GB2135223A - Expanding tubes in tube plates - Google Patents

Abstract

A one stage method of (and apparatus for) expanding small metal tubes 14 into holes in metal tubeplates 10 including walls of drums and headers (e.g. condensers) using an elastomeric body 16 compressed axially in the tube 14 and which expands radially to expand the tube 14 end to stress the tube 14 and the annular zone of the tubeplate 10 around the tube 14 beyond their respective elastic limits substantially throughout the axial distance equal to the axial separation of the axially outermost limits of annular supports 18 arranged about end portions of the elastomeric body 16. The supports 18 each comprise an annular array of pieces (50) bonded to the body 16. The pieces (50) separate uniformly to transmit substantially uniform pressure to the tube 14. <IMAGE>

Description

SPECIFICATION Method & apparatus for expanding tubes in tubeplates The invention relates to methods and apparatus for expanding tubes in tubeplates. The term "tubeplates" includes any tubeplate as such or the wall of a drum, header or other component (such as a tube already expanded or welded into a tubeplate thereby forming an integral part of the tubeplate) to which a tube or tubes are joined.

Conventionally, such tubes are joined to tubeplates by expanding the tubes using a roller expander, a method used for many years but having notorious drawbacks.

The assignees of the present invention have developed and successfully commercially applied a method, described in British Patent Specification No. 2069388B, by which relatively large tubes of outside diameter around 50.8 mm (2 inches) and above are expanded in a tubeplate by uniform pressure, applied by an annular body of elastomeric material which is compressed by an axially applied load. The body expands radially to expand the tube. The method is performed in two stages, the first expanding the tube beyond its elastic limit and into contact with the tubeplate and the second expanding the tube further and stressing the tubeplate beyond its elastic limit.

In the second stage apparatus is used different from that used in the first stage and in which the body of elastomeric material is supported by two annular supports at its ends, each support comprising an annular array of pieces which remain in contact with each other throughout so that the array remains closed and no gaps are permitted between the pieces through which the body can extrude. Relatively high elastomer pressures were used of 3000 bar or greater. The second stage apparatus is described in British Patent Specification No. 20693878.

That method and apparatus is not applicable to the expansion of relatively smaller tubes such as condensor and similar tubes where it is required to expand the tubes in a single-stage operation and where it is required to use a relatively cheap disposable assembly comprising the elastomeric body and its annular supports. The pieces of the annular supports described in British Patent Specification No. 2069387B are relatively complex in shape and expensive to manufacture.

Tubes of the condenser type would require such pieces to be scaled down if they were to be used in expanding such tubes and manufacture of the pieces would be even more costly.

Ideally, the economical expansion of a range of sizes of condenser and similar tubes requires the use of pieces which are of standard size throughout the tube range and are of similar shape and each support should comprise a relatively small number of pieces.

Expansion of tubes using elastomeric bodies has been proposed in US Patent Specifications No.4006619 (Anderson) and Nos. 4068372 and 4142581 (assigned to Hitachi).

Anderson uses only very low elastomer pressure to expand the tube only outside the tubeplate. He proposes using as supports either slightly expansible complete annular bands which remain closed or alternatively annular arrays of twenty-four steel pieces which move out of contact as the support expands.

Anderson does not stress the tubeplate at all and states that the end parts of the elastomeric body cannot apply as high a pressure to the tube as the central part. Anderson is concerned only with local expansion of the tube and does not use the end portions of the elastomeric body to expand the tube nor do the supports transmit any useful pressure to the tube.

The annular arrays of pieces proposed by Anderson are required to support the elastomeric body and small gaps between the pieces are said to be essential. However, there is no disclosure of how the spacing between the pieces is to be kept uniform. Such uniformity was perhaps not critical at the low elastomer pressures he used but at the higher elastomer pressures required in the present invention the loss of uniformity of spacing which would be inevitable using Andersons's proposal would be quite unacceptable.

Hitachi propose using relatively high elastomer pressure but rely on complete annular seals of synthetic plastic material as the supports for the elastomeric body. Such supports always remain closed and lie beyond the body at either end and do not transmit any effective pressure whatsoever to the tube.

