JPS6143128B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for connecting pipes, and more particularly to a method for connecting pipes suitable for reducing residual stress generated at the joints of pressure pipes used in pressure tube nuclear reactors.

Conventional pressure tubes applied to pressure tube reactors
Figure 1 shows the structure of the lower roll joint.

After each part of the upper and lower roll joint parts A and B is finished, the upper extension pipe 5 or inner ring 3 is expanded using a roller expansion device inserted inside.
The pressure pipe 1 is connected to the lower extension pipe 2 and the upper extension pipe 5. 4 is an outer ring. Such a joint provided the necessary sealing function and mechanical strength as a rolled joint. However, in this structure, the residual stress generated in the pressure pipe 1 is high, especially in the lower rolled joint part A, and it is necessary to reduce the residual stress in order to improve the soundness of the pressure pipe, and this requires a large amount of time. A necessary local stress relief annealing had to be performed.

An object of the present invention is to reduce residual stress occurring at the joints of tubes.

In the present invention, the end of the second tube is inserted between the first tube and a ring attached to the end of the first tube, the ring is present inside the second tube, and the ring is attached to the tip of the ring. In the pipe joining method of joining the first pipe and the second pipe by expanding the first pipe or the ring which has been subjected to a taper processing treatment, the first pipe
The tube and one member located on the outside of the ring are heated so that the inner diameter of the one member becomes larger than the outer diameter of the first two tubes, and the one member is returned to its original state. The first step before cooling to the
inserting an end of the second tube between the tube and the ring, and then joining the first tube and the second tube by expanding the tube after the one member has cooled. A pipe connection method characterized in that, according to this connection method, the rigidity of the tapered part tends to be weaker than other parts, so that when receiving a pipe expansion force, the second pipe is The second part can also be used to buffer against forceful expansion at the end of the inner member.
In addition to reducing the stress and smoothing the stress distribution in the region corresponding to the tapered portion of the tube and the tapered portion, since the second tube is inserted after the heating, the second tube is heated. It is possible to use a pipe with a diameter as large as possible, which means that the amount of pipe expansion required during the subsequent pipe expansion is small, and the increase in stress due to pipe expansion is also small, resulting in a good pipe connection with little residual stress overall. .

An outline of an embodiment of the present invention is as follows.

The residual stress that occurs in the pressure pipe at the rolled joint is related to the radial displacement of the pressure pipe during rolled joint, and especially at the lower rolled joint, the tip of the inner ring pushes the tapered part of the pressure pipe wider. The price was relatively high because of this.

Therefore, in the lower rolled joint part, the tip of the inner ring should be separated from the tapered part of the pressure pipe, so that the tapered part is not pushed out, and the thickness of the tip of the inner ring should change gradually. This smoothes the distribution of residual stress and eliminates peaks.Furthermore, by heating the lower extension tube and inserting the pressure tube between them during component assembly before rolling joint, the outer surface of the pressure tube and the inner surface of the lower extension tube are heated. By making the initial gap negative or close to zero and reducing the radial displacement of the pressure pipe due to roller expansion during rolled joint,
Measures to reduce residual stress.

In addition, in the upper roll joint part,
By making the wall thickness change at the tip of the upper extension tube gentler, the distribution of residual stress is smoothed and peaks are eliminated, and by heating the outer ring and inserting the pressure tube between them, the outer surface of the pressure tube and the outer ring are The initial gap with the inner surface is negative or close to zero, and the radial displacement of the pressure pipe due to roller expansion during roll joint is reduced to reduce residual stress.

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIGS. 2 to 4.

FIG. 2 shows the structure of the rolled joint part. The lower rolled joint part B is composed of a pressure pipe 1, a lower extension pipe 2, and an inner ring 3.
A roller tube expansion device is installed inside the inner ring 3 (not shown).
The lower extension tube 2, pressure tube 1, and inner ring 3 are brought into close contact by inserting the tube and expanding the tube from the inside (hereinafter referred to as a rolled joint), thereby providing the necessary sealing function and mechanical strength.

Further, the upper roll joint part A is composed of an outer ring 4, a pressure pipe 1 and an upper extension pipe 5,
A roller tube expansion device is inserted into the upper extension pipe 5 in the same way as the lower rolled joint part, and the outer ring 4, pressure pipe 1, and upper extension pipe 5 are brought into close contact with each other by rolling the joint from the inside. The structure has a strong sealing function and mechanical strength.

