GB2028199A

GB2028199A - Method and apparatus for positioning and expanding tubes in tube plates

Info

Publication number: GB2028199A
Application number: GB7927074A
Authority: GB
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1978-08-11
Filing date: 1979-08-03
Publication date: 1980-03-05
Also published as: FR2432903B1; IT1119144B; JPS5524742A; FR2432903A1; DE2932055A1; GB2028199B; IT7968652A0; JPS5622409B2; DE2932055C2

Abstract

Three elastic members 12, 11, 5 are placed in a tube 2 to be inserted into a tube-receiving bore in the tube plate 1. A rod 6 is pulled to axially press the first elastic member 12 so that the same is expanded radially outwardly into frictional engagement with the inner surface of the tube. The rod 6 is further pulled to axially move the tube by means of the frictional engagement between the first elastic member 12 and the tube. This movement occurs as the second elastic member 11 is axially contracted and is stopped when the tube-end engages a tube positioning sleeve 10 and bushes 15, 16 pressurising the member 11 come together with the member still clear of the tube-wall. Continued movement of the rod 6 expands the third elastic member 5 whereby the tube end is radially outwardly expanded into intimate engagement with the inner surface of the bore. <IMAGE>

Description

SPECIFICATION Method and apparatus for positioning and expanding tubes BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to method of and apparatus for expanding a tube end to fix the same to an object such as a tube plate and, more particularly, to a tube expanding technique in which a tube is precisely positioned or located in relation to the object and then expanded and fixed to the latter through a radial expansion of a resiliently deformable tube expanding medium.

DESCRIPTION OF THE PRIOR ART Generally, in multi-tube heat exchangers or boilers, welding and tube expansion are jointedly used for fixing the tube ends to tube plates. In some cases, the tube expansion is effected before the welding in order to avoid weld defects. It has also been proposed and conducted to fix the tube end solely by the tube expansion, eliminating the welding, particularly when the heat exchanger or the like is used under a low temperature and a low pressure. In these cases, it is required to precisely locate the tubes relative to the holes in a tube plate before effecting the tube expansion.

Particularly, in case of a main intermediate heat exchanger of a nuclear power station, expansion of a tube must be conducted in the manner shown in Fig. 1; namely, the tube 1 is inserted into the corresponding tube-receiving hole or bore 1 a in the tube plate 1 to a depth I which is 1.2mm, for example. The insertion of the tube has to be made highly precisely because an insertion depth which falls out of the range of 1.2 + 0.2mm tends to cause weld defects.

Hitherto, there have been proposed and used various tube-expanoi#ng methods, such as a mechanical tube expansion by means of a tube expander, and explosion tube expansion by means of an explosive and a uniform tube expansion conducted by the application of a uniform internal pressure to a tube.

Fig. 2 illustrates the conventional mechanical tube expansion technique which makes use of a tube expander. A tube 2 which is to be expanded and fixed to a tube plate 1 is inserted at its one end into a tube-receiving bore in the tube plate 1. The tube expander for expanding the tube has a tapered mandrel 3 and an expander roller 4.

For closely fitting and fixing the tube 2 to the inner surface of the tube-receiving bore through a tube expansion effected by the tube expander, the tube expander as a whole is driven into the tube, i.e., in the direction of an arrow Q, while the mandrel 3 is rotated in the direction of an arrow P. As a result, the tapered mandrel 3 presses radially outwardly the expander roller 4 which in turn presses and expands the tube 2 radially outwardly into tight contact with the inner surface of the tube-receiving bore.

The application of this mechanical tube expansion to the tube-fixing technique shown in Fig. 1 involves the following problems: (i) It is impossible to precisely locate the tube in relation to the tube-receiving bore by means of the tube expander.

(ii) The tube insertion depth falls out of the proper range due to axial movement and axial elongation of the tube caused by the tube expansion.

(iii) It is difficult to expand the tube only over the extremely small insertion depth I (1 .2mm) of the tube Fig. 3 illustrates an example of another conventional tube expanding method which relies upon a uniform application of internal pressure to a tube through a tube expansion medium made of an elastic material. A tube 2 to be expanded is received at its one end in a tube-receiving bore formed in a tube plate 1.

