GB2113598A

GB2113598A - Heat exchanger maintenance

Info

Publication number: GB2113598A
Application number: GB08137768A
Authority: GB
Inventors: John Forrest; Alan Mcarthur; Douglas Thomas Craig
Original assignee: OMEGA SOFTWARE
Current assignee: OMEGA SOFTWARE
Priority date: 1981-12-15
Filing date: 1981-12-15
Publication date: 1983-08-10
Also published as: GB2113598B

Abstract

A method of separating a tube bundle from a heat exchanger casting or shell consists of employing a first withdrawing apparatus to effect initial separation or 'breakout', and a separate second withdrawing apparatus to effect completion of separation. The first withdrawing apparatus constitutes a heavy duty puller and is designed using a thrust ring and part-circular tube plate engaging elements for even distribution of breakout forces to minimise risk of damage to parts of the heat exchanger. The second withdrawing apparatus constitutes a lighter structure incorporating a step-by-step extractor for pulling the tube bundle out and on to cradling elements. Withdrawal by the method is therefore accomplished in two stages, the first by a relatively high force over a short distance, the second by a relatively low force over a long distance. <IMAGE>

Description

SPECIFICATION Heat exchanger maintenance THIS INVENTION relates to a method of and to apparatus for use in separating a tube bundle from an buter casing or shell of a heat exchanger.

In this specification, the term "heat exchanger" is intended to include heaters, coolers and condensers. The term "tube bundle" means the assembly of tubes together with tube plates with which the tube ends are firmly engaged, and usually diaphragm plates which are disposed mutually spaced along the length of the tube bundle to provide support for the tubes intermediate their ends, for example against vibration.

In the maintenance or servicing of heat exchangers, it is required occasionally to separate the tube bundle from the outer casing or shell to expose normally inaccessable surfaces for cleaning, descaling etc. This separation usually can be achieved only by shifting the tube bundle axially from the shell and by shifting the tube bundle axially from the shell and the operation may involve difficulties arising from the extreme force required to effect the shifting against the bonding effect of corrosion and/or deposits on mutually engaged metal parts. One of the more serious of said difficulties is that previously proposed screw-jacking techniques applied at points around a tube plate/shell flange connection tend to effect permanent distortion of the tube plate which may on later reassembly cause leakage problems.Another of said difficulties is that such techniques have proved to be unduly time consuming.

An object of the present invention is to provide a method and aparatus by means of which at least one of the aforesaid difficulties is obviated or mitigated.

According to one aspect of the present invention, there is provided a method of separating a tube bundle from an outer casing or shell of a heat exchanger, in which a first withdrawing apparatus is used to shift the tube bundle initially with respect to the shell, and a second withdrawing apparatus is used to complete shifting of the tube bundle to separate same from the shell, the first withdrawing apparatus being adapted to be capable of shifting the tube bundle by a relatively short distance and with a relatively high force, and the second withdrawing apparatus being adapted to be capable of shifting the tube bundle by a relatively long distance and with a relatively low force.

We have found that the force required to shift the tube bundle with respect to the shell after an initial or "breakout" shift has been achieved is significantly less than the force required to effect the initial shift. Whereas in previously proposed methods for separating a tube bundle from a shell the same screwjacking appliances are used both for initial and for subsequent shifts, in the method of the present invention different withdrawing apparatuses are used respectively for initial shifting and subsequent shifting. The first withdrawing apparatus is required to exert high force over a short distance; the second withdrawing apparatus is required to exert a lower force over a greater distance.The first and second withdrawing apparatuses are, according to the present invention, adapted appropriately each to their respective functions and thereby an improved efficiency of the separating operation is achieved.

According to a second aspect of the present invention, there is provided a first withdrawing apparatus for use in shifting a tube bundle with respect to an outer casing or shell of a heat exchanger, comprising a carrier of generally elongate stiff construction intended to be disposed transversely of a heat exchanger adjacent an end thereof, the carrier having a location for an actuator for exerting a pull force, and a pair of thrust arms mounted on the carrier and extending normally therefrom, each of said thrust arms being position-adjustable on the carrier along respective portions thereof on opposite sides of the actuator location.

