GB2146435A

GB2146435A - Temperature control during annealing

Info

Publication number: GB2146435A
Application number: GB08323995A
Authority: GB
Inventors: Edward Duncombe; Alexander Thompson; Robert Arthur Evans
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1983-09-07
Filing date: 1983-09-07
Publication date: 1985-04-17
Also published as: DE3478312D1; DE136810T1; GB8323995D0; EP0136810B1; EP0136810A3; EP0136810A2; GB2146435B

Abstract

Temperature control at a weld (52) between a tube (51) and tube plate (53) having heat input from an inductive heating probe (50) to effect annealing of the weld is performed with the aid of a signal generating receptor coil (54) coupled with the probe (50). The signal from the coil (54) experiences a characteristic change when the temperature of the weld reaches the required annealing temperature and this signal is used to control the heat input to the weld. The receptor coil can be inside the tube (51), outside the tube (51), embracing a number of similar tubes (51) or may be inside an adjacent tube (51). At the required anneal temperature, the materials of the tube and weld reach their Curie point which brings about a permeability change. <IMAGE>

Description

1 GB 2 146 435 A 1

SPECIFICATION

Temperature control during annealing This invention relates to temperature control dur- 70 ing annealing of ferromagnetic members.

The invention has arisen in response to prob lems arising in the course of annealing welds where ferritic tubes are welded to tube plates of shell and tube heat exchangers and especially heat 75 exchangers as used in the nuclear field for steam generation such as in fast and pressurised water reactors. In these heat exchangers the tubes are closely spaced and access to their welds for an- nealing and temperature measurement is difficult. 80 Thus annealing tends to be carried out by an in ductive probe internally of the tube in the region of the weld. The probe may be in the form of an RIF energised and water-cooled coil or may be as de scribed in our copencling British Application No 85 8232386. Anneal temperature control is performed by control of power into the probe which has been predetermined by trials on a model to obtain the required anneal. This form of control leaves uncer tainties and a real time control would be preferred. 90 The present invention provides such a control.

In accordance with the invention a weld at a fer ritic tube to a tube plate is annealed by an induc tive heating probe inserted inside the tube by a process characterised in that a signal generating 95 receptor is provided having coupling with the probe and the heat input to the anneal is con trolled by the signal generated at said receptor.

The invention relies on the fact that the tempera- ture of anneal is close to the Curie point of the ma- 100 terial of the tube which is having its weld annealed. Thus, at above annealing temperature, there is a significant change in the permeability of the tube and hence also in the voltage induced in the receptor signal and this can be used to reduce power input to the probe and vice-versa. The change is so significant that the receptor can be located inside an adjacent unheated tube and, despite the fact that the unhQated tube acts as a shield round the receptor, a detectable signal arises.

The invention, in various forms, will now be described further with reference to the accompanying diagrammatic drawings in which:

Figure 1 is a sectional elevation of a part of a heat exchanger being repaired and involving annealing of a braze used in the repair, the signal generating receptor of the invention being located in an adjacent tube.

Figure 2 is a sectional elevation of a tube to tube 120 plate weld involving an anneal at the weld, the signal generating receptor being located inside the tube having its weld annealed.

Figure 3 is a circuit diagram of a control circuit for use with the arrangement of Figure 2, and Figure 4 shows an alternative arrangement.

In Figure 1 a tube 20 in a nest of closely spaced similar parallel tubes in a tube plate 21 is assumed leaking at the weld 22. To close off this leak a repair tube 23 is inserted into the leaking tube 20 through the tube plate. The upper end of tube 23 is explosively welded to the tube plate at a region 24 (indicated by crosses) and the lower end of tube 23 is brazed to the tube 20 at a region 25.

To effect the braze at region 25 an induction heating probe 30 (see also our co-pending application No 82 32386) is inserted inside the tube 23. This probe has a service box 32, water conducting cables 33, 34 and a handle 35.

Inside the probe 30 there is a magnetic flux generating unit and when the probe is powered the braze at region 25 is effected. After making the braze an annealing process is required. To perform this anneal the probe is retained on power but the anneal operation requires control.

