JPS6362992A - Low residual stress type pipe body connecting structure - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a low residual stress type pipe connection structure, particularly for pipes used in corrosive environments of materials such as atomic couplants, thermal power plants, and chemical plants. The present invention relates to a low residual stress type tube connection structure suitable for reducing residual stress generated in a connection portion.

[Conventional technology]

As shown in FIG. 6, the conventional sandwich-type tube connection structure for tubes consists of inserting an inner tube 1 to be connected between an outer tube 2 and an inner ring 3 for support. It was a jointed structure.

In this joining method, as shown in FIG. 6, a joining groove 4 is provided on the inner surface of the outer tubular body 2, and
By pushing in the mandrel 5, the tube is expanded by rollers 6, and the tube 1 and inner ring 3 are mechanically expanded and joined to the tube 2.

[Problem that the invention seeks to solve]

Fig. 7 is an explanatory diagram of the residual stress distribution generated on the inner surface of the pipe body 1 near the joint part measured in the conventional connection structure.
The figures are diagrams showing the results, where (a) is a diagram showing axial residual stress, and (b) is a diagram showing circumferential residual stress.

From FIGS. 8(a) and 8(b), both the axial residual stress and the circumferential residual stress show high tensile residual stress in the portion A near the tip of the inner ring.

This high tensile residual stress causes material failure such as stress corrosion cracking or hydrogen delayed cracking of the tube 1 due to corrosion of the material by the internal fluid flowing inside the tube 1.

Therefore, it is necessary to keep this residual stress below the critical stress value at which stress corrosion cracking or hydrogen delayed cracking occurs.

One method for reducing this residual stress is to heat the portion A in FIG. 7 to remove the stress after the connection work is completed.

However, in this method, it is necessary to cool part B in order to maintain the bonding strength at the joint, and a complicated and expensive device with heating and cooling functions is required. Moreover, stress relief annealing requires a large amount of working time and has the disadvantage that it is extremely uneconomical.

Therefore, it is necessary to improve the connection structure to reduce residual stress without increasing the number of work steps, without using special equipment, and without reducing the sealing performance and mechanical strength of the connection. there were.

An object of the present invention is to provide a low residual stress type tube connection structure that can prevent material failure due to residual stress at a connection portion of a tube used in a corrosive environment.

[Means for solving problems]

The above purpose is to reduce the residual stress generated on the inner surface of the inner tube near the tip of the inner ring of the sandwich type tube connection structure.
As shown in the figure, we focused on the force Q that pushes and expands the inner tube due to the expansion of the inner ring, and the elastic recovery forces P1 and P2 due to the outer tube. Since the inner tube does not come into direct contact with the internal fluid, stress corrosion cracking does not occur, and the inner surface of the inner ring receives the elastic recovery force of the outer and inner tubes. , compressive stress is generated, and material failure such as stress corrosion cracking or hydrogen delayed cracking does not occur on the inner surface of the inner ring.As a result, material failure due to corrosion may occur in the sandwich type pipe connection structure. This is the part of the inner tube that is in contact with the internal fluid and near the tip of the inner ring where residual stress is high.In order to reduce this residual stress, the pressing force by the inner ring is It is thought that the elastic recovery forces Ps and P2 of the outer pipe body are reduced, but since the pressing force Q is directly related to the bonding force of the joint, the reduction in the pressing force Q is This is undesirable because it causes a decrease in the bonding force. Also, of the elastic recovery forces P1 and P2, the degree to which they affect the residual stress in part A is P due to the relationship between force and moment due to distance.
l is considerably larger than P2, and therefore this is achieved by reducing the elastic recovery force P1.

Here, in order to reduce the elastic recovery force P1, it is sufficient to reduce the rigidity of the outer tubular body corresponding to Pl, in other words, it is sufficient to reduce the volume. However, the problem here is that Since the rigidity of the outer tube greatly contributes to the bonding force at the joint, a large decrease in the stiffness of the outer tube will result in a decrease in the bonding force at the joint. Since the stiffness of the tube directly contributes to the bonding force,
Stiffness cannot be reduced. The above description has been made for the case where the outside is a tube body, but the same applies to the case where the outside is a tube plate.

As described above, in the present invention, firstly, in order to effectively reduce residual stress with a small decrease in rigidity, the present invention is applied to the position where the moment is as large as possible, that is, near the joining groove on the inner surface of the outer tube body or tube sheet. Second, a circumferential groove is provided in the portion located near the outer end of the inner ring on the inner surface of the outer tube body or tube plate. The above object was achieved by using a structure in which two grooves were also provided.

[Effect]

Since a circumferential groove is provided in a portion of the inner surface of the outer tube body or tube sheet near the joining groove, the contact area between the tube body and the tube body or tube sheet can be reduced. Pressing can reduce residual stress by lowering the direction PI. Second, in addition to the first groove in the circumferential direction, a second groove in the circumferential direction is also provided in a portion located near the outside of the end of the inner ring, which further reduces residual stress. can be reduced.

〔Example〕

The present invention will be described in detail below with reference to the embodiments shown in FIGS. 1, 3, and 5, and FIGS. 2 and 4.

