GB2265962A

GB2265962A - Tube plug

Info

Publication number: GB2265962A
Application number: GB9307559A
Authority: GB
Inventors: David Bland Pierce
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-04-09
Filing date: 1993-04-13
Publication date: 1993-10-13
Anticipated expiration: 2013-04-13
Also published as: GB9307559D0; GB2265962B

Abstract

A tube plug for fitting into the bore of a heat exchanger or condenser tube comprises a deformable sleeve-like locking member 20, a tapered member 30 engagable with the sleeve, and a spindle 10 having a threaded part 14, the sleeve carrying a nut 22 engagable with the threaded part of the spindle, whereby rotation of the spindle moves the sleeve axially relative to the tapered member. The bore is plugged by inserting the tube plug into the bore and rotating the spindle to produce relative movement of the locking member and tapered member to deform part of the locking member into locking engagement with the bore. <IMAGE>

Description

TUBE PLUG AND TUBE PLUGGING METHOD FIELD OF THE INVENTION This invention relates to a tube plug and tube plugging method, and in particular to a plug for fitting into the bore of a heat exchanger or condenser tube and its method of fitting.

BACKGROUND TO THE INVENTION Heat exchangers are widely used, for instance in the power supply and chemical industries, and for marine applications such as for marine engines. A plurality of tubes (typically linear but perhaps curved e.g. U-shaped) are fitted between headers to carry heat exchanger fluid. These tubes may on occasion have to withstand internal pressures of 150 kg/sq cm.

If one or more tubes develops a leak, perhaps because of local thinning of the tube wall during manufacture, damage during assembly or corrosion during use, then each such tube has to be plugged so that it can be isolated until the heat exchanger can be taken out of service and the defective tube(s) replaced.

DESCRIPTION OF THE PRIOR ART One known method for isolating an individual tube in a header assembly is to insert a plug into each end of the leaking tube. It has for instance been common practice to force a frusto-conical plug into position; the force necessary for effective securement can however damage the tube end, and the respective header plate. Furthermore if a plug is not securely held, or works loose under vibration, then the plug can be ejected from the end of a tube at high speed.

In GB 1,518,425 there is disclosed a plug comprising a deformable sleeve circumferentially continuous at its ends; tapered members engage opposite ends of the sleeve, and when these tapered members are drawn together each end of the sleeve is deformed into circumferential engagement with the interior of the tube bore.Disadvantages of this plug are (a) the operative spindle has a threaded end which in use projects from the tube; this projecting end can be damaged in use and can also interfere with a header gasket or the header itself; (b) once fitted, it is difficult to remove from the tube, so that the tube may be discarded rather than repaired; (c) an operative spindle used to draw the tapered members together cannot be removed independently of one of the tapered members to allow subsequent removal of that tapered member; (d) the operative spindle is hollow and cross-bored, to allow the injection of sealant between the sleeve ends; and (e) the cross-bores may not coincide with apertures in the sleeve, so that for this or other reasons the sealing may be ineffective or insufficient.

In an alternative to that of the preceding paragraph and disclosed in GB 1,563,762 from the same applicant, the plug is of a hard material which can bite into the tube, so itself providing a seal. Furthermore only the sleeve-end furthest into the bore need be so formed. This plug has the disadvantages (a), (b) and (c) above, but also needs a complicated shape of sleeve relatively difficult and expensive to produce.

DISCLOSURE OF THE INVENTION We now propose an improved plug wherein the sleeve carries a nut, and wherein the spindle has a threaded portion engageable with the nut, so that rotation of the spindle can move the sleeve axially relative to the spindle. Because the nut is carried by the sleeve it will be internal of the heat exchanger tube in use, so that the need for a portion of the plug to project from the tube is avoided.

In our preferred embodiment our plug utilises a locking sleeve with outwardly deformable locking fingers, the tube engaging end of the sleeve thus being discontinuous. Separate pressure sealing means are provided, with the further feature that the sealing pressure is increased with increased outward finger-deforming force.

The sleeve fingers are positioned so that during insertion of the plug the fingers, if they inadvertently engage the tube interior wall, do not sprag but rather are deformed radially inwards; thus for locking engagement with the tube wall the fingers are drawn towards the tube end into which the plug was inserted.