The tube expansion device for expanding and fixing the tube 2 to the tube plate 1 has a tube expansion medium 5 made of an elastic material 5, a pressurizing rod 6 extending through the tube expansion medium 5, a back-up ring 7 through which the pressurizing rod 6 slidably extends, seal rings 8 made of an elastic material having a higher rigidity than the tube expansion medium 5 and a hydraulic cylinder 9 operatively connected to the pressurizing rod 6.

For expanding and fixing the tube 2 to the inner surface of the tube-receiving bore of the tube plate 1 by means of the tube expanding device having the described construction, a pressurized working fluid is supplied into the hydraulic cylinder 9 after the tube expanding device is placed in the tube, so that the piston in the hydraulic cylinder 9 is actuated to impart an axial force F to the pressurizing rod 6 to displace the latter in the axial direction.

In consequence, a head 6a of the pressurizing rod 6 pressurizes the tube expanding medium 5 in the axial direction to cause a radial expansion of the same which in turn functions to uniformly expand the tube 2 in the radial direction to fix the tube to the inner surface of the tube-receiving bore of the tube plate 1.

During this tube expanding operation, the clearances between the tube 2 and the pressurizing rod head 6a as well as between the tube 2 and the back-up ring 7 would be widened as the tube 2 is expanded radially outwardly, which in turn would otherwise cause a tendency of plastic flow of the tube expanding medium 5 to the outside of the tube expanding device through the widened clearances. This tendency, however, is avoided by the seal rings 8 which are interposed between the tube expanding medium 5 and the back-up ring 7 and between the tube expanding medium 5 and the pressurizing rod head 6a, respectively.

The use of the tube expanding device having the described construction in fixing the tube to the tube plate in the manner shown in Fig. 1 still involves the following problems: (i) It is not possible to precisely locate the tube with respect to the tube plate, i.e., to the tube-receiving bore.

(ii) Since the tube expansion is effected only at the end portion of the tube, the tube is undesirably displaced in the axial direction to make it impossible to properly expand the tube end.

Similar problems are experienced when the tube is expanded and fixed by the aforementioned explosion tube expanding method.

Thus, the conventional tube expanding methods, i.e., the mechanical method using a tube expander, the explosion method and the method employing a uniform internal pressure, have various drawbacks such as a difficulty to precisely locate a tube with respect to a tube-receiving bore, an undesirable increase or decrease in the insertion depth of the tube beyond the allowable limit as caused due to the tube expansion, etc. These drawbacks in turn cause various problems, such as weld defects produced during welding which is conducted subsequently to the tube expansion, and a difficulty in fixing the tube to the tube plate solely by the tube expansion, which results in a lowered reliability of the final products, such as heat exchangers and boilers.

SUMMARY OF THE INVENTION It is, therefore, an object of the invention to eliminate the afore-mentioned prior art problems and to provide improved method of and apparatus for expanding and fixing a tube to a tube plate by means of an expansion medium of an elastic material, in which the tube is precisely located with respect to a tube-receiving bore of the tube plate and then expanded and fixed to the tube plate, so that the reliablilty of the connection between the tube end and the tube plate is remarkably improved to overcome above described problems of the prior art.

According to one feature of the invention, there is provided a method of positioning an end of a tube in a tube-receiving bore in a tube plate and expanding the tube end to fix the same to the tube plate, said method comprising the steps of: actuating a pressurizing means to press a first elastic member into frictional engagement with the inner surface of the tube and maintaining the frictional engagement, further actuating said pressurizing means to displace said tube in the axial direction by the frictional engagement between said tube and said first elastic member and by the axial displacement of a second elastic member which is also compressed in the axial direction of said tube, thereby to locate the tube end at a predetermined position in said tube-receiving bore, and further actuating said pressurizing means to expand radially outwardly a third elastic member which is located at a position corresponding to the portion of said tube to be expanded, to thereby uniformly expand said portion of said tube to tightly fix the latter to said plate.

