GB2576062A

GB2576062A - An apparatus and a method for loosening a tube section from a tube plate

Info

Publication number: GB2576062A
Application number: GB1819955.4A
Authority: GB
Inventors: Sabotin Izidor; Valentincic Josko; Pleterski Matej; Jerman Marko; Lebar Andrej; Dresar Pavel
Original assignee: Numip Eng Construction Maintenance And Production Ltd; Univerza V Ljubljani Univ Of Ljublijana
Current assignee: Numip Eng Construction Maintenance And Production Ltd; Univerza V Ljubljani Univ Of Ljublijana
Priority date: 2018-08-02
Filing date: 2018-12-07
Publication date: 2020-02-05
Anticipated expiration: 2038-12-07
Also published as: GB201819955D0; GB2576062B

Abstract

An apparatus for loosening an electrically conductive tube section 4 from a tube plate 5 surrounding, at least partially, the tube section at its outer surface comprises: an electrode 6 which is adapted to be introduced into the tube section such that a longitudinal axis A of the electrode is at least in substance arranged in parallel to or collinear with a central axis C of the tube section; a motor 1 for rotating the electrode around the longitudinal axis of the electrode; a coupling element 3 for coupling the electrode to the motor, the coupling element being adapted to transmit a rotational movement of the motor, in particular of a motor shaft 9, to the electrode such that the electrode rotates around its longitudinal axis; and an electric voltage source 8 for providing an electric voltage between the electrode and the tube section, in particular for generating electric discharges between the electrode and the tube section, the voltage source having a first terminal 10 connectable to the electrode and a second terminal 11 connectable to the tube section. Electric discharges generated between the electrode and the tube section cause heating and plastic deformation of the tube section, allowing subsequent mechanical extraction of the tube section from the tube plate using a reduced pull force.

Description

An Apparatus and a Method for Loosening a Tube Section from a Tube Plate

The present invention relates to an apparatus for loosening an electrically conductive tube section from a tube plate which surrounds at least partially the tube section at its outer surface. The present invention also relates to a method of loosening an electrically conductive tube section from a tube plate.

In various applications, a tube is to be extracted from a surrounding tube plate, for example of a heat exchanger system, in particular a boiler, condenser or evaporator. The tube usually passes through a cutout in the tube plate. Thus, the tube plate may surround a section of the tube at its outer surface. The tube may be fixedly connected to the tube plate, in particular in such a way that the outer surface of the tube and the inner surface of the cutout contact each other areally and form a fluid and/or gas tight connection.

Heat exchanger systems are for example used in nuclear power plants and other facilities. Such heat exchanger systems maybe monitored on a regular basis to ensure a proper functioning. Because of malfunctions or during a normal maintenance process, it maybe necessary to remove a tube from a tube plate.

CA 2 506 375 Ai and US 7 305 756 B2 describes a tube extracting device for compressing a tube and extended from a conventional drum of a boiler to remove the tube. US 4 776 072 A describes a process for extracting a section of a heat-exchanger tube.

It is further known to use electrical discharges in a manufacturing process which is called electrical discharge machining (EDM). This is also known as spark machining or spark erosion. A desired shape of a work piece is obtained by using electrical discharges to remove material from the work piece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid or air and subject to an electric voltage.

EP o 004 751A2 describes an electrical discharge heating device, where a material can be heated by being introduced into, or into the vicinity of, a discharge.

Furthermore, it is known to use electrical discharges in illumination devices as for example disclosed by US 2 945 986, US 1 930 148, US 2 087 845 and US 2 945 987.

As a tight connection may exist between a tube and a tube plate, tooling may be required to extract such a tube from a tube plate. Prior to the extraction of a tube from a tube plate, it could further be necessary or helpful to loosen the tube from the tube plate as, for example, the tube may have been mechanically expanded to seal against the inner diameter of the cutout in the tube plate.

The present invention seeks to provide a simple and easy to use apparatus for loosing an electrically conductive tube section from a tube plate surrounding, at least partially, the tube section at its outer surface. The invention also seeks to provide a simple and easy to use method for loosening an electrically conductive tube section from a tube plate surrounding, at least partially, the tube section at is outer surface.

The problem is solved by an apparatus in accordance with the features of claim 1 and, respectively, by a method in accordance with the features of claim 9. Preferred embodiments of the present invention are described in the dependent claims.

