GB2218177A

GB2218177A - Plug for heat exchanger tubes

Info

Publication number: GB2218177A
Application number: GB8810761A
Authority: GB
Inventors: Norman Epstein
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-05-06
Filing date: 1988-05-06
Publication date: 1989-11-08
Also published as: FR2631434A1; GB8810761D0; AU1610388A; DE3826597A1

Description

-1 PLUG FOR HEAT EXCHANGER TUBES 2r r 5 11'' 18 17 7 The present invention

relates to heat exchange equipment and, more particularly, to tube plugs for plugging tubes in heat exchange equipment.

Boilers and other heat exchange equipment used in the power generation and chemical industries require a plug to seal tubes, pipes and similar conduits against the passage of steam, liquid or gasses under pressure. Such a plug should preferably offer ease of installation, relatively low cost, and the ability to maintain a seal against leakage of steam, water or other gasses or fluids, over an extended period of time, with a high degree of reliability. Such tubes conventionally have thin walls in order to maximise heat transfer. Such thin walls require special care to prevent a tube plug from cutting into the tube wall, or otherwise weakening the tube and thus enabling tube failure under pressure.

The present invention is defined in the appended claims and provides a tube plug for a heat exchanger tube employing a housing having a conical bore with a blind threaded cylindrical bore communicating therewith. An insert member includes a threaded shank fittable into the blind threaded bore and a conical section with external threads. An eccentric assembly at the forward end of the housing helps lock the housing against rotation as the insert member is threaded thereinto. The threads on the conical section contact, and expand, the conical bore until an external surface of the housing is'expanded into sealing contact with the surface of the conical bore. The shape of the threads controls the local pressure exerted on the conical surface. A piggy-back version of the tube plug employs an eccentric assembly for locking a leading tube plug in a tube and a second tube plug includes a socket in its front end engageable with a nut portion on the leading tube plug. As the second tube plug is expanded into frictional contact with the inside 2 of the tube, this frictional contact adds to the torque resisting action of the eccentric assembly and the frictional contact of the leading tube plug to permit more torque to be applied to the second tube plug without damaging the tube. Additional tube plugs, identical to thd second tube plug, may be chained together as necessary.

According to a particular embodiment of the invention, there is provided a tube plug for plugging a heat exchanger tube comprising: a tubular body fittable into the tube, an eccentric assembly at a forward end of the tubular body, the eccentric assembly including a ring member eccentrically affixed to rotate with respect to the tubular body, first knurling on a peripheral surface of the ring member, second knurling on a peripheral surface of the tubular body at least adjacent the forward end, an insert member, the insert member and the tubular body including first cooperating means for threaded engagement therebetween, the insert member and the tubular body further having second cooperating means for expanding a surface of the tubular body into sealing frictional contact with an inner surface of the tube, and the first knurling engaging the inner surface and urging _the second kurnling into engagement with the inner surface whereby rotation of the tubular body is resisted for enabling tightening the ^insert member into the tubular body.

According to a feature of the invention, there is provided a tube plug for plugging a heat exchanger tube comprising: a tubular body fittable into the tube, an insert member, the insert member and the tubular body including first cooperating means for threaded engagement therebetween, the insert member and the tubular body further including second cooperating means for expanding a surface of the tubular body into sealing frictional contact with an inner surface of the tube, means for resisting rotation of the tubular body whereby torque may 1 41 3 c' 1 be applied to the insert member for employing the first cooperating means and the second cooperating means is enabled to expand the surface of the tubular body into the sealing contact, and the second cooperating means including a conical inner surface in the tubular member and a conical outer surface on the insert member, the conical outer surface being drawn into engagement with the conical inner surface by the threaded engagement.

According to a further feature of the invention, there is provided a tube plug for plugging a heat exchanger tube comprising: a tubular body fittable into the tube, means for resisting rotation of the tubular body, an insert member, the insert member and the tubular body including first cooperating means for threaded engagement therebetween, the insert member including a conical outer surface thereon, the tubular body having a conical inner surface engageable with the conical outer surface, a plurality of parallel circular grooves in an external surface of the tubular body enclosing the conical inner surface, and the plurality of circular grooves having depths effective to make sections from the conical inner surface to bottoms thereof substantially equal.