Preferably, there is provided a thrust ring adapted for location on the heat exchanger shell around an end thereof, and the thrust ring and the free end of said thrust arms are adapted for mutual locating engagement.

Preferably, there is provided a coupling means for constituting part of a connection between said actuator and a tube bundle, comprising a central boss, a plurality of arms each having one end connected to the boss, and arm positioning means operable to engage the arms adjacent their ends and to hold the arms in a divergent configuration for facilitating connection of the free ends of the arms to the tube bundle.

Preferably, there is provided, for use in the case where a tube bundle comprises a circular tube plate having a radially outwardly presented circumferential groove or recess, a two-piece clamp assembly for constituting a second part of a connection between said actuator and a tube bundle, said clamp assembly comprising a pair of part-circular elements for engaging said groove or recess over at least 50% of the length thereof.

Preferably, the second withdrawing apparatus comprises a frame of generally elongate construction intended to rest on a floor or ground surface, cradling elements on the frame top side for receiving and cradling a tube bundle in the course of and upon completion of its separation from an outer casing or shell of a heat exchanger, the frame being adapted to one end portion to locate the said outer casing or shell, a guideway extending on the frame top side lengthwise thereof, a carriage shiftable along the guideway, locking means for locking the carriage on the guideway at different stations therealong, and an actuator on the carriage for exerting a pull force, the arrangement being operable on a cycle comprising locking of the carriage with the actuator extended, retraction of the actuator to pull a tube bundle, unlocking of the carriage, extension of the actuator to shift the carriage on the guideway, and so on.

Preferably, there is provided a second locking means associated with the retractable mewmber of the actuator for locking said retractable member to the frame at different stations along the guideway to hold a tube bundle while the first mentioned carriage is unlocked.

Preferably, the said thrust ring is adapted for locating engagement with the frame at said one end portion.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic representation in plan view, partly in cross section, showing a first withdrawing apparatus in accordance with the present invention; Figure 2 is a sectional elevation on the line ll-ll in Fig. 1, to a larger scale than Fig. 1; Figure 3 is a front elevation of part of a two-piece clamp assembly; Figure 4 is a cross section on the line IV-IV in Fig. 3; Figure 5 is a diagrammatic representation in end view of a frame having cradling elements and a guideway; and Figure 6 is a diagrammatic representation in side elevation illustrating a stage in the operation of second withdrawing apparatus in accordance with the present invention.

In Figs. 1 and 6 of the drawings, a heat exchanger outer casing or shell is indicated generally by reference numeral 10; and a tube bundle comprises a tube plate 11 and a plurality of heat exchange tubes which are represented in chain-dotted outline by reference numeral 1 2. In use of the heat exchanger, the tube plate 11 is sealed to the adjacent face of a flange 1 3 which is part of the shell 10, there being a manifold (not shown) bolted to the flange 1 3 for conducting fluid through the tubes of the heat exchanger.

The apparatus and technique described below is used in the maintenance or servicing of the heat exchanger after removal of the said manifold.

In Figs. 1 and 2, a first withdrawing appa ratus consists of a carrier 14, an actuator 15, and a pair of thrust arms 1 6. The carrier 14 is of generally elongate stiff construction of two steel beams 1 7 which are mutually located by means of end plates 1 8 and flange plates 1 9.

