GB2196556A

GB2196556A - Plugging a tube plate by means of a brazed-in plug

Info

Publication number: GB2196556A
Application number: GB08720969A
Authority: GB
Inventors: Umberto Guerreschi
Original assignee: Ansaldo SpA
Current assignee: Ansaldo SpA
Priority date: 1986-10-29
Filing date: 1987-09-07
Publication date: 1988-05-05
Anticipated expiration: 2007-09-07
Also published as: GB2196556B; GB8720969D0; NL8702543A; DE3732630A1; FR2606132A1; IT8612569A0; IT1200309B; FR2606132B1

Description

GB2196556A 1

SPECIFICATION sonic testing.

The process according to the invention con- Process for plugging tube plates by means sists of making an annular groove in the tube of braze-welded plugs -plate around each hole corresponding to a 70 damaged pipe, so as to create a holed spigot.

The subject matter of this invention consists Furthermore, the inside of the pipe has to be of a process for plugging tube plates of steam flared, for a depth substantially equal to that generators by means of braze-welded plugs, of said annular groove. Inside the flared hole It is known that a steam generator normally prepared as explained above, a thimble-shaped has a number of pipes located between two 75 plug is then inserted. This has an internal ta tube plates. per identical to that of the flaring of the hole The pipes in question separate the heating in the tube plate.

fluid from the heated fluid, and this separation This thimble-shaped plug may be made by may be interrupted if one or more of the turning and boring a bar of suitable material.

pipes is damaged. 80 Once the thimble-shaped plug has been ob- In this case, it is the known procedure, after tained, a layer of solder is deposited on its identifying the broken pipe, to seal it off from outer surface, extending at least for an area the steam generator by plugging its ends at corresponding to the surface of contact be the height of the two tube plates. tween the outer surface of the plug and the In general this operation is not easily per- 85 flared hole in the tube plate into which the formed since the headers located next to said plug has to be inserted.

tube plates often have limited dimensions. The The depth of the thimbleshaped blind hole difficulties increase in the case of very com- made in the plug shall be at least as deep as plex steam generators, in which the tube bun- the area of contact between the inside surface dle is made up of a large number of pipes, 90 of the flared hole in the tube plate; further very close to one another. more, it is preferable for the internal diameter According to a known procedure, solid spi- of this blind hole to be equal to the inside gots are inserted into the ends of the damdiameter of the pipes of the steam generator.

aged pipes and are then welded to the tube It is also advisable for the wall of the thim- plate by means of a continuous corner-seam 95 ble-shaped plug and the wall of the holed spi weld. got to be substantially identical.

To X-ray this weld seam it is however The process according to the invention then necessary to make a hole in the spigot which envisages the insertion of a heating cartridge has Just been welded in place, and to carry inside the blind hole in the thimble-shaped out the X-ray through this hole. A plug is then 100 plug, so as to melt the solder deposited on inserted into the holed spigot and is welded the outer surface of the plug.

to the upper edge of the holed spigot. Once it has melted, this solder penetrates As this new weld protrudes over the inter- slightly into the basic material of the tube nal surface of the tube plate, it is possible to plate and of the thimble- shaped plug.

X-ray it by transparency. 105 The thicknesses to be braze-welded are This process leads to complications if a relatively small and the solder is already pre- series of pipes near to one another have to sent over the whole area to be jointed (and be plugged, since welding of the spigot betherefore it does not have to penetrate into comes very difficult if it has to be carried out the coupling gap by capillarity); this facilitates with the presence of other already welded spi- 110 the local brazewelding heat treatment to bring gots in the vicinity. the plug and the holed spigot in the plate- to The welding process creates problems for the brazing temperature.

some materials particularly suitable for steam The braze-welding heat treatment is carried generators and having structures which tend out at a temperature of about 1000'C, and it to become brittle in the melted and altered 115 is therefore necessary to create a protective area. atmosphere around the heated pieces. This Other problems arise due to the difficult may be done either by means of inert gas or choice of the material to be added. by means of a vacuum.

Welding of these materials necessarily en- The conical coupling in the joining area has tails pre- or post-heating treatment and final 120 the advantage of forming the ideal gap re stress-relieving, which become very difficult to quired by the solder, and since the solder is carry out if the pieces to be secured together already present on the whole coupling surface, have very different thicknesses and sizes from there is no risk of trapping inclusions or air or one another. gas in the gap or of oxidation of the surfaces The purpose of this invention is to eliminate. 125 in the joining area.

the drawbacks mentioned and to achieve The braze-welded area may subsequently be plugging of the hole in the tube plates corre- checked by X-raying with a microfocus source sponding to both ends of the damaged pipe, operating inside the hole in the plug, or even using a braze-welding procedure which may by ultrasonic testing with a special focused be inspected both by X-raying and by ultra- 130 probes system to check the braze-welded -area 2 GB2196556A 2 from inside the plug. length equal to (a). The axial position of the After the non-destructive tests, the part of length (a) coated with solder is such that the plug which protrudes from the tube plate when the thimble-shaped plug 40 is inserted may be removed. in the hole 20, the area of contact between The essential characteristics of the invention 70 the outer surface of the hole 40 and the flared are summarized and schematically represented surface 24 of the hole 20 consists of said in the claims; the aims and advantages thereof area (a).

are also indicated in the following description At this point of the sealing process of the of forms of embodiment chosen by way of hole 20, a heating head 50 is inserted inside example only and with particular reference to 75 the blind hole present in the thimble-shaped the attached drawings, of which plug 40.

