Plug for sealing tubes of shell and tube heat exchangers

Abstract

A plug for sealing tubes of shell and tube heat exchangers, said plug (12) comprising: a tie rod (30); a spacer (20) of said tie rod (30); a gasket (51) set between said tie rod (30) and said spacer (20); means (50) for drawing back said tie rod (30); said tie rod (30) comprises, at a first end thereof, a threaded portion (31); said tie rod (30) comprises a second tapered end (33) thereof having a diameter larger than the diameter of said tie rod (30).

Description

[0001] The present invention relates to a shell and tube heat exchanger having a plug for sealing tubes of shell and tube heat exchangers, and in particular to a plug for sealing tubes of shell and tube heat exchangers. US 4 474 216 discloses a plug having the features of the preamble of claim 1.

[0002] A shell and tube heat exchanger 1 of a known type is mainly constituted by a tube-bundle 2 made up of tubes 9 (the tubes may be either straight tubes or U-tubes) located within an envelope having a more or less cylindrical shape referred to as shell 3, where a fluid, which enters from a first inlet 4, passes into the inlet distributor head 8 flows in the tubes 9 of the tube-bundle 2, gathers in the outlet distributor head 8A and exits from a first outlet 5 (tube-side circuit) and another fluid, which enters from a second inlet 6 and exits from a second outlet 7, and flows in the shell 3 (shell-side circuit), i.e., in the room delimited between the inner surface of the shell 3, the outer surfaces of the tubes 9 of the tube-bundle 2, and the faces of the tube-sheets 11 oriented towards the shell itself.

[0003] The tubes 9 of the tube-bundle 2 are fixed to one or more perforated plates referred to as tube-sheets 11 by means of expanding, welding, or threading or a combination of the three methods. Figure 1 described, illustrates one type of tube-bundle heat exchanger, but the invention may be applied to all heat exchangers, such as, for example, ones with straight tubes, U-tubes, fixed heads, floating heads, one-pass or multi-pass tube-side or shell-side, etc.

[0004] One of the problems that can affect this heat exchanger is the leakage from one circuit to the other, i.e., when the two fluids come into direct contact. This drawback may have several consequences, which ranges from the drop in performance of the items to undesired chemical-physical reactions between the two fluids, from the reduced service life of the items to problems on pieces of equipment set upstream and downstream the items, as well as unexpected corrosion on metallurgies of the heat exchanger that are designed to be wetted only by one of the two fluids.

[0005] The leakage previously mentioned may occur in a wide range of points and for multiple reasons including also concomitant ones; amongst these, erroneous construction, erroneous assembly, operating and chemical conditions of the fluids not according to design, gaskets not appropriately tightened, poorly welded joints, operativeness beyond service life, failure of the process tube placed inside the shell, etc.

[0006] In the prior art, in the event of leakage due to a loss of integrity of the tubes placed in the volume of the shell, the tubes involved are normally plugged by welding to their inlet and outlet two metal plugs, one for each end of the damaged tube. In particular, if the tube is straight, the two plugs are welded on the inlet tube-sheet and on the outlet tube-sheet; if the tube is U-shaped, the two plugs are welded on the single tube-sheet that works as inlet / outlet.

[0007] In the cases where the plug has to be located and ensure a seal on the face 11A of the tube-sheet accessible directly from the distributor head, the problem is solved by the prior art with a wide range of metal plugs that adapt to the various geometries in question.

[0008] The thicknesses of the tube-sheet and in general the arrangement of the exchanger, the weights and dimensions of the distributor heads involved, and the overall dimensions are important parameters in the choice of the plug and of the methodology of repair; it is likewise fundamental to take into account also the metallurgy of the tubes and of the existing sheet.

