EP0078728B1 - Antivibration support for a tube bundle, particularly for a steam generator, and assembly method for this support - Google Patents

Description

The present invention relates to a device intended to hold in place a set of tubes forming a bundle while minimizing the possibility of vibrations of these tubes. This device can be applied in particular to the maintenance of a bundle of tubes constituting the water-steam circuit of a sodium-water type steam generator which is used in particular in nuclear power plants of the fast neutron type.

The invention also relates to the method of mounting such a device.

In heat exchangers, one of the circuits of which consists of a bundle of tubes, it is common to encounter difficulties in positioning and holding these tubes in place. One difficulty lies in the fact that there are often differential expansions between the tubes, which prohibits any absolutely rigid fixing at different points of the tubes. Another difficulty resides in the fact that the tubes being in a fluid flow at high speed this results in phenomena of vibrations in the tubes, and it is therefore necessary to have supports which absorb these vibrations and which are distributed in such a way that the free sections of the tubes do not have a natural frequency close to the frequency of the vibrations.

Such a problem of fixing a bundle of tubes is particularly important and delicate in the case of a steam generator of the sodium-water type in which the water-steam circuit consists of a bundle of tubes extending to inside an enclosure in which hot liquid sodium circulates. The essential difficulty inherent in the sodium water type steam generator stems from the fact that the liquid sodium has excellent thermal conductivity, a quality highly appreciated but which has the drawback of inflicting violent temperature variations on the tube bundle during transient operation resulting in the significant differential expansions in these tubes.

We know in DE-C-2-16.732 a device for holding a bundle of tubes housed in an enclosure in the lagoon a fluid circulates around these tubes arranged in rows comprising on each side of each row at least one pair of metal strips each having corrugations adapted to receive the tubes.

FR-A-2.198.289 relates to a support for power transmission lines comprising two beams between lesguels are placed. at determined intervals, transverse spacers comprising two section pieces having recessed portions intended to receive the power transmission lines.

In these devices the undulations of the supports are adapted to the contour of the transport line to be supported, so that the contacts between the different elements are made according to surfaces so that there is significant wear and excessive matting of said transport lines.

In FR-A-2,336,621 and US-A-4,156,299 the contacts between the supports and the tubes to be maintained are established in the transverse plane or in the longitudinal plane along a line also causing excessive matting.

In addition, these various tube bundle holding devices have other drawbacks, notably a relatively large complexity, a risk of deformation of the tubes when clamped by the support, a lack of control over the level of internal stresses developing in tubes due to their differential expansions and a lack of constancy over time of the fixing and anti-vibration characteristics.

The present invention relates to a device which maintains tubes with elasticity by means of metal strips. The dimensions and shapes of these bands provide a point contact on the tubes which allows movements (rotations and axial sliding) of these tubes during operation. The arrangement of the device helps to distance the frequency bands oDD the tubes could be excited on a common mode. 11 allows the flow of fluid around the tubes. The elasticity of the bands makes it possible to accept differences in position during assembly.

The present invention relates to a device for holding a bundle of tubes housed in an enclosure in which a fluid circulates around these tubes arranged in rows comprising on each side of each row at least one pair of metal strips having each of the corrugations adapted to receive the tubes, the corrugations of the two strips arranged on either side of a row being located opposite so that the tubes are clamped under the action of clamping elements arranged between said undulations and clamping said strips towards each other.

According to the invention, each metal strip whose ends are capable of being fixed to the fixed parts of the enclosure has at the level of each corrugation in contact with a tube on the one hand in the longitudinal direction a greater radius of curvature that the radius of the tube and on the other hand, in the transverse direction a slight curvature continues so that the contact between each metal strip and the tube is established in a quasi-punctual zone.

According to a preferred characteristic, the metal strips are made of steel with high elastic limit.

• La figure 1 est une vue simplifiée en coupe longitudinale de la partie supérieure du faisceau tubulaire d'un générateur de vapeur.
• La figure 2 est une coupe partielle selon A-A de la figure 1. au niveau d'un dispositif de support.
• La figure 3 est une coupe partielle selon B-B de la figure 1. au niveau d'un autre dispositif de support.
• La figure 4 est une vue agrandie d'un dispositif de support de la figure 1.
• La figure 5 est une coupe selon C-C de la figure 4.
• La figure 6 est une coupe selon D-D de la figure 5. La figure 7 est une coupe selon E-E de la figure 5. L'exemple de réalisation a été pris dans le domaine des générateurs de vapeur du type sodium-eau utilisés dans une centrale nucléaire de type à neutrons rapides.

Other advantages and characteristics specific to the invention will appear during the embodiment which follows. illustrated by the appended figures.

