Patent Grant
7032655
This invention relates to tube supports devices, commonly referred to as tube stakes which are useful with tube bundles in heat exchangers and similar fluid-handling equipment.
Tube bundle equipment such as shell and tube heat exchangers and similar items of fluid handling devices utilize tubes organized in bundles to conduct the fluids through the equipment. In such tube bundles, there is typically fluid flow both through the insides of the tubes and across the outsides of the tubes. The configuration of the tubes in the bundle is set by the tubesheets into which the tubes are set. One common configuration for the tubes is the rectangular formation with the tubes set in aligned rows with tube lanes (the straight paths between the tubes) between each pair or rows, aligned orthogonally to one another. In this formation, each tube is adjacent to eight other tubes except at the periphery of the tube bundle and is directly opposite a corresponding tube across the tube lane separating its row from the two adjacent rows. In the triangular tube formation, the tubes in alternate rows are aligned with one another so that each tube is adjacent six other tubes (the two adjacent tubes in the same row and four tubes in the two adjacent rows).
Fluid flow patterns around the tubes as well as the changes in the temperature and density of the fluids which arise as they circulate a result of the heat exchange between the two fluids flowing in and around the tubes may give rise to flow-induced vibrations of an oscillatory nature in the tube bundle. If these vibrations reach certain critical amplitudes, damage to the bundle may result. Tube vibration problems may be exacerbated if heat exchange equipment is retubed with tubes of a different material to the original tubes, for example, if relatively stiff materials are replaced with lighter weight tubes. Flow-induced vibration may also occur when equipment is put to more severe operating demands, for example, when other existing equipment is upgraded and a previously satisfactory heat exchanger, under new conditions, becomes subject to flow-induced vibrations. Vibration may even be encountered under certain conditions when an exchanger is still in the flow stream but without heat transfer taking place.
Besides good equipment design, other measures may be taken to reduce tube vibration. Tube support devices or tube stakes as these support devices are commonly known (and referred to in this specification) may be installed in the tube bundle in order to control flow-induced vibration and to prevent excessive movement of the tubes. A number of tube supports or tube stakes have been proposed and are commercially available. One type, described in U.S. Pat. No. 4,648,442 (Williams) has a U-shaped configuration in which the distance between the top and bottom surfaces of the channel is the same as the distance between adjacent rows in the tube bundle (i.e. is substantially the same as the tube lane dimension). This type of stake is inserted between the rows in the bundle and is secured at end by an arcuate segment which engages a segment of a tube at the periphery of the tube bundle so as to lock the stake in place in its appropriate position between the rows in the bundle. Stakes of this type are typically made of a corrosion-resistant metal, for example, type 304 stainless steel with a thickness between 0.7 and 1.2 mm to provide both the necessary rigidity for the staked tube bundle as well as sufficient resilience in the U-shaped channel to allow the stakes to be inserted into the lanes between the tubes in the bundle.
Another form of anti-vibration tube stake is described in U.S. Pat. No. 4,919,199 (Hahn) which discloses a stake made in a soft V-configuration strip in which saddles are formed perpendicular to the longitudinal axis of the strip in the open ends of these V-shaped cross sections. The saddles are formed in the strip with a pitch (distance between saddles) equal to the tube pitch and with a radius which matches that of the tubes in the tube bundle so the saddles engage with the tubes on one side of the tube lane. The engagement between these tubes and the saddles locks the tube into place in the tube bundle. The resilient nature of the strip, coupled with the spring type action provided by the V-configuration permits the arms of the V to open and reduce the effective overall width of the stake enables the stake to engage the tubes on both sides of a tube lane in so that the V-shaped stake is locked into place between the two rows of tubes.
A similar type of tube stake is described in U.S. Pat. No. 5,213,155 (Hahn) which discloses a U-shaped stake which is inserted between two tube lanes with the closed end of the U over one of the peripheral tubes in the bundle. Saddles are formed in the open ends of the V-shaped cross section to engage with opposite sides of the tubes in a single row in the bundle. The U-shaped stake is fastened in place around the tubes of the bundle by suitable fasteners extending between the two arms of the stake.