According to a still further feature of the invention, there is provided a tube plug for plugging a heat exchanger tube comprising: a tubular body fittable into the tube, an insert member, the insert member and the tubular body including first cooperating means for threaded- engagement therebetween, the insert member and the tubular body further including second cooperating means for expanding a surface of the tubular body into sealing frictional contact with an inner surfac-e of the tube, means for resisting rotation of the tubular body whereby torque may be applied to the insert member for employing the first cooperating means and the second cooperating means is enabled to expand the surface of the tubular body into the sealing contact, and the means for 4- resisting rotation including a socket in a forward end of the tubular member engageable by engagement means for resisting the rotation.

According to a. still fu rther feature of the invention, there is provided a piggy-back tube plug for plugging a heat exchanger tube comprising: a first tubular body fittable into the tube,- an eccentric assembly at a forward end of the tubular body, the eccentric assembly including a ring member eccentrically affixed to rotate with _re.spect to the tubular body, knurling on a peripheral surface of the ring member engageable with an inner surface of the tube for resisting rotation of the first tubular body, a first insert member, the first insert member and the first tubular body including first cooperating means for threaded engagement therebetween, the first insert member and first the tubular body further having second cooperating means for expanding a surface of the tubular body into sealing frictional contact with an inner surface of the tube, a first engagement portion at an end of the insert member engageable by a tool for applying torque to the insert member, a second tubular body fittable into the tube, an eccentric assembly at a forward end of the tubular body, the eccentric assembly i-ncluding a ring member eccentrically affixed tp rotate with respect to the tubular body, knurling on a peripheral surface of the ring member engageable with an inner surface of the tube for resisting rotation of the second tubular body, a second insert member, the second insert melaber and the second tubular body including third cooperating means for threaded engagement therebetween, the second insert member and second the tubular body further having fourth cooperating means for expanding a surface of the second tubular body into sealing frictional contact with an inner surface of the tube, a second engagement portion on the second tubular body engageable with the first engagement portion on the first insert, and a third engagement portion on the second insert engageable by a tool for applying torque to the second insert.

Thus the present invention provides a tube plug which can be quickly and easily installed in the end of a tube, usually within a heat exchanger tube sheet, to provide an effective leakproof seal, which is capable of withstanding operational pressures. The seal is effective for both liquids and gasses.

The tube plug does not weaken the tube during or after installation and comprises a relatively small number of simple component parts resulting in a relatively low manufacturing cost.

The invention also provides a piggy-back tube plug system wherein a leading plug at least partly plugs the tube and provides torque for further tightening a second plug following it'into the tube.

Tube plugs for heat exchanger in accordance with the present invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a disassembled view of a heat exchanger tube plug according' to one embodiment of the invention, with a portion shown in cross-section, Figure 2 is an exterior side view of the housing of Figure 1, Figure 3 is a cross section taken along III-III in Figure 2, Figure 4 is a cross section of the tube plug of Figure 1 shown assembled and inserted into the end of a boiler tube prior to tightening thereof, Figure 5 is a cross-sectional view similar to Figure 4 shown expanded into sealing engagement with an internal surface of the boiler tube, Figure 6 is a side view of a piggy-back tube plug according to a further embodiment of the invention, and 6 Figure 7 is a cross section taken along VII-VII in Figure 6.

Referring to Figure 1, there is shown, generally at 10, a boiler tube plug including a hollow housing member 12 and an insert member 14. Housing member 12 ine-ludes a cylindrical body 16 having a bore 18 therein. Bore 18 includes a conical inner surface 21. A relatively smaller, internal ly-threaded blind cylindrical bore 28 communicates with the large bore 18.

An eccentric assembly 32 at a front end 30 of the housing member 12 assists in locking the housing member 12 against rotation within a boiler tube (not shown in Figure 1). Eccentric assembly 32 includes a cylindrical post 34 projecting from the front end 30 and a ring member 36 mounted eccentrically on post 34 and rotatable thereon. Post 34 is preferably integrally formed with the remainder of housing 12. A bore 40 in the ring member 36 is disposed eccentrically to a cylindrical surface 46 thereof. A front 42 of the ring member 36 includes-a chamfered portion 44.