In accordance with the present invention, an apparatus for loosening an electrically conductive tube section from a tube plate surrounding, at least partially, an outer surface of the tube section comprises an electrode which is adapted to be introduced into the tube section such that a longitudinal axis of the electrode is at least in substance arranged in parallel to or collinear with a central axis of the tube section, a motor for rotating the electrode around the longitudinal axis of the electrode, a coupling element for coupling the electrode to the motor, the coupling element being adapted to transmit a rotational movement of the motor, in particular of a motor shaft, to the electrode such that the electrode rotates around its longitudinal axis, and an electric voltage source for providing an electric voltage between the electrode and the tube section, in particular for generating electric discharges between the electrode and the tube section, the voltage source having a first terminal which is connected or connectable to the electrode and a second terminal which is connectable to the tube section.

The electrode of the apparatus can be introduced into the tube section. The electrode can therefore be brought into the inner volume of the tube section, preferably in such a way that it is facing the portion of the tube section which is surrounded by the tube plate. The portion of the tube section may in particular pass through a cutoff or the like of the tube plate, and the inner surface of the cutoff maybe in contact with the outer surface of this portion, in particular in such a way that there is a leak-tight connection between the tube section and the tube plate.

The dielectric in a gap between the electrode and the inner surface of the tube section may preferably be gas, such as air, or alternatively a non-conducting fluid. Due to the electric voltage applied between the electrode and the tube section, electric discharges between the electrode and the tube section can be generated. This causes a heat-up of the tube section and/or of a joint between the tube section and the tube plate. The tube section’s temperature of annealing may thereby be reached. The heat-up causes an expansion of the tube segment in radial direction. Since the surrounding tube plate heats up at a slower rate, which is in particular due to the larger volume of the tube plate, the tube plate extends less. This may have the effect that the tube section deforms plastically and shrinks after cooling down. The shrinkage of the tube section’s outer diameter enables a mechanical extraction of the tube section using a lower pull force. For example, the pull force maybe ten times lower in comparison with the unloosened tube section.

The electric discharges generated between the electrode and the tube section may not only cause a heat-up of the tube section, but may also remove material from the inner surface of the tube section, similar to an electrical discharge machining process. This may also be regarded as a dry electroerosion process. The discharges, which may result in sparks, melt and evaporate a small part of the inner surface of the tube section. This material is mainly removed in very small pieces which leave microscopic craters on the inner surface of the tube section. The small material pieces are usually not a concern if they remain in the system, since the small material pieces usually do not cause problems, for example in a heat exchanger system.

The electric voltage source may provide voltage pulses on the two terminals. The magnitude of the supplied voltage may be sufficient to cause the generation of electrical discharges between the electrode and the tube section.

The electrode can be rotated around its longitudinal axis by use of the motor. The shaft of the motor is preferable arranged such that it is collinear with the central axis of the tube section. Furthermore, the rotation of the electrode may bring the electrode in a position where the longitudinal axis of the electrode is also collinear with the central axis of the tube section. The rotation stabilizes the position of the electrode with respect to the radial direction. As the electrode’s outer diameter is in particular smaller than the inner diameter of the tube section, the electrode does not touch the inner surface of the tube section. A gap therefore exists between the outer diameter of the electrode and the inner surface of the tube section.

The coupling element for coupling the electrode to the motor may consist of or comprise an electric cable. The electrode may not only be mechanically coupled to the motor, but the coupling element may also provide a means, in form of the electric cable, for providing electric voltage from the voltage source to the electrode.

The electric cable may have an insulation. In particular, the cable maybe a braided cable.

The coupling element, and in particular the electric cable, maybe extendable or may extend along the longitudinal axis and one end of the coupling element maybe attached to a shaft of the motor and one end of the coupling element maybe attached to the electrode. A rotational movement of the motor shaft is in this setup easily transmitted to the electrode.

A very simple and cost-effective setup may be obtained if the coupling element only consists of the electric cable. Thus, the only part used to couple the electrode to the motor’s shaft is the electric cable which is preferably a braided cable. Preferably, one end of the cable is connected to the shaft while the other end of the cable is connected to the electrode. The first terminal of the voltage source maybe electrically connected to the end of the cable which is connected to the motor shaft.

Preferably, the electrode has a cylindrical form. The electrode may thereby rotate around its longitudinal axis in a balanced way. Other geometric forms are also possible. For example, the electrode may have an elliptical, rectangular or similar form.