One problem with the pressed configuration of the type shown in U.S. Pat. No. 4,648,442 is that the stakes do not create a positive location for each individual tube, although the stake is locked into place in its selected tube lane. The tubes remain free to vibrate in one plane parallel to the tube lane and parallel to the stake. A different problem exists with the design shown in U.S. Pat No. 5,213,155: although the tubes in rows encircled by the U-shaped stakes are fully supported, the tubes at the periphery of the tube bundle which are not directly encircled by one of the stakes i.e., retained within one of the closed ends of the U-shaped stakes (these are the outer tubes in alternate rows which are not encircled by the ends of the U-shaped stakes), are free to move and vibration in these tubes can be expected under certain conditions. In addition, because the corrugation of the tube support has a transition region before reaching its full depth the two tubes adjacent to each of the outermost tubes do not receive any vibration mitigation either.
One disadvantage of the stake designs which use channel pressings to accommodate the distance between the tubes forming a single tube lane is that deep channel pressings are required or other measures necessary when the tube lane is relatively wide. A more complicated form of tube support is shown in U.S. Pat. No. 6,401,803 (Hahn). This stake uses two V-shaped pressings separated by compression springs which force the stakes against the tubes on opposite sides of the tube lane in order to dampen oscillatory vibrations. This form of stake is, however, quite expensive to manufacture. A unitary stake which will accommodate relatively wide tube lanes without the complication of separate parts therefore remains desirable.
According to the present inventions, a tube support device or tube stake which is useful to mitigate the possibility of tube damage from flow-induced vibration in tube bundles comprises an elongated member or strip which is intended to be inserted in a tube lane between the tubes of a tube bundle in a heat exchanger, condenser or other tube bundle device. Raised-tube-engaging zones are disposed in transverse rows across the strip at successive longitudinal locations along the length of the strip; these tube-engaging zones extend laterally from both faces of the strip, away from the medial plane of the strip, to engage with tubes on opposite sides of the tube lane into which the stake is inserted. The tube-engaging zones are preferably arranged so that they extend laterally from the two opposed faces of the strip in an alternating manner, with the tube-engaging zones in each row alternately extending first from one face of the strip and then the other, along the row. This alternating arrangement within each transverse row is preferably used with a second alternating arrangement in which the raised tube-engaging zones alternate from one face of the strip to the other at the same transverse location in successive rows. The raised, tube-engaging zones may suitably be formed as dimples or corrugations which extend longitudinally along the strip to engage the successive pairs of tubes which are opposite one another on a tube lane and located adjacent to one another in a tube row. In one form, the tube-engaging zones are in the form of corrugations on the inner portion of the tube stake and dimples at the outer portion; this hybrid configuration allows ready insertion of the tube stake into the tube bundle but provides good locking once the stake is emplaced.
The tube stakes may be used in both conventional tube formations, either the rectangular formation or the triangular tube formation. The stakes may be inserted into each tube lane or into alternate tube lanes. When inserted into each tube lane, the tubes receive support from stakes on both sides. Because the effective gap between the tubes (tube lane dimension) is smaller with the triangular formation the thickness as well as the height of the raised tube-engaging zones will normally be smaller in order for the stake to be inserted between the tube lanes with this configuration.
The tube stakes of the present invention may be conveniently and inexpensively fabricated by pressing with dies equipped with suitably arranged protrusions and cavities to form the dimples, corrugations or other forms of tube-engaging zones or by the use of pairs of rollers which have protrusions and cavities (alternating between the top and bottom rollers of the set) to form the raised zones on the strip. Many of the known types of tube stake do not lend themselves to this economical and convenient method of fabrication.
The tube support device or tube stake of the present invention is arranged to provide direct support for tubes which are adjacent to one another but on opposite sides of a tube lane. The tube stake may be inserted between the tubes in the tube bundle along a tube lane between adjacent tube rows. Where the construction of the exchanger permits, the stake may be made sufficiently long to extend from one side of the tube bundle to the other to provide support for the tubes across the entire width of the bundle; in this case, the length of the tube stakes will vary according to the length of the tube lanes across the bundle. In many cases, however, the location of pass lanes in the bundle will create discontinuities in the lanes so that it will not be possible to insert the stakes all the way across the bundle. In such cases, it may be possible to insert the stakes into the bundle from different angles along the length of the bundle in order to provide as much support as possible for the tubes. Thus, the stakes will be inserted transversely into the bundle at each axial location in an angularly variant direction (at a different angle in the transverse plane of the tubes) from the direction of insertion at the next axially adjacent location. This may, however, leave the tubes without staked support in some parts of the bundle, normally in the middle of the bundle where access from the periphery is precluded. In view of their simple and repetitive configuration, the present tube stakes may be readily cut to the desired length to fit the bundle, whether extending entirely across it or only part of the way.
