Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment – Metal or metal alloy
Patent
1995-05-25
1996-06-18
Tung, T.
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
Metal or metal alloy
205737, 205739, C23F 1300
Patent
active
055274404
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION AND FIELD OF THE INVENTION
This invention relates to a method of repairing a damaged elongate electrode.
INTRODUCTION TO THE INVENTION
Elongate electrodes are frequently used in impressed current corrosion protection systems, used for example to protect buried tanks or pipelines. Such impressed current corrosion protection systems function by establishing a potential difference between the substrate to be protected and a "spaced" apart electrode. The substrate and the electrode are connected to each other through a power supply of constant sign (DC or rectified AC) and the circuit is completed when electrolyte is present in the space between the substrate and the electrode. In most such impressed current systems, the substrate is the cathode (i.e. receives electrons). However, with substrates which can be passivated, e.g. Ni, Fe, Cr and Ti and their alloys, it is sometimes also possible to use impressed current systems in which the substrate is the anode. In both cathodic and anodic systems, the substrate is often provided with a protective insulating coating; in this case the impressed current flows only through accidentally exposed portions of the substrate. If the system is to have an adequate life, the electrode must not itself be corroded at a rate which necessitates its replacement; this is in contrast to the "sacrificial anodes" which are used in galvanic protection systems.
The electrode and the power supply must be such that the current density at all points on the substrate is high enough to prevent corrosion but not so high as to cause problems such as damage to the substrate (e.g. embrittlement) or disbonding of a protective coating on it. The power consumption of the system depends inter alia on the distance between the various parts of the substrate and electrode. In view of these factors, the theoretically best type of electrode is one which can be positioned so that it is relatively close to all points on the substrate. To this end it may have a shape corresponding generally to the shape of the substrate. Such an electrode is referred to herein as a "distributed electrode".
European Patent Publication No. 67,679 describes a distributed electrode, usually a distributed anode comprising a metal e.g. copper conductive core and a conductive polymeric jacket. The jacket provides the electrically active outer surface and is at least 500 .mu.m, preferably at least 1000 .mu.m, thick. The term "conductive polymer" is used herein to denote a composition which comprises a polymer component, and dispersed in a polymer component, a particulate conducive filler which has good resistance to corrosion especially carbon black or graphite. In particular the electrode comprises a low resistance core electrically surrounded by a conductive polymer composition, wherein the anode is an electrode spaced apart from the substrate, the electrode being in the form of an elongate flexible strip which can be bent through an angle of 90.degree. over a 10 cm radius, the electrode comprising (1) a continuous, elongate core which is composed of a material having a resistivity at 23.degree. C., of less than 5.times.10.sup.4 ohm.cm and a resistance at 23.degree. C. of less than 0.03 ohm/meter; and (2) an element which of at least 10%, according to ASTM D1708, of the electrode, and is in electrical contact with the core, and which is at least 500 .mu.m thick.
In a modification to the product described in European Patent Publication No. 67,679 the electrode is surrounded by coke-breeze pre-packaged in a fabric jacket. Such a configuration is used in a product sold by Raychem Corporation and /or its subsidiary companies under the name Anodeflex 1500 (Anodeflex is a registered Trade Mark), and is also described in PCT Patent Application PCT/GB92/01374, published as International Publication No. WO93/02311 on Feb. 4, 1993.
Although the fabric jacket containing the coke used in the Anodeflex 1500 product and described in the PCT Patent Application PCT/GB92/01374 is extremely hard wearing and abrasio
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Patent Abstracts of Japan, vol. 014, No. 489 (E-0994), Oct. 24, 1990 (abstract of Japanese Publication No. 2-202312 (Furukawa Electric Co. Ltd.)).
Search Report for British Application No. 9221706.6, dated 11 Nov. 1992.
Search Report for International Application No. PCT/GB93/02094, dated 16 Dec. 1993.
Pierre Christian J. H. Y.
Steeno Freddy L.
Burkard Herbert G.
Gerstner Marguerite E.
NV Raychem SA
Tung T.
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