GB1588971A

GB1588971A - Method of lining damaged internal tube surfaces

Info

Publication number: GB1588971A
Application number: GB3014076A
Authority: GB
Original assignee: IMI YORKSHIRE IMPERIAL Ltd
Current assignee: IMI YORKSHIRE IMPERIAL Ltd
Priority date: 1977-07-18
Filing date: 1977-07-18
Publication date: 1981-05-07

Description

(54) METHOD OF LINING DAMAGED INTERNAL TUBE SURFACES (71) We, IMI YORKSHIRE IMPERIAL LIMITED, formerly known as YORKSHIRE IMPERIAL METALS LIMITED, a British Company, of Haigh Park Road, Stourton, Leeds, LS1 1RD do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to the repair of metallic tubes, particularly but not exclusively heat exchanger tubes, which have been eroded in service.

According to the present invention there is provided a method of repairing a damaged internal surface of a metallic tube comprising the steps of: a) counter-boring the tube so as substantially to remove said damaged internal surface and to leave a portion of enlarged bore, b) locating a metallic, tubular liner in said portion of enlarged bore, and c) expanding the liner, by explosive means, into engagement with the internal surface of said portion.

In preferred embodiments of the invention, explosive expansion of the liner causes the liner to become welded to the tube over at least a localised region of their engagement. Preferably the remainder, or a substantial portion of the remainder, of the liner is expanded into contact with the tube.

The tube may be already secured to another body such as a tube-plate of a heat exchanger or like structure, or a flange. The connection between the tube and the other body may be localised eg a fusion weld at the front face of a tube-plate, or it may extend over a substantial length of the tube eg a rolled in joint in a tube-plate. In the case of a localised connection, any explosively formed weld between the tube and liner is preferably made at a region of the tube/liner interface spaced from the connection of the tube to the body because that connection may be unable to withstand forces applied to it in order to effect explosive welding of the liner to the tube.

Arrangements for making explosive welds between tubular bodies are now well known. Techniques are described, for example, in US Patent Specifications 3 503 110, 3 409 969 and 3 140 537. Preferably, however, the weld between the liner and the tube is made by an angle geometry technique of the type disclosed In US Patent Specification 3 503 110 for joining tubes to tube-plates.

To enable production of a weld by angle geometry explosive welding, the counterbored portion of the tube is preferably cylindrical and the liner has an externally tapered portion that becomes welded, during explosive expansion, to a portion of the cylindrical counterbore. Such a liner may be produced by deformation of a hollow cylindrical blank and the deformation is preferably carried out in such a manner that the liner maintains a substantially constant wall-thickness. The tapered portion of the liner is preferably adjacent to one end of the liner and there is preferably a cylindrical portion between the tapered portion and that end.

For explosive expansion of the liner, the charge is preferably elongate eg rod-like. It may be located within a tubular insert of solid, energy transmitting material. A suitable material is a synthetic plastics such as polyethylene. The charge may comprise two portions, one of which is arranged to form a weld between a portion of the liner and the tube, and the other of which is arranged merely to expand a length of the liner into mechanical engagement with the tube, without necessarily forming a weld. At least a portion of the insert is preferably of the same internal shape as the interior of the liner, thereby functioning to locate the welding charge relative to the liner.

The invention is particularly useful in lining surfaces of heat exchanger tubes.which extend completely through a tube-plate and which are fusion welded (ie welded by a technique other than a high energy rate technique) to the front face of the tubeplate. The liner is then conveniently located with at least a portion thereof within the tube-plate, the weld between the liner and the tube being made at a location within the plate spaced from the fusion weld between the tube and the plate.

In preferred embodiments of the invention, the wall of the liner is of such a thickness that the liner substantially reestablishes, after expansion thereof, the original bore of the tube.

y way of example an embodiment of the invention will be described with reference to the accompanying diagrammatic drawings, in which Figures 2 to 4 illustrate successive stages in re-surfacing of a heat exchanger tube which has been eroded as shown in Figure 1.

