Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment – Metal or metal alloy
Patent
1993-10-13
1996-06-11
Tung, T.
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
Metal or metal alloy
204280, 204294, 205737, 205739, C23F 1300
Patent
active
055252087
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to electric protection of various objects, and, more specifically, to methods for electric protection of a metal object, grounding electrodes for effecting the method and compositions for the grounding electrodes.
The invention can be used in systems of anti-corrosion cathodic protection of elongated metal structures, for example, underground main pipelines, as well as for electric protection of metal objects, including those of a complex shape, from external voltages.
BACKGROUND ART
Known in the art is a method for anti-corrosion cathodic protection of an elongated metal object, in which a long-line anode in the form of a continuous flexible steel core in an electrically conductive polymer envelope is installed in an electrolytic medium near the surface to be protected. In this case, the anode is disposed along the object at a pre-set distance therefrom determined by the thickness of the electric insulation plate between the anode and the surface to be protected, then the object and anode are connected to a polarizing current source (U.S. Pat. No. 4,487,676).
This known method however has a number of significant drawbacks. Thus, the anode is disposed in the immediate vicinity of the surface to be protected, the distance between them is hot optimized with respect to the electrical characteristics of the whole system. This fact, even in the case of a plane-parallel electric field, reduces the protection and results in nonuniform distribution of potential, especially with aged insulation.
Furthermore, the prior art method of disposition of the protective grounding (anode) is associated with a danger of over-protection at the drain point, i.e. there is a danger that the whole protection system will more rapidly fail.
Attempts to avoid over-protection by reducing the potential have resulted in reduction of the protection zone, i.e. impairment of the protection efficiency as a whole.
Known in the art is a method of cathodic protection of extended objects by means of a flexible long-line anode, which provides an optimum distance between the anode and the surface to be protected. The known method includes installation of a long-line anode in the form of a continuous flexible metal core encased by an electrically conductive flexible polymer envelope in contact therewith and installed in an electrolytic medium at a preset distance from the object, connection of this object and anode to current sources and polarization of the object from the anode. According to this method, the anode material resistance must be within 0.1 to 1000 ohm cm, while its longitudinal resistance must not exceed 0.03 to 0.003 ohm m. In so doing, the anode must be arranged relative to the object to be protected so as to keep a ratio (b+D)/(a+D)<2, where a is the minimum distance between the anode and the object to be protected, b is the maximum distance between the anode and the object to be protected and D is the maximum linear size of the object to be protected in the direction normal to the anode axis (U.S. Pat. No. 4,502,929).
This method is still characterized by some drawbacks hindering its application. For example, the known method does not provide needed uniformity of distribution of the protective difference of potentials along the circumference of the insulated pipe in the process of long-term operation. A similar negative result occurs when the pipe surface has no installation. This is due to the fact that the protective difference of potentials includes both the pipe potential proper determined by the integral value of the linear density of the polarizing current and the potential of the surrounding medium depending on the differential densities of the current flowing at each point of the volume of the current-conductive space. Under otherwise equal conditions, the latter is substantially determined from not only the ratio of the distances between the anode and the object to be protected and the linear size of the latter but also depends on the disposition of damage and discontin
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Delektorsky Alexander A.
Kornev Anatoly E.
Kudinova Rimma V.
Nekljudov Jury G.
Pritula Vsevolod V.
N. V. Raychem S.A.
Tung T.
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