Aufgabe gemäß der Erfindung dadurch gelöst, daß das Potential (Eist) nach einem geringfügigen zeitlichen Intervall als Wartephase nach dem Abschalten gemessen und als Regelgröße in der Regelphase für den in der Einschaltzeit fliessenden Schutzstrom herangezogen wird.With a method of the type mentioned in the introduction, this object is achieved according to the invention in that the potential (ice) is measured after a slight time interval as a waiting phase after switching off and is used as a control variable in the control phase for the protective current flowing in the switch-on time.

Durch die Unterteilung des Intervalles, in welchem der Schutzstrom abgeschaltet ist, in eine Wartephase und eine Meß- und Regelphase, wird erreicht, daß das Potential unabhängig von der Größe des vorher geflossenen Schutzstromes gemessen wird. Dabei macht sich die Erfindung die Erkenntnis zunutze, daß nach dem Abschalten nicht etwa wie vorher angenommen wurde, eine z.B. platinierte Titananode sofort und für einen längeren Zeitraum ein sehr stabiles konstantes Potential aufweist, sondern daß nach dem Abschalten zwar sofort der Abfall des Potentiales, der dem Ohm'schen Spannungsabfall an der Elektrode entspricht, erfolgt, und daß sich daran aber ein weiterer relativ schneller Potentialabfall anschließt, der von der Höhe der vorausgegangenen Polarisation und damit von dem in dem Einschaltintervall, geflossenen Strom abhängt. Das stabile Potential, das es zu messen gilt, wird erst nach einer gewissen Zeit erreicht, was die Erfindung ausnutzt.By dividing the interval in which the protective current is switched off into a waiting phase and a measurement and control phase, it is achieved that the potential is measured regardless of the size of the protective current that has previously flowed. The invention makes use of the knowledge that after switching off it was not as previously assumed, e.g. Platinized titanium anode has a very stable constant potential immediately and for a longer period of time, but that after switching off, the potential corresponding to the ohmic voltage drop at the electrode drops immediately, and that there is another relatively rapid potential drop connects, which depends on the level of the previous polarization and thus on the current flowing in the switch-on interval. The stable potential to be measured is only reached after a certain time, which the invention exploits.

War die bekannte Regelungsart schon anderen Schutzarten des kathodischen Korrosionschutzes überlegen, nicht zuletzt deswegen, weil die inerte Elektrode als Fremdstromanode und als Bezugselektrode herangezogen wurde, so war doch nicht mit Sicherheit auszuschließen, daß sich Meßfehler einschlichen, daß z.B. zu niedrig oder zu hoch gemessen wurde und damit ein zu niedriger oder zu hoher Schutzstrom aufgelegt wurde, was entweder keinen ausreichenden Korrosionsschutz mit sich brachte oder aber eine unerwünschte Wasserstoffentwicklung. Dem beugt die vorliegende Erfindung vor.While the known type of control was already superior to other types of protection against cathodic corrosion, not least because the inert electrode was used as an external current anode and as a reference electrode, it could not be ruled out with certainty that measurement errors would creep in, e.g. was measured too low or too high and thus too low or too high a protective current was applied, which either did not provide adequate corrosion protection or an undesirable evolution of hydrogen. The present invention prevents this.

Da die beschriebenen Erscheinungen insgesamt vergleichsweise kurze Zeiten benötigen, sieht die Verfahrensweise in Ausgestaltung vor, daß die gesamte Abschaltzeit, d.h. die Summe aus Wartephase und Regelphase kleiner gleich 10 ms ist, wobei die Erfindung auch vorsieht, daß die Einschaltphase des Schutzpotentiales ein Mehrfaches dieser Gesamtabschaltzeit beträgt.Since the phenomena described require comparatively short times overall, the procedure in one embodiment provides that the total switch-off time, i.e. the sum of the waiting phase and control phase is less than or equal to 10 ms, the invention also providing that the switch-on phase of the protection potential is a multiple of this total switch-off time.