In Figure 1, 10 indicates a tube-plate of a heat exchanger having a tube 12 secured therein. The tube 12 extends completely through an aperture 14 in the tube-plate and is fusion welded to the front face of the plate at 16. The portion of the tube bore adjacent to the front face of the tube-plate is surface eroded as indicated at 18.

The first step in repairing the damaged tube is to bore it out to a depth less than the total wall thickness of the tube and preferably equal to the liner wall thickness. This boring out shown in Figure 2, extends over the full eroded length of the tube as shown at 19.

The boring out is preferably effected by means of a machine tool comprising a cutting bit and a pilot device for aligning the bit substantially in axial alignment with the tube. The bit may be tubular, and the pilot device may be on a shaft extending through the tubular bit. Thus. the pilot device may be held stationary in the tube while the bit is rotated to remove material from the tube wall. The pilot device is preferably radially expandablc, so that it can be easily inserted into a tube and expanded therein to engage the tube wall to guide the bit. For example.

the pilot device may comprise a wedging means on or associated with the shaft and operable to wedge gripping members radially outwardly into engagement with the tube wall. There should be at least three such members to provide positive location of the pilot device. and hence the bit axis, relative to the tube axis. in an alternative arrangcment, a bearing surface may be pro vidcd between a shaft providing the body and a pilot device, so that the shaft can rotate within the pilot device which engages the tube wall.

An explosive device comprising a liner, tubular insert and an explosive charge is then located in the bored out portion of the tube, as shown in Figure 3. Each of these portions of the device will be briefly discussed in the following sub-paragraphs: (a) Liner: This is in the form of an open ended metal tube having first and second tubular sections 24, 26 joined by an intermediate swaged section 28. The external diameter of section 24 is approximately equal to the internal diameter of the bored out portion of tube 12 so as to locate the liner substantially axially within the bored out portion of the tube. Swaged section 28 provides a tapering space between itself and the bored out portion of the tube for the purpose described in US Patent 3 503 110 referred to above. Section 26 extending to the forward edge of the liner engages the step formed in tie tube 12 by the boring out referred to above and prevents over insertion of the liner. It also facilitates substantially uniform liner velocity during expansion of the full length of swaged section 28.

(b) Insert: This has an external shape corresponding with the internal shape of the liner and is made of a synthetic plastics material, preferably polyethylene. The insert has a central axial bore 30 which receives the explosive charge. Where the insert and charge are pre-assembled, surfaces of the insert and the liner locates the insert in the desired position relative to the liner and hence the charge in the correct position.

However, the insert and liner may be preassembled and the charge inserted immediately before use.

(c) Charge: This is in two portions indicated at 32 and 34 respectively. Portion 32 is an explosive of high detonation velocity, for example an explosive of PETN. It may be in an aluminium tube having one open end. Charge portion 32 is aligned with the swaged section 2S of the liner and extends substantially through that section to or near the front of cylindrical section 26. Charge portion 34 is an explosive cord of high detonation velocity but low weight/unit length comparcd with charge portion 32. Cords supplied under the name "lPrimacord" are suitable for this purpose. The cord extends from the charge 32 beyond the front face of the tube plate for connection to a suitable initiating device.

then the cord 34 is initiated, a detonation front progresses longitudinally of the cord in a direction inwardly of the tube 12.

The explosive force produced by the cord is transmittcd by the insert 22 to the liner section 24 and is sufficient to expand that section into mechanical engagement with the bored out section of tube 12. The explosive forces are not, however, sufficient to form a weld, and they are not sufficient to damage the fusion weld 16 between the tube and the tube plate. This can be ensured by suitable choice of charge weight/unit length in the cord 34, bearing in mind the relatively poor transmission of explosive forces between the cord and the insert 22 due to the air gap between those parts. If required, the insert can be deliberately bored out to increase the air gap.