Upon rotation of the spindle, the locking sleeve is drawn onto an annular tapered member loosely mounted about the spindle whereby to effect outward deformation of the fingers. Resilient "O"-rings are mounted around the spindle, axially compressible into sealing engagement with the tube wall.

For more powerful locking, more than one sleeve and annular tapered member can be mounted on the spindle.

Even if the locking sleeve becomes rigidly coupled to the tube wall, at least the spindle and its "O"-rings and tapered member can be removed, usually without need to resort to the application of a controlled pressure applied to the opposite tube end. Thereafter the locking sleeve can be released from the tube, or in extreme cases left in situ, since it is annular and the working fluid can still flow therethrough.

Thus, according to one feature of the invention we provide a tube plug which includes a deformable sleeve and a tapered member engagable with the sleeve characterised in that the sleeve carries a nut engagable with a threaded spindle, whereby rotation of the spindle moves the sleeve axially relative to the tapered member. Preferably the deformable sleeve is circumferentially discontinuous, to form axially extending fingers. Usefully, the fingers are arranged to extend towards the open end of the bore, when fitted into a tube, to lock the plug against removal from the bore with a sprag action.

According to a further feature of the invention we provide a tube plug which includes a deformable sleeve to fit inside a bore to be plugged, and a tapered member interfitting with the sleeve to expand the sleeve against the bore to lock the plug against movement relative to the bore characterised in that the sleeve has outwardly deformable locking fingers, the tube engaging end of the sleeve thus being discontinuous.

Usefully there are a plurality of annular sealing members mounted on the spindle, so that those sealing members outward of (i.e. nearest the adjacent "insertion" tube end) the first sealing member will become operative, should the first (inward) sealing member be ineffective i.e. if damaged by particulate matter within the bore. Preferably there is a resilient member provided, which can also be the outermost sealing member, to help suspend and centralise the plug within the bore.

According to another feature of the invention we provide a method of plugging a bore characterised by the steps of inserting into the bore a tapered member and a deformable sleeve engagable by the tapered member, the sleeve carrying a nut, and producing relative movement of the sleeve and tapered member to urge the sleeve into locking engagement with the bore. Further, said relative movement effects squeezing of deformable, preferably resilient, members into sealing contact with the bore.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which: Fig.1 is a side-section view of a plug according to the invention; and Fig.2 is a side-section view of another embodiment of plug fitted in a tube.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Plug 2 comprises spindle 10, annular locking sleeve or member 20, externally tapered annular member 30, "0"-rings 40a-c, annular spacers 50a-b, and annular tube abutment 60 generally of top-hat shape.

Spindle 10 has a head 12 of larger diameter at one end, and has threads 14 at the other (inwards) end 13. The head is recessed at 16 to receive rotatable drive means such as an "Allen" key. In an alternative embodiment the spindle can be threaded along its full length. The head 12 has a planar engagement surface 18 in face to face contact with the surface 65 of the tube abutment 60.

Locking member 20 has a first portion 21 carrying a nut 22, and a second frusto-conical portion 23 slotted as at 24 to form deformable fingers 25. In this embodiment there are four equi-sized fingers, and each finger terminates at sharp edge 26. Nut 22 has internal threads sized to mate with the threads 14 on spindle 10, so that rotation of spindle 10 in one angular direction causes locking member to move to the left (as viewed in Fig.1) relative to spindle 10.

Externally tapered member 30 has a cylindrical portion 32 integral with a frusto-conical tapered portion 34. The tapered portion 34 is arranged to mate with the fingers 25, and to force them outwardly as the locking member is moved to the left. Opposed to the tapered portion 34 is a planar face 36, providing an abutment face.

Primary "O"-ring 40a is trapped between planar face 36 and spacer 50a. Secondary "O"-ring 40b is trapped between spacers 50a and Sob. Secondary "O"-ring 40c is trapped between spacer 50b and tube abutment 60. The spacers can be of the same size, or not, as desired. In alternative embodiments more or fewer spacers and "O"-rings may be used.

Tube abutment 60 has a body portion 62 carrying at the left hand (outer) end an external abutment flange 64; the body portion 62 is recessed to receive the head 12 in engagement with face 65. Flange 64 typically has a thickness of lmm, to correspond to the thickness of the header gasket (not shown) of the heat exchanger, the tube of which is to be plugged by tube plug 2. Thus in use neither the flange 64 nor the head 12 will stand proud of the gasket.