The outer diameter of the electrode may be smaller than the inner diameter of the tube section. The electrode can be easily arranged within the tube section in such a way that there is a gap between the outer diameter of the electrode and the inner diameter of the tube section.

Preferably, the outer diameter of the electrode is at least 0.5 mm to 10 mm smaller than the inner diameter of the tube section. The generation of repeatedly recurring electric discharges between the outer diameter of the electrode and the inner diameter of the tube section can thereby be ensured and thereby result in a heat-up of the tube section and/or of the joint between the tube section and the tube plate. A rotation of the electrode around its longitudinal axis stabilizes its position with respect to the radial direction and helps to prevent a direct contact between the electrode and the tube section even if the gap between the electrode and the tube section is in the order of 0.5 mm.

The electrode may be made of or may comprise a metal, such as silver, gold or copper. Preferably, the electrode is made of or may comprise electrolytic copper.

Preferably, the electrode has - when seen along the longitudinal axis of the electrode - a length in the range of 10 - 50 mm, further preferably in the range of 20 - 40 mm.

The invention also relates to a method of loosening an electrically conductive tube section from a tube plate surrounding, at least partially, the outer surface of the tube section. The method comprises the steps of: introducing an electrode of a loosening apparatus into the tube section such that a longitudinal axis of the electrode is at least in substance arranged in parallel to or collinear with a central axis of the tube section, rotating the electrode around the longitudinal axis of the electrode, and providing an electric voltage between the electrode and the tube section to generate electric discharges between the electrode and the tube section.

The generation of the electric discharges between the outer surface of the electrode and the inner surface of the tube section may ensure a heat-up of the tube section and/or the joint between the tube section and the tube plate. This may result in a loosening of the tube section and may therefore facilitate the extraction of the tube section from the tube plate.

The method may further include the step of changing the position of the electrode within the tube section along the direction of the longitudinal axis. The electric discharges between the outer surface of the electrode and the inner surface of the tube section can thereby be generated at different positions along the direction of the longitudinal axis. This ensures a heat-up of the tube section and/or the joint between the tube section and the tube plate along the complete surface region where the tube section is surrounded by the tube plate. Therefore, a shrinkage of the tube section over the complete region can be achieved. A complete loosening of the tube section from the tube plate may therefore be ensured.

The electric voltage between the electrode and the tube section may be provided at or above a voltage value at which electric discharges between the electrode and the tube section occur repeatedly. Thereby, a heat-up of the tube section and/or the joint between the tube section and the tube plate can be ensured.

The electric voltage between the electrode and the tube section may be provided at least until the tube section and/or the joint between the tube section and the tube plate is heated up to a temperature of annealing. A deformation and/or a shrinkage of the tube section may thereby be obtained.

The temperature of the tube section and/or the joint maybe monitored, for example by use of a temperature sensor. However, a temperature sensor is only an option. The loosening apparatus also functions without any monitoring means. The design of the loosing apparatus may therefore be rather simple.

The electric voltage may be provided for at least a predefined period of time. The period of time may be monitored from a starting point which corresponds to the point in time from which on the electric voltage is provided. The starting point may alternatively correspond to the point in time when the temperature of annealing is achieved.

The method may further comprise the step of connecting a first terminal of a voltage source of the apparatus to the electrode. The method may also comprise a step of connecting a second terminal of the voltage source to the tube section.

Preferably, the electrode is rotated around its longitudinal axis such that a contact of the outer diameter with the inner surface of the tube section is avoided. Due to the rotation of the electrode, its position in the radial direction is stabilized, in particular in such a way that the longitudinal axis of the electrode is arranged collinear with the central axis of the tube section. Thereby, it can be avoided that the electrode touches the inner surface of the tube section.

The electrode may be rotated around its longitudinal axis with a rotational velocity of more than loo, 200, 300, 400 or 500 rotations per minute.

One or more examples will hereinafter be described in conjunction with the following drawing figures, where like numerals denote like elements, and

FIG. i is a schematic side view of a loosening apparatus in accordance with the present invention; and

FIGS. 2-4 illustrate the principle of plastic deformation due to an elevated workpiece temperature in a constraint space.