Figure 1 is a cross-section view of the end, The heat provided by the heating head 50 to be sealed off by means of a plug, of a hole causes the layer of solder deposited on the through a tube plate: portion of outer surface of the plug 20 and Figure 1 /A is a diametral section of a thim80 this molten solder penetrates into the micro- ble-shaped plug, to be used, according to the porosity of the material of which the plug is invention, to seal off the hole shown in figure made and of the material of the tube plate in 1; contact with same.

Figure 2 is a section similar to that shown It should be noted that no flow of molten in figure 1, and in which the thimble-shaped 85 material has to pass through the thin gap plug illustrated in figure 1/A has been in- existing between the outer surface of the plug serted; and the flared inner surface 24 of the hole 20 Figure 3 shows the brazing process of the: this would lead to blowholes and discontinui- thimble-shaped plug inside the hole in the tube ties in the joining area.

plate; 90 On the contrary, since the area (a) of the Figure 4 shows the final appearance of the plug 40 is already coated beforehand with hole sealed by the thimble-shaped plug after said solder, it is sufficient for this to melt to removal of the end of the plug protruding permeate the microporosity of the two oppo from the surface of the tube plate. site pieces, creating a perfect braze. After With particular reference to the above 95 brazing, the heating head 50 is taken out and figures, 10 indicates as a section a tube plate the protruding part 45 of the plug 40 is re and a hole 20 in same, which has to be moved with a tool.

plugged since the corresponding pipe, not It should be noted that an Xray or ultra- shown in the figure, is damaged and must be sonic head may be inserted inside the hole in sealed off from the steam generator. 100 the thimble-shaped plug for inspecting the The holes 20 in a tube plate are cylindrical brazing.

as shown in figure 1 by the continuous line It should also be noted that the wall of the 21 for most of the depth of the hole 20, and thimble-shaped plug is of the same order of by the dashed line 22 at the extreme right size as the thickness of the wall of the spigot end in the figure. 105 created by the groove 30: this ensures ab- According to the invention, an annular grove sorption of any expansion due to heating is made with a tool in the surface 23 of without prejudice for the weld.

the tube plate 10, around the hole 20. Subse- Although for descriptive reasons this inven- quently, still according to the invention, the tion is based on the above description and end part of the hole 20 is flared, as shown by 110 drawinqs by way of example only with parti the straight line 24. cular reference to the attached drawings, In this way, a hollow spigot 31 is formed many changes and variations may be brought around the end of the of the hole 20, the about within the scope of the invention.

thickness of which decreases gradually from

Claims

the root towards the end, due to the flared 115 CLAIMS wall 24. 1. A

process for plugging a hole in a tube The flared end of the hole 20 is suitable to plate, wherein the end part of the hole is take a thimble-shaped plug 40 having a sub- flared towards its outer end an annular groove stantially sernispherical bottom 41 and in any is made around the hole to a substantial axial case tapered, and a side-wall 42 internally 120 depth, and the hole is sealed off by means of cylindrical and externally conical, having the a blind plug whose outer surface has substan same taper as the flared wall 24 of the hole tially the same taper as the end part of the 20. hole, a layer of metal is provided between the The plug 40 may therefore be inserted in flared part of the hole and the plug so as to the hole 20 in such a way that, as illustrated 125 be in the area of contact between the plug in figure 2, the outer surface of the wall 42 and the wall of the hole, and the metal layer and the wall 24 are substantially in contact is melted by heat provided by a heating head with one another. inside a blind hole in the plug.

The outer surface 42 of the thimble-shaped
2. The process of Claim 1, wherein the plug 40 is coated with solder for an axial 130 metal layer is a coating on the outer surface 3 GB2196556A 3 of the plug.
3. The process of Claim 1 or 2, wherein the annular groove has a thickness generally equal to the thickness of the wall of the blind plug.
4. The process of any preceding Claim, wherein the annular groove defines a hollow spigot having a thickness generally equal to the thickness of the wall of the blind plug.
5. The process of any preceding Claim, wherein the axial depth of the annular groove is generally equal to the length of the flared part.
6. The process of any of Claims 1 to 4, wherein the axial depth of the annular groove is at least substantially equal to the axial length of the zone of contact between the plug and the wall of the hole.
7. The process of any of the preceding Claims, wherein a protruding part of the plug is removed after melting the metal layer.
8. A process for plugging a hole in a tube plate, substantially as herein described with reference to the accompanying drawing.
9. A tube plate which has been plugged by the process of any preceding Claim.

Published 1988 at The Patent Office, State House, 66/71 HighHolborn, London WC 1 R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD.

Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.