A bore 62 in an end 60 of the post 34 defines a relatively thin wall 64. An end portion 66 of the wall 64 is flared outwardly into the space pro vided by the chamfered portion 44, thereby retaining the ring member 36 on the post_ 34 while leaving it free to rotate upon the post 34.

Insert member 14 has a conical portion 68 with threads 69 on its outer surface. The angle of the conical portion 68 is substantially equal to the angle of conical inner surface 21 of the bore 18 in the housing 12. The pitch of the threads 69 is axially constant. That is, a measurement of thread spacing taken parallel to an axis of the insert member 14 is constant along the length of conical portion 68. A threaded shank 72 at an inner end 70 of the insert member 14 is sized to be received in the threaded blind cylindrical bore 28. An outer end 74 of the insert member 14 includes a -1 cylindrical portion 76 and a centrally disposed, integrally formed nut portion 78. Nut portion 78 is proportioned so that it may be grasped by a wrench for the screwing insert member 14 into the housing member 12. It will be appreciated that instead of a projecting nut portion 78, a hexagonal recess may be formed in the end of cylindrical portion 76 for insertion-of a hex wrench or similar tool. Both the insert member 14 and the housing member 12 are integrally formed. Insert member 14, housing member 12, andring member 36 are preferably made of steel.

Referring now to Figure 2, the ring member 36 includes knurling 79 on ring member 36. In addition, a knurled portion 80 is disposed on a portion of the cylindrical body 16 adjacent the front end 30. A series of circular grooves 82, 84, 86 and 88 are disposed in the surface of an end portion 22.

Referring now also to Figure 3, it will be noted that the circular grooves 82, 84, 86 and 88 have depths increasing progressively from the outer end of the bore 18. A dashed line 90, -tangential to the bottoms of the circular grooves 82, 84, 86 and 88, is seen to be substantially parallel to the conical inner surface 21 of the bore 18. This leaves a constant thickness of fflaterial between the conical inner surface 21.and the bottoms of the circular grooves 82, 84, 86 and 88.

Referring now to Figure 4, a threaded shank 72 of insert member 14 is turned finger tight into the blind cylindrical bore 28 until stopped conical portion 68 and conical Eccentric ring member 36 is rotated body 16 of housing member 12. The plug 10 is inserted into an end 92 tube 24. Although not necessary to by contact between inner surface 21. into alignment with heat exchanger tube of a heat exchanger the practice of the invention, boiler tube plug 10 is frequently aligned at a position where an outside of the boiler tube 24 is supported by a tube sheet 94.

8 Nut portion 78 is turned with a wrench. Initially, the housing 12 tends to rotate with insert member 14. A boiler tube 24 that has been in service long enough to require plugging almost always contains a buildup of scale and other debris (not shown) on its internal surfaces. Knurling 79 on the ring member 36 (Figure 2) engages such scale or debris sufficiently to rotate ring member 36 eccentrically toward a locking position which produces a reaction displacing the front end 30 in the opposite direction in boiler tube 24. This displacement engages knurled portion 80 on cylindrical body 16 (Figure 2) with the interior surface of the boiler tube 24, thereby stopping rotation of the housing 12.

Referring now also to Figure 5, nut portion 78 is turned by a wrench (not shown) whereby the threaded shank 7 12 is advanced into the threaded blind cylindrical -bore 28. Threads 69 on the conical portion 68 engage the conical inner surface 21 of the large bore 18. As the increasing diameter of the conical portion 68 enters the large bore 18, its expanding contact with the conical inner surface 21 deforms a surrounding wall 20 of the housing member 12 outwardly, increasing its outer diameter into sealing contact with an inne r surface 95 of boiler tube 24. Once substantial contact is attained between the end portion 22 of the wall 20 and inner surface 95, the torque retarding rotation of housing 12, provided by the eccentric assembly 32 and knurled portion 80, is augmented by friction between the end portion 22 and the inner surface 95. - This permits the application of more installation torque to insert member 14 than can be resisted by the eccentric assembly 32. Circular grooves 82, 84, 86 and 88 (Figures 2 and 3), provide weak spots- in the cylindrical body 16 making the expansion easier. The increasing depths of these grooves, in providing generally equal thicknesses between their bottoms and the adjacent surface of conical inner surface 21, standardises the strengths of the weak spots for h, 9 improved performance. As soon as the end portion 22 is expanded into contact with the inner surface 95, friction between them aids in resisting torque applied to the insert member 14.