Each part of the rolled joint part is manufactured by mechanical processing, etc., but in the case of the lower rolled joint part B, it is structurally necessary to widen the pressure pipe 1 by flaring it from the base pipe (straight pipe). be. At this time, the outer diameter dimensional accuracy of the flare portion 8 is greater than the inner diameter dimensional accuracy of the lower extension tube 2, which is a machined part. Considering the gap required for parts assembly, the flare part 8
The gap between the outer diameter of the lower extension tube 2 and the inner diameter of the lower extension tube 2 needs to be in the range of 0.03 to 0.8 mm on one side during normal parts assembly and subsequent rolled joint work. Similarly, in the case of the upper rolled joint part A, a gap of 0.01 to 0.43 mm is required.

The tip of the inner ring 3 of the lower rolled joint part B is designed to smooth the deformation that occurs in the pressure pipe 1 when the pressure pipe 1 is pushed out by the inner ring 3 during the roll joint. The purpose is to reduce residual stress by smoothing the distribution of residual stress and eliminating peaks.

The same applies to the upper roll joint portion A.

The residual stress generated in the rolled joint pressure pipe 1 in the structure shown in FIG. 2 can be reduced compared to the structure shown in FIG. 1, but as a method for further reducing it,
The lower roll joint portion will be explained with reference to FIG. 3 as an example.

The pressure pipe 1 is subjected to flaring processing similar to the conventional method, and the inner diameter of the contact portion with the flare portion 8 of the lower extension pipe 2 is machined to be smaller than the outer diameter of the pressure pipe 1. The inner ring 3 has the same processing dimensions as the conventional one.

When assembling the parts, first, the lower extension tube and the inner ring 3 are screwed together.

In this state, connect the lower extension tube 2 to the outer heating coil 6.
Heat it up. In this case, the appropriate heating range is considered to be heating section 7 (the section in FIG. 3).

By heating the lower extension tube 2, the lower extension tube 2 thermally expands and its inner diameter also increases. Therefore, when the heating section 7 of the lower extension tube 2 reaches a predetermined temperature, heating is stopped and the pressure tube 1 is inserted.

At this time, if the inner ring 3 is also heated in the same way as the lower extension tube 2, the inner diameter of the flared portion 8 may come into contact with the outer diameter of the inner ring 3, making it impossible to insert the flared portion 8, but this is not necessary. According to
Measures shall be taken to cool the inside of the unit using a cooler.

The flared portion 8 of the pressure tube 1 is inserted into the lower extension tube 2, and after the lower extension tube 2 has cooled, a rolled joint is performed to complete a structure having the necessary sealing function and mechanical strength.

The upper roll joint part A is also carried out in the same manner. That is, the outer ring 4 is attached to the upper extension tube 5, and then the outer ring 4 is heated. The pressure pipe 1 is inserted between the outer ring 4 and the upper extension pipe 5, and after the outer ring 4 has cooled, the pressure pipe 1 and the upper extension pipe 5 are rolled together.

When heating the lower extension tube 2 (or outer ring 4 in the case of the upper rolled joint),
The material of the pressure tube 1 inserted after heating is a zirconium alloy, and considering the final heat treatment temperature during manufacturing, the pressure tube 1 is made of a zirconia alloy.
400℃ as a guide, and after inserting pressure tube 1
Even if the lower extension tube 2 comes into contact with the lower extension tube 2 and immediately becomes the same temperature as the lower extension tube 2, there will be no problem in terms of the material.

In addition, when heating the lower extension tube 2, it is better to heat the lower extension tube 2 uniformly and in a short time.
High-frequency heating is considered to be suitable as a heating method because it prevents the temperature of the inner ring 3 from rising and also facilitates the insertion of the pressure tube 1.

The effect of reducing residual stress will be explained by taking the lower rolled joint part as an example in FIG.

In Fig. 4, the mark □ indicates the maximum circumferential residual stress generated in the pressure pipe 1 with the structure shown in Fig. 1, and it is related to the amount of change δ in the inner diameter of the inner ring 3 before and after the rolled joint. show.

The circle mark indicates the circumferential residual stress generated in the pressure pipe 1 in the structure shown in FIG. 2 in relation to the amount of change δ in the inner diameter of the inner ring 3 before and after the rolled joint.