According to another feature of the invention, there is provided an apparatus for positioning a tube in a tube-receiving bore in a tube plate and expanding the tube to fix the same to said tube plate, said apparatus including a tube expanding medium to be placed in the tube responsive to an axial pressure to expand the tube radially outwardly, and pressurizing means including a rod for applying the axial pressure to said tube expanding medium, characterized in that the apparatus further includes a tube positioning sleeve to be slidably mounted on said rod and disposed in the tube-receiving bore to locate the end of the tube at a predetermined position in said tube-receiving bore, a pull-force generating means associated with said pressurizing rod and including an elastic member to be pressed into frictional engagement with the inner surface of the tube, and an axial displacement means axially compressible by an axial pressure to allow the tube to be axially displaced by the frictional engagement of the tube with said elastic member.

The invention will be described by way of example with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic sectional view showing how a tube has conventionally been expanded and fixed at its end to a tube plate in a main intermediate heat exchanger of a nuclear power plant; Figure 2 is a schematic illustration of a conventional mechanical tube expanding method; Figure 3 schematically shows the construction of a conventional tube expanding device including a tube expanding medium made of an elastic material; Figure 4 is a sectional view of an embodi ment of a tube positioning and expanding apparatus in accordance with the invention; Figure 5 illustrates in an enlarged axial section a tube expanding medium, seal rings and auxiliary seal rings shown in Fig. 4; ; Figure 6 is a sectional view of a pull-force generating device and an axial displacement device which are incorporated in the tube positioning and expanding device in accor dance with the invention; Figures 7, 8 and 9 are schematic illustra tions of respective steps of a tube positioning and expanding process conducted with the tube positioning and expanding apparatus of the invention; Figure 10 is a graphical illustration of the insertion depth of the tube as observed before and after a tube expansion effected by the tube positioning and expanding apparatus of the invention; Figure 11 is a longitudinal sectional view of a model used in a measurement from which the result shown in Fig. 10 is derived; Figure 12 is a sectional view of another embodirnent of a tube positioning and expanding apparatus; and Figure 13 is a sectional view of the tube locating and expanding apparatus of the invention when used for expanding and fixing a tube to a tube plate in an ordinary heat exchanger.

DESCRIPTION OF PREFERRED EMBODI MENTS Fig. 4 shows a tube positioning and expanding apparatus constructed in accordance with the invention. This apparatus differs from the prior art device shown in Fig. 3 in that it comprises a tube positioning sleeve 10, an axial displacement device 11 and a pull-force generating device 12.

Fig. 5 shows in detail a tube expanding medium 5, seal rings 8 and auxiliary seal rings 18. The seal rings 8 are formed with frusto-conical recesses in the end faces directed to the tube expanding medium 5 so that the seal rings 8 are of generally dishshaped axial sections, respectively. The auxiliary rings 18 are of frusto-conical shape and are disposed in the frusto- conical recesses in the seal rings 8, respectively. When an axial pressure is applied to the seal rings 8, they are subjected to radial deformation according to the Poisson's ratio and to rolling deformation so that the seal rings are brought into intimate contact with the inner peripheral surface of a tube to be expanded, with a result that plastic flow of the tube expanding medium 5 is prevented.The auxiliary seal rings 18 are operative to block small gaps formed between the seal rings 8 and pressurizing rod 6 due to the deformation of the seal rings, so that the auxiliary seal rings also prevent plastic flow of the tube expanding medium 5.

Referring to Fig. 5 showing an example of the axial displacement device 11 and, thus, of the pull-force generating device 12, each of these devices includes an elastic member 14 made of an elastic material such as silicon rubber and two stoppers 15 and 16 between which the elastic member 14 is cramped. As an axial compression load is applied to the tension generating device 12, the load acts to reduce the distance between the two stoppers 15 and 16 to axially press the intermediate elastic member 14. As a result, the elastic member 14 is expanded radially outwardly into frictional engagement with the inner surface of the tube. Therefore, the axial compression load, i.e., the axial force applied by the rod 6 is transmitted to the tube 2 through the frictional engagement between the elastic member 14 and the tube 2.As the axial compression force is increased beyond a predetermined level, the clearance 17 between the stoppers 15 and 16 is extinguished to cause a direct mutual contact between the two stoppers 15 and 16 thereby to prevent a further axial compression of the elastic member 14.

