JPS6357130B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method of connecting pipes, and in particular to a method of connecting pipes suitable for reducing residual stress generated at the joints of pressure pipes used in pressure tube nuclear reactors. Regarding connection method.

[Background of the invention]

FIG. 1 shows the structure of a conventional pressure tube upper and lower rolled joint section applied to a pressure tube type nuclear reactor.

For both upper and lower rolled joint parts A and B, machining of parts other than pressure pipe 1 and pressure pipe 1
As shown in Figure 2, insert the punch 6 into the lower roll joint part, perform flare processing based on the inner diameter, and finish to the required surface finish accuracy.
The upper extension pipe 5 and the inner ring 3 are expanded using a roller expansion device inserted and installed inside the parts, and the upper extension pipe 5 and the lower extension pipe 2 at both ends of the pressure pipe 1 are mechanically connected to each other. It is a structure that connects.
Here, 4 is an outer ring which is a part for sandwiching the pressure pipe 1 at the upper roll joint part.

Note that the upper rolled joint portion side of the pressure pipe 1 is only subjected to surface finishing with the necessary precision.

This mechanical joining method provides the sealing function (airtightness) and mechanical strength against tension, bending, and torsion required for a rolled joint.

However, with this structure, the residual stress generated in the pressure pipe 1, especially in the lower rolled joint part B, may be relatively high.In order to improve the soundness and reliability of the pressure pipe 1, this residual stress must be reduced. If it is considered better to carry out local stress relief annealing after the rolled joint to reduce the residual stress to the target reduction target, it will require a lot of work time.

[Purpose of the invention]

The purpose of the present invention is to improve the soundness and reliability by reducing the residual stress generated in the pressure pipe at the rolled joint without performing local stress relief annealing after rolling the joint. .

[Summary of the invention]

The present invention was made based on the following study results.

The residual stress generated in the rolled joint pressure pipe is related to the radial displacement of the pressure pipe after jointing, especially in the lower rolled joint part.
The tip of the inner ring may come into contact with the tapered portion of the pressure tube and become relatively high because it is being pushed apart. As a countermeasure in this case, in the lower rolled joint part, the flare part of the pressure pipe is lengthened so that the tip of the inner ring does not touch the tapered part of the pressure pipe, and the shape is such that the tapered part is not pushed out. By making the change in wall thickness at the tip of the inner ring gentler and reducing the rigidity of the tip, the distribution of residual stress generated in the pressure pipe is smoothed and peaks are eliminated, and it is also possible to When processed, the wall thickness tolerance is ±7.5%, i.e.
The wall thickness changes by up to 15%, and the outer diameter after processing also changes by about twice the wall thickness after processing, which is approximately 15%.
In this case, the maximum outside diameter change is about 1.2 mm, but by expanding the tube using the rubber tube expansion method, which processes based on the outside diameter dimension, the outside diameter of the flare part of the pressure pipe can be finished with precision, and when rolled joint By setting the initial gap between the outer surface of the pressure tube and the inner surface of the lower extension tube to be close to 0 mm and reducing the radial displacement of the pressure tube due to roller tube expansion during rolled joint, the residual stress generated in the pressure tube can be reduced.

Also, in the upper roll joint part,
In order to further improve reliability and soundness, similar to the lower rolled joint, the change in wall thickness at the tip of the upper extension tube is made gentler and the rigidity of the tip is reduced, thereby reducing the rigidity of the pressure tube. We smoothed the distribution of residual stress to eliminate peaks, and also applied a small amount of flaring to the pressure pipe using the rubber tube expansion method, which processes based on the outer diameter, to finish the outer surface to the required accuracy and improve the outer surface of the pressure pipe at the time of jointing. By setting the initial gap on the inner surface of the outer ring to around 0 mm and reducing the radial displacement of the pressure tube due to roller tube expansion during roll joint, the residual stress generated in the pressure tube can be reduced.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 3 to 8.

FIG. 3 shows the structure of the upper and lower rolled joint parts according to the present invention. The lower rolled joint part B is composed of the pressure pipe 1, the lower extension pipe 2, and the inner ring 3. , insert a roller tube expansion device (not shown) inside the inner ring 3,
By expanding the tube from the inside with rollers (or rolling joint), the lower extension tube 2, pressure tube 1, and inner ring 3 are brought into close contact through mechanical coupling, resulting in a structure that has the necessary sealing function and mechanical strength. ing.

The upper rolled joint part A is composed of the outer ring 4, the pressure pipe 1, and the upper extension pipe 5, and is equipped with a roller tube expansion device (like the lower rolled joint part) inside the upper extension pipe 5. (not shown) and roll joint from the inside, the outer ring 4 pressure pipe 1 and upper extension pipe 5 are brought into close contact by mechanical coupling, and the structure has the necessary sealing function and mechanical strength. It is becoming.