• Figure 1 is a simplified view in longitudinal section of the upper part of the tube bundle of a steam generator.
• Figure 2 is a partial section along AA of Figure 1. at a support device.
• Figure 3 is a partial section along BB of Figure 1. at another support device.
• FIG. 4 is an enlarged view of a support device from FIG. 1.
• FIG. 5 is a section along CC of FIG. 4.
• Figure 6 is a section along DD of Figure 5. Figure 7 is a section along EE of Figure 5. The embodiment was taken in the field of steam generators of the sodium-water type used in a power plant fast neutron type nuclear.

Referring to FIG. 1, the upper part of a structure or enclosure of a steam generator which consists essentially of an external vertical cylindrical envelope 1 and of a central cylindrical tube 2 providing between an annular space.

Tubes 3 are housed in this annular space separating the tube 2 and the casing 1. Hot liquid sodium circulates in the annular space between the casing 1 and the tube 2 which confine the sodium stream. This current is parallel to the axis of cylinders 1 and 2 and goes from bottom to top. The sodium gives way in the heat to pressurized water which circulates in the tubes 3 and which then turns into vapor.

The tubes 3 are arranged thus wound in the greater part of the steam generator and their lower and upper ends open in a known manner outside the envelope 1 of the steam generator.

In Figure 1 we see the connection with the outside of the upper end of the tubes 3. After the end of the winding zone 4 of the tubes 3 constituting the tube bundle proper, these tubes are arranged longitudinally in their part 5 , then gathered and used in the form of lyres in their part 6 before crossing the envelope 1 and extending outside of the envelope 1 from which they are collected in a known manner and not shown here. All of the longitudinal parts 5 of the tubes will be called Thereafter the bundle of tubes and the curved parts 6 of the tubes will hereinafter be called lyres.

In the steam generator that we took as an example of reslisation, the tubes, after having completed their winding phase 4 are bent so as to form the parts 5 extending longitudinally and all located along radii 9a and 9b distributed regularly in the steam generator.

The invention particularly relates to the devices 7 and 8 serving for maintaining and damping the vibrations of the ends of the tubes 3. The device 7 is arranged at the longitudinal parts of the tubes 5 and the device 8-farthest from the beam is disposed pre lyres 6. In FIG. 2, the beam holding devices are shown in plan view, and in FIG. 3 is shown, in top view, the device for holding the beams. It is noted that the holding devices of these two types are constructed in an entirely similar manner.

Each device comprises strips of sheet metal of constant thickness 7a, 7b, 8a, 8b, which each form corrugations 16 adapted to the tubes and between which zones 17 extend. The strips extend transversely to the tubes 5 - and perpendicularly with sodium current and they are mounted in pairs on either side of each row 9a, 9b of tubes 5 so as to grip the tubes as in a collar and to hold them in place.

To describe in more detail the shape of the meta11i-c bands 7 or 8, we will now refer to Figures 5, 6 and 7. We see in Figures 6 or 7 that the corrugated metal strips 7a, 7b are curved forming the undulations 16 at the level of each tube. The two strips associated with the same row of tubes form housings through which the tubes pass. The bands are curved in the zones 17 extending between the waves and corresponding to the intervals separating the tubes. In FIG. 7, a distinction is made between the zones 17 of the bands 7a and 7b at the level of which they are most closely spaced so as to provide a space 18 which is relatively weak. In each of these zones 17 are provided orifices through which pass bolts 19, 21 intended to bring the metal strips 7a and 7b together so as to cause the zones 16 of these metal strips to pinch the tubes and thus obtain a holding in place of all the tubes, however, allowing a certain elasticity in the assembly as well as a certain longitudinal sliding of the tubes due to the differential dilststions and a certain damping of the vibrations in the whole of the tube bundle.

Each metal strip is applied against the tubes on one side only. In this way two adjacent metal strips applied against the tubes of two adjacent rows are separated and provide a space for the circulation of sodium.

The ends of the two strips 7a, 7b mounted on either side of the same row of tubes are joined together. In addition, the ends of the strips associated with the different rows are joined together. For this purpose, the ends of the bands are fixed by known means to circular parts 12, 13, 14, 15 which are integral with components 1 and 2 Ce the resin.

The force of pinching the tubes must be strong enough to be effective, without, however, causing the matting or nicking of these tubes. 11 is moreover intended, for this purpose, to give the metal strips, at the pinching zones 16 a slight curvature in the transverse direction, as can be seen in FIG. 5, so that the lateral parts of the tape are slightly away from the tube on which the tape comes into contact, and that only the part Central 20 of the strip is in contact with the tube. It is moreover preferable to provide for the curved zone 16 of the metallic strip a radius of curvature R1 slightly larger than the radius R2 of the tube 5 or of the part 11 so that the mounting of the metal strips on the tubes admits slight variations. distractions separating the tubes without creating abnormal stresses in them.