The top or upper of the beams 1 7 is provided with lifting lugs 20 to facilitate manipulation of the apparatus with the aid of a crane (not shown). The actuator 1 5 is a stroke hydraulic ram the piston of which carries a screwthreaded spindle 15A. The actuator 1 5 is located in position between the beams 1 7 with the aid of the flange plates 1 9 and fastening means (not shown). A heavy flange member 21 of the actuator 15 distributes pull force to the beams 1 7 when the apparatus is used as explained hereinafter.The thrust arms 1 6 are disposed normal to the longitudinal axis of the carrier 14 and each arm 1 6 is position-adjustable along the respective portion of the carrier. Thus each beam 1 7 has welded to its inner face longitudinal slideways 22 each of rectangular cross section. The upper and lower side of each thrust arm 1 6 is provided with a recessed slider 23 which engages a respective one of the slide ways 22 to enable each arm 1 6 to be shifted longitudinally of the carrier 14.To assist such adjustment of the arms 16, each arm is provided with a screw threaded lug 24 which engages a rotatable and longitudinally extending screwed rod 25 the inner end of which is journalled within the structure of the carrier 14 and the outer end of which projects through its associated end plate 18 and is thereat provided with a drive-end. Rotation of either rod 25 effects adjustment of the position of the associated arm 16. The free ends of the arms 1 6 are provided with locating pins 26.

Coupling means for connecting the spindle 15A with the tube plate 11 may be regarded as being in two distinct parts as follows. The first part of such coupling means consists of a central boss 27, a plurality of pull-arms 28, and arm positioning means 29. The central boss 27 is in screw threaded engagement with the spindle 15A. In Fig. 1, only two pullarms 28 are shown in the interests of clarity, but six such arms are proposed. The boss 27 is provided with six pairs of lugs 30 which provide a means of pivotal connection of the inner ends of the arms 28 to the boss 27.

The outer ends of the arms 28 are pivotally connected to a second part of the connecting means as described hereinbelow. The arm positioning means 29 consists of a circular plate having a bevelled face 31. The circular plate is centrally screw threaded and thus shiftable along the spindle 15A. Manual adjustment of the positioning means is assisted by means of spokes 32. The inner end por tions of the pull-arms 28 are shaped for engagement with the bevelled face 31, and also are provided with projections 33 for abutment with the boss 27 when the arms 28 have been brought to a divergent configuration consistent with connection of the arms with the second part of the coupling means.

The second part of the coupling means is shown diagrammatically in Fig. 1 and consists of a two-piece clamp assembly 34. A realisation of the clamp assembly 34 is illustrated in Figs. 3 and 4 which show one half of such assembly, the other half being of identical construction. Each half of the clamp assembly consists of a part circular element 35 having a cross section of returned configuration machined for close-fitting engagement with a radially outwardly present recess 36 in the tube plate 11. The element 35 has welded thereto a web plate 37 which carries a pair of bolting lugs 38 to enable the elements 35 to be clamped in place on the tube plate 11 by means of bolts 39. The clamp assembly 34 incorporates lug plates 40 adapted for pivotal connection with the outer end of the pull-arms 28.The part-circular elements 35 distribute pull force evenly to the tube plate 11 in that they extend for well over 50% of the circumferential length of the recess 36.

Figs. 5 and 6 illustrate different aspects of a second withdrawing apparatus. In Fig. 5, a frame 41 carries on its top side cradling elements indicated generally by reference numeral 42 and consisting of wood packing blocks 43 which are interposed between the plurality of tubes 1 2 and a series of cradling rollers 44 disposed at regular intervals along the length of the frame 41. In the interests of clarity, the cradling elements are omitted from Fig. 6. A guideway 45 is shown in Fig. 5; and also longitudinally-extending catwalk components 46.

In Fig. 6, a carriage 47 is shiftable on the guideway 45 by means of a series of rollers 48 incorporated in the carriage 47. The carriage carries a hydraulic actuator 49 having its cylinder pivotally connected to the carriage 47 at 50. The piston of the actuator 49 is connected to the clamp assembly 34 by means of a spider 51 fitted in place of the pull arms 28. The carriage 47 incorporates a locking means 52 for locking the carriage on the guideway 45 at different stations therealong. The locking means 52 consists of pneumatic piston 53 connected to a locking pin 54. The piston 53 can be raised against a return spring 55 by means of compressed air introduced at 56 to withdraw the locking pin 54 and allow the carriage 47 to move.