[0009] The problem is not solved in a satisfactory way by the prior art in all the cases where the plug has to be positioned on the accessible side 11A of the distributor head, but the seal is required on the face 11B of the tube-sheet not directly accessible from the distributor head. This circumstance occurs when the metallurgy of the tube 9 corresponds to that of the tube-sheet wetted by the shell-side fluid 11B, but does not correspond to that of the accessible part 11A of the tube-sheet wetted by the tube-side fluid, in the distributor head. In this case, plugging the tubes by means of a welded plug (as per the known art) presents drawbacks, which, according to the cases, render repair slow and complicated or even impossible or with a high risk of jeopardizing the integrity of the exchanger undergoing repair.

[0010] It should be recalled that the tube-sheet 11 may consist of a single metallurgy where the technique according to the known art can be applied, but there are heat exchangers in which the tube-sheet consists of different materials. In this latter case, the tube-sheet is usually made of different thicknesses of two dissimilar materials, that is made of two materials which are different for technical and also commercial reasons. The first material, usually of lower quality but such as to withstand most of the mechanical stress, faces the distributor head and is wetted by the less aggressive fluid, side 11A; and the second material applied on the first (the coating is obtained by addition of material, weld overlay cladding, explosion welding, or some other technique) corresponding in general to the material of the heat-exchanger tubes, has a higher quality than the previous material, and is such as to enable connection with the tubes, faces the shell and the tubes themselves, being wetted by the more aggressive and dangerous fluid, side 11B.

[0011] The aim of the present invention is to provide a plug for sealing tubes of shell and tube heat exchangers that will overcome the drawbacks of the known art.

[0012] A further aim is to provide a plug for positioning a gasket in a specific pre-defined plane in the thickness of the tube-sheet and within a tube of a heat exchanger or of a hole in the tube-sheet.

[0013] Another aim is to provide a plug that will be simple to produce. A further aim is to provide a plug that will be simple to apply.

[0014] Yet another aim is to provide a plug that will enable fast application.

[0015] According to the present invention, the above aims and still others are achieved by a plug for sealing tubes of shell and tube heat exchangers according to claim 1.

[0016] The above aims and still others are besides achieved by a shell and tube heat exchanger according to claim 6.

[0017] Further characteristics of the invention are described in the dependent claims.

[0018] The plug according to the present invention enables, in particular, positioning of a gasket in a specific pre-defined plane within a tube of a heat exchanger or within a hole of the tube-sheet, at a pre-set distance from the surface of access to the tube-sheet, i.e., from the distributor head side.

[0019] The plug hence enables positioning of a gasket in the portion of the tube-sheet wetted by the shell-side fluid (side 11B) that is made of a high-quality material as compared to the lower-quality material of the part of tube-sheet wetted by the tube-side fluid (side 11A) by entering the distributor head, i.e., from the hole present in the portion of lower-quality material of the tube-sheet.

[0020] The characteristics and advantages of the present invention will emerge clearly from the ensuing detailed description of a practical embodiment thereof, illustrated by way of non-limiting example in the annexed drawings, wherein: Figure 1 shows a shell and tube heat exchanger according to the known art; Figure 2 shows a plug for sealing tubes of shell and tube heat exchangers, in sectional view and in an insertion position in a tube of a heat exchanger or a hole of a tube-sheet, according to the present invention with the gasket resting in place and ready for final positioning; Figure 3 shows a plug, in sectional view and in a working position in a tube of a heat exchanger or a hole of a tube-sheet, according to the present invention, with the gasket properly positioned; Figure 4 shows a rod or tie rod and a corresponding sectional view, of a plug for sealing tubes of shell and tube heat exchangers according to the present invention; Figure 5 shows the sectional view of a spacer and cross-sectional views thereof of a plug for sealing tubes of shell and tube heat exchangers, according to the present invention; Figure 6 shows a constraint or bushing of a plug for sealing tubes of shell and tube heat exchangers according to the present invention, in side sectional view and in axial sectional view; Figure 7 shows a nut for drawing back the tie rod of a plug for sealing tubes of shell and tube heat exchangers according to the present invention, in side view and in front view; Figure 8 shows a gasket of a plug for sealing tubes of shell and tube heat exchangers according to the present invention, in lateral side view and in front view; Figure 9 shows a shim of a plug for sealing tubes of shell and tube heat exchangers, in side sectional view and in front view.

