EP0074463B1 - Method and apparatus for cleaning the inner walls of metallic tubular systems by electropolishing by means of moving electrodes - Google Patents

Description

The invention relates to a method for cleaning the inner walls of metallic line systems by electropolishing with the aid of moving electrodes, in which the electrolyte is filled into the line system, and a device for carrying out the method.

The removal of contaminants from metallic surfaces that are difficult to access, such as. B. the inner walls of pipes or other elements of metallic piping systems, especially the decontamination of radioactive contaminants in such systems, has so far not always been successful or satisfactory. One of the most common methods of doing this is electroplicing. However, previously dismantled pipes with movable electrodes could only be treated on the inside. For this purpose, both the entire immersion of the tube in the electrolyte and the filling of previously sealed chambers in the tube (tube pieces) were used (RP Allen and HW Arrowsmith, Materials Performance, Vol. 18, No. 11, pages 21 to 26 (1979) ). From DE-B-24 35 277 an anode for the galvanic treatment of a hollow profile is also known, which consists of a conductive anode body and spacers attached to it made of non-conductive material.

One of the serious disadvantages of this process was the need to remove the pipes to be cleaned before electropolishing. In addition, it was not possible to drive through several bends or through gate valves or taps.

The invention has for its object to provide a method and an apparatus with which (which) a metallic pipe system can be cleaned without having to disassemble it. Under piping system should be understood here: a system of straight and curved pipes, including the associated shut-off devices, such as. B. ball valves, slide or the like. The process should also be able to successfully clean rising and falling pipes immediately. The method and the device should be usable in particular for the decontamination of radioactive contaminated line systems.

The object is achieved in that the electrolyte is applied by means of high pressure of approximately 5 MPa or more to a section of the wall of the line system, and that the cathode is moved in the line system with the aid of the high pressure jet.

The device according to the invention for carrying out the method is characterized by an elastic high-pressure hose with a metallic stabilizing element serving as a current conductor or with a metallic strand serving as a current conductor, which is provided at its end with a high-pressure nozzle with a plurality of openings arranged radially and at an angle to the inner wall of the line system and by an elastic, metallic electrode which is arranged around the end piece of the high-pressure hose and connected to the current conductor, and by several insulating spacers which are arranged on the high-pressure hose in a fixed or displaceable manner, at least in the electrode area.

The electrode of the device according to the invention can be designed as a spiral cathode or as a coiled strip. In an advantageous embodiment of the device according to the invention, there is an elastic cap at the head of the high-pressure nozzle and a spacer at the end of the electrode facing away from the nozzle with an area which is> 1 times larger than that of the spacer (s) within the electrode area, however, a smaller area than the smallest cross-section of the pipe system to be traversed is provided.

Due to the elasticity of the electrodes, an adaptation to curved surfaces is possible. Due to the independent conveying by means of high-pressure jet recoil, dismantling of the pipes to be polished is no longer necessary and work can be carried out using elbows and slides as well as in inclined lines. By using high pressure jets at the same time, the pipes can be cleaned much better. The independent funding makes it possible to electropolish pipes remotely, which can significantly reduce the radiation exposure of the personnel. The electrolyte to be used is thrown through the high-pressure jet nozzle at a pressure from approx. 5 MPa to approx. 60 MPa onto the inner wall of the tube. The independent forward movement of the electrode inside the tube is achieved by the electrolyte jets directed obliquely against the tube wall. The electrolyte rays allow the current to pass through. A current between 300 and 400 amperes is sufficient in most cases.

