JPH0718531B2 - How to remove the heat transfer tube - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heat exchanger such as a steam generator, and particularly to a heat transfer tube partially expanded and fixed to its tube sheet. It concerns the method of removal.

[Prior Art] As shown in FIG. 5, a heat transfer tube 2 such as a heat exchanger.
Is inserted into the thick tube sheet 1 and is fixed to the tube sheet 1 by a method such as roller tube expansion or hydraulic tube expansion at its expanded portion or tube end portion 3 over a part or the whole thickness of the tube sheet 1. And is welded to the tube sheet 1 by the seal weld 4 at one end surface side of the tube sheet 1, that is, at the lower end surface in FIG. It has a structure that creates a seal between them. As well known to those skilled in the art, the heat transfer tube 2 may be extracted from the tube sheet for sampling after a certain period of operation by a method such as evaluating its structural integrity.

An example of a conventional pipe removing method for extracting the heat transfer tube 2 from the tube sheet 1 will be described with reference to FIGS. 7 (a) to (d). Cutting,
It was carried out according to the following steps, which involved a series of operations such as TIG arc heating of the guide surface of the tube expansion section 3 and drawing of the heat transfer tube 2.

That is, in the first step shown in FIG. 7 (a), the seal welding portion 4 of the heat transfer tube 2 to be extruded is cut and removed from the one end surface side of the tube sheet 1 by a rotary tool 5 such as an end mill. Next, as shown in FIG. 7 (b), the heat transfer tube 2 is cut in a ring-shaped shape in the wall thickness direction of the tube at a predetermined portion immediately above the sampling target portion. This ring cutting is performed from the inside of the heat transfer tube 2 using the rotary cutting tool 6 as shown in the figure. Numeral 7 is a circular cutting section. After that, in order to relax the stress of the expanded tube portion 3, as shown in FIG. 7 (c),
Insert the TIG arc heating torch 8 from the one end surface side of the tube sheet 1 into the expulsion target portion, scan the inner surface of the tube expansion portion 3 of the heat transfer tube 2 in the axial direction as indicated by the double-headed arrow, and scan the inner surface in the axial direction. The wire is heated and melted to weaken the fixing force between the tube sheet 1 and the heat transfer tube 2. Finally, as shown in FIG. 7 (d), a cutting tool 9 having a screw-shaped blade shape is turned on the pipe expanding portion 3 of the heat transfer tube 2 from which the seal welding portion 4 is removed, from the inside of the tube sheet 1. After screwing in, the cutting tool 9 is pulled downward to complete the partial extubation.

As is clear from FIGS. 5 and 6, the above pipe removing method is carried out for a heat transfer tube having a circular cross-sectional shape and an outer diameter of the unexpanded portion smaller than the hole diameter of the tube sheet. However, there are various types of heat transfer tubes, and there are also heat transfer tubes having a maximum outer diameter larger than the hole diameter of the tube sheet, for example, a heat transfer tube having a protrusion or a rib.

[Problems to be Solved by the Invention] Therefore, in the conventional pipe removing method, even if an attempt is made to pull out a heat transfer tube whose maximum outer diameter portion is larger than the hole diameter of the tube sheet, the maximum outer diameter portion passes through the hole of the tube sheet. However, there is a problem that it cannot be applied to such a heat transfer tube.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a method for removing a heat transfer tube, which can extract even a heat transfer tube having a maximum outer diameter portion larger than the hole diameter of the tube sheet. It is a thing.

[Means for Solving the Problems] In order to achieve the above-mentioned object, according to the present invention, the tube is inserted into a hole of a thick tube plate traversing the inside of the heat exchanger body, and expanded and fixed at a portion in the hole. Seal welded to one end surface of the tube sheet,
A method for removing a heat transfer tube having circumferentially spaced axial projections on the outer surface of a portion other than the tube expansion fixing portion, wherein the seal welding portion is cut off, and the tube sheet is inserted from the other end surface side of the tube sheet. Cut the heat transfer tube at a position away from the outside,
Among the heat transfer tube portions retained in the hole of the tube sheet by cutting and remaining, in the heat transfer tube wall of the inter-projection portion without the projections, the slot opened at the cut end of the heat transfer tube is axially formed. It is formed, and the tube expanding and fixing part is heated from inside the hole of the tube sheet to relax it, and then the heat transfer tube part is pulled out.