Accordingly, the length of tube which can be expanded is considerably less than the overall length of the assembly of the body and its supports. Also, the method and apparatus is consequently incapable of expanding the tube throughout the entire thickness of the tubeplate. Such a requirement is nevertheless often of considerable importance in the manufacture of condensers or similar heat exchangers exposed to fluids that are liable to cause corrosion and stress at crevices between the tubes and tubeplate. Nuclear power installations typically call for condensers or heat exchangers in which such crevices are virtually absent or else insignificant. The methods of Anderson and Hitachi cannot meet such requirements.

The applicant has found that, surprisingly, the elastomeric body can be adequately supported to prevent extrusion under very high elastomer pressures from 3000 bar upwards using supports which open as they expand and which comprise pieces which move out of contact with one another as the supports expand.

However, the spacing between the pieces is critical and must be kept uniform. The preferred spacing is around 0.38 mm to 0.51 mm (0.015 to 0.020 inch). If the pieces were allowed to move circumferentially in the array (as in Anderson's proposal) an unacceptably large gap would arise through which the elastomeric body would extrude.

The applicant has found that a relatively small number of pieces is feasible in an array. The pieces are not then excessively small and uniform spacing under all conditions has been found to be maintained by bonding of the pieces to the elastomeric body. This enables the operator to handle the combined body and support very readily when it is necessary for him to replace the elastomeric body when its useful life is exhausted (say after at least 50 expansion cycles or possibly 100 to 200 expansions, depending on the duty required). Such pieces can be sized so as to be usable in making up supports for a range of tube sizes.

Supports which comprise such pieces and which, although they are closed at commencement of expansion, become open owing to the mutual moving apart of the pieces to form gaps, have been successfully used by the applicant in a single stage operation not only to support the elastomeric body against extrusion but also to transmit uniform pressure radially from the body to the tube substantially equal to the uniform pressure applied by the body between the two supports directly to the tube.

The supports lie within the overall length of the body so that the tube and the tubeplate can be fully stressed throughout the entire length of the combined support and body assembly.

In particular, where the manufacturing application calls for it, the tube and tubeplate can be stressed beyond their respective elastic limits by very high elastomer pressures applied to the tube throughout the entire thickness of the tubeplate giving the extremely important advantage that crevices between the tube and the tubeplate can be virtually eliminated or rendered insignificant.

A method of expanding a metal tube less than 50 mm in outside diameter within a hole in a metal tubeplate, according to the invention, comprises using an annular body of elastomeric material in a single stage operation which body is supported by respective annular supports arranged about respective end portions of the body of reduced diameter, each support comprising an annular array of pieces each bonded to the body, the rubber body being axially compressed by applied load to expand the body radially to apply substantially uniform pressure directly to the tube intermediate the supports and also to the radially inner surfaces of the pieces to expand the supports radially and to separate the pieces uniformly whereby said pieces transmit substantially uniform pressure to the tube so that the tube and an annular zone of the tubeplates around the tube are stressed beyond their respective elastic limits substantially throughout the axial distance equal to the axial separation of the axially outermost limits of the supports.

The method can if required by used to stress the tube and tubeplate beyond their respective elastic limits throughout the thickness of the tubeplate.

Apparatus for expanding a metal tube less than 50 mm in outside diameter within a metal tubeplate, according to the invention comprises an annular body of elastomeric material, means operable to apply a load to said body parallel to the central longitudinal axis thereof to compress said body and to expand the same radially to apply substantially uniform pressure to the tube, the body comprising end portions of reduced diameter, said apparatus further comprising two support means respectively arranged about said end portions, each said support means comprising an annular array of pieces each bonded to the body and each support means being expansible radially by expansion of the respective end portion of the body thereby to separate the pieces uniformly to transmit uniform pressure to the tube, said support means being positioned within the overall length of the body, said means being such as to apply said load in a single stage operation to expand the tube into contact with the tubeplate and to stress the tube and an annular zone of the tubeplate around the tube beyond their respective elastic limits substantially throughout the axial distance equal to the axial separation of the axially outermost limits of the supports.

