EP0536053B1 - Individually making method of heat exchanger tubes - Google Patents

Description

The invention relates to a method for carrying out the individual identification of the tubes of a heat exchanger such as a steam generator used in a nuclear power station, in order to ensure immediate identification of any tube throughout the duration life of the device.

The steam generators fitted to nuclear power plants have several thousand inverted U-shaped tubes arranged in bundles, the two ends of which pass through a thick plate, called tube plate, in which each of the tubes is welded and then expanded. This bundle of tubes ensures the heat exchange between the water circulating in the primary circuit of the reactor, called primary water, and the water circulating in the secondary circuit, called secondary water. The temperature of the primary water inside each of the tubes therefore decreases appreciably between their inlet end and their outlet end. For this reason, commonly called "hot branch" and "cold branch" the rising and falling branches of the tubes, respectively extending the inlet and outlet ends of the primary water.

The inverted U tubes of the bundle of tubes of a steam generator are housed inside a cylindrical envelope, of vertical axis, in which the tube plate is fixed. This has the consequence that most of these tubes have different geometrical characteristics from each other. Since the tubes are generally manufactured in different places from the place where the assembly takes place steam generators, an individual identification of the tubes must be made before their routing on the place of assembly. Currently, this identification is carried out by affixing on each of the tubes a glued label, on which is written a code guaranteeing the mounting of the tubes at the location which returns to them on the tube plate of the steam generator. Once this location has been identified, the label is removed and the tube is placed in the steam generator and welded to the tube plate.

This current technique for locating tubes is only partially satisfactory. Indeed, the glued labels can get lost during the handling of the tubes, and they require a significant subsequent management time, with all the risks of associated errors.

In addition, the current technique of individual location of the tubes does not in any case make it possible to locate the tubes in Cartesian coordinates on the tube plate, to perform certain machining, inspection or maintenance operations on these tubes, after they have been attached to the tube plate.

In particular, it is currently not possible to individually locate the tubes of a generator, in Cartesian coordinates, in order to automatically perform machining in the factory or obturation on site of some of them, after an inspection carried out at using an eddy current probe. This results in an appreciable loss of time and, on site, the exposure of the control personnel to the strongly irradiating medium of the primary circuit for a time much longer than that strictly necessary for the obturation of some of the tubes.

Furthermore, the individual identification of the tubes from the start of their manufacture would make it possible to manage the latter under particularly advantageous conditions, which is obviously not possible when the tubes are identified with the aid of labels which can only be placed on the tubes when their manufacture is finished.

Furthermore, it is known from document US-A-4 780 009 to engrave identification characters of the tubes on the tube plate of a steam generator.

The subject of the invention is mainly an original method of individual identification of the tubes of a heat exchanger such as a steam generator, making it possible to ensure the individual identification of each of the tubes throughout the lifetime of the apparatus and, if necessary, during the manufacture of the tubes.

According to the invention, this result is obtained by means of a method of individual identification of the tubes of a heat exchanger comprising a bundle of tubes, the end portions of which are embedded in at least one tube plate, characterized by the fact that it consists in marking each of the tubes with an individual identification code capable of being read by reading means at least during the operation of the exchanger, by making imprints on the tubes modifying their thickness, by embossing, without removal of material.

The individual marking of each of the tubes, which can be done either at the time of assembly of the steam generator, or even from the individual manufacture of the tubes, authorizes in all cases the identification of each of the tubes of a completely exchanger. throughout the life of it. An appreciable saving of time, as well as a considerably less exposure of the personnel to the radiations are thus obtained, after a prior learning operation has been carried out, immediately after the manufacture of the steam generator, so as to associate with each of the tracking codes tubes of the position coordinates of the ends of the tubes on the tube plate.

Because the marking of the tubes is carried out by making imprints modifying their thickness by embossing, without removal of material, it is possible to ensure the reading of the individual code assigned to each of the tubes using the current probe Foucault which also ensures the control of the tubes. No additional operation is thus necessary.

Preferably, the individual identification code of each of the tubes is a bar code, which includes a preset number of signs regularly spaced along the axis of the tube, each sign being chosen from two signs, one of which is a circular imprint and the other of which is an absence of imprint.

In the particular case of a steam generator comprising inverted U-shaped tubes each including a cold branch and a hot branch and the ends of which are embedded in the same tube plate, the method according to the invention consists in marking the parts d 'end of each of the tubes by an individual code comprising the same identification code of the tube and a branch identification code. In this case, the sign closest to the end of the tube may constitute the code for locating the branch.