On the other hand, when an axial compression force is applied to the axial displacement device 11, the two stoppers 15 and 16 are moved toward each other to axially press the elastic member 14 so that the axial displacement device 11 as a whole is axially contracted. The axial displacement device 11 and the pull-force generating device 12 are of substantially similar construction. These devices, however, are not exactly identical in construction and are differentiated in that the elastic member 14 of the axial displacement device 11 has a cross-sectional area greater than that of the elastic member 14 of the pullforce generating device 12.Accordingly, when these two devices 11 and 12 are subjected to the same magnitude of axial compression forces, the elastic member 14 of the pull-force generating device 12 is radially outwardly expanded more than the elastic member 14 of the axial displacement device 11.

Hereinafter, the process of positioning and expanding a tube of a main intermediate heat exchanger of a nuclear power station will be fully described with specific reference to Figs.

7 to 9.

Referring first to Fig. 7, the tube positioning and expanding apparatus is placed in the tube 2 such that a clearance a is left between the end of the tube and the end of a tube positioning sleeve 10 which is adapted for setting a predetermined insertion depth of the tube 2 into the tube receiving bore, i.e., for precisely locating the tube 2 in relation to the tube plate 1. Then, a hydraulic cylinder (not shown) is energized to actuate its piston to apply a relatively small axial force F, to the pressurizing rod 6 to displace the latter in the axial direction.The elastic member 14 of the pull-force generating device 12 is compressed in the axial direction by this relatively small axial force F, until the stoppers 15 and 16 come into contact with each other, so that the elastic member 14 is expanded radially outwardly into tight contact with the inner surface of the tube 2 to generate a contact pressure P. Due to the contact pressure P, the tube 2 is fixed to the rod 6 and, as the rod 6 is axially moved, the tube is pulled in the axial direction by a pull force f During the compression of the elastic member 14 of the pull-force generating device 12, the elastic member 14 of the axial displace ment device 11 and the tube expanding medium 5, which are both made of silicon rubber, are also compressed in the axial direction.

However, the elastic member 14 of the axial displacement device 11 and the tube expanding medium 5 do not contact the inner surface of the tube at this stage partly because they have cross-sections greater than that of the elastic member 14 of the pull-force generating device 12 and partly because they have comparatively small outside diameters to present comparatively large annular gaps between themselves and the inner surface of the tube 2.

Referring now to Fig. 8, as the force acting on the pressurizing rod 6 is increased to F2, the elastic member 14 of the axial displacement device 11 is axially compressed through sleeves 13 until the stoppers 15 and 16 come into contact with each other. At this time, the rod 6 is axially displaced a distance corresponding to the contraction of the elastic member 14 of the device 11 and, thus, the tube 2 is axially displaced by the pull-force f until the end of the tube 2 is contacted and stopped by the tube positioning sleeve 10 which is made of a metal. As a result, the tube 2 is precisely positioned at the predetermined insertion depth I into the tube receiving bore. At this time, the inner surface of the tube 2 is not yet contacted by the tube expanding medium 5, so that the tube 2 is not expanded yet.

Finally, referring to Fig. 9, as a load or force F3 which is large enough to expand the tube is applied to the pressurizing rod 6, the tube expanding medium 5 is further compressed in the axial direction and, accordingly, is expanded radially outwardly. As a result of this radial expansion of the tube expanding medium 5, the tube 2 is expanded radially outwardly until the tube is fixedly secured to the inner surface of the tube 2. Seal rings 8 and auxiliary seal rings 18 made of urethane rubber having higher hardness than the silicon rubber constituting the tube expanding medium 5 are displaced on both sides of the tube expanding medium 5. Each seal ring 8 has a frusto-conical recess formed in the end surface thereof directed to the tube expanding medium 5.Each auxiliary seal ring 18 is disposed in the frusto-conical recess in one of the seal rings 8 to effectively prevent the tube expanding medium 5 from plastically flowing outwardly during a tube expansion operation.