The invention includes an assembly of tubes joined to a tubeplate by the method.

One form of method and apparatus for performing it will now be described by way of example to illustrate the invention with reference to the accompanying drawings, in which: Figures 1 and 2 are longitudinal vertical sections through part of the apparatus and through parts of a tube and tubeplate showing the position before and at full expansion pressure, respectively, Figures 3 and 4 are, respectively, an end elevation of, and a longitudinal vertical section through, the rubber body with its support means shown in Figures 1 and 2; and Figures 5 and 6 are scrap sectional views through parts of tubeplates showing two forms of grooves which may optionally be provided in the wall of the tubeplate hole receiving a tube, if desired.

The drawings show the following principal items: a metal tubeplate 10 having a plurality of cylindrical holes extending through the tubeplate 10, one hole 12 being shown; a cylindrical metal tube 14 extending adjacent one end through the hole 12; an annular body 16 of elastomeric material positioned in the tube 14 and made up of two similar halves; annular support 18, one at each end of the body 16; and means for applying load to the body 16 parallel to the central longitudinal axis thereof being a split annular collar 20 which engages one end of the body 16 and through which extends a mandrel 22. The mandrel 22 extends through the body 16 and has an enlarged integral head 24, of outer diameter less than the tube, engaging the other end of the body 16.

The collar 20 has an annular groove 26 accommodating the end of the tube 14 protruding from the tubeplate 10 so that the collar 20 can abut the tubeplate 10.

Figure 1 show the positions of the parts before the rubber body 16 is compressed. All clearances have been exaggerated for clarity. Accordingly, in Figure 2, which shows the positions when the body 16 is fully compressed, the very slight deformation of the tube 14 outside the tubeplate 10 is correspondingly exaggerated. In actual fact, such deformation is virtually non-existent and not discernible.

The remainder of the apparatus need not be described. Reference may be had to British patent specification No. 20693878 for a detailed description of similar apparatus for an understanding of the principles involved. The present apparatus includes a hydraulic piston-and-cylinder mechanism operable to pull the mandrel 22 through the collar 20 from the position shown in Figure 1 to the position shown in Figure 2 to compress the body 16 axially. The mechanism is powerful enough to exert forces on the body 16 such that when fully loaded it exerts pressures on the tube 14 sufficiently high to stress both the tube 14 and an annular zone of the tubeplate 10 around the tube 14 beyond their elastic limits.

Typically, that zone has a diameter some 1.7 times the diameter of the hole 12. That ensures maximum residual stress in the tubeplate 10 so that the gripping load on the tube 14 when the applied load is removed is at or near to the maximum possible. That gripping load determines the effective strength of the joint between the tube and the tubeplate, as measured by the force necessary to push the tube 14 out of the tubeplate 10 ("push-out strength"). As explained further below such elastomer pressures in the body 16 exceed 3000 bar.

Initially on loading the body 16, the body expands radially into contact with the tube 14, which expands elastically initially. After passing its elastic limit the tube 14 expands plastically, moving into intimate contact with the wall of the hole 12. Further loading of the body 16 causes the tubeplate 10 to deform elastically and then, after its elastic limit is exceeded, plastically in the annular zone just referred to.

When a sufficiently high, predetermined elastomer pressure in the body 16 is reached (as indicated by a monitor responsive to the corresponding hydraulic pressure) the pumping of hydraulic fluid to the hydraulic cylinder is discontinued for a dwell period of typically 5 seconds to allow the joint to form and the system pressures to reach equilibrium.

The pressure is then released and the body 16 recovers, contracting radially away from the tube and lengthening as the mandrel 22 returns to its position shown in Figure 1. The mandrel is then withdrawn from the tube 14. Atypical total cycle time is 15-20 seconds including the dwell period.