• Zur Dekontamination der mit radioaktiven Verunreinigungen kontaminierten Innenwand 2 eines Leitungssystems 1 wurde in dieses ein elastischer Hochdruckschlauch 5, der an seinem Ende 7 mit einer Edelstahlhochdruckstrahldüse 9 versehen war und um welchen eine Elektrode 4 aus einem 3 mm starken VA-Draht, ca. 30 mm lang gewickelt war und der zwei Abstandshalter 11 und 12 aus Kunststoff aufwies, eingeführt. Mit einer Hochdruckstrahlpumpe (in der Zeichnung nicht dargestellt) mit einer Leistung von 5 MPa wurde der Elektrolyt mit einer Geschwindigkeit von 1 200 I/Stunde durch den Hochdruckschlauch 5 und die Strahldüse 9 in das Rohrsystem, dessen Nennweite 150 mm betrug, bzw. auf dessen Innenwand 2 geschleudert. Das Rohrsystem bestand in diesem Falle aus einem 5 m langen Rohr mit einem Bogen von 90° in der Mitte. Die Hochdruckdüse 9 wies eine Reihe von Öffnungen 10 auf, die so angeordnet waren, daß der Elektrolyt winkelig zur Innenwand 2 des Rohres 1 auf die Wand auftraf. Die Geschwindigkeit der Vorwärtsbewegung der Vorrichtung innerhalb des Rohres betrug 5 cm/Minute. Der Strom floß von der nichtdargestellten Stromquelle durch den Stromleiter 6, durch die mit diesem verbundene, um das Endstück 8 des Hochdruckschlauches 5 angeordnete Elektrode 4 und wurde durch den Elektrolyten 3 und die metallische Innenwand 2 der Rohres 1 zurückgeleitet. Die Stromstärke lag bei ca. 300 Ampere. Die Hochdruckdüse 9 besaß an ihrem Kopf eine elastische Kappe 13, die gemeinsam mit dem an dem der Düse abgewandten Ende der Elektrode angeordneten Abstandshalter 12 bewirkte, daß der durch die Hochdruckdüse 9 geschleuderte Elektrolyt 3 nicht zu rasch wieder abfloß. Die isolierenden Abstandshalter 11 und 12 waren in - diesem Falle dreiarmige Sterne, die eine zentrale Öffnung aufwiesen, so daß sie auf den Hochdruckschlauch 5 aufgeschoben werden konnten. Der Abstandshalter 12 wies dabei eine doppelt so große Querschnittsfläche wie der Abstandshalter 11 auf.

The invention is explained below using an exemplary embodiment and the drawing:

• In order to decontaminate the inner wall 2 of a line system 1 contaminated with radioactive contaminants, an elastic high-pressure hose 5, which was provided at its end 7 with a stainless steel high-pressure jet nozzle 9 and around which an electrode 4 made of a 3 mm thick VA wire, approx. 30 mm, was placed was wrapped long and the two spacers 11 and 12 made of plastic, introduced. With a high-pressure jet pump (not shown in the drawing) with an output of 5 MPa, the electrolyte was passed through the high pressure at a speed of 1200 I / hour hose 5 and the jet nozzle 9 in the pipe system, the nominal width was 150 mm, or thrown onto the inner wall 2. In this case the pipe system consisted of a 5 m long pipe with an elbow of 90 ° in the middle. The high pressure nozzle 9 had a series of openings 10 which were arranged such that the electrolyte struck the wall at an angle to the inner wall 2 of the tube 1. The speed of advancing the device within the tube was 5 cm / minute. The current flowed from the current source, not shown, through the current conductor 6, through the electrode 4 connected to it, around the end piece 8 of the high-pressure hose 5, and was conducted back through the electrolyte 3 and the metallic inner wall 2 of the tube 1. The current was about 300 amps. The high-pressure nozzle 9 had an elastic cap 13 on its head which, together with the spacer 12 arranged on the end of the electrode facing away from the nozzle, caused the electrolyte 3 thrown by the high-pressure nozzle 9 not to drain off too quickly. The insulating spacers 11 and 12 were - in this case, three-armed stars, which had a central opening, so that they could be pushed onto the high-pressure hose 5. The spacer 12 had a cross-sectional area twice as large as that of the spacer 11.

A decontamination factor of 300 was achieved, which could be increased by a factor of 10 after the inner wall 2 of the pipe had been sprayed again with warm water and high pressure, so that a total decontamination factor of 3,000 was achieved.

Claims (5)

1. Method for cleaning the inner walls of metallic pipework systems by electropolishing using mobile electrodes, wherein the electrolyte is filled into the pipework system, with the electrode applied to a sector of the pipework wall by means . of about 5 MPa high pressure, and the cathode moved in the pipework system by means of the high pressure jet.

2. Device for application of the method as defined in Claim 1 including an elastic high pressure hose (5), a metallic element of stabilization serving as a current conductor (6) or a stranded wire serving as a current conductor (6) provided at its end (7) with a high pressure nozzle (9) with several holes (10) placed radially and at angles with respect to the inner wall (2) of the pipework system (1) and with an elastic, metallic electrode (4) surrounding the end piece (8) of the high pressure hose (5) and connected with the current conductor (6), and several insulating spacers (11, 12) which, at least in the electrode zone, are firmly attached or movable on the high pressure hose (5).

3. Device as defined in Claim 2, wherein the electrode is made as a spiral cathode (4).

4. Device as defined in Claim 2, wherein the electrode (4) is made as helical band.

5. Device as defined in Claim 2, wherein at the head of the high pressure nozzle (9) an elastic cap (13) is provided and at the end of the electrode opposing the nozzle a spacer (12) with surfaces greater by the factor 1 each than that of the spacer(s) (11) within the electrode zone, although smaller than corresponding to the smallest cross section to be passed of the pipework system (1).

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