In the processing of each part of the rolled joint part, in the case of the lower rolled joint part B, the pressure pipe 1 must be structurally flared from the base pipe (straight pipe) to widen it to a predetermined amount.

This flaring method is shown in FIGS. 4 and 5. Figure 4 shows the pressure pipe 1 before flaring, the 5th
The figure shows the state after flaring.

A straight pressure pipe 1 is inserted inside a mold 7, and a ring-shaped rubber 9 is placed inside the pressure pipe 1.
A shaft 9 with a mark attached thereto is inserted, and a protrusion 11 is provided at the tip of the shaft.

The flaring operation is carried out by moving the shaft 8 at the center in the direction of the arrow using a hydraulic cylinder 10, and
The rubber 9 is compressed at the axial joint, and since its volume is constant, it spreads in the radial direction, is loaded as internal pressure to the pressure pipe 1, and spreads until it contacts the inner surface of the mold 7 and deformation is restrained, completing the flaring work. do.

Here, when applying rubber tube expansion to the flare of a pressure tube, there are the following problems. First, in the case of conventional rubber tube expansion, as shown in the example of a heat exchanger, there are holes drilled in the tube plate and small diameter piping (outer diameter of about 10 to 40 mm).
Most of the pipes are used for connection with pipes, etc., and the amount of pipe expansion at this time is usually about 1% (maximum of 2 to 3% in conventional cases) in terms of change in outer diameter, but in the case of pressure pipes, It is very large, about 10%. Second, pressure pipes are made of high-strength material and have nearly twice the tensile strength of piping used in heat exchangers and the like.

That is, a large amount of deformation and a high flaring pressure are required, and it is also necessary to improve and stabilize the outer diameter dimensional accuracy of the post-flare pressure pipe.

FIGS. 4 and 5 show an example of pressure pipe flaring using rubber tube expansion that solves these problems.

Specifically, the shape of the mold is such that the center part has a large diameter and both ends have a small diameter, and the seal part of the rubber tube expansion is located in this small diameter part. This is to prevent it from spreading like this.

That is, the case where the small diameter part on the right side of the mold 7 shown in FIG. However, it could not follow the amount of deformation of the pressure pipe and could not flare at all.

Therefore, a small diameter portion was provided on the right side of the mold 7 to prevent the seal portion from deforming.

Further, if the a dimension at this time is too short, seal leakage will occur, so it is preferable to set the a dimension to about 20 mm or more.

As a result, the pressure at the sealing part is increased, and the pressure pipe, which is made of high-strength material, can be flared to a predetermined shape.By increasing the pressure above a certain level, the accuracy of the outside diameter of the pressure pipe can be improved, and it is also stabilized. I can figure it out.

After flaring the pressure pipe in this way, it is necessary to cut the unflared part by about 60 mm, but this cutting dimension was determined by setting the a dimension to the minimum value.
There is no need to purchase pressure pipes longer than necessary, and pressure pipe materials can be used effectively.

The total length of the pressure pipe is approximately 5m, and by cutting it by approximately 60mm, the purchase cost will not be high.We originally purchased a pipe that was longer than the product dimensions as a processing adjustment fee, so it was sufficient to fit within this range. This is the cutting fee.

As for the flare conditions for the pressure pipe 1, the flare pressure is approximately 1100Kgf/ ^cm2 to 1400Kgf/cm2 as shown in Figure 8.
There is no particular restriction on the upper limit of Kgf/cm ² or pressure, but from the standpoint of safety it is better not to be too high. Moreover, the pressure fluctuates somewhat due to variations in the pressure tube wall thickness. Therefore, considering safety and margin, the upper limit of the pressure is set at approximately 1400 Kgf/cm ² . The retention time is
By setting the time in the range of about 10 seconds to 30 seconds, the flare processing on the pressure pipe 1 is based on the outer diameter, and it is no longer affected by the wall thickness of the pressure pipe 1, and the amount of spring back after processing can be adjusted. This will change the outer diameter later. In addition, when the pressure is low, the amount of change in the outer diameter is about 1 mm as in the case of punch expansion, but when the pressure is increased to about 1100 Kgf/cm ² or more, the outer diameter varies from 0.2 mm to 0.4 mm. This improves the accuracy of the outer diameter dimension. Furthermore, although it is necessary to achieve finishing accuracy after cutting the unflared part, machining can be performed because the dimensional accuracy is good, and this processing allows the outside diameter of the pressure pipe flare part to be controlled within the tolerance range of machining. I can do it.

Note that parts other than the pressure pipe 1 are processed by general machining.