FIG. 1 is a longitudinal cross-sectional view showing an embodiment of the low residual stress type tube connection structure of the present invention, and FIG. 2 is a residual stress distribution diagram in FIG. 1, where (a) shows the axial residual stress distribution, b) is a diagram showing the circumferential residual stress distribution. Figure 1 shows the inner tube 1,
It is composed of an outer tube 2 and an inner ring 3, and a circumferential groove 7 is provided on the inner surface of the tube 2 near a joining groove 4 provided inside the outer tube 2.

According to the structure shown in FIG. 1, the contact area between the tube 2 and the tube 1 in the vicinity of the joining groove 4 is extremely small, so the elastic recovery force Pz of the tube 2 that presses the tube 1 is extremely small. It becomes minute.

As a result, the moment due to Pl applied to the A section of the tube body 1 becomes smaller (see Fig. 7), so the axial residual stress and the circumferential residual stress generated on the inner surface of the tube body 1 at the A section are reduced as shown in Fig. 2 (a). ) and (b), it can be significantly reduced.

Note that the stress caused by the pressure of the internal fluid is generally designed to be below the elastic limit of the material of the tube, so the deformation of the tube 1 is as small as 0.2% or less, and the outer surface of the tube 1 is The cutout portion, that is, the groove 7, does not swell and always maintains a healthy shape.

FIG. 3 is a longitudinal sectional view corresponding to FIG. 1 showing another embodiment of the present invention, and the same parts as in FIG. 1 are designated by the same reference numerals.

FIG. 4 is a residual stress distribution diagram in FIG. 3, in which (a) is a diagram showing the axial residual stress distribution, and (b) is a diagram showing the circumferential residual stress distribution. In FIG. 3, the joining groove 4 of the tube body 2 is
A circumferential groove 7 is provided on the inner surface of the tube body 2.
A circumferential groove 8 is provided near the outer end of the inner ring 3 on the inner surface of the inner ring 3, thereby increasing the elastic recovery force P2 shown in FIG.
As shown in FIG. 4, the residual stress can be further reduced.

FIG. 5 is a longitudinal sectional view corresponding to FIG. 1 showing still another embodiment of the present invention, and FIG. 5 shows a case where a tube body is connected to a tube plate. In FIG. 5, a tube body 10 is connected to a tube plate 9 by an inner ring 11.
In this case, grooves 12 and 13 are provided on both sides of the portion of the tube sheet 9 that contacts the tube body 10, and each groove 12 is provided on the left and right sides of the tube sheet 9 near the joining groove 14. Each groove 13 is provided near the outer end of the inner ring 11 outside the respective groove 12. According to the embodiment shown in FIG. 5, the residual stress generated on the inner surface of the tube body 10 at the tip of the inner ring 11 can be reduced.

〔Effect of the invention〕

As explained above, according to the present invention, when the tube body or tube sheet and the tube body are connected in a sandwich type using the inner ring, the inner surface of the connecting portion of the outer tube body or tube sheet has a circumferential surface. Since the directional grooves are provided, the residual stress generated in the inner pipe body can be reliably reduced, which has the effect of preventing the occurrence of material failure such as stress corrosion cracking or hydrogen delayed cracking caused by residual stress. .

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing one embodiment of the low residual stress type tube connection structure of the present invention, FIG. 2 is a residual stress distribution diagram in FIG. 1, and FIG. 3 is a diagram showing another embodiment of the present invention. Fig. 4 is a longitudinal cross-sectional view corresponding to Fig. 1, and Fig. 4 is a residual stress distribution diagram in Fig. 3.
FIG. 5 is a vertical cross-sectional view corresponding to FIG. 1 showing still another embodiment of the present invention, FIG. 6 is a vertical cross-sectional view for explaining a conventional sandwich type joining method, and FIG. 7 is a vertical cross-sectional view corresponding to FIG. 8th longitudinal cross-sectional view for explaining the residual stress generation state in the case of
The figure is a residual stress distribution diagram in FIG. 7. 1.2... Pipe body, 3... Inner ring, 4... Joining groove, 5... Mandrel, 6... Roller, 7, 8,
12゜13...Groove, 9...Tube plate, 10...Tube body,
11... Inner ring, 14... Joining groove. 18th Figure 3 of this big kick 40. 5121 7g of grass 9, tube bottle 10g 141. 11 Inner〉7゛1 Otsu, Mizo + J-ko January Second Damizo Inhibition No. 6 5.7〉 Tor 6.0-La No. 70

Claims (1)

[Claims] 1. Consisting of an outer tube body or tube plate, an inner tube body, and an inner ring, a joining groove is provided in the outer tube body or tube plate, and the inner ring is expanded. Therefore, in the sandwich-type tube connection structure in which the inner tube is joined to the outer tube or tube sheet, the portion of the inner surface of the outer tube or tube sheet near the joining groove is A low residual stress type tube connection structure characterized by a circumferential groove. 2. Consisting of an outer tube body or tube plate, an inner tube body, and an inner ring, by providing a joining groove in the outer tube body or tube plate, and expanding the inner ring, the outer tube In a sandwich type tube connection structure in which the inner tube body is joined to a body or a tube sheet, a circumferential groove is formed on a portion of the inner surface of the outer tube body or tube sheet near the joining groove. 1. A low residual stress type tube connection structure, characterized in that a second groove is provided in the circumferential direction in a portion located near the outside of the end of the inner ring.