The body 16 applies substantially uniform pressure to the tube 14 producing a joint with little or no work-hardening of the tube surface. The tube is not subjected to cyclic loading as is the case when a conventional roller expander is applied to tubes. This is an advantage especially where the tube is of notch-sensitive material, in which crack propagation would be likely to occur if cyclic loading were applied.

Hole ovality is not a critical parameter and satisfactory joints can be made in out-of-round holes. The tube and hole must be free of swarf and scale and the hole must be free of axial scoring.

The condition of the surface of the hole 12 affects the joint strength, the rougher the surface the stronger the joint. The leak tightness is also affected by condition, being less at higher roughness. Optimum surface finish is therefore a compromise and is selected to suit the joint geometry and the joint properties required.

The method is applicable particularly to tubes having outside diameters from 19.05 mm (0.75 inch) to 38.1 mm (1.50 inch) with wall thicknesses from 22 gauge (0.71 mm, 0.028 inch) to 18 gauge (1.22 mm, 0.048 inch) and tubeplate thicknesses from 25.40 mm (1 inch) to 152.4 mm (6 inches).

Typically, the assemblies made by use of the invention are steam condensers for steam boiler applications where the tubeplate would typically be at the lower end of the thickness scale and heat exchangers generally in which case the whole range of thicknesses is applicable.

The invention is applicable to a range of tube and tubeplate materials. For example, tubes of brass, cupro-nickel and stainless steel joined to tubeplates of mild steel. Alternatively, the tubeplate may be of Munz metal (a 70130 brass) and stainless steel.

Where the tube has a relatively high elastic limit and the tubeplate a relatively low limit, for example, or the elastic moduli differ it may be necessary to use a grooved hole. A typical groove is shown at 30 in Figure 5.

For example, in a tubeplate having a thickness of 25.4 mm (1 inch) the groove is centrally positioned and is 4.45 mm (0.175 inch) wide and 0.51 mm (0.020 inch) deep.

Alternatively, two triangular section grooves as shown at 60 in Figure 6 may be used. They are in accordance with a standard prescribed by The American Thermal Equipment Manufacturers' Association. In the example shown, the tubeplate is 25.4 mm (1 inch) thick. The maximum depth of each groove is 1.587 mm (0.0625 inch) and the maximum width is 3.175 mm (0.125 inch). The distance between the inner edges of the grooves (i.e. the minimum distance between the grooves) is 3.175 mm (0.125 inch).

Typical examples of joints made using the method are given below; where: "od" means the outside diameter of the tube; "tw" means the wall thickness of the tube; "tm" means tube material; "T" means tubeplate thickness; "TM" means tubeplate material; "ep" means the maximum pressure exerted by the elastomer upon the tube; "pi" means the push-out load (i.e. the force necessary to push the tube out of the tubeplate after it has been joined to the tubeplate). The last-mentioned parameter is a generally recognised measure of the mechanical strength of the joint. All dimensions quoted are in millimetres. Pressures are in bar and loads in kilo-Newtons.

od tw tm T TM ep pl 25 1.2 brass 25 mild steel 3160 10.68 25 1.2 cupronickel 25 mild steel 3160 8.90 25 0.7 AL6X 25 carbon steel 3255 > 16.46 25 0.7 AL6X 25 Munz metal 2465 8.90 25 0.7 AL29-4C 25 carbon steel 3255 > 15.57 The codes "AL6X" and AL29-4C" denote ferritic stainless alloy steels available from the Allegheny Ludlum company of the USA.

In the first three examples given above the walls of the holes in the tubeplate in which the tubes were received were plain. The hole walls had a surface finish of 32 Centre Line Average. In the last two examples the walls of the holes each had two triangular-section grooves as described above with reference to Figure 6.

Figures 1 and 2 typically represent a tubeplate having a thickness of 25.4 mm (1 inch) and a tube of outside diameter 25.4 mm (1 inch). If taken as representing a typical condenser the tubes would be distributed uniformly at triangular pitching of 34.90 mm (1.375 inch).