The dimples in row 12 are formed as shown in
The arrangement shown in
a pair of rows in a wider strip with four raised tube-engaging zones might suitably have the following arrangement:
The use of the larger number of tube-engaging zones on this wider strip permits, however, a deviation from the alternating arrangement of tube-engaging zones while still retaining a symmetrical disposition, for example:
Note: the designations “UP” and “DOWN” do not refer to true vertical directions but only to the relative directions from the medial plane and faces of the strip.
The number of dimples may be varied according to the width of the strip and the depth (or height) of the dimples The total depth (d) of the dimples (peak to valley, including plate thickness) will naturally be related to the separation between the tubes which are to be engaged byte tube-engaging zones of the strip, i.e. to the dimension of the tube lane. It will also vary according to the diameter of the tubes because this will affect the level (relative to the tube) at which engagement will occur when the stake is in place in the tube bundle. Typically, the total depth of the tube-engaging zones, 4 will be from 0.5 to 2 mm, preferably 0.5 to 1.5 mm greater than the spacing between the tubes at the point where tube engagement occurs so that a tube deflection of similar magnitude is achieved at this point. The exact deflection achieved in practice will be less than the total depth of the stake because the dimples fit around the tube but this stake depth will normally be found suitable to give a tube deflection which provides good support and vibration resistance and results in a very rigid tube bundle. The elasticity of the stake itself and the elasticity of the tubes, coupled with engagement between the raised tube-engaging zones and the tubes will not only make the tubes more resistant to vibration but also retain the stake in place in the bundle. Desirably, the total depth of the tube-engaging zones (the tip-to-valley distance including strip thickness, b, is selected so that each stake deflects the tube from its rest position with a minor tube deflection, typically about 0.5 to 2 mm. This is a feature of the present type of stake which permits the use of a smaller number of stakes than has been customary, typically, about 50% fewer than would otherwise be needed. One advantage of the present type of tube stake is that relatively wide tube lanes can be accommodated without deep pressing of the strips since about half the tube lane dimension is taken up by each raised zone.
In addition to the total depth of the stake, the thickness and stiffness of the metal of the strip will be factors in fixing the final tube deflection when the stakes are inserted into the bundle. Normally, with the metals of choice, a strip thickness of from 1 to 2 mm will be satisfactory to provide adequate tube support and ability to resist the stresses of insertion into the bundle.
The raised, tube-engaging zones are not necessarily in the form of circular dimples. As shown in
In case of the triangular tube formation, the tubes on opposite sides of a tube lane are both supported by the tube stake, receiving their support from the tube-engaging zones extending out from both faces of the strip but, in this case, the support is given in a staggered, alternating manner which matches the staggered, alternating tube formation. Thus, the first pair of transverse rows (22, 23) supports tube 21B on side of tube lane L but one adjacent tube, 21A, on the opposite side of the tube lane receives support from this pair of rows; its support is also received from a row (not shown) of the next successive row pair. Similarly, tube 21D is supported by the tube-engaging zones in row pair 23, 24 but these two rows support two tubes, 21B and 21C on the opposite side of the tube lane.
Because the effective gap between the tubes (tube lane dimension) in the triangular tube formation is smaller than that of the rectangular formation, the plate thickness as well as the total depth of the dimples (peak to valley, including plate thickness) will typically be smaller than that for the rectangular arrangement. In the same way as described above, the tube stake may be inserted into the tube lane between the tubes and pushed into place until engagement with the tubes on both sides of the tube lane. Retention between the tube stake and the tubes is maintained by the elasticity of the metal and by the tube-engaging zones on the stake.
