METHOD FOR THE NON-DESTRUCTIVE REMOVAL OF TUBES FROM HEAT EXCHANGERS AND TOOL USEFUL TO THAT PURPOSE

Abstract: Method for then non-destructive removal of tubes or of portions of tubes from heat exchangers, comprising: a) the lengthwise cutting along at least one generatrix of one tube or of a plurality of tubes of said exchanger, to a depth at least ecual to the thickness of the tube plate and to a width of up to 2% of the outer perimeter of the tubes; b) the approaching to each other of the edges of the so-­ obtained cut section up to the complete release of the tube, or of the tubes, from the tube plate; c) the possible crossways cutting of the tube, or of the tubes, to a height at least equal to the double of the thickness of the tube plate; and d) the recovery of the tube, or of the tubes, by sliding it/­ them out of the same plate.

Description: The invention relates to a method for the non-destructive removal of tubes from heat exchangers according to the pre-characterising portion of claim 1 and to a tool according to the pre-characterising portion of claim 2. The pre-characterising portion of Claim 1 is based on the disclosure of the document US-A-2834106. A tool of the type defined in the pre-characterising portion of Claim 2 is known from e.g. US-A-2000824. US-A-3,729,806 discloses a method and an apparatus for relieving the hoop stresses securing a tube in a tube sheet to allow a removal of the tube therefrom, the hoop stresses being relieved by removing material from the tube to form two axial slots having a radial depth less than the tube wall thickness and depressing the portion of the tube between the slots to break the portion loose from the remainder of the tube to relieve the hoop stresses therein. US-A-2,834,106 discloses an apparatus for splitting tubes for removing tubes from tube sheets by cutting the tubes longitudinally, collapsing the tube within the tube sheet and thereafter punching or pulling the tube out of its position. The cutter assembly comprises a shank provided with a cutter which is held in its radial position by set screws inserted in the shank. The shank is secured to a cylindrical support by a connecting stud, and the free end of the support can be connected to a pneumatic hammer or other suitable device. A purpose of the present invention is providing a method for the removal of tubes, or of tube portions, from heat exchangers, which does not require the destruction of the tube length comprised inside the tube plate. A further purpose of the present invention is providing a tool for carrying out the non-destructive removal of tubes, or of tube portions, from heat exchangers. This object is achieved by the features in the characterizing part of claims 1 and 2. Should the tubes of the heat-exchanger be fastened onto the plate, besides by rolling, also by inner and/or outer welding, according to the method of the present invention an initial step must be performed, consisting in the complete destruction of such a weld, by chisel, or by a mechanical means, such as, e.g., by a pneumatic hammer, by a guided anger bit or by a milling cutter, and so on. The tool can be driven by a normal electrical or pneumatic drill. The milling-cutter-holder shank can be constituted either by a constant-section metal round, or by two metal rounds having different sections, rigidly connected to each other, and lying on the same axis. The round which is of lower cross-sectional surface area is provided with the blocking means, and on it inserted is the guide sleeve. The milling-cutter-holder shank constituted by two rounds can be preferably obtained by the lathe-machining of a constant-section metal round. The two rounds which form the milling-cutter-holder shank have an L A /L B ratio - wherein L A is the length of the lower cross-sectional surface-area round and L B is the length of the greater cross-sectional surface-area round - comprised within the range of from 0.1 to 1; and a D A /D B ratio - wherein D A is the diameter of the lower cross-sectional surface-area round and D B is the diameter of the greater cross-sectional surface-area round, comprised within the range of frog 0.1 to 1. When the D A /D B ratio is equal to 1, the tool of the present invention is provided on the milling-cutter-holder shank with a shoulder, to the purpose of preventing the guide sleeve from sliding. The milling-cutter-holder shank is generally constituted by carbon steels, with a carbon content comprised within the range of from 0.02 to 1.5% by weight; other metals, such as stainless steels, or special alloy steels or non ferrous metal alloys can be used as well. The guide sleeve has an outer diameter slightly shorter than the inner diameter of the tube which has to be removed from the heat exchanger, but longer than the diameter of the milling-cutter-holder shank. Said sleeve can be of any length, even if having a length about equal to that of the lower cross-sectional surface-area round is preferred. The opening in the guide sleeve can be provided in any part thereof, on condition that it coincides, when the sleeve is inserted on the milling-cutter-holder shank, with the blocking means. In said opening inserted is the milling-cutter-shank, the teeth of which protrude by a length equal to the thickness of the tube to be extracted. The offset of the longitudinal bore of the guide sleeve relatively to its own axis is equal to the thickness of the tube if the diameter of the milling cutter is identical to that of the same sleeve, or is equal to the thickness of the tube, increased by the difference of diameters, if the milling cutter has a diameter lower than that of the sleeve. The guide sleeve can be also constituted by any types of metals or of metal alloys, even if bronze is the most preferred one. The milling cutter can be of steel or of other metal alloys. To the purpose of better understanding the tool of the instant invention, hereunder a description of a preferred embodiment of the tool in greater detail is given, referring to the figures of the attached drawing, wherein: Fig 1 shows a perspective schematic exploded view of the tool of the present invention; Fig. 2 shows a perspective schematic view of the tool in its operating position inside the tube to be removed; Fig. 3 shows a longitudinal sectional view of the tool in its operating position inside the tube; and Fig. 4 shows a transversal sectional view of Fig. 3, carried out by a plane passing along AA. Referring to the figures, the tool of the present invention comprises: a milling-cutter-holder shank constituted by a round of greater cross-sectional surface area 1, which is applied to the operating machine; a round of lower cross-sectional surface area 2, provided with blocking means 3 and 3'; a guide sleeve 5 provided with an opening (10) and with a longitudinal bore 6; and an end milling cutter 4, provided with a bore 4' for the rigid connection to the milling-cutter-holder shank. The milling cutter 4 is housed inside the opening 10 of the guide sleeve 5, and the whole assembly is applied on round 2. Whilst the sleeve remains free, the milling cutter is rigidly blocked onto the round by means of pin 3', which is inserted inside the two bores 3 and 4. The longitudinal bore 6 of the guide sleeve, by being offset relatively to the axis by a length at least equal to the thickness of tube 7 fastened to the tube plate 8, allows the teeth of milling cutter 4 to protrude by a length identical to its offset and to grind the tube according to the intersection 9. During the operation of the tool, the milling-cutter-holder shank is connected to an operating machine, such as, e.g., a drill, and the milling-cutter-housing guide sleeve is slid inside the tube. On actuating the drill, the milling cutter, which operates on its end, removes a portion of the tube, and the guide sleeve, by being not constrained to the milling-cutter-holder shank, does not rotate and allows the milling cutter to wear away a straight length of tube.