[0021] In the ensuing description, it is to be assumed that there is a loss of integrity or leakage along a tube 9 of the tube-bundle 2 located within the shell, which is wetted on the outside by the fluid 14 and on the inside by the fluid 13, is connected to a tube-sheet 11, on the shell side, and is to be plugged with a plug 12.

[0022] The tube-sheet 11 in design and integrity conditions keeps a first tube-side fluid 13 (which flows inside the tube 9, inside the hole of the tube-sheet and inside the distributor head) separate, on the left in Figures 2 and 3, from a second shell-side fluid 14 (which flows only on the outside of the tube 9), on the right in Figures 2 and 3.

[0023] The tube-sheet 11 (having a thickness of tens of centimetres) is made of a first portion 15, which has a first thickness, manufactured of a first material of not particularly high quality, for example carbon steel, which is set on the side of the distributor head 8 on the left in the figures, and is in contact only with the (less aggressive) fluid 13 via the surface 11A, and of a second portion 16, which has a second thickness, manufactured of a second material of higher quality than the previous one, for example a chromium alloy, is set on the side of the shell where the tubes are present, on the right in the figures, and is in contact with the (more aggressive) fluid 14 via the surface 11B.

[0024] Normally, the thickness of the first portion 15 is greater than the thickness of the second portion 16.

[0025] Normally, the fluid 13 of the tube-side circuit has a pressure lower than that of the fluid 14 of the shell-side circuit and is less aggressive from the chemical-physical standpoint than the fluid 14.

[0026] The shell and tube heat exchanger can be installed either horizontally or vertically and the plug 12 may be used in both installations, for plugging both ends of the faulty tube.

[0027] With reference to the attached figures, a plug 12 for sealing tubes 9 of shell and tube heat exchangers according to the present invention comprises a spacer 20 having a tubular shape, which has the function of positioner and has dimensions such as to guarantee insertion into the hole 10 present in the tube-sheet 11 with extremely strict machining tolerances and requiring only limited interventions on the tube-sheet itself.

[0028] The cross section, length and other geometrical parameters of the spacer 20 depend on the internal diameter of the pre-existing hole 10 in the tube-sheet 11, used in the production stage for connection of the tube-bundle to the tube-sheet on the shell side, and on the thicknesses of the portions 15 and 16 which tube-sheet 11 is made of.

[0029] The spacer 20 has at the right-hand end (towards the shell side) a head portion 21, which has its end surface machined to form a seat for a gasket and is internally tapered to engage the tapered section 34 of the rod 30.

[0030] The plug 12 comprises a rod 30 (or tie rod) formed by a cylindrical rod designed to be inserted in the spacer 20.

[0031] At one end, i.e., the one on the distributor-head side, on the left in the figures, the rod has a threaded portion 31, which, preferably, terminates with a head portion 32 designed to be fastened / held in position by a purposely provided blocking tool.

[0032] At the other end, i.e., the one on the shell side (on the right in the figures), the rod 30 has a head portion 33 having a diameter larger than the diameter of the central part of the rod 30.

[0033] The transition of diameter between the diameter of the central part of the rod 30 and the head 33 is obtained by a tapering 34.

[0034] The cross section and the length of the rod 30 depend upon the dimensions of the spacer 20.

[0035] The plug 12 comprises a constraint (or bushing) 40 consisting of a bushing having a first external diameter 41 and a second external diameter 42 and a through-hole 43.