Zur Lösung der gestellten Aufgabe und zum Erreichen der oben angesprochenen Vorteile sieht die Erfindung auch eine Vorrichtung vor, die sich dadurch auszeichnet, daß sie zur Verzögerung des Meßbeginns nach Abschalten des Schutzpotentiales mit einem elektronischen Verzögerungsglied versehen ist.To achieve the stated object and to achieve the advantages mentioned above, the invention also provides a device which is characterized in that it is provided with an electronic delay element in order to delay the start of the measurement after the protective potential has been switched off.

Hierbei kann das Verzögerungsglied so ausgebildet sein, daß die Verzögerung im Bereich von 30 µs, insbesondere im Bereich von 25 - 50 µs liegt.Here, the delay element can be designed such that the delay is in the range of 30 microseconds, in particular in the range of 25-50 microseconds.

Die Vorrichtung weist erfindungsgemäß auch ein Regelglied auf, durch welches die Abschaltzeit zur Ermittlung der Regelgröße für den Schutzstrom auf höchstens 10 ms begrenzbar ist, wobei darüber hinaus ein Regelglied vorgesehen sein kann, durch welches die Aufschaltzeit des Schutzstromes auf ein Vielfaches der gesamten Abschaltzeit ausdehnbar ist.According to the invention, the device also has a control element, by means of which the switch-off time for determining the controlled variable for the protective current can be limited to a maximum of 10 ms, wherein a control element can also be provided, by means of which the activation time of the protective current can be extended to a multiple of the total switch-off time .

Die Erfindung ist nachstehend anhand der Zeichnung beispielsweise näher erläutert, diese zeigt in

  • Fig. 1 eine Potential-Zeit-Kurve sowie in
  • Fig. 2 ein vereinfachtes Schaltbild einer Vorrichtung nach der Erfindung.
The invention is explained below with reference to the drawing, for example, which shows in
  • Fig. 1 shows a potential-time curve and in
  • Fig. 2 is a simplified circuit diagram of a device according to the invention.

Die in der Fig 1 als Beispiel dargestellte Potential-Zeit-Kurve zeigt den Verlauf des Potentials nach Abschalten des Stromes bei zwei verschiedenen Stromstärken. Dabei handelt es sich um Ströme, die in der Einschaltzeit durch eine platinierte Titan-Anode geflossen waren.The potential-time curve shown as an example in FIG. 1 shows the course of the potential after switching off the current at two different current intensities. These are currents that flowed through a platinum-coated titanium anode during the switch-on time.

Aus den Kurvenverläufen ist ersichtlich, daß der Abfall des Potentials, der dem Ohm'schen Spannungsabfall an der Elektrode entspricht, wie oben bereits angegeben, zwar sofort erfolgt. Diesem Abfall schließt sich aber ein weiterer Potentialabfall an. Dieser zweite vergleichsweise rasche Abfall ist von der Höhe der vorausgegangenen Polarisation und damit von dem in der Einschaltphase geflossenen Strom abhängig.It can be seen from the curves that the drop in the potential, which corresponds to the ohmic voltage drop at the electrode, as stated above, occurs immediately. This drop is followed by a further drop in potential. This second, comparatively rapid drop depends on the level of the previous polarization and thus on the current flowing in the switch-on phase.

Wie sich aus dem Diagramm ergibt, wird das Potential erst nach einer Zeit von ca. 40 µs erreicht.As can be seen from the diagram, the potential is only reached after a time of approx. 40 µs.

Wie sich aus Fig. 2 ergibt, steht die zu schützende Oberfläche 1 in Kontakt mit einem Elektrolyten 2, beispielsweise Meerwasser bei einem Schiffsrumpf oder Haushaltswasser bei einem Warmwasserboiler oder dgl. Die zu schützende Oberfläche 1 ist mit einem Sollspannungsgeber 3 verbunden, mit dem das Schutzpotential (Esou) eingestellt werden soll.As can be seen from FIG. 2, the surface 1 to be protected is in contact with an electrolyte 2, for example sea water in a ship's hull or household water in a hot water boiler or the like. The surface 1 to be protected is connected to a setpoint voltage generator 3 with which the protection potential (Esou) should be set.