In Figs. 1 and 6, a thrust ring 57 is fitted around the heat exchanger flange 1 3. The thrust ring 57 is in two parts which may be bolted together by means of bolts and boltflanges (not shown). The thrust ring carries a pair of thrust lugs 58 each of which is recessed to receive one of the locating pins 26 on the thrust arms 1 6. Also the thrust ring 57 is provided with a third single thrust lug 59 which, in Fig. 6, is accommodated between a pair of transverse members 60 of the frame 41 in order to locate the thrust ring 57 with reference to the frame 41 in the longitudinal direction.

The manner of operation of the apparatus described above is as follows. The first withdrawing apparatus of Fig. 1 is used to effect initial shifting of the tube bundle with reference to the shell 10. The thrust ring 57 is fitted to the heat exchanger flange 1 3. At this stage, the heat exchanger is preferably aligned with the frame 41 and the locating lug 59 located between the transverse thrust members 60 of the frame 41. Next, the clamp assembly 34 is fitted to the tube plate 11.

Thereafter, with the aid of a crane, the carrier 14 and its associated components are brought into position and the thrust arms 1 6 are adjusted so that the locating pins 26 locate in the complementary recesses in the lugs 58. In preparing the carrier 14 and its associated components, the first part of the connecting means will be disposed generally retracted, but with the pull-arms 28 in a divergent configuration by means of the positioning means 29. When the carrier 14 and the thrust arms 1 6 are in position, the first part of the connecting means is manipulated to bring the outer end of the pull-arms 28 into position with the lugs 40 so that pivot pins may be inserted to connect the pull-arms to the clamp assembly 34.The positioning means 29 is then retracted along the spindle 15A. Pretensioning of the entire assembly may be achieved by appropriate rotation of the spindle 1 5A manually. Thereafter, the actuator 1 5 may be operated to exert a high pull-force to "break out" or effect initial shifting of the tube bundle with respect to the heat exchanger shell.

When the initial shifting described above has been achieved, the carrier 14 and its associated components are removed leaving the clamp assembly 34 in position. Thereafter, the spider 51 is fitted to the clamp assembly 34 and the carriage 47 is moved to the forward end (the left hand end in Fig. 6) of the guideway and the piston of the ram 49 is connected to the spider 51. The ram 49 may then be adjusted to place the carriage 47 at a locking station on the guideway 45 and the locking means 52 operated to extend the locking pin 54. With the carriage 47 locked in position, the ram 49 is operated to further withdraw the tube bundle.When a withdrawing increment has been achieved, the locking means 52 is operated to retract the locking pin 54 and the ram 49 is extended to shift the carriage 47 rearwardly to the next locking station whereat the cycle of withdrawing increment is repeated and so on until the tube bundle is completely separated from the heat exchanger casing. In the course of withdrawing the tube bundle, the wood blocks 43 are inserted so that the bundle is cradled by the rollers 44.

When the tube bundle has been separated from the shell 10, the latter may be removed from the frame 41 together with the carriage 47 and its associated components. Lifting lugs (not shown) on the frame 41 may be used to lift the frame together with the tube bundle in transporting the latter to a work place for further treatment.

It is to be appreciated that Fig. 6 is a diagramatic representation. In practice, the arrangement will preferably be such that the actuator 49 is horizontal. This may be achieved by the carriage 47 incorporating a height-adjustable feature so that the pivot 50 can lie approximately co-incident with the tube bundle centre-line. Thus, the tube bundle will be pulled without undesirable lateral forces.

In a modification of the Fig. 6 arrangement, a second carriage is interposed on the guideway 45 between the first carriage and the heat exchanger, the second carriage being connected to the piston of the actuator 49 at the same height as the pivot 50. A link is provided between the second carriage and the spider 51, the link being height-adjustable on the second carriage to co-incide with the tube bundle centre-line. The second carriage is provided with a (second) locking means operable to hold the second carriage and hence the tube bundle while the first carriage is unlocked. Thus, any risk of a tube bundle shifting unexpectedly or out of control is reduced.