Detonation of the cord 34 initiates deto nation of charge section 32, also in a direction inwardly of the tube 12. This detonation, therefore, progresses in the direction of the increasing spacing between liner section 28 and the bored out surface of the tube. The section 28 is, therefore, welded to the tube as described in US Patent 3 503 110 referred to above. Finally, charge section 32 expands liner section 26 into firm engagement with the interior of the tube.

However, this expansion may merely form a mechanical joint as the collision front velocity between liner and tube may be too high for welding.

The depth of boring out of tube 12 is such that the liner just fills that depth, as shown in Figure 4. The interface portion 40 between the liner and the tube will be welded, by the mechanism described above, and the remainder of that interface will provide a mechanical joint. One advantage of the present invention is that the liner can itself be bored out when it has become eroded in service, and the re-surfacing operation can be repeated at a later date.

The above description applies to only a single heat exchanger tube. It will be appreciated that the tube plate 10 will contain many apertures 14 each with its own tube 12, and many of these tubes will have to be re-surfaced at the same time. Preferably, therefore, each tube is fitted simultaneously with its own liner, insert and charge, and the cords 34 for the individual tubes are connected to a common initiator.

For this purpose, the length of the cord projecting from the front face of the tube plate may be looped as shown in Figure 3, and a further length of a similar cord may be passed through the various loops. Cord 42 can then be initiated from a single detonator.

The invention is not limited to details of the illustrated embodiments. Firstly, the invention may be used with tubes other than those fusion welded to tube plates. If the explosive would distort an unsupported tube, it could be re-surfaced by temporarily locating it in a die which would absorb the explosive forces produced by the charge.

Where the tube is secured in a plate, the invention is equally applicable to tubes retained by roller expansion and other conventional joining techniques. It is not essential to use angle geometry to produce the weld; parallel geometry techniques are also well known.

It may not be necessary to weld a liner into a bored out tube. The welding step ensures accurate location of the liner in the desired position in service. In some circumstances however, a mechanical joint may be thought satisfactory. In this case, the remaining tube surface prior to expansion can be roughened and/or grooved to key with the liner surface. It will be apparent that tapered staging of the liner is unnecessary if a weld is not required.

As mentioned above, the depth of boring out is preferably substantially equal to the wall thickness of the liner to avoid restriction of the flow passage of the lined tube.

Small differences in cross-section of the lined tube may however not be that serious.

The depth of boring out is also limited to some extent by the erosion depth. It is not essential to remove all erosion marks before expansion of the liner. The critical factor is whether the remaining erosion marks will cause damage to the liner because of uneven expansion requirements. In any event, if severe erosion marks remain after boring out, or if the tube has a through hole, the remaining mark or hole may be filled with a suitable material prior to expansion of the liner to avoid damage to the liner. It is believed possible to remove up to about 75% of the wall thickness of the tube while obtaining an adequate repair.

One advantage of the present invention in its application to lining of tubes in tubeplates is the simultaneous expansion of the tube against the tube-plate aperture, improving the seal between the tube and the tube-plate.

WHAT WE CLAIM IS: 1. A method of repairing a damaged internal surface of a metallic tube comprising the steps of: a) counter-boring the tube so as substantially to remove said damaged internal surface and to leave a portion of enlarged bore, b) locating a metallic, tubular liner in said portion of enlarged bore, and c) expanding the liner, by explosive means, into engagement with the internal surface of said portion.

2. A method as claimed in Claim 1 wherein explosive expansion of the liner causes the liner to become welded to the tube over at least a localised region of their engagement.

A A method as claimed by in Claim 2 wherein the weld is produced by an angle geometry explosive welding technique.

4. A method as claimed in Claim 3 wherein the counter-boring step produces an internally cylindrical surface in the tube and wherein the liner has an externally tapered portion that becomes welded, during expansion of the liner, to a portion of said cylindrical surface.