In order for the tubes to be identified as soon as they enter the eddy current control probe, and also to avoid weakening the working parts of the tubes, the individual identification code is advantageously marked on the end of each of the tubes which is embedded in the tube plate.

In a first embodiment of the invention, the individual code is marked on an external surface of each of the tubes, during the manufacture of the latter. In addition, because it allows individual identification of the tubes even before manufacturing the steam generator, this solution makes it possible to relax the tubes by heat treatment during their manufacture, in order to remove any residual stresses created in the marking areas.

In another embodiment of the invention, the individual code is marked on an inner surface of each of the tubes, after the fixing of the latter in the tube plate. It is clear that this solution does not eliminate the need for glued labels, nor the drawbacks which result therefrom. However, it makes it possible to ensure individual management of the tubes of a steam generator which was not possible until now.

• la figure 1 est une vue en perspective illustrant schématiquement un premier mode de réalisation de l'invention, selon lequel les tubes sont marqués individuellement, sur leur surface extérieure, lors de leur fabrication ;
• les figures 2A et 2B sont des vues en perspective illustrant deux étapes successives du procédé de repérage selon l'invention, dans un deuxième mode de réalisation de l'invention, selon lequel le marquage des tubes s'effectue à l'intérieur de ces derniers, lors de l'assemblage du générateur de vapeur ;
• la figure 3 est une vue en coupe partielle illustrant à plus grande échelle l'une des extrémités d'un tube sur lequel a été marqué un code individuel de repérage, les moitiés gauche et droite de la figure illustrant respectivement le premier et le deuxième modes de réalisation de l'invention ;
• la figure 4 représente schématiquement un tube en U renversé d'un générateur de vapeur, dont les deux extrémités ont été repérées à l'aide d'un code barres, conformément à l'invention ; et
• la figure 5 est un diagramme montrant comment le procédé de marquage selon l'invention peut permettre d'acheminer sans perte de temps une sonde de contrôle ou un outillage quelconque vers un tube déterminé du faisceau.

Various embodiments of the invention will now be described, by way of non-limiting examples, with reference to the appended drawings, in which:

• Figure 1 is a perspective view schematically illustrating a first embodiment of the invention, according to which the tubes are marked individually, on their outer surface, during their manufacture;
• FIGS. 2A and 2B are perspective views illustrating two successive stages of the tracking method according to the invention, in a second embodiment of the invention, according to which the marking of the tubes is carried out inside the latter , during assembly of the steam generator;
• Figure 3 is a partial sectional view illustrating on a larger scale one end of a tube on which has been marked an individual identification code, the left and right halves of the figure respectively illustrating the first and second modes of carrying out the invention;
• FIG. 4 schematically represents an inverted U-shaped tube of a steam generator, the two ends of which have been identified using a bar code, in accordance with the invention; and
• FIG. 5 is a diagram showing how the marking method according to the invention can make it possible to route, without loss of time, a control probe or any tool to a determined tube of the bundle.

Each of the individual tubes of a steam generator has the shape of a U-shaped tube, this U being in the inverted position when the steam generator is in operation. As already mentioned, almost all the tubes have different dimensional characteristics, depending on their location inside the steam generator. In particular, the radius of curvature of the central part of the tube and the length of the hot and cold branches of each tube varies practically from one tube to another.

One of these tubes, designated by the reference 10 in Figure 1, was shown in this figure towards the end of its manufacture, that is to say when it already has its final shape.

According to a first embodiment of the invention, it is at this stage, or even before the curvature of the tube 10, that this tube is marked, on its end portions, by means of an individual bar code 12a, 12b, which we will see below that it includes, for a given tube 10, the same identification code, as well as a code for identifying the branch concerned.

The principle used for the barcode will be explained in detail later. Barcode marking is obtained by making impressions, by embossing without removing material, so that the thickness of the tube is slightly reduced at the places where impressions are made. Each of the imprints used to produce the bar codes 12a and 12b is a circular imprint 24, produced on a complete or partial circumference of the tube, and the depth of which can in particular be a few hundredths of mm while having the minimum functional thickness of resistance tube mechanics.

In the first embodiment of the invention illustrated in FIG. 1, the end portions of each of the tubes 10 can be marked on the external surface of the latter, since they are not yet mounted in the plate steam generator tubes. As shown schematically, the marking tool 14 is then a rotary tool, able to be mounted on the tube 10 and provided with marking rollers capable of making the desired impressions. This marking tool 14 is advantageously mounted on a carrier (not shown) for controlling coordinates, making it possible to place the imprints of the bar codes 12a and 12b in very precise locations relative to the ends of the tube 10. In fact, the location of each of the imprints 24 is decisive for the reading of the bar code.