Claims

1. A method of separating a tube bundle from an outer casing or shell of a heat exchanger, in which a first withdrawing apparatus is used to shift the tube bundle initially with respect to the shell, and a second withdrawing apparatus is used to complete shifting of the tube bundle to separate same from the shell, the first withdrawing apparatus being adapted to be capable of shifting the tube bundle by a relatively short distance and with a relatively high force, and the second withdrawing apparatus being adapted to be capable of shifting the tube bundle by a relatively long distance and with a relatively low force.

2. A first withdrawing apparatus for use in shifting a tube bundle with respect to an outer casing or shell of a heat exchanger, comprising a carrier of generally elongate stiff construction intended to be disposed transversely of a heat exchanger adjacent an end thereof, the carrier having a location for an actuator for exerting a pull force, and a pair of thrust arms mounted on the carrier and extending normally therefrom, each of said thrust arms being position-adjustable on the carrier along respective portions thereof on opposite sides of the actuator location.

3. A first withdrawing apparatus according to claim 2, wherein there is provided a thrust ring adapted for location on a heat exchanger shell around an end thereof, and the thrust ring and the free end of said thrust arms are adapted for mutual locating engagement.

4. A first withdrawing apparatus according to claims 2 or 3, wherein there is provided a coupling means for constituting part of a connection between said actuator and a tube bundle, comprising a central boss, a plurality of arms each having one end connected to the boss, and arm positioning means operable to engage the arms adjacent their ends and to hold the arms in a divergent configuration for facilitating connection of the free ends of the arms to the tube bundle.

5. A first withdrawing apparatus according to any one of claims 2 to 4, wherein there is provided, for use in the case where a tube bundle comprises a circular tube plate having a radially outwardly presented circumferential groove or recess, a two-piece clamp assembly for constituting a second part of a connection between said actuator and a tube bundle, said clamp assembly comprising a pair of partcircular elements for engaging said groove or recess over at least 50% of the length thereof.

6. In combination with a first withdrawing apparatus according to any one of claims 2 to 5, a second withdrawing apparatus comprising a frame of generally elongate construction intended to rest on a floor or ground surface, cradling elements on the frame top side for receiving and cradling a tube bundle in the course of and upon completion of its separation from an outer casing or shell of a heat exchanger, the frame being adapted to one end portion to locate the said outer casing or shell, a guideway extending on the frame top side lengthwise thereof, a carriage shiftable along the guideway, locking means for locking the carriage on the guideway at different stations therealong, and an actuator on the carriage for exerting a pull force, the arrangement being operable on a cycle comprising locking of the carriage with the actuator extended, retraction of the actuator to pull a tube bundle, unlocking of the carriage, extension of the actuator to shift the carriage on the guideway, and so on.

7. A combination according to claim 6, wherein there is provided a second locking means associated with the retractable member of the actuator for locking said retractable member to the frame at different stations along the guideway to hold a tube bundle while the first mentioned carriage is unlocked.

8. A combination according to claim 6 or 7 when dependent from claim 3, wherein the said thrust ring is adapted for locating en gagement with the frame at said one end portion.

9. A method of separating a tube bundle from an outer casing or shell of a heat exchanger, substantially as hereinbefore de scribed with reference to the accompanying drawings.

10. A first withdrawing apparatus for use in shifting a tube bundle with respect to an outer casing or shell of a heat exchanger, substantially as herein before described with reference to and as shown in Figs. 1 to 4 of the accompanying drawings.

11. In combination, a first withdrawing apparatus according to claim 10, and a second withdrawing apparatus substantially as hereinbefore described with reference to and as shown in Figs. 5 and 6 of the accompanying drawings.

1 2. Any novel features or novel combination of features disclosed herein.