It is not essential for the tube-engaging areas to be in the form of dimples which engage a segment of each tube at two points. As shown in
When the tube stake is inserted into the tube lane as shown in
The corrugated tube stake may, however, be dimensioned, both in terms of corrugation length and total depth so that it may be inserted into the tube lane as shown in
When the tube support stakes are inserted into the tube bundle, the raised tube-engaging zones have to be pushed past the tubes until the stake is in its proper place in the bundle. With the dimpled type of tube stake, each row of dimples has to be pushed through the gap between each pair of facing tubes until the stake is in place. Because the total depth of the tube engaging zones (peak-to-valley including plate thickness) is preferably greater than the inter-tube spacing, the tubes have to bend slightly to let the dimples pass; although this maintains the stake in place when it is in its final position, it makes insertion that much more difficult as the resistance to bending of each row of tubes has to be overcome. The variation in which raised corrugations are used is better in this respect, making insertion easier but at the expense of not having such multi-point retention once the stake is in place. The hybrid form of tube stake described below and shown in
In the hybrid form of tube stake the raised tube-engaging zones are in the form of raised corrugations at the inner end of the stake (the end which is to be inserted into the center of the tube bundle) and in the form of dimples at the outer end of the stake (the end which is at the periphery of the tube bundle). As before, the tube-engaging zones are disposed in transverse rows across the strip at successive longitudinal locations along the length of the strip, extending laterally from both faces of the strip, away from the medial plane of the strip, to engage with tubes on opposite sides of the tube lane into which the stake is inserted. The corrugations on the inner end of the stake slide more readily between the tubes in the bundle, enabling the stake to be inserted more easily into the bundle while the dimples at the out end of the stake interlock with the tubes near the periphery of the bundle to provide good stake location and retention capabilities.
In this type of stake, the number of transverse rows of dimples at the outer end of the stake may be chosen more or less at wish, depending upon the relative importance attached to ease of stake insertion and positive stake retention. Typically, from three to ten rows of dimples in a normal length (about 20 to 50 cm) stake will be adequate to ensure good stake retention. The outer tube row may be supported on only one side by the outermost row of dimples depending on the configuration of the tubes at the periphery of the tube bundle but by providing a sufficient number of dimpled rows, adequate stake retention may be provided.
Like the dimples in rows 42 to 45, the corrugations in rows 47 and onwards extend out from each face of the strip in an alternating arrangement across each transverse row and along each axial line A, B, C. In
The transverse rows are arranged at successive longitudinal locations along the length (longitudinal axis) of the strip: each pair of successive rows is positioned to provide support for a pair of tubes which are adjacent one another on one side of tube lane L, with each row (except the outermost row) providing support for a pair of tubes which are adjacent one another but on opposite side of the tube lane. Thus, rows 42 and 43 provide support for tube 41A on one side of tube lane L and tube 41B on the other side of the lane. Similarly, rows 44 and 45 provide support for tubes 41C and 41D on opposite sides of the tube lane by means of the dimples extending out on each side of the strip.
The dimples in row 42 are formed as shown in
As with the configurations shown in
The arrangement shown in
a pair of rows in a wider strip with four raised tube-engaging zones might suitably have the following arrangement:
The use of the larger number of tube-engaging zones on this wider strip permits, however, a deviation from the alternating arrangement of tube-engaging zones while still retaining a symmetrical disposition, for example:
Note: as before, the designations “UP” and “DOWN” do not refer to true vertical directions but only to the relative directions from the medial plane and faces of the strip.
The placings of the transverse rows of raised, tube-engaging zones on the tube stake are to provide the desired engagement between the tube stake and the tubes in the tube bundle with which they are being used. To accommodate pass lanes in the tube bundles, the distances between successive transverse rows of raised, tube-engaging zones (dimples, corrugations) may be increased correspondingly, consistent with the arrangement of tubes in the bundle.
As can be seen from the drawings, each tube stake engages with tubes on opposite sides of a tube lane so that insertion of a stake in each tube lane provides support for two rows of tubes within the outer periphery of the tube bundle. At the periphery of the bundle some tubes may receive support from a stake which does not support a tube on the other side. This reduces the effective support given to those tubes but since the length of stake extending out from the last pair of tubes within the bundle is relatively short, some effective support is given to these outer tubes on one side at least by the cantilevered end of the stake.
While the frictional engagement between the stakes and the tubes will provide for retention of the stakes in the bundle, the end of the tube stake may be provided with a tube-engaging crook, to hook over the end of a tube on one side of the tube lane to prevent withdrawal of the stake in one direction. Alternatively, the stakes may be folded into a U-shaped or hairpin configuration which has, effectively, a pair of the stakes conjoined at one end by means of an arcuate, tube-engaging segment. This configuration provides stiffening for three tube rows simultaneously with additional positive location for the stake from the closed end of the hairpin (the arcuate segment) being locked over of the peripheral tubes at one end to the bundle. Because each stake provides stiffening for three tube rows simultaneously, the U-shaped tube stakes will be inserted over alternate rows to provide stiffening for each row of tubes in the tube bundle. If desired, additional stake retention may be provided by retention members such as bolts extending between the arms of the hairpin at one or more points along its length. Additional locking for single-line stakes (not formed into the U-configuration) may be provided by punching out a small hole in the end of the stake through which a metal band can be passed. This metal band would be secured, for example, to tie rods that are available in the tube bundle device adjacent to the outer tube circumference of the tube bundle, to reduce the possibility of tube supports sliding down the tubes.
