EP0128644B1 - Reparieren von Wärmetauscherrohren - Google Patents

Reparieren von Wärmetauscherrohren Download PDF

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Publication number
EP0128644B1
EP0128644B1 EP19840302486 EP84302486A EP0128644B1 EP 0128644 B1 EP0128644 B1 EP 0128644B1 EP 19840302486 EP19840302486 EP 19840302486 EP 84302486 A EP84302486 A EP 84302486A EP 0128644 B1 EP0128644 B1 EP 0128644B1
Authority
EP
European Patent Office
Prior art keywords
tube
leaking
strain
repair
probe
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
EP19840302486
Other languages
English (en)
French (fr)
Other versions
EP0128644A3 (en
EP0128644A2 (de
Inventor
Peter Francis Roach
Edward Duncombe
Ian Hulse
John Stacey
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
UK Atomic Energy Authority
Original Assignee
UK Atomic Energy Authority
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GB838309988A external-priority patent/GB8309988D0/en
Priority claimed from GB838313266A external-priority patent/GB8313266D0/en
Application filed by UK Atomic Energy Authority filed Critical UK Atomic Energy Authority
Publication of EP0128644A2 publication Critical patent/EP0128644A2/de
Publication of EP0128644A3 publication Critical patent/EP0128644A3/en
Application granted granted Critical
Publication of EP0128644B1 publication Critical patent/EP0128644B1/de
Expired legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F11/00—Arrangements for sealing leaky tubes and conduits
    • F28F11/02—Arrangements for sealing leaky tubes and conduits using obturating elements, e.g. washers, inserted and operated independently of each other