Über die Leitung 4 ist der Sollspannungsgeber 3 mit einem Trennverstärker 5 verbunden, dessen einer Ausgang 6 den einen Teil 7 eines Doppelschalters 8 beaufschlagt. Der andere Teil des Doppelschalters 8 ist mit 9 bezeichnet. Zwischen den beiden Teilen 7 und 9 des Doppelschalters 8 liegt ein Integrator 10.Via the line 4, the target voltage generator 3 is connected to an isolation amplifier 5, one output 6 of which is part 7 of a double scarf ters 8 applied. The other part of the double switch 8 is designated 9. An integrator 10 is located between the two parts 7 and 9 of the double switch 8.

Der Doppelschalter 8 wird, wie sich aus Fig. 2 ergibt, von einem Steuerelement 11 betätigt, welches einmal einen Zeitgeber umfaßt und die Funktionen "Ein/Aus" ausübt. Hinter dem Teil 9 des Doppelschalters 8 ist ein Stromverstärker 12 geschaltet, dessen einer Ausgang über die Leitung 13 mit einer mit Elektrolyten 2 eintauchenden Elektrode 14 verbunden ist. Die Elektrode 14 ihrerseits ist auch über die Leitung 15 mit dem Trennverstärker 5 verbunden. Zusätzlich ist ein elektronisches Verzögerungsglied 17 vorgesehen.The double switch 8, as can be seen in FIG. 2, is actuated by a control element 11, which once comprises a timer and performs the functions "on / off". A current amplifier 12 is connected behind part 9 of the double switch 8, one output of which is connected via line 13 to an electrode 14 immersed in electrolyte 2. The electrode 14 in turn is also connected to the isolation amplifier 5 via the line 15. In addition, an electronic delay element 17 is provided.

Angedeutet ist die Möglichkeit zur Regelung und zur Aufrechterhaltung des Schutzpotentiales die notwendige Energie durch ein Netzteil 16 zu beziehen, dessen Ein- und Ausgänge mit den entsprechenden Spannungsbezeichnungen, die denen der Ein- und Ausgänge des Schutzsystems entsprechen, bezeichnet sind.The possibility of regulating and maintaining the protection potential is drawn from a power supply unit 16, the inputs and outputs of which are labeled with the corresponding voltage designations, which correspond to those of the inputs and outputs of the protection system.

Die Wirkungsweise der Vorrichtung ist dabei die folgende: Während einer vom Steuerelement 11 definierbaren Einschaltzeit fließt der Schutzstrom. Soll nun geregelt werden, wird der Schutzstrom über das Steuerglied 11 abgeschaltet und nach einer Wartephase, die vom Verzögerungsglied 17 bestimmt wird, das Potential (Eist) zwischen der in diesem Schaltzustand als Bezugselektrode wirkenden Elektrode 14 und der zu schützenden Oberfläche 1 verglichen, wobei die zu schützende Oberfläche auf Masse liegt. Eine ggf. vorhandene Regelabweichung (Eist-ESoll) wird vom Integrator 10 in der Regelphase mehrfach aufintegriert, wobei die aufintegrierte Spannung zur Steuerung des nachfolgend wieder zugeschalteten Schutzstromes dient. Dieser Vorgang wird periodisch wiederholt.The mode of operation of the device is as follows: The protective current flows during a switch-on time that can be defined by the control element 11. If it is now to be regulated, the protective current is switched off via the control element 11 and, after a waiting phase, which is determined by the delay element 17, the potential (Eist) between the electrode 14, which acts as a reference electrode in this switching state, and the surface 1 to be protected is compared, the surface to be protected lies on ground. Any existing control deviation (E ist -E Soll ) is integrated several times by the integrator 10 in the control phase, the integrated voltage being used to control the protective current which is subsequently switched on again. This process is repeated periodically.

Claims (8)

