JPH11118074A - Weld overlaying method for socket welded joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To check the occurrence of any welding residual stress of tension in a gap part, and to prevent the stress corrosion cracking of a socket welding joint from occurring by forming the final layer of a weld overlay, plurally layered toward the upside, in a part contacting with a pipeline. SOLUTION: At the time of executing the weld overlaying of a socket welded joint to be applied to a pipeline 1 or the like in various plants including a nuclear power related plant and so on, the pipeline 1 is inset in the inner diameter side of a socket 2, and then overlay welding is applied to the pipeline 1 and an end of the socket 2, and thereby a layered part 4 is formed. In this layered part 4, the pipeline 1 and the socket 2 are first welded into one body by the first layer padding, and then those of sesond to fourth layers are overlaid up to the upper part in order, and the final fifth layer padding is overlaid on a part contacting with the pipeline 1 separated from a gap part 3 between this pipeline 1 and the socket 2 and completed. Thus, since the fifth layer is formed in a part contacting with the pipeline 1 separated from the gap 3 between this pipeline 1 and the socket 2, any possible occurrence of a welding residual stress of tension in the gap part 3 is checked, thereby preventing the stress corrosion cracking from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for overlaying a socket-welded joint applied to piping of various plants.

[0002]

2. Description of the Related Art In many cases, socket welded joints are used as welded joints in nuclear power plants or various energy plants.

As shown in FIG. 5, in conventional socket welded joints, the weld overlay is laminated in order from the first layer to the fifth layer in an orderly manner, although there is a slight difference in the amount of each overlay. Was served.

[0004]

In the conventional socket welded joints, as described above, the welded joints are laid up in order toward the upper part.

However, in the case of this overlay method, FIG.
As shown in the figure, in the gap 3 between the socket 2 and the pipe 1,
Very high tensile welding residual stress was generated, which often resulted in leakage of the internal fluid 6 due to stress corrosion cracking 4a. The present invention seeks to solve the above problems.

[0006]

The present invention provides a method for overlaying a socket weld joint by laminating a final layer on a pipe side.

[0007] The welding overlay method for a socket-welded joint according to the present invention has the following differences when compared with the conventional method. After welding the final layer, shrinkage of the cladding causes a bending moment in the pipe axis direction, opening the gap between the pipe and the socket.In the conventional method, this causes a large tensile residual stress in the gap. On the other hand, in the case of the method of the present invention, the above-mentioned residual stress is small because the build-up portion is away from the gap.

[0008] Further, in the above-mentioned built-up portion, there is a drop in the build-up portion in the radial direction due to shrinkage. In the case of the present invention, a large tensile residual stress is generated, whereas in the case of the present invention, since the gap portion behaves in a closing direction, a large compressive residual stress is generated.

Further, regarding the axial stress and the circumferential stress in the gap, in the case of the conventional method, a large compressive plastic strain generated at the time of welding changes to a tensile strain at the time of cooling. On the other hand, in the case of the present invention, a small compressive residual stress is generated in the present invention because of the distance from the overlay.

[0010] In the method of the present invention, as described above,
Since it becomes possible to suppress the occurrence of tensile welding residual stress in the gap compared to the conventional method, it becomes possible to prevent the stress corrosion cracking of the socket welded joint which occurred in the case of the conventional method. .

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for overlaying a socket weld joint according to an embodiment of the present invention will be described with reference to FIG. In FIG. 1, 1 is a pipe, 2 is a socket, and the inner diameter of the socket 2 is large so that the pipe 1 can be inserted.

In the welding overlay method according to the present embodiment, after the pipe 1 is inserted into the inner diameter side of the socket 2, overlay welding is performed on the ends of the pipe 1 and the socket 2 to form a laminated portion 4. I have.

The laminated portion 4 is first welded and connected between the pipe 1 and the socket 2 by overlaying the first layer, and then sequentially moves upward to the second, third and fourth layers (toward the outer diameter). 3) The buildup is performed, and the final buildup of the fifth layer is completed by laminating a portion of the pipe 1 and the socket 2 that is in contact with the pipe 1 distant from the gap 3.
The gap 5 between the pipe 1 and the socket 2 is a portion through which the internal fluid 6 passes.

In the present embodiment, the fifth residual layer, which is the final layer, is formed at a portion of the pipe 1 and the socket 2 which is in contact with the pipe 1 and is separated from the gap 3 so that the tensile welding residual stress in the gap 3 is increased. Generation can be suppressed, and the stress corrosion cracking observed in the case of the conventional method can be prevented.

The present embodiment is realized by repeating trial and error. The reason why a socket welded joint having a small welding residual stress can be obtained by the welding overlaying method according to the present embodiment is as follows. This will be described below in comparison with the case of (1).