Comparing the □ and ○ marks, when δ is approximately 0.7 mm, it is approximately 66Kgf/mm ² (note that this value is the value before stress relief annealing, and after stress relief annealing it will be reduced to approximately 30Kgf/mm ² ) has a maximum residual stress of approximately 35Kgf/
mm ² , which is a reduction of approximately 27Kgf/mm.

The above δ, that is, the amount of displacement of the inner ring 3 before and after the rolled joint, cannot be determined until after the rolled joint. Therefore, the residual stress generated in the pressure pipe 1 cannot be determined until after the rolled joint.

The △ symbol allows you to determine the degree of residual stress that will occur in the pressure pipe 1 when assembling the parts before rolling joint. Gap δ
₀ and the circumferential residual stress generated in the pressure pipe 1. Section C shows a shrink fit.

When the rolled joint shown in FIG. 2 is manufactured using the conventional method, the lowest residual stress occurs when the initial gap δ ₀ is the minimum, and its value is approximately 22 Kgf/mm ² . According to the method, this decreases again, and when the previous heating temperature is set to 400℃, δ ₀ shown in Figure 3 can be adjusted by about 0.2 mm, so it is about 15
It will be about Kgf/mm ² .

Therefore, in the case of the lower part of the pressure pipe rolled joint, it is necessary to smooth the change in wall thickness at the tip of the inner ring, and to heat the lower extension pipe when assembling the parts before the rolled joint. By adopting the shrink fit method of inserting the pressure pipe and then processing the rolled joint, the residual stress that occurs in the pressure pipe after the rolled joint can be greatly reduced. The soundness of the substructure is greatly improved.

Similarly, for the upper rolled joint part, by smoothing the wall thickness change at the tip of the upper extension tube and by adopting a shrink fit method in which the outer ring is heated and the pressure tube is inserted, the lower Similar to the rolled joint part, residual stress can be reduced, and the soundness of the upper rolled joint part structure is greatly improved.

In addition, when assembling parts before rolling joint, it is possible to estimate the residual stress generated in the pressure pipe after rolling joint, and if the residual stress is likely to be high, it is possible to reduce the residual stress by changing the combination of parts, etc. There is no need to manufacture a rolled joint part.

According to this embodiment, it is possible to estimate the degree of residual stress that will occur in the pipe after the rolled joint when assembling parts, and in the case of a combination that will result in high residual stress, the combination This is a rolled joint processing method that can prevent the residual stress from becoming high by changing the amount of stress, and can further reduce the residual stress, and the soundness of the rolled joint part is greatly improved.

As described above, according to the pipe connection method according to the present invention, the rigidity of the tapered part applied to the pipe or ring tends to be weaker than other parts, so when the pipe is subjected to expansion force, the outer periphery of the tapered part It is possible to buffer the tube from being forced wide at the end of the tube, which is present in the pipe, and reduce the stress and smooth the stress distribution in the part corresponding to the tapered part of the pipe and that taper part, and also to reduce the stress on the outermost pipe or ring. Since the pipes to be connected are inserted after heating, the diameter of the pipes to be connected can be as large as possible, and the amount of expansion (displacement) required during subsequent tube expansion can be reduced. The increase in stress is also small, and even when connecting tubes by expanding the tubes, it is possible to obtain a good tube connection portion with generally little residual stress.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a conventional rolled joint part of a pressure pipe, Fig. 2 is a sectional view of a rolled joint part of a pressure pipe according to the present invention, and Fig. 3 is a shrink fit operation during rolled joint work. Figure 4 is a cross-sectional view of the lower rolled joint of the pressure pipe showing the amount of change in the inner ring inner diameter of the lower rolled joint, the initial gap between the outer surface of the pressure pipe and the inner surface of the lower extension pipe, and the circumferential residual that occurs in the pressure pipe. It is a figure showing the relationship with stress. 1...Pressure pipe, 2...Lower extension pipe, 3...Inner ring, 4...Outer ring, 5...Upper extension pipe, 6...
...Heating coil.

Claims (1)

[Claims] 1. The end of a second tube is inserted between the first tube and a ring attached to the end of the first tube, and the end of the second tube is present inside the second tube and the tip is tapered. In the pipe joining method of joining the first pipe and the second pipe by expanding the first pipe or the ring which has been subjected to heating the first member so that the inner diameter of the one member becomes larger than the outer diameter of the first two pipes, and before the one member is cooled to its original state, the first pipe is heated. and the end of the second tube is inserted between the ring, and after the one member has cooled, the first tube and the second tube are joined by the tube expansion. How to connect pipes.