The body portion 62, the spacers 50 and the cylindrical portion 32 in this embodiment are of the same external diameter, selected to be 8% less than the internal diameter of the tube to be plugged. Thus for a typical heat exchanger tube the outside diameter of the body portion, spacers and cylindrical portion will be 0.5mm less than the tube internal dimension.

Fig.2 shows a tube plug 102 fitted into a tube 70.

Typically for a heat exchanger, the end 72 of the tube 70 will be expanded to provide a sealing contact with the header plate 74. In this embodiment, the tube abutment 160 does not have a flange external to the tube, but rather is of a diameter larger than the general internal diameter of the tube 70, but of a size to fit within the expanded end 72 of the tube. Thus, the insertion of the tube plug 102 is limited by the abutment 160.

This tube plug 102 also has enlarged "O"-rings, of a size to engage, when in the compressed condition of Fig.2, both the bore of the tube 70 and the spindle 10. Thus, the "O"-rings 140 prevent fluid escape between the spacers 50 and the spindle 10 as well as between the tube plug and the bore.

When tube 70 requires to be sealed, the plug 2,102 is inserted in the tube and spindle 10 is rotated to draw the parts to the left, to squeeze the "O"-rings 40,140 into sealing engagement with the internal tube wall, whilst sharp edge 26 is squeezed into locking engagement with the inner tube wall. Thus the locking position is inward of the tube compared to the sealing position.

In normal use, only primary "O"-ring 40a,140a is needed to effect sealing against the bore. However, to provide additional security against this "O"-ring being damaged by abrasives or reactants in the tube fluids, the additional back-up "O"-rings 40b, 40c, 140b, 140c are usefully provided. "O"-ring 140c is larger than "O"-rings 140a,140b and can also act to centralise the plug in the tube 70 prior to tightening.

For the tube plug 2 of Fig.1, where the "O"-rings prevent only "outwards" fluid flow along the bore i.e a radially "outer" flow path between the plug and inner bore surface, if necessary a further seal (preferably an annular washer, not shown), is provided between surfaces 18,65.

If required, a longer spindle can be used, arranged to mount more than one nut 22 and thus a respective locking member 20, whereby to provide a greater locking force e.g.

from two or three sets of fingers 25, each set being axially spaced from the other(s). As with the provision of multiple "O"-rings, such a facility could also be useful for sealing tubes likely to be internally corroded and thus of questionable retention ability.

When the tube has been removed for repair, the plug can be removed by unscrewing the spindle head 12 to reduce the outward deformation force on fingers 25, thereafter pulling spindle head 12 to the left. If however the fingers 25 will not release, the spindle can be unscrewed wholly out of nut 22, leaving the locking member 20 in place (temporarily) whilst the remainder of the plug is removed on and with the spindle. Since the locking member 20 is annular and located only a short distance into the tube it can usually then easily be released from engagement with the tube and removed, but in extreme circumstances could be left in situ for the tube fluid to flow therethrough.

Heat exchangers traditionally have a large number of tubes, e.g. two hundred, closely spaced and extending between two tube plates or headers. Two plugs according to the invention can be used to plug opposite ends of any number of these tubes. Furthermore since only axial access is required for a tightening tool to recess 16, there is minimal if any damage to neighbouring tubes or header plates; this is of particular advantage for those tubes to be plugged which are positioned adjacent either the header plate centre line or the header plate outer periphery.

We have thus provided a plug with (a) a lock section, expandable radially outwards when drawn towards a frusto-conical surface, into locking engagement with the inner surface of the tube; (b} an externally tapered member which compresses the seal(s) and thus the end spacer of a spacer/seal sub-assembly, so that the seals (resilient "O"-rings) are expanded radially outwards into tube engagement; and (c) an abutment member to limit the insertion of the plug into the tube whilst avoiding the plug standing proud.

The plug materials are selected to match those of the heat exchanger tube (to prevent electrolytic corrosion) and are typically naval brass, stainless steel, or mild steel.

However, I do not exclude the use of a suitable plastics material, such as nylon, for any part of the tube plug, such as the locking member for example. Typically, the "O"-rings will be made of natural or synthetic rubber.