Definitions

  • This invention relates to the repair of heat exchanger tubes.
  • the quality of the braze can be affected by the presence of strain in the tube being repaired, such strain arising during the heating necessary to effect the braze.
  • a predetermined tolerable level of said strain can be assessed by tests involving the brazing of specimens under various strains and then inspecting the brazes.
  • the present invention provides a method for the repair of a leaking heat exchanger tube in a nest of tubes welded to a tube plate which the tube is of U-tube shape and/or passes through one or more support grid plates, said method involving the known step of inserting a length of repair tube into the leaking tube with one end of the repair tube brazed to the leaking tube characterised in that compressional strain in the leaking tube is measured whilst heating the tube to the brazing temperature and the brazing is only effected if the strain is below a predetermined level.
  • the invention also provides apparatus for carrying out the above method, said apparatus being in the form of a probe which can enter along the leaking tube, the probe being provided with a strain gauge head comprising at least one strain gauge of the kind which can be held in contact with and later released from the inside wall of the leaking tube, characterised in that a heating element is provided in the body of the probe for internally heating the tube to the brazing temperature, and the strain gauge head is connected to means for recording the compressional strain that arises during heating of the leaking tube prior to brazing.
  • Strain of a magnitude sufficient to impede the brazing process, does not always occur when a tube is heated. When it does it may be due to the fact that the complete heat exchanger tube is "U" shaped and heating one leg will cause a strain, the magnitude of which is dependent on the bend radius. On the other hand, the stress may be caused by the tube binding in the first (top) support grid plate or any of the lower grid plates through which it passes. In either case, the strain produced may be higher than can be tolerated.
  • the length of the probe apparatus is such that, for a given heat exchanger, the strain gauge head reaches a region close to but just above the first tube support grid plate.
  • the heater (and heated region) is kept as remote from the strain gauge as possible, the heater extending downwards from just below the tube plate.
  • FIG. 1 a repaired tube 10 is shown.
  • This tube 10 is one of a nest of similar "U" shaped tubes in a heat exchanger having a tube plate 11 and a top tube support grid plate 12.
  • the tube 10- is welded to the tube plate at a weld 13. It is this weld that can leak after the heat exchanger has been used and it is inaccessible for repair because of the close proximity of other tubes in the nest. If the heat exchanger has been in use as a part of a nuclear reactor installation it is probable that the weld is also inaccessible because of nuclear activation.
  • the tube 10 is subjected to a strain- on-heating test prior to effecting the repair. This is illustrated with reference to Figure 2.
  • a probe form of apparatus 20 is inserted into the tube 10.
  • the probe has at its nose a strain gauge head 21.
  • the body 22 of the probe extends from the tube plate 11 to a point close to the gauge head 21, space being left for a junction box 30 (see Figure 4) between the body 22 and gauge 21.
  • the body has an electric heater coil 23 and a coil spacer 24. Service connectors to the probe are indicated diagrammatically by the tube 25 and are described in more detail below.
  • the strain gauge is of the kind disclosed in GB-A-1,395,263.
  • This gauge has a casing 26 and windows 27 at 90° through which strain gauges 28 having abrasive surfaces 29 can be advanced by a pressure internal to the casing 26. The pressure urges the surfaces 29 into non-slip engagement with the tube 10. This action can be performed remotely by air pressure in a line in the services tube 25. Disengagement of the gauges 28 and tube 10 is effected by releasing the air pressure. In this application of the gauge described above, only one strain gauge is used. The second being held as a spare.
  • the tube 10 is heated by the coil 23 and the strains in gauge 28 are monitored. If strain below a predetermined level is registered then the repair shown in Figure 1 can be made.
  • Figure 3 shows various schematic arrangements of the measuring system.
  • the service lines When using a strain gauge of the kind disclosed in GB-A--1,395,263, the service lines must pass through the heated zone and must therefore be of a high temperature type (e.g. mineral insulated cable).
  • a high temperature type e.g. mineral insulated cable
  • a junction box is required to join the flexible, relatively low temperature service lines used on the gauge described in GB-A-1,395,263, to the rigid high temperature lines required. This box is shown in Figure 4.
  • the gauge head 21 has two two-wire cables 31, 32, (one for each strain gauge) and a plastic tube air line 33.
  • the wires 31a, 31b of cable 31 are connected to mineral insulated thermocouple cable 34.
  • the wires of cable 32 are similarly connected to mineral insulated cable 35.
  • the line 33 is connected to a rigid air tube 36.
  • the cables 34, 35 are both four-wire mineral insulated thermocouple cable having two alumel conductors and two chromel conductors. When the instrument is in use, one of these cables is coupled with a four terminal digital strain indicator 37.
  • the conductors are disposed within the junction box as shown in one or other of Figures 3A-C.
  • the air line 33 has a glass sleeve covering.
  • the heater element 23 comprises five-start helical coils of swaged heater cable (1 mm) wound round the body 22.
  • the cable has unswaged, thicker tails which pass outside the tube 25.
  • the swaged coils are held in place on the body 22 with tack welded thin stainless-steel plates.
  • the body 22 is penetrated at a point midway along the element 23 to provide a thermocouple junction at the end of a thermocouple cable which passes along the tube 25 and body 22 so that the temperature of the tube 10 can be assessed.
  • the coil spacers 24 (each of 1.5 mm diameter wire) centralise the heater in the tube 10 and are held in position by thin tack welded plates. Thus spacers can be provided at the end and centre of the body 22.
  • Figures 3A-C various ways of connecting the strain gauge 21 to a digital strain indicator 37 via a junction box 30 and 4-core mineral insulation cable 34, 34a, 34b are shown.
  • Figure 3A is a quarter bridge arrangement and Figure 3B is a half bridge arrangement.
  • the conductors are marked "Cr" for a chromel conductor and "Al" for an alumel conductor.
  • Figure 3C shows a fully compensated arrangement.
  • the principal strain may be caused by the fact that one leg of the U-shape is being heated whilst the other is not.
  • the magnitude of this basic strain tends to be related to the spacing apart of the legs of the U-shape: a wide spacing gives low strain whilst a close spacing gives a higher strain.
  • Such strains can be relieved by executing a heating step on one leg whilst the other leg is also heated. Said other leg may even be given a repair tube so that both legs have equal treatment even though a leak on the other leg does not exist.
  • the principal strain may be caused by the leaking tube binding in a support grid plate.
  • Such strain can be relieved by creating in the leaking tube, in the region between weld and braze, a weakness zone so that the tube strain relieves itself at that zone when heated.
  • a weakness created by simple thinning of the tube does not give the required strain relief, neither does cutting nor drilling. Cutting and drilling is also undesirable as it causes loss of back-up containment that the leaking tube provides despite the fact that it has a leak. This loss also arises if the leaking tube is severed.
  • the weakness zone is created first by a thinning operation (such as by undercutting) and second by an expansion or bulging operation at the point of thinning.
  • the expansion or bulging can be performed by using an axially compressed recoverable isostatic ring, such as a rubber ring. With such a zone created, strain arising by the heating of the heat exchanger tube relieves itself at least to a degree not affecting the braze.
  • a leaky heat exchanger tube 50 having an external diameter of 25 mm and a wall thickness of 2.5 mm is given an annular undercut 51 to remove 2 mm of wall thickness over a length of 12 mm. Sharp corners 52 are removed and the undercut has rounded corners 53.
  • the undercut is made above the region at which a braze is to be effected between the tube 50 and a repair tube but close enough to experience the heat of the braze.
  • a rubber plug 54 is shown subjected to axial compression (arrows 55) so that is expands into the undercut 51 to give the tube 10 a bulge 56 at the undercut.
  • Figure 5C shows the shape 57 taken by the undercut 51 when the tube 50 yields (arrows 58) 1.5 mm, on being heated due to the fact that the tube 50 is binding in a grid plate. Yield takes places at about 900°C.
  • the braze is effected at about 1000°C. In this way no troublesome axial strain exists in the heat exchanger tube 50 during the course of the braze and hence there is no tendency for the tube 50 to distort under the strain in the region of the braze. Such distorting, if it occurs, is believed to cause unsatisfactory brazing as the capillary gap between the tube 50 and the repair tube becomes irregular and the braze metal does not spread uniformly.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Monitoring And Testing Of Nuclear Reactors (AREA)

Claims (6)