5. A method as claimed in any one of Claims 1 to 4 wherein the wall of the liner is of such thickness that the liner substantially re-establishes the original bore of the tube.

6. A method as claimed in any one of Claims 1 to 5 wherein the tube is one having an end portion thereof secured in a tubeplate and wherein the portion of enlarged

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. nation of charge section 32, also in a direction inwardly of the tube 12. This detonation, therefore, progresses in the direction of the increasing spacing between liner section 28 and the bored out surface of the tube. The section 28 is, therefore, welded to the tube as described in US Patent 3 503 110 referred to above. Finally, charge section 32 expands liner section 26 into firm engagement with the interior of the tube. However, this expansion may merely form a mechanical joint as the collision front velocity between liner and tube may be too high for welding. The depth of boring out of tube 12 is such that the liner just fills that depth, as shown in Figure 4. The interface portion 40 between the liner and the tube will be welded, by the mechanism described above, and the remainder of that interface will provide a mechanical joint. One advantage of the present invention is that the liner can itself be bored out when it has become eroded in service, and the re-surfacing operation can be repeated at a later date. The above description applies to only a single heat exchanger tube. It will be appreciated that the tube plate 10 will contain many apertures 14 each with its own tube 12, and many of these tubes will have to be re-surfaced at the same time. Preferably, therefore, each tube is fitted simultaneously with its own liner, insert and charge, and the cords 34 for the individual tubes are connected to a common initiator. For this purpose, the length of the cord projecting from the front face of the tube plate may be looped as shown in Figure 3, and a further length of a similar cord may be passed through the various loops. Cord 42 can then be initiated from a single detonator. The invention is not limited to details of the illustrated embodiments. Firstly, the invention may be used with tubes other than those fusion welded to tube plates. If the explosive would distort an unsupported tube, it could be re-surfaced by temporarily locating it in a die which would absorb the explosive forces produced by the charge. Where the tube is secured in a plate, the invention is equally applicable to tubes retained by roller expansion and other conventional joining techniques. It is not essential to use angle geometry to produce the weld; parallel geometry techniques are also well known. It may not be necessary to weld a liner into a bored out tube. The welding step ensures accurate location of the liner in the desired position in service. In some circumstances however, a mechanical joint may be thought satisfactory. In this case, the remaining tube surface prior to expansion can be roughened and/or grooved to key with the liner surface. It will be apparent that tapered staging of the liner is unnecessary if a weld is not required. As mentioned above, the depth of boring out is preferably substantially equal to the wall thickness of the liner to avoid restriction of the flow passage of the lined tube. Small differences in cross-section of the lined tube may however not be that serious. The depth of boring out is also limited to some extent by the erosion depth. It is not essential to remove all erosion marks before expansion of the liner. The critical factor is whether the remaining erosion marks will cause damage to the liner because of uneven expansion requirements. In any event, if severe erosion marks remain after boring out, or if the tube has a through hole, the remaining mark or hole may be filled with a suitable material prior to expansion of the liner to avoid damage to the liner. It is believed possible to remove up to about 75% of the wall thickness of the tube while obtaining an adequate repair. One advantage of the present invention in its application to lining of tubes in tubeplates is the simultaneous expansion of the tube against the tube-plate aperture, improving the seal between the tube and the tube-plate. WHAT WE CLAIM IS:

1. A method of repairing a damaged internal surface of a metallic tube comprising the steps of: a) counter-boring the tube so as substantially to remove said damaged internal surface and to leave a portion of enlarged bore, b) locating a metallic, tubular liner in said portion of enlarged bore, and c) expanding the liner, by explosive means, into engagement with the internal surface of said portion.

bore is within the confines of the tube-plate.

7. A method of repairing a damaged internal surface of a tube conducted substantially as hereinbefore described with reference to, and as illustrated in Figures 2 to 4 of, the accompanying drawings.

8. A tube that has been repaired by a method as claimed in any one of Claims 1 to 7.