As illustrated in more detail in FIGS. 3 and 4, the end parts of the tubes 10 on which the individual bar codes 12a and 12b are marked correspond to the parts of the tubes 10 intended to be embedded in the tube plate 16 of the generator steam.

More specifically, the marking area, identified by the letter M in FIG. 3, is intended to be located inside the bore 20 of the tube plate 16, in which the end portion of the tube is received. 10. This marking area M is delimited between the region immediately adjacent to the weld 18, by which the end of the tube 10 is fixed on the lower face of the plate 16, on the side of the primary water, and the region adjacent to the upper face of the plate 16, corresponding to the expansion zone of the expansion of the tube 10 inside the bore 20, on the side of the secondary water. Indeed, these two regions constitute the sensitive parts of the connection of the tube 10 on the plate 16, which it is important not to weaken by the marking of the tubes.

When each of the tubes 10 is marked with an individual bar code during its manufacture, as illustrated diagrammatically in FIG. 1, all the characteristics linked to this tube, such as its metallurgical, quality, etc. characteristics are then attached to the individual code worn on this tube. This solution eliminates the identification of the tubes using glued labels, which is currently carried out before their shipment to the place of assembly of the steam generator. The disadvantages linked to the use of these labels, such as their lossability, the risks of error which result from them, the time necessary for their subsequent management, etc. are deleted.

After being transported to the place of manufacture of the steam generators, each of the tubes individually identified by its code is fixed to the tube plate 16, in the bores 20 intended to receive it, by carrying out the welding 18, then by expansion , according to the usual technique. Each of the tubes 10 and the two bores 20 associated therewith thus create an inseparable assembly, individually identified by the code marked on the end of the tube. Computer mapping is then carried out in the factory, or after the steam generator is installed in the nuclear power plant, in order to associate at each individual bar code, position information, in Cartesian coordinates, representative of the position on the tube plate 16 of the end of the tube 10 carrying this code, and of the bore 20 in which this end is received. Monitoring and management of each of the tubes throughout its life, from its manufacture to the shutdown of the steam generator, can thus be ensured.

This first embodiment of the invention, according to which the marking is carried out on the external skin of each of the tubes, also makes it possible to ensure good protection of the marking area which is located as illustrated in the figure. 3 in part M, deemed waterproof. This embodiment also has the advantage of not modifying the manufacturing cycles of the steam generators and of allowing, if necessary, the stress relieving of the marking zones, by heat treatment or others, during the manufacture of the tubes, if turns out that the marking creates residual stresses in the tubes.

In a second embodiment of the invention, illustrated in FIGS. 2A and 2B, the marking of the tubes is only carried out after the latter have been fixed to the tube plate of the steam generator, that is to say in the factory, when the manufacture of the device, either directly in nuclear power plants on steam generators already in operation.

FIGS. 2A and 2B illustrate more precisely the case where the marking of the tubes is carried out immediately after their mounting on the tube plate 16. As illustrated in FIG. 2A, the tubes 10 then arrive at the assembly plant for the generators steam each equipped with their locating label 22, in accordance with the technique currently used. As soon as the tube 10 is placed in the appropriate bores 20 of the tube plate 16, as illustrated in FIG. 2B, it is fixed in this plate according to the usual technique, by welding and then expansion. An individual bar code is then marked inside the end part of each of the branches of the tube which is located in the area M in FIG. 3, in accordance with the tracking codes initially carried on the labels 22.

In this embodiment, the marking tool 14 ′ can be in the form of a special dudgeon or an expandable ring provided with a shell containing a marking punch. In order to ensure precise positioning of each of the imprints formed by the tool 14 ', the latter is mounted on a carrier (not shown) for controlling coordinates such as a robot.

In the particular case where the marking is carried out directly on the site of the nuclear power plant, the marking tool is mounted on a carrier capable of moving under the tube plate, according to a technique comparable to that of the machines which support the eddy current control probes and equivalent systems, during control operations at the plant site.

The characteristics relating to the imprints 24, as regards both their position and the manner of producing them (without removal of material), are similar to those which have been described previously with regard to the first embodiment of the invention, in particular referring to figure 3.

The principle used for the individual coding of each of the tubes, which will now be explained with reference to FIG. 4, is also the same in both of the two embodiments previously described.

As already mentioned, this coding, operating according to the bar code principle, is based on the production of indentations 24, of circular shape and having in section a geometry, completely reproducible, determined by the type of tool used for carry out the marking. The particular coding proposed here is based on the use of a single type of imprint 24, capable of being decoded by all or nothing during the passage of an eddy current probe also used to control the corresponding tube.