Fig. 10 graphically illustrates the results of tests in which the apparatus according to the present invention was used to position a tube relative to a model of a main intermediate heat exchanger of a nuclear power station and to expand the tube to the model. The model was formed of a tubular member 1 of a metal (SUS 304). The tubular member 1 had a length L of 65mm and an outer diameter D, of 60mm and was formed therein with a tube receiving bore 1 a having an inner diameter D2 of 22mm, as shown in Fig. 11A. The tube 2 to be expanded and secured to the model 1 was also made of the same kind of metal (SUS 304) and had an outer diameter dof 21.4mm and a thickness of tof 1.2mm and was inserted into the bore 1 a a distance or depth a.Then, the tube 2 was expanded and fixed to the inner surface of the tube receiving bore 1 a by the apparatus of the present invention and at an expanding pressure of 1500 kg/cm2. The length I over which the tube 2 was fixed to the tubular model 1, as shown in Fig. 11 B, was measured. This length I is termed herein as "tube insertion depth after tube expansion", whereas the depth a is termed as "tube insertion depth before tube expansion". As will be seen in the graphical illustration, according to the present invention, tubes 2 can be expanded and fixed to the tube plate 1 always precisely at the predetermined insertion depth I (1.2mm) after tube expansion irrespective of variation in the tube insertion depth a before tube expansion.

Fig. 12 illustrates another embodiment of the invention. This embodiment differs from the first embodiment shown in Fig. 4 in that the end surface of the tube positioning sleeve 10 is recessed to receive the tube expanding medium 5 and that the tube expanding medium 5 is made of urethane rubber while the seal ring 8 is made of fiber reinforced plastic (FRP) having a hardness higher than that of the urethane rubber. The tube positioning and expanding apparatus of this embodiment ensures that the tube can be uniformly secured to the tube receiving bore. In addition, the use of the hard FRP as the material of the seal ring 8 advantageously avoids the undersirable local deformation of the tube which otherwise would tend to be caused at the portion of the tube where the tube is not backed up by the tube plate 1, to thereby assure a tube expansion of a high quality.

Fig. 13 illustrates a modification of the tube positioning and expanding apparatus of the present invention, the modification being applied to a usual heat exchanger. In constructing a usual heat exchanger, a tube 2 is welded to a tube plate 1. For this purpose, the tube 2 is positioned and expanded such that the end 'of the tube 1 to be expanded projects a predetermined distance cfrom the tube plate. This distance cwill be termed hereunder as "projecting length". The principle of the positioning and expansion of the tube 2 in a tube receiving bore in the tube plate 1 is similar to that discussed in connection with Figs. 7 to 9. Namely, a pull-force is applied to the rod 6 in the direction shown by an arrow in Fig. 13 so that the pull-force generating device 12 drivingly connects the rod 6 to the tube 2. Then, the axial displacement device 11 is axially contracted to allow the tube to be axially moved by the device 12 until the forward end of the tube 2 is engaged by the back-up ring 7 which is designed to position the tube 2 such that the forward end of the tube 2 projects the predetermined distance cfrom tube plate 1. Then, the axial force applied to the rod 6 is increased to axially press the tube expansion medium 5 so that the latter is radially outwardly deformed to expand the tube wall into intimate contact with the tube plate 1.

The apparatus shown in Fig. 13 was used to expand stainless steel tubes of 25.4mm in diameter and 2.0mm in thickness. The pressure required for the tube expansion was 3,000 kg/cm2. The tube ends projected various distances from the tube plate before the tubes were expanded. However, the apparatus was operative to expand the tubes in such a manner that the tubes are positioned such that the tube ends projected the predetermined distance cfrom the tube plate 1.