[Operation] In the removing method of the present invention, when the heat transfer tube portion to be extruded is pulled out after heating the tube expansion fixing portion in the hole of the tube sheet,
The end of the ridge first comes into contact with the peripheral edge of the hole in the tube sheet,
Since the heat transfer tube wall without protrusions has a step of axially forming a slot to be opened at the cut end of the heat transfer tube in the heat transfer tube wall, when the drawing operation is continued, the protrusion section that defines the slot is formed. Bends inward in the radial direction, and the maximum outer diameter becomes smaller than the hole diameter. Therefore, even if the heat transfer tube portion to be extruded has a diameter larger than the hole diameter of the tube sheet, it can be pulled out from the tube sheet.

[Embodiment] Next, a preferred embodiment of the method for removing a heat transfer tube according to the present invention will be described in detail with reference to FIGS. 1 to 4, in which the conventional method shown in FIGS. The same reference numerals as those used for the technology indicate the same or corresponding parts.

FIG. 1 is a cross-sectional view showing a state in which a heat transfer tube 2 to which the present invention can be applied is expanded and fixed to a tube plate 1, and FIG. 2 is II of FIG.
It is a II sectional view. As you can see from these figures,
In addition, like the circular heat transfer tube shown in FIG. 5, the heat transfer tube 2
Is inserted into a thick tube sheet 1 that traverses the body of a heat exchanger (not shown), and its expanded portion or tube end portion (expanded fixed portion) 3 over a part or the whole thickness of the tube sheet 1 Then, it is typically fixed to the tube sheet 1 by a method such as roller tube expansion or hydraulic tube expansion, and a seal is made at one end surface side of the tube sheet 1, that is, at the lower end surface as seen in FIG. The welded portion 4 is seal-welded to the tube sheet 1 to form a seal between both end surfaces of the tube sheet 1. Further, as is apparent from FIGS. 1 and 2, several (four in the embodiment, four at 90 ° circumferential intervals) ridges or ribs 2a are formed on the outer surface of the heat transfer tube 2 to form a tube sheet. The dimension between the radially outermost portions of the pair of ridges extending in the axial direction from slightly above the other end surface of 1 and facing each other in the radial direction, that is, the diameter d ₁ of the maximum outer diameter portion is It is larger than the diameter d _{2 of} a hole.

When pulling out such a heat transfer tube 2 from the tube sheet 1 according to the present invention, the end portion of the seal welded portion 4 between the tube sheet 1 and the heat transfer tube 2 is end milled in the same manner as in the step of the conventional method shown in FIG. Is cut by a mechanical method using, or cut by an electric method such as electric discharge cutting or machining, and then the heat transfer tube portion to be extruded is retained in the hole of the tube sheet 1 and left, 2 is cut in a slice shape in the thickness direction. This cutting method may be performed as described with reference to FIG. 7 (b), or may be performed by the mechanical method or the electrical method described above.

Next, as is clear from FIG. 3 which shows only the expulsion target portion (heat transfer tube portion) of the heat transfer tube 2, an appropriate space between adjacent ridges of the heat transfer tube 2 with ridges, that is, a portion between ridges without ridges. (In the embodiment, a total of four pieces are provided between all adjacent ridges) are longitudinally cut to form slots 2b extending in the axial direction, and the state is like a bamboo sword of kendo. It is essential that the slot 2b is opened to the cut end 2c of the heat transfer tube 2. In this case, the slot width in the circumferential direction takes into consideration the height of the ridges 2a or the ratio of the diameters d ₁ and d ₂ described above, and when the axial portion remaining after the longitudinal cutting is focused in the radial direction, The outside diameter is appropriately determined so as to be smaller than the diameter d ₁ . After this, as shown in FIG. 7 (c), the tube expansion portion 3 of the heat transfer tube 2 with respect to the tube sheet 1 is axially moved from the inside of the tube sheet 1 to the inner surface of the heat transfer tube by TIG arc heating, as in the case of the normal tube removal work. After melting and fusing several lines in the direction to relax the fixing force between the tube sheet 1 and the heat transfer tube 2, as shown in FIG. 4, the tool of FIG. 7 (d) having a screw blade shape. A tool 9 similar to the above is screwed into the lower end of the heat transfer tube 2, and the part of the heat transfer tube 2 to be removed is pulled out in the direction indicated by the arrow.

At this time, each ridge 2a becomes gradually thinner toward the tube sheet 1 side.
The tapered end part 2d of the guide plate serves as a guide, and the heat transfer tube 2
Will slide into the hole of the tube sheet 1. When the pulling-out operation is continued, the ridged portion defining the slot 2b bends inward in the radial direction, and the maximum outer diameter d ₁ becomes smaller than the hole diameter d ₂ . Therefore, even the heat transfer tube 2 to be extruded, which initially had the maximum outer diameter d ₁ larger than the hole diameter d _2, can be easily pulled out from the tube sheet 1.