Claims: Method for the non-destructive removal of tubes or of portions of tubes from heat exchangers, comprising: the lengthwise cutting along at least one generatrix of one tubs or of a plurality of tubes of said exchanger, to a depth at least equal to the thickness of the tube plate the approaching to each other of the edges of the so-obtained cut section up to the complete release of the tube, or of the tubes, from the tube plate; the possible crossways cutting of the tube, or of the tubes, to a height at least equal to the double of the thickness of the tube plate; characterized in that the lengthwise cutting is carried out to a width of up to 2% of the outer perimeter of the tubes by a tool Tool for the non-destructive removal of tubes, or of tube portions, from heat exchangers, according to the method of claim 1, comprising a milling-cutter-holder shank (1,2), a guide sleeve (5) and an end milling-cutter (4), characterized in that: a) the milling-cutter-holder shank (1,2) is at least equal in length to the depth of the cutting to be accomplished in the tube (7) and is provided with a blocking means (3,3'), b) the guide sleeve (5) is constituted by a cylinder provided with a longitudinal bore (6), inserted, without any rigid connections, on the milling-cutter-holder shank (1,2) and is provided with an opening (10) for housing the milling cutter (4), said longitudinal bore (6) being offset relatively to the axis by a length at least equal to the thickness of the tube (7) to be removed; and c) the end milling cutter (4) is housed inside the opening (10) of the guide sleeve (5), and rigidly fixed on the milling-cutter-holder shank (1,2) comprising: a) a milling-cutter-holder shank (12), at least equal in length to the depth of the cutting to be accomplished in the tube (7), and provided with a blocking means (3,8'), b) a guide sleeve (5) constituted by a cylinder provided with a longitudinal bore (6), inserted, without any rigid connections, on the milling-cutter-holder shank (1), and provided with an opening (10) for housing a milling cutter (4), said longitudinal bore (6) being offset relatively to the axis by a length at least equal to the thickness of the tube (7) to be removed; and c) an end milling cutter (4) housed inside the opening (10) of the guide sleeve (5), and rigidly fixed on the milling-cutter-holder shank (1,2). Tool according to claim 2, wherein the milling-cutter-holder shank (1,2) is constituted by a constant-section metal round. Tool according to claim 2, wherein the milling-cutter-holder shank (1,2) is constituted by two metal rounds having different cross-sectional surface areas, rigidly connected to each other and lying on the same axis. Tool according to claim 4, wherein the round of lower cross-sectional surface area (2) is provided with the blocking means (3,3'), and on said round the guide sleeve is inserted. Tool according to claim 4 or 5, wherein the milling-cutter-holder shank (1,2) is obtained by lathe-machining of a constant-section metal round. Tool according to any of claims from 4 to 6, wherein the L A /L B ratio - wherein L A is the length of the round with lower cross-sectional surface area (2) and L B is the length of the round with greater cross-sectional surface area (1) - is comprised within the range of from 0.1 to 1. Tool according to any of claims from 4 to 6, wherein the D A /D B ratio - wherein D A is the diameter of the round with lower cross-sectional surface area (2) and D B is the diameter of the round with greater cross-sectional surface area (1) - is comprised within the range of from 0.1 to 1. Tool according to claim 8, wherein, when the D A /D B ratio, is equal to 1, the milling-cutter-holder shank (1,2) is provided with a shoulder to the purpose of preventing the guide sleeve (5) from sliding. Tool according to any of claims from 2 to 9, wherein the guide sleeve (6) has an outer diameter slightly shorter than the inner diameter of the tube (7) to be removed, and longer than the diameter of the milling-cutter-holder shank (1,2). Tool according to any of claims from 4 to 9, wherein the guide sleeve (5) has a length preferably equal to the length of the round having the lower cross-sectional surface area (2). Tool according to any of claims from 2 to 11, wherein the opening (10) of the guide sleeve (5) coincides, when the sleeve is applied on the milling-cutter-holder shank (1,2), with the blocking means (3,3'). Tool according to any of claims from 2 to 12, wherein the offset of the longitudinal bore (6) of the guide sleeve (5) relatively to its own axis is equal to the thickness of the tube (7) if the diameter of the milling cutter (4) is identical to that of the sleeve, or is equal to the tube thickness increased by the difference of diameters if the milling cutter (4) has a diameter lower that that of the sleeve (5).

Inventors: FERRARI, FRANCESCO, STIGNANI, RENATO
Applicants: ECP ENICHEM POLIMERI S.R.L.
Application year: 1986
Main classification: B23P19
IPC codes: B23C3, B23P19, B25B27, B23P21