The described and illustrated embodiments of the invention assure precise positioning of tubes in tube receiving bores to thereby improve the reliability of the tube ends.

The present invention is advantageous in that a tube end can be expanded with the tube end inserted into a bore precisely to a predetermined depth. In addition, the invention advantageously assures that a welding operation following a tube expansion operation can be conducted without causing any defects, which in turn assures a remarkable improvement in the reliability of the tube end.

Moreover, the invention advantageously assures an automatic precise positioning of a tube end in a bore simultaneously with the tube expansion operation, whereby the time needed for the tube expansion can be remarkably shortened.

Claims

1. A method of positioning an end of a tube in a tube-receiving bore in a tube plate and expanding the tube end to fix the same to the tube plate, said method comprising the steps of: actuating a pressurizing means to press a first elastic member into frictional engagement with the inner surface of the tube and maintaining the frictional engagement, further actuating said pressurizing means to displace said tube in the axial direction by the frictional engagement between said tube and said first elastic member and by the axial displacement of a second elastic member which is also compressed in the axial direction of said tube, thereby to locate the tube end at a predetermined position in said tube-receiving bore, and further actuating said pressurizing means to expand radially outwardly a third elastic member which is located at a position corresponding to the portion of said tube to be e#xpanded, thereby to uniformly expand said portion of said tube to tightly fix the latter to said plate.

2. An apparatus for positioning a tube in a tube-receiving bore in a tube plate and expanding the tube to fix the same to said tube plate, said apparatus including a tube expanding medium to be placed in the tube and responsive to an axial pressure to expand the tube radially outwardly, and pressurizing means including a rod for appling the axial pressure to said tube expanding medium, characterized in that the apparatus further includes a tube positioning sleeve to be slidably mounted on said rod and disposed in the tube-receiving bore to locate the end of the tube at a predetermined position in said tube-receiving bore, a pull-force generating means associated with said pressurizing rod and including an elastic member to be pressed into frictional engagement with the inner surface of the tube, and an axial displacement means axially compressible by an axial pressure to allow the tube to be axially displaced by the frictional engagement of the tube with said elastic member.

3. A tube positioning and expanding apparatus as defined in Claim 2, wherein said pull-force generating means further includes a pair of stoppers clamping said elastic member for axial movement and wherein said axial displacement means also comprises a second elastic member and a second pair of stoppers clamping said second elastic member for axial movement.

4. A tube positioning and expanding apparatus as defined in Claim 2 or 3, further including sleeves disposed between said tube expanding medium and said axial displacement means and between said axial displacement means and said pull-force generating means, respectively.

5. A tube positioning and expanding apparatus as defined in Claim 2, 3 or 4, further including seal rings disposed adjacent to the opposite end faces of said tube expanding medium, respectively, said seal rings having conical end faces.

6. A tube positioning and expanding apparatus as defined in Claim 5, further including auxiliary seal rings disposed adjacent to said conical end faces of said seal rings, respectively.

7. A tube positioning and expanding apparatus as defined in Claim 6, wherein said tube expanding medium is in the form of a soft elastic member and said seal rings and auxiliary seal rings are formed of a hard elastic material.

8. A tube positioning and expanding apparatus as defined in Claim 7, wherein said soft elastic member and said elastic members of said pull-force generating means and said axial displacement means are all formed of silicon rubber, and hard elastic material is urethane rubber, and said sleeves and said stoppers are all made of a metal or metals.

9. A tube positioning and expanding apparatus as defined in Claim 2, 3 or 4, wherein said tube expanding medium comprises urethane rubber and wherein a seal ring of a fiber reinforced plastic material is disposed adjacent to the axial end of said tube expanding medium which is adjacent to said tube.

10. A method of positioning an end of a tube in a tube-receiving bore in a tube plate and expanding the tube end to fix the same to the tube plate substantially as hereinbefore described, with reference to Figs. 4 to 13 of the accompanying drawings.

11. A tube positioning and expanding apparatus, substantially as hereinbefore described with reference to and as shown by Figs. 4 to 13 of the accompanying drawings.