Advantages of the disclosed arrangement are {a} that a leaking tube can be quickly plugged; (b) that the plugs are relatively cheap to make and to assemble, and compact to store; (c) that at least the internals of a plug can be removed e.g. if an incorrect (non-leaking) tube has been plugged, or for reworking of the tube after removal; (d) that the "lock" is inwards of the tube, so that the tube plate is not damaged upon fitting (which would require the plug to remain permanently fitted); (e) one or more of the "O" rings can be sized to seal in use also against the spindle whereby to restrain fluid flow both along the bore and along the spindle; and (f) the resilient sealing rings when sized to engage the spindle can hold the spindle against rotation (and possible unscrewing and release), under the vibration conditions commonly found in heat exchangers.

Although the embodiments described relate to tube blocking to prevent access into and out of the tube end, alternatively or additionally it is possible to seal an access pipe or channel-way leading into a tube end or bore.

Furthermore, although the locking member need not be of a material of a hardness selected to bite into the bore material, the use of such materials e.g. stainless steel, is not excluded, particularly if the internal bore conditions are corrosive to intended softer materials.

Although we prefer to use a sleeve with a sharp edge or terminal ridge to ensure firm gripping even if the tube wall is corroded or carries deposits, this is not essential.

Preferably the tube sealing is effected by sealing means (usefully deformable "O"-rings) separate from the locking means for the plug in the tube, but we foresee that a deformable locking means could provide part of the tube sealing requirement (or perhaps full tube sealing, especially for low-duty i.e. low pressure tubes).

Claims

1. A tube plug comprising a deformable sleeve, a tapered member engagable with the sleeve, and a spindle, the spindle having a threaded part, in which the sleeve carries a nut engagable with the threaded part of the spindle, whereby rotation of the spindle moves the sleeve axially relative to the tapered member.

2. A tube plug according to Claim 1 in which the sleeve includes at least one finger.

3. A tube plug according to Claim 1 or Claim 2 in which the spindle has an enlarged head, and in that the head is recessed to receive a rotatable drive means.

4. A tube plug according to any of Claims 1-3 in which the tube plug also carries pressure sealing means.

5. A tube plug according to Claim 4 in which the tapered member has a tapered portion and a cylindrical portion, in which the cylindrical portion terminates in an abutment face, and in which the abutment face engages part of the pressure sealing means.

6. A tube plug according to Claim 4 or Claim 5 in which the pressure sealing means is at least one resilient "0" -ring.

7. A tube plug for a tube, the tube having an end, a bore and an internal surface, the internal surface surrounding the bore, the tube plug being located adjacent the said end, the tube plug comprising a deformable sleeve, a tapered member engagable with the sleeve, and a spindle, the spindle having a threaded part, in which the sleeve carries a nut engagable with the threaded part of the spindle, whereby rotation of the spindle moves the sleeve axially relative to the tapered member.

8. A tube plug according to Claim 7 having an abutment flange, the flange having a diameter larger than the diameter of the bore, the flange having a thickness of lmm.

9. A tube plug according to Claim 7 having an abutment portion within the end of the tube, the abutment portion engaging a part of the said internal surface.

10. A tube plug according to either of Claims 8 or 9 in which the tube plug carries a resilient member to suspend and centralise the plug within the bore.

11. A tube having at least one tube plug according to any preceding claim.

12. A heat exchanger having a tube plug according to any of Claims 7-11.

13. A heat exchanger having at least one tube according to Claim 11.

14. A method of plugging a tube, the tube having a bore, comprising the steps of (a) inserting into the bore a tube plug comprising a deformable sleeve, a tapered member engagable with the sleeve, and a spindle, the spindle having a threaded part, the sleeve carrying a nut engagable with the threaded part of the spindle; and (b) producing relative movement of the sleeve and tapered member to deform part of the sleeve into locking engagement with the bore.

15. A method according to Claim 14 in which concurrent with said relative movement of the sleeve and tapered member, a pressure sealing means is moved into sealing contact with the bore.

16. A tube plug constructed and arranged substantially as described with reference to Fig.l or Fig.2.

17. A tube fitted with a tube plug constructed and arranged substantially as described with reference to Fig. 1 or Fig.2.

18. A method of plugging a tube substantially as described with reference to Fig. 1 or Fig.2.