In order to provide control of the anneal a signal generating flux receptor coil probe 40 is inserted into a tube 20 adjacent to the tube 20 being annealed. The tube 20 having the probe 40 can itself be a repaired tube (as shown) or an unrepaired tube.

Connections 41 are provided to the flux receptor probe 40 and these connect with a control unit 42 which controls the power input to the induction heating probe 30 along a control line 43 according to the signal generated at probe 40.

As the annealing temperature is reached at the braze region 25 the Curie point of the repair tube is also reached This causes a measurable rise in the flux (1 microvolt per turn of the coil of probe 40) received from probe 30 at probe 40 despite the shielding effect of the unheated tube 20. The link from the coil of probe 40 (ie connectors 41) is preferably by optical fibre so that 1nduced error signals do not occur in the link as may arise from the intense magnetic field which is created by the probe 30.

In Figure 2 an induction heating probe 50 is shown inside a tube 51, welded at 52 to a tube plate 53. The probe is located so that the weld can be annealed. Around the probe 50 there is a single turn 54 of a Imm diameter mineral insulated conductor. This acts as a signal generating receptor and typically it provides a signal of 1.0-1.5 mV when the weld 52 is above the Curie temperature and a signal of about 0.5 0.7mV when the weld is below the Curie temperature.

Figure 3 shows a circuit for use with the arrangement shown in Figure 2.

A 20 KHz generator 60 is used to power the heat ing probe 50. The signal in the receptor turn 54 is backed off against an EMF derived from a current transformer 61 via a potentiometer 62. In this way the output signal from receptor 54 can be made zero prior to the Curie temperature being reached and of a magnitude to effect control at the Curie temperature. The backed-off signal passes to an amplifier 63 and thence to a control unit 64 which controls output from the generator 60 to the probe.

In Figure 4 a nest of tubes 51 is shown in sec tional plan. In one of these tubes a probe 50 is lo cated. A single turn receptor coil 54A is provided enclosing a number of the tubes 51. As the probe is moved from one tube 51 to the next the same receptor coil 54A can be used for control purpose.

2 GB 2 146 435 A 2 In another alternative arrangement the receptor coil 54A encloses only a single tube 51 and is moved from tube to tube as annealing takes place. In yet another alternative arrangement each tube 51 has its own individual mineral insulated receptor coil tack welded to it as the heat exchanger is constructed and the coil terminates at a point of access remote frorn the tubes. In this way, later annealing can be performed without the need for ac- cess to the outside of the tubes (which may be impossible either due to the close packing of the tubes or because the tubes are radioactive). radioactive).

In arrangements having a coil 54 enclosing one, or more, tubes a substantial signal is generated at the Curie temperature. This may typically be 1.5 volts for a single turn.

The invention, particularly as exemplified by the arrangement of Figure 2, can be used to control an anneal at the explosive weld 24 indicated in Figure 1.

Claims

1. A method of effecting temperature control during heating at a joint between a ferritic tube and a tube plate or between a ferritic repair tube and a ferritic tube in a tube plate, comprising inserting an inductive heating probe inside said ferri- tic tube or repair tube, providing a signal generating receptor having coupling with the probe, powering said probe to heat the joint, and providing means whereby the heat input to the joint is controlled by the signal generated at said receptor when the metal at the joint enters the Curie point region.

2. A method as claimed in claim 1 in which the receptor is located in an adjacent ferritic tube, which does not enter the Curie Point region.

3. A method as claimed in claim 1 in which the receptor is a coil (one or more turns) located inside the tube at which the joint is being effected.

4. A method as claimed in claim 1 in which the receptor is a coil enclosing one or more tubes joined with the tube plate.

5. A method as claimed in any preceding claim in which the heating is performed to effect an anneal at a weld made by fusion between a tube and tube plate.

6. A method as claimed in any one of claims 1 to 4 in which the heating is performed at an explo sive weld made between a repair tube and a tube in a tube plate.

7. A method as claimed in any preceding claim in which the control signal is transmitted by optical fibre connections in regions where those connections are subjected to an intense field from the heating probe.

8. A method as claimed in any preceding claim in which the receptor is a coil of one or more turns of mineral insulated cable which may be permanently or removably associated with the joint.

Printed in the UK for HMSO. D8818935, Z85, 7102. Published by The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.