When a comparison is made between the present embodiment and the socket-welded joint up to the fourth layer according to the conventional method, the respective residual stress distributions and residual stress values are similar since the respective laminated states are the same. It will be.

In the case of the conventional method in which the final layer is laminated on the fourth layer, as shown in FIG. 2A, a bending moment M is generated in the pipe axis direction due to the contraction of the built-up portion 7 after welding. As a result, the gap 5 between the pipe 1 and the socket 2 is deformed to open, and a large tensile residual stress is generated in the gap 3.

On the other hand, in the case of the method according to the present embodiment in which the final layer is laminated on the portion in contact with the pipe 1, although a similar bending moment acts, there is a welded portion between the gap 3 and the distance, so that the distance is small. Since it is far away, there is no significant effect.

Concerning the shrinkage of the build-up portion after the above-mentioned welding, it may be considered that a concomitant effect of a fall in the final layer in the radial direction due to the build-up is caused. In the case of the conventional method, FIG.
As shown in (b), the gap portion 5 behaves as if it were opened due to the fall of the build-up portion, and eventually, in this case, a large tensile residual portion acts on the gap portion 3.

On the other hand, in the case of the method according to the present embodiment, as shown in FIG. 2 (c), the gap 5 is closed on the contrary due to the radial drop at the pipe portion, and the gap 3 is closed. Causes a large compressive residual stress.

The above describes the deformation behavior.
Next, the behavior due to heat will be described with reference to FIG. In the case of the conventional method, the axial stress after welding in the XX section becomes a compression at the outer diameter side and a tensile stress at the inner gap 3 as shown in FIG.

This is because a large compressive plastic strain is generated in the gap portion 5 during welding due to the generation of plastic strain in the plate thickness in the process from welding to cooling, and changes to an opposite tensile strain during cooling. It is.

As for the stress in the circumferential direction, a compressive plastic strain is generated due to a high temperature at the time of welding of the XX section, and a tensile strain is generated at the time of cooling.
As shown in (b), after welding, tensile stress is generated. Therefore, according to the conventional method, a large tensile stress is generated in the gap 3 in both the axial direction and the circumferential direction.

On the other hand, according to the method of the present embodiment, the axial stress and the circumferential stress are as shown in FIGS. 3 (c) and 3 (d). That is, in the Y-Y section, FIG.
Although the same stress distribution as that shown in (b) occurs after welding, in the XX section, the size is reduced due to the distance, and the stress distribution reverse to that in the YY section occurs. In the gap 3, a residual stress of compression occurs.

FIG. 4 shows the residual stress distribution after welding caused by the above-described behavior in the case of the conventional method and in the case of the method of the present embodiment, which are obtained by the analysis in the pipe axis direction and the radial direction. a) and (b).

As can be seen from FIGS. 4 (a) and 4 (b), in the gaps 3 and 5, a large tensile residual stress is generated in the former case, and a compressive residual stress is generated in the latter case. In the case of the welding overlay method according to the present embodiment, the stress generated in the gap 3 where stress corrosion cracking is concerned can be reduced.

In this embodiment, the number of layers of the overlay welding is five, but it is needless to say that the number of layers is not limited to this number.

[0028]

According to the method for overlaying a socket welded joint of the present invention, the final layer of the weld overlay, which is formed by laminating a plurality of layers toward the upper portion, is formed by laminating a portion in contact with a pipe. Since it is possible to suppress the occurrence of tensile welding residual stress in the gap, it is possible to prevent stress corrosion cracking of the socket welded joint, which has occurred in the case of the conventional method.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a method for overlaying a socket weld joint according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of the effect of shrinkage of a build-up part in the case of the method according to the embodiment and the case of a conventional method;
(A) is the bending moment in the case of the conventional method,
(B) shows the fall of the built-up part in the case of the conventional method,
(C) is an explanatory view of a fall of a built-up part in the case of a method of this embodiment.

FIGS. 3A and 3B are explanatory diagrams of stress in the case of the method according to the embodiment and in the case of the conventional method, wherein FIG. 3A shows the stress in the tube axial direction in the case of the conventional method, and FIG. (C) is an explanatory diagram of a pipe axial stress in the case of the method of the present embodiment, and (d) is an explanatory diagram of a circumferential stress in the case of the method of the present embodiment.

FIG. 4 is a comparative explanatory diagram of a welding residual stress distribution in the case of the method according to the embodiment and the case of the conventional method;
(A) is an explanatory view in the tube axis direction, and (b) is an explanatory view in the radial direction.

FIG. 5 is an explanatory diagram of a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piping 2 Socket 3 Gap 4 Stacking part 5 Gap

Claims (1)

[Claims] 1. A method for overlaying a socket weld joint comprising the steps of: laminating a final layer on a pipe side;