The apparatus shown in FIG. 1 comprises an electric motor 1 for rotating an electrode 6 around a longitudinal axis A of the electrode 6. The electrode 6 may be made out of copper and the electrode 6 is introduced into a tube section 4 such that the longitudinal axis A of the electrode 6 is arranged at least approximately in parallel or collinear with a central axis C of the tube section 4. A coupling element 3 couples the electrode 6 to the motor 1. A shaft 9 of the motor 1 which is connected to one end of the coupling element 3 is rotatable. The coupling element 3 is adapted to transmit the rotational movement of the motor shaft 9 to the electrode 6 which is connected, as shown in FIG. 1, to the other end of the coupling element 3. The electrode 6 thereby rotates around its longitudinal axis A. Due to the rotation, the electrode 6 can be kept in a position such that the longitudinal axis A of the electrode 6 is collinear with the central axis C of the tube section 4. The electrode 6 has a cylindrical form. The electrode 6 is therefore balanced when it is rotating around the longitudinal axis A.

The outer diameter of the electrode 6 is for example 1 mm smaller than the inner diameter of the tube section 4. There is therefore a gap between the electrode 6 and the tube section 4, so that, when the electrode 6 rotates around its longitudinal axis A, it contacts the tube section 4 on random places and with random frequency. Thus, discharges and consequently heat are generated between electrode 6 and tube section 4. The electrode 6 preferably has a length, seen along the longitudinal axis A, in the range of 10 to 50 mm.

The coupling element 3 comprises a cable 2, which may in particular be a braided cable. A voltage source 8 comprises a first terminal 10 which is connected, for example by use of a further electrical cable, with the electric cable 2. As illustrated in FIG. i, the connection is made in the region where the cable 2 is connected to the shaft 9. The voltage source 8 has a second terminal 11 which is connected to the tube section 4. The first terminal 10 corresponds in the depicted example to the minus pole, while the second terminal 11 corresponds to the plus pole of the electric voltage provided by the electric voltage source 8.

The tube section 4 maybe a part of a heat exchanger system and passes through a cutout or a tube hole arranged in a tube plate 5 which surrounds the tube section 4. The tube plate 5, and more specifically the surface of the cutout, contacts the outer surface of the tube section 4. For example, the tube section 4 may have been mechanically or thermally expanded to seal against the surface of the cutout. A high force may therefore be required to remove the tube section 4 from the tube plate 5.

The apparatus as shown in Fig. 1 is particularly useful in loosening the tube section 4 from the tube plate 5, which facilitates the extraction of the tube section 4 from the tube plate 5. The electric voltage source 8 provides voltage pulses on the two terminals 10 and 11 and thus between the outer surface of the electrode 6 and the inner surface of the tube section 4 which is facing the outer surface of the electrode 6. The magnitude of the supplied voltage is sufficient to cause the generation of electrical discharges between the electrode 6 and the tube section 4.

The electric discharges between the electrode 4 and the tube section 6 heatup the tube section 4 and/or a joint 7 between the tube section 4 and the tube plate 5, in particular up to the tube section’s temperature of annealing. The heat-up causes an expansion of the heated tube segment in the radial direction. Since the surrounding tube plate 5 heats up at a slower rate, which is in particular due to the larger volume of the tube plate 5, the tube plate 5 extends less. The tube section 4 therefore deforms plastically and shrinks after cooling down. The shrinkage of the tube section’s outer diameter enables a mechanical extraction of the tube section 4 using a lower pull force in comparison with the unloosened tube section.

The electric discharges generated between the electrode 6 and the tube section 4 may also remove material from the inner surface of the tube section

4. However, the material is mainly removed in very small pieces which are usually not a concern.

FIGS. 2-4 illustrate the principle of plastic deformation due to an elevated workpiece temperature in a constraint space. Fig. 2 shows a cross sectional view of a bar 12 before and after heating (solid line) and during the heating (dashed line). The bar 12 expands when heated, but has in substance the same cross section before and after heating.

Fig. 3 illustrates the situation where the bar 12 is restrained during the heating process by a solid element 13 arranged on two sides of the bar 12. During the heating process, the bar 12 can extend only to the sides which are not blocked by the solid element 13, see the dashed lines in Fig. 3.

Fig. 4 shows a cross sectional view of the restrained bar 12 after cooling (solid line). The dashed lines to the left and right indicate the positions of the solid element 13. As illustrated the thickness of the bar 12 decreases so that it can be removed from the space in between the solid element 13.

The same principle as illustrated by Figs. 2-4 applies for the loosing of the tube section 4 from the tube plate 5. Due to the heating of the tube section 4 and/or the joint 7 between the tube section 4 and the tube plate 5, the tube section 4 decreases its outer diameter and thus can be loosened from the tube plate 5.