[Advantages of the Invention] As described above, according to the heat transfer tube removing method of the present invention, the slot opened to the cut end of the heat transfer tube is axially formed in the heat transfer tube wall of the inter-projection section without the projections. Therefore, when the heat transfer tube is pulled out, each portion having the ridge is bent inward in the radial direction, and the outer diameter of the portion having the gathered ridge is smaller than the hole diameter of the tube sheet. Therefore, it is possible to easily pull out a heat transfer tube such as a ribbed heat transfer tube having an outer diameter larger than the hole diameter, which could not be solved by the conventional removal method, and to properly maintain the soundness of this type of heat transfer tube. Can be evaluated.

[Brief description of drawings]

FIG. 1 is a sectional view showing a heat transfer tube to which the present invention can be applied in a state of being expanded and fixed to a tube sheet, FIG. 2 is a sectional view taken along line II-II of FIG. 1, and FIG. FIG. 4 is a perspective view showing a state in which a slot is provided in an expulsion target portion of a heat tube, FIG. 4 is a schematic perspective view showing a final step of a method for removing a heat transfer tube according to the present invention, and FIG. 5 is extruded by a conventional removal method. FIG. 6 is a cross-sectional view showing a heat transfer tube in a state of being expanded and fixed to a tube plate, FIG. 6 is a cross-sectional view taken along line VI-VI of FIG. 5, FIGS. 7 (a) and (b),
(C) And (d) is sectional drawing explaining each step of the conventional removal method. 1 ... Tube plate, 2 ... Heat transfer tube, 2a ... Projection, 2b ... Slot, 2c ... Cut end of heat transfer tube, 2d ... Projection end, 3 ...
Expansion part or pipe end (expansion fixed part), 4 ... Seal weld.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (71) Applicant 999999999 Japan Atomic Power Company 1-6-1, Otemachi, Chiyoda-ku, Tokyo (71) Applicant 999999999 2-5-1 Marunouchi, Chiyoda-ku, Tokyo No. (72) Inventor Kazuo Tanimoto 2-1-2 Watanabe-dori, Chuo-ku, Fukuoka-shi, Kyushu Electric Power Co., Inc. (72) Inventor Masaru Shimizu 1-1-6 Otemachi, Chiyoda-ku, Tokyo Nihon Nuclear Power Incorporated (72) Inventor Susumu Masano 2-1-1 Niihama, Arai-cho, Takasago-shi, Hyogo Mitsubishi Heavy Industries, Ltd. Takasago Research Laboratory (72) Inventor Seiji Beppu 2-1-1 Shinhama, Arai-cho, Takasago-shi, Hyogo Mitsubishi Takasago Research Institute, Heavy Industries, Ltd. (72) Inventor Naruo Sakamoto 2-1-1, Niihama, Arai-cho, Takasago-shi, Hyogo Mitsubishi Heavy Industries Stock Association Takasago Laboratory (72) Inventor Yoshihisa Nishikawa 2-1-1 Niihama, Arai-cho, Takasago-shi, Hyogo Mitsubishi Heavy Industries, Ltd. Takasago Laboratory (72) Inventor Akihiko Kimura 2-1-1 Niihama, Arai-cho, Takasago, Hyogo Mitsubishi Heavy Industries Takasago Research Institute Co., Ltd. (72) Inventor Takaya Kusakabe 1-1-1 Wadasaki-cho, Hyogo-ku, Kobe-shi, Hyogo Mitsubishi Heavy Industries Ltd. Kobe Shipyard

Claims (1)

[Claims] 1. A thick tube plate that traverses the inside of a heat exchanger body is inserted into a hole in the thick tube plate to be expanded and fixed at a portion within the hole, and is seal-welded to one end surface side of the tube plate, not to the expanded tube fixing portion. A method for removing a heat transfer tube having axial projections circumferentially spaced on the outer surface of a portion, wherein the seal weld is cut off and separated from the other end surface side of the tube sheet to the outside of the tube sheet. The heat transfer tube is cut at a position where the heat transfer tube is retained in the hole of the tube sheet by cutting, and then the heat transfer tube wall is formed on the heat transfer tube wall of the inter-projection section without the projection. A method for removing a heat transfer tube, in which a slot opened to a cut end of the heat tube is formed in an axial direction, the tube expansion fixing portion is heated and relaxed from inside the hole of the tube sheet, and then the heat transfer tube portion is pulled out.