1. A method of maintaining cathodic protection from corrosion for metal surfaces which are in contact with an electrolyte, with external current, using an inert electrode as the external current anode and a portentiostat, wherein the protection current is periodically switched off and the existing potential (Eist) is directly measured between the external current anode which acts in this phase as a reference electrode, and the surface to be protected, and compared to the protection potential (ESoll) which is set at the potentiostat, and the difference (Elst- Esoll) is used directly as a regulating parameter for the protection current, characterised in that the potential (Elst) is measured after a short period of time as a waiting phase after switching off and is used as a regulating parameter in the regulating phase for the protection current which flows in the switched-on time.
2. A method according to claim 1 characterised in that the waiting phase lasts for at least 30 µs.
3. A method according to claim 2 characterised in that the total switched-off time is less than/equal 10 ms.
4. A method according to one of the preceding claims characterised in that the switched-on time for the protection current is a multiple of the total switched-off time.
5. Apparatus in particular for carrying out the method of one of the preceding claims characterised in that its is provided with an electronic delay member (17) to delay the beginning of measurement after the protection current is switched off.
6. Apparatus according to claim 5 characterised by an electronic delay member (17) which produces delays in the region of 30 µs, in particular in the region 25-50 µs.
7. Apparatus according to one of the preceding claims characterised by a regulating member (11) by which the switched-off time for detecting the regulating parameter for the protection current can be restricted to at most 10 ms.
8. Apparatus according to claim 7 characterised by a regulating member (11) by which the switched-on time of the protection current can be extended to a multiple of the total switched-off time.
EP88100558A 1987-03-11 1988-01-16 Process and apparatus for sustaining the cathodic protection of metal surfaces Expired - Lifetime EP0285747B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT88100558T ATE59414T1 (en) 1987-03-11 1988-01-16 METHOD AND DEVICE FOR MAINTAINING CATHODIC CORROSION PROTECTION FOR METALLIC SURFACES.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE3707791 1987-03-11
DE3707791A DE3707791C1 (en) 1987-03-11 1987-03-11 Method and device for maintaining cathodic corrosion protection for metallic surfaces with external current

Publications (2)

Publication Number Publication Date
EP0285747A1 EP0285747A1 (en) 1988-10-12
EP0285747B1 true EP0285747B1 (en) 1990-12-27

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EP (1) EP0285747B1 (en)
AT (1) ATE59414T1 (en)
DE (2) DE3707791C1 (en)
ES (1) ES2020584B3 (en)
GR (1) GR3001389T3 (en)
NO (1) NO172352C (en)

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Publication number Priority date Publication date Assignee Title
DE4025088A1 (en) * 1990-08-08 1992-02-13 Vaw Ver Aluminium Werke Ag CATHODICAL CORROSION PROTECTION FOR AN ALUMINUM CONTAINING SUBSTRATE
IT1253258B (en) * 1991-08-14 1995-07-14 Cgr Di Cadignani Gino PROCESS OF MAINTENANCE OF A CATHODIC PROTECTION AGAINST CORROSION AND DEVICE FOR THE IMPLEMENTATION OF SUCH PROCESS
SE502703C2 (en) * 1993-09-02 1995-12-11 Stri Ab Device for compensating an AC voltage occurring between a medium and a metallic pipeline located in the medium
DE4332922A1 (en) * 1993-09-28 1995-03-30 Kloeckner Humboldt Deutz Ag Two-high roller machine and process for the pressure comminution of granular moist material
BE1012223A3 (en) * 1998-10-07 2000-07-04 Mts Technical S A Protection device impose on current corrosion of water heater and similar equipment.
GB2518191B (en) * 2013-09-12 2017-08-02 Advantica Intellectual Property Ltd Survey device and method of surveying
CN111621792B (en) * 2020-07-03 2022-03-22 中国石油化工集团有限公司 Pipeline cathode protection output adjusting system and adjusting method
CN115558934B (en) * 2022-07-12 2024-04-19 国家管网集团浙江省天然气管网有限公司 Network-based constant potential rectifier fuzzy control method

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DE2361547A1 (en) * 1973-12-11 1975-06-19 Karl Heinz Ortmann Cathodic protection of buried metal objects - using periodic switch-off potential for adjusting protective current
DE2916934C2 (en) * 1979-04-26 1981-05-07 Vereinigte Elektrizitätswerke Westfalen AG, 4600 Dortmund Method and device for maintaining cathodic protection against corrosion

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NO880790L (en) 1988-09-12
NO172352C (en) 1993-07-07
NO172352B (en) 1993-03-29
GR3001389T3 (en) 1992-09-11
ES2020584B3 (en) 1991-08-16
DE3707791C1 (en) 1988-03-31
DE3861403D1 (en) 1991-02-07
EP0285747A1 (en) 1988-10-12
NO880790D0 (en) 1988-02-23
ATE59414T1 (en) 1991-01-15

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