The illustrated positioning of the heat exchanger tube plug 10 within the boiler tube 24, at a position where the boiler tube 24 is supported by the tube sheet 94, offers the additional benefit of expanding an external surface of the boiler tube 24 into sealing contact with the tube sheet 94, thereby sealing leaks existing between the boiler tube 24 and the tube sheet 94.

Boiler tube plug 10 may achieve a satisfactory seal with the threads 69 omitted from the conical portion 68.

However, several advantages have been discovered arising from including the threads 69 on the conical portion 68.

One significant advantage is the localisation of force between the threads 69 and the conical inner surface 21, thus aiding in the expansion of the end portion 22. As is well known, for a given total force, the exerted pressure is inversely proportional to the area of contact. To illustrate, if the contact area between the threads 69 and the conical inner surface 21 is about 20 percent of the facing areas of the threads 69 and conical inner surface 21, the outward pressure, in pounds per square inch, or other units, exerted locally at lines of contact between the tips of the threads 69 and the conical inner surface 21 is quintupled, compared to a pressure which would be produced by contact between corresponding smooth surfaces. I have further discovered that the local pressure can be tailored by shaping the contour of the threads 69. For example, if the threads 69 are made with flat tops, a greater contact area between such flat tops and the conical inner surface 21 reduces the local pressure exerted. Also, pressure tailoring can be applied systematically along the length of threads 69. That is, the sharpness of the tips of threads 69 may increase from one end of the conical portion 68 to the other. It may be useful, for example, to shape portions of the. conical portion 68 nearer the small end of the conical portion 68 with sharper tips than those providLd nearer the large end to enhance expansion in that region as the insert member 14 is drawn into the housing 12.

A still further advantage is attained from the threads 69. As previously noted, the pitch of the threads 69 is constant parallel to the axis of the insert member 14. Thus, one rotation of the insert member 14 produces a linear thread travel which varies with the position along the conical portion 68. That is, measuring the linear length of the threads 69 passing a point at the narrow end of the conical portion 68 yields a substantially smaller length than that measured at the wide end of the conical portion 68. This change in linear thread travel tends to work the material of the end portion 22 during the tightening process and significantly improves the resulting seal.

In one embodiment of the invention, the pitch of the threads on the threaded shank 72 and blind cylindrical bore 28 is equal to the pitch of the threads 69 taken parallel to the axis of insert member 14. In a further embodiment the pitch on the threaded shank 72 may differ slightly from that of the threads 69. This difference tends to wipe the threads 69 in an axial direction during tightening for producing a more secure plug.

As previously noted, tube plugging is usually performed after a heat exchanger has been in service for an extended period. By the time_plugging is indicated, erosion, corrosion and thermal stress may have thinned and weakened the boiler tube 24 so badly that attempting to tighten a boiler tube plug 10 in place may cause tube failure, particularly in the vicinity of the eccentric assembly 32 and knurled portion 80 (Figure 2). It thus may be impossible to attain sufficient resistance to 4 1 rotation of the housing 12 to produce a satisfactory seal. In the prior art, two, three, or more tube plugs are inserted into the tube in an attempt to attain a seal with at least one of them.

Referring now to Figure 6, a piggy-back tube plug system 96 is shown for overcoming the above problem. Piggy-back tube plug system 96 includes a boiler tube plug 10 as described in the foregoing. In addition, a backup boiler tube plug 10' includes a socket-front hoilsing 98, together with an insert member 14 substantially the same as that forming part of boiler tube plug 10. Socket-front housing 98 dispenses with eccentric assembly 32, knurling 79 and knurled portion 80. Instead, a forward end 100 of socket-front housing 98 includes a socket 102 (see also Figure 7) fittable over nut portion 78.