As shown in Figure 2 the rubber body 16 when fully loaded extends throughout the thickness of the tubeplate, the ends of the body being substantially coplanar with the faces of the tubeplate. The end faces of the supports 18 are also substantially coplanar with the tubeplate faces.

This means that there is substantially no crevice between the tube and the tubeplate at either face of the tubeplate, which is in sharp contrast to the disclosures in U.S. Patents Nos. 4068372 and 4142581. There, it is clear that the tube cannot be fully expanded to eliminate crevices since the larger seal rings at the ends of the rubber body are not active to transmit radially outwardly to the tube the full pressure developed in the rubber body.

The present invention is applicable where required to eliminate crevices at both sides of the tubeplate, or to reduce them to acceptable level whether in relatively thin tubeplates of around 25 mm (1 inch) or in thicker tubeplates of around 150 mm (6 inches) and intermediate thicknesses.

The invention yields joints which are totally liquid-tight and which are gas-tight to an extremely high degree indeed better than a leak rate typically of 2 x 10-4 milliber litres/second.

Thus, the joints are of extremely high quality in relation to condenser applications in which typically the water-side working pressure is 3.4 bar gauge (50 ibf/in2 gauge) and the steam-side working pressure is 170 mbar absolute (2.5 lbf/in2 absolute).

The rubber body 16 and the supports 18 are shown in detail in Figures 3 and 4.

The body 16 is made up of two identical halves 40,42 each of which is split at 44 longitudinally to facilitate assembly about the mandrel 22. The body 16 is for example made of a polyether-based polyurethane resin with a three component methyl di-isocyanate termination system. This has good abrasion resistance and suitable elastic recovery. The hardness in this example is 80 Shore A.

The body halves 40, 42 are each cast in a mould and the nine pieces 50 (Figure 3) of the respective support 18 are present in the mould so that the pieces 50 are bonded at the same time to the body. Alternatively, the body halves may be cast first and the pieces 50 bonded to the body half after casting. The pieces 50 are all in mutual engagement in the finished body half.

The pieces 50 are segments of hard steel forming a closed annular array when the body 16 is unloaded.

Typically each piece 50 has a radial thickness of 2.5 mm (0.10 inch) and an axial width of 3.8 mm (0.15 inch).

The external circumferential dimension of each piece 50 is 7.4 mm (0.28 inch).

The radial thickness of the rubber body 16 is 5 mm (0.20inch).

To prepare the apparatus for use the two body halves 40, 42 are opened out to C shape so that they can be passed over the mandrel 22 and then closed up so as to position the two body halves appropriately one in relation to the other, as shown in Figures 1,3 and 4. When the body halves 40,42 are thus opened the supports 18 are also opened, the pieces 50 remaining bonded to the elastomeric material of the body halves.

When the body halves close about the mandrel 22 the supports 18 close up so that the pieces 50 are uniformly positioned about the mandrel 22 as shown in Figure 3.

The bonding of the pieces 50 to the body halves 40,42 ensures that, when the supports 18 expand during the loading and expansion of the body 16, the pieces 50 are uniformly spaced apart as they separate from one another. The resulting gaps between the pieces 50 are maintained at a minimum value typically in the range 0.38 mm to 0.51 mm (0.015 to 0.020 inch). This ensures that the elastomeric material of the body 16 is adequately supported throughout and does not extrude past the supports 18 under the high pressures to which the body 16 is subjected (3000 bar and above).

The body 16 is sized so as to have a 0.13 mm (0.005 inch) diametral clearance fit in the tube (at minimum tolerance tube bore).

It is worth noting that the very high elastomer pressures employed in the apparatus according to the present invention impose very high stresses in the mandrel 22. At an elastomer pressure of 3480 bar the tension in the mandrel is some 97 kilo-Newtons and the stress in the mandrel is 740 mega-Newtons per square metre. At such stresses the mandrel head 24 (Figures 1 and 2) must be integral with the mandrel stem 22 the join between the two being appropriately radiussed as shown. Both Anderson and Hitachi referred to above disclose the use of screw-threaded joints of radius equal to the stem radius for joining the mandrel head to the stem. No radiussed joining portions are shown where the head merges with the stem. It is apparent that the elastomer pressures proposed to be used by Anderson and Hitachi were relatively lower than those proposed in the present invention.Indeed, Hitachi apparently achieve the necessary strength or leak tightness of the joint by the use of grooves in the wall of the tubeplate hole.