The tube stakes are suitably made of a metal which will resist corrosion in the environment of the tube bundle device in which it is to be used. Normally, to resist corrosion in both water and other environments, stainless steel will be satisfactory. Stainless SS 304 is suitable except when chloride corrosion is to be expected when duplex stainless steel will be preferred. The duplex stainless steels which contain various amounts of the alloying elements chromium, nickel and optionally molybdenum are characterized by a mixed microstructure with about equal proportions of ferrite and austenite (hence the common designator “Duplex”). The chemical composition based on high contents of chromium, nickel and molybdenum provides a high level of intergranular and pitting corrosion resistance. Additions of nitrogen promote structural hardening by interstitial solid solution mechanism, which raises the yield strength and ultimate strength values without impairing toughness. Moreover, the two-phase microstructure guarantees higher resistance to pitting and stress corrosion cracking in comparison with conventional stainless steels. They are also notable for high thermal conductivity low coefficient of thermal expansion, good sulfide stress corrosion resistance and higher heat conductivity than austenitic steels as well as good workability and weldability. The duplex stainless steels are a family of grades, which range in corrosion performance depending on their alloy content. Normally, duplex grades such as 2304, 2205 will be adequate for heat exchanger service with the final selection to be made consistent with recognized corrosion resistance requirements.
Insertion of the tube stakes into the tube bundle is facilitated by first inserting a metal bar with beveled edges having a thickness that is slightly greater than the total depth of the stake (including the dimples or other raised zones) after which the stake is inserted into place and the metal bar is slowly removed to ensure the proper locking in of the tubes and the tube stake. The bar may also be used in a similar manner to facilitate removal of the stakes. The stakes may be inserted at axial locations determined by experience or by vibration studies for the relevant equipment. The stakes may be inserted into the bundle in different transverse directions at different axial locations, for example in a vertical direction at the first axial location, in the horizontal at the second location, followed in alternate sequential manner at successive axial locations along the length of the tube bundle.
Besides its good stake retention capability, another major advantage of the present type of stake is its simplicity. Unlike the stakes shown in U.S. Pat. Nos. 4,919,199 and 5,213,155 which require the metal strip to be formed by pressing in two directions, longitudinally into the U- or V-shaped channel and transversely to form the tube-receiving saddles, an expensive operation involving large machines in which the press force could be as large as 10 tonnes. The tube-engaging zones of the present stakes, by contrast, can be formed by a single pressing operation in the transverse direction, fabricating several rows of dimples or corrugations at a time, with successive pressings along the length of the stake, in a simple press with a low pressing force. The use of two press rolls would, of course, represent be the most economical option for large scale manufacture but is not necessary and the cheaper, simpler equipment could be used failing access to greater resources.
This application claims priority from application Ser. No. 60/480,921, filed 24 Jun. 2003, entitled “Anti-Vibration Tube Supports” of M. M. Calanog, T. M. Rudy, R. C. Tomotaki and A. S. Wanni and from application Ser. No. 60/511,623, filed 15 Oct. 2003, entitled “Anti-Vibration Tube Support” of T. M. Rudy and A. S. Wanni, the disclosures of which are incorporated by reference.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3933583 | Jabsen | Jan 1976 | A |
| 4160477 | Roffler | Jul 1979 | A |
| 4175003 | Beuchel et al. | Nov 1979 | A |
| 4359088 | Jabsen | Nov 1982 | A |
| 4570703 | Ringsmuth et al. | Feb 1986 | A |
| 4648442 | Williams | Mar 1987 | A |
| 4781884 | Anthony | Nov 1988 | A |
| 4860697 | Malaval | Aug 1989 | A |
| 4919199 | Hahn | Apr 1990 | A |
| 5072786 | Wachter | Dec 1991 | A |
| 5213155 | Hahn | May 1993 | A |
| 6401803 | Hahn | Jun 2002 | B1 |
| Number | Date | Country | |
|---|---|---|---|
| 20050006075 A1 | Jan 2005 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60480921 | Jun 2003 | US | |
| 60511623 | Oct 2003 | US |