More precisely, the bar code which is carried on each of the end parts M (FIG. 3) of each of the tubes 10 comprises a predetermined number of signs regularly spaced apart by a known distance, these signs being able to be according to the case either a circular imprint 24, or an absence of imprint. The position of each of the signs relative to the end of the tube is also known.

The number of signs worn on the end part of each of the tubes is chosen, according to the total number of tubes contained in a steam generator, so that each of the tubes carries an individual code making it possible to identify it. Given the binary nature of the coding used (imprint: 1; absence of imprint: 0), each of the tubes of a steam generator comprising around 5600 tubes can thus be identified using a code consisting of thirteen signs consecutive, regularly spaced, each formed either of a footprint 24 or an absence of footprint. To facilitate reading, only six signs have been shown in Figure 4.

Advantageously, one of the signs, for example the closest to the end of the tube 10, identified by the letters CRB in FIG. 4, corresponds to a code for locating the concerned branch of the tube 10, an absence of imprint corresponding for example to the cold branch, while an imprint 24 corresponds to the hot branch. The rest of the signs contained in each of the individual codes 12a and 12b is moreover identical and corresponds to the identification code of the tube, identified by the letters CIT in FIG. 4.

Of course, this solution is only indicated here by way of example, any comparable coding making it possible both to identify the branch concerned of a given tube and to identify this tube with respect to all the tubes entering in the context of the invention.

Whatever the embodiment concerned, as soon as the individual marking of the tubes is finished or at the end of the manufacture of the steam generator when the marking of the tubes takes place before this manufacture, the learning or acquisition of all the signals corresponding to these codes using an eddy current probe 26 mounted on a mobile carrier 28, associating with them the positions of the corresponding ends of the tubes 10 on the tube plate 16. It is established thus a computer mapping of the position of these signals on the tube plate 16. This acquisition operation is illustrated diagrammatically in FIG. 5 by the arrow 30, which connects the eddy current probe 26 to an acquisition circuit 32 signals delivered by the probe 28. The acquisition circuit 32 communicates to a computer 34 coding signals 36, to which the computer 34 assigns a position, in Cartesian coordinates, from a coordinate table. The desired cartography is thus stored.

When it is subsequently desired to go and perform any operation on a tube 10, for example machining or sealing, a message of position 38 corresponding to the desired tube is sent to the computer 34, as symbolized by the arrow 36 in FIG. 5. From this message, the computer consults the map previously acquired, to control an automatic movement of the carrier 30 towards the desired position, by acting on the control members 40 of the carrier.

Of course, the invention is not limited to the embodiments which have just been described by way of examples. The invention can also be applied to the individual identification of the tubes of a heat exchanger comprising a bundle of straight tubes, the ends of which are fixed on two opposite tube plates.

Claims (9)

1. Process for the individual identification of the tubes of a heat exchanger comprising a bundle of tubes (10), whereof the end portions are fixed in at least one tube plate (16), characterized in that it consists of marking each of the tubes with an individual code (12a, 12b), which can be read by reading means at least during the operation of the exchanger, by making on the tubes impressions modifying their thickness, by embossing, and with no material removal.
2. Process according to claim 1, characterized in that after fixing the tubes (10) to the tube plate (16), a learning operation is carried out, during which with each of the tube marking codes are associated position coordinates of the tube ends on the tube plate.
3. Process according to any one of the preceding claims, characterized in that the individual code is a bar code (12a, 12b).
4. Process according to claim 3, characterized in that the bar code (12a, 12b) comprises a predetermined number of signs regularly spaced along the tube axis, each sign being chosen from among two signs, whereof one is a circular impression (24) and the other an absence of an impression.
5. Process according to any one of the preceding claims, applied to the identification of U-tubes having a cold branch and a hot branch and whereof the end portions are fixed in the same tube plate, characterized in that it consists of marking the end portions of each of the tubes with an individual code having the same tube identification code and a branch identification code.
6. Process according to claim 4, combined with claim 5, characterized in that the sign closest to the end of the tube constitutes the branch identification code.
7. Process according to any one of the preceding claims, characterized in that the individual code (12a, 12b) is marked on the end portion of each of the tubes (10) fixed in the tube plate (16).
8. Process according to any one of the preceding claims, characterized in that the individual code (12a, 12b) is marked on an outer surface of each of the tubes (10) during their manufacture.
9. Process according to any one of the claims 1 to 7, characterized in that the individual code (12a, 12b) is marked on an internal surface of each of the tubes (10) after the fixing of the latter in the tube plate (16).

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