[0036] The first diameter 41 is larger than the second diameter 42 and, as represented in the figures, the first diameter 41 is located on the left of the second diameter 42; i.e., it projects further into the volume of the distributor head. The right-hand side of the bushing, having an external diameter 42, will come into direct contact with the non-machined end of the spacer (on its left) or else shims 52 will be inserted therebetween.

[0037] The plug 12 further comprises a nut 50 (or other means for drawing back the tie rod 30) and a gasket 51.

[0038] The gasket 51 is a self-energized gasket with an usually silvered surface, capable of guaranteeing the seal between the rod and the hole in the design conditions of the heat exchanger, and in any case its metallurgy must be such as to withstand contact with the aggressive fluids in operating conditions. Via the positioning of the rod and the pressure of the fluid, the gasket must moreover prevent local conditions of marked corrosion that might culminate in a leakage.

[0039] In practice, the gasket 51 is constituted by a toroidal spring usually wrapped in a silver or equivalent metallurgy sheet. The sheet of coating is selected for its resistance to aggressive fluids, its malleability, and its deformability, and has a thickness comprised between 0.2 and 1 mm. The purpose is to guarantee a good seal.

[0040] This gasket 51, properly sized and shaped, does not undergo compression in its own equatorial plane, as in the case of normal gaskets or packing seals made of metal or other materials, but is gently pushed into position by the relative movement between the rod 30 and the spacer 20. The properly tapered shape 34 of the non-threaded end 33 of the rod 30 and the properly machined shape of the corresponding end portion 21 of the spacer, in the case of relative motion (approach of the tapered part 34 to the end portion 21 of the spacer) lead the gasket 51 to position itself in the cylindrical terminal section 33 of the rod itself. The aforesaid self-energized gasket 51 hence increases its original diameter passing from the smaller diameter of the rod 30 to the larger final diameter of the head 33. In this movement of expansion, the diameter of the gasket 51 is calculated in the design stage so as to obtain the required tightness when the gasket reaches the operating position.

[0041] The gasket 51 constitutes, with the top circular surface of the head 33, a sealing surface made of a material adequate for the shell-side process fluid 14, which has penetrated into the tube 9 due to the loss of integrity of the latter, as initially assumed. This sealing surface is in turn located within the section 16 of the tube-sheet with metallurgy different from the other section 15. In this way, any possible leakage of corrosive fluid 14 that from the shell penetrates into the defective or broken tube 9 comes into contact only with surfaces that have a metallurgy suitable for the shell-side process fluid 14, so that it cannot penetrate into the hole section of the tube-sheet 11 reaching the portion 15 made of lower-quality material, thus preventing corrosion and / or mixing with the tube-side fluid 13 and triggering unforeseeable chemical-physical reactions.

[0042] The relative movement between the rod 30 and the spacer 20 is ensured by the threaded end 31 of the rod, by the constraint 40, and by the nut 50. After welding 53 of the constraint 40 to the section 15 of the tube-sheet 11 made of lower-quality material, rotation of the rod thereof is prevented by blocking the terminal section 32 and simultaneously the nut 50 is turned. By doing so, the rod 30 tends to come out of the hole towards the fluid 13, approaching / compressing the spacer 20.

[0043] In Figure 2, the plug is assembled and inserted, while in Figure 3 the plug is in operating condition. It may be noted the different position of the rod with respect to the spacer (in Figure 3 the rod is more shifted towards the left than it is in Figure 2) and the weld 53 between the constraint 40 and the tube-sheet 11.

[0044] The pressure due to the shell-side fluid 14 prevalently acts on the head 33 of the rod and on the exposed surface of the gasket. In either case, the thrusts via direct contact are discharged on the spacer 20 and therefrom on the constraint 40. Said constraint 40 is welded to the inlet part of the hole of the tube-sheet 11 (on the side 11A), and the weld 53 is calculated in such a way as to mechanically withstand the thrust of the pressure of the shell-side fluid. As an alternative to the welding seam 53 of the constraint 40, it is possible to foresee other means of constraint, such as screwing.