All the details of the shape of the strips 7a and 7b described above are applicable to the metal strips 8a, 8b which form the support device for the lyres 6.

The tube parts 5 do not occupy all of the possible locations on the different radii 9a, 9b, etc. This is of course only linked to the method of construction of this steam generator which has been taken as an exemplary embodiment. We therefore see, in Figures 1 and 2, locations 10 which are not occupied by one of the sections 5 of the tubes. As the distribution of the tubes 5 on spoke 9 is different for turns these spokes, instead of constituting different metal support plates adapted to each of the rows of tubes arranged on the different rents adapted to each of the rows of tubes arranged on the various spokes 9a , 9b. etc, the metal strips have been constructed all identical, of corrugated shape and the locations without tubes are occupied by cylindrical parts of diameter equal to that of the tubes. In FIG. 4, which is an enlarged side view of FIG. 2, there are such cylindrical parts 11 intended to replace the missing tubes 5.

As in this embodiment all the tubes arranged on the same radius 9a, 9b, etc., are then assembled equidistantly to form the lyres 6, to the lyres support device 6 which is shown in FIG. 3, no more missing tubes, and therefore there is no longer any need to have cylindrical parts 11. The corrugated metal strips 8a, 8b, etc., are therefore quite similar to the metal strips 7a and 7b. They are just shorter.

It is desirable that this pinching force of the tubes remains constant over time. In the case of a sodium-water steam generator, which must operate for several decades, and which is subjected to a temperature of around 525 °, as well as to significant thermal shocks, the choice of the material making up the strips. metallic becomes delicate. The present invention solves this problem by choosing the material comprising the metal strips, which is a high elastic limit when hot. A suitable steel is an austenitic alloy steel with structural hardening preferably comprising titanium and aluminum. Such a steel is entirely suitable for the use which is made of it here in a steam generator of the sodium-water type because it has both a high elastic limit comparable to that of hardened steel and a high coefficient of elongation or a high ductility which is the characteristic of stainless steels. It can therefore maintain at 525 ° C. This even more a high elastic stress without practically any creep, even after a relatively long time.

The invention also relates to the method of mounting the antivibration support device described above. It is in fact important that the clamping force of the tubes which is established at the zones 20 of the metal strips has a substantially constant value for all the tubes. This pinching force is achieved by screwing the bolts 19. In good sequence, the assembly process specific to the invention consists in placing the metal strips 7a and 7b, or 8a and 8b, on either side of the tubes. to install the bolt 19 by screwing its nut 21 therein with a minimum torque so that the rotation of the nut is interrupted as soon as the metal bands begin to exert a pinching force on the neighboring tubes, then continue to screw the nut 21 on the bolt 19 at a predetermined constant angle of rotation, so as to create in the strips, between each tube, a predetermined constant arrow, and consequently to create a force for pinching the tube itself relatively constant and predetermined, then finally to immobilize the nut 21 on the bolt 19 by any appropriate means, for example by carrying out a heavy soaking, a pinning, or a welding point.

Claims (5)

1.- Support device for a tube bundle (5) housed in a vessel (1, 2) within a fluid flows around these tubes arranged in rows (9a, 9b) comprising on each side of each row at least one pair of metal strips (7a, 7b, 8a, 8b) each having undulations (16) adapted to receive the tubes, the undulations of the two strips arranged on each side of a row being located facing each other so that the tubes are gripped under the effect of clamping elements (19, 21) arranged between said undulations and clamping said strips towards one another, characterized in that, the ends of strips being joined to fix portions of said vessel, each of said strips having, at the level of each undulation (16) in contact with a tube (5), in the longitudinal direction, a radius of curvature (R1) greater than the radius of curvature (R2) of said tube, and, in the transverse direction, a slight continuous curvature (20) so that each said strip and the corresponding tube are in contact in a quasi- pontual zone.

2.- Device according to claim 1, characterized in that the undulate metal strips (7a, 7b, 8a, 8b) are formed of steel with a high yield strength.

3.- Device according to claim 2, characterized in that said steel is an austenitic steel with structural hardening.

4.- Device according to any preceding claim, characterized in that, for each undulated metal strip, all the undulations incurved (16) in the direction of the tubes come into contact with a tube (5) or, failing this, with a replacement part (11) of cylindrical shape and of diameter equal to that of the tubes.

5.- Method of assembling an anti-vibration , support device for a tube bundle in accordance with claim 1, said method comprising applying an undulated strip (7a, 7b, 8a, 8b) on each side of the row of tubes to be immobilized, screwing the bolts (19,21) mounted on the undulated strips until they are in a position of commencing to clamp the strips to the tubes, then continuing the screwing of the boltsthrough a pre-determined constant angle of rotation amount, so as to create in the strips, between each tube, a pre-determined constant yield.

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