In the case of the upper rolled joint part A, similarly to the lower rolled joint part B, there is no need to structurally flare the pressure pipe 1 from the raw pipe, but if the raw pipe is left as it is, the outer diameter dimension will vary. Because there is
Flare the lower pressure pipe 1 in the same way as the flaring to increase the accuracy of the outer diameter dimension. Note that the amount of flaring may be about 1 mm for the upper part compared to about 20 mm for the lower part, and it is not necessary to perform flaring for all pressure pipes 1, but only for those with small outer diameter dimensions.

In the upper rolled joint part, as in the lower rolled joint part, other parts other than the pressure pipe 1 are generally machined.

FIG. 6 is a diagram showing the assembled state of each part of the lower rolled joint part B before the rolled joint. The gap δ ₀ between the inner surface of the lower extension pipe 2 and the outer surface of the flared part of the pressure pipe 1 is , can be reduced to a range of 0.2 mm or less by the processing method described above.

Incidentally, when the pressure pipe 1 is flared with the punch 6 shown in Fig. 2, the variation in the wall thickness of the pressure pipe 1 is directly affected by the outside of the flaring part of the pressure pipe 1 because the processing method is based on the inner diameter. This affects the diameter dimension, and for this reason the gap δ ₀ at the end is up to 0.8 mm.
That's about it.

The gap δ ₀ in the case of the upper rolled joint portion A is the gap between the inner surface of the outer ring 4 and the outer surface of the pressure pipe 1, and in this case, it can be set to 0.2 mm or less. In addition, when not flaring, the maximum range is about 0.4 mm.

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

The broken line shows the maximum residual stress distribution in the circumferential direction after rolling joint with the shape and method shown in Figure 1, and this value is high because the tip of the inner ring was pushing out the tapered part of the pressure pipe. was.

Therefore, local stress relief annealing (SR) was performed to reduce the residual stress as shown by the dashed line.

The solid line shows the residual stress measurement results using the shape and method according to the present invention, and it can be seen that the residual stress can be reduced considerably.

The same applies to the upper roll joint portion.

Therefore, in the case of the lower part of the pressure pipe rolled joint, it is necessary to smooth out the change in wall thickness at the tip of the inner ring, and to flare the pressure pipe with rubber tube expansion in the parts processing before the rolled joint. Although it is necessary to cut the unflared part, by finishing the outer surface with machining, the gap δ ₀ can be reduced and the residual stress generated in the pressure pipe after the rolled joint can be greatly reduced, and the lower rolled joint can be cut. The soundness and reliability of the substructure are greatly improved.

Also, in the upper roll joint part,
By smoothing the wall thickness change at the tip of the upper extension tube and flaring the pressure tube with a small amount of rubber expansion if necessary, the gap δ ₀ can be reduced and the residual stress generated in the pressure tube after the roll joint can be increased. As with the lower rolled joint, the soundness and reliability of the upper rolled joint structure are greatly improved.

〔Effect of the invention〕

As described above, according to the present invention, by reducing the residual stress in the lower rolled joint where the residual stress is relatively high without annealing, the soundness and reliability can be improved without requiring much work time. You can improve your sexual performance.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional pressure pipe roll joint, FIG. 2 is a diagram showing a conventional pressure pipe flaring method, and FIG. 3 is a sectional view of a pressure pipe roll joint according to the present invention. 4 is a diagram showing the state of the pressure pipe flare according to the present invention before flaring by rubber tube expansion, FIG. 5 is a diagram showing the state after flaring of the pressure pipe flare according to the present invention by rubber tube expansion, and FIG. FIG. 7 is a diagram showing the gap position, FIG. 7 is a diagram showing the effects of the present invention, and FIG. 8 is a diagram showing the relationship between flare pressure and outer diameter dimension. 1...Pressure pipe, 2...Lower extension pipe, 3...Inner ring, 4...Outer ring, 5...Upper extension pipe, 7...
...Mold, 9...Rubber.

Claims (1)

[Claims] 1 one end of the pressure tube is arranged between the outer lower extension tube and the inner inner ring, the other end of the pressure tube is arranged between the outer outer ring and the inner upper extension tube,
A rolled joint method in which a pressing force is applied from the inside of the inner ring to the outside, and a pressing force is applied from the inside of the upper extension tube to the outside, thereby pressure-welding the pressure tube with both the upper and lower extension tubes and the inner and outer rings. In this step, the joint part on the one end side of the pressure pipe before joining is set in a mold, the pipe is expanded from the inside using a viscous material, the unnecessary part of the pressure pipe is cut, and the outside diameter of the expanded part is machined. Then, one end of the pressure tube is machined between the inner ring and the lower extension tube so that the tapered part of the pressure tube does not overlap with the inner ring, which has a smooth wall thickness change at the tip. The rolled joint method is characterized in that the inner ring, which is disposed between the inner ring and the inner ring having a smooth thickness change at the tip thereof, is pressure-welded by applying a pressing force from the inside to the outside.