[0045] In the case where it is asked to monitor possible leakages of the plug to intervene by shutting down the equipment and carrying out replacement, the possibility is envisaged of bringing the leakages of shell-side fluid 14 out of the hole of the tube-sheet 11 directly towards / into the tube-side fluid 13, where they may be detected by sensors (not illustrated).

[0046] The rod 30 may be provided with one or more grooves X throughout its cylindrical length, excluding the tapered section in order not to dent the seat where the gasket works, such as to convey a possible leakage between the internal diameter of the gasket and the head of the rod in the gap between the internal diameter of the spacer and the rod and therefrom outwards into the area where the fluid 13 is present.

[0047] Also the spacer 20 may be provided with one or more grooves X throughout its entire length located on the internal diameter of the spacer and facing the rod 30 but also with one or more external grooves Y throughout its entire length. One or more grooves Y are located also on the constraint 40, thus completing the hydraulic circuit that enables exit of the leaking fluid between the hole of the tube-sheet and the external diameter of the gasket towards the area where the fluid 13 is present, exploiting the gap between the external diameter of the spacer and the internal diameter of the hole of the tube-sheet.

[0048] It is also possible to connect the circuit X with the circuit Y via through-holes on the spacer highlighted in the section C-C of Figure 5 in order to increase circulation of the fluid that wets the room between the hole and the spacer and between the spacer and the rod.

[0049] Operation of the plug according to the invention appears evident for the person skilled in the art from what has been described and, in particular, in what follows.

[0050] The plug is prepared with the gasket not loaded; i.e., all the pieces are already assembled but not tightened; in other words, the gasket 51 is inserted on the rod 30 until it reaches the root of the tapering 34, and the rod 30, together with the gasket 51, is inserted in the spacer 20, at the same time causing the thread 31 to pass into the hole 43 of the constraint 40.

[0051] The above assembly is screwed manually and without tightening via the nut 50 located on the thread 31 of the rod 30 and after the constraint 40 on the side of its larger diameter 41.

[0052] It is necessary to make sure, by analysing the as-built drawings and via measurement carried out on the exchanger, that the insertion of the plug with the gasket not loaded enables the gasket to be brought to the right depth of insertion into the hole of the tube-sheet, i.e., to be located in the correct area 16 of the tube plate, that is in a specific plane set at a pre-set distance from the plane of insertion of the plug 12 of the tube-sheet 11.

[0053] The plug 12 thus assembled is inserted in the hole 10 by operating from the distributor head 8, i.e., from the side where there is the fluid 13; access and insertion hence takes place from the surface 11A.

[0054] In case where the plane of positioning of the gasket 51 is within the first portion 15 of tube-sheet (made of lower-quality material), i.e., out of the plane where the gasket is to be positioned, before tightening, it is possible to insert the shims 52 between the shim spacer 20 and the constraint 40.

[0055] Instead, in case where the sealing seat of the gasket ends up beyond the correct area 16 and hence directly in a portion of tube 9 located in the shell, it is necessary to properly reduce the length of the spacer 20.

[0056] After this first step of seeking and obtaining the right depth of insertion, the constraint 40 is welded or fixed in a stable way to the tube-sheet from the side made of the lower-quality material 15 (side 11A).

[0057] The rod 30 is held in position via a blocking wrench on the end 32, and the nut 50 is tightened on the threaded part 31 of the rod 30. The rod 30 will move from right to left, and the gasket 51 will climb up the tapering 34 until it reaches the head portion 33 that coincides with the head of the plug.

[0058] The torque exerted during tightening creates the relative axial motion between the rod and the spacer and the sliding of the tapers causes the gasket 51 to draw towards the section with larger diameter of the rod, expand, albeit maintaining its toroidal shape, and fit the properly machined and shaped seat provided on the hollowed surface of the head 21. Figure 3 exemplifies the condition of service.