By contrast, the present invention achieves very high push-out loads and virtually total liquid-tightness in joints made in holes without grooves.

In general, tubes expanded in relatively thinner tubeplates using the method of the invention will be expanded throughout the full tubeplate thickness to stress both the tube and the tubeplate beyond their elastic limits throughout the full thickness of the tubeplate.

In thicker tubeplates, the tube will be similarly expanded if necessary, for example, if crevices are to be eliminated. Alternatively, the expansion will be effected throughout a depth of the tubeplate sufficient to obtain the required joint strength, the tube and tubeplate being stressed beyond their elastic limits throughout that depth.

Claims (12)

1. A method of expanding a metal tube less than 50 millimetres in outside diameter within a hole in a metal tubeplate comprising using an annular body of elastomeric material in a single stage operation which body is supported by respective annular supports arranged about respective end portions of the body of reduced diameter each support comprising an annular array of pieces each bonded to the body, the rubber body being axially compressed by applied load to expand the body radially to apply substantially uniform pressure directly to the tube intermediate the supports and also to the radially inner surfaces of the pieces to expand the body radially and to separate the pieces uniformly whereby said pieces transmit substantially uniform pressure to the tube so that the tube and an annular zone of the tubeplate around the tube are stressed beyond their respective elastic limits substantially throughout the axial distance equal to the axial separation of the axially outermost limits of the supports.

2. A method according to claim 1, in which the tube and tubeplate are stressed beyond their respective elastic limits throughout the thickness of the tubeplate.

3. An assembly of metal tubes each less than 50 millimetres in outside diameter and each joined to a metal tubeplate by the method claimed in claim 1 or claim 2.

4. An assembly according to claim 3, in which each said tube is expanded in a respective hole comprising at least one annular groove defined by a surface of said tubeplate surrounding said hole.

5. An assembly according to claim 4, in which there is only one groove and said groove is located centrally between the ends of said hole and has a rectangular cross-sectional shape of radial depth less than the width of said groove.

6. An assembly according to claim 4, in which there are only two grooves each of triangular cross-sectional shape.

7. Apparatus for expanding a metal tube less than 50 millimetres in outside diameter within a hole in a metal tubeplate comprising an annular body of elastomeric material, means operable to apply a load to said body parallel to the central longitudinal axis thereof to compress said body and to expand the same radially to apply substantially uniform pressure to the tube, the body comprising end portions of reduced diameter, said apparatus further comprising two support means respectively arranged about said end portions, each said support means comprising an annular array of pieces each bonded to the body and each support means being expansible radially by expansion of the respective end portion of the body thereby to separate the pieces uniformly to transmit uniform pressure to the tube, said support means being positioned within the overall length of the body, said means being such as to apply said load in a single stage operation to expand the tube into contact with the tubeplate and to stress the tube and an annular zone of the tubeplate around the tube beyond their respective elastic limits substantially throughout the axial distance equal to the axial separation of the axially outermost limits of the supports.

8. For use in a method of expanding a metal tube less than 50 millimetres in outside diameter, an annular body of elastomeric material having end portions of reduced diameter each having a respective support means arranged thereabout, each said support means comprising an annular array of pieces each bonded to the body and being expansible radially by expansion of the respective end portion of the body thereby to separate the pieces uniformly to transmit uniform pressure to the tube.

9. A method according to claim 1 substantially as hereinbefore described with reference to the accompanying drawings.

10. An assembly according to claim 3 substantially as hereinbefore described with reference to the accompanying drawings.

11. Apparatus according to claim 7 substantially as hereinbefore described with reference to the accompanying drawings.

12. An annular body according to claim 8 substantially as hereinbefore described with reference to the accompanying drawings.