1. Verfahren zur Reparatur eines lecken Wärmeaustauscherrohres in einem Satz von Rohren, die mit einer Rohrplatte verschweißt sind, wobei dieses Rohr U-förmig ist und/oder durch eine oder mehrere Trage-Gitterplatten hindurch verläuft, mit dem bekannten Schritt, einen Längenabschnitt eines Reparaturrohres in das lecke Rohr einzuführen, wobei ein Ende des Reparaturrohres mit dem lecken Rohr hart verlötet wird, dadurch gekennzeichnet, daß die Druckspannung im lekken Rohr gemessen wird, während man das Rohr auf die Löttemperatur erwärmt, und daß der Hartlötvorgang nur dann durchgeführt wird, wenn die Spannung unter einem bestimmten Niveau liegt.
2. Vorrichtung zur Durchführung des Verfahrens nach Anspruch 1, wobei die Vorrichtung die Form einer Sonde aufweist, die längs des lecken Rohres eindringen kann, und die Sonde mit einem Spannungsmeßkopf versehen ist, der mindestens eine Spannungsmeßeinrichtung jener Art aufweist, welche in Berührung mit der Innenwand des lecken Rohres gehalten und später hiervon gelöst werden kann, dadurch gekennzeichnet, daß ein Heizelement im Körper der Sonde vorgesehen ist, um das Rohr von innen her auf die Löttemperatur zu erwärmen, und daß der Spannungsmeßkopf an eine Einrichtung zum Aufzeichnen jener Druckspannung angeschlossen ist, welche während des Erwärmens des lecken Rohres vor dem Löten auftritt.
3. Vorrichtung nach Anspruch 2, in Verbindung mit einem lecken Rohr, das durch eine Trage-Gitterplatte hindurchtritt, wobei die Länge der Sonde so bemessen ist, daß der Spannungsmeßkopf nahe bis zur Trage-Gitterplatte und gerade bis über diese reicht.
4. Vorrichtung nach Anspruch 2, wobei der oder jeder Spannungsmeßfühler flexible Niedertemperaturanschlüsse an einer Anschlußdose hat, an der Verbindungen zu einer starren Freileitung und über ein mineralisoliertes Vier-Draht-Thermoelementkabel zu einer Spannungsanzeigeeinrichtung mit vier Anschlüssen hergestellt sind, die entweder eine Viertelbrückenanordnung, eine Halbbrückenanordnung oder eine voll kompensierte Anordnung liefert.
5. Reparaturverfahren nach Anspruch 1, wobei das lecke Rohr U-förmig ist, mit der Erwärmung beider Schenkel der U-Form, so daß die Spannung im lecken Rohr entlastet wird.
6. Reparaturverfahren nach Anspruch 1, mit der Erzeugung einer schwächezone im lecken Rohr vor dem Ausführen des Lötvorganges dadurch, daß man das Rohr in einem Bereich dünner macht und ausbaucht, der nahe genug am Bereich der Lötung liegt, daß die Schwächungszone die Wärme des Lötvorganges erfährt, um in dieser Zone ein Nachgeben zu ermöglichen.
EP19840302486 1983-04-13 1984-04-11 Reparieren von Wärmetauscherrohren Expired EP0128644B1 (de)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB8309988 1983-04-13
GB838309988A GB8309988D0 (en) 1983-04-13 1983-04-13 Heat exchanger tube repair
GB8313266 1983-05-13
GB838313266A GB8313266D0 (en) 1983-05-13 1983-05-13 Heat exchanger tube repair

Publications (3)

Publication Number Publication Date
EP0128644A2 EP0128644A2 (de) 1984-12-19
EP0128644A3 EP0128644A3 (en) 1985-07-10
EP0128644B1 true EP0128644B1 (de) 1987-09-16

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP19840302486 Expired EP0128644B1 (de) 1983-04-13 1984-04-11 Reparieren von Wärmetauscherrohren

Country Status (2)

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EP (1) EP0128644B1 (de)
DE (1) DE3466279D1 (de)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3717032C1 (de) * 1987-05-21 1988-11-10 Bbc Reaktor Gmbh Verfahren und Einrichtung zur Simulation der Betriebsbeanspruchungen einer Bauteilverbindung
CN101347862B (zh) * 2008-06-06 2011-04-06 上汽通用五菱汽车股份有限公司 一种应用微负压于管道裂缝焊补的作业方法

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1395263A (en) * 1973-01-03 1975-05-21 Atomic Energy Authority Uk Strain gauges
GB2032559A (en) * 1978-10-04 1980-05-08 Atomic Energy Authority Uk Tube-in-shell heat exchangers
GB2094435B (en) * 1981-03-10 1984-08-15 Nat Nuclear Corp Ltd Repairing tubes
GB2130860A (en) * 1982-11-12 1984-06-06 Atomic Energy Authority Uk Induced current heating probe

Also Published As

Publication number Publication date
DE3466279D1 (en) 1987-10-22
EP0128644A3 (en) 1985-07-10
EP0128644A2 (de) 1984-12-19

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