[0059] The dimensions, and in particular the diameters of the various elements constituting the plug 12, must be chosen in such a way that a hermetic seal of the plug 12 on the hole 10 will be obtained.

[0060] The dimensions, and in particular the lengths of the rod 30 and of the spacer 20, must be geometrically such that the sealing line of the gasket 51 on the hole of the tube-sheet is in a plane of the section 16 made of high-quality material (wetted by the shell-side fluid) of the tube-sheet itself. Adjustments on the sealing line may be made in both directions, by means of the shims 52 or by cutting the spacer 20.

[0061] Between the nut 50 and the constraint 40 it is possible to carry out a further welding in order to ensure that there will be no movement of the rod during operation.

[0062] In an alternative embodiment, the constraint 40 and the nut 50 may be constituted by a single appropriately shaped and machined piece.

[0063] The materials used, as well as the dimensions, may be any according to the needs and to the state of the art. In addition, they will have to be chemically, mechanically, and thermally compatible with the fluids that wet them.

[0064] For instance, in an embodiment of the invention in a heat exchanger having water and steam as tube-side fluid and having aggressive fluid as shell-side fluid, the material of the spacer 20 is a chromium alloy, the material of the rod 30 is a chromium alloy, the material of the gasket 51 is a chromium alloy with surface deposition of high-quality material, the material of the constraint 40 is a chromium alloy, and the material of the nut 50 is a chromium alloy.

[0065] The plug thus devised may undergo numerous modifications and variations, all of which fall within the scope of the inventive idea as set up in the appended claims.

Claims

1. A plug for sealing tubes of shell and tube heat exchangers, said plug (12) comprises: a tie rod (30); a spacer (20) of said tie rod (30); a gasket (51) set between said tie rod (30) and said spacer (20); said tie rod (30) comprises at a first end (32) thereof a threaded portion (31); the plug further comprising means (50) for drawing back said tie rod (30) and a constraint (40) to be set between said spacer (20) and said means (50); said tie rod (30) comprises a second tapered end (33) thereof that has a diameter larger than the diameter of said tie rod (30); characterized in that said spacer (20) comprises at the right-hand end a head portion (21), which has its end surface machined to form a seat for said gasket (51) and is internally tapered to engage a tapered section (34) of said tie rod (30).

2. The plug according to claim 1, characterized in that said gasket (51) is a self-energized gasket with silvered or metallurgically equivalent surface.

3. The plug according to claim 1, characterized in that said spacer (20) has a tubular shape and said tie rod (30) comprises a rod formed by a cylindrical rod designed to be inserted in said spacer (20).

4. The plug according to claim 1, characterized in that said threaded portion (31) terminates with a head (32) designed to be tightened by a purposely provided blocking tool.

5. The plug according to claim 1, characterized in that said means (50) for drawing back said tie rod (30) comprise a nut (50) that co-operates with said threaded portion (31).

6. A shell and tube heat exchanger having a plug for sealing tubes of shell and tube heat exchangers according to any one of the preceding claims, where said tubes (9) are connected to holes (10) set in a tube-sheet (11) of said shell and tube heat exchanger; said plug (12) being set in at least two of said holes (10) of said tube-sheet (11), said gasket (51) being positioned in said tube-sheet (11), in a specific plane set at a pre-set distance from the surface of said tube-sheet (11).

7. The shell and tube heat exchanger according to claim 6, characterized in that said tube-sheet (11) is formed by a first portion (15) made of a first material and by a second portion (16) made of a second material; said gasket (51) being set in said second portion (16).

8. The shell and tube heat exchanger according to claim 6, characterized by said constraint (40) is constrained to said tube-sheet (11).

9. The shell and tube heat exchanger according to claim 7, characterized in that said first portion (15) is in contact with a first fluid (13) and said second portion (16) is in contact with a second fluid (14); said gasket (51) constitutes a sealing surface made of a material adequate for said second fluid (14).

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