List of reference signs electric motor cable coupling element

4 tube section tube plate electrode joint voltage source io 9 shaft io first terminal n second terminal bar solid element

A longitudinal axis

C central axis

Claims

1. An apparatus for loosening an electrically conductive tube section (4) from a tube plate (5) surrounding, at least partially, the tube section (4) at its outer surface, the apparatus comprising:

an electrode (6) which is adapted to be introduced into the tube section (4) such that a longitudinal axis (A) of the electrode (6) is at least in substance arranged in parallel to or collinear with a central axis (C) of the tube section (4), a motor (1) for rotating the electrode (6) around the longitudinal axis (A) of the electrode (6), a coupling element (3) for coupling the electrode (6) to the motor (1), the coupling element (3) being adapted to transmit a rotational movement of the motor (1), in particular of a motor shaft (9), to the electrode (6) such that the electrode (6) rotates around its longitudinal axis (A), and an electric voltage source (8) for providing an electric voltage between the electrode (6) and the tube section (4), in particular for generating electric discharges between the electrode (6) and the tube section (4), the voltage source having a first terminal (10) which is connected or connectable to the electrode (6) and a second terminal (11) which is connectable to the tube section (4).

2. The apparatus of claim 1, characterized in that the coupling element (3) consists of or comprises an electric cable (2), in particular a braided electric cable.

3. The apparatus of claim 2, characterized in that the electric cable (2) is connected or connectable to the first terminal (10) of the electric voltage source (8).

4. The apparatus of claim 1, 2 or 3, characterized in that the coupling element (3) is extendable or extends along the longitudinal axis (A) and one end of the coupling element (3) is attached to a shaft (9) of the motor (1) and one end of the coupling element (3) is attached to the electrode (6).

5. The apparatus of any one of the preceding claims, characterized in that the electrode (6) has a cylindrical, elliptical or rectangular form, the outer diameter of the electrode (6) being smaller than the inner diameter of the tube section (4).

6. The apparatus of claim 5, characterized in that the outer diameter of the electrode (6) is at least approximately 0.5 mm to 10 mm, preferably at least approximately 1 mm, smaller than the inner diameter of the tube section (4).

7. The apparatus of any one of the preceding claims, characterized in that the electrode (6) is made of or comprises a metal, such as silver, gold or copper, in particular electrolytic copper.

8. The apparatus of any one of the preceding claims, characterized in that the electrode (6) has along the longitudinal axis a length of 10 to 50 mm.

9. A method of loosening an electrically conductive tube section (4) from a tube plate (5) surrounding, at least partially, an outer surface of the tube section (4), in particular by use of an apparatus in accordance with any one of the preceding claims, the method comprising:

introducing an electrode (6) of a loosening apparatus into the tube section (4) such that a longitudinal axis (A) of the electrode (6) is at least in substance arranged in parallel to or collinear with a central axis (C) of the tube section (4), rotating the electrode (6) around the longitudinal axis (A) of the electrode (6), and providing an electric voltage between the electrode (6) and the tube section (4) to generate electric discharges between the electrode (6) and the tube section (4).

10. The method of claim 9, characterized in that the electric voltage between the electrode (6) and the tube section (4) is provided at or above a voltage value at which electric discharges between the electrode (6) and the tube section (4) occur repeatedly, and/or the position of the electrode (6) in the tube section (4) is changed along the direction of the longitudinal axis (A).

11. The method of claim 9 or 10, characterized in that the electric voltage between the electrode (6) and the tube section (4) is provided at least until the tube section (4) and/or a joint (7) between the tube section (4) and the tube plate (5) is heated up to a temperature of annealing.

12. The method of claim 11, characterized in that the temperature of the tube section (4) and/or the joint (7) is monitored.

13. The method of claim 11 or 12, characterized in that the electric voltage is provided for at least a predefined period of time.

14. The method of any one of claims 9 to 13, characterized in that the method comprises connecting a first terminal (10) of a voltage source (8) of the apparatus to the electrode (6), and/or connecting a second terminal (11) of the voltage source (8) to the tube section (4).

15. The method of any one of claims 9 to 14, characterized in that the electrode (6) is rotated around its longitudinal axis (A) such that a contact of the outer diameter with the inner surface of the tube section (4) is avoided, and/or the electrode (6) is rotated around its longitudinal axis (A) with a rotational velocity of more than 100, 200, 300, 400 or 500 rotations per minute.