Piggy-back ttibe plug system 96 is installed by first installing the boiler tube plug 10 in the manner described in the preceding until it is as tight as allowed by the condition of the tube. Then a boiler tube plug 10', including an insert member 14 finger tight in the socket-front housing 98, is inserted into boiler tube 24 until a socket-102 seats over the nut portion 78. Installation torque is then applied to the insert member 14 of boiler tube plug 10' for expanding the end portion 22 against the boiler tube 24. During the early part of such installation, both the engagement of the boiler tube 24 by the knurled portion 80 on the cylindrical body 16, and the frictional torque provided by the - expansion of the end portion 22 into sealing contact with the boiler tube 24, is effective to resist rotation of the socketfront housing 98. Then, as the end portion 22' of the socket-front housing 98 is expanded into frictional sealing contact with the boiler tube 24, this additional friction is added to that already existing for resisting rotation of the socket-front housing 98. In this manner, a total torque may be applied to the insert member 14 of 12 the boiler tube plug 10' which exceeds that which boiler tube 24 is capable of withstanding from either the boiler tube plug 10 or the boiler tube plug 10' alone.

The above described piggy-backing may be continued as desired to attain the required seal. One or more additional socket-front housings 98'' with their associated insert members may be daisy chained as indicated in dashed line.

A boiler tube plug 10', including the socket-front housing 98, may be employed in some installations without requiring a boiler tube plug 10. In such an installation, a wrench (not shown) may be inserted through the length of the boiler tube Z4 for engagement with the socket 102, thereby to resist rotation of socket-front housing 98 while the insert member 14 is rotated into socket-front housing 98. A further boiler tube plug 10' may be installed after the first boiler tube plug 10' to improve the final seal.

Instead of using a socket 102 engaging a nut portion, a- square, hexagonal, or other shaped opening (not shown) may be made in the end of the insert 14 and socket-front housing 98 may be modified to provide a mating protrusion (not shown) extending therefrom for engaging the opening.

-1 r 91

Claims

Claims 1. A tube plug for plugging a heat exchanger tube comprising: a

tubular body fittable into said he-at exchanger tube; an eccentric assembly at a forward end of the tubular body; the eccentric assembly including a ring member eccentrically affixed to rotate with respect to the tubular body; first knurling on a peripheral surface of the ring member; second knurling on a peripheral surface of the tubular body at least adjacent the forward end; an insert member; the insert member and the tubular body including first cooperating means for threaded engagement therebetween; the insert member and the tubular body further including second cooperating means for expanding a surface of the tubular body into sealing frictional contact with an inner surface of the heat exchanger tube; and the first knurling being engageable with said inner -surface for urging the second knurling into engagement with said inner surface, whereby rotation of the tubular body is resisted to enable tightening of the insert member in said tubular body.
2. A tube plug according to claim 1, wherein the first cooperating means includes a blind threaded cylindrical hole in the tubular body and a threaded shank on the insert member engageable in the blind threaded cylindrical hole and effective for drawing at least a portion of the insert member into the tubular body.
3. A tube plug according to claim 2, wherein the second cooperating means includes a hole having a conical inne r surface in the tubular body communicating with the blind 14 threaded cylindrica 1 hole, a conical portion on the insert member being engageable with the conical inner surface for expansion thereof.
4. A tube plug according to claim 3, wherein said conical inner surface and said conical portion make substantially equal angles with respect to an axis thereof.
5. A tube plug according to claim 3 or 4, wherein said conical portion includes threads thereon, these threads being engageable with said conical inner surface.
6. A tube plug according to claim 5, wherein said threads have a uniform pitch along a line parallel to an axis thereof.
7. A tube plug for plugging a heat exchanger tube comprising; a tubular body fittable into the heat exchanger- tube; an insert member; the insert member and the tubular body including first cooperating means for threaded engagement therebetween; the insert member including second and the tubular body further cooperating means for expanding a.surface of the tubular body into sealing frictional contact with an inner surface of the heat exchanger tube; means for resisting rotation of the tubular body, whereby torque may be applied to the insert member for employing the first cooperating means, and the second cooperating means is enabled to expand said surface of the tubular body into said sealing frictional contact; and the second cooperating means includes a conical inner surface in the tubular member and a conical outer surface on the insert member, the conical outer surface being drawn into engagement with the conical inner surface by said threaded engagement.

Q
8. A tube plug according to claim 7, wherein the first cooperating means includes a blind threaded cylindrical hole in said tubular body and a threaded shank on the insert member engageable in the blind threaded cylindric al hole and effective for drawing at least a portion of the conical outer surface into forceful contact with the conical inner surface.
9. A. tube - plug according to claim 8, wherein the conical inner surface and the conical outer surface make substantially equal angles with respect to an axis there of.
10. A tube plug according to any of claims 7 to 9, wherein the conical outer surface includes threads there on, these threads being engageable with the conical inner surface.
11. A tube plug according to claim 10, wherein:

the first cooperating means includes a first pitch; the threads on the conical outer surface have a second pitch parallel to an axis of the tube plug; the- first and second pitches are substantially equal. -
12. A tube plug according to claim 10, wherein:

the first cooperating means includes a first pitch; the threads on the conical outer surface have a second pitch parallel to an axis of the tube plug; and the first and second pitches are substantially different.
13. A tube plug according to claim 10, wherein the threads have a uniform pitch along a line parallel to an axis thereof.
14. A tube plug for plugging a heat exchanger tube comprising:

a tubular body fittable into the heat exchanger tube; means for resisting rotation of the tubular body; an insert member; 16 the insert member and the tubular body including first cooperating means for threaded engagement therebetween; the insert member thereon; including a conical outer surface the tubular body having a conical inner surface engageable with the conical outer surface; a plurality of parallel circular grooves in an external surface of the tubular body enclosing the conical inner surface; and the plurality of parallel circular grooves having depths effective to make sections from the conical inner surface to bottoms thereof substantially equal.
15. A tube plug for plugging a heat exchanger tube comprising: a tubular body fittable into the heat exchanger tube; an insert member; the insert member and the tubular body including first cooperating means for threaded engagement therebetween; the insert member and the tubular body further including second cooperating means for expanding a surface of the tubular body into sealing frictional contact with an inner surface of the heat exchanger tube; means for resisting rotation of the tubular body, whereby torque may be applied to the insert member for employing the first cooperating means, and the second cooperating means is enabled to expand the surface of the tubular body into the sealing frictional contact; and the means for resisting rotation include a socket in a forward end of the tubular member engageable by engagement means for resisting said rotation.
16. A piggy-back tube plug for plugging a heat exchanger tube comprising: a first tubular body fittable into the heat exchanger tube; v, -X z 17 an eccentric tubular body; the eccentric assembly including a ring member eccentrically affixed to rotate with respect to the first tubular body; knurling on a peripheral surface of the ring member engageable with an inner surface of the heat exchanger tube for resisting rotation of the first tubular body; a first insert member; the first insert member and the first tubular body including first cooperating means for threaded engagement therebetween; the first insert member and the first tubular body further having second cooperating means for expanding a surface of the tubular body into sealing frictional contact with an inner surface of the heat exchanger tube; a f irst engagement portion at an end of the first insert member engageable for applying torque to the first insert member; a second tubular body fittable into the heat exchanger tube; a second engagement portion at an end of the second tubular body engageable with the first engagement portion for applying torque to the first engagement portion; a second insert member; the second insert member and the second tubular body including third cooperating means for threaded engagement therebetween; the second insert member and the second tubular- body further having fourth cooperating means for expanding a surface of the second tubular body into sealing frictional contact with an inner surface of the heat exchanger tube; and a third engagement portion on the second insert engageable by a tool for applying torque to the second insert member.

assembly at a forward end of the Published 1989 atThe Patent Office, State House, 6671 High Holt orn. L0ndonWCIR4TP. Further copies maybe obtained from The Patent Office. Sales Branch, St Mary Cray, Orpington. Kent BR5 3RD Printed by Multiplex techniques ltd